Plywood is an unusual sheet material, with properties that are so unique that it can be used for both hobby crafts and ship cladding. In the production of plywood, the technology used to obtain material with special qualities has its own specifics. But there is a general sequence of operations that are repeated in the manufacture of plywood for any purpose.
What is plywood made of
The technology of plywood production is developed in such a way as to obtain a certain structure, which is a layer of wood, the number of which can reach up to 21, glued together with adhesives. Moreover, the most popular types of wood that are used for the manufacture of plywood are pine and birch, which give special properties to the material. Adhesive compositions for joining wood layers are made on the basis of resins, which affect the properties of plywood no less than wood.
Plywood production technology
The production technology of birch veneer plywood is a complex multi-stage process that requires precise adherence to techniques in order to obtain high-quality sheet material.
The main stages of plywood production:
- Wood preparation. Birch trunks are selected by size. That is, to obtain sheet plywood measuring 1.2 m by 2.4 m, you need trunks 5.20 m long with a diameter of 20 to 40 cm, which are sawn into chocks from 1.3 m to 2.6 m. After that, birch chocks are boiled in the pool during the day. This means that the water should have a temperature of about 40 o C;
Important! If the time spent in the pool is violated during the boiling stage of the trunks or the water temperature is too hot, then the quality of the veneer will be low.
- Barking and sawing. On a debarking machine with special knives, the bark is removed, which is used to heat the plywood mill. After that, the wood is examined with a metal detector to detect nails or wire that can damage the equipment;
- Sawing and peeling. The logs are sawn, and peeling begins on special machines, that is, a thin strip of veneer is cut off. Birch produces a very thin veneer with a thickness of about 1.5 mm, which is better than the veneer of other types of wood. During peeling, the quality of the veneer is controlled, and the peeling machines are adjusted for each batch;
- Veneer cutting. The veneer is cut into cut sheets with automatic scissors. To get plywood measuring 1.2 m by 2.4 m, the veneer must be cut into sheets measuring 1.3 m by 2.6 m.
- Drying veneer. In the dryer, veneer sheets are blown with heated air for 10 minutes. During this time, 90% of the moisture leaves the wood.
- Veneer sorting. When sorting, sheets that are damaged, for example, cracks, fallen knots, are revealed. In addition, under-dried veneer is rejected, which is sent for re-drying.
Note! The sorting quality largely depends on the equipment used at the mill. The greatest number of defects is detected where there is automated equipment that scans the surface of the veneer.
- Rolling and gluing veneer. At this stage, a plywood structure is created, the strength of which is achieved by the fact that the veneer is folded so that the direction of the fibers of one sheet of veneer is perpendicular to the direction of the fibers in adjacent layers. After the sequence of layers is determined, the veneer is placed in a typesetting package, and the sheets alternate so that the dry veneer alternates with the veneer sheets that have undergone rolling, during which glue is applied on both sides;
The technological process used in modern factories allows creating the most efficient production of high quality plywood. As a result, a building material is obtained, which is used in the manufacture of furniture, various structures and for other purposes.
Scope of application
Plywood is a building material in the form of a multi-layer board, created by gluing layers of peeled veneer with the use of additional fixing components. For the production of structures, a plate with a different number of layers glued according to a certain principle is used.
Plywood is used:
- For the construction of large and small aircraft.
- For the construction of structures of different sizes.
- In all areas of furniture production.
- In the production of facing materials.
- In the production of building materials.
- In making musical instruments.
- As the basis of billboards.
- To install formwork.
- In the production of containers.
- And in other areas.
Varieties of plywood
Today, factories produce products that differ in technological and design features depending on the scope of application. It has a different internal structure, which determines its performance.
Types of plywood:
- Sanded and not sanded.
- Profiled plywood.
- General purpose.
- Bakelized.
- Laminated.
- Reinforced.
- Facing.
- Construction.
- Aviation.
- Waterproof.
Depending on the quality of the outer layer veneer, plywood is divided into 5 grades: A/AB, AB/B, B/BB, BB/C, C/C.
Stages of plywood production
The factory production of plywood of different types is slightly different at some stages, but the main technological process of its manufacture remains the same.
There are the following production steps:
- Wood preparation.
- Veneer preparation.
- Gluing veneer into sheets.
- Application of a protective and facing coating.
Harvesting wood for plywood
For the production of plywood, veneer from hardwood and softwood is used. For the outer layers, birch is preferred, less often hornbeam, poplar, beech and alder. The price of birch veneer in the purchase of material is the cheapest, which is why it has gained such popularity among manufacturers. Hornbeam, poplar, beech and alder are considered expensive materials, because they are used for the production of veneer for individual orders. From coniferous trees, the inner layer is often made, due to the good strength and low cost of this wood in the purchase.
The brought material is first of all calibrated on a special machine. All excess, knots and bark are removed, resulting in an even circle on the cut in relation to the center of the wood. Long logs are cut into identical chocks and sent to the cooking stage.
Wood must have the same moisture content. This is necessary to maintain the integrity of the structure of the future plate and avoid problems at the production stage. Before peeling, all blanks are soaked for a long time in warm water, thereby leveling their overall moisture content.
A log softened in water lends itself more easily to the blades of machine tools, this speeds up the cutting process several times and maintains the pliability of the material for a long time.
Substances that give additional properties to future products can be added to water. As soon as the wood is evenly saturated with moisture, it is sent to the veneer manufacturing stage.
Veneer manufacturing and finishing procedure
Prepared logs are loaded into special installations, fixing them between three rollers and, with the help of blades, sheets or veneer tape are cut off. The rollers simultaneously fix and rotate the logs at a given speed. Dimensions are determined depending on the technical characteristics of the peeling machine and the dimensions of the finished product. Sheets are stacked, and the tape is wound into a roll.
It is carried out in special closed rooms, with automatic temperature control. They try to distribute hot air unevenly in order to divide the drying into several successive stages. Rolls or sheets in a suspended state are moved along a multi-storey roller system. This allows you to carry out the drying process as efficiently as possible in compliance with all time constraints. The moisture content of the veneer should be between 4 and 6%.
After drying, the veneer passes the Quality Control Department. Inspectors and workers remove all defective areas, sheets are sorted according to the required dimensions and moisture content. The finished element is sent to the plywood production shop.
Technological process of production
The technological process of manufacturing plywood takes place in several stages.
Gluing
Veneer sheets of the same size are placed on specially equipped tables. Their surface is cleaned of wood dust and small debris so that no extra tubercles are created during gluing. Further, they are collected and grouped by size into stacks for future gluing of each plate.
First, coniferous plywood is made, as an inner layer and a future frame. Moisture-resistant glue, bakelite film or resin is applied to the first sheet. From above it is pressed with the next sheet of veneer, as a result, a kind of sandwich is obtained. The process can be repeated until 3 or more layers are obtained. All work is carried out in well-ventilated areas due to the increased toxicity of certain substances in the composition of the adhesive.
Often, the number of layers is increased to increase strength. For example, this method is used during the production of construction plywood.
When gluing the wood fibers of each new layer, they try to position them perpendicular to the previous one, which increases the strength of the future structure several times. If the number of layers in the board is even, this means that the direction of the internal fibers of the wood is parallel to each other. To obtain wide full-length sheets, the method of rib gluing along the longitudinal edges is used.
If damaged areas are found on the sheets, they are cut out and replaced with special pre-prepared patches. They try to use damaged veneer to create the inner layers of plywood.
Sometimes on the saw cut of the sheet you can see sharp changes in the color of the fibers with black inclusions. This suggests that the manufacturer saved on the purchase of high-quality wood, used rotten second-rate raw materials, or violated the technological process of manufacturing products. Such a plate rarely withstands the required loads and can collapse after a short time.
Cold bonding or pressure heat treatment
First way- in cold gluing, a plywood sheet is placed in a press and left there at room temperature for 6 hours. After hardening, it is sent to the drying stage.
Second way- finished carefully glued sheets are sent under a heat press, where, with pressure and high temperature, the joints gain final strength.
Coating
In a separate workshop, the surface is ground and various coatings are applied. To do this, use all kinds of varnishes, paints or ready-made stickers with images.
Depending on the coating, plywood is divided:
- On the facing - consists of several layers of peeled veneer. Has a facing covering from one or from two parties.
- Laminated plywood - the coating most often imitates the wood structure.
- Sanded and not sanded - a specific texture is created on the surface.
Features of the production of different types of plywood
Bakelized plywood- has increased structural strength. The effect is achieved by impregnating veneer sheets with bakelite resin with further pressing under high pressure at a temperature of 270 °C.
Waterproof– water-resistant phenol-formaldehyde or urea-formaldehyde glue is used for production.
Profiled- has a complex wavy structure of fibers to increase the longitudinal strength.
reinforced- a layer is placed inside, which gives additional strength to the future plate, the insert can be metal-plastic, fiberglass or in the form of a metal mesh.
Aviation plywood- made from birch veneer (one of the lightest materials). It can be used in the aircraft industry and the creation of lightweight structures.
The production of plywood does not require large financial investments for the purchase of equipment and the launch of the production process. The principle of the technological process is simple and low-cost, therefore every entrepreneur can start his own business.
Video: Plywood production
In Russia, there are a lot of forests that are used for the production of plywood and other building materials. And if rounding logs, sawing and other most commonly used methods of wood processing do not raise questions, then making plywood can be quite an interesting process.
At a woodworking plant, materials for the production of plywood go through several stages. And it all starts with birch logs that are brought here. In fact, logs do not undergo any special preparation before starting production. They are simply cut down and brought to the factory.
The first stage of production is the preparation of logs. They are specially soaked in warm water so that they absorb as much moisture as possible and become ready for use. After that, they are taken out and cut in length to the required size.
The logs are cut in special machines that cut the logs in a spiral into very thin plates. Of course, real plates are not obtained at this stage, the output is something like a thin wooden spiral, which is then stretched into one sheet and cut into plates. As waste at this stage, the cores from logs remain, which are then used as secondary raw materials for the production of other types of building materials.
After receiving wooden sheets, the resulting material is carefully sorted. After that, several plates are folded together and glued together. In this case, each subsequent plate in the layer is laid in such a way that there is an alternation based on the direction of the fibers: along and across in turn. Such alternation of plates during laying is mandatory, because they make plywood more durable.
If the thickness of each sheet of wood is on the order of a millimeter, then it takes about five or six layers to make plywood five millimeters thick. For gluing, a special adhesive material is used, which dries for several days after gluing. This dries directly the glue itself, as well as each layer of plywood.
After drying, the plywood is cut into plates of a given size. Depending on the received plates, plywood is sorted by size, thickness, its quality is checked.
Depending on the type of plywood, impregnation can be carried out not only with water, but also with special means. In addition, after impregnation with water, plywood can be impregnated with agents to acquire certain properties, for example, to give it greater durability, heat resistance or fire resistance.
Also, the resulting plywood sheets can be subjected to external processing, such as sanding, painting, and so on.
Plywood can be called one of the most versatile materials that man has come up with. This raw material is widely used in the construction industry. In terms of price-quality ratio, plywood has no competitors. Most often it is used for flooring and floor repair. However, the high functionality of this material also determines a large number of methods for working with it, so you need to consider all the nuances in detail.
How is plywood made? Such a question as the manufacture of plywood is of interest to many builders and people who want to build their house or other premises using very environmentally friendly materials.
Stages of plywood production
The manufacture of plywood begins with the selection of logs from the felled forest (high quality, no butt parts, the presence of a clean trunk without various moldiness). In Russia, trees such as fir, pine, spruce, cedar (coniferous) or birch are taken (the most suitable and affordable option among hardwoods).
The next step is the delivery of wood and the processing of trunks from bark, branches, which are subsequently steamed in water. Heat and moisture weaken the bond between fibers. Steaming wood in water occurs in two ways: at a temperature of 30-40 degrees. (soft mode) and at 70-80 degrees. (hard mode). Without steaming the logs, dry wood cannot be processed. Logs are clamped from the ends on a peeling machine, and rotation begins at a fairly high speed.
A peeling knife, as long as a log of wood, peels off a thin layer of fibers from it, pressing against the log. The surface of the churak is the front side of the veneer, and the side of the veneer that is turned towards the churak is the left reverse side. The waste from peeling is used for secondary raw materials such as particle boards. The resulting long tapes are subject to straightening, cutting and drying.
This is how the main component is made, which is called peeled veneer. The output of veneer is maximum. The defective moments of sawing can be called an oblique cut (the saw is incorrectly installed or the ridge is not placed on the conveyor in the right way), flakes and bevels (all this is the result of the fact that sawing was carried out on weight), and the wrong length of the block (a consequence of an oblique cut).
At the next stage of plywood manufacturing, stacks begin to form (veneer is selected in a certain way: low-quality sheets are stacked inside, and good ones are outside). Separate the right (front) and left (back) sides. The quality of the right side is much better than the left.
One of the most important operations in this process, because this is how the grade of plywood is determined. The stack is again disassembled and the surface of the sheets is already covered with glue. The adhesive layer is applied one-sided or two-sided (depending on the machine) on glue-applying machines. The pre-pressing stage makes it possible to remove excess air and adhesive between the sheets. High temperature affects the quality of veneer bonding, thereby forming a plywood sheet. The final stages of the process are cutting the plywood to the desired format, sanding the sheets and sorting the plywood sheets.
Products are packed in packs, but the main requirement is that the front layer must be put inside. The process "How plywood is made" is quite technological and lengthy, it requires strict control at every stage of production.
Plywood is known to be a very common building material. It is used in the production of construction works (fsf plywood), as well as in the manufacture of furniture (fk plywood). Plywood is also actively used in other areas of production. Get plywood from coniferous trees and from birch.
Basically, plywood is layers of veneer that are glued together. Wood material that is made from logs by planing is called sliced veneer, and made by peeling, respectively, is peeled veneer. Subsequently, it is glued and pressed. In addition, there are varieties in which veneer is combined with other kinds of materials. For example, a moisture-resistant grade of veneer is impregnated with organic-type polymers, and a laminated grade is coated with a phenol film. According to the quality of plywood processing, it can be divided into sanded and non-sanded types. The most popular formwork plywood, which is used when working with concrete.
When gluing plywood layers, natural or synthetic type thermosetting adhesives are used. It is they who do not allow the fabric to exfoliate. Moreover, even serious temperature fluctuations or a sharp change in humidity levels are not a hindrance to this.
Coniferous plywood, main advantages
Coniferous moisture-resistant plywood is made, as a rule, from spruce. It provides high strength at the output and at the same time the canvas weighs very little. To this it is worth adding that such plywood is resistant to decay and practically does not deform. Plywood layers impregnated with phenol-formaldehyde glue do not allow fungi and putrefactive bacteria to multiply.
Coniferous plywood is not inferior in strength to edged board, despite the fact that it is 25% lighter than birch plywood. When using it, the load on the rafters in the roof is reduced. At the same time, functional qualities are not lost. Moisture-resistant plywood, in comparison with other lumber, practically does not warp. In extreme cases, warping is easy to straighten out by gluing, stretching and strengthening with nails.
Plywood stretches and does not crack. Simplifies the work with plywood the fact that it is made in large sizes. The need for rallying, as is the case with other lumber, is completely eliminated. Plywood can be easily bent, making it easy to transport.
In addition to spruce and birch, plywood is also made from pine, fir and cedar. In some cases, you can even meet plywood based on oak, beech, linden, aspen, maple, larch, alder, ash and elm. If we are talking about elite plywood, then it is made from walnut. Moisture resistant plywood differs in the number of sheets. It is three-layer, five-layer and multi-layer.
Coniferous plywood is always very even, resistant to environmental influences, and therefore very durable. However, it is worth touching on the dimensions of moisture-resistant plywood. So, the overall size is 1.22 x 2.44 m (w x d). At the same time, the thickness of plywood can be very thin at 9 millimeters, as well as 12 millimeters, 18 millimeters and even 22 millimeters.