How to bend a board - the simplest technology. Proper bending of wood and its technology

Often during the process repair work There is a need to obtain curved surfaces of products made from wood. How to bend a board so that the bend is strong and does not crack during the bending process? Well, if you have already decided to do major renovation with your own hands, then you should not retreat in the face of such difficulties. In this article we will talk in detail about how to give 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 about wood building materials. How to bend a tree so that it bends and does not break? Bending method wooden products 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 it in hot water (the higher the temperature, the faster the processes occur) or steam ( a steam generator can be made from a kettle or use an iron). The higher the temperature, the faster the wood yields and you can start bending it. Moistened and heated wood can be bent under the influence of a load (the ends of the board are placed on supports), and a load is placed in the place of the future bend. Dried wood perfectly preserves minimum radius curvature that was achieved during the bending process. Now we know how to bend wood, we can dwell on this issue in more detail.

Wood reaction to external influences

The fact is that wood reacts differently to bending. The convex part is subject to tension, the concave part is subject to compression. Moreover, the material also reacts differently to steaming. For example, the ability to compress increases by as much as a third, but the ability to stretch - just a couple of percent. That’s why you shouldn’t think about how to bend a board more than two centimeters thick at home. It is also necessary to take into account that different types wood reacts differently to bending. For example, such species as oak, larch, and maple bend poorly, but beech, ash, and walnut bend 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 humidity, then ironing it (an iron is required), and fixing it in a template. Any frame element can serve as a template and its shape does not necessarily have to be curvilinear. The product is attached to the template using tape. Can be clamped bent plywood between two spacers, give it a bent shape using ropes, tying them around the product in several places along the radius of curvature. Plywood can only be used after it has dried. It seems that we have figured out how to bend plywood - let's 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 two ways: either bend thin sheets (no more than 5 mm) and glue them together, or use flexible MDF, in which there are transverse slots on one side. The thickness of such sheets is usually 8 mm. When bending, they are placed on top of each other with their milled sides, and then glued together. That's all!

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 takes up 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. Its main task is to 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 desired shape. To hold the bent wood piece in the desired shape, clamps should be used. 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 ways require the application of force of varying magnitude.

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 lignin bonds between fibers, you can act on wood chemicals, and it is quite possible to do this 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.

How longer wood is in an 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 front side. So, they can be added together with the least 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. He has high level grip, but takes a long time to dry. Can also be used epoxy resin, but such a 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.

Blank from bent wood should be placed in 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 must be with inside bending 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. More often outside treated with veneer, in some cases laminate. This action allows you to correct the bend and hide any defects made during the manufacturing 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 a box or metal corner.

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 demands: 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 others wood materials, where shredded 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 retains 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 woody substance, and, reacting with these components, purposefully change the physical and operational properties 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 impregnating the wood with an aqueous solution of urea, we, paradoxically, “dry” it, “taking away” part wood moisture to 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. Technological process production of 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 of wooden products prefer to do without this operation, and if they use bent elements, 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 (age) wood. How younger 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 It is 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 outer side fold coincided 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 whole 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 work is supposed to be put on stream, then it is possible to produce 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 under the lid rubber gasket. 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. Bent parts should be dried 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 blanks are steamed in specialized chambers. Stabilization of the workpiece is carried out by high frequency current.
This equipment has found wide application in the manufacture of chairs, sleds, and 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

Except traditional use bent, today building structural elements made using this method are increasingly used. Usage load-bearing elements from bentwood allows you to create new interesting views architectural solutions, which in combination with optimal economic indicators such structures explains the increased interest in them from outside practical application not only in industrial, but also in private housing construction.

Make curved structure You can make bent wood in two ways: sawing it out of boards, bending timber (solid bent products) or layers of wood while 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 it is almost impossible to cut a product of large size and curvature from a board, 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. Selected as blanks unedged board or timber without knots, the cross-section of which does not exceed 10% of the surface area. 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 difficult, so at home it is easier to organize boiling wood in a cooking tank 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 comfortable 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 designer models, rounded designs and complex shapes with multiple radii, which cannot be created from traditional materials, are produced 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 modern manufacturers furniture and carpentry. Flexible plywood (bending plywood) is cheaper than pre-made wood forms. Significant time savings, less labor intensity and greater profitability 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've been floating for an hour inch board and when I tried to bend it, it cracked - there is no need to conclude that there was not enough time. There are other influencing factors that explain this, but we'll get to those later. Steaming the same workpiece for a longer time 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:

Usually, the best option it will if you can find freshly cut wood. I understand that 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 of white oak, clamp one end of it in a workbench and bend it to any desired curvature - fresh wood is so malleable. 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.

Despite all its strength and durability, wooden parts can be easily and simply bent if something special is suddenly required during the construction process, and original parts oval or round shape. Tree at correct processing can easily be changed in shape, and you can carry out this procedure with your own on our own without resorting to the help of professionals.

Types of work

There are two main ways to bend wood to the desired shape, one of them is cold, the other is hot. As the name implies, the methods differ only in the use of hot temperatures; in terms of effectiveness, both of these methods are exactly the same, just hot way fixing the tree is much faster. For each method you will need glue, pva or wallpaper, depending on what you have at hand, you don’t need to buy anything special. And with the help metal parts you can create a kind of press or frame that will hold the tree in the desired shape. In order to bend the beam, you need to lubricate it with glue, firmly and thoroughly, without fear that the wood will become wet. In fact, under the influence of the adhesive solution, the entire excess moisture will leave the tree, and it will become even more durable and strong, which is extremely important. After the timber has been lubricated with glue, it must be secured using tools in the desired shape, and in the case of a cold work process, simply left fixed to dry. If you choose a hot one, then cover the timber with regular film so that it dries faster and all the moisture evaporates.

Durability

Whichever method is chosen, they are both effective and work the same way. The beam is completely fixed in its new form, and will no longer return to the old one. You can bend a wet beam with glue as much as possible without fear that it will break. And as a result, you will receive an original and beautiful piece of furniture or detail to create an even more attractive interior of the house or its facade. The beam bent with glue will not even need to be treated with anything for durability, which is extremely convenient. Moisture will not penetrate through adhesive solution, and insects will not encroach on a tree that contains much more glue. That is why this method is the most optimal and practical if you urgently need to bend a wooden beam.

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