Gear sprocket work condition. Chain transmissions, purpose, advantages, disadvantages, classification

View: this article has been read 11372 times

Pdf Select language... Russian Ukrainian English

Full material is downloaded above, after selecting the language

Chain transmission is based on the meshing of the chain and sprockets.

Advantages and disadvantages

The principle of engagement and high strength steel chain allow you to provide a greater load capacity of the chain drive compared to the belt drive. The absence of sliding and slipping ensures the constancy of the gear ratio (average per revolution) and the ability to work with short-term overloads.

The meshing principle does not require pre-tensioning the chain, which reduces the load on the supports. Chain drives can operate at smaller center distances and at large gear ratios, as well as transfer power from one drive shaft to several driven ones.

The main reason for the shortcomings of the chain transmission is that the chain consists of separate rigid links located on the sprocket not in a circle, but in a polygon. This results in wear of the chain joints, noise and additional dynamic loads. Chain drives need to organize a lubrication system.

Application area:

• at significant center distances, at speeds less than 15-20 m / s, at speeds up to 35 m / s, lamellar chains are used (a set of plates of two tooth-like protrusions, the principle of internal engagement);
• when transferring from one drive shaft to several driven ones;
• when gears are not applicable and belt drives are unreliable.

Compared to belt drives, chain drives are noisier, and they are used in gearboxes at low-speed levels.

The main characteristics of the chain drive

Power
Modern chain transmissions can operate in a fairly wide range: from fractions to several thousand kilowatts. But at high power, the cost of transmission increases, so chain transmissions up to 100 kW are most common.

Peripheral speed
With increasing speed and speed, wear, dynamic loads and noise increase.

Gear ratio:
The gear ratio of the chain drive is limited to 6, due to the increase in dimensions.

KKD transmission
Losses in the chain transmission consist of friction losses in the chain joints, on the teeth of the sprockets and in the shaft bearings. In lubrication by immersion in a lubricating bath, the mixing losses of the lubricating oil are taken into account. Average value of KKD

Center distance and chain length
The minimum value of the center distance is limited by the minimum allowable gap between the sprockets (30...50 mm). To ensure durability, depending on the gear ratio

Types of drive chains

• Roller
• bushing
• jagged

All chains are standardized and manufactured at special enterprises.

Drive chain sprockets

Sprockets are like gear wheels. The pitch circle passes through the centers of the hinges of the chain.

The profile of the teeth of roller and sleeve chains can be convex, straight and concave, in which only the main lower section the profile is concave, at the top the shape is convex, in the middle part there is a small rectilinear transitional section. The concave profile is the most common.

The quality of the profile is determined by the angle of the profile, which for concave and convex profiles varies with the height of the tooth. With an increase in the angle of the profile, the wear of the teeth and hinges decreases, but this leads to an increase in the impact of the hinges when engaging, as well as to an increase in the tension of the idle branch of the chain.

materials

Chains and sprockets must be resistant to wear and shock loads. Most chains and sprockets are made from carbon and alloy steels with further heat treatment (improvement, hardening).

Sprockets, as a rule, are made from steels 45, 40X, etc., chain plates - from steels 45, 50, etc., rollers and rollers - from steels 15, 20.20X, etc.

Hinge parts are cemented to increase wear resistance while maintaining impact strength.

In the future, it is planned to manufacture sprockets from plastics, which can reduce dynamic loads and transmission noise.

Forces in engagement

• tension forces of the leading and driven branches,
• district force,
• pretension force,
• centrifugal force.

Kinematics and dynamics of chain drives

The movement of the driven sprocket is determined by the speed V 2 , the periodic changes of which are accompanied by the variability of the gear ratio and additional dynamic loads. The speed V 1 is associated with transverse oscillations of the chain branches and impacts of the chain hinges against the teeth of the sprocket, causing additional dynamic loads.

With a decrease in the number of teeth z 1, the dynamic properties of the transmission deteriorate.

Shocks cause noise during transmission operation and are one of the causes of chain failure. For restriction harmful influence shocks, recommendations have been developed for choosing a chain pitch depending on the speed of the transmission. At a certain speed, a circuit vibration resonance phenomenon may occur.

During operation, wear of the chain hinges occurs due to an increase in the gaps between the roller and the sleeve, as a result, the chain is stretched.

The wear life of the chain depends on the center distance, the number of teeth of the small sprocket, the pressure in the joint, the lubrication conditions, the wear resistance of the chain material, the allowable relative wear

As the chain length increases, the service life increases. With a smaller number of sprocket teeth, the dynamics worsens. An increase in the number of teeth leads to an increase in dimensions, the permissible relative clearance decreases, which is limited by the possibility of losing the chain engagement with the sprocket, as well as a decrease in the strength of the chain.

Thus, with an increase in the number of teeth of the sprocket z, the permissible relative wear of the hinges decreases, and as a result, the life of the chain before the loss of engagement with the sprocket decreases.

The maximum service life, taking into account the strength and the ability to engage, is ensured by the choice of the optimal number of sprocket teeth.

Chain transmission performance criteria

The main reason for the loss of performance is the wear of the chain joints. The main design criterion for the wear resistance of hinges

The wear life of a chain depends on:

• from the center distance (the length of the chain increases and the number of runs of the chain per unit time decreases, i.e. the number of turns in each hinge of the chain decreases);
• on the number of teeth of a small sprocket (with an increase in z1, the angle of rotation in the hinges decreases).

The method of practical calculation of the chain transmission is given in.

chain drive, chain, sprocket, chain pitch

An example of the calculation of a spur gear
An example of the calculation of a spur gear. The choice of material, the calculation of allowable stresses, the calculation of contact and bending strength were carried out.

An example of solving the problem of beam bending
In the example, diagrams of transverse forces and bending moments are plotted, a dangerous section is found, and an I-beam is selected. In the problem, the construction of diagrams using differential dependencies was analyzed, comparative analysis different cross sections of the beam.

An example of solving the problem of shaft torsion
The task is to test the strength of a steel shaft for a given diameter, material and allowable stresses. During the solution, diagrams of torques, shear stresses and twist angles are built. Self weight of the shaft is not taken into account

An example of solving the problem of tension-compression of a rod
The task is to test the strength of a steel rod at given allowable stresses. During the solution, plots of longitudinal forces, normal stresses and displacements are built. Self weight of the bar is not taken into account

Application of the kinetic energy conservation theorem
An example of solving the problem of applying the theorem on the conservation of kinetic energy of a mechanical system

Determination of the speed and acceleration of a point according to the given equations of motion
An example of solving the problem of determining the speed and acceleration of a point according to the given equations of motion

Lecture 10 CHAIN ​​GEARS

P lan l e c t i o n

1. General information.

2. Drive chains.

3. Features of the operation of chain drives.

4. Asterisks.

5. Forces in the branches of the chain.

6. The nature and causes of chain drive failures.

7. Calculation of transmission by a roller (sleeve) chain.

1. General information

Chain transmission (Fig. 10.1) is classified as gearing with a flexible connection. The movement is transmitted by an articulated chain 1, covering the driving 2 and driven 3 sprockets and engaging with their teeth.

Chain transmissions perform both lowering and increasing.

Advantages of chain drives:

Compared to gears, chain drives can transmit movement between shafts at significant center distances

compared to belt drives, chain drives are more compact, transmit more power, can be used in a wide range of center distances, require significantly less pretensioning force, provide a constant gear ratio (no slipping and slipping), and have high efficiency;

can transmit the movement of one chain to several driven sprockets.

Disadvantages of chain drives:

significant noise during operation due to the impact of the chain link on the tooth of the sprocket when engaging, especially with a small number of teeth and a large pitch, which limits the use of chain drives at high speeds;

relatively fast wear of the chain hinges (increase in the chain pitch), the need to use a lubrication system and installation in closed cases;

elongation of the chain due to wear of the hinges and its coming off the sprockets, which requires the use of tensioners;

uneven rotation of sprockets; the need for high precision transmission assembly.

Chain transmissions are used in machine tools, motorcycles, bicycles, industrial robots, drilling equipment, road construction, agricultural, printing and other machines to transmit movement between parallel shafts over long distances when the use of gears is impractical, and the use of belt drives is impossible. Chain transmissions with a power of up to 120 kW at peripheral speeds of up to 15 m / s have received the greatest application.

2. Drive chains

The main element of the chain transmission - the drive chain consists of individual links connected by hinges. Drive chains are used to transmit mechanical energy from one shaft to another.

The main types of standardized drive chains are roller, sleeve and toothed.

Roller drive chains. The standard provides for the following types of roller chains: drive roller chains (PR, Fig. 10.2), light series (PRL), long-link (PRD), two-, three- and four-row (2PR, 3PR, 4PR).

Links of roller chains (Fig. 10.3) consist of two rows of outer 1 and inner 2 plates. Axes 3 are pressed into the outer plates, passed through bushings 4, which, in turn, are pressed into the inner plates. The bushings are pre-fitted with freely rotating hardened rollers5. The ends of the axles after assembly are riveted to form heads that prevent the plates from falling off. With relative rotation of the links, the axle rotates in the sleeve, forming a sliding hinge. The chain is engaged with the sprocket through a roller, which, turning on the bushing, rolls over the sprocket tooth. This design equalizes tooth pressure on the sleeve and reduces wear on both the sleeve and the tooth.

The plates are outlined with a contour resembling the number 8 and providing equal strength of the plate in all sections.

Pitch P chain is the main parameter of the chain transmission. The larger the pitch, the higher the load capacity of the chain.

The pitch circle of the sprockets passes through the centers of the hinges

where Z is the number of sprocket teeth.

Pitch P for sprockets is measured along the chord of the dividing circle.

Roller chains are widely used. They are used at speeds of 15–30 m/s.

Sleeve drive chains (Fig. 10.4) are similar in design to roller chains, but do not have rollers, which reduces the cost of manufacturing the chain, reduces its weight, but significantly increases the wear of the chain bushings and sprocket teeth. Sleeve chains are used in non-critical gears at speeds of 15–35 m/s.

Sleeve and roller chains are made single-row and multi-row with the number of rows of 2-4 or more. A multi-row chain with a smaller pitch P allows you to replace a single-row chain with a larger pitch and thereby reduce the diameters of the sprockets and reduce the dynamic loads in the transmission. Multi-row chains can operate at significantly higher chain speeds. The load capacity of the chain increases almost in direct proportion to the number of rows.

The connection of the ends of the chain with an even number of its links is made by a connecting link, with an odd number - by a transitional link, which is less strong than the main ones. Therefore, chains with an even number of links are used.

Gear drive chains (Fig. 10.5) consist of links made up of a set of plates pivotally connected to each other. Each plate has two teeth and a cavity between them to accommodate the sprocket tooth.

The number of plates determines the chain width, which in turn depends on the power to be transmitted. The working faces are the planes of the plates located at an angle of 60º. With these faces, each chain link is wedged between two sprocket teeth having a trapezoidal profile. Thanks to this, toothed chains run smoothly, with little noise, better absorb shock loads and allow speeds of 25–40 m/s.

To eliminate the lateral fall of the chain from the sprockets, guide plates are used, located in the middle or on the sides of the chain. The pitch diameter of the sprocket for toothed chains is greater than its outer diameter.

The relative rotation of the links is provided by sliding or rolling joints.

The rolling hinge ((Fig. 10.5)) consists of two prisms1 and2 with cylindrical working surfaces and a length equal to the width of the chain. Prisms rest on flats. Prism 1 is fixed in the shaped groove of plate B, prism 2 - in plate A. The prisms, when the links turn, roll over one another, providing a clean rolling. Chains with rolling joints are more expensive, but have low friction losses.

The sliding hinge consists of an axis, two liners fixed in the figured grooves of the plate A and B. When the plates are rotated, the insert slides along the axis, turning in the groove of the plate. Inserts allow you to increase the contact area by 1.5 times. The hinge allows the plate to be rotated through an angle

max. Usually max = 30°.

Compared to others, toothed chains are heavier, more difficult to manufacture and more expensive.

At present, roller and bush chain transmissions are predominantly used.

Chain material. Chains must be durable and strong. Chain plates are made from steel grades 50, 40X and others, hardened to a hardness of 40–50 HRC, axles, bushings, rollers and prisms are made from case-hardened steels of grades 20, 15X and others, hardened to a hardness of 52–65 HRC. By increasing the hardness of the parts, the wear resistance of the chains can be increased.

Optimum transmission center distance taken from the chain durability condition (Fig. 10.6):

a = (30–50)P ,

where P is the chain pitch.

When the axis of the chain drive is tilted, with dividing circles d 1 and d 2, to the horizon at an angle α, the driven branch sags by the value f.

3. Features of the operation of chain drives

Variability of the instantaneous value of the gear ratio.

The speed v of the chain, the angular speed2 of the driven sprocket and the gear ratio i =1/2 are variable at a constant angular speed1 of the driving sprocket.

The movement of the hinge of the link that was last engaged with the drive sprocket determines the movement of the chain in a running gear. Each link guides the chain as the sprocket rotates one pitch and then gives way to the next link.

Consider a chain drive with a horizontal drive branch. The leading hinge on a small sprocket at some point in time is rotated relative to the vertical axis by an angle of 1 . Peripheral speed on the tooth of the drive sprocket v 1 \u003d 1 R 1, where R 1 \u003d d 1 / 2 is the radius of the chain hinges. The speed of the chain v = v 1 cos1, where 1 is the wrap angle of the leading sprocket relative to the perpendicular to the leading branch. Since when the sprocket is rotated, the angle1 changes in absolute value within (/ Z 1 - 0 - / Z 1), then the speed v of the chain when turning one

the angular step varies within (v min -v max -v min), where v min \u003d 1 R 1 cos (/ Z 1) and v min \u003d 1 R 1. Instantaneous angular velocity of driven sprocket

2 \u003d v / (R 2 cos2),

where angle 2 on the driven sprocket varies within (/Z 2 - 0 - /Z 2).

Instantaneous transfer ratio (taking into account v = 1 R 1 cos1)

The gear ratio of the chain drive is variable within the rotation of the sprocket by one tooth. The inconsistency of i causes uneven transmission stroke, dynamic loading due to the acceleration of the masses connected by the transmission, and transverse vibrations of the chain. The uniformity of movement is the higher, the greater the number of teeth of the sprockets (the lower the limits for changing angles1,2).

Average gear ratio. The chain travels the path S = PZ in one revolution of the sprocket. Time, s, for one revolution of the sprocket: t = 2 /1 = 60/n . Therefore, the speed v, m/s, of the chain

v \u003d S / t \u003d PZ 1 10–3 / (60 / n 1) \u003d PZ 2 10–3 / (60 / n 2),

where P is the chain pitch, mm; Z 1, n 1 and Z 2, n 2 are the number of teeth and the speed of rotation of the driving and driven sprockets, respectively, rpm.

From the equality of the chain speeds on the sprockets, it follows

i = n1 / n2 = Z2 / Z1 = R2 / R1 .

The average gear ratio i per revolution is constant. The maximum allowable value of the gear ratio of the chain drive is limited by the arc of the chain around the small sprocket and the number of hinges located on this arc. It is recommended to take the wrapping angle at least 120°, and the number of hinges on the wrapping arc - at least five. This condition can be met for any center distances, if i 7 the center distance goes beyond the optimal values. Therefore, usually i 6.

Hitting the chain links against the teeth of the sprockets when engaging.

The circumferential speed of the sprocket tooth at the moment preceding the entry of the chain hinge into engagement is v 1, and the vertical projection of this vector is v ". Since the previous hinge is still leading, the entire chain, including the engaging hinge, moves with speed v 1. Vertical projection of the velocity vector v 1 involved in the engagement

asterisks.

Rotation of links under load. When the sprocket is rotated by one angular step, the links connected by the leading hinge rotate by

corner. Rotation in the hinge occurs when the circumferential force is transmitted and causes wear. The angle of rotation, which determines the path of friction (wear), is smaller, the greater the number of sprocket teeth.

4. Stars

Sprockets (Fig. 10.7) of chain drives in accordance with the standard are made with a wear-resistant tooth profile. To increase the durability of the chain drive, the largest possible number of teeth of the smaller sprocket is taken. The number Z 1 of the teeth of a small sprocket for roller and sleeve chains, provided Z 1 min 13,

Z 1 \u003d 29 - 2i,

where i is the gear ratio.

The minimum allowable number of teeth of a small sprocket is taken:

at high speeds Z 1 min = 19–23; at medium –Z 1 min = 17–19; at low –Z 1 min = 13–15.

With the wear of the hinges and the increase in connection with this step, the chain tends to rise along the profile of the teeth, and the higher, the greater the number of sprocket teeth. At large numbers teeth, even with a little worn chain, as a result of radial slipping along the profile of the teeth, the chain jumps off the driven sprocket. Therefore, the maximum number of teeth of a large sprocket is limited by: Z 2 90 for a sleeve chain; Z 2 120 for a roller chain. It is preferable to take an odd number of sprocket teeth, which, in combination with an even number of chain links, contributes to its more even wear.

The sprocket material must be wear-resistant and resist shock loads well. Stars are made from steel.

grades 45, 40X and others with hardening to a hardness of 45–55 HRC or case-hardened steel grades 15, 20X with hardening to a hardness of 55–60 HRC. In order to reduce the noise level and dynamic loads in transmissions with light conditions works produce a gear rim of sprockets from polymeric materials: fiberglass and polyamides.

5. Forces in the branches of the chain

The leading branch of the chain during transmission operation is loaded with a force F 1, consisting of a useful (circumferential) force F t and a force F 2 of the tension of the driven branch of the chain:

Circumferential force F t N transmitted by the chain:

F t = 2 103 T/d,

where d is the pitch diameter of the sprocket, mm.

The tension force F 2 of the driven branch of the chain is the tension force F 0 from its own gravity and the tension force F c from the action of centrifugal forces:

Tension F 0 , N from gravity with a horizontal or close to it position of the line connecting the axes of the stars:

F0 = qga2 / 8 f =1.2 qa2 / f,

where q is the mass of 1 m of the chain, kg / m; g \u003d 9.81 m / s2 is the acceleration of free fall; a is the center distance, m; f is the sagging boom of the driven branch, m (Fig. 10.6).

With a vertical position or close to it, the line of the centers of the stars

Chain tension from centrifugal forces, N,

where v is the speed of the chain, m/s.

The force F c acts on the chain links along its entire contour and causes additional wear of the hinges. Chain drives are tested for strength according to the values ​​of the breaking force given in the standard, and the tension force of the leading branch, which is calculated taking into account additional dynamic loading from the uneven movement of the chain, the driven sprocket and the masses brought to it. The tension of the driven branch of the chain F 2 is equal to the largest of the tensions F 0 or F c.

The centrifugal force does not load the shafts and supports. The calculated load F in on the chain drive shafts is slightly greater than the useful circumferential force due to the tension of the chain from its own gravity. Conditionally accept

where K in is the shaft load factor; for horizontal gears, K in \u003d 1.15, for vertical gears, K in \u003d 1.05. The direction of the force F in is along the line of the centers of the stars.

6. The nature and causes of chain drive failures

Drive chains are characterized by the following main types of limit states:

wear of hinge parts due to their mutual rotation under load. Causes chain pitch to increase. As they wear, the hinges are located closer to the tops of the teeth and there is a danger of the chain jumping off the sprockets;

wear of the sprocket teeth due to relative slip and seizure in the roller-sprocket tooth interface. Leads to an increase in the sprocket pitch;

fatigue failure of chain plates due to cyclic loading. They are observed in high-speed heavily loaded gears operating in closed cases with good lubrication;

shock-fatigue destruction of thin-walled parts - rollers and bushings. These failures are due to the impact of the hinges on the teeth of the sprockets at the entrance

into engagement.

AT In a properly designed and operated chain drive, the increase in chain pitch as the joints wear outpaces the increase in sprocket pitch. Associated with this is a violation of the engagement, unacceptable sagging of the idle branch of the chain, jumping off the sprocket, rubbing against the walls of the casing or crankcase, as well as an increase in vibrations and noise. As a result, the chain is usually replaced before fatigue failure occurs. Thus, the main mode of failure of chain drives is the wear of the joints.

7. Calculation of transmission by a roller (sleeve) chain

The wear resistance of hinges is the main criterion for the performance and calculation of chain drives. Wear depends on the pressure p in the hinge and the friction path S, quantified

n1.doc

General information

Transmission of mechanical energy between parallel shafts by means of two wheels- sprockets 1 and 2 and the chain 3 covering them is called a chain drive(Fig. 1). Serve to transfer rotation between parallel shafts remote from each other.

Fig.1. Chain drive: 1 - leading sprocket; 2 - driven sprocket;

3 - chain; 4 - stretching device

A chain drive, like a belt drive, belongs to the category of gears with a flexible connection. In this case, the flexible link is the chain that engages with the teeth of the sprockets. The chain consists of links connected by hinges, which provide mobility or "flexibility" of the chain. Engagement provides a number of advantages over belt drive.

Chain transmission can be classified as flexible linkage transmission(belt - friction with a flexible connection). The engagement eliminates the need for pre-tensioning the chain. In the design of chain drives to compensate for the elongation of the chain when drawing and to provide an operational slack boom f the driven branch is sometimes provided with special tension devices (see Fig. 1). In addition to the listed basic elements, chain drives include lubricators and guards.

The angle of the chain around the sprocket is not as critical as the angle around the pulley with the belt in a belt drive.

Chain drives can be used for both large and small center distances. They can transmit power from a single master link 1 several asterisks 2 (Fig. 2).

Fig.2. Ladder scheme: 1 - leading sprocket; 2 - three driven sprockets

Fig.3. Multilink transmission

Classification

Chain transmissions are divided according to the following main features:

By type of chains: with roller (Fig. 4, a); with bushings (Fig. 4, b); with gear (Fig. 4, in).

According to the number of rows, roller chains are divided into single-row (see Fig. 4, a) and multi-row (for example, two-row, see Fig. 4, b).

According to the number of driven sprockets: normal two-link (see Fig. 1, 4, 5); special - multilink (see Fig. 2, 3).

By the location of the stars: horizontal (Fig. 5, a); inclined (fig.5, b); vertical (fig.5, in).

a) b) c)

Rice. 4. Types of chain drives: a - with roller chain; b- with sleeve chain; in - with toothed chain

Rice. 5. Types of chain drives: a- horizontal;

b- inclined; in- vertical

Rice. 6. Chain drive with tension roller

5. According to the method of chain slack control: with a tensioner (see Fig. 1); with a tension sprocket (roller, fig. 6).

6. By design: open (see Fig. 3), closed (Fig. 7).

Fig.7. Chain Drive Installation

Advantages and disadvantages

Advantages:

The greater strength of the steel chain compared to the belt allows the chain to transfer large loads with a constant gear ratio and with a much smaller center distance (the transmission is more compact);

Possibility of transmission of movement by one chain to several sprockets;

Compared with gears - the possibility of transmitting rotational motion over long distances (up to 7 m);

Less than in belt drives, the load on the shafts;

Relatively high efficiency (>> 0.9 h 0.98);

No slip;

Small forces acting on the shafts, since there is no need for a large initial tension;

Easy chain replacement.

Flaws:

Relatively high cost of chains;

The impossibility of using gear when reversing without stopping;

Transmissions require mounting on crankcases;

Difficulty in supplying lubricant to the chain joints;

The speed of the chain, especially with small numbers of sprocket teeth, is not constant, which causes fluctuations in the gear ratio. The main reason for this shortcoming is that the chain consists of separate links and is located on the sprocket not in a circle, but in a polygon. In this regard, the speed of the chain with uniform rotation of the sprocket is not constant. Fig. 8 shows the speeds of the chain joints and sprocket teeth. At the moment when the hinge BUT is engaged, joint speed and peripheral speed of the sprocket at a point coinciding with the center, the hinges are equal. Let's decompose this speed into two components: directed along the branch of the chain, and perpendicular to the chain. The movement of the driven sprocket is determined by the speed. Since the angle value varies from (the moment of engagement of the hinge BUT) up to (the moment of engagement of the hinge AT), then the speed also changes, and this is the reason gear ratio inconstancyi and additional dynamic loads in the transmission.

Increased noise, especially at high speeds, due to the impact of the chain link when engaging and additional dynamic loads due to the versatility of the sprockets; Velocity is associated with transverse oscillations of chain branches. At the moment of engagement of the hinge AT with tooth FROM the vertical components of their velocities and are directed towards each other, the contact of the hinge with the tooth is accompanied by a blow. Successive impacts cause transmission noise and breakage of chain joints and sprocket teeth. To limit the harmful effects of impacts, recommendations have been developed for choosing a chain pitch depending on the speed of the drive sprocket.

They operate in the absence of fluid friction in the hinges and, consequently, with their inevitable wear, which is essential in case of poor lubrication and ingress of dust and dirt. For one run, four turns are made in each hinge: two on the leading and two on the driven sprockets. These rotations cause wear on the bushings and hinge pins. The wear of the chain and sprocket teeth is also associated with the movement of the hinges along the tooth profile in the process of engagement. This leads to chain stretching, which requires the use of tensioners to eliminate the consequences. To reduce wear, it is necessary to ensure that the joints are satisfactorily lubricated.

They require a higher shaft alignment accuracy than V-belt drives to avoid chain slippage from the sprocket and more difficult care and maintenance - lubrication, adjustment.

Application area

Chain transmissions are widely used in transporting devices (conveyors, elevators, motorcycles, bicycles), in drives of machine tools and agricultural machines, in chemical, mining and oilfield engineering.

In addition to chain drives, chain devices are used in mechanical engineering, i.e. chain drives with working bodies (buckets, scrapers) in conveyors, elevators, excavators and other machines.

Chain transmissions with a power of up to 120 kW at peripheral speeds of up to 15 m/s have received the greatest application.

Drive chain and sprocket designs

Chains used in mechanical engineering, by the nature of the work they perform divided into two groups: drive and traction. Chains are standardized, they are produced at specialized factories. The output of drive chains alone in Russia exceeds 80 million m per year. More than 8 million cars are equipped with them annually.

Drive chains carry out the transfer of motion directly from the energy source to the working body or through intermediate devices. Structurally, they are divided into roller, sleeve and jagged(Table 1). In the CIS, drive chains are standardized and manufactured at specialized factories. They are characterized by small steps (to reduce dynamic loads) and wear-resistant hinges (to ensure durability).

The main geometric characteristics of the chains are the pitch and width, the main power characteristic- breaking load, established empirically. In accordance with international standards, chains are used with a pitch that is a multiple of 25.4 mm (i.e. ~ 1 inch)

In Russia, the following drive roller and sleeve chains are manufactured in accordance with GOST 13568-75 *:

PRL - roller single-row normal accuracy;

PR - roller high precision;

PRD - roller long-link;

PV - sleeve;

PRI - roller with curved plates,

As well as roller chains according to GOST 21834-76 * for drilling rigs (in fast gears).

roller chain(Fig. 9) consists of external H and domestic Vn links (each of which consists of two plates), pivotally connected with the help of rollers and bushings. The outer and inner links in the chain alternate. Coupling with an asterisk is carried out by a roller 1, loosely seated on the sleeve 2, pressed into plates 3 internal link. Roller 4 pressed into the plates 5 of the outer link. The rollers (axes) of the chains are stepped or smooth. The ends of the rollers are riveted, so the chain links are one-piece. The ends of the chain are connected by connecting links with the pins fixed with cotter pins or riveting. If it is necessary to use a chain with an odd number of links, special transition links are used, which, however, are weaker than the main ones. Therefore, it is usually sought to use chains with an even number of links. The connecting link C serves to connect the two ends of the chain with an even number of steps, and the transition link P- with odd. Rollers replace sliding friction between chain and sprocket with rolling friction, which reduces wear on the sprocket teeth. The plates are outlined with a contour resembling the number 8 and bringing the plates closer to bodies of equal tensile strength.

Roller chain plate material - steel 50 (hardened to HRC 38-45); rollers, bushings, rollers - steel 15, 20, 25 (with subsequent carburizing and hardening to HRC 52-60).

Rice. 9. Roller chain: 1 - video clip; 2 - sleeve; 3 - inner link plates;

4 - roller; 5 - outer link plates

In mechanical engineering, single-row roller chains are more often used (see Fig. 4, a and 9). At high loads and speeds, in order to avoid the use of chains with large steps, which are unfavorable in relation to dynamic loads, multi-row chains are used. Multi-row chains (two-row - see fig. 4, b) contain several branches of single row chains connected by elongated rollers. The transmitted powers and breaking loads of multi-row circuits are almost proportional to the number of rows.

Roller chains of normal accuracy PRL are standardized in the range of steps 15.875...50.8 and are designed for breaking load 10...30% less than that of chains of increased accuracy.

Long Link Roller Chains PRD is performed in double steps compared to conventional roller ones. Therefore, they are lighter and cheaper than conventional ones. It is advisable to use them at low speeds, in particular, in agricultural engineering.

Sleeve chains(Fig. 10) are similar in design to the previous ones. These chains differ from roller chains in the absence of a roller, which reduces the cost of the chain and reduces the dimensions and weight with an increased hinge projection area. The sleeve directly engages with the sprocket teeth; sprocket wear is much greater than when using a roller chain. These chains are made with a pitch of only 9.525 mm and are used, in particular, in motorcycles and in cars (camshaft drive). The chains show sufficient performance.

Roller chains with curved plates PRI are recruited from identical links, similar to the transitional link. Due to the fact that the plates work in bending and therefore have increased compliance, these chains are used for dynamic loads (shocks, frequent reverses, etc.).

The designation of a roller or sleeve chain indicates: type, pitch, breaking load and GOST number (for example, Chain PR-25.4-5670 GOST 13568 -75 *). For multi-row chains, the number of rows is indicated at the beginning of the designation.

Rice. 10. Bush chain: 1 - inner link plates; 2 - outer link plates

Table 1. Main technical characteristics of drive chains

toothed chains(fig. 11) consist of a set of toothed plates 1, hinged to each other by means of rollers 2 (Fig. 11, a). Each plate has two teeth with a cavity between them to accommodate the sprocket tooth. The working (outer) surfaces of the teeth of these plates (the contact surfaces with the sprockets are limited by planes and inclined to one another at an angle of wedging equal to 60°). With these surfaces, each link sits on two sprocket teeth. The sprocket teeth have a trapezoidal profile. To prevent the chain from coming off the sprockets, internal guide plates are provided. 3. Number of plates 1 depends on the transmitted power. The plates in the links are moved apart by the thickness of one or two plates of the mating links. These plates are made from 50 steel, hardened to HRC 38-45.

4 - hinge; 5 - prisms

Timing chains are supplied with a joint 4 (sliding friction, see fig. 11, b) or hinge 5 (prisms fixed in plates) (rolling friction, see fig. 11, in). At present, chains are mainly manufactured with rolling joints, which are standardized (GOST 13552-81*). To form hinges, prisms with cylindrical working surfaces are inserted into the holes of the links. The prisms rest on flats. With special profiling of the plate bore and the corresponding surfaces of the prisms, it is possible to obtain practically pure rolling in the hinge. There are experimental and operational data that the resource of gear chains with rolling joints is many times higher than that of chains with sliding joints.

To prevent lateral slipping of the chain from the sprockets, guide plates are provided, which are ordinary plates, but without recesses for the teeth of the sprockets. Use internal or side guide plates. The inner guide plates require the corresponding groove on the sprockets to be machined. They provide better guidance at high speeds and are of primary use. Insert 4 and prisms 5 are made of cement steels 15 and 20 with hardening up to HRC 52-60. Depending on the location of the teeth, the chains are single-sided (see Fig. 11) and double-sided (see Fig. 3).

Compared to roller chains, the advantages of gear chains are lower noise, increased kinematic accuracy and allowable speed, as well as increased reliability associated with a multi-plate design. However, they are heavier, more difficult to manufacture and more expensive. Therefore, they are of limited use and are being replaced by roller chains.

Rice. 12. Bush and roller chain sprocket

Sprockets for drive chains. Sprockets are similar in design to gear wheels. The profile of their teeth depends on the type of chain. The sprockets of the roller and sleeve chains (Fig. 12) have a working tooth profile outlined by an arc of a circle; sprockets of toothed chains (Fig. 13) - a straight working profile. Due to the fact that the teeth of sprockets in roller gears have a relatively small width, sprockets in roller gears have a relatively small width, sprockets are often made from a disk and a hub connected by bolts, rivets or welding.

To facilitate replacement after wear, the sprockets mounted on the shafts between the supports, in machines with difficult disassembly, are made split along the diametrical plane. The parting plane passes through the cavity of the teeth, for which the number of teeth of the sprocket has to be chosen even. The durability and reliability of transmission chains largely depends on the correct choice of the sprocket tooth profile, its parameters, material and heat treatment.

Fig.13. Timing chain sprocket

An important factor for increasing the durability of the chain drive is the correct choice of the number of teeth of the smaller sprocket. With a small number of teeth, the smoothness of the transmission decreases, there is an increased wear of the chain due to the large angle of rotation of the hinge and significant dynamic forces. With the wear of the hinges and the increase in connection with this step, the chain tends to rise along the profile of the teeth, and the higher, the greater the number of sprocket teeth. With a large number of teeth, even with a little worn chain, as a result of radial sliding along the tooth profile, the chain jumps off the driven sprocket.

The recommended number of teeth of the smaller sprocket, depending on the gear ratio, are given in Table 1. Max number of teeth on larger sprocket also limited: for sleeve chain
The material of the sprockets is chosen depending on the purpose and design of the transmission. Sprockets with a large number of teeth of low-speed gears (up to 3 m/s) in the absence of shock loads can be made from cast iron grade SCH 20, SCH 30 with hardening. In unfavorable conditions in terms of wear, for example, in agricultural machines, anti-friction and hardened ductile cast iron is used. For the manufacture of drive sprockets with a small number of teeth ( > 50), in addition to the listed materials, gray cast iron SCH15, SCH20, SCH35, etc. can be used. RЈ 5 kW and Ј 8 m/s, it is possible to manufacture rims of sprockets from plastics - textolite, polyformaldehyde, polyamides, which leads to noise reduction and increased chain durability (due to a decrease in dynamic loads).

Due to the low strength of plastics, metal-plastic sprockets are also used.

Traction chains

Traction chains are divided into three main types: lamellar according to GOST 588-81 *; collapsible according to GOST 589 85; round-link (normal and increased strength), respectively, according to GOST 2319-81.

Leaf chains are used to move goods at any angle to the horizontal plane in transporting machines (conveyors, lifts, escalators, etc.). They usually consist of plain shaped plates and axles with or without bushings; they are characterized by large steps, since side plates are often used to secure the conveyor belt. The speeds of this type of chains usually do not exceed 2...3 M/S.

Round link iepi They are mainly used for hanging and lifting loads.

There are special chains that transmit movement between sprockets with mutually perpendicular axes. The rollers (axes) of two adjacent links of such a chain are mutually perpendicular.

All chains are standardized worldwide. The main parameter is the chain pitch t, ​​which is expressed in millimeters or inches. The GOST tables also contain standard chain widths, the minimum number of sprocket teeth, the maximum number of revolutions, permissible loads and weight.

Chain variators

chain variators, like friction, they are designed for stepless change in gear ratio. They are made in a closed housing and consist of two pairs of sliding toothed cones 1, 2 and the chain that embraces them 3 special design with retractable plates included in the grooves of the cones (Fig. 7.16). Gear ratio adjustment is carried out by approaching one pair of sprockets-cones and expanding the other. In this case, the chain changes its position on the cones. All star cones 1 , 2 made in the same size z K =60. The power transmitted by such variators reaches 70 kW; =6...10 m/s; =0.85...0.95 with control range.

Variety chain variators - friction chain variators. They differ in that the cones are smooth, and the chains instead of transverse plates include rollers that replace the pads found in friction variators. These variators have a control range D10. Compared to friction variators, chain variators are more difficult to manufacture, so their use in mechanical engineering is limited.

Rice. 14. Chain variator

Basic geometric and kinematic relationships, transmission efficiency

Geometric transmission parameters(see fig.15).

1. Center distance

Where t- chain pitch.

Chain pitch is the main parameter of the chain transmission and is accepted according to GOST. The larger the pitch, the higher the load capacity of the chain, but the stronger the impact of the link on the tooth during the run-on to the sprocket, the less smoothness, noiselessness and durability of the transmission.

At high speeds, chains with a small pitch are chosen. In high-speed gears at high power, small pitch chains are also recommended: large-width gear or multi-row roller chains. The maximum value of the chain pitch is limited by the angular velocity of the small sprocket.

The minimum center distance (mm) is selected from the condition of the minimum allowable gap between the sprockets:

, (2)

Where, - diameters of the tops of the teeth of the driving and driven sprocket.

Maximum center distance = 80L

Fig.15. chain drive diagram

With a known chain length, the center distance

, (3)

where L p - chain length in steps (or number of chain links); z 1 , z 2 - the number of teeth of the driving and driven sprocket.

2. The number of chain links is determined by the approximate formula

. (4)

Meaning L p rounded up to an integer, which is desirable to take even, so as not to use special connecting links.

The transmission works better with a little slack in the idle chain. Therefore, the calculated center distance is recommended to be reduced by approximately (0.002 - 0.004) a.

3. Permissible sag

4. Pitch diameter of the sprocket

5. Tooth tip diameter: for sleeve and roller chains

; (7)

For toothed chains

.

Average gear ratio determined from the equality of the average speeds of the chain . For chain transmission chain speed

, (8)

Where - chain pitch, mm; z 1 and z 2 - the number of teeth of the driving and driven sprocket; and - average angular speeds of the leading and driven sprockets, rad/s.

Chain speed and sprocket speed are associated with wear, noise and drive dynamic loads. The most widespread are low-speed and medium-speed transmissions with v up to 15 m/s and n up to 500 min -1 . AT In high-speed engines, a chain drive is usually installed after the gearbox.

From formula (8) we have the gear ratio

(9)

Common Meanings u up to 6.When large values u it becomes impractical to perform a single-stage transmission due to its large dimensions.

The gear ratio of the chain drive changes within the rotation of the sprocket by one tooth, which is noticeable with a small number z. The inconstancy does not exceed 1 ... 2%, but causes uneven transmission stroke and transverse oscillations of the chain. The average gear ratio per revolution is constant. Recommended for single stage chain drives. and? 7(in some cases take u? 10 ).

In chain drive

,

T. e. .

efficiency transmission depends on the following losses: friction in the hinges (and between the plates of adjacent links), friction in the bearings and losses due to agitation (splashing) of oil.

To increase the efficiency of the chain drive, it is desirable to improve the lubrication conditions for the hinges and bearings. This will reduce losses and increase efficiency. The average efficiency values ​​for the transfer of the full design power of fairly accurately manufactured and well-lubricated gears are 0.96 ... 0.98.

Forces in the branches of the chain

A simplified scheme for the transmission of forces in a chain drive is similar to a power scheme in a belt drive.

District Power

Where T- torque on the sprocket; d- dividing diameter of the sprocket (see Fig. 12 and 13).

Tension forces:

The leading branch of the chain of a working transmission (Fig. 16)

; (11)

Driven strand chain

From chain slack

Where - slack factor dependent on drive location and chain slack arm f

At f= (0.01 h0.002)a for horizontal gears K f =6; for inclined (? 40°) - K f = 3 ; for vertical K f =1

q- weight of 1 m chain, kg (see Table 1);

a- center distance, m; g= 9.81 m / s 2;

From centrifugal forces;

Rice. 16. Forces of tension in the chain drive

The shaft and support perceive tension forces from chain slack and circumferential force. Approximately

, (15)

To B - shaft load factor (Table 2).

The load on the shafts and supports in a chain drive is much less than in a belt drive.

Table 2. Shaft load factor value To in

The method of selection and testing of circuits, taking into account their durability

Calculation of the chain for the wear resistance of the hinges. Medium pressure R in the hinge should not exceed the permissible value (indicated in Table 1), i.e.

Where F t - circumferential force transmitted by the chain; BUT - projection area of ​​the bearing surface of the hinge, for roller and sleeve chains A =dB; for toothed chains BUT= 0,76 dB; TO - exploitation factor;

(17)

(values ​​of coefficients - see table. 3).

Table 3The value of various coefficients in the calculation of the chain for the wear resistance of hinges

We transform formula (16):

A) we express the circumferential force in terms of the moment on the smaller sprocket chain pitch t and the number of teeth of this sprocket z 1 ;

B) represent the area of ​​the bearing surface of the hinge as a function of the pitch t. Then we get an expression for determining the chain pitch:

For roller and sleeve chains

; (18)

For toothed chain with sliding joint

, (19)

Where t - number of rows in a roller or sleeve chain;

Cog chain width factor.

Breaking Load Design(according to the margin of safety). In critical cases, the selected chain is checked by the safety factor

- total load in the driving circuit;

Required (permissible) safety factor (selected according to Table 1).

Durability according to the number of engagements with both sprockets(number of strokes) is checked by the formula

, (21)

Where L p - total number of chain links; - number of teeth and rotational speed of the sprocket (driven or driven); U- the actual number of inputs of chain links into engagement in 1 s; v- circumferential speed, m/s; L- chain length, m; [ U] - allowable number of chain inputs into engagement in 1 s (see Table 1).

The sequence of design calculation of chain drives.

1. Select the type of chain according to its intended speed and from the operating conditions of the transmission (roller, sleeve, gear).

2. By gear ratio and choose according to table 1 the number of teeth of a small sprocket z 1 , using formula (9), determine the number of teeth of the larger sprocket z 2 . Check if the condition is met.

3. Determine the torque T X on a small sprocket, according to Table 1, select the allowable pressure in the hinges [R], set the calculated coefficients, and by formula (17) determine the operating factor . After that, from the condition of wear resistance of the hinges [see. formulas (18), (19)] determine the chain pitch. Received step value t round up to standard (see Table 1).

4. Check the adopted step by the allowable angular velocity of the small sprocket (see Table 1). If the condition is not met, increase the number of rows of the roller (sleeve) chain or the width of the toothed chain.

5. Using formula (8), determine the average speed of the chain v and strength F t , then, according to formula (16), check the wear resistance of the chain. If the condition is not met increase the chain pitch and repeat the calculation.

6. Determine the geometric dimensions of the transmission.

7. For especially critical chain drives, according to formula (20), check the selected chain according to the safety factor.

8. According to formula (21), check the transmission by the number of strokes in 1 s.

Gear chain calculation

The chain pitch is selected depending on the maximum allowable speed P 1 max smaller star.

Number of teeth z 1 smaller sprocket is taken according to the formula, while taking into account that with an increase in the number of teeth z 1 joint pressure, chain pitch and width are reduced, and chain life is correspondingly increased.

Based on the criterion of wear resistance of the gear chain hinge according to the known R 1 (kW), (mm) and v(m/s) calculate the required width AT(mm) chains:

Where To uh = K d- operation factor for toothed chains;

K v- speed coefficient, taking into account the decrease in the bearing capacity of the chain due to centrifugal forces.

K ? \u003d 1 ... 1.1 10 -3 v 2 (23)

Criteria for the performance of chain drives.

Chain materials

Experimental observations show that the main causes of failure of chain drives are:

1. Wear of the hinges (due to shocks when the chain engages with the teeth of the sprocket and due to their wear from friction), leading to elongation of the chain and disruption of its engagement with the sprockets (the main criterion for performance for most gears).

2. Fatigue failure of lug plates is the main criterion for high-speed heavy-duty roller chains operating in closed crankcases with good lubrication.

3. Turning the rollers and bushings in the plates in the places of pressing is a common cause of failure of the chains, associated with insufficiently high quality workmanship.

4. Chipping and destruction of rollers.

5. Achieving the maximum sagging of an idle branch is one of the criteria for gears with an unregulated center distance, operating in the absence of tensioners and cramped dimensions.

6. Wear of sprocket teeth.

In accordance with the above reasons for the failure of chain gears, it can be concluded that the service life of the gear is most often limited by the durability of the chain.

The durability of the chain primarily depends on the wear resistance of the hinges.

In critical cases, check safety factor (s>[ s]), the number of inputs of the chain hinges in engagement in 1 s (U? [ U] ).

The material and heat treatment of chains are of decisive importance for their durability.

The plates are made of medium carbon or alloy hardened steels: 45, 50, 40X, 40XN, ZOHNZA with a hardness of mainly 40 ... 50HRCe; toothed chain plates - mainly from steel 50. Curved plates, as a rule, are made from alloyed steels. Plates, depending on the purpose of the chain, are hardened to a hardness of 40.-.50 HRCe. Hinge parts - rollers, bushings and prisms - are mainly made of carburized steels 15, 20, 15X, 20X, 12XHZ, 20XIZA, 20X2H4A, ZOHNZA and are hardened to 55-65 HRCe. Due to the high requirements for modern chain drives, it is advisable to use alloyed steels. The use of gas cyanidation of the working surfaces of hinges is effective. A multiple increase in the service life of chains can be achieved by diffusion chromium plating of hinges. The fatigue strength of the roller chain plates is significantly increased by crimping the edges of the holes. Hand blasting is also effective.

Plastics are beginning to be used in roller chain joints for operation without lubrication or with its meager supply.

The resource of chain drives in stationary machines should be 10 ... 15 thousand hours of work.

Friction loss. Gear Design

Friction losses in chain drives are the sum of the losses: a) friction in the hinges; b) friction between the plates; c) friction between the sprocket and chain links, and in roller chains also between the roller and the bushing, when the links engage and disengage; d) friction in the bearings; e) oil spatter loss.

The main ones are friction losses in hinges and supports.

Losses due to oil splashing are significant only when the chain is lubricated by dipping at the speed limit for this type of lubrication = 10…15 m/s.

Chain drives are arranged so that the chain moves in a vertical plane, and the relative height position of the driving and driven sprockets can be arbitrary. Optimal chain drive locations are horizontal and inclined at an angle of up to 45° to the horizontal. Vertically located gears require more careful adjustment of the chain tension, since its slack does not provide self-tensioning; therefore, at least a slight mutual displacement of the stars in the horizontal direction is expedient.

Leading in chain drives can be both the upper and lower branches. The leading branch must be the top branch in the following cases:

A) in gears with a small center distance (a and> 2) and in gears close to vertical, in order to avoid the capture of additional teeth by the sagging upper driven branch;

B) in horizontal gears with a large center distance (a> 60P) and a small number of sprocket teeth to avoid contact between branches.

Chain tension

As the hinges wear and contact crumpling, the chain stretches, the sagging arrow f of the driven branch increases, which causes the chain to overwhelm the sprocket. For gears with an angle of inclination ? f] a; at ? > 45°[ f] And where a- center distance. Therefore, chain drives, as a rule, must be able to regulate its tension. Preload is essential in vertical gears. In horizontal and inclined gears, chain engagement with sprockets is provided by tension from the chain's own gravity, but the chain's slack arrow must be optimal within the above limits.

The chain tension is controlled by devices similar to those used for belt tension, i.e. by moving the shaft of one of the sprockets, pressure rollers or pull sprockets.

The tensioners must compensate for the elongation of the chain within two links, with a larger stretch, two links of the chain are removed. An increase in the chain pitch due to wear in the joints is not compensated by its tension. As the chain wears, the pivots move closer to the tops of the teeth and there is a danger of the chain jumping off the sprockets.

Adjusting sprockets and rollers should, if possible, be installed on the chain branches in the places of its greatest sagging. If it is impossible to install them on the driven branch, they are placed on the leading one, but to reduce vibrations, they are placed on the inside, where they work as pull-offs. In gears with a PZ-1 toothed chain, the control sprockets can only work as pullers, and the rollers as tensioners. The number of teeth of the control sprocket is chosen equal to the number of the small working sprocket or greater. At the same time, there must be at least three chain links in engagement with the adjusting sprocket. The movement of control sprockets and rollers in chain drives is similar to that in belt drives and is carried out by a load, spring or screw. The sprocket design with an eccentric axis pressed by a helical spring has the greatest distribution.

Successful use of chain drives with high quality roller chains in closed crankcases with good lubrication with fixed sprocket axles without special tensioners is known.

crankcases

To ensure the possibility of continuous abundant lubrication of the chain, protection against contamination, quiet operation and to ensure the safety of operation, chain drives are enclosed in crankcases.

The internal dimensions of the crankcase must allow the chain to slack, as well as the possibility of convenient service of the transmission. To monitor the condition of the chain and the oil level, the crankcase is equipped with a window and an oil level indicator.

Lubrication

Lubrication of the chain has a decisive influence on its durability.

For critical power transmissions, continuous crankcase lubrication of the following types should be used whenever possible:

A) dipping the chain in an oil bath, and immersing the chain in oil at the deepest point should not exceed the width of the plate; apply up to a chain speed of 10 m/s to avoid unacceptable agitation of the oil;

B) spraying with the help of special splashing protrusions or rings and reflective shields, through which oil flows onto the chain, is used at a speed of 6 ... 12 m / s in cases where the oil level in the bath cannot be raised to the location of the chain;

C) circulation jet lubrication from a pump, the most advanced method, is used for powerful high-speed gears;

D) circulating centrifugal with oil supply through the channels in the shafts and sprockets directly to the chain; they are used with limited transmission dimensions, for example, in transport vehicles;

E) circulating lubrication by spraying oil droplets in a jet of air under pressure; used at speeds over 12 m/s.

In medium speed gears that do not have sealed crankcases, plastic inter-hinge or drip lubrication can be used. Plastic internal hinge lubrication is carried out periodically, after 120...180 h, by immersing the chain in oil heated to a temperature that ensures its dilution. Grease is applicable for chain speeds up to 4 m/s and drip lubrication up to 6 m/s.

In gears with large pitch chains, the speed limits for each lubrication method are somewhat lower.

With periodic operation and low speeds of the chain, periodic lubrication with a manual oiler is permissible (every 6 ... 8 hours). Oil is supplied to the lower branch at the entrance to the engagement with the sprocket.

With manual drip lubrication, as well as jet lubrication from a pump, it is necessary to ensure the distribution of the lubricant over the entire width of the chain and its entry between the plates for lubricating the hinges. It is preferable to supply lubricant to the inner surface of the chain, from where, under the action of centrifugal force, it is better supplied to the hinges.

Depending on the load, industrial oils I-G-A-46 ... I-G-A-68 are used for lubricating chain drives, and at low loads N-G-A-32.

Abroad, they began to produce chains for operation in light modes that do not require lubrication, the rubbing surfaces of which are covered with self-lubricating antifriction materials.

1. In drives with high-speed motors, the chain drive is usually installed after the gearbox.

3. To ensure sufficient self-tensioning of the chain, the angle of inclination of the line of sprocket centers to the horizon should not exceed 60°. At > 60 0, a pull sprocket is installed on the driven branch in the places of the greatest sagging of the chain.

4. The diameter of the pull sprocket is larger than the diameter of the change of the transmission sprocket, it must engage with at least three chain links.

5. Since the chain is not flexible in cross section, the chain shafts must be parallel and the sprockets must be installed in the same plane.

6. The use of three- and four-row chains is undesirable, as they are expensive and require increased precision in the manufacture of sprockets and gear assembly.

Questions for self-examination

1. Briefly describe the chain drive device.

2. List the classification features point by point, characterizing the design features associated with chains and sprockets.

3. Specify the main advantages and disadvantages of chain transmission in comparison with other types of transmission known to you.

4. Why does a bicycle use a chain drive? What other transmission can be used for this purpose?

5. Formulate the definition of a chain variator.

6. What are the profiles of the sprocket teeth for bush, roller and tooth chains?

7. What explains the lower load on the chain drive shafts compared to the belt drive for the same transmitted power?

8. What is the most common cause of failure of the chain drive.

9. By what formula is the center distance determined if the length on the chain is known?

10. Which branch (leading or driven) of a working chain drive is more loaded?

11. What are the advantages and disadvantages of chain drives compared to belt drives? Where are chain drives used?

12. What is the design of roller and sleeve chain?

13. In what cases are multi-row roller chains used?

15. What caused the uneven movement of the drive chains and why does it increase with increasing pitch?

16. What are the restrictions on the minimum number of teeth of a small sprocket and the maximum number of teeth of a large sprocket?

18. What is the main criterion for the performance of chain drives? How is the circuit checked according to this criterion?

19. What is the exploitation factor, what does it depend on?

20. What caused the need to use tensioners in chain drives? What are chain tension methods?

21. What lubrication methods are used in chain drives?

22. Chain transmission provides at a constant angular speed of the drive sprocket ...

1) ... constant average speed of the sprocket

2) ... non-constant average angular velocity of the driven sprocket

23. What circuit is shown in the figure?

2. Sleeve

2. Roller

3. Serrated

4. It is impossible to determine, but not jagged

24. What parameter is the base for calculating the chain transmission?

1. Roll diameter

2. Chain width

25. On what parameter does the chain sag depend?

1. t

3. L P

4. d a

5. V

26. What formula is used to determine the tension of the driven branch of the chain drive?

27. What is the most typical cause of destruction of the chain hinges?

1. Action of forces F 1 , F 2 , F v

2. Shocks when the chain engages with the teeth of the sprockets

3. Action of variable bending stresses

28. What is the main criterion by which check calculations of chain drives should be carried out

1. Wear resistance of chain joints

2. Margin of safety (according to the chain that breaks on the load)

3. Durability (by number of strokes)

29. What is the name of the parameter U, determined in the calculation of chain drives?

1. Mean circumferential pressure

2. Safety factor

3. Number of beats in 1 second

30. What chain transmission can be recommended for a stepless change in gear ratio?

1. With bush chain

2. With roller chain

3. With toothed chain

4. Chain variator

5. Any of the above

lecture №7.doc

chain drive - this is a gearing with a flexible connection. It consists of a driving and driven sprockets, wrapped around a chain.

Symbol for chain drives on kinematic diagrams:

ADVANTAGES OF CHAIN ​​GEARS

Can drive several shafts with one chain

compared to gears

Ability to transmit movement over long distances (up to 8 m)

compared to belt drives

More compact

Transmit high power

Ensure constant gear ratio

^ DISADVANTAGES OF CHAIN ​​GEARS

Significant noise during operation

Poor performance at high speeds

Rapid wear of chain joints

Elongation of the chain during wear and its removal from the sprockets.
^ CHAIN ​​GEAR APPLICATIONS

Chain drives are used in machine tools, transport, agricultural and other machines to transmit movement between parallel shafts over considerable distances, when the use of gears is impractical, and belts are impossible.

Chains of chain drives are called drive chains.
^ TYPES OF DRIVE CHAINS

C epi are:

1 . roller

t - chain pitch

The chain consists of outdoor and internal links . The outer link is assembled from two outer plates and rollers pressed into their holes. The inner link consists of two inner plates and bushings fixed in the holes of the inner plates. Hardened rollers are freely put on the bushing. The outer and inner links assemblies form a cylinder. The rollers, rolling over the teeth of the sprockets, reduce their wear. Roller chains are used at speeds up to 15 m / s.

2 . sleeve

Sleeve chains do not have rollers, so they are cheaper and lighter than roller chains, but their wear resistance is lower. Sleeve chains are used in non-critical gears at speeds ≤ 1 m / s
R olive and sleeve chains can be:
single row multi-row
The use of multi-row chains significantly reduces the dimensions of the transmission in a plane perpendicular to the axes.

An example of the designation of drive chains in accordance with GOST 13568-97.
PR - 25.4 - 60 – single-row drive roller chain with a pitch of 25.4 mm and a breaking force of 60 kN.

2PR - 25.4 - 114 – double-row drive roller chain with a pitch of 25.4 mm and a breaking force of 114 kN.

For high-speed transmissions of high power, gears are used.

The chain links consist of a set of two-tooth plates hinged to each other. The working edges of the plates are located at an angle of 60˚

The number of plates determines the chain width B, which depends on the power to be transmitted. Tooth chains have now been superseded by more technologically advanced and cheaper roller chains.
^ MAIN PARAMETERS OF CHAIN ​​GEARS.

Sprocket speeds and chain speeds are limited by:

Impact force in engagement

Hinge wear

transmission noise
The chain speed is usually up to 15 m/s, but with effective lubrication it can reach up to 35 m/s.
average chain speed: υ = z 1n1t/ 60000

z 1 - the number of teeth of the small sprocket

n1 - the frequency of its rotation

t - chain pitch

Gear ratio chain transmission is determined from the conditions of equality of the average chain speed υ on asterisks:

υ = z 1n1t = z 2n2t → U = n1/n2 = z 2 /z 1

z 2 - number of teeth of the big sprocket

n2 - the frequency of its rotation
The gear ratio is limited by:

Transmission dimensions

Large sprocket diameter

Wrap angle of small sprocket chain
usually U≤7
The number of sprocket teeth is limited by:

Hinge wear

Noisy transmission
How less number teeth, the greater the wear of the hinges.

The number of teeth of a small sprocket is taken z 1=29-2U , at low speeds allowed z 1min=13

Number of teeth of big sprocket z 2 = z 1U

As the chain wears out, the pitch of the chain increases, and its pivots rise along the profile of the sprocket tooth by a larger diameter, which can cause the chain to jump off. Therefore, the number of teeth of a large sprocket is limited: z 2max = 120.

W chain sprockets differ from gears in the profile of the teeth, the size and shape of which depends on the type of chain.

The sprocket pitch is equal to the chain pitch. Step t asterisks are measured along the chord of the dividing circle.

pitch circle sprockets passes through the centers of the hinges of the chain: d=t /sin(180˚/z )
Optimal center distance transmission is determined from the chain durability condition: a = (30…50)t
chain length determined by analogy with the length of the belt

Number of links chains W pre-determined by the formula:

W = 2a /t ( z 1 z 2) / 2 ( z 2 – z 1 /2π)² t/a
In order not to use a transition link for the connecting ends of the chain, the calculated value of the number of links, W rounded to the nearest whole even number. After the final choice of the number of links, the center distance is specified, limiting amax =80 t
^ MATERIALS FOR CHAINS AND SPROCKETS

The material of the chains and sprockets must be wear resistant and withstand cyclic and shock loads. Asterisks are made from steels 50.40 X and other brands with subsequent hardening. Chain plates are made from steels 50.40 X and others with subsequent hardening to hardness 40. . 50 HRC. Axles, bushings and rollers are made from case-hardened steels 20.15 X and others with hardening 56. . . 65HRC . In high-speed gears, to reduce noise and wear of the chain, the sprocket ring gear is made of reinforced plastics.
Section 2: Forces in the chain drive.
^ FORCES IN THE BRANCHES OF THE CHAIN.

1. 
   circumferential force transmitted by the chain

1. 
   chain pretension (from sagging of the driven branch)

To – chain slack factor

q - weight of 1 meter chain

1. 
   chain tension from centrifugal force

1. 
   tension of the leading branch of the chain of the working gear

1. 
   the tension of the driven branch of the chain is equal to the largest of the tensions

at Fυ > Fo F2 = Fυ

Since the hinge of the running link of the chain rests on the tooth, the force F2 is not transmitted to the links located on the sprocket.
The chain acts on the sprocket shafts with a force fn .

Fn = Kb Ft 2Fo
To - shaft load factor, taking into account the effect of chain sagging f depending on the inclination of the center line to the horizon θ and load dynamics.

^ PERFORMANCE CRITERIA AND CALCULATION OF CHAIN ​​GEARS

The main criterion for the performance of drive chains is wear resistance their hinges.
The load capacity of the chain is directly proportional to the pressure in the joints.
The durability of the chain is inversely proportional to the pressure in the joints.
load capacity the chain is determined from the condition: the average design pressure in the hinge of the chain link R during operation of the transmission should not exceed the permissible [ R ].

R ≤ [ R ]

Value [ R ] is listed in the handbooks and is set for a typical transmission with – resource 3000 5000 hours.
Design hinge pressure : p = Ft Ke /A

Ft- circumferential force transmitted by the chain, N

A – projection area of ​​the bearing surface of the hinge, depending on the chain pitch and its design, mm²

Ke - the operating factor, which takes into account:

Load dynamics

Lubrication method

The inclination of the center transmission line to the horizon

Job shifts, etc.

Quantities Ke are given in the reference literature.

To determine the value BUT produce preliminary design calculation at which the value of the chain pitch is approximately chosen t , mm.

t = 4.5 ³√T1

T1 – torque on the small sprocket, Nm

Found step value t coordinate with the standard and according to the reference data, the area of ​​the projection of the bearing surface of the hinge is determined BUT for the selected circuit. Durability sleeve and roller chains, selected according to the criterion of wear resistance, is usually eight . . 10 thousand hours .

In this case, the chain itself includes numerous moving links. They are interconnected in the form of a closed circle.

Usually the number of teeth on the sprocket and the number of link elements in the chains is determined by a relatively prime number. Due to this, the most uniform wear of the mechanism as a whole is ensured.

Advantages and disadvantages of chain transmission

In addition to chain drives, there are also belt drives. However, in most cases they resort to chain ones, since they have a number of important advantages:

1. No slippage, as happens under certain conditions in belt drives.
2. A high degree of compactness of the mechanism can be achieved.
3. The average gear ratio is at a constant level.
4. Due to the absence of such a phenomenon as pre-tensioning, there are no secondary loads on the key components of the mechanism.
5. Even if the speed drops, the power figures remain quite high.
6. Chain drives are practically insensitive to humidity and temperature changes.
7. You can quickly adapt such a transmission to almost any mechanism by adding or removing a chain link.
8. If necessary, you can transfer the torque to several sprockets at once with just one chain.
9. It is possible to organize the transmission of torque over fairly long distances - up to 7 meters.
10. chain drive is different large coefficient useful action - about 98 percent.
11. If necessary, failed links, the chain itself or sprockets can be quickly replaced.

However, chain drives also have certain disadvantages:

1. With prolonged intensive use, the hinges in the chain links wear out, which leads to stretching of the plates and an increase in the total length of the chain.
2. The transmission can be applied without the need to stop the movement during the reverse stroke.
3. The chain in some types of mechanisms is quite difficult to lubricate.
4. It is possible to observe the non-uniformity of the gear ratio and, as a result, the non-uniformity of the speed. Especially this effect noticeable if the sprocket does not have a large number of teeth.

All of the above should certainly be taken into account when making a choice between chain and belt types of gears.

What are the characteristics of chain drives

Among the most important characteristics of almost any chain transmission should be called:

1. Chain pitch indicator - this parameter affects the smoothness and accuracy of the stroke. With a decrease in this parameter, the indicators of accuracy and smoothness increase.
2. The number of teeth on the driving and driven sprockets.
3. The radii of the inscribed and circumscribed circles of the stars.
4. The ratio of the radii of the driving and driven sprocket. Accordingly, the larger the diameter of the drive sprocket in relation to the driven one, the easier it will be to transmit the movement.
5. The distance between the centers of the circles of the stars - this will determine, for example, the length of the chain.

All these points also need to be taken into account.

What is a chain drive made of?

Chain transmissions are fairly simple mechanisms in terms of design. However, it will not be superfluous to know what elements they consist of.

Star. Usually, only two sprockets are structurally provided in chain drives (although there are options). One of them acts as a leader, and the second as a slave. The stability and efficiency of the operation of chain types of transmission will largely depend on their quality and production accuracy: compliance with the dimensions (up to a millimeter) used in the manufacture of the material.

It is worth noting that the size and shape of the sprockets will be determined by the quantitative characteristics of the chains (and not vice versa, as some people think), the number of gear ratios, the number of teeth on the smallest drive sprocket in the mechanism. Parametric and other characteristics of sprockets are determined by GOST 13576 - 81. The characteristics of sprockets for chains of roller and sleeve varieties are determined by GOST 591 - 69.

Sprockets must be made of sufficiently strong and wear-resistant materials that can be used for a long time under significant mechanical loads, including those of a shock nature. According to GOST, steel grades 40, 45, 40X and other types with a degree of hardening HRC 50 - 60 can act as such a material. Sprockets that are not intended for high-speed mechanisms can be made from modified types of cast iron grades SCH 15, SCH 20.

Today you can find sprockets with tooth tips made of various kinds plastic. Such products are characterized by a reduced degree of wear and quiet operation.

Another component of chain drives is, of course, the chain. Chains are produced on industrial production lines. Their parameters are strictly regulated by the relevant standards. Today, the industry can offer such varieties of chains as:

1. Cargo - intended for raising and lowering loads and for hanging them. Such chains are used, as a rule, on various kinds of forklifts.
2. Traction - they serve to move goods and are used in transporting devices.
3. Drive - are used to transfer mechanical energy from one sprocket to another. A striking example of the use of such a transmission is the most ordinary bicycle and other types of vehicles.

The main elements of a standard chain are shown in the figure below.

Circuit classification

Since it is drive chains that are the most common variety, it makes sense to consider in more detail what varieties of it exist.

Roller chains (item III in the figure) include inner and outer links. Those, alternating with each other, form mobile relative to each other serial connections. Each link includes two plates pressed onto axial or sleeve bearings. Bushings are put on the axis of the link, forming a swivel joint. In order to avoid increasing the degree of wear of the sprockets, a roller is usually put on the bushing, which should replace the sliding friction with rolling friction.

The ends of the chain can be interconnected:

1. Through connecting links - with an odd number of links.
2. Through the transition link - with an even number of links.

If the transmission must operate in intensive mode for a long time, then a multi-row roller chain is used. This allows you to reduce the size of each sprocket and its pitch.

Roller chains can also be made with curved plates on each link (position IV in the figure). This type is used if the connection is expected to operate under conditions of high shock loads. Due to the special shape of the plate, the impact force is significantly damped.

Sleeve chains (position V) are structurally the same as roller chains, but do not have rollers. Due to this, the production of such chains is cheaper and their weight is reduced. But this also contributes to faster wear of the teeth.

Silent toothed chains (in the figure, position VI) include special plates equipped with teeth. The plates themselves are hinged. Thanks to this design, it is possible to ensure a low noise level of the mechanism, as well as smooth running. In this case, the teeth are located at an angle of 60 degrees. These types of chains are used in mechanisms with high speed. Therefore, the plate should be made of hardened steel with a hardness of H RC 40 - 45. The disadvantage of such chains can be considered their relative high cost, as well as the need for special care.

Hook chains (item VII). In their composition, they include links of a special form without any additional elements.

Bush-pin chains (position VIII in the figure) - in them the links are connected using pins. This kind of chains is used in various fields of agriculture and engineering.

Since any chain will stretch over time during intensive work, its tension should be periodically adjusted. This is achieved by moving one sprocket or two at once, depending on the design features of the adjusting mechanism. It allows, as a rule, to carry out adjustment if the chain is stretched by only one or two links. If the degree of stretching is greater, then the chain is simply replaced with a new one.

Do not forget about the timely lubrication of any chain. From this will directly depend on the duration of its work. If the chain speed is not too high - up to 4 meters per second, then lubrication is allowed using a conventional manual oiler. At speeds up to 10 meters per second, a dropper lubricator is used.

For deeper lubrication, the chain is immersed in a container filled with oil. The degree of immersion of the chain must not exceed the width of each plate.

If you have to deal with powerful high-speed mechanisms, then circulation jet lubrication with the help of pumps is used.

When choosing a particular lubrication method, it is necessary to rely on design features each specific type of mechanisms, as well as the nature of energy losses during friction. Friction losses occur due to the friction of hinged joints, plates with each other, between the teeth and chain elements, as well as in the support elements of the structure. In addition, there are losses due to splashing of the lubricant. True, they are significant only if the lubrication is carried out by immersing the chains in lubricants and when operating at speeds close to the maximum allowable.

Application areas of chain transmission

It is noteworthy that this species transmission has been known to mankind for a long time. At least in theory. A study of the works of the famous inventor and artist Leonardo da Vinci showed that he thought about various options for using chain drives in various mechanisms. In the drawings you can see the prototypes of modern bicycles and many other mechanisms known today. True, it is not known for certain whether the great Leonardo was able to put his ideas into practice. The industry of that time did not allow the manufacture of mechanisms with the required degree of accuracy.

For the first time in practice, it was possible to use this type of transmission only in 1832. It is worth noting that the appearance of a modern bicycle, as well as its technical and operational characteristics, was largely influenced by the fact that in 1876 the inventor Lawson had the idea to use a chain drive. Until that moment, the wheels were driven either directly through the pedals, or the rider had to push off with his feet from the ground.

This type of gear in various modifications is now used extremely extensively in various fields machine building. Transport, industrial machine tools, agricultural units - it is not possible to list all the mechanisms without exception in which varieties of chain transmission find their use.

It is also resorted to when the center distances are large enough. In these cases, the use of a belt-type transmission is impractical, and gears cannot be used due to a significant complication of the design and an increase in the mass of the mechanism. Do not forget about the friction force, which increases in direct proportion to the number of gears in the mechanism. In the case of chain drives, as already noted, there is a rolling friction force, which is several times less than the sliding friction force.

You can also find this type of gear in technology that uses the chain as a direct working element, and not as a drive one. These, for example, include snow removal units, elevator and scraper mechanisms, as well as similar ones.

As a rule, they resort to chain transmissions open type which are manually lubricated if necessary. In such designs, either moisture-dust protection is not carried out at all, or it is present at a minimum level, as is the case with a bicycle.

Typically, certain types of chain drives are used if it is necessary to transfer power up to 120 kilowatts at external speeds of no more than 15 meters per second.

A little about stars

The efficiency and duration of the entire chain mechanism will depend to a large extent on how the sprockets in the mechanism were made. This applies to both compliance with all exact dimensions and materials of manufacture.

The number of teeth is one of the most important characteristics of any sprocket.

The idler sprocket is used where the effect of chain slack needs to be prevented. Usually it is installed on the driven parts of the mechanisms.

The main parametric characteristics of sprockets are described in the relevant paragraphs of GOST 13576-81.

Chain types of transmissions are a really highly efficient and, moreover, economical type of mechanism. They are used in many areas of transport and machine building.

Varieties of chain transmission

Today you can face the most different classifications this type of transmission. It all depends on what kind of classification is carried out:

1. According to their purpose, transmissions are traction, drive, and also cargo.
2. Complex or simple - if we classify according to total number stars in the mechanism. It is customary to refer to complex mechanisms those mechanisms, which include more than two stars.
3. Also, transmissions can be master and slave.
4. If we classify gears based on the direction of rotation, then they can be direct and reverse.
5. According to the principle of location, they are closed, horizontally or vertically located.
6. Also, the stars can be centered differently. In this case, it is customary to distinguish between horizontal and vertical gears, as well as at a certain angle.
7. Low and high gears - according to the speed.
8. open and closed type gears - depending on whether they are placed in dust covers or not. Gears of a closed type can also be placed inside the mechanism, the case of which protects them from the ingress of dust and moisture.
9. Finally, according to the method of applying the lubricant, the gears can be manual, oil and circulation. Their specificity has already been mentioned a little above.

Each of these types is used in certain areas of technology.

Chain transmission is a transmission in which the energy between several parallel shafts is produced by a hitch using a flexible chain and sprockets. It consists of a chain and two sprockets. One asterisk is leading and the other is driven. The chain drive functions without slipping and is provided with tensioners and lubricators.

Chain transmission makes it possible to transfer movement between shafts in a larger range of center distances in comparison with a gear one. The chain transmission efficiency is - 0.96 ... 0.97. It has less effect on the shaft than it differs from a belt drive. One chain transmits speed to several sprockets for chain drives.

Varieties and scope of chain drives

Chain transmissions are classified into several categories, which differ in their design features and the principle of functional operation. Depending on the type of chains, transmission devices are divided into roller, sleeve and gear. By the number of rows of the chain, on the mechanisms of applying force for movement, there are single-row and multi-row. Depending on the number of driven star elements, there are two-link and multi-link mechanisms. According to the location of sprockets for chain drives, devices are divided into horizontal, inclined, vertical.

The negative qualities of transmission mechanisms include: spasmodic movement, increased roar during the implementation of work processes, the need for a carefully maintained assembly according to the established parameters and regular maintenance, constant adjustment of the tension of the chain device and lubrication of mechanical connections in time, rapid exposure to shock-absorbing action of the hinges of the chain device, high cost devices, chain stretching during use, etc.

Chain drives gained great popularity in a variety of machine tools, bicycles and motorcycles, in machines that lift loads, winches, in drilling rigs, in nodes and cranes, and exclusively in agricultural machines. For example, the C-4 self-propelled grain harvester has 18 chain drives that drive many of its working mechanisms. Chain transmission mechanisms have also become widespread in light industry enterprises.

Basic parameters of chain drives

The functioning of a chain-type device that changes the transmitting force depends on the characteristics of the star components: the correctness of their production, the hardening of the surface of the teeth, metal and the quality of processing. The sizes and shapes of sprockets are made according to the selected chain and gear ratio, which determines the number of teeth of the smaller drive sprocket. The gear ratio of a chain drive changes during operation and is calculated similarly to the gear ratio of a cylindrical gear. The assembly of the chain drive is limited to installing and fixing the sprockets on the shafts, putting on the chain and adjusting it.

When calculating the chain transmission, it is necessary to refrain from obtuse corners between the line that aligns the centers of the stars and the horizontal line. The leading branch is usually placed on top. In gears with large angles of elevation, it is necessary not to forget about tensioners. Chain drives, due to the inevitable stretching of the chain links, due to wear and tear in the hinges, usually require the possibility of adjusting their tension.

Initial tension is only important in vertical transfer actions. In horizontal and inclined transmission processes, the connection of the chain device with the star elements is guaranteed by the tension from the gravity of a particular chain link, while the sagging arrow of the chain connection must be optimal within the initially listed boundaries.

View: this article has been read 14944 times

Pdf Select language... Russian Ukrainian English

Short review

Full material is downloaded above, after selecting the language

Chain transmission is based on the meshing of the chain and sprockets.

Advantages and disadvantages

The principle of engagement and the high strength of the steel chain make it possible to provide a greater load capacity of the chain drive compared to the belt drive. The absence of sliding and slipping ensures the constancy of the gear ratio (average per revolution) and the ability to work with short-term overloads.

The meshing principle does not require pre-tensioning the chain, which reduces the load on the supports. Chain drives can operate at smaller center distances and at large gear ratios, as well as transfer power from one drive shaft to several driven ones.

The main reason for the shortcomings of the chain transmission is that the chain consists of separate rigid links located on the sprocket not in a circle, but in a polygon. This results in wear of the chain joints, noise and additional dynamic loads. Chain drives need to organize a lubrication system.

Application area:

• at significant center distances, at speeds less than 15-20 m / s, at speeds up to 35 m / s, lamellar chains are used (a set of plates of two tooth-like protrusions, the principle of internal engagement);
• when transferring from one drive shaft to several driven ones;
• when gears are not applicable and belt drives are unreliable.

Compared to belt drives, chain drives are noisier, and they are used in gearboxes at low-speed levels.

The main characteristics of the chain drive

Power
Modern chain transmissions can operate in a fairly wide range: from fractions to several thousand kilowatts. But at high power, the cost of transmission increases, so chain transmissions up to 100 kW are most common.

Peripheral speed
With increasing speed and speed, wear, dynamic loads and noise increase.

Gear ratio:
The gear ratio of the chain drive is limited to 6, due to the increase in dimensions.

KKD transmission
Losses in the chain transmission consist of friction losses in the chain joints, on the teeth of the sprockets and in the shaft bearings. In lubrication by immersion in a lubricating bath, the mixing losses of the lubricating oil are taken into account. Average value of KKD

Center distance and chain length
The minimum value of the center distance is limited by the minimum allowable gap between the sprockets (30...50 mm). To ensure durability, depending on the gear ratio

Types of drive chains

• Roller
• bushing
• jagged

All chains are standardized and manufactured at special enterprises.

Drive chain sprockets

Sprockets are like gear wheels. The pitch circle passes through the centers of the hinges of the chain.

The tooth profile of roller and sleeve chains can be convex, straight and concave, in which only the main lower section of the profile is concave, the shape is convex at the top, and there is a small straight transition section in the middle part. The concave profile is the most common.

The quality of the profile is determined by the angle of the profile, which for concave and convex profiles varies with the height of the tooth. With an increase in the angle of the profile, the wear of the teeth and hinges decreases, but this leads to an increase in the impact of the hinges when engaging, as well as to an increase in the tension of the idle branch of the chain.

materials

Chains and sprockets must be resistant to wear and shock loads. Most chains and sprockets are made from carbon and alloy steels with further heat treatment (improvement, hardening).

Sprockets, as a rule, are made from steels 45, 40X, etc., chain plates - from steels 45, 50, etc., rollers and rollers - from steels 15, 20.20X, etc.

Hinge parts are cemented to increase wear resistance while maintaining impact strength.

In the future, it is planned to manufacture sprockets from plastics, which can reduce dynamic loads and transmission noise.

Forces in engagement

• tension forces of the leading and driven branches,
• district force,
• pretension force,
• centrifugal force.

Kinematics and dynamics of chain drives

The movement of the driven sprocket is determined by the speed V 2 , the periodic changes of which are accompanied by the variability of the gear ratio and additional dynamic loads. The speed V 1 is associated with transverse oscillations of the chain branches and impacts of the chain hinges against the teeth of the sprocket, causing additional dynamic loads.

With a decrease in the number of teeth z 1, the dynamic properties of the transmission deteriorate.

Shocks cause noise during transmission operation and are one of the causes of chain failure. To limit the harmful effects of impacts, recommendations have been developed for choosing a chain pitch depending on the speed of the transmission. At a certain speed, a circuit vibration resonance phenomenon may occur.

During operation, wear of the chain hinges occurs due to an increase in the gaps between the roller and the sleeve, as a result, the chain is stretched.

The wear life of the chain depends on the center distance, the number of teeth of the small sprocket, the pressure in the joint, the lubrication conditions, the wear resistance of the chain material, the allowable relative wear

As the chain length increases, the service life increases. With a smaller number of sprocket teeth, the dynamics worsens. An increase in the number of teeth leads to an increase in dimensions, the permissible relative clearance decreases, which is limited by the possibility of losing the chain engagement with the sprocket, as well as a decrease in the strength of the chain.

Thus, with an increase in the number of teeth of the sprocket z, the permissible relative wear of the hinges decreases, and as a result, the life of the chain before the loss of engagement with the sprocket decreases.

The maximum service life, taking into account the strength and the ability to engage, is ensured by the choice of the optimal number of sprocket teeth.

Chain transmission performance criteria

The main reason for the loss of performance is the wear of the chain joints. The main design criterion for the wear resistance of hinges

The wear life of a chain depends on:

• from the center distance (the length of the chain increases and the number of runs of the chain per unit time decreases, i.e. the number of turns in each hinge of the chain decreases);
• on the number of teeth of a small sprocket (with an increase in z1, the angle of rotation in the hinges decreases).

The method for practical calculation of the chain transmission is given in.

chain drive, chain, sprocket, chain pitch

An example of the calculation of a spur gear
An example of the calculation of a spur gear. The choice of material, the calculation of allowable stresses, the calculation of contact and bending strength were carried out.

An example of solving the problem of beam bending
In the example, diagrams of transverse forces and bending moments are plotted, a dangerous section is found, and an I-beam is selected. In the problem, the construction of diagrams using differential dependencies is analyzed, a comparative analysis of various beam cross sections is carried out.

An example of solving the problem of shaft torsion
The task is to test the strength of a steel shaft for a given diameter, material and allowable stresses. During the solution, diagrams of torques, shear stresses and twist angles are built. Self weight of the shaft is not taken into account

An example of solving the problem of tension-compression of a rod
The task is to test the strength of a steel rod at given allowable stresses. During the solution, plots of longitudinal forces, normal stresses and displacements are built. Self weight of the bar is not taken into account

Application of the kinetic energy conservation theorem
An example of solving the problem of applying the theorem on the conservation of kinetic energy of a mechanical system

Determination of the speed and acceleration of a point according to the given equations of motion
An example of solving the problem of determining the speed and acceleration of a point according to the given equations of motion

The transfer of energy between two or more parallel shafts, carried out by engagement with a flexible endless chain and sprockets, is called chain.

The chain drive consists of a chain and two sprockets - leading 1 (Fig. 190) and driven 2, works without slipping and is equipped with tensioning and lubricating devices.

Rice. 190

Chain drives make it possible to transmit movement between shafts in a significant range of center distances compared to gear drives; have a sufficiently high efficiency equal to 0.96 ... 0.97; have less than in a belt drive, the load on the shaft; one chain transmits rotation to several sprockets (shafts).

The disadvantages of chain drives include: some uneven travel, noise during operation, the need for careful installation and maintenance; the need to adjust the chain tension and timely lubrication; rapid wear of chain hinges; high cost; chain pulling during operation, etc.

Chain drives are most widely used in various machine tools, bicycles and motorcycles, in hoisting and transport machines, winches, in drilling equipment, in running gears of excavators and cranes, and especially in agricultural machines. So, for example, in the self-propelled grain combine C-4 there are 18 chain gears that set in motion a number of its working bodies. Chain transmissions are also often found in the textile and cotton industries.

Chain parts

Asterisks. The operation of a chain transmission largely depends on the quality of the sprockets: the accuracy of their manufacture, the quality of the surface of the teeth, material and heat treatment.

The design dimensions and shape of the sprockets depend on the parameters of the selected chain and the gear ratio, which determines the number of teeth of the smaller drive sprocket. The parameters and quality characteristics of the sprockets are established by GOST 13576-81. The sprockets of roller and sleeve chains (Fig. 191, I) are profiled in accordance with GOST 591-69.

Rice. 191

The working profile of the sprocket tooth for roller and sleeve chains is outlined by an arc corresponding to the circle. For gear chains, the working profiles of the sprocket teeth are straight. In cross section, the sprocket profile depends on the number of chain rows.

The sprocket material must be wear-resistant, capable of withstanding shock loads. Sprockets are made from steels 40, 45, 40X and others with hardening to HRC 40...50 hardness or case hardened steel 15, 20, 20X and others with hardening to HRC 50... .60 hardness. For sprockets of low-speed gears, gray or modified cast iron SCH 15, SCH 20, etc. are used.

Currently, sprockets with a ring gear made of plastics are used. These sprockets are characterized by reduced chain wear and low transmission noise.

Chains. Chains are manufactured at special factories, and their design, dimensions, materials and other indicators are regulated by standards. According to their purpose, circuits are divided into the following types:

• cargo chains (Fig. 192, I) used for suspension, lifting and lowering loads. They are mainly used in lifting machines;
• traction chains (Fig. 192, II), which serve to move goods in transporting vehicles;
• drive chains used to transfer mechanical energy from one shaft to another.

Rice. 192

Let us consider in more detail the drive chains used in chain drives. There are the following types of drive chains: roller, sleeve, toothed and hook.

roller chains(Fig. 192, III) consist of alternating external and internal links, which have relative mobility. The links are made of two plates pressed onto axles (outer links) or bushings (inner links). The bushings are put on the axis of the mating links and form hinges. To reduce the wear of sprockets when running chains on them, rollers are put on the bushings, which replace sliding friction with rolling friction (Fig. 191, II and III).

The axles (rollers) of the chains are riveted and the links become one-piece. The connection of the ends of the chain is carried out: with an even number of links - a connecting link, and with an odd number - a transitional one.

At high loads and speeds, in order to reduce the pitch and diameter of the sprockets, multi-row roller chains are used.

Roller chains with curved plates (Fig. 192, IV) consist of identical links, similar to the transition link. These chains are used when the transmission is working with a shock load (reversing, jolts). The deformation of the plates contributes to the damping of shocks that occur when the chain enters into engagement with the sprocket.

Sleeve chains(Fig. 192, V) in their design do not differ from the previous ones, but do not have rollers, which leads to increased wear of the teeth. The absence of rollers reduces the cost of the chain and reduces its weight.

Sleeve chains, like roller chains, can be single-row and multi-row.

Toothed (silent) chains(Fig. 192, VI) consist of a set of plates with teeth, hinged in a certain sequence. These circuits provide smooth and quiet operation. They are used at high speeds. Toothed chains are more complex and more expensive than roller chains and require special care. The working faces of the plates, which perceive pressure from the teeth of the sprocket, are the planes of the teeth, located at an angle of 60°. To ensure sufficient wear resistance, the working surfaces of the plates are hardened to a hardness of H RC 40...45.

In order to prevent the gear chains from slipping off the sprockets during operation, they are equipped with guide plates (side or internal).

Hook chains(Fig. 192, VII) consist of identical links of a special shape and do not have any additional details. Connected separation of the links is carried out with a mutual inclination at an angle of approximately 60 °.

Bush-pin chains(Fig. 192, VIII) are assembled from links using pins made of StZ steel. The pins are riveted, and in the connecting links they are fixed with cotter pins. These chains are widely used in agricultural engineering.

To ensure good chain performance, the materials of its elements must be wear-resistant and durable. For plates, steel 50 and 40X is used and hardened to a hardness of HRC35 ... 45, for axles, rollers and bushings - steel 20G, 20X, etc. with a hardness of HRC54 ... 62-, for rollers - steel 60G with a hardness of HRC48 .. .55.

Due to the wear of the hinges, the chain gradually stretches. The chain tension is controlled by moving the axis of one of the sprockets, using adjusting sprockets or rollers. Typically, tensioners allow you to compensate for the elongation of the chain within two links, with a greater stretch of the chain for the link, it is removed.

The durability of the chain depends largely on the correct application of the lubricant. At a chain speed (v) equal to or less than 4 m/s, periodic lubrication is used, which is carried out with a manual oiler every 6–8 hours. At v s 10 m/s, lubrication with dropper greasers is used. More perfect lubrication by dipping the chain in an oil bath. In this case, the immersion of the chain in oil should not exceed the width of the plate. In powerful high-speed gears, circulating jet lubrication from a pump is used.