How to bend a board is the simplest technology. Correct bending of wood and its technology

Often in the process renovation works there is a need to obtain curved surfaces of products made of wood. How to bend the board so that the bending point is strong and does not crack during the bending process? Well, if you already decided to do overhaul do it yourself, then you should not retreat in front of such difficulties. In this article, we will talk in detail about how to give woody material a curved shape.

How to bend a tree?

No, our task is not at all to bend an innocent plant. It is about woody building materials... How to bend a tree so it bends rather than breaks? Bending method wooden products It has been known since ancient times: to give the wood 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 take place) or steam ( the steam generator can be built from a kettle or use an iron). The higher the temperature, the faster the wood will give up and you can start bending it. The moistened and heated wood can be bent under the action of the load (the ends of the board are laid on the supports), and a load is placed in the place of the future bend. Dried wood perfectly retains minimum radius the 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.

Reaction of wood to external influences

The fact is that wood reacts differently to bending. The convex part is stretched, the concave part is compressed. 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 of percent... That is why you should not think about how to bend a board more than two centimeters thick at home. It should be borne in mind that different types woods react differently to bending. For example, such species as oak, larch, maple bend poorly, but beech, ash, walnut are good. So before thinking about how to bend your board, decide on the type of wood it is made of.

How to bend plywood, fiberboard, MDF

At home, plywood is bent by increasing its moisture content, followed by ironing (an iron is required), and fastening in a template. Any frame element can serve as a template and its shape does not have to be curvilinear. The product is attached to the template with adhesive 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 is dry. It seems like we 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 in 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 of the sides. The thickness of such sheets is usually 8 mm. When bent, they overlap each other with milled sides, after which they are glued. That's all, actually!

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 so happens that tensile forces lead to rupture of the outer fibers. This can be prevented by conducting preliminary hydrothermal treatment.

So, you can bend a piece of timber made of solid wood and glued wood. In addition, sliced \u200b\u200band 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 should be noted that in the total volume of bent-glued blanks birch veneer takes about 60%.

When the workpiece is steamed, the compressive ability is significantly increased, namely by a third, while the stretchability is increased by only a few percent. And, therefore, thinking about whether it is possible to bend a tree thicker than 2 cm is not worth a priori.

Steam box heating

The first step is to prepare the steam box. It can be hand made. Its main task is to hold the tree that needs to be bent. It must have an opening for the steam pressure to escape. Otherwise, it will explode.

The steam outlet must be located in the bottom of the box. In addition, the box should have a removable lid through which it will be possible to pull out the bent tree after it has acquired the desired shape. Clamps should be used to hold the wood bent part in the desired shape. You can make them yourself from wood or buy in a specialized store.

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

Now is the time to steam the wood, for this you need to take care of the heat source and close the wood blank in the steam box. For every 2.5 cm of the thickness of the workpiece, it takes about an hour to steam the product. After the expiration of time, the tree must be taken out of the box and given the required shape. The process must be very fast. The workpiece bends gently and gently.

Some types of wood bend more easily than others due to different elasticity. Different ways require the application of force of different magnitude.

Once the desired result is achieved, the bent tree must be fixed in this position. You can fix the tree when it is being formed. This makes it easier to control the process.

Using chemical impregnation

To break the bonds of lignin between fibers, you can act on a tree chemicals, and it is quite possible to do this at home. Ammonia is ideal for this. The workpiece is soaked in 25% aqueous ammonia solution. After that, it becomes very obedient and elastic, which allows you to bend, twist it and squeeze out relief forms in it under the press.

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

Than longer wood is in an ammonia solution, the more plastic it becomes. After soaking the workpiece and shaping it, you need to leave it in this curved form. This is necessary for fixing the shape, and for the ammonia to evaporate. Again, leave the bent tree in a ventilated area. Interestingly, after the evaporation of ammonia, the wood fibers will regain their former strength, and this will allow the workpiece to keep its shape!

Layering method

First you need to make a wood blank, which will be bent. The boards should be slightly longer than the length of the finished piece. This is because the bend will shorten the lamellas. Before starting to cut, draw a diagonal line with a pencil. This must be done across the underside of the board. This will maintain the consistency of the lamellas after they are moved.

The boards are cut with a straight edge, in no case face... So, they can be added together with the smallest change. A cork layer is applied to the mold. This will help to avoid roughness in the shape of the saw, allowing for a sharper 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 adhesive is applied to the lamellas with a roller. It is best to use a 2-part urea-formaldehyde adhesive. He possesses high level adhesion, but dries for a long time. You can also use 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 it is very soft, which is not welcome in this situation.

Workpiece from bent wood should be placed in the mold as soon as possible. So, another lamella is laid on the lamella smeared with glue. The process is repeated until the bent workpiece acquires desired thickness... The boards are held together. After the glue is completely dry, shorten it to the desired length.

Drank like a method

The prepared piece of wood must be sawed off. The cuts are made 2/3 of the thickness of the workpiece. They should be with inside bending. Be extremely careful, as rough cuts can break the tree.

The key to success when cutting cuts is keeping the distance between the cuts as even as possible. Ideally 1.25 cm.

Cuts are made across the wood pattern. Next, squeeze the edges of the workpiece so as to connect the resulting gaps together. The bend will acquire this shape at the end of the work. Then the bend is corrected. More often outside processed with veneer, in some cases laminate. This action allows you to correct the bend and hide any defects in the manufacturing process. The gaps between the bent tree are easy to hide - for this, glue and sawdust are mixed, and then the gaps are filled with this mixture.

Regardless of the bending method, after the tree has been removed from the shape, the bend will relax slightly. In view of this, it needs to be done 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 business; it takes a certain amount of time to steam the wood, which depends on its thickness.

Processes of changing the properties of wood to meet the needs: technology and properties Wood is a natural polymer composite material that changes its properties under mechanical and chemical action. Knowing the patterns of material changes, you can create them purposefully, giving the qualities required by the consumer. This is called the wood modification process. It is necessary for chipboard production, MDF, OSB, WPC and others wood materialswhere the shredded wood mixed with a polymer binder is pressed into a uniform material of standard sizes.
The proposed technology for modifying wood changes the properties of wood in the array, that is, to the entire depth of the processed material, without resorting to its crushing. This is achieved by the fact that the molecules of the modifier, i.e., a substance that contributes to a change in the properties of wood, is comparable in size to the molecules of wood substance and less than the size of the intercellular spaces in it. Therefore, by means of 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 in the wood substance.

Thus, the technology allows not to grind wood, not to use expensive polymer binders, and to achieve the same effect that was achieved with production of MDF, 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 should, in a dissolved state, penetrate into the cellular, be chemically active for the components that make up the wood substance, and, reacting with these components, purposefully change the physical and performance 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 wood with an aqueous solution of urea, we paradoxically "dry" it, "taking" part wood moisture for hydrophilic carbamide. Carbamide or urea actively react with such components of wood matter as lignin, hemicelluloses, extractives.
And since the polycondensation reaction occurs in the macromolecules of the wood substance, the wood mass acquires new ones specified by the manufacturer useful qualitieskeeping 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. The wood modified with urea 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 building and joinery products, thermally modified wood is also used, the technology of which is similar to the one 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, extractive substances and xylans.
Due to thermal destruction, the physical and mechanical properties of thermally modified wood are partially reduced. Technological process production of mechanochemically modified wood consists in impregnation of the original wood of any species and any moisture content with a modifier solution. Impregnation can be carried out by the method of "hot-cold baths" - diffusion or in an autoclave - forced. Then drying is carried out, if necessary - with compaction (pressing), and heat treatment, fixing the new properties of wood. It should be noted that it is more economical to use low-value rocks, since their operational properties after modification are superior to those of expensive rocks.

How to bend wood correctly and in what way?

Currently, manufacturers of wood products prefer to do without this operation, and if they use bent elements, then from plywood. Bending plywood is easier. It should be noted, however, that furniture makers natural wood have long ceased to pamper the buyer. All furniture is made of wood or fiberboard. Curved wood products, whether it be a chair or something else, are undoubtedly stronger, lighter and more elegant.

Wood selection

The bending success largely depends on the type of wood chosen. Almost any breed can be bent, but elm, oak, beech have the best flexibility. If carefully dried wood is needed for carpentry work, then in our case it is better to use freshly prepared wood. You should not take old (by age) wood. Than younger tree, the more flexible it is. From the desired breed, you need to choose pieces without cracks, without knots. At least there should be no knots in the place of the intended bend. It is important that the wood is straight-grained, without streaks, cross-grades 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 to get it not by sawing, but by splitting the round timber. The direction of the split should be along the chords of the circumference to exclude a brittle and unbendable core. Cooked this way wooden blocks and the planks will not flake off when bent. The future part is marked so that the bend direction coincides with the radius of the round timber from which the workpiece was split off, and outside fold coincided with outer part the former round timber. Chipped blanks are processed with planers up to required sizes with a small allowance for finishing.

Steaming the workpiece

To give the workpiece the best plasticity, it must be steamed. This requires a metal container of a certain size. In it the workpieces will be "steamed" as a whole or only in the place of bending. The latter is preferable, since it is more convenient to take the workpiece simply by hand (without accessories), which you cannot do if the workpiece is all steamed.

If given view work is supposed to be put on stream, then you can make a special metal container with a sealed lid and two holes for placing the bent part inside the "steam room". All this simple structure must be tightly closed in order to reduce the escape of steam to the outside. Place under the lid rubber gasket... Do not screw tightly, it may swell or even explode under steam pressure. A cap that is heavy enough will ensure tightness and at the same time will operate the relief valve if the pressure is too high.

It is difficult to indicate the time of complete steaming. It depends on the type of wood, the section of the workpieces, the degree of dryness of the workpieces. It's just that from time to time you need to take out the workpiece and try it for bending. The readiness of the workpiece is immediately felt by the flexibility to bend.

Workpiece bending

It is best to fold the workpiece in a template. The blank bent and dried in the 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 act like a shower for a horse harness is done - the steamed workpiece is bent and the ends are tied with a rope. Leave in this form until completely dry. Dry the bent parts in a ventilated place protected from the sun. Attempting to artificially accelerate drying by heating can lead to wood cracking.

It should be noted that after removing the part from the template, it “loses” a little, i.e. straightens up. Taking this property into account, the workpieces must be bent a little "steeper" in order to obtain the desired shape upon release. How much cooler is a matter of experience. Much depends on the section of the workpiece, the type of wood, the degree of its steaming before bending.

Press for bending wood materials

Manufacturer ORMA, Italy

Appointment
This equipment is designed for bending (bending) wood materials. Before bending, the workpieces are steamed in specialized chambers. The workpiece is stabilized by high frequency current.
This equipment has found wide application in the manufacture of chairs, sledges, school furniture.

Specifications:

The complete bending kit includes
- Steam chamber - a reservoir for moistening the workpieces with a condensate collector, complete with a steam generator (a separate generator for each autoclave)
- Pre-bending press (required depending on tasks and performance)
- The press for bending and stabilization (selected depending on the tasks and performance), depending on the complexity of the product, can be equipped with additional side cylinders. 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

Norms and strength of bent timber construction

Besides traditional use bent, today building structural elements made in this way are increasingly used. Using load-bearing elements of bent wood allows to create new interesting views architectural solutions that, in combination with optimal economic performance such designs explains the increased interest in them from practical application not only in industrial, but also in private housing construction.

To make curvilinear structure bent wood can be made in two ways: by sawing it out of boards, bending a bar (solid-bent products) or layers of wood with their simultaneous gluing (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 a dome crowning a decorative turret of a house, you should prepare everything you need for bending wood. Just as website optimization allows you to increase the rating of an Internet resource, so does the choice quality material for bending improves its result. Selected as blanks unedged board or a bar without knots, oblique in which no more than 10% of the surface area. The best varieties woods with increased plasticity are hornbeam, maple, beech, oak, ash and elm.

After the material is selected, you can start the bending process, the main stages of which are: hydrothermal treatment, bending the workpiece and drying the product. Optimal parameters, in which the bending is of the highest quality, the moisture content of the wood is within 25-30% and the temperature in the center of the workpiece is from 80 to 90 ° C

Professional promotion of sites devoted 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 consists in steaming or boiling the workpiece in hot water.

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

Flexible plywood and its applications

Flexible plywood (bending plywood) is now in great demand, due to the fact that it is convenient material for the manufacture of structures in which rounding is necessary. The use of such flexible plywood is effective and expedient, since it takes any necessary shape. Its flexibility allows to embody the wildest fantasies of designers and produce the most fashionable and modern furniture, whether it be a wardrobe with original design for your living room, cute kitchen shelves 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: Wig, Keruing. Flexible (bending) plywood is, as a rule, a 3-layer board that is glued in the transverse or longitudinal version of the jackets.

Flexible plywood, can be used for all types of bends, even with very small radii. It does not need to be heated and treated with water. The self-supporting structure of the bending plywood makes the use of structural and special supports unnecessary. Unique designer models, rounded structures and complex shapes with multiple radii that cannot be created from traditional materials are easily and quickly manufactured. 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.

Plywood from tropical high Quality is a combination modern technologies and traditional materials. A product designed to satisfy the most sophisticated needs modern manufacturers furniture and joinery. Flexible plywood (plywood for bending) is cheaper than prefabricated wood forms. Significant time savings, less laboriousness 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 - Ultra-light plywood. The range of use of this plywood is also quite wide: it is the production of door panels, the production of cabinet furniture, sofas, armchairs, shelves. Ultra-light plywood is new Product in our market, it is 1.8 times lighter than birch. This plywood is well veneered with veneer, finished with films and varnishes, and most importantly, it can significantly reduce the weight of the finished product!

Specifications

Bending direction Across grain: Along width

Composition Tropical wood, hot pressed with thermal setting adhesive

Density 300-400 kg / cubic meter.

Thickness 5 mm, 8 mm, etc.

Dimensions 2500/2440 mm x 1220 mm, etc. on separate order

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

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

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

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

Any wood glue can be used.

Transport panels on a hard, flat surface. Individual panels can be twisted, 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 resins - thermoplastics. (Thanks to John McKenzie for the last two sentences).

To do this, you need heat and steam at the same time. In Asia, people bend wood and just over fire, but that wood is definitely quite wet - usually freshly cut. Boat builders in ancient Scandinavia procured materials for the hulls of their ships and put them in a swamp of salt water so that they retain their flexibility until such time as they need to be used. However, we do not always manage to get freshly harvested wood for these purposes and excellent results can be achieved using conventional air-dried wood. It will be very nice if, a few days before the operation itself, you immerse the blanks in water so that they gain moisture - those Vikings knew what they were doing. You need warmth and you need moisture.

The general rule of thumb is for steaming time: one hour for every inch of wood thickness.

Be aware that along with the likelihood of undercooking the workpiece, there is also the likelihood of overcooking it. If you've been hovering for an hour inch board and when trying to bend it, it cracked - no need to conclude that time was not enough. There are other influencing factors that explain this, but we will return to them later. A longer steaming of the same workpiece will not give a positive result. It is not bad in such a situation to have a workpiece of the same thickness as the one intended for the bend and which is not a pity. Preferably from the same board. They must be steamed together and after the supposedly necessary time, get out the test sample and try to bend it in shape. If it cracks, then let the main workpiece steam for another ten minutes. But no more.

Wood:

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

Rot is the main evil in shipbuilding. If you are concerned about this issue, then note that the very fact of steaming fresh wood removes its tendency to rot. So you don't have to worry - boat frames are usually made of fresh bent oak under the steam and will not rot if taken care of. It also means that in this way you can make at least blanks for the Windsor chair. But air-dried oak also gives excellent results.

When selecting wood for bending, one should be avoided - oblique. If you try to bend, such a workpiece may burst.

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

If all you have is after the dryer and nothing else is available - well, then you have no choice. Still, if you can get air-dried wood, it will be much better.

Despite all its strength and strength, wooden parts can be easily and simply bent, if suddenly during the construction process you need some special one, and original details oval or round shape... Tree at correct processing easy to change its shape, and you can carry out this procedure with your own on their ownwithout the help of professionals.

Types of work

There are two main ways to bend a tree to the desired shape, and 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 efficiency, both of these methods are completely the same, just hot way fixing the tree is much faster. For each method, you will need glue, pva or wallpaper, depending on what is at hand, you do not 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 timber, it is necessary to grease it with glue, strongly and thoroughly, without fear that the tree will become wet from this. In fact, under the influence of the glue solution, all excess moisture will leave the tree, and it will become even stronger and stronger, which is extremely important. After the timber has been greased with glue, it must be fixed with tools in the desired shape, and in the case of a cold work process, simply leave it fixed to dry. If you choose hot, then the timber should be covered with ordinary film so that it dries faster and all the moisture evaporates.

Durability

Whichever method is chosen, both are effective and work in the same way. The bar is completely fixed in its new form, and will no longer return to the old one. You can bend a wet bar from the glue as much as possible without fear that it will break. As a result, you will receive an original and beautiful piece of furniture or a detail to create an even more attractive interior of the house or its facade. The timber bent with glue does not even need to be processed for durability, which is extremely convenient. Moisture will not soak through adhesive solution, and insects will not encroach on such a tree, in which there will be 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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