Plywood is one of the cheapest and most practical building materials. Despite the multilayer structure, it is characterized by convenient installation and can be processed at home without special equipment. The standard production of plywood involves the use of wood lamellas, with proper processing of which it is possible to obtain a finishing material that is resistant to a wide variety of threats.
General manufacturing technology
Plywood sheet is a kind of heterogeneous wood material. Only as a basis is used thin-sheet veneer, superimposed on each other under high pressure of the press. Actually, the whole process can be divided into three main stages - preparation of wood, its processing and gluing. Also, at different industries additional steps may be included that improve or modify certain qualities of the workpieces or finished products. For example, modern plywood manufacturing techniques provide for multiple impregnation of the veneer structure in order to give it refractory and frost-resistant qualities. This is especially important if in the future plywood will be used in the construction of the roof. After the production of this material, there also remains a lot of waste (mainly after peeling) that can be spent in the process of manufacturing chipboards.
Selection and preparation of wood blanks
Wood blanks for plywood are called logging. Arrays of birch, linden, alder and some of conifers are usually used for them. As in the case of the production of other wood materials, plywood blanks undergo rigorous quality control, during which defective and simply unsuitable raw materials are screened out.
The main processing procedure is to increase the ductility of the wood structure, which is important from the point of view of further obtaining lamellas. According to the regulations, the production of veneer plywood is possible only when cutting workpieces that have passed hydrothermal treatment. This operation consists in steam processing of logs and settling them in the aquatic environment. For example, for birch blanks, pools with a water temperature of about 40 º are used. Soaking lasts several days, depending on external microclimatic conditions.
At the final stage of wood preparation, mechanical debarking is performed. The bark is removed, after which churaks are formed on the sawing machines. These are pieces of whole logs, the length of which varies from 130 to 150 cm on average. They are used for slicing veneers.
Getting veneer
In modern factories, several methods are used for cutting lamellas for plywood. Of these, peeling with a circular machine, planing of churaks, and also their cutting into thin strips are distinguished. However, the processes of planing and sawing due to low productivity and efficiency are increasingly replaced by peeling. For this operation, special machines are used that carry out the cutting of workpieces in cross section. The log is fixed on a circular base and in the process of rotation around its axis is trimmed with high-precision peeling knives. This is how the most crucial stage in the plywood manufacturing process is carried out, on which the main characteristics of the future product depend. Finished lamella tapes come out of the peeling machine. They are stacked in piles, and then sent for further processing.
Veneer drying
For this procedure, a special conveyor is used, on which the lamellas are surrounded by warm air currents. Using measuring devices such as a moisture meter, the line operator monitors and sort the veneers. According to the technology, the optimum moisture coefficient of the slats for the manufacture of plywood should be 6%. Excessively wet sheets after heat treatment are either sent to dryness or rejected. Since the lamellas have a very delicate fine structure, mechanical defects are often found. But in the presence of minor damage, the veneer is not discarded. At this stage, it is possible to repair plywood sheets using artificial inserts of fragments of new veneer, which is selected according to the texture, moisture index and size. Successfully passed this stage, the lamellae are checked by the scanner and sent for daily storage.
Gluing lamellas
As glue special compositions are sometimes used with unique recipes. Each plant seeks to develop its own methods of manufacturing an adhesive mixture that will distinguish a plywood sheet from the total mass of competitors. For example, some compounds already within the structure provide the effect of lamination with phenol-formaldehyde resins. But more often practiced is the manufacture of laminated plywood with a paper tar film, which makes the material stronger and more resistant to moisture absorption.
Binder is applied on special machines using cylindrical grooved drums. Glue-processed lamellas are sent to a set where veneer packets are formed. Here, the sheets are cold pressed, which is the preparatory stage before the final gluing. Flattening sheets is perpendicular to each other. The basic bonding procedure uses a hydraulic hot press provided with mechanical loading. Ready plywood sheets are aged 24 hours in the workshop.
DIY plywood making
The technology for the production of plywood at home does not fundamentally differ from the factory. At a minimum, the same machining and preparatory operations like stripping, cutting and gluing are performed. Log raw materials (preferably from birch) are also used, after which sawing and peeling is carried out - the most difficult operation for hand-made processing, which with small volumes can be replaced with special planers. If in-line production is required, it is better to organize a small conveyor line. For example, small plywood factories in a modest area are provided with compact lines with equipment that automatically performs cutting, sawing, peeling, drying, glue pressing and grinding operations.
Plywood Applications
This is a universal material that finds application both in professional environments and in households. Perhaps the largest volumes of plywood are spent in construction and furniture production. At home, such sheets can be used in interior decoration, decoration and household needs. Industrial production of plywood with improved technical and physical qualities allows us to offer decent products for automobile and car building. Again, the popularity of this material is determined by its low cost and decent performance. Plywood is not so strong in comparison with metal and fiberglass, but it is more attractive against the background of wood-shaving products. The only serious limiter on the use of such sheets is the presence of chemically unsafe adhesive mixtures in the structure. That is, we are not talking about environmental cleanliness either.
Conclusion
Today, plywood production technologies are fairly standardized and optimized. Developers of manufacturing methods for this material tend to focus more and more on the inclusion of the latest protective coatings and impregnations that eliminate the physical imperfections of the tree itself. However, the cost of the modified sheet increases markedly. By the way, today the manufacture of plywood to order on average varies from 300 to 600 rubles / sheet. Large-format panels can cost even 1000 rubles or more. At the same time, the inclusion in the technological process of additional operations of high-precision abrasive grinding or fire-resistant impregnation raises the price tag by another 10-15%. Much will also depend on the species of wood used, the quality of peeling and the variety of churaki for veneer.