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2.16. Balancing rotors and armatures
The repaired rotors and armatures of electrical machines are sent for static, and if necessary, for dynamic balancing, complete with fans and other rotating parts. Balancing is carried out on special machines to detect imbalance (imbalance) of the masses of the rotor and armature. The reasons for the uneven distribution of masses can be: different thicknesses of individual parts, the presence of shells in them, unequal overhang of the frontal parts of the winding, etc. Any part of the rotor or armature can be unbalanced as a result of the shift of the axes of inertia relative to the axis of rotation. Unbalanced masses of individual parts, depending on their location, can be summed up or mutually compensated.
Rotors and armatures, in which the central axis of inertia does not coincide with the axis of rotation, are called unbalanced.
The rotation of an unbalanced rotor or armature causes vibration that can destroy the bearings and foundation of the machine. To avoid this, the rotors are balanced, which consists in determining the size and location of the unbalanced mass and eliminating the imbalance.
Unbalance is determined by static or dynamic balancing. The choice of balancing method depends on the balancing accuracy that can be carried out on this equipment. With dynamic balancing, better imbalance compensation results are obtained than with static balancing.
Static balancing is performed with a non-rotating rotor on prisms, disks or special scales (Fig. 2.45). To determine the imbalance, the rotor is unbalanced with a slight push. An unbalanced rotor will tend to return to a position where its heavy side is at the bottom. After the rotor stops, mark with chalk the place that turned out to be in the upper position. The process is repeated several times. If the rotor stops in the same position, then its center of gravity is shifted.
Rice. 2.45. :
a - on prisms; b - on disks; c - on special scales; 1 - cargo; 2 - cargo frame; 3 - indicator; 4 - frame; 5 - rotor (armature)
In a certain place (most often, this is the inner diameter of the pressure washer rim), test weights are installed, attaching them with putty. After that, the balancing procedure is repeated. By increasing or decreasing the weights of the loads, the rotor is stopped in an arbitrary position. This means that the rotor is statically balanced.
At the end of balancing, test weights are replaced by one weight of the same mass.
Unbalance can be compensated for by drilling an appropriate piece of metal from the heavy part of the rotor.
More accurate than on prisms and disks is balancing on special scales.
Static balancing is used for rotors with a rotation speed of not more than 1000 rpm. A statically balanced rotor can be dynamically unbalanced, therefore, rotors with a speed of more than 1000 rpm are subjected to dynamic balancing, which also eliminates static imbalance.
Dynamic balancing of the rotor, which is performed on a balancing machine, consists of two operations: measurement of the initial vibration; finding the location point and weight of the balancing weight for one of the ends of the rotor.
Balancing is done on one side of the rotor, and then on the other. After balancing, the load is fixed by welding or screws. Then perform a test balancing.
Most machine tools of repair plants are made according to the principle of measuring the magnitude of the imbalance vector by the maximum deviation of the supports at resonant rotational frequencies. This measures the magnitude of the vector. The direction of the vector is fixed by the servo system according to the angle of rotation of the tested body of revolution. The indicators are summarized in the measuring device, according to the mutual reaction of the coils of the device, according to the principle of an electrodynamic wattmeter.
Initially, the existing imbalance is measured. Its correction consists in the installation of balancing weights provided by the drawing of the product in the direction directly opposite to the measured vector. Or in a small removal of metal in the direction strictly corresponding to the measured vector.
Loads, depending on the design of the unit, are fixed temporarily or permanently. The vector is re-measured and the installed weights are adjusted, or their final fixing, provided for by the design, if the value of the residual imbalance corresponds to the allowable
Mass-produced machines for dynamic balancing
Machine tools manufactured by the Minsk Machine Tool Plant of the type 9717, 9718, 9719 are widely used. This equipment has significant dimensions and requires a large volume for the installation of reinforced concrete foundations. They balance parts and assembly units from 0.5 to 5.0 tons. These are anchors of electric cars and wheelsets. Since the mid-80s, the design of generator anchor flanges has been changed. The outer surface of the socket for the installation of the centering ring is made in the form of an elongated collar of a cylindrical shape, which can directly serve as a base surface for dynamic balancing of the armature. This made it possible to abandon the installation of additional bushings, reduce the complexity of the operation and increase its accuracy.
Fig. 20 Armature balancing on machine 9719
New generation of machines
Recently, a new generation of balancing machines has appeared in the factories, which are offered on the market today. In particular, these are DIAMEX machines. A feature of the machines is that the unbalance is measured not due to the maximum deviation of the movable bearing supports, but due to the reaction of rigidly fixed supports. In this case, the reaction itself is measured as a magnitude of stresses by a tensometric method using built-in sensors. All results are summarized and processed on the computer built into the machine with information displayed on the display.
This design of the machine does not require foundations for its installation. The machine is installed directly on the floor surface. The dimensions of these machines slightly exceed the dimensions of the product being balanced.
Fig. 21 Dynamic balancing on the BM3000 machine from DIAMEX
A very characteristic detail for new generation machines is the absence of a foundation and the transmission of the rotation part by a belt drive.
April 4, 2011For static balancing, a machine is used, which is a supporting structure made of profiled steel with trapezoidal prisms installed on it. The length of the prisms must be such that the rotor can make at least two revolutions on them.
The width of the working surface of the prisms a is determined by the formula:
where: G is the load on the prism, kg; E is the modulus of elasticity of the prism material, kg/cm2; p is the calculated specific load, kg / cm 2 (for hard hardened steel p \u003d 7000 - 8000 kg / cm 2); d is the shaft diameter, cm.
In practice, the width of the working surface of the prisms of balancing machines for balancing rotors weighing up to 1 ton is 3–5 mm. The working surface of the prisms must be well ground and capable of supporting the mass of the balanced rotor without deforming.
Machines for balancing rotors (armatures) of electrical machines:
a - static, b - dynamic;
1 - rack, 2 - balanced rotor, 3 - pointer indicator, 4 - disengagement clutch, 5 - drive motor, b — segments, 7 - clamping bolts, 8 - bearing, 9 - plate.
Static balancing of the rotor on the machine is carried out in the following sequence. The rotor is placed with the shaft necks on the working surfaces of the prisms. In this case, the rotor, rolling on prkzma, will take such a position in which its heaviest part will be at the bottom.
To determine the point of the circle at which the balancing weight should be installed, the rotor is rolled five times and after each stop the lower “heavy” point is marked with chalk. After that, five chalk lines will appear on a small part of the rotor circumference.
Having marked the middle of the distance between the extreme chalk marks, the installation point of the balancing weight is determined: it is located in a place diametrically opposite to the average heavy current. At this point, a balancing weight is installed.
Its mass is selected empirically until the rotor stops rolling, being stopped in any arbitrary position. A correctly balanced rotor, after rolling in one direction and the other, should be in a state of indifferent equilibrium in all positions.
If it is necessary to more fully detect and eliminate the remaining unbalance, the rotor circumference is divided into six equal parts. Then, laying the rotor on prisms so that each of the marks is alternately on the horizontal diameter, small weights are alternately hung into each of the six points until the rotor comes out of rest.
The masses of goods for each of the six points will be different. The smallest mass will be at the heavy point, the largest - at the diametrically opposite point of the rotor.
With the static balancing method, a balancing weight is installed only at one end of the rotor and thus eliminates static unbalance.
However, this balancing method is applicable only for short rotors of small and low-speed machines. To balance the masses of the rotors of large electrical machines (with a power of more than 50 kW) with high rotation speeds (more than 1000 rpm), dynamic balancing is used, in which a balancing weight is installed on both ends of the rotor.
This is explained by the fact that when the rotor rotates at high speed, each of its ends has an independent beat caused by unbalanced masses.
"Repair of electrical equipment of industrial enterprises",
V.B. Atabekov
In modern electrical machines, mainly ball or roller bearings are used. They are easy to operate, withstand temperature fluctuations well, and can be easily replaced when worn. Plain bearings are used in large electrical machines. Rolling bearings When repairing an electric machine with rolling bearings, as a rule, they are limited to washing the bearings and laying in them a new portion of the corresponding ...
The final stages of checking the repaired electric motor are gap measurements and a test run. The gaps are measured using a set of steel plates - probes with a thickness of 0.01 to 3 mm. For asynchronous machines, the gap is measured from both ends at four points between the active steel of the rotor and stator. The gap must be the same around the entire circumference. Sizes of gaps in diametrically…
The degree of wear of rolling bearings is determined by measuring their radial and axial (axial) clearances on simple fixtures manufactured in the electrical workshops of the enterprise. To measure the radial clearance on such a device, the bearing 11 is mounted on the vertical plate 8 of the device. Putting a steel hose 10 on the inner ring 2 of the bearing, fix it with a nut screwed onto the rod 9 welded to the vertical plate; ...
In the practice of repairing electrical machines, it often becomes necessary to calculate the windings or recalculate them to new parameters. Winding calculations are usually carried out if the electric motor to be repaired does not have passport data or if the motor is received for repair without a winding. The need to recalculate the windings also arises when it is necessary to change the number of revolutions or voltage, convert single-speed motors to ...
The current-collecting system of electrical machines includes collectors, slip rings, brush holders with traverses and a brush-lifting mechanism, short-circuiting rings of phase rotors of old designs. During the operation of the machine, individual elements of the current-collecting system wear out, as a result of which its normal operation is disrupted. The most common defects of the current-collecting system are: unacceptable wear of the collector and slip rings, the appearance of irregularities on their working surfaces and ...
Unbalance of any rotating part of a diesel locomotive can occur both during operation due to uneven wear, bending, accumulation of contaminants in one place, when the balancing weight is lost, and during repair due to improper processing of the part (shift of the axis of rotation) or inaccurate alignment of the shafts. To balance the parts, they are subjected to balancing. There are two types of balancing: static and dynamic.
Rice. 1. Scheme of static balancing of parts:
T1 is the mass of the unbalanced part; T2 is the mass of the balancing load;
L1, L2 are their distances from the axis of rotation.
Static balancing. In an unbalanced part, its mass is located asymmetrically relative to the axis of rotation. Therefore, in the static position of such a part, i.e. when it is at rest, the center of gravity will tend to take a lower position (Fig. 1). To balance the part, a load of mass T2 is added from the diametrically opposite side so that its moment T2L2 is equal to the moment of the unbalanced mass T1L1. Under this condition, the part will be in balance in any position, since its center of gravity will lie on the axis of rotation. Equilibrium can also be achieved by removing part of the metal part by drilling, sawing or milling from the side of the unbalanced mass T1. On the drawings of parts and in the Repair Rules, a tolerance is given for balancing parts, which is called unbalance (g / cm).
Flat parts with a small ratio of length to diameter are subjected to static balancing: a gear wheel of a traction gearbox, a refrigerator fan impeller, etc. Static balancing is carried out on horizontally parallel prisms, cylindrical rods or on roller bearings. The surfaces of prisms, rods and rollers must be carefully processed. The accuracy of static balancing largely depends on the condition of the surfaces of these parts.
Dynamic balancing. Dynamic balancing is usually applied to parts whose length is equal to or greater than their diameter. On fig. 2 shows a statically balanced rotor, in which the mass T is balanced by a load of mass M. This rotor, when rotating slowly, will be in equilibrium in any position. However, with its rapid rotation, two equal, but oppositely directed centrifugal forces F1 and F2 will arise. In this case, a moment FJU is formed, which tends to rotate the rotor axis at a certain angle around its center of gravity, i.e. there is a dynamic imbalance of the rotor with all the ensuing consequences (vibration, uneven wear, etc.). The moment of this pair of forces can only be balanced by another pair of forces acting in the same plane and creating an equal counteracting moment.
To do this, in our example, it is necessary to attach two loads with masses Wx = m2 to the rotor in the same plane (vertical) at an equal distance from the axis of rotation. The weights and their distances from the axis of rotation are selected so that the centrifugal forces from these weights create a moment /y counteracting the moment FJi and balancing it. Most often, balancing weights are attached to the end planes of the parts or a part of the metal is removed from these planes.
Rice. 2. Scheme of dynamic balancing of parts:
T is the mass of the rotor; M is the mass of the balancing load; F1,F2 - unbalanced, reduced to the planes of the mass of the rotor; m1,m2 are balanced masses of the rotor reduced to planes; P1 P 2 - balancing centrifugal forces;
During the repair of diesel locomotives, such fast-rotating parts as the rotor of a turbocharger, the armature of a traction motor or other electric machine, the impeller of the blower assembly with the drive gear, the shaft of the water pump assembly with the impeller and gear wheel, cardan shafts of the drive of power mechanisms are subjected to dynamic balancing.
Rice. 3. Scheme of a cantilever type balancing machine:
1 - spring; 2 - indicator; 3 anchor; 4 - frame; 5 - machine support; 6 - bed support;
I, II - planes
Dynamic balancing is underway on balancing machines. A schematic diagram of such a cantilever type machine is shown in fig. 3. Balancing, for example, the armature of the traction motor is carried out in this order. Anchor 3 is placed on the supports of the swinging frame 4. The frame rests at one point on the support of the machine 5, and the other on the spring 1. When the anchor rotates, the unbalanced mass of any of its sections (except for the masses lying in the plane II - II) causes the frame to swing. The frame oscillation amplitude is fixed by indicator 2.
To balance the anchor in the I-I plane, test weights of various masses are attached to its end face from the side of the collector (to the pressure cone) in turn and the frame oscillations are stopped or reduced to an acceptable value. Then the anchor is turned over so that the plane I-I passes through the fixed support of the frame 6, and the same operations are repeated for the plane II-II. In this case, the balance weight is attached to the rear thrust washer of the anchor.
After completion of all work on the acquisition, the parts of the selected kits are marked (letters or numbers) according to the requirements of the drawings.
Page 13 of 14
Banding.
When the rotors and armatures of electrical machines rotate, centrifugal forces arise, tending to push the winding out of the grooves and bend its frontal parts. To counteract centrifugal forces and keep the winding in the grooves, wedging and shrouding of the windings of the rotors and armatures is used.
The application of the winding fastening method (wedges or bandages) depends on the shape of the rotor or armature slots. With half-open and half-closed grooves, only wedges are used, and with open grooves, bandages or wedges are used. The grooved parts of the windings in the cores of the armatures and rotors are fixed with wedges or bandages made of steel bandage wire or glass tape, and also with wedges and bandages at the same time; the frontal parts of the windings of the rotors and anchors - bandages. Reliable fastening of the windings is important, since it is necessary to counteract not only centrifugal forces, but also the dynamic forces that the windings are subjected to with rare changes in current. For shrouding the rotors, tinned steel wire with a diameter of 0.8–2 mm is used, which has a high tensile strength.
Before winding the bandages, the frontal parts of the winding are upset by hammer blows through a wooden spacer so that they are evenly located around the circumference. When shrouding the rotor, the space under the shrouds is preliminarily covered with strips of electric cardboard in order to create an insulating gasket between the rotor core and the shroud, protruding by 1–2 mm on both sides of the shroud. The entire bandage is wound with one piece of wire, without rations. On the frontal "parts of the winding, in order to prevent their swelling, coils of wire are applied from the middle of the rotor to its ends. If the rotor has special grooves, the bandage wires and locks should not protrude above the grooves, and in the absence of grooves, the thickness and location of the bandages should be the same as they were before repair.
Brackets mounted on the rotor should be placed over the teeth, not over the grooves, and the width of each of them should be less than the width of the top of the tooth. The brackets on the bandages are evenly spaced around the circumference of the rotors with a distance between them of no more than 160 mm.
The distance between two adjacent bandages should be 200-260 mm. The beginning and end of the binding wire are sealed with two lock brackets 10-15 mm wide, which are set at a distance of 10-30 mm from one another. The edges of the brackets are wrapped around the turns of the bandage and. soldered with POS 40 solder.
To increase strength and prevent their destruction by centrifugal forces created by the mass of the winding during rotation of the rotor, fully wound bandages are soldered over the entire surface with POS 30 or POS 40 solder. The bandages are soldered with an electric arc soldering iron with a copper rod diameter. 30 - 50 mm, attached to the welding transformer.
In repair practice, wire bandages are often replaced with glass tapes made of unidirectional (in the longitudinal direction) glass fiber impregnated with thermosetting varnishes. For winding bandages made of glass tape, the same equipment is used as for banding with steel wire, but supplemented with devices c. the form of tension rollers and tape handlers.
In contrast to bandaging with steel wire, the rotor is heated up to 100 °C before winding bandages made of glass tape. Such heating is necessary because when a bandage is applied to a cold rotor, the residual stress in the bandage during its baking decreases more than when a heated one is bandaged.
The cross section of the bandage made of glass tape must be at least 2 times greater than the section of the corresponding bandage made of wire. The fastening of the last turn of the glass tape with the underlying layer occurs during the drying of the winding during sintering of the thermosetting varnish with which the glass tape is impregnated. When shrouding the windings of the rotors with glass tape, locks, brackets and underband insulation are not used, which is an advantage of this method.
Balancing.
Repaired rotors and armatures of electrical machines are subjected to static and, if necessary, dynamic balancing as an assembly with fans and other rotating parts. Balancing is carried out on special machines to detect imbalance (imbalance) of the masses of the rotor or armature, which is a common cause of vibration during. machine operation.
The rotor and armature consist of a large number of parts and therefore the distribution of masses in them cannot be strictly uniform. The reasons for the uneven distribution of masses are the different thickness or mass of individual parts, the presence of shells in them, unequal, the departure of the frontal parts of the winding, etc. Each of the parts included in the assembled rotor or armature may be unbalanced due to the displacement of its axes of inertia from. axis of rotation. In the assembled rotor and armature, unbalanced masses of individual parts, depending on their location, can be summed up or mutually compensated. Rotors and armatures, in which the main central axis of inertia does not coincide with the axis of rotation, are called unbalanced.
Rice. 155. Ways of static balancing of rotors and anchors:
a - on prisms, b - on disks, c - on special scales; 1 - cargo, 2 - cargo frame, 3 - indicator, 4 - frame, 5 - balanced rotor (anchor)
Unbalance, as a rule, consists of the sum of two imbalances - static and dynamic.
The rotation of a statically and dynamically unbalanced rotor and armature causes vibration that can destroy the bearings and foundation of the machine. The destructive effect of unbalanced rotors and armatures is eliminated by balancing them, which consists in determining the size and location of the unbalanced mass;
Unbalance is determined by static or dynamic balancing. The choice of balancing method depends on the required balancing accuracy, which can be achieved with the existing equipment. With dynamic balancing, better results of imbalance compensation (less residual imbalance) are obtained than with static balancing. Such balancing can eliminate both / dynamic and static unbalance / If it is necessary to eliminate unbalance (imbalance) at both ends of the rotor or armature, only dynamic balancing should be performed. Static balancing is performed with a non-rotating rotor on prisms (Fig. 155, i), disks (Fig. 155.5) or special weights (Fig. 155, c). Such balancing can only eliminate static imbalance.
To determine the imbalance, the rotor is unbalanced with a slight push; An unbalanced rotor (anchor) will tend to return to a position in which its heavy side is at the bottom. After the rotor stops, mark with chalk the place that is in the upper position. The reception is repeated several times to check whether the rotor (armature) always stops in this position. Stopping the rotor in the same position indicates a shift in the center of gravity.
In the place reserved for balancing weights (most often this is the inner diameter of the pressure washer rim), test weights are installed, attaching them with putty. After that, the balancing procedure is repeated. By adding or decreasing the mass of loads, the rotor is stopped in any, arbitrarily taken position. This means that the rotor is statically balanced, i.e. its center of gravity is aligned with the axis of rotation. At the end of balancing, the test weights are replaced with one of the same section and mass, equal to the mass of the test weights and putty and the part of the electrode reduced by the mass, which will be used for welding the permanent load. Unbalance can be compensated for by drilling out an appropriate piece of metal from the heavy side of the rotor.
More accurate than on prisms and disks is balancing on special scales. The balanced rotor 5 is mounted by the shaft journals on the supports of the frame 4, which can rotate around its axis at a certain angle by turning the balanced rotor, the highest indicator reading J is achieved, which will be provided that the center of gravity of the rotor shown in the figure is located (at the greatest distance from the axis of rotation of the frame ). By adding an additional load-frame 2 with divisions to the load 1, the rotor is balanced, which is determined by the indicator arrow. At the moment of balancing, the arrow is aligned with the zero division.
If the rotor is rotated by 180, its center of gravity will approach the swing axis of the frame by a double eccentricity of the displacement of the center of gravity of the rotor relative to its axis. This moment is judged by the lowest reading of the indicator. The rotor is balanced again by moving the cargo frame 2 along the ruler with a scale calibrated in grams per centimeter. The magnitude of the imbalance is judged by the readings of the scale of the scales.
Static balancing is used for rotors rotating at a speed not exceeding 1000 rpm. A statically balanced rotor (armature) may have a dynamic imbalance, therefore, rotors rotating at a frequency above 1000 rpm are most often subjected to dynamic balancing, in which both types of imbalances - static and dynamic - are simultaneously eliminated.
Dynamic balancing during the repair of electrical machines is carried out on a balancing machine at a reduced (compared to the operating) speed or when the rotor (armature) rotates in its own bearings at the operating speed.
For dynamic balancing, the most convenient machine is a resonant type (Fig. 156), consisting of two welded posts U support plates 9 and balancing heads.
Rice. 156. Resonance type machine for dynamic balancing of rotors and armatures
Heads consisting of bearings 8 and segments 69 can be fixed with bolts 7 or swing freely on the segments. The balanced rotor 2 is driven by the electric motor 5, the clutch 4 serves to disconnect the rotating rotor from the drive at the moment of balancing.
Dynamic balancing of rotors consists of two operations: measuring the initial vibration, which gives an idea of the size of the unbalance of the masses of the rotor; finding the placement point and determining the mass of the balancing weight for one of the ends of the rotor.
During the first operation, the machine heads are fixed with bolts 7. The rotor 2 is set in rotation with the help of an electric motor 5, after which the drive is turned off, disengaging the clutch, and one of the machine heads is released. Released head under the action of a radially directed unbalance force
swings, which allows you to measure the amplitude of the vibration of the head with a pointer indicator 3. The same measurement is made for the second head.
The second operation is performed by the “load bypass” method. Dividing both sides of the rotor into six equal parts, a test load is fixed at each point in turn, which should be slightly less than the expected unbalance. Then, in the manner described above, the vibrations of the head are measured for each position of the load. The required place for placing the load will be the point at which the amplitude of oscillations is minimal. The mass of the load is selected empirically. -
After balancing one side of the rotor, balance its other side in the same way. Having finished balancing both sides of the rotor, the installed load is finally temporarily fixed by welding or screws, while taking into account the mass of the weld or screws.
As a load, most often pieces of strip steel are used. The fastening of the load must be reliable, since an insufficiently firmly fixed load can break away from the rotor during the operation of the machine and cause a severe accident or accident.
Having secured a constant load, the rotor is subjected to test balancing and, with satisfactory results, is transferred to the assembly department for assembling the machine.
