Wood bending technologies. Cold bending of wood How to bend timber at home

Nature does not like straight lines and it takes a lot of time and effort to make wooden products straight. However, bending wood is also a rather labor-intensive process. Bent wood elements are often used in Scandinavian furniture in the form of beautiful, light and durable products with unity of structure and form. In this article we will look at several ways to bend wood: simple power bending, bending using cuts, steam bending and layer bending.

This is the simplest method and involves bending wood by hand and attaching it to a mold to secure the bend. The thinner the wood, the easier it is to bend. It follows from this that the greater the bend, the thinner the wood should be. Veneer can take on almost any bend, while an oak blank 2 cm thick is almost impossible to bend. It should also be taken into account that different breeds woods have varying degrees of flexibility. So the ratio of the thickness of the workpiece and the minimum bending radius for some species will be: beech - 1/2.5; oak - 1/4; birch - 1/5.7; alder - 1/8; spruce - 1/10; pine - 1/11. That is, with a beech blank thickness of 10 mm, the minimum bending radius will be 25 mm.

As a rule, the workpiece is fixed with glue, since the use of nails or screws in bending areas can lead to the formation of cracks and breaks. There is an unspoken rule - what can be fixed by hand can also be fixed with glue. When gluing, to reduce gaps, you need to move from the center to the edges, or from one edge to the other.

This method of bending wood is the least durable because the wood is sawed through almost the entire thickness and very little strength remains in it. Therefore, this method of bending wood is used only where there is no heavy load, for example rounded corners, etc.

The main material for the manufacture of bent-sawn parts is plywood. For achievement best results it is better to make cuts on circular saw using a limit stop. The cuts should be made across the grain at a distance of about 5-10 mm. from each other. The depth of the cut should be about 1/5 of the thickness of the workpiece.

To fix the bend, you can use glue or wood filler. By gluing and fixing two curved slats with cuts inward, you can create interesting elements in some designs, although with limited strength.

In terms of its physical properties, such wood is close to hydrothermally bent wood, and in terms of some indicators of dynamic loads, it has even better mechanical properties, rather than solid wood.

The first step is to prepare the slats. The thickness of the lamellas is largely determined by the amount of bending. The greater the bend, the thinner the lamellas should be and vice versa. As a rule, the thickness of the lamellas should not exceed 3.2 mm.

The cut layers of wood are then coated with glue and pressed into the template using grippers. You cannot use regular wood glue to connect the slats. For these purposes, adhesives based on urea-formaldehyde or epoxy resins are best suited.

Before removing the part from the template, the glue should set within 24 hours. It should also be taken into account that after the mold is released, the workpiece may straighten out a little. This effect can be minimized by reducing the thickness of the lamellas or creating a shape with a slight bend.

Hydrothermal bending of wood gives the highest quality results, but requires a lot of labor and technical equipment.

Before starting the bending process, due attention should be paid to the choice of wood. Almost any type of wood can be bent, but hardwoods such as oak, beech, elm, birch, cherry, maple, walnut, and ash have the best flexibility. It is not recommended to use coniferous and soft species such as spruce, pine, cedar, and alder. It is also important that the wood is free of cracks and knots at the intended bend.

Each cell of wood fibers is coated with lignin, a glue-like chemical that binds the fibers tightly together at normal temperatures. The heat transferred by the steam softens the lignin, allowing the fibers to shrink and stretch. As the lignin cools, it hardens and binds the fibers tightly together again.

Freshly cut wood is best suited for bending. The best option Atmospheric drying wood is also an option, since during chamber drying lignin is noticeably strengthened, making bending more difficult. Before steaming, kiln-dried wood can be soaked overnight in water. Processing of atmospheric-dried wood and pre-soaked kiln-dried wood requires the same amount of time.

Wood acquires its best plastic properties at a humidity of 25-30% and at a temperature of about 100°C. Steaming time depends on the thickness of the wood. So, for example, to steam a workpiece with an initial humidity of 30% and a thickness of 25 mm until the temperature in the center of the workpiece reaches 100°C, it takes 1 hour, and with a thickness of 35 mm - about 2 hours.

Before removing the workpiece, make sure that all tools are at hand, as the wood cools and hardens very quickly. Be sure to wear thick gloves to avoid getting burned by the steam. Remove the part and immediately secure it with the grips.

Removal of the product from the mold is usually accompanied by a slight bending. Therefore, the form must have a bend a little more than required in order to maintain the desired curvature of the product. To minimize flex, leave the piece secured in the mold for at least a few days.

When bending wood, you need to take into account many points: fresh wood is best suited for this task; you need to steam the wood for a certain amount of time, which depends on its thickness.

Processes for changing the properties of wood to meet requests: technology and properties Wood is a natural polymer composite material that changes its properties under mechanical and chemical influence. Knowing the patterns of material changes, you can create them purposefully, imparting the qualities required by the consumer. This is called the wood modification process. It is necessary when chipboard production, MDF, OSB, WPC and other wood materials, where crushed wood mixed with a polymer binder is pressed to produce a homogeneous material of standard sizes.
The proposed wood modification technology changes the properties of wood in the massif, that is, to the entire depth of the processed material, without resorting to grinding it. This is achieved by the fact that the molecules of the modifier, i.e., a substance that helps change the properties of wood, are comparable in size to the molecules of the wood substance and less than the size of the intercellular spaces in it. Therefore, by diffusion or forced impregnation under pressure, the modifier penetrates the entire thickness of the impregnated product, and then, under the influence of temperature and pressure, reacts with natural chemicals found in the wood substance.

Thus, the technology makes it possible not to chop wood, not to use expensive polymer binders, and to achieve the same effect that was achieved with MDF production, for example, but in a cheaper way. At the same time, it is preserved with all its positive properties, the texture stands out brighter, you can change the color (lamination is not required).
So, the modifier must penetrate into the cells in a dissolved state, be chemically active for the components that make up the wood substance, and, reacting with these components, purposefully change the physical and operational properties of the material. The most suitable substance for this is urea, because in the previously mentioned MDF or OSB, the most applicable binders are urea. Urea is soluble in water, including that contained in a bound state in wood, which means that by saturating the wood with an aqueous solution of urea, we, paradoxically, “dry” it, “taking” part of the wood moisture onto hydrophilic urea. Urea or urea actively reacts with components of wood substances such as lignin, hemicelluloses, and extractives.
And since the polycondensation reaction occurs in the macromolecules of the wood substance, the solid wood acquires new characteristics specified by the manufacturer useful qualities, preserving the positive old ones. The urea solution is not harmful, chemically neutral, moreover, grade A urea according to GOST 6691-77 is used as a feed additive for livestock. Urea-modified wood is certified (GOST 24329-80) and is mainly used under the Destam or Lignoferum trademarks in the production of bearing shells. In the production of construction and joinery products, thermally modified wood is currently also used, the technology of which is similar to that proposed, except that the chemical modification of the wood substance is carried out in the absence of urea due to the polycondensation of decomposition products of lignin, hemicelluloses, extractives and xylans.
Due to thermal degradation, the physical and mechanical properties of thermally modified wood are partially reduced. The technological process for producing mechanochemically modified wood consists of impregnating the original wood of any species and any moisture content with a modifier solution. Impregnation can be carried out using the “hot-cold bath” method - diffusion or in an autoclave - forced. Then drying is carried out, if necessary - with compaction (pressing), and heat treatment, which fixes the new properties of the wood. It should be noted that it is more economical to use low-value rocks, since their performance properties after modification exceed the properties of expensive rocks

How to bend wood correctly and in what ways?

Currently manufacturers wooden products they prefer to do without this operation, and if they use bent elements, then they are made from plywood. It's easier to bend plywood. It should be noted, however, that furniture makers natural wood They stopped pampering the buyer a long time ago. All furniture is made from wood board or fiberboard. Products made from bent wood, be it a chair or something else, are without a doubt stronger, lighter and more elegant.

Wood selection

The success of bending largely depends on the type of wood chosen. Almost any species can be bent, but elm, oak, beech, etc. have the best flexibility. If carefully dried wood is needed for carpentry work, then in our case it is better to use freshly harvested wood. You should not use old (aged) wood. The younger the tree, the more flexible it is. From the desired rock you need to select pieces without cracks or knots. At the very least, there should be no knots in the area of ​​the intended bend. It is important that the wood is straight-grained, without strands, cross-layers and “screws”. It is best to prepare not sawn boards and beams, but solid round timber.

Making a blank

Blanks for bending wooden elements are best obtained not by sawing, but by splitting round timber. The direction of splitting should be along the chords of the circle to eliminate the core, which is fragile and unsuitable for bending. Prepared this way wooden blocks and the planks will not flake during bending. The future part is marked so that the direction of the bend coincides with the radius of the round timber from which the workpiece was split off, and the outer side of the bend coincides with outer part former round timber. The chipped workpieces are processed with planes until required sizes with a small allowance for finishing.

Steaming the workpiece

To give the workpiece the best plasticity, it must be steamed. To do this, you will need a metal container of a certain size. The entire workpiece will be “steamed” in it or only at the bend. The second is preferable, since it is more convenient to take the workpiece simply with your hands (without tools), which cannot be done if the workpiece is all steamed.

If this type Since the work is supposed to be put on stream, it is possible to make a special metal container with a sealed lid and two holes for placing the bendable part inside the “steam room”. This entire simple structure must be tightly closed to reduce the escape of steam to the outside. Place a rubber gasket under the cover. Do not screw it tightly; it may swell or even explode under steam pressure. A sufficiently heavy lid will ensure a tight seal and at the same time act as a safety valve if the pressure increases excessively.

It is difficult to indicate the time for complete steaming. It depends on the type of wood, the cross-section of the workpieces, and the degree of dryness of the workpieces. You just need to take the workpiece out from time to time and test it for bending. The readiness of the workpiece can be felt immediately by its flexibility in bending.

Workpiece bending

It is best to bend the workpiece using a template. A blank bent and dried in a template will provide the part configuration we need. Moreover, if you need not one, but several completely identical parts.

With a certain skill, you can do as they do a shower for horse harness - the steamed workpiece is bent and the ends are tied with a rope. Leave it in this form until completely dry. Dry bent parts It is necessary in a ventilated place, protected from the sun. Trying to artificially speed up drying by heating can lead to cracking of the wood.

It should be noted that after removing the part from the template, it “gives up” a little, i.e. straightens up. Taking into account this property, the workpieces must be bent a little “steeper” so that upon release the desired shape is obtained. How “cooler” is a matter of experience. Much depends on the cross-section of the workpiece, the type of wood, and the degree of steaming before bending.

Press for bending wood materials

Manufacturer ORMA, Italy

Purpose
This equipment is intended for bending (bending) wood materials. Before bending, the workpieces are steamed in specialized chambers. Stabilization of the workpiece is carried out by high frequency current.
This equipment found wide application in the manufacture of chairs, sleds, school furniture.

Specifications:

Complete bending kit includes
- Steaming chamber - a reservoir for moistening workpieces with a condensate collector, complete with a steam generator (a separate generator for each autoclave)
- Pre-bending press (necessary depending on tasks and productivity)
- The bending and stabilizing press (selected depending on the tasks and productivity), depending on the complexity of the product, can be equipped with additional side cylinders. The possible total force varies from 30 to 120 tons. Specific pressure up to 7.5 kg/cm2
- Electronic frequency generator – with the ability to work on two presses for bending and stabilization

Standards and structural strength of bent wood

In addition to the traditional use of bent, today building structural elements made using this method are increasingly used. Usage load-bearing elements from bent wood allows you to create new interesting views architectural solutions, which in combination with optimal economic indicators Such structures explain the increased interest in them from practical applications not only in industrial, but also in private residential construction.

There are two ways to make a curved structure from bent wood: sawing it out of boards, bending timber (solid bent products) or layers of wood and simultaneously gluing them together (bent-glued products). The process of bending wood is based on its ability, under certain conditions, under the influence of external loads, to change its shape and maintain it in the future.

It is clear that cutting a product from a board large sizes and curvature is almost impossible, therefore, in order to make a bent board or beam at home for the construction of a beautiful or dome crowning a decorative turret of a house, you should prepare everything necessary for bending wood. Just as website optimization allows you to increase the ranking of an Internet resource, so does the choice quality material for bending improves its result. An unedged board or timber without knots, with a cross-layer of no more than 10% of the surface area, is selected as a blank. The best varieties woods with increased plasticity are hornbeam, maple, beech, oak, ash and elm.

After the material has been selected, you can begin the bending process, the main stages of which are: hydrothermal treatment, bending the workpiece and drying the product. Optimal parameters conditions at which bending takes place with the highest quality are the wood moisture content in the range of 25-30% and the temperature in the center of the workpiece from 80 to 90°C.

Professional promotion of sites dedicated to the intricacies of wood bending technology will certainly arouse the interest of a wide audience, since the simplicity of this process is incomparable with the result obtained. Hydrothermal involves steaming or boiling the workpiece in hot water.

Steaming is technically more complex, so at home it is easier to organize the boiling of wood in a cooking tank of a suitable size. The workpiece removed from the cooking tank should be immediately secured to the tire using clamps while the wood is still warm. Otherwise, stress will arise in its outer layers, leading to cracks.

Flexible plywood and its application

Flexible plywood (bending plywood) is now in great demand due to the fact that it is a convenient material for the manufacture of structures that require rounding. The use of such bending plywood is effective and expedient, since it can take any necessary shape. Its flexibility allows you to embody the wildest fantasies of designers and produce the most fashionable and modern furniture, be it a closet with original design for your living room, cute shelves for the kitchen or modern and comfortable office furniture.
Such plywood is made from tropical trees, mainly from CEIBA wood, but sometimes flexible plywood is made from other woods: Parika, Keruing. Flexible (bending) plywood is, as a rule, a 3-layer board that is glued together in the transverse or longitudinal design of the shirts.

Flexible plywood, can be used for all types of bends, even with very small radii. No need to heat or treat with water. The self-supporting design of bending plywood makes the use of structural and special supports unnecessary. Unique design models, rounded designs and complex shapes with several radii, which cannot be created from traditional materials, are manufactured easily and quickly. Flexible plywood fulfills almost all thickness requirements by increasing the number of layers of material (for example, increasing the thickness to 10mm, 15mm, 16mm, 18mm, 20mm, etc.). Greater sheet thickness can be obtained by gluing several sheets of thinner bending plywood together.

Tropical plywood High Quality- this is a combination modern technologies and traditional materials. A product created to satisfy the most sophisticated needs of modern furniture and joinery manufacturers. Flexible plywood (bending plywood) is cheaper than pre-made wood forms. Significant savings time, less labor intensity and greater profitability - these are its advantages over any other method of changing the shape of plywood.

In addition to flexible plywood, our company offers another unique product - this is Ultra-light plywood. The range of use of this plywood is also quite wide: this is the production of door panels, the manufacture of cabinet furniture, sofas, armchairs, shelves. Ultralight plywood is New Product in our market, it is 1.8 times lighter than birch. This plywood can be veneered well, finished with films and varnishes, and most importantly, it can significantly reduce the weight of the finished product!

Specifications

Bend direction Across the grain: along the width

Composition Hot-pressed tropical wood with heat-set adhesive

Density 300-400 kg/cub.m.

Thickness 5 mm, 8 mm, etc.

Dimensions 2500/2440 mm x 1220 mm, etc. by department. order

Bending radius For 5 mm thick, minimum 7 cm for 8 mm thick, minimum 10 cm

Elasticity
Perpendicular to grain: 210 N/mm2
Parallel to grain: 6300 N/mm2
(For 5mm panel at 10% humidity)

Store panels horizontally in a clean, shaded, dry place.

Apply glue to the panels, fixing the desired shape. After the glue dries, the panel will retain its shape. H.P.L. or the plywood can be glued both during the initial molding and at a separate, final stage.

You can use any wood glue.

The panels must be transported on a hard, flat surface. Individual panels can be rolled up, but they cannot be stored in this position for a long time.

Bending is widely used in industries such as shipbuilding. To begin with, there are a few basic rules that are always followed.

By steaming wood to bend it, you soften the hemicellulose. Cellulose is a polymer that behaves like thermoplastic resins. (Thanks to John MacKenzie for the last two suggestions).

To do this, you need heat and steam at the same time. In Asia, people bend wood over fire, but that wood is definitely quite wet - usually freshly cut. Shipbuilders in ancient Scandinavia prepared hull materials for their ships and placed them in a saltwater swamp so that they would remain flexible until they were ready for use. However, we are not always able to obtain freshly harvested wood for these purposes and excellent results This can also be achieved by using conventional air-dried wood. It would be very good if, a few days before the operation itself, you immerse the workpieces in water so that they gain moisture - those Vikings knew what they were doing. You need warmth and you need moisture.

The main rule concerns steaming time: one hour for every inch of wood thickness.

Know that along with the probability of understeaming the workpiece, there is also the probability of oversteaming it. If you hovered an inch board for an hour and when you tried to bend it, it cracked, do not conclude that the time was not enough. There are other influencing factors that explain this, but we'll get to those later. Longer steaming of the same workpiece will not give a positive result. In such a situation, it’s a good idea to have a workpiece of the same thickness as that intended for bending and which you don’t mind. Preferably from the same board. They need to be steamed together and after the presumably required time, take out a test sample and try to bend it into shape. If it cracks, then let the main workpiece steam for another ten minutes. But no more.

Wood:

Typically, the best option is if you can find freshly cut wood. I understand that the cabinet makers will shudder at these words. But the fact remains that fresh wood bends better than dry wood. You can take a two-meter inch board from white oak, clamp one end of it in a workbench and bend it along any necessary curvature - fresh wood is so pliable. However, naturally, it will not remain in this state and you will still have to float it.

In shipbuilding, the main evil is rot. If you are concerned about this issue, then please note that the very fact of steaming fresh wood eliminates its tendency to rot. Therefore, you don’t have to worry - the frames of boats are usually made from fresh steam-bent oak and do not rot if it is taken care of. This also means that in this way it is possible to make at least blanks for the Windsor Chair. But air-dried oak also gives excellent results.

When selecting wood for bending, one thing to avoid is cross-layering. When trying to bend such a workpiece may burst.

Therefore, regarding wood moisture content, the rules are as follows:
1.Fresh wood is best.
2. Air-dried wood is a second good option.
3. - the third and very far from the first two option.

If all you have is from the dryer and you can’t get anything else - well, then you have no choice. But still, if you can get air-dried wood, it will be much better.

If there is a need to manufacture a curved wooden element, then at first glance it may seem easier to cut out required element in a curved form, but in this case the fibers of the wood material will be cut, thus weakening the strength of the part, and as a result, the entire product. In addition, when sawing, a large waste of material is obtained, which cannot be said about the method when the wooden blank is simply bent.

Wood is cellulose fibers bound together by a chemical called lignin. The flexibility of the tree depends on the arrangement of the fibers.

Only well-dried wood will be reliable and durable source material for the production of various products. However, changing the shape of a dry wooden blank is a difficult process, because dry wood can break, which is very undesirable.

Having studied the technology of how to bend wood, as well as the basic physical properties wood, which allow you to change its shape and subsequently preserve it, it is quite possible to take up bending wood at home.

Some features of working with wood

Bending of wood is accompanied by its deformation, as well as compression of the inner layers and stretching of the outer ones. It happens that tensile forces lead to rupture of the outer fibers. This can be prevented by carrying out preliminary hydrothermal treatment.

So, you can bend blanks of timber made from solid and laminated wood. In addition, planed and peeled veneer is used for bending. The most plastic are hardwoods. These include beech, ash, birch, hornbeam, maple, oak, poplar, linden and alder. Bent glued blanks are best made from birch veneer. It is worth noting that in the total volume of bent-glued blanks, birch veneer occupies approximately 60%.

When steaming the workpiece, the compressibility increases significantly, namely by a third, while the tensile ability increases by only a few percent. This means that it is not a priori worth thinking about whether it is possible to bend wood thicker than 2 cm.

Steam box heating

First you need to prepare the steam box. It can be made by yourself. Her the main task- hold the tree that needs to be bent. There should be a hole in it to allow the steam pressure to escape. Otherwise it will explode.

The steam outlet should be located in the bottom of the box. In addition, the box should have a removable lid through which you can pull out the bent wood after it has acquired the required form. Clamps should be used to hold the bent wood piece in the desired shape. You can make them yourself from wood or buy them at a specialty store.

Round cuttings should be made from wood - several pieces. Off-center holes are drilled in them. After this, you need to push the bolts through them, and then drill another hole through the sides to push them in tightly. Such simple crafts can become excellent clips.

Now it’s time to steam the wood; to do this, you should take care of the heat source and close the wood piece in the steam box. For every 2.5 cm of thickness of the workpiece, the product needs to be steamed for about an hour. After time has passed, the tree must be removed from the box and given the required shape. The process must be completed very quickly. The workpiece bends neatly and softly.

Some types of wood bend more easily than others due to different elasticity. Different methods require different amounts of force to be applied.

Once the desired result is achieved, the bent tree must be fixed in this position. You can secure the tree while shaping it. This makes it easier to control the process.

Using chemical impregnation

To destroy the lignin bonds between the fibers, you can treat the wood with chemicals, and this can be done at home. Ammonia is ideal for this. The workpiece is soaked in a 25% aqueous ammonia solution. After which it becomes very obedient and elastic, which allows you to bend, twist it and squeeze out relief shapes in it under pressure.

Ammonia is dangerous! Therefore, when working with it, you should follow all safety rules. Soaking the workpiece should be carried out in a tightly closed container located in a well-ventilated room.

The longer the wood is in the ammonia solution, the more plastic it becomes. After soaking the workpiece and giving it a shape, you need to leave it in this curved form. This is necessary to fix the shape, and also for the ammonia to evaporate. Again, bent wood should be left in a ventilated area. Interestingly, after the ammonia evaporates, the wood fibers will regain their former strength, and this will allow the workpiece to retain its shape!

Delamination method

First you need to make a piece of wood that will be bent. The boards should be slightly longer than the length of the finished part. This is because bending will shorten the slats. Before you start cutting, you should draw a diagonal line with a pencil. This needs to be done across the underside of the board. This will maintain the sequence of the slats after they have been moved.

The boards are cut with a straight-layer edge, in no case with the front side. So, they can be folded together with smallest change. A layer of cork is applied to the mold. This will help avoid any unevenness in the shape of the saw, allowing for a cleaner bend. In addition, the cork will keep the delamination in shape. Now glue is applied to the top side of one of the wooden slats.

The glue is applied to the lamellas with a roller. It is best to use urea-formaldehyde glue, consisting of 2 parts. It has a high level of adhesion but takes a long time to dry. You can also use epoxy resin, but this composition is very expensive, and not everyone can afford it. Standard wood glue cannot be used in this case. It dries quickly, but is very soft, which is not welcome in this situation.

The bentwood blank should be placed into the mold as quickly as possible. So, another lamella is placed on top of the lamella coated with glue. The process is repeated until the bent workpiece acquires required thickness. The boards are fastened together. After the glue has completely dried, you should shorten it to the desired length.

I drank it as a method

The prepared piece of wood needs to be sawn through. The cuts are made 2/3 of the thickness of the workpiece. They should be on the inside of the bend. You should be extremely careful, because rough cuts can break the tree.

The key to success when cutting kerfs is to keep the spacing between cuts as even as possible. Ideally 1.25 cm.

The cuts are made across the grain of the wood. Next, you should squeeze the edges of the workpiece so as to connect the resulting gaps together. This is the shape the bend will take upon completion of the work. Then the bend is corrected. Most often, the outer side is treated with veneer, or in some cases with laminate. This action allows you to correct the bend and hide any defects made during the production process. The gaps between the bent wood are hidden simply by mixing glue and sawdust, and then filling the gaps with this mixture.

Regardless of the bending method, once the wood is removed from the mold, the bend will relax slightly. In view of this, it needs to be made a little more in order to subsequently compensate for this effect. The sawing method can be used when bending part of the box or metal corner.

If there is a need to create a curved wooden element, then most likely you will encounter a number of difficulties. It may seem easier to cut the required component in a curved form, but in this case the wood fibers will be cut and weaken the strength of the part. In addition, the execution results in a fairly large waste of material.

Stages of performing work on bending boards at home:

	Preparation. Choice suitable variety wood and familiarization with the general principles of working with it.
	Wood bending options. Heating in a steam box, chemical impregnation, delamination, cutting.

Wood is cellulose fibers bound together by lignin. The straight arrangement of the fibers affects the flexibility of the wood material.

Advice: reliable and durable wood material for creating various products can only be obtained if the wood is well dried. However, changing the shape of a dry piece of wood is a rather difficult process, since dry wood can easily break.

Having studied the technology of bending wood, including its main physical properties of wood, which allow you to change its shape, it is quite possible to perform bending wooden material at home.

Features of working with wood

Bending of a wooden material is accompanied by its deformation, stretching outer layers and compression of internal ones. It happens that the tensile force leads to rupture of the outer fibers. This can be prevented by pre-hydrothermal treatment.

You can bend blanks of timber made of laminated wood and solid wood. In addition, peeled and sliced ​​veneer is used to give the required shape. The most plastic is hardwood. Which includes beech, birch, hornbeam, ash, maple, oak, linden, poplar and alder. Glued bent blanks are best made from birch veneer. It should be noted that in the total volume of such blanks, about 60% falls on birch veneer.

According to the technology for manufacturing bent wood, when the workpiece is steamed, its ability to compress significantly increases, namely by a third, while the ability to stretch increases by only a few percent. Therefore, you cannot even think about bending wood thicker than 2 cm.

How to bend a board at home: heating in a steam box

First you need to prepare a steam box, which can be done by yourself. Its main task is to hold the tree that needs to be bent. It must have a hole for steam to escape. Otherwise, an explosion may occur under pressure.

This hole should be in the bottom of the box. In addition, the box must have a removable lid through which the bent wood can be removed after it has received the desired shape. In order to hold the bent wood workpiece in the required shape, it is necessary to use special clamps. You can make them yourself from wood or purchase them at a hardware store.

Several round scraps are made from wood. Holes are drilled in them, offset from the center. After that, you should push the bolts through them, and then drill another one through the sides in order to push them in tightly. Such simple crafts can perfectly serve as clamps.

Now you can start steaming the wood. To do this, you need to close the wooden piece in a steam box and take care of the heat source. For every 2.5 cm of product thickness, the time spent on steaming is about an hour. After its expiration, the tree should be removed from the box and given the required shape by bending it. The process should be carried out very quickly, and the bending itself should be gentle and careful.

Tip: due to different degrees of elasticity, some types of wood will bend more easily than others. Different methods require different amounts of force to be applied.

As soon as the desired result is achieved, the bent workpiece must be fixed in this position. Fastening the tree is possible during the process of forming it new form, making it much easier to control the process.

How to bend a board at home using chemical impregnation

Since lignin is responsible for the durability of wood, its bonds with the fibers must be broken. This can be achieved chemically, and it is quite possible to do this at home. Ammonia is best suited for such purposes. The workpiece is soaked in a 25% aqueous ammonia solution, which significantly increases its elasticity. This will make it possible to bend, twist it, or squeeze out any relief shapes under pressure.

Tip: Please note that ammonia is dangerous! Therefore, when working with it, you must strictly adhere to all safety regulations. Soaking of wood should be carried out in a tightly closed container, which is located in a well-ventilated area.

The longer the wood is soaked in an ammonia solution, the more plastic it will become later. After soaking the workpiece and forming its new shape, you should leave it in a similar curved form. This is necessary not only to fix the shape, but also to evaporate ammonia. However, bent wood should be left in a ventilated area. Interestingly, when the ammonia evaporates, the wood fibers will regain the same strength as before, allowing the workpiece to retain its shape!

How to bend a board at home: layering method

First, it is necessary to harvest wood, which will subsequently be subject to bending. It is extremely important that the boards are slightly longer than the length of the required part. This is explained by the fact that the bending tames the lamellas. Before you start cutting, you will need to draw a diagonal straight line with a pencil. This must be done across the bottom side of the workpiece, which will make it possible to maintain their sequence after moving the lamellas.

The boards need to be cut with a straight-layered edge, and not with the right side. This way they can be put together with the least amount of change. A layer of cork is applied to the mold, which will help avoid any unevenness in the shape of the saw and will make it possible to make a more even bend. In addition, the cork will keep the delamination in shape. After this, glue is applied to the upper side of one of the lamellas with a roller.

It is best to use urea-formaldehyde glue, consisting of two parts. He has high level clutch, but takes a long time to dry.

You can also use epoxy resin, but such a composition will be very expensive, and not everyone can afford it. Standard option Wood glue will not work in this case. Although it dries quickly, it is very soft, which in this case is not welcome.

The bentwood product must be placed into the mold as soon as possible. So, another one is placed on the lamella coated with glue. The process must be repeated until the bent workpiece reaches the desired thickness. The boards are fastened together. After the glue has completely dried, you should shorten it to the required length.

How to bend a board at home: cut

The prepared piece of wood must be sawn through. The cuts are calculated at 2/3 of the thickness of the workpiece. They should be located on the inside of the bend. You need to be extremely careful, as rough cuts can not only deform the tree, but even break it completely.

Tip: The key to success when cutting is to keep the distance between cuts as even as possible. Perfect option 1.25 cm.

The cuts are made across the grain of the wood. Then you need to compress the edges of the workpiece, which will allow you to connect the resulting gaps into one whole. This is the shape it gets bent at the end of the work. After that it is corrected.

In most cases outer side processed with veneer, less often with laminate. This action makes it possible to correct the bend and hide almost any defects made during the manufacturing process. Gaps in bent wood are hidden very simply - for this, sawdust and glue are mixed, after which the gaps are filled with the mixture.

Regardless of the bend option, after the workpiece is removed from the mold, the bend will relax a little. In view of this, it should be made a little larger in order to subsequently compensate for this effect. The sawing method is used when bending a metal corner or part of a box.

So, using these recommendations, you can bend a tree with your own hands without any problems.

The layers are carefully lubricated with glue, placed in a template and pressed into place. Bent glued units made from veneer, from hardwood and softwood boards, from plywood. In bent-laminated veneer elements, the direction of the fibers in the veneer layers can be either mutually perpendicular or identical.

When manufacturing 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.

As the bending radius of the slab increases, the distance between the cuts decreases, as can be seen in the figure above. That is, the width of the cut directly depends on the bending radius of the slab and the number of cuts.

Now let's consider theoretical aspects bending

Curved solid wood parts can be made in two basic ways:

cutting out curved workpieces and giving a straight bar a curved shape by bending it on a template. Both methods are used in practice and have their advantages and disadvantages.

Sawing curved blanks is characterized by simplicity of technology and does not require special equipment. However, when sawing, the wood fibers are inevitably cut, and this weakens the strength so much that parts with large curvature and a closed contour have to be made up of several elements by gluing. On curved surfaces, half-end and end cut surfaces are obtained and, in connection with this, the processing conditions on milling machines and finishing. In addition, cutting produces a large amount of waste. The production of curved parts by bending requires a more complex technological process and equipment compared to sawing. However, when bending, the strength of the parts is completely preserved and even in some cases increases; no end surfaces are created on their faces, and the modes of subsequent processing of bent parts do not differ from the modes of processing straight parts.

Element bending
A- nature of the workpiece deformation during bending;
6 - bending the workpiece with the tire according to the template:
1 - template; 2 - notches; 3 - pressing roller; 4 - tire

When the workpiece is bent within the limits of elastic deformations, stresses normal to the cross section arise: tensile on the convex side and compressive on the concave side. Between the zones of tension and compression there is a neutral layer, the normal stresses in which are small. Since the magnitude of normal stresses changes along the cross-section, shear stresses arise, tending to move some layers of the part relative to others. Since this shift is impossible, bending is accompanied by stretching of the material on the convex side of the part and compression on the concave side.

The magnitude of the resulting tensile and compressive deformations depends on the thickness of the bar and the bending radius. Let us assume that the block rectangular section bent in a circular arc and that the deformations in the bar are directly proportional to the stresses, and the neutral layer is located in the middle of the bar.

Let us denote the thickness of the bar H, its initial length through Lo, bend radius along the neutral line through R(Fig. 60, a). The length of the block along the neutral line when bending will remain unchanged and is equal to Lo = p R( j /180) , (84) where p is the number pi(3, 14...), j - bend angle in degrees.
The outer stretched layer will receive elongation D L (delta L). The total length of the stretched part of the bar is determined from the expression Lo+ D L= p (R + H/2) j /180 (85)
Subtracting the previous one from this equation, we obtain the absolute elongation
D L= p (H/2)( j /180). (86)
Relative extension Er will be equal to D L/Lo = H/2R, i.e. bending elongation D Ll/Lo depends on the ratio of the thickness of the bar to the bending radius; the thicker the block, the larger it is H and the smaller the bend radius R. A similar relationship for the value of relative compression during bending can be obtained in a similar way.
Let's assume that around the pattern R" bent block with initial length Lo and at the same time maximum compressive and tensile deformations are achieved. Designated by E szh the value of permissible compressive deformation of wood along the fibers, and through E grow the value of the permissible tensile strain along the fibers, we can write a relationship for the stretched side
L = Lo(1 + Erast)= p (R" + H) j /180 (87)
From here R" + H = / p ( j /180) .
For the compressed (concave) side there will be L 2 = Lo (1 - Eczh) = p R"(j/180)
or R" = / p ( j /180 ). (88)
Subtracting the second from the first expression, we get
H = )