Steam bending wood or how to bend a strong, unbending oak to the shape you want without too many problems.

I have been working with flexible wood for 13 years now, and during this time I have built many steam chambers and tested various steam generation systems in operation. What you are reading now is based on reading literature and personal practical experience. Even mostly from experience. As a rule, I worked with oak and mahogany (mahogany). Dealt a little with thin birch veneer. I have not tried other breeds, since I am engaged in the construction and repair of boats. Therefore, I cannot autonomously judge the work with other species such as cedar, pine, poplar, etc. And since I myself have not done this, then I cannot judge about it. I write here only about what I have experienced personally, and not just read in a book.

After such an introduction, let's get down to business ...

To begin with, there are a few basic rules that are always followed.

By steaming wood to bend it, you thereby soften the hemicellulose. Cellulose, on the other hand, is a polymer that behaves like resins - thermoplastics. (Thanks to John McKenzie for the last two suggestions).

To do this, you need heat and steam at the same time. I am aware that 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 the time when they need to be used. However, we are not always able to get freshly prepared 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.

As I found out, along with the probability of undershooting the workpiece, there is also the likelihood of overcooking it. If you soared 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 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 expected 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:

Generally, the best option is 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. I can take a 2-inch white oak plank, clamp one end of it in a workbench and bend it to whatever curvature I need - that is how malleable fresh wood is. However, naturally, it will not remain in such a state and it will still have to soar.

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 oak bent under 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. However, I also worked a lot with air-dried oak and the result was great too.

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:

• Fresh wood is best.
• Air dried wood is a good second option.
• Wood after the dryer is 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. I've dealt with this too. Still, if you can get air-dried wood, it will be much better. Just that week I bent 20mm walnut planks for my yacht's transom. The workpieces have been dried for several years and bending went perfectly smoothly.

Steam chambers.

It is absolutely worthless, and even harmful for the bending result, to strive to make an absolutely sealed chamber. Steam must leave her. If you do not provide a steam flow through the chamber, it will not be possible to bend the workpiece and the result will be the same as if you soared it for only five minutes. After all my experiences, this is familiar to me.

Cameras come in a wide variety of shapes and sizes. It should be large enough so that the workpiece seems to be in a suspended state and steam flows around all sides of it. A good result is pine planks about 50 x 200. One way to "hang" the workpiece is to drill through holes in the side walls of the chamber and drive in round hardwood rods. With their help, the workpiece will not touch the bottom and the area of ​​closed wood will be minimal. However, you should not make a chamber of such a size that the amount of generated steam is not enough to fill its volume. The chamber should be such that it is humid inside and the steam rolls in waves. This means that the dimensions of the chamber must correspond to the capabilities of the steam generator (well, or vice versa).

When I needed to bend a five-meter mahogany board with a section of about 200 x 20 for the new deckhouse of my yacht, I made a chamber from pine boards with a section of 50 x 300. A 20-liter metal tank served as a steam generator. The energy source was a propane burner. The thing is absolutely wonderful because it is convenient and mobile. Performance 45000 BTU (1 BTU ~ 1 kJ). This is an aluminum cylinder with three legs and one burner with a diameter of 200 mm.

I recently discovered a 160,000 BTU propane burner in the West Marine catalog for $ 50 and bought that too. With its help I can bend frames even for "Constitution".

When I say one hour of steaming per inch of thickness, I mean one hour of SERIOUS CONTINUOUS steaming. Therefore, the boiler must be such as to provide steam for the required time. I used a new 20-liter fuel container for this purpose. Putting the workpiece into the chamber is only possible when the installation is at full capacity and the chamber is completely filled with steam. It must be absolutely guaranteed that the water does not run out prematurely. If this happens and you have to top up the water, it is better to quit this business. Topping up with cold water will inhibit steam generation.

One way to make the most of the water is to keep the chamber at a slight incline so that the condensed water inside drains back into the boiler. But at the same time, it is necessary that the fitting through which the steam enters inside was closer to the far wall. Another way is to make a siphon system that replenishes its level as the water boils away.

This is what a photo of such a system looks like:

In the picture, you can see a wooden camera tilted slightly. Directly below it is the boiler of the steam generator. They are connected to each other by means of a radiator hose. If you take a closer look, you can see the L-shaped pipe coming out at the base of the boiler on the left. This is poorly visible in the photo, but its vertical part is actually translucent and thus we will know about the water level inside the boiler. To the left of the boiler, you can see a white bucket in which there is water for make-up. Take a closer look and you will notice a brown tube connecting the bucket to the vertical part of the level gauge pipe. Since the bucket is on a hill, the siphon effect is observed: as the water level in the main boiler falls, water enters it from the bucket. It can be topped up from time to time, but it should be done very carefully so that it does not rush quickly into the boiler and does not cool it too much.

To minimize the need to add water during the steaming process, it is best to start with a bucket full to the top. I myself prefer to leave a small air gap in the boiler.

Many chambers have a door at the end through which you can move the workpieces if necessary and remove them if necessary. For example, if you are engaged in the manufacture of bent frames and you would like to cope with it as much as possible in a day, you heat up the boiler and (when it reaches full capacity) put the first blank inside. After 15 minutes, put the second one. After another 15 - the third and so on. When it's time for the first one, you take it out and bend it. I assume this procedure will take less than 15 minutes. When she sits in place, the second is already on the way ... etc. This allows a great deal of work to be done and avoids overcooking.

The door also has another important function. It doesn't even have to be made of solid material - on my small camera, just a hanging rag serves for this purpose. I say "hanging" because the steam has to come out from the end (since a flow of steam is needed). It must not be allowed that excessive pressure builds up in the chamber, which impedes the flow of steam inside. And besides, the very picture of a wooden box, from which steam is pouring in clubs, looks pretty cool - passers-by simply freeze. The second purpose of the door is to prevent cold air from entering the chamber from the bottom of the workpieces.

So, let's assume that our wood is being cooked (with a pleasant smell) and the templates are ready. Try to organize everything in such a way that the operation of removing the workpiece from the chamber and its bending is quick and smooth. The most important thing here is time. You have a few seconds for this. As soon as the wood is ready, quickly take it out and bend it right there. How quickly human dexterity allows it. If pressing to the template takes time, simply bend with your hands (if possible). For the frames of my yacht (which have a double curvature), I took out the blanks from the chamber, poked one end into the clamp and bent this end and then the other just with my hands. Try to bend more than is necessary for the template, but not much. And only then attach it to the template.

But I repeat once again - the curvature of the wood must be given immediately - within the first five seconds. With every second the wood cools, it becomes less pliable.

The length of the workpieces and the curvature at the ends.

It is almost impossible to make workpieces to the exact length and expect to be able to bend around the ends. You just don't have the strength to do it. For this reason, if you need a workpiece with a length of one meter, and its thickness is more than 6 mm, you better cut off a piece of two meters and bend it. I'm just assuming you don't have a hydraulic press in your workshop - I certainly don't have one myself. When cutting a workpiece with a margin, remember that the shorter it is, the more difficult it will be to bend.
And if it is with a margin, then at the end of the real part there will be a large curvature - for an inch oak board, the last 150 mm are absolutely straight. Depending on the radius required at the end, it may be necessary to resort to woodcarving in such places and take into account the required thickness when choosing the material.

Templates.

After steaming the workpiece and clamping it on the template, you must wait a day for complete cooling. When the clamps are removed from the workpiece, it straightens somewhat. The extent of this depends on the structure and type of wood - it is difficult to say in advance. If the workpiece already has some natural bend in the desired direction, which can be used (I try to do this whenever possible), the degree of straightening will be less. Therefore, if you need a certain curvature of the final product, the template should have a greater curvature.

How much more?

Here we are dealing with pure black magic and I personally cannot give you any numbers. One thing I know for sure: it is incomparably easier to unbend an overly bent workpiece than to bend a cold unbent one (provided that you do not have a giant lever).

Warning. If you are bending laminating blanks, the template should be exactly in the shape of the laminate blank - I rarely have cases of large bending of well-bent glued timber.

There are endless options for bending templates. And it doesn't matter at all which one you choose if you happen to be the owner of a factory for the production of clamps - there are never too many of them. If wood with a thickness of more than 12 mm bends, the template must have significant mechanical strength - it will experience quite high loads. You can see how it looks in the photo at the beginning of the article.
Quite often, when bending, people use a metal strip on the outside of the bend. This helps to distribute stresses evenly along the length of the workpiece and avoid cracks. This is especially true if the outside of the fibers are located at an angle to the surface.

Well, that's probably all my thoughts at the moment.

Bending is one of the methods of making beautiful and durable wood parts, for example, for furniture. A home craftsman is quite capable of mastering such a technology, a bent part is much stronger than a sawn one, less wood is consumed for its production, and one-and-a-half and end cuts are obtained on the sawn surfaces, complicating the further processing and finishing of parts.

There are three ways to bend wood. One of them - the most famous one - consists in preliminary steaming of wood, followed by giving it the required shape in powerful presses. This hot bending method is mainly used in series production of, for example, chairs.

Along with it, especially at home, two other methods of bending wood are practiced, but already in a cold state.

1. First - bending solid wood with preliminary bending cuts.
2. The second is bending gluing, in which a bent part is obtained by the method of pressure in molds from a workpiece, which is a package of several layers of thin strips of wood coated with glue.
3. When bending by the second method - with notches - narrow parallel grooves are cut into the workpiece to a depth of 2 / 3-3 / 4 of its thickness, after which the workpiece is given the desired shape.

The maximum bending radius depends on the depth of the cuts (and, accordingly, on the thickness of the blanks), the distance between them and the flexibility of the wood. The incisions are made both parallel and perpendicular to the fibers. This work step is carried out using a miter saw or hand-held circular saw with a guide stop. If there is no special tool, a regular hacksaw for wood will do. The main thing is that the depth of the cuts is the same.

GLUING WITH SIMULTANEOUS BENDING

At bending wood the fibers on the inside are compressed, and on the outside they are stretched. The wood "transfers" the compression of the fibers relatively easily, especially if it is pre-steamed. It is almost impossible to stretch it.

Flexibility also depends on the type of wood and the thickness of the workpieces. For example, hard wood from temperate climatic zones - beech, oak, ash, elm - lends itself to bending more easily than tropical wood species (mahogany, teak, sipo, etc.). Conifers are too tough for this.

The resistance value of the bending wood until the moment of its destruction is determined by the ratio 1:50, i.e. the bending radius should be at least 50 times the workpiece thickness. For example, a workpiece with a thickness of 25 mm requires a radius of at least 1250 mm. The thinner the wood, the easier it bends. Therefore, where possible, it is advisable to make a part of the corresponding shape by bending gluing (Fig. 1).

In this method, individual strips of wood of the same thickness and width are glued, laid in several layers so that their fibers are parallel, and placed in a mold made of hardwood. The die and punch of the mold are squeezed with clamps and the bag is left in this position until the glue dries.

The thickness of the strips glued to each other can fluctuate in the range of 1-6 mm, again depending on the required bending radius. Cold curing glue is suitable for gluing the layers. If the bent-glued workpieces are intended for use in outdoor structures, it is best to use waterproof glue.

BENDING USING CLAMPING DEVICES AND MOLDS

To determine the permissible thickness of veneer strips or planks to be bent (with a greater thickness, the wood may break), you need to know the smallest bending radius. Most of all, wood deforms on the inside of the bend. Therefore, it is always necessary to measure here.

As an auxiliary device, it is advisable to use a template that you can make yourself. To determine the bending radius, we take an ordinary school compass and draw several circles on tracing paper (with a slight increase in their radius), having a common center. As a result, we get a template. We apply it to the surface of the bend, for example, a mold and move it until we find a suitable circle with the largest diameter. We measure its radius on the template. Divide the resulting value by 50. The quotient of division will be the maximum allowable strip thickness of a strip or veneer.

When working with molds, the bend on the outside of the workpiece should be smoother than on the inside. In this case, we draw two circles from one center, the radii of which differ by the total thickness of the strip material.

The most difficult situation is when it is required to bend a part of a complex configuration with different bending radii. Here, bends for the inner or outer side of the workpiece can be built freely if its shape is not tied to the contours of any piece of furniture.

The line for the second cut (the first - at the beginning of the bend) can be constructed in this case as follows. We measure the total thickness of the layers to be glued with a compass, draw a circle with it on hard cardboard, cut out a circle and attach it in several places to the line of the first cut. At the same time, we apply a circle so that it touches the first line, and draw its outline, respectively, on the opposite side. The second cut line will be a through link between these construction lines.

BENDING TECHNOLOGY WITH IMPLEMENTATION OF CUTTING ON BILLS

When determining the number of cuts that are cut into the workpiece for bending along a known radius (it also depends on the width of the groove and the type of wood), we use an auxiliary structure. To do this, take a block similar to the workpiece (Fig. 2). We cut one single cut on it with a depth of 2 / 3-3 / 4 of the thickness of the bar. Draw a straight line on a piece of paper and mark the notch point on it.

We put the block on the paper so that its lower edge until the notch coincides with the drawn line and the marked point of the notch, and fasten the block with a clamp to the work table. Set aside the distance of the required radius b on the line and the bar and bend the bar until the upper edges of the notch close. The distance a between the end of the line and the mark on the block will be the distance between the individual cuts that can be marked on the workpiece.

If the cuts need to be cut on the outside of the workpiece, the distance between them and, accordingly, their number is determined in the same way. We bend the workpiece as much as the elasticity of the wood allows. If the test piece of wood breaks, then this can be expected from the workpiece fixed in the mold.

Based on materials from the magazine "Doing It Yourself"

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One of the ways of processing joinery blanks is bending. Wooden blanks treated with hot steam are able to bend and, after drying, retain their shape. Such a technological process does not present any particular difficulties, but some features of how to bend wood should be taken into account. You may also be interested in pine staircases, which you can order on the website http://mirdereva.ru/.

The fibers of the wood are bonded with a special substance - lignin, which softens under the influence of high temperature, and after cooling it again bonds the fibers. This is the basis for the process of bending blanks. It should be borne in mind that wood of different species lends itself to bending in its own way. For bent products, it is best to use oak, beech, birch, yew, cherry, elm. But pine, spruce, cedar, alder should not be used for these purposes.

Work on bent parts begins with material selection. The workpieces must be straight-layered, the use of wood with curved grains is not allowed. The prepared material is dried under natural conditions, under awnings, to a moisture content of no more than 20%. But artificially dried wood should not be used for bending, since it is less susceptible to such processing. If you have to use such a material, then before bending it must be soaked in water (for at least a week). Soaking is also necessary for hardwoods such as oak, ash, beech.

It is best to use a steam chamber to heat the workpieces before bending. Such a camera is easy to make at home using a plastic pipe of suitable sizes and a regular kettle. The parts are placed in a pipe and steam is supplied from the kettle. The exposure time in the camera depends on the size of the part and is determined empirically. In this case, you can focus on the fact that for 1 cm of the thickness of the workpiece, 30-40 minutes of steaming the wood is needed.

In places of bending on parts, if the design of the product allows it, you can slightly reduce the thickness of the material, remove chamfers. This will make the bending process easier. Thin workpieces, in the absence of a steam chamber, can be heated over an electric or gas stove.

Before you start bending wood, you need to prepare the form on which the part will be fixed, and the clamps for fixing. It should be borne in mind that after warming up the wood, there will be very little time to fix the workpiece, no more than 5 minutes. Therefore, everything must be done quickly, if the part began to cool down, then it should be heated again. Otherwise, the workpiece may break.

Therefore, it is important to provide for such a design of molds and clamps that would allow you to quickly fix the workpiece in the desired position. If the forms are made of wood, then they should not be covered with any protective compounds, painted, varnished. Firstly, they deteriorate from heating, and secondly, they will interfere with the drying of the workpieces.

Short workpieces are bent on mandrels with a larger radius, and then they are fixed in the mold. This pre-bending reduces the likelihood that the part will break when the bend is formed. It is necessary to maintain the parts in the form until they dry completely so that they do not unbend back. This usually takes 6 to 9 days, and is determined empirically.

After releasing the workpiece from the clamps, it must be postponed for a day, and only then proceed to processing and finishing. This is necessary in order to relieve residual extension stresses. The tips are simple, but they will allow you to easily master the process of how to bend wood.

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In the woodworking industry, curved parts are produced in large quantities. Curved parts are manufactured in two ways: by sawing out of boards or slabs and bending straight bars (solid-bent parts) or layers of wood with simultaneous gluing (bent glued parts).

Technological process of bending wood. The technological process of bending solid wood bars includes the following operations: material preparation for bending, hydrothermal treatment, bending and drying.

Procurement of material for bending. Blanks for bending are obtained from unedged boards by cutting them on circular saws. The following requirements are imposed on blanks for bending.

The oblique layer should not exceed 10 °. With conventional bending methods, knots are absolutely not allowed in the workpieces. In blanks with simultaneous pressing, knots are allowed within wide limits, which sharply increases the output of blanks. The blanks should be cut out taking into account the allowances for the subsequent processing of parts. When bending with simultaneous pressing, in addition to the allowance for processing, there must be an allowance for pressing the wood across the fibers and an increased allowance along the length of the workpiece. In order to increase the yield of blanks for bending, it is recommended to cut boards after preliminary marking.

At small enterprises, the method of obtaining billets for bending by splitting blocks has been preserved. The chipped workpiece does not have a cross-layer, therefore, when bent, it gives a lower percentage of scrap. However, this method is very laborious, since it is performed manually and gives 20-25% lower output of blanks from the log than when sawing it.

After cutting (or splitting) blanks for circular section parts are processed on turning-copying or circular-rod lathes, and blanks for rectangular section parts - on longitudinal milling machines. You can also bend non-planed workpieces, but in this case, the boards are cut with planing saws, which give a clean and accurate cut.

Hydrothermal treatment. Hydrothermal treatment of wood before bending is carried out in order to increase the plasticity of wood. Optimum plasticity of wood is achieved when it is heated in a wet state. This is due to the fact that when heated, some of the substances that make up the cells pass into a colloidal state.

As a result, the ability of cells and all wood to deform is increased. When drying deformed (bent) wood, colloidal substances solidify and retain the shape given to the workpiece.

Hydrothermal treatment of wood before bending is carried out by boiling in hot water or steaming. For boiling, use wooden vats or metal baths and tanks. The water in baths and vats is heated by steam.

The temperature of the water is maintained at 90-95 ° C, without bringing it to a boil. The cooking time depends on the initial moisture content, size and type of wood.

When boiling, it is difficult to obtain a uniform temperature and humidity of the entire workpiece, the outer layers are oversaturated with water. Therefore, boiling in hot water is used only in cases where steaming is technically difficult.

The most widely used in production is the steaming of wood in an atmosphere of saturated steam. Steaming allows you to heat the wood to the desired temperature (70-80 ° C), regulate the moisture content of the wood and get it always close to optimal for bending, i.e. about 25-30%.

For steaming, low-pressure saturated steam (0.02-0.05 MPa) is used, which corresponds to a temperature of 102-105 ° C. Wood steaming is carried out in hermetically sealed metal drum boilers or concrete chambers. The capacity of boilers and chambers is small, designed for laying bars in the amount of 30-40 pcs.

Boilers are located at each bending machine and are connected by a steam line to each other to form a battery. Bars are placed in boilers and chambers on gaskets in order to ensure better washing with steam.

The duration of steaming depends on the initial moisture content and temperature of the wood, the size of the blocks and the steam pressure in the boiler. The steaming time is determined according to a special diagram. For example, for workpieces with a thickness of 40 mm with an initial moisture content of 30% and a steam pressure in a steaming boiler of 0.03-0.05 MPa, the duration of steaming is 12-13 minutes, and for workpieces with a thickness of 80 mm - 65 minutes.

Plywood in the case of bending to small radii of curvature can also be subjected to hydrothermal treatment. Plywood glued with synthetic adhesives is boiled, and glued with casein or albumin glue is only steamed.

The workpieces removed from the steamer or brewing tank must be bent immediately. Cooling of the outer layers of wood, which experience the greatest stresses during bending, must not be allowed.

Bending of wood and equipment. Wood bending machines are divided into two types: cold and hot forms.

Machine tools of the first type (Fig. 4.13) are used for bending into a closed loop. The bars are bent around a removable unheated rotating template 6. Template with tire 2 fits on vertical shaft 8 , which is driven in rotary motion by an electric motor through a gearbox 7.

The free end of the bar is fixed in the carriage 4, sliding on guides 3. Block 5 is laid between the template 6 and bus 2 and is fixed with a movable stop. Then the electric motor turns on, while the shaft turns 8 with a template put on it and the bar is bent together with the tire.

In the place of the bend, a roller / is installed, tightly pressing the bar to the template. The rear end of the tire is secured with a clip to the template. The template with a bar and a tire is removed from the machine and sent to the dryer, and a new template is put on the machine, and the operation is repeated.

Rice. 4.13.

7 - pressure roller; 2 - tire; 3 - guide; 4 - bar; 5 - blank;

b - template; 7 - reducer; 8 - shaft

Rice. 4.14.

7 - hook; 2 - template; 3 - emphasis; 4 - tire; 5 - blank

Roll-forming machines with hot forms are called bending-drying machines, they can be with two- and one-sided heating. Machines with double-sided heating are a hydraulic or pneumatic press with heated profile template plates, between which bending bars are clamped. In these machines, the bars are held in a clamped state until the shape is completely fixed and the workpieces are dried.

In machines with one-sided heating (Fig. 4.14), blanks 5 are laid between the hot template 2, heated steam, and a tire 4 and are fastened with an emphasis 3. Curved blanks 5 together with tires are fixed on the template with special hooks /. The workpieces remain in the machine until the shape is fixed.

This is achieved by drying the wood to approximately 15% moisture content, which takes 90-180 minutes. To increase the productivity of the bending-drying machines, the workpieces are recommended to be dried to 20% moisture before bending, kept in the machine to a moisture content of 12-15%, and the final drying of the workpieces removed from the machine to the production humidity in drying chambers.

Bending of plywood is carried out in templates consisting of two parts: a matrix and a punch, between which plywood is laid and folded. This uses special tools, screws, pneumatic and hydraulic presses.

Bending with simultaneous pressing consists in the fact that the wood is bent around a template provided with a notch, and in the process of bending from the outside of the workpiece it is pressed against the template through a tire by a pressing roller.

The billet is rolled. The thickness of the workpiece decreases, the layers of wood on the concave side of the workpiece take a wavy shape from the indentation of the notch of the template, the outer layers are compacted. This contributes to an increase in the compression resistance of the concave layers in the wood and the tension of the outer ones.

Bending with simultaneous pressing significantly improves the bending ability of wood, allows bending wood with large knots located on the outside of the workpiece. It is used for bending softwood and softwood.

Drying of workpieces after bending. The bent blanks are dried in drying chambers to operating humidity, and the blanks are placed in the chamber together with the templates and the tires covering them. The design of the drying chambers is similar to those used for drying sawn timber.

The dried workpieces are unloaded from the chambers and sent to the cooling compartment, where they are kept for at least 48 hours to equalize internal stresses. Only after that, the workpieces are freed from templates and tires and sent to the machining workshop.

The sequence and principles of machining bent blanks on machine tools, i.e. giving them final dimensions and a clean surface do not fundamentally differ from the processing of straight workpieces.

Manufacturing of bent glued parts. To obtain bent-glued parts, hydrothermal treatment of wood before bending and drying after bending are not required. Bent parts are made of rotary cut veneer or plywood. The technological process for producing bent-glued parts consists of preparing raw materials (veneer, plywood or thin strips), applying an adhesive solution to the surfaces to be glued, gluing the blanks with simultaneous bending in molds or in templates, and holding the parts after pressing to equalize moisture and stress.

Gluing is done either in blocks or in separate parts. Pressing is carried out in hydraulic presses with molds or templates. One of three types of heating of the pressed package is used: electrical contact, steam or high-frequency currents (HFC). The most progressive heating of HDTV. This method requires less pressing time and a more even temperature distribution over the cross section of the bag.

Adhesives based on carbamide resins of high concentration and increased curing speed are used as a binder in the manufacture of bent-glued parts. The consumption of such adhesives per 1 m 2 of the surface to be spread is 110-120 g.