How to bend a wooden beam. Manufacturing technology for bending wood with steaming How to bend a wooden

Often, in the manufacture of structural elements from wood, it is necessary to obtain curved parts, and it is not always possible to make such an element by simple sawing or milling. For this purpose, it is used wood bending . This technology makes it possible to use wood more economically than the technology of its mechanical processing, which is especially important for areas with a shortage of timber.

Actually, wood bending – the old fashioned way obtaining curvilinear blanks, based on the property of wood to change shape under the influence of moisture, temperature and external load, as well as its ability to retain its shape even after the load is removed. External loads in this case- these are bending forces combined with the plasticity of wood, allowing you to bend wooden blanks.
Theoretically, the essence of these processes is the occurrence in the material of normal (perpendicularly directed with respect to the cross section) stresses that stretch the material along the convex side and compress it along the concave sides. This process is associated with a shift of material layers along the fibers. Therefore, the saw cut should pass just along the fibers, and knots are unacceptable.

The magnitude of the resulting stresses depends on the thickness of the bar, and they differ significantly in the areas of tension and compression: the allowable tension of wood does not exceed 1-2%, but the compression limit reaches 15-20%. That is why, with free bending, wood parts are destroyed due to the rupture of the outer layers, which are affected by tensile forces.
To avoid such gaps, you should use the boiling or steaming of wood - wood bending in this case will occur without its destruction. The steaming method is preferable, since in this case the wood fibers are saturated with moisture more evenly, however, in artisanal conditions, this method is technically not always possible. Therefore, instead of it, it is better to use boiling, especially if you need to bend small plot details.

Boiling should be carried out in water heated to 90-95 ° C; water should not be brought to a boil. The duration of welding is determined by the type of wood, its initial moisture content and the thickness of the bar. For example, a 40 mm thick beech bar with an initial moisture content of 15% must be boiled for 1 hour and 30 minutes. Then the part must be fixed in the clamp of the template and, gradually increasing the load, give it the desired shape.

Hardwood (birch, beech, ash, hornbeam, maple, linden, etc.) is the most plastic, therefore it is more often used to obtain bent wood blanks.

How to bend plywood with your own hands

To obtain bent glued parts, birch veneer is more often used - wood fibers conifers less plastic, so they are less often used.
How to bend plywood to get a blank with a small radius of curvature from plywood? In this case, it can also be subjected to boiling or steaming.

However, here it is necessary to take into account the type of glue used to glue the plywood layers. When gluing with waterproof adhesives, it is quite possible to use boiling, if protein glues were used for gluing, then only steaming is possible, moreover, only from the side where the plywood will be stretched. To bend thick plywood (over 5 mm thick), it is necessary to use additional techniques in the form of cuts along the inside, if the design of the part allows it.

Also, curved parts can be obtained by combining bending with simultaneous gluing. Such parts do not require additional drying, since the stabilization of the shape occurs during gluing. The thickness of the glued layers can be from 3 to 12 mm. In thick layers, additional cuts are made, into which strips of veneer smeared with glue are inserted. The thickness of the strip should be 0.1 mm less than the width of the cut.

How to bend a board, plywood, fiberboard, MDF with your own hands

Often during the course of repair work there is a need to obtain curved surfaces of products made of wood. How to bend the board in such a way that the bend is strong and does not crack during the bending process? What if you decide to do overhaul with your own hands, then you should not retreat before such difficulties. In this article, we will talk in detail about how to give a wood material a curved shape.

How to bend a tree?

No, our task is not at all to bend an innocent plant. It's about wood. building materials. How to bend a tree so that it bends and does not break? Bending method wooden products It has been known since ancient times: to give wood a shape, only heat and moisture are needed, under the influence of which the plasticity of the material increases with all the ensuing consequences. How to bend a tree? Hold him in hot water (the higher the temperature, the faster the processes) or steam ( a steam generator can be built from a kettle or use an iron). The higher the temperature, the faster the wood gives up and you can start bending it. Moistened and heated wood can be bent under the action of the load (the ends of the board are placed on the supports), and the load is placed in the place of the future bend. Dried wood perfectly retains the minimum radius of curvature that was achieved during the bending process. Now we know how to bend a tree, we can dwell on this issue in more detail.

The reaction of wood to external influences

The fact is that wood reacts differently to bending. The convex part is under tension, the concave part is under compression. Moreover, the material also reacts differently to steaming. For example, the ability to compress increases by as much as a third, but to stretch - just a couple percent. That is why it is not worth thinking about how to bend a board more than two centimeters thick at home. It must also be taken into account that different types Woods react differently to bending. For example, such species as oak, larch, maple bend poorly, but beech, ash, walnut - well. So before you think about how to bend the board, decide on the type of wood from which it is made.

How to bend plywood, fiberboard, MDF

At home, plywood is bent by increasing its moisture content, then ironing (an iron is required), and fixing it in a template. Any frame element can serve as a template, and its shape does not have to be curvilinear at all. The product is attached to the template with adhesive tape. Can be clamped bent plywood between two spacers, give it a bent shape due to the ropes, tying the product with them in several places along the radius of curvature. Plywood can only be used after it has dried. It seems that we figured out how to bend plywood - we move on.

How to bend fiberboard? The technique is the same as in the previous case! How to bend MDF? In this case, you can go in two ways: either bend thin sheets (no more than 5 mm) and glue them together, or use flexible MDF. in which on one side there are transverse slots. The thickness of such sheets is usually 8 mm. When bent, they overlap each other with milled sides, after which they are glued together. That, in fact, is all!

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First of all, you need to steam wooden beam OK. This can be done in several ways. Sometimes builders limit themselves to steaming in hot water, but it is best to build a special box into which hot and humid air. This is done very simply. Water is poured into any pot or kettle and brought to a boil. Then a rubber tube is inserted into any hole in this container, and its other end is inserted into a pre-cut hole in the box. So wet and hot air will go into the box. As a rule, 1 hour of steaming is enough for the full effect. Try not to over-steam your bar, because. it won't do any good either.

2 step

Now you can begin the process of bending. For this, special templates are used, according to which it is necessary to fold, i.e. one part of the bar is leaning against a wooden template and with the help of strong pressure it receives the same shape. It is important that one side of the bent bar is firmly fixed. The probability of cracks is extremely small, but still it is better to bend the bar carefully, without strong and sharp pressure.

3 step

After bending, the bar must be left alone and allowed to dry. When it dries, it will not change its shape, so you can simply put it on dry and hit sun rays place. After drying, it can be varnished or painted.

In the manufacture of furniture, you can not do without curvilinear parts. You can get them in two ways - sawing and bending. Technologically, it would seem that it is easier to cut a curved part than to steam, bend and then withstand it for a certain time until it is fully ready. But sawing has a number of negative consequences.

Firstly, there is a high probability of cutting the fibers when working with a circular saw (it is used in this technology). The result of cutting the fibers will be the loss of strength of the part, and, as a result, of the entire product as a whole. Secondly, sawing technology involves a greater consumption of material than bending technology. This is obvious and no comment is required. Third - all curved surfaces sawn parts have end and half-end cut surfaces. This significantly affects the conditions for their further processing and finishing.

Bending avoids all these disadvantages. Of course, bending involves the presence of special equipment and fixtures, and this is not always possible. However, bending is possible in the home workshop. So, what is the technology of the bending process?

The technological process of manufacturing bent parts includes hydro heat treatment, bending blanks and drying them after bending.

Hydrothermal treatment improves the plastic properties of wood. Plasticity is understood as the property of a material to change its shape without destruction under the influence of external forces and keep it after the action of the forces is eliminated. Wood acquires the best plastic properties at a moisture content of 25 - 30% and a temperature in the center of the workpiece by the time of bending of about 100 ° C.

Hydrothermal treatment of wood is carried out by steaming in boilers with saturated steam. low pressure 0.02 - 0.05 MPa at a temperature of 102 - 105°C.

Since the duration of steaming is determined by the time it takes to reach the set temperature in the center of the steamed workpiece, the steaming time increases with increasing thickness of the workpiece. For example, for steaming a workpiece (with an initial humidity of 30% and an initial temperature of 25°C) with a thickness of 25 mm to reach a temperature in the center of the workpiece of 100°C, 1 hour is needed, and with a thickness of 35 mm - 1 hour and 50 minutes.

When bending, the workpiece is placed on a tire with stops (Fig. 1), then in a mechanical or hydraulic press, the workpiece together with the tire is bent to a given contour; in presses, as a rule, several workpieces are bent simultaneously. At the end of bending, the ends of the tires are pulled together with a coupler. The bent blanks are sent for drying along with the tires.

The workpieces are dried for 6-8 hours. During drying, the shape of the workpieces stabilizes. After drying, the blanks are freed from templates and tires and kept for at least 24 hours. After holding, the deviation of the dimensions of the bent blanks from the original ones is usually ± 3 mm. Next, the blanks are processed.

For bent blanks, peeled veneer, urea-formaldehyde resins KF-BZh, KF-Zh, KF-MG, M-70, particle boards P-1 and P-2 are used. The thickness of the workpiece can be from 4 to 30 mm. Blanks can have a wide variety of profiles: angular, arc-shaped, spherical, U-shaped, trapezoidal and trough-shaped (see Fig. 2). Such blanks are obtained by simultaneous bending and gluing together veneer sheets lubricated with glue, which are formed into packages (Fig. 3). This technology makes it possible to obtain products of a wide variety architectural forms. In addition, the production of bent glued parts from veneer is economically feasible due to the low consumption of timber and relatively low labor costs.

Layers of plots are smeared with glue, laid in a template and pressed in (Fig. 4). After exposure under the press until the glue has completely set, the knot retains the shape given to it. Bent glued knots are made from veneer, from hardwood and coniferous plates, from plywood. In curved glued veneer elements, the direction of the fibers in the veneer layers can be either mutually perpendicular or the same. The bending of the veneer, in which the wood grains remain straight, is called a bending across the grains, and in which the fibers are bent - bending along the grains.

When constructing bent glued veneer units that carry significant loads during operation (legs of chairs, cabinet products), the most rational designs are those with a bend along the fibers in all layers. The rigidity of such knots is much higher than knots with mutually perpendicular direction of wood fibers. With a mutually perpendicular direction of the veneer fibers in the layers, curved glued knots up to 10 mm thick are designed that do not carry heavy loads during operation (walls of boxes, etc.). In this case, they are less susceptible to form change. The outer layer of such nodes should have a fractional direction of the fibers (bending along the fibers), since when bending across the fibers, small fractional cracks appear at the bending points, which exclude good finish products.

Permissible (curvature radii of curved veneer elements depend on the following design parameters: veneer thickness, number of veneer layers in a package, package design, billet bending angle, mold design.

In the manufacture of bent profile units with longitudinal cuts, it is necessary to take into account the dependence of the thickness of the bent elements on the type of wood and the thickness of the bent part.

In the tables, the elements remaining after the cuts are called extreme, the rest - intermediate. Minimum distance between the cuts that can be obtained is about 1.5 mm.

With an increase in the bending radius of the plate, the distance between the cuts decreases (Fig. 5). The width of the cut depends on the bending radius of the board and the number of cuts. To obtain rounded nodes, in the slab, after veneering and grinding, a groove is selected in the place where the bend will be. The groove can be rectangular or dovetail. The thickness of the remaining plywood bridge (the bottom of the groove) should be equal to the thickness of the facing plywood with an allowance of 1-1.5 mm. A rounded bar is inserted into the rectangular groove with glue, and a strip of veneer is inserted into the dovetail groove. Then the plate is bent and kept in the template until the glue sets. To give the corner greater strength in it with inside you can put a wooden square.

Instruction

For the manufacture of curved wood parts, two main methods are used: sawing according to a template and bending pre-steamed wood using a template on special machine. The first method leads to cutting the fibers and reducing the strength of the parts. Bending also provides a high percentage of useful output of parts and significant strength. Bent parts can be finished with high quality and subjected to various machining (profiling, forming spikes, eyes, etc.).

Ability wooden board to bending is determined by the plasticity of wood and depends on the type of wood. Beech, birch, oak, pine and spruce have the highest plasticity. But it is possible to control the plastic properties of the workpiece by carrying out its hydrothermal treatment.

At a temperature of 100°C and a humidity of 30%, some of the substances that make up the cells of the material go into a gel state, while the cell walls and wood fibers become elastic and soft. This wood bends easily. After drying bent board retains the shape given to it, since the colloidal substances harden.

Processing of the workpiece consists in boiling it in hot water or steaming it with low-pressure saturated steam. Steaming is more common, because during this treatment the wood warms up more evenly, there is no excessive moisture in the wood.

When a board treated in this way is bent on a pattern or in a special clamping device, internal stresses arise in the material. Wood stretches on the convex side and contracts on the concave side. In the middle neutral layer, the stresses are zero.

The outer layer under the action of tensile stresses will receive elongation, and the inner one will become shorter. The amount of deformation depends on the thickness of the dock and the radius of the bend. To limit the elongation of wood fibers and prevent their possible rupture, a special tire made of steel up to 2.5 mm thick is placed on the convex side of the bent part. The workpiece is bent together with the tire. In this case, the neutral line extends towards the stretched fibers beyond the board, and the bending occurs only due to compression.

When making a wide variety of joinery, the craftsman often has to use curved parts. It is not always possible to obtain the required shape by sawing, since it is important here to ensure the strength of the material and its economy. In such cases, you have to bend the wood at different angles.

You will need

• - hot water;
• - open fire;
• - sample;
• - steel strip;
• - ammonia water.

Instruction

Use steaming or heat treatment for bending. If you endure wood within a few hours under the influence of high temperature and moisture, it is possible to achieve a change in the plasticity of the material and bend the workpiece at the required angle.

Carefully select which you will subsequently bend. Use boards sawn lengthwise for this processing. Avoid defective and kinky boards, as well as those blanks that have knots. If materials with damaged fibers are used, the workpiece may crack at the location of the defect.

If the original workpiece is made from freshly cut material, heat it over an open fire or in a closed oven. At the same time, do not allow overdrying of wood and its charring. To do this, it is enough to moisten periodically abundantly wood