This material is widely used in furniture production - for the manufacture of cabinets, drawers, bases upholstered furniture and other things, as well as in construction, shipbuilding and automotive industries. Fiberboard, or fiberboard, has excellent quality and good structural properties, and costs significantly less than natural wood. Flexibility, elasticity, isotropy and resistance to cracking make it a widely sought after and valuable material. What is it, what does it consist of and what technologies and equipment are used for the production of fiberboard? This article will answer these questions.
Composition of fibreboard
The main ingredients for the manufacture of this sheet material are low quality round wood or wood waste. Sometimes they are used simultaneously. After steaming and breaking this raw material, sheets are produced from it. In order to increase the performance properties of fiberboard, various synthetic resins (hardening agents), as well as rosin, paraffin (water repellents), antiseptics, etc. are added to the wood pulp.
Fiberboard production technology
The production of fiberboard can be carried out in two ways - wet and dry. In the first case, slabs of one-sided smoothness are obtained, in the second - double-sided. Let's take a closer look at these methods and what equipment is used for the production of fiberboard.
Wet method
Wet technology is the most widely used. It implies that the formation of a wood fiber carpet is carried out in an aquatic environment. The wet method of fiberboard production includes the following main steps:
- The wood chips are washed and ground twice. After which the resulting mixture is diluted with water (pulp) and stored (while it is constantly stirred).
- The pulp is mixed with phenol-formaldehyde resin and other additives. Then it is heated to 60 degrees. This process is called mass sizing.
- Next, equipment is used to produce fiberboard, called a casting machine. It allows you to form a wood fiber carpet from the finished mass.
- After this, the slabs are pressed, dried and hardened. Together these three procedures are called pressing. The result should be fiberboard with a moisture content of no more than 1.5%.
- The final stage of production is the final drying and moistening of the boards before cutting them. The finished sheets are kept for at least a day to fix their shape.
The disadvantage of this production method is that it leaves large number waste water Another significant disadvantage is the use of phenol-formaldehyde resin, since phenol is almost impossible to remove from finished fiberboard sheets.
Dry method
This production technology makes it possible to obtain fiberboard with improved performance characteristics. Many stages, with the exception of the last ones, are similar to the wet manufacturing method. The fibers are also milled twice, but the addition of water to produce pulp is eliminated.
During the grinding process, various additives (organic and not) are introduced into the mass, which makes it possible to give the material the required properties. Next, felting is carried out to form a carpet, its compaction and pressing. At this stage, special equipment is used for the production of fiberboard - vacuum installations and belt-roll format presses.
The slabs are pressed at high temperatures (up to 200 degrees) and under strong pressure, which is maintained for half a minute and then gradually decreases (from 6.5 to 1 MPa). The final stages are curing and final fixing of the sheets during the day. Then the finished slabs are given the required size on format-edging circular saws.
With the dry production method, fiberboard sheets are smooth on both sides and have specific performance properties - fire resistance, moisture resistance, etc.
What equipment is used to make fiberboard?
Regardless of the production method (dry or wet method), the equipment used is similar and always high-tech. The process of manufacturing fibreboards involves:
- six-saw machine for the production of fiberboard (cutting wood raw materials into blanks);
- chippers (grinding raw materials into chips);
- special high-power magnet (cleaning the mass from metal impurities);
- defiberators and refiners (for coarse and fine grinding of mass into fibers);
- casting machines (formation of fibrous mass);
- format and belt-roll presses (giving the fibrous mixture the appearance of sheets);
- hydraulic press (carpet compaction);
- grinding machines (leveling the thickness and making fiberboard sheets smooth).
To produce high-quality fiberboards, it is important not only to use modern high-tech equipment, but also to configure it correctly in order to produce material with a minimum amount of waste.
Making fiberboard is a rather labor-intensive process, but this business is in great demand today. This material is in good demand among consumers, as it has advantageous advantages (quality, wear resistance and price) over more expensive and less functional ones.
Fiberboards are sheet materials that are formed from wood fibers. They are made from wood waste or low-quality round wood. Sometimes both wood waste and low-grade wood can be used as raw materials at the same time.
Fiberboards come in soft and hard types. Solid fiberboard is one of the most important and popular structural materials used in furniture production. As a rule, such boards are used to make the back walls of cabinets, end caps and base boxes of upholstered furniture, the bottoms of furniture drawers, etc. In addition, hard packaging elements for disassembled furniture are made from fiberboard. The slabs have also found their application in construction (external and internal elements, agricultural buildings), in automobile and shipbuilding, in the production of containers and boxes, and in other industries.
Fiberboards compare favorably with natural wood and plywood in price, quality and design features. They are isotropic, not subject to cracking, have increased flexibility and at the same time have good elasticity. Soft fiberboards are used in standard wooden house construction for insulation of panels, panels of enclosing structures, attic floors, sound insulation of interior partitions and sound insulation of special-purpose premises. Solid boards are also used for internal lining walls, flooring, making panel doors and filling door panels.
Superhard boards are used to construct clean floors in industrial buildings and office premises, for the manufacture of electrical panels, shields and other structures at specialized construction sites. Fiberboards have a long service life - more than twenty years. Conventional paint on the surface of slabs retains its properties for 15-18 years when used outdoors. At the same time, natural wood painted with the same paint quickly fades.
Depending on the strength and type of front surface, fiberboards are divided into several grades: T (hard boards with an untreated front surface), T-S (hard boards with a front layer of fine wood pulp), T-P (hard boards with a tinted front layer ), T-SP (solid slabs with a tinted front layer of finely divided wood pulp), ST (hard slabs of increased strength with an untreated front surface), ST-S (solid slabs of increased strength with a front layer of finely divided wood pulp). Solid slabs of brands T, T-S, T-P, T-SP are also divided into two groups A and B, depending on the level of their physical and mechanical properties.
These products, due to their properties and wide application, are in constant high demand, so their production is a profitable business. True, its organization (on a large scale) requires significant investments.
There are two most popular technologies for the production of solid fiberboard: wet and dry. There are also intermediate methods (wet and semi-dry), but they are rarely used, so we will not consider them in detail in this article. With the wet method, a wood fiber carpet is formed in an aqueous environment. Then the carpet is cut into individual sheets, which in a wet state (humidity reaches 70%) are hot pressed.
With the dry method, the carpet is formed from air-dried wood fiber mass, and the slabs are obtained by hot pressing of sheets with a moisture content of 5-8%. With the semi-dry method, a carpet made from dried wood fiber mass is finally dried in an air environment, and the canvases themselves, with a moisture content of about 20%, are processed by hot pressing. The wet-dry method is based on the formation of a carpet from wood fiber mass in an aqueous environment, drying the canvases and subsequent hot pressing of dry canvases with a humidity close to zero.
Natural wood is used as a raw material for the production of boards by any method. First, it is crushed into chips, then turned into fibers, from which the carpet is subsequently formed. For the production of fibreboards, waste from sawmilling and wood processing, wood waste, logging waste, and small round timber from thinnings are most often used. As a rule, raw materials arrive at the enterprise site in the form of round wood, chips or slats, and they are supplied to the production workshop in the form of conditioned chips that meet certain requirements.
To produce quality chips, wood is cut into sizes corresponding to the receiving cartridge of the chipper, then it is chopped into chips, sorted to select the required size with additional crushing of the coarse fraction and removal of fines, metal objects are removed from the chips, then it is washed to remove dirt and foreign waste.
The most widespread among domestic fiberboard manufacturers is wet technology, although it is already considered outdated. Its popularity is explained relative simplicity, but it is more expensive and less environmentally friendly.
This technology is reminiscent of paper and cardboard manufacturing technology. The boards are cast from wet wood fiber pulp, which is formed on a mesh metal belt and fed into a hot press. Excess water is squeezed out and evaporates, resulting in compaction of the slab structure. Various emulsions (paraffin, oil and resin), as well as precipitants (usually aluminum sulfate) can be additionally introduced into this composition to give the final product such qualities as strength and water resistance. The back surface of the slab with this production method has a corrugated texture from contact with the mesh.
Dry board production technology has certain differences, the main one of which is that the formation of a fibrous carpet occurs in an air environment, and not in an aqueous suspension. The main advantages of this method compared to the previous one: the absence of runoff and low consumption of fresh water during production. The technological process of dry fiberboard production includes several stages: acceptance, storage of raw materials and chemicals; cooking wood chips; steaming, grinding wood chips into fibers; preparation of binder and water-repellent additives; mixing fiber with binder and other additives; fiber drying; carpet molding; preliminary compaction (pre-pressing); pressing; stove conditioning; mechanical processing of plates.
When producing fiberboard using the dry method, experts recommend choosing wood as a raw material. hardwood, which is due to the fact that they provide a more uniform density of the carpet than long fibers coniferous species. However, to reduce costs, you can mix different types of wood, but taking into account the peculiarities of its structure (the mixed species must have the same or similar densities).
During the process of steaming and grinding wood, its partial hydrolysis occurs. Continuous units are used for steaming various systems, and for grinding - defibrators and refiners. With the dry production method, it is assumed that thermosetting resins are introduced into the wood fiber mass, since the plasticity of the fibers at low humidity is not high enough, and the short pressing cycle under such conditions does not ensure the strength of the connection between the components of the wood board. In addition, molten paraffin or other additives are introduced into the chips or wood fiber mass to increase the water resistance of the finished product. Sometimes, when producing special-purpose boards, chemicals are added to the mass. At the same time, they are not washed out into the drains, as with the wet method, but remain on the fibers. For gluing, as a rule, phenol-formaldehyde resins are used, with preference given to resins with a minimum content of free phenol.
The ground fiber that has passed through the defibrators is separated from the steam in dry cyclones, from where it is then fed using pneumatic transport for drying or to the second grinding stage - into closed-type grinding apparatus. In this case, the raw material loses up to 10-15% of its moisture content. Fiber drying can be carried out in any type of dryer (tubular, drum, air fountain, etc.) in one or two stages (but experts advise giving preference to two-stage drying). In the dryer, the fiber is dried to an air-dry state, and its moisture content is reduced to 8-10%. In dry fiberboard production, the carpet is formed using air on a mesh conveyor belt. A vacuum is created over the belt to increase the density of the fibers. The mass is spread onto the conveyor either by vacuum forming or by free-falling fiber on special machines.
The continuous carpet that is obtained after passing through a vacuum-forming machine is quite difficult to transport, since its height can range from 100 to 560 mm, and its strength is not yet strong enough. Therefore, before the blade enters the hot press, it is pressed in continuous belt presses, and the edges along the movement of the blade are cut with circular saws.
Depending on the composition of the raw materials (types of wood) and the type of binder used, the pressing temperature of the web can range from 180 to 260°C. For example, for soft wood it does not exceed 220 °C, and for hard wood it does not exceed 230 °C and above. As pressing pressure increases, the density and, therefore, strength of the boards increases, but their water absorption and swelling decrease. Post-press processing of slabs involves preliminary trimming of the edges of products coming out of the hot press, moistening the slabs, format cutting of slabs to specified sizes and their storage. The slabs, which are then sent for finishing, must be sanded.
There are two main advantages of using the dry method of fiberboard production over the wet method: high water consumption in the latter case, as well as the same type of structure (smooth on one side and mesh on the other).
When using dry technology, special equipment and additional raw materials will be required. For example, water-soluble phenol-formaldehyde resin and paraffin are used as water-repellent additives. The list of typical equipment used in fiberboard production plants includes: drum ruby machines, gyratory type flat sorting machines, steam-grinding system, air and drum dryers (for drying carried out in two stages), double-mesh vacuum forming machine, hydraulic press, loading and unloading device, hydraulic pump station, chambers for conditioning, mixer, containers, sawing machines, conveyors, etc.
Setting up an enterprise for the production of fibreboards requires considerable investment, but competition in this segment is relatively small. In total, in Russia, Ukraine and Belarus there are a little more than thirty relatively large factories that produce solid fiberboards. They sell their products to domestic market. Indirect competitors of solid fiberboard manufacturing plants are enterprises that produce boards using wet method technology. Around the world, about 7 million cubic meters of insulating fiberboard are produced per year, with Germany alone accounting for 2.7 million cubic meters.
The payback period of the project (construction of a large plant for the production of solid fiberboard) is five years, taking into account financing. It is worth considering that the construction period of such an enterprise reaches 1.5-2 years from the month of receipt of investments and only six months will be spent on the development of project documentation. But you can reduce this time to a year, including three months for the development of project documentation, if you purchase an existing woodworking enterprise and technically re-equip it.
The internal rate of return of the project without taking into account investments is 27%. And the profitability of production is estimated at 116%.
The average annual net profit can be estimated at 270-280 million rubles. The total investment amount reaches 1200 million rubles. To work at a large plant with a planned sales volume of 130 thousand cubic meters of fiberboard per year, a staff of 180-200 employees will be required.
Introduction
Carpet cast
Pressing plates
Format cutting of slabs
Selection of chipping machine
Selection of sorting machine
Selection of disintegrator
Selection of steaming unit
Conclusion
References
wood fiber impregnation equipment
INTRODUCTION
Fiberboards are sheet materials formed from wood fibers. They are made from wood waste or low-quality round wood. In some cases, depending on the conditions of supplying the enterprise with raw materials, both wood waste and low-grade wood in round form are used simultaneously. When pressing using the wet method, slabs of one-sided smoothness are obtained - their surface coming out from under the press will be smooth, and on the reverse side there will be traces of the mesh on which the pressing took place.
Fig.1 Fiberboard.
Fiberboards are used in various areas of the national economy: in construction (external and internal elements, agricultural buildings); for the manufacture of built-in furniture (kitchen cabinets); in furniture production; automobile - and shipbuilding; production of containers, boxes, etc. In our country, the volume of production of fiberboards increases every year. This is a high-quality, cheap finishing and construction material that compares favorably with natural wood and plywood. Fiberboards are isotropic, not subject to cracking, and have great flexibility with a high modulus of elasticity.
The slabs are durable: having served for more than 20 years, they are in good condition. Ordinary oil paint used on slabs used outdoors lasts 15-18 years, i.e. longer than paint used on natural wood.
Fiberboards are widely used in various fields of activity due to the variety of their properties.
GOST regulates the following physical and mechanical properties of fiberboards: format and thickness, bending strength, humidity, swelling, water absorption. For soft slabs, one of the main quality indicators is thermal conductivity. In addition to those listed, additional non-regulated information about the slabs is important for consumers.
Thermal conductivity indicators are of paramount importance for soft slabs, since their main purpose is thermal insulation. Fiberboards are a good thermal insulation material.
Fiberboards lend themselves well to gluing. Soft boards are glued together, as well as with hard boards, wood, linoleum, metals (tin, galvanized iron, aluminum foil), cement plaster. Bonding is achieved using urea resins or polyvinyl acetate emulsions. Given the high porosity of soft boards, it is necessary to add a filler - wood or rye flour - to adhesives and adhesive emulsions. Hard slabs are glued together, with soft wood, linoleum and sheet metals. Hard and soft boards lend themselves perfectly to painting with oil, water-based and various synthetic enamels, pasting with paper, synthetic wallpaper and linkcrust, as well as paper plastics and other sheet synthetic films.
The most common methods for making slabs are wet and dry. Intermediate between them are wet-dry and semi-dry methods, which are less widespread.
The wet method is based on the formation of a carpet from wood fiber mass in an aqueous environment and hot pressing of individual cloths cut from the carpet, which are in a wet state (at a relative humidity of about 70%).
In the process of making slabs using the wet method, wood is crushed into chips; it is then turned into fibers that are used to form a carpet. Next, the carpet is cut into sheets. Dry webs are pressed into hard slabs. Wet webs are either pressed to form hard and semi-hard boards, or dried to form soft (insulating) boards. Using the above methods, it is possible to produce fiber boards from any organic materials that can be split into fibers.
Fig.2 General diagram of the technological process for the production of fiberboard
Raw materials, their preparation and storage
The choice of raw materials is determined by economic feasibility, taking into account the size of its reserves, conditions of procurement, delivery and storage. For the production of fibreboards, sawmill and wood processing waste, wood waste, small round timber from thinning and logging waste are used.
One of the main requirements for raw materials is the ability to obtain the longest fiber from it. In this regard, coniferous wood species have an advantage over deciduous trees: the length of the fibers of coniferous trees (pine, spruce, fir) ranges from 2.6 to 4.4 mm, and deciduous trees (birch, aspen, poplar) - from 0.7 to 1.6 mm.
The characteristic of wood is its density in an absolutely dry state (Table 1).
Table 1
Species Mass of 1 m3 of wood, kg absolutely dry air-dry Freshly cut Oak 6507401030 Beech 625710968 Birch 370650878 Larch 520680833 Papilla 4585 20863 Wasp willow 4505 10762 Fir 4144 20827 Spruce 39545079 4
Chips without crumpled edges, with a particle length of 10-35 mm (optimal 20 mm), a thickness of no more than 5 mm, and a cutting angle of 30-60°C are used in the production of fiberboard using the wet method. The rot content is allowed no more than 5%, mineral inclusions no more than 1%, bark no more than 15% (in chips from branches - up to 20%). With an increase in the proportion of bark, the appearance of the slabs and their strength deteriorate.
Hydrophobizing (petroleum paraffin, ceresin),
Strengthening agents (black technical albumin, pine rosin, SFZh),
Emulsifiers (oleic acid, SDB concentrate, sodium hydroxide),
Precipitators (technical sulfuric acid, aluminum sulfate),
Additives to impart special properties to slabs (petroleum and road bitumens, ammonium silicofluoride).
Raw materials arrive at the enterprise site in the form of round timber, sawmill waste (slats, slabs) or wood chips. To facilitate stacking of thin round timber and sawmill waste, as well as for better supply to chippers, their length is 2-3 m. It is advisable to tie such raw materials into bundles with paper ropes and stack them.
Wood is stored in dense, unlined stacks. Process chips arriving at the enterprise site from outside can be stored in a pile, the most common shape of which is a truncated cone.
Raw materials are supplied to production in the form of conditioned chips, which must meet the following basic requirements: length - 25 (10-35) mm, thickness - up to 5 mm, clean cuts without crumpled edges, bark contamination - up to 15%, rot - up to 5%, mineral impurities - up to 1%, relative humidity of wood chips - not less than 29%.
Preparation of raw materials for the production of boards, which consists of preparing conditioned chips, includes the following operations: cutting wood into sizes corresponding to the receiving cartridge of the chipper; cutting wood into chips; sorting of chips to select the required size with additional grinding of the coarse fraction and removal of fines; removing metal objects from wood chips; washing the wood chips to clean them from dirt and foreign matter.
Cutting logs is necessary to give the raw material sizes corresponding to the parameters of the chipper, as well as to cut out areas that are severely affected by rot when the diameter of the wood is less than 200 mm, the length of the logs entering the cutting can be up to 6 m, with a larger diameter it should not exceed 3 m. The maximum permissible diameter of logs is determined by the size of the receiving cartridge of the chipping machine. Wood intended for the production of high-quality slabs and finishing the outer layer of slabs is debarked on OK-66M debarking machines.
Balance saws, slashers (Fig. 3) and chain saws are used for cross-cutting logs.
Fig.3. Scheme of a 12-saw slasher for cross-cutting round timber. 1-bed; 2-stand; 3-beam; 4-bracket; 5-blade saw; 6-mechanical separator; 7-belt conveyor for thin logs; 8-belt conveyor for thick logs.
If the diameter of the wood exceeds the permissible limit, the length is cut into stubs (1 - 1.25 m) and split using a mechanical cleaver.
Multi-skin chipping machines are used to crush prepared wood into chips. When chopping wood using chippers, the yield of quality wood chips is 85-92%; this produces about 10% coarse woodchips and up to 5% sawdust.
To obtain conditioned chips that ensure the normal operation of grinding machines and to obtain high-quality fibrous mass, the chips are sorted in chip sorting plants. Large chips that do not pass through the sorting sieves are further crushed in disintegrators. To catch metal objects, wood chips are passed through magnetic separators.
Sorted from small and large chips, the conditioned chips are fed by belt conveyors (through magnetic separators that catch metal objects) and a chip washing installation into bunkers, the capacity of which is designed to store at least a 24-hour supply of chips. The supply of chips from the bunkers is controlled by vibrating or auger disk unloaders.
Obtaining wood fiber mass
Wood grinding is one of the important operations in the production technology of fiberboards.
Today, the thermomechanical method of obtaining fiber from wood chips has become predominant. Since lignin, which holds individual wood fibers together, softens at temperatures above 100°C and melts at 172°C, wood chips are steamed before mechanical abrasion to reduce their strength. Primary hot grinding is carried out in defibrators, secondary - in refiners or rolls (hollanders).
Fig.4 General view of the hot grinding installation: 1 - bunker for wood chips; 2 - screw feeder; 3 - steaming boiler; 4 - auger for feeding heated chips; 5 - defibrator; 6 - main engine; 7 - return steam line
For ease of transportation, the fibrous mass is mixed with water to a concentration of 3%.
Since during the initial grinding of wood chips, separate unground bundles of fibers and wood chips remain, the mass is subjected to additional grinding in refiners or rolls (hollanders).
The resulting mass can be coarse or finely ground. Coarse grinding has a weak degree of fibrillation (combing). If the fibers are severely chopped and shortened, the formation of “dead grind” is possible - a loose mass in which the fibers do not intertwine (do not felt), and when forming a carpet from them, it will tear on the mesh. Fine grinding ensures reliable felting of fibers and the formation of a fairly durable carpet.
The grinding installation, shown schematically in Fig. 4, consists of a hopper with a screw feeder, through which the chips are fed into a heater with a stirrer, and from there through another screw into the defibrator itself, consisting of a fixed and movable disk. Falling through the central hole of the stationary disk onto the rotating washer, the chips are thrown into the grinding zone. The working surfaces of the disks are equipped with grooves and corrugations, in which the heated wood particles are ground into individual fibers and bundles of fibers. Under the influence of centrifugal forces and steam pressure, the resulting fibrous mass is thrown out from the disks.
To ensure that the supply of chips by the screw feeder is maintained uniformly, the unloading screw of the heater is made in a conical shape.
The compressor plug it creates prevents the return flow of steam and pulsation of the chip flow. With a uniform supply of chips, the defibrator works more steadily and the fibers are more uniform.
At the second stage of grinding, refiners are used, and in the production of soft fiberboard, to obtain even finer grinding, hollenders or conical mills with basalt and ceramic grinding sets are used.
In a hollender (Fig. 5), the crushed mass moves in a spiral.
Fig.5 Gollender - a and its cross section - b:
Drum; 2 - bars; 3 - box with basalt liner; 4 - drain hole
The degree of grinding of the mass is measured using a Defibrator-Second apparatus, characterized in degrees of grinding and designated DS. In numerical terms, the degree of grinding is equal to the time (in seconds) required to dehydrate a mixture of 128 g of absolutely dry fiber mass and 10 liters of water (concentration 1.28%) placed on the mesh. For soft slabs, the degree of grinding should be in the range of 28-35 DC.
Sizing of wood fiber mass
Sizing the wood fiber mass helps reduce water absorption and swelling, as well as increase the mechanical strength of the boards. To make the boards waterproof, a hydrophobic substance is introduced into the wood fiber mass. By enveloping wood fibers and filling the pores in the finished board, the hydrophobic substance prevents moisture from penetrating into it. In addition, paraffin, used as a sizing material, prevents fiber bundles from sticking to the glossy sheets of press plates and backing (transport) nets, and also adds shine to the front surface of the plate.
Hydrophobic substances for sizing are the following: paraffin, slack, ceresin composition, etc. Their content in the boards does not exceed 1.0% by weight, since these substances weaken the bond between the fibers, thereby reducing the strength of the boards. Hydrophobizing additives are introduced into the fibrous mass in the form of aqueous emulsions. To obtain a finely dispersed emulsion, high-molecular acids (oleic, stearic, palmitic, etc.) are used as emulsifiers. To reduce the cost of finished slabs, enterprises use a concentrate of sulfite-barian mash, bottoms from the distillation of synthetic fatty acids, and sulfate soap as an emulsifier. Prerequisite for deposition of hydrophobic substances on fibers - creation of an acidic environment in the wood fiber mass - pH 4.5-5.0. Such a medium is formed as a result of introducing into the wood fiber mass a solution of alumina sulfate or potassium alum, which serves as coagulators or precipitants. Recently, sulfuric acid has become widely used.
To increase the mechanical strength of fiberboards, adhesive additives are introduced into the mass. The introduction of albumin significantly improves the strength properties of the manufactured slabs. Low-toxic water-soluble phenol-formaldehyde resin SFZh-3024B and resin SFZh-3014 are also used as an adhesive additive.
Chemical warehouses are designed and built separately. The stock of chemicals is created based on the monthly work of the workshop. In the fiberboard workshop itself, a daily storage warehouse is located, which is located next to the room for preparing working compositions. Chemicals are delivered from the main warehouse to the supply warehouse by electric forklift in special containers or shipping containers.
Many enterprises receive paraffin in a railway tank, which is installed near the finished product warehouse. The paraffin is heated with live steam, after which it drains by gravity through the lower hole and flows through a pipeline laid with a slope into a storage tank with a capacity of 60 m3. Next, the paraffin goes into a supply tank, which is installed in the workshop on a pedestal. Then the paraffin is drained by gravity through a measuring tank into the paraffin emulsion preparation tank (emulsifier). The finished emulsion is pumped into a special container (tank) for storage.
Preparation of the working composition of phenol-formaldehyde resin SFZh-3024B consists of diluting it to a working concentration of 5-10%. The dissolution of precipitants is carried out in a special tank, which is similar in design to the tank for preparing the emulsion.
Preparation of a sulfuric acid solution used to precipitate resin emulsions involves diluting sulfuric acid with water to a concentration of 1.5-3%. A concentration of introduced sulfuric acid of more than 3% is undesirable, as this can cause stains on the plates during pressing and sticking to glossy sheets and transport meshes.
Chemical consumption per technological instructions VNIIDreva is determined depending on the species composition of raw materials, the chemical products used and the capacity of the enterprise.
Sizing compositions are introduced into the fibrous mass before it is cast into continuous sizing boxes. A prerequisite for sizing is the initial introduction of a sizing emulsion into the mass and only after mixing the emulsion with the mass - adding a precipitant solution.
Carpet cast
The casting and formation of a carpet from wood fiber mass occurs as a result of sequential operations: the flow of mass onto the forming mesh, free filtration of water through the mesh, suction of water by a vacuum unit and additional mechanical pressing. When the mass flows onto the mesh, free water is filtered, going into the circulating system, and suspended fibers settle on the mesh. Due to the developed outer surface of the fibers obtained during grinding, conditions are created for a greater degree of their adhesion and interweaving. This connection is strengthened during the process of vacuum suction and mechanical extraction of water from the fabric. The relative humidity of the canvas is adjusted to 68-72%. In this state, the canvas becomes transportable, and in addition, maximum water removal reduces steam consumption and reduces the time for subsequent drying of the slabs. This is especially important in the production of soft boards, since they are dried not in presses, but in drying chambers.
The casting of the mass and the formation of the web are carried out on casting machines of periodic or continuous operation.
The wood fiber carpet, previously dehydrated by vacuum, is subjected to further dehydration mechanically - by pressure from several pairs of rollers covered with mesh. The relative humidity of the carpet is about 80%. With this moisture content, the carpet leaves the vacuum-forming drum and is sent on a roller conveyor for trimming and additional dewatering in a roller press. By additional dehydration, the moisture content of the wet web can be increased to 60%.
The formed endless wood fiber tape-carpet is cut along its length into separate sheets - blanks. The side edges are cut at the same time.
The main conditions for the formation of a wood-fiber web: uniform distribution of the mass over the entire width and thickness of the web, good mixing of different fiber fractions, obtaining a random orientation of the fibers, maximum reduction of losses of small fibers and chemical products introduced into the mass, achieving the required moisture content of the carpet.
For uniform distribution mass and good mixing require careful storage and organized transportation of the mass to the casting machine. Each particle of the fibrous mass, while suspended in suspension, moves. It occurs, firstly, under the influence of gravity (the particle falls), and secondly, depending on its shape, it can be rotated. Forming complex movements, fiber particles and fibers collide with each other, interlock and create conditions for flocculation. At the same time, in a rapidly moving suspension, the formation of flocs is accompanied by ruptures and dynamic equilibrium is established. Taking this fact into account, it is necessary to create such conditions so that the flow of the suspension in the pipelines is not disrupted by mechanical obstacles in the flow path. Angles, curvatures, and unevenness should be avoided internal surfaces mass pipelines.
All operations for forming a wood fiber carpet should be carried out with a gradually increasing load. It has been established that the forced dehydration regime at any stage of the process causes destruction of the fibrous structure of the carpet, a decrease in its mechanical properties in the absence of any external visible signs.
In wood fiber board workshops using the wet method, the process of returning fiber to production is of great technological and economic importance. Along with the discharged water, fibers also leave, the content of which in waste water is about 1600 mg/l. Extracting wood fibers from waste water allows for maximum use of raw materials and circulating water, which reduces the consumption of raw materials and fresh water per unit of produced slabs. In addition, reducing the content of fibrous substances in wastewater creates favorable conditions for its subsequent processing at wastewater treatment plants. Process filters are used to return the fiber to production. In our country, factories that produce fiberboards install Polish-made filters.
Pressing plates
Pressing is the main operation of the technological process, which determines the quality of the produced slabs and the productivity of the equipment. During pressing, the wet fiberboard is subjected to high pressure at high temperatures and turns into fiberboard. This transformation occurs due to physical, chemical and morphological changes in the moisture-saturated wood fiber.
During the pressing process, changes occur in the cellulose part of the wood complex. The dimensions of the elementary crystal lattice decrease, and the crystalline sections become larger. The ordering of the structure makes it possible to bring cellulose molecules and segments of macromolecules closer to the distances necessary for the formation of chemical bonds between wood fibers. At elevated pressure and high temperature, thermohydrolytic transformations of hemicelluloses are observed, which causes an increase in the content of water-soluble products in the pressed material, oxidation of the primary hydroxyl groups of sugars with the formation of carboxyl groups, and the establishment of simple and ester bonds as a result of dehydration and esterification reactions. This explains that the strength and water resistance of the boards are in accordance with quantitative changes in extractives, changes in functional groups, hydrogen bonds, free radicals and the mobility of the carbohydrate skeleton of wood fiber.
The strength of the slabs is determined by the strength of the fibers and interfiber bonds. The tensile strength of the fibers depends on the type of wood. All the main components of the carbohydrate lignin complex participate in the formation of interfiber bonds, a significant part of which is in a softened, plasticized state. The presence of low-molecular substances, a slight decrease in the degree of polymerization of cellulose, softening of lignin, and an increase in the flexibility of macromolecular chains during piezothermal treatment contribute to an increase in the contact surface between the fibers and the adhesive interaction between them.
Depending on the raw materials and methods of conducting the technological process, the required physical and mechanical properties of the plates can be obtained. To select parameters and pressing mode, it is necessary to take into account the following initial factors: rock composition and quality of raw materials; method and quality of preparation of the mass; characteristics of sizing materials and method of their introduction; technical capabilities of the press.
In the wet production process, hot, hydraulic multi-story batch presses are most widely used.
The pressing mode depends on many factors: the quality of raw materials and mass, humidity and thickness of wood fiber sheets, technological parameters of the process, the condition of the press and its clothing. The entire period (cycle) of pressing is divided into three technological phases: pressing, drying, hardening.
The relative humidity of the sheets before pressing is 68-72%. At low humidity (less than 65%), deterioration in the quality of the slabs and sometimes even delamination is observed. The duration of the first pressing phase is 50 - 90 s. The humidity of the fibrous webs is adjusted to 45 - 50%. At the first stage of pressing, the density of the slab is determined.
After the first phase of pressing (squeezing), they move on to the second phase (drying the slabs), since further removal of water is possible only by evaporation. To carry out the drying process, the specific pressing pressure is reduced in order to create favorable conditions for removing steam from the canvas. It is maintained at 0.8 MPa. To ensure uniform release of steam from the wet fibrous web, the pressure is kept constant during the drying period.
The temperature of the press plates also has a great influence on the progress of the pressing process. With the wet method of producing fibreboards, the pressing temperature is 200 - 215 °C. The increase in pressing temperature is caused by the desire to speed up the process of evaporation of water from the wood fiber web.
The duration of drying is influenced by the degree of grinding of the mass and the thickness of the pressed sheets. The higher the degree of grinding of the mass and the greater the thickness of the slab, the longer the drying period. Its time, depending on specific conditions, is 3.5 - 7 minutes. During the second pressing phase, water is removed until the relative humidity of the fiberboard is 7%. This humidity is necessary for the condensation reaction in the final pressing stage. The practical moment of the end of the drying phase is determined by the cessation of steam emission from the slabs. In the third phase of pressing (hardening), the slabs are subjected to heat treatment at elevated pressure, bringing the humidity to 0.5 - 1.5%. The duration of the third phase is selected empirically and usually does not exceed 3 minutes. The technological instructions developed by VNIIDrev recommend the following pressing modes: humidity (relative) of wood fiber sheets entering the press 72 ± 3%; humidity of the slabs after the press is 0.8 - 1.2%; specific pressing pressure in the spinning phase is 4.2 - 5.5 MPa (with a hardwood content of more than 70% - 5.5 MPa), in the drying phase 0.65 - 0.85 MPa, in the hardening phase 4.2 - 5.5 MPa (with a hardwood content of more than 70% - 5.5 MPa). The temperature of the press plates (coolant at the inlet) depends on the species composition of the wood raw materials used.
Oil impregnation, heat treatment and moistening of fiberboards
To increase strength and moisture resistance, the boards are impregnated with oil. In fiberboard factories, special lines are placed in an isolated room, which include: a loading device, an input roller conveyor, an impregnation machine, an output roller conveyor and an unloading device. The slabs coming out of the press are fed for impregnation, i.e. hot. To impregnate fiberboards, a mixture of linseed and tall oils (40 and 60%) or tall oil with the addition of lead-manganese drier (93.5 and 6.5%) is usually used. Oil consumption is 10 ± 2% of the weight of the plates.
Heat treatment increases the physical and mechanical properties of hard and super-hard fiberboards, improving water absorption, swelling and flexural strength. The improvement of these indicators occurs as a result of the processes of thermochemical transformations of the carbohydrate-lignin complex of the fibrous mass of the boards.
During heat treatment, under the influence of dry hot air, residual moisture is removed from the slab, and surface tension forces bring cellulose macromolecules together at distances sufficient for the formation of non-oriented sites of hydrogen bonds between the hydroxyls. In addition, heat treatment of lignin and carbohydrates leads to the formation of easily polymerized substances with high reactivity and the creation of resinous products. Heat treatment is carried out in special heat treatment chambers of periodic or continuous action. Heat treatment is carried out at a temperature of 160 - 170°C.
Fiberboards are porous bodies. Dried, being in a hot state after a press or heat treatment chambers, they begin to adsorb water vapor from the surrounding air. If these slabs are laid in a dense package, their edges absorb water to a greater extent, which leads to an increase in the linear dimensions of the slabs in the peripheral zone. As a result of the occurrence of significant internal stresses, waviness is formed. To give the slabs dimensional stability, it is necessary to carry out acclimatization, which consists of: moistening while cooling the slabs. To moisten the slabs, humidifying machines and chambers are used.
Format cutting of slabs
Fiberboards are cut to final sizes on format-edging machines that perform longitudinal and transverse cutting. Fiberboards are cut to final sizes on format-edging machines that perform longitudinal and transverse cutting. Cutting tool - circular saws. To cut out defective areas and more conveniently cut slabs into blanks for joinery, construction and other special products, a preliminary cross-cut saw is installed in front of the format-edging machines.
When formatting finished slabs, edge trimmings, small pieces of slabs, and sawdust remain, which should be returned to production. The crushed waste together with sawdust is sent by pneumatic transport to a mixing tank filled with water. Thoroughly mixed waste with a pulp concentration of 3-4% is pumped into a mass container in front of the secondary grinding mills. Small crushers are used to crush defective pieces of slabs. The crushed particles are fed by a pneumatic transport system into a hydraulic pulper and through an intermediate basin for secondary grinding. The waste is also supplied for secondary grinding by pneumatic transport without the use of a hydropulper.
Description of the technological scheme for the production of fiberboards
The raw materials for the production of fibreboards using the wet method are sawmill and wood processing waste, firewood, small round timber from thinning and logging waste.
Preparation of raw materials for production involves the preparation of conditioned wood chips. Initially, the wood is cut into sizes corresponding to the receiving chuck of the chipping machine. Balance saws are used to cut logs to length.
The resulting chips after the chipper are supplied to a sorting machine, where process chips that meet the requirements for them are selected. To sort process chips we use a sorting machine model SShch-1M.
From the sorting machine, the selected chips enter the chip storage silo. Chips with dimensions exceeding the established ones are transferred for additional grinding to a DZN-1 hammer disintegrator, and then returned to the chipper. The fines that are screened out during the sorting process are removed from the workshop as waste.
The conditioned chips are sent to stock bins or supply bins in the grinding department. We install three DBO-60 brand bunkers, one of which is a reserve one.
From the supply hopper, through the feeder hopper, wood chips, preheated with saturated steam at a temperature of 160 °C in a heater, are fed into the steaming apparatus. We install two Bauer-418 steaming units. The steaming boiler is designed for pressure up to 1 MPa. The chips pass through the steaming boiler under the influence of a screw conveyor. The residence time of the chips in the boiler is from 1 to 10 minutes.
The chips are fed at the same pressure by a screw conveyor into the grinding apparatus. We use a defibrator brand RT-70 as a grinding apparatus. The temperature in the defibrator is maintained by supplying saturated steam. The steam simultaneously serves to remove air oxygen from the reaction space of the defibrator, which has a destructive effect on wood. Steam is supplied to the apparatus through a steam valve. Steam consumption is 700 - 1500 kg/t, depending on the type of wood. The chips, having entered the grinding chamber, are directed by the blades of the rotating disk between the disks to the grinding sectors, which grind it into fibers.
The resulting wood fiber mass, under the influence of steam pressure and the blades of the rotating disk, is fed into the outlet pipe to the outlet device. The wood-fiber mass, having passed through the outlet device, enters the diffuser, in which it gradually expands, and at high speed, together with the steam, it enters the cyclone, from where the fibers, which have lost a certain amount of moisture as a result of self-evaporation, are sent to the secondary grinding mill - the refiner. The fiber leaves the defibrator with a moisture content of 40 - 60%.
To improve the properties of the boards, waterproofing additives are introduced into the chips or wood fiber mass. The paraffin emulsion is introduced through special nozzles of the steaming unit before grinding the chips into fibers from the paraffin supply tank. Mixing of fiber with water-soluble phenol-formaldehyde resin SFZh-3014 occurs in mixer 10, which is installed between the drying stages.
After grinding, the fiber is fed into the cyclone of the first stage dryer 9. To carry out the first stage of drying, we install four air fountain dryers, one of which is a reserve one. The drying agent is air heated in a heater to a temperature of up to 160 °C. The air and fiber are moved by a centrifugal fan at a pressure of 22 MPa. After the first stage, the moisture content of the wood fiber mass is reduced to 40%.
Next, the fiber is sent to the second stage dryer. The second stage of drying is carried out in drum dryers. After the first stage of drying, the fiber is fed through a rotary valve into the drying drum, in which, moving along the drum, it is mixed with the drying agent. The drying agent is fed into the drying drum through a special channel tangential to the cylindrical surface. The flow picks up the fiber and passes through the drying drum along a helical line with intense heat exchange and mixing. The fiber is then released from the dryer through a special rotary valve. The second stage dryer uses the principle of low temperature with a large volume of drying agent. The air temperature at the inlet to the dryer is 180 - 200 °C, and the volume of air passing through the dryer, reduced to a standard temperature of 21 °C, is 52500 m3/h. After the second stage of drying, the fiber has a moisture content of no more than 8%.
Next, the fibrous mass is sent to the forming machine 12. To form the carpet, double-mesh vacuum forming machines are used, in which molding is carried out by deposition of mass fibers by an air flow passing from top to bottom through a moving mesh. The carpet is laid on a moving mesh that combines three chambers and a belt-roll press. The fiber from the dosing hoppers enters the corresponding chamber, the air from which is sucked out by a fan that creates a vacuum, as well as a system for removing excess fibers from the sizing roller. The wood fiber mass is distributed across the width of the chamber using an oscillating nozzle. The vacuum value under the mesh in the chambers is approximately 20 - 30 kPa. Depending on the density of the produced slabs, the height of the layer to be laid is determined. With a density of 1 t/m3, the value of the mass of 1 m2 of carpet corresponds to the thickness of the fiberboard in mm.
A continuous carpet formed on a vacuum-forming machine is fed to a pre-pressing belt press, designed to ensure the transportability of the carpet, as well as for the rational use of the hot press, reducing the gap between its plates and increasing the speed of their closing. The specific pressure in the press is increased gradually. The specific prepress pressure is 0.1 - 0.15 MPa; linear pressure is 1400 N/cm. The operation of the press is synchronized with the operation of the forming machine. The speed is infinitely adjustable from 9 to 50 m/min.
Next, the continuous carpet is cut into sheets. From the belt press, the carpet moves along a conveyor belt to cross-cut saws designed to cut the endless carpet into sheets. There, on top of the main carpet, fiber, formed in the form of a thin carpet, comes from the finishing layer forming head for applying the finishing layer to the slabs. Then, slitting saws 16 cut the carpet to a specified width. An oscillating conveyor tip distributes the webs onto a two-tier belt conveyor system. This system consists of three sections of two-deck conveyors that provide a supply of webs to the press loader and a supply of webs until the hot press loader can take them.
Wood fiber sheets are fed into the press by a loader. The loading device, which ensures palletless loading of fiberboards into the press, consists of a fixed frame, a loading shelf, a mechanism for raising and lowering the shelf, and twenty-two conveyor loaders with individual drives. The limit switch stops the loader, after which it moves backwards, leaving the webs in the press.
Depending on the rock composition of the raw material and the type of binder used, the pressing temperature at different plants ranges from 180 to 260 °C. For soft hardwood wood, the pressing temperature is 180 - 220 °C, for hardwood - 230 - 260 °C. To obtain fibrous boards with a density of 1 g/cm3, it is necessary to have a specific pressure of 6.5 - 7 MPa at the initial stage of pressing. The holding time at maximum pressure is determined by the humidity of the carpet, the pressing temperature, as well as the thermochemical treatment of the raw materials. Holding at maximum pressure to avoid the appearance of bubbles and stains due to steam accumulating in the fabric should not exceed 40 s. To remove steam, it is advisable to reduce the pressure. The pressure is reduced to a value slightly less than the steam pressure in the web, which is determined by the temperature of the heating plates of the press and the conditions of thermochemical processing of the raw materials. The duration of pressing depends on the specified thickness of the finished slab. The complete pressing cycle must be regulated so that after the plates pass through the press they have a moisture content of 0.3 - 0.5%.
After pressing, the fiberboards are transferred by a system of levers of the unloading device to the unloading shelf, and from there, one at a time, they are sent to the conveyor for trimming and conditioning.
After the press, the slabs have a humidity of less than 1% and a high temperature. During the process of unloading the press, cutting edges and filling the trolleys, the slabs are cooled to 50 ° C and gain moisture up to 2%. The equilibrium humidity of the slabs under normal conditions (at a temperature of 20°C and a relative air humidity of 65%) is 5 - 9%. Therefore, after the pressing stage, the slabs enter the conditioning stage. The loading device ensures automatic loading of slabs into trolleys, which are then fed into the conditioning chambers. Conditioning time 3 - 5 hours.
After the conditioning chamber, the slabs are transported to the cutting and machining area by electric forklifts. They are then placed on the receiving platform of the conveyor, and from there, one at a time, they are fed to the longitudinal sawing machine. The feed speed is adjustable from 10 to 75 m/min. The longitudinal sawing machine has three saws, of which the two outer ones are used for cutting edges, and the central one, if necessary, can perform a longitudinal cut: The outer saws are equipped with devices for crushing edges up to 50 mm wide. Slab size after clean cutting, mm: maximum 1830, minimum 1700.
Next, the slabs are fed to a cross-cutting machine equipped with five saws, the position of which is adjustable. External saws have devices for crushing edges up to 50 mm wide. The maximum length of the slabs after cutting is 5500 mm.
After cutting, the slabs are stacked by a stacker and end up in a slab storage unit, from where they are transported by a forklift.
Calculation and selection of main and auxiliary equipment for wet fiberboard production
Selection of chipping machine
Raw materials are supplied to production in the form of conditioned chips. Preparation of raw materials for the production of boards, which consists of preparing conditioned chips, includes the following operations: cutting wood into sizes corresponding to the receiving cartridge of the chipper; cutting wood into chips; sorting of chips to select the required size with additional grinding of the coarse fraction and removal of fines; removing metal objects from wood chips; washing the wood chips to clean them from dirt and foreign matter.
To prepare wood chips we use a drum chipper DRB-2.
The productivity of the apparatus is 4 - 5 m3/h, the drum diameter is 1160 mm and the number of cutting knives is 4.
From material balance calculations, we find that the chipping department receives 243,661.95 kg of wet wood per day, i.e. 10152.58 kg per hour. Taking the density of wood equal to 1540 m3/kg, we obtain:
58/1540 = 6.59 m3/h
According to calculations, it is necessary to install two chipping machines.
Selection of sorting machine
The resulting chips after chipping machines are sorted, as a result of which process chips are selected that meet the requirements for them.
According to the material balance, 236,565 kg of wet chips per day are received for sorting, which is 9,857 kg per hour. Taking the weighted average conditional density of wood raw materials equal to 650 kg/m3, we determine the bulk density ?n, kg/m3, according to the equation:
N = ? k n (1)
where kp is the full wood coefficient for wood chips, equal to 0.39.
?n = 650 ·0.39 = 253.5 kg/m3
Then we find that 9857/253.5 = 39 bulk m3 per hour is received for sorting.
To sort process chips, we use a gyratory type sorting machine, model SShch-1M, the technical characteristics of which are given in Table. 3.
Table 2. Technical characteristics sorting machine
IndicatorsValueProductivity, bulk m3/h60Number of sieves3Sieve inclination, deg3Electric motor power, kW3Weight, t1.3
Selection of disintegrator
Hammer disintegrators are used to crush large chips. We select a disintegrator of the DZN-1 type, the technical characteristics of which are given in table. 3.
Table 3. Technical characteristics of the disintegrator DZN-1
IndicatorsValueProductivity, bulk m3/h18 Overall dimensions, mm length2300 width1620 height825Weight, kg2248Electric motor power, kW11.4
Selection of consumable bins for conditioned chips
The conditioned chips are sent to stock bins or supply bins in the grinding department. According to their plan configuration, stock bins are of two types: rectangular and round.
We use rectangular bins, placing them in the building of the wood chip preparation department. For small stocks, wood chips can be stored in vertical bins. We use a DBO-60 type bunker, the technical characteristics of which are given in table. 4.
Table 4. Technical characteristics of the vertical bunker DBO-60
IndicatorsValuesHopper capacity, m360Number of unloading screw conveyors3Performance of one screw conveyor, m3/h3.8 - 40Installed engine power, kW21.9Height of supports, m4Total height of the hopper, m11.75Total weight of the hopper,t18.5
The required number of bins nb is determined by the formula:
b = Gsh · t/Vb · ? n kzap (2)
where Gsh is the hourly demand of the designed workshop for technological chips, kg/h (according to the material balance data Gsh = 9857 kg/h); t is the time during which the bins ensure uninterrupted operation of the flow, h (when the chip preparation department operates in three shifts, t = 3 h); Vb - bunker volume, m3; ?n - bulk density of wood chips, kg/m3 (determined in paragraph 4.2); kzap - filling factor of the working volume of the hopper (for vertical kzap = 0.9).
b = 9857 3/60 253.5 0.9 = 2
Accordingly, we install three bunkers, one of which is a reserve one.
Selection of steaming unit
From the feeder hopper, the chips are fed by a screw dispenser into the drum feeder low pressure, from which it is sent to the heater, where it is heated with saturated steam at a temperature of 160°C. A nozzle is mounted in the output section of the heater, through which paraffin is introduced into it in a molten state, sprayed with compressed air with a pressure of 0.4 MPa. From the heater, paraffin-impregnated wood chips enter directly into the hydrodynamic treatment apparatus. Fiberboard factories use continuous operating devices of various systems.
We install the Bauer-418 steam-grinding system, which has the following characteristics: horizontal steaming boiler, tubular type, diameter 763 mm, length 9.15 m, designed for pressure up to 1 MPa. The productivity of the steaming unit is up to 5 t/h.
According to calculations of the material balance, 238 tons of paraffin-impregnated wood chips per day are supplied for steaming, which is about 10 t/h. Accordingly, it is necessary to install two steaming units.
CONCLUSION
The integrated use of wood aims to increase economic efficiency forestry and wood processing industries by reducing logging and at the same time making full use of wood waste and low-grade wood as technological raw materials. This problem continues to remain relevant, despite the fact that careful attitude towards natural resources and protection environment have become a natural requirement for human activity.
It is necessary to make more complete use of forest raw materials and create integrated enterprises for forest growing, harvesting and processing of wood. The solution to the problem of waste-free production in the forestry, pulp and paper and woodworking industries is facilitated by the production of slab (sheet) materials, since they are made from various wood waste and non-commercial wood.
The use of board materials in construction increases the industrialization of production and reduces labor costs. In furniture production, their use saves labor costs and reduces the consumption of more expensive and scarce materials.
Calculations have established that 1 million m2 of fiberboards replace 16 thousand m3 of high-quality lumber in the national economy, for the production of which it is necessary to harvest and export 54 thousand m3 of wood. The production of 1 million m2 of fiberboards provides savings of more than 2 million rubles. by reducing the volume of logging and removal, and the costs of reforestation; railway transport, as well as a reduction in the number of workers in forestry.
LIST OF LITERARY SOURCES USED
1. Rebrin S.P., Mersov E.D., Evdokimov V.G. Technology of fiberboards, ed. Timber industry, M., 1971. 272 p.
Karasev E.I. Equipment for enterprises for the production of wood-based panels. - M.:MGUL, 2002. - 320 p.
Sokolov P.V. Drying wood. Timber industry, M., 1968. 340 p.
Volynsky V.N. Technology of wood panels and composite materials. St. Petersburg: Publishing house "Lan", 2010. - 336 p.
Stepanov B.A. Materials science for professions related to wood processing. - M.: ProfObrIzdat, 2001.-328 p.
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The fiberboard market has been falling for the fourth year in a row; it has already halved in quantitative terms compared to 2012. This situation, of course, can largely be attributed to a protracted crisis, but a careful look at the situation may reveal signs of structural changes.
Fiberboard (Fiberboard) is a material in the form of a rectangular sheet, obtained by hot pressing or drying wood fiber mass formed into a carpet. Fiberboard is distinguished by wet, dry, semi-dry and wet-dry production methods. This review will focus on wet-process fiberboard. Solid fibreboards, the front side of which is varnished or lined, are also called hardboard. In addition to finishing with paints and varnishes, hardboard is refined with PVC-based synthetic films and melamine films (but not natural veneer). Accordingly, the surface of fiberboard can be matte, glossy, pigmented, or imitating the texture of wood - such a material is called treated fiberboard (DFB).
Fiberboards, like particle boards, are a widespread and well-known finishing material, which has been produced in Russia since Soviet times, approximately since the 40s of the twentieth century.
Advantages of fiberboard: ease and manufacturability of use (light weight and ease of processing); long term operation; affordable price; high heat and sound insulation properties; fairly good water resistance in its class (fibreboard is inferior in water resistance to MDF and HDF boards, but superior to chipboard). Disadvantages of fiberboard: narrow scope of application; low fire safety rating (fibreboards belong to category G4, that is, it is a completely combustible material); increased toxicity of some species due to their formaldehyde content.
Dynamics of fiberboard production
In Russia, mainly super-hard fiberboards with a thickness of 2.5-3.2 mm are now produced. There is no wide variety of products. The quality of most fiberboard slabs is essentially the same, so sellers in price lists often do not even indicate the name of the manufacturer, only the size range. Low-density slabs (even hard ones) are extremely rare in the assortment of domestic manufacturers, except that you can find TN brand slabs with a thickness of 5-6 mm. Semi-hard and soft fiberboards of medium and large thickness were produced in small volumes by individual pulp and paper mills, but have now abandoned their production. It turns out that from this segment, fiberboard (which are made by the wet method) were completely replaced by MDF boards (which are made by the dry method), which are gaining popularity. Not only do fiberboards compete with plywood, but recent years they are being quite actively pushed out of the market by HDF boards (high-density fiberboards, which are also produced using a dry process).
Let's look at the dynamics of production. After the crisis of 2008-2009, when manufacturers of almost all building materials perked up and actively resumed growth in production volumes, the production of fiberboard, on the contrary, is almost not increasing. If in 2009 174 million m2 of fiberboard were produced, then in 2012 there was only 10 million m2 more. And in 2013, the production of fiberboards fell by 16.8%, in 2014 - by 1%, in 2015 - by 7%. It is already clear that 2016 will not be an exception: according to the results of the first half of the year, the production of wet fiberboard decreased by 13% compared to the same period last year. And even if in the second half of the year enterprises slightly increase output, a decrease in output volumes of at least 8-9% will still be recorded. It is also unlikely that the situation will improve in 2017.
Until recently, the Siberian Federal District was the leader in fiberboard production in Russia, but after 2012 its share began to rapidly decline. The reason for the reduction is obvious: the cessation of production by one of the leading factories in the Irkutsk region. The Volga District has taken the lead and still maintains its position, accounting for about 40% of the total volume of fiberboard production in Russia. The North-Western Federal District is also rapidly increasing its fiberboard production; its share now accounts for almost 30%. The shares of the Ural and Central districts are 6-8% each. There are no fiberboard manufacturers in the Southern and Far Eastern districts yet.
Fiberboard manufacturers in Russia
Table 2. Production volumes of wet fiberboard in
Russia by federal districts in 2009-2015 and forecast for
2016, thousand m2
The leading Russian manufacturer of wet fiberboard is now the Sukhonsky Pulp and Paper Mill, accounting for 19% of total fiberboard production in 2015. In second place is the Demyanovsky Manufactory plant with 16%, in third place is Lesosibirsk LDK No. 1 (10%), in fourth place is Ufa Timber Plant, with 9.6%. 8-9% each falls on such plants as Plitprom LLC (Trade House Perm DSK), Turinsky Pulp and Paper Plant CJSC, Knyazhpogostsky Fiberboard Plant LLC (DrevPlitGroup company), Novoyenisei Timber Chemical Complex CJSC. Other enterprises have significantly smaller shares.
Rice. 1. General dynamics of wet fiberboard production in Russia in
2009-2015 and forecast for 2016, thousand m2
Rice. 2. Dynamics of wet fiberboard production according to federal
districts in 2009-2015 and forecast for 2016, thousand m 2
Table 3. Operating fiberboard manufacturers in Russia and their
brief description
Rice. 3. Structure of distribution of fiberboard production at individual plants in
2015, %
Rice. 4. Comparative dynamics of import and export of fiberboard in 2009-2015
and forecast for 2016, thousand m2
The facilities of most enterprises are quite old, the equipment has been used since Soviet times. Machines are only rarely subject to local modernization. Therefore, the potential for overcoming the decline and resuming growth in fiberboard production in Russia is not yet noticeable. If we recall the events that have occurred in the industry over the past seven to eight years, we can note that there was almost no positive news: only two enterprises are investing in production development. In 2012, at the Sukhonsky Pulp and Paper Mill (Vologda Region), the third workshop for the production of fiberboard was launched, and therefore the plant’s production capacity increased from 19 to 28 million m2. At the Knyazhpogost fiberboard plant (Emva, Komi Republic), a second workshop with a design capacity of 980 thousand m2 per month was put into operation in 2013.
Since 2012, many Russian factories began to experience serious difficulties. Under the current conditions, most enterprises are forced to gradually reduce production volumes, and some had to completely abandon the production of fiberboard. As a rule, among the “refusers” are pulp and paper mills where the production of fiberboard was a non-core product: these are PJSC Sokolsky Pulp and Paper Mill (Investlesprom), JSC Arkhangelsk Pulp and Paper Mill and a real industry giant - Ilim Bratsk DOK (" Ilim Timber"), whose capacity allowed the production of up to 40 million m2 of fiberboard per year.
But developing enterprises regularly face problems. Thus, the above-mentioned Knyazhpogostsky Fiberboard Plant LLC is in a pre-bankruptcy state. The plant continues to produce products, the company employs about 1,000 people, but the bankruptcy procedure has been going on for three years. To develop production at the Knyazhpogost Fiberboard Plant, it is necessary, in fact, to 100% update the production capacity. LLC "Plitny Mir" (tenant of the plant) is ready to invest money subject to the purchase of the enterprise, but the current owner (DrevPlitGroup group) is not deciding on the sale of the plant. By the end of 2016, Plitny Mir plans to change the lease relationship with the plant to that of the owner, for which it plans to buy out the enterprise in order to be able to fully invest, but not in the production of fiberboard, as the future owner openly states, but in the launch of a number of other projects in the woodworking industry.
More recently, the Knyazhpogostsky Fiberboard Plant was part of the Woodway Group (Woodway investment and industrial group), which also included the Poleko LPK (Kirov region). Now this plant is called Demyanovskie Manufactories LLC (former names: Poleko LLC, Poleko LPK and Podosinovsky Timber Processing Plant OJSC). The endless change of names, legal forms and owners reveals the problems into which this, without exaggeration, permanently falls into the abyss. The plant is located in the village. Demyanovo, Podosinovsky district, Kirov region, is a city-forming city; the company employs more than 900 people.
Demyanovskie Manufactories LLC is the only enterprise in Russia whose products have a European NFB (Natural Fiber Board) certificate, guaranteeing the environmental friendliness of their products. Due to its environmental friendliness, the Demyanovskaya stove (out of habit is still often called the “Poleko” stove) can be widely used in the production of furniture, including children’s, as well as for interior decoration premises. The company was declared bankrupt in 2010, one of the reasons was the high dependence on borrowed funds, then the bankruptcy procedure was resumed in 2013, as a result of which the plant got a new director in 2014, and production grew at a record pace. But in August 2016, information appeared that the company was forced to sell off part of its property, possibly in order to pay off accumulated wage debts: several lots related to the sale of property of Demyanovskie Manufactories LLC were put up on a single electronic trading platform.
In addition, it became known that in February 2016, the fiberboard production workshop at the Nelidovsky DOK (Tver Region) was closed, which recently produced no more than 1 million m2 per year, although the enterprise’s capabilities allowed it to produce much more. The production of the Seletsky DOK TPK (Bryansk region) was also greatly reduced. Many other woodworking enterprises are also not doing well. Important fact: over the past ten years, not a single new plant for the production of wet fiberboard has been opened in Russia, and this says a lot, since in the construction industry, perhaps, there is not a single segment that has been so forgotten by investors, especially when it comes to woodworking. In other segments of the wood-based panel market (plywood, OSB, chipboard, MDF and HDF), factories are opened almost every year.
Export potential of fiberboard
Rice. 5. Ratio of internal and external sales
Russian fiberboard in 2009-2015 and forecast for 2016, %
The general situation on the Russian fiberboard market is disappointing. Faced with a sharp drop in demand in the domestic market, fiberboard manufacturers turned their attention to exports, the volumes of which have been growing markedly since 2010, which is especially noticeable when compared with imports of fiberboard. On Russian market Fiberboard used as furniture facades, ceiling panels (finished and semi-finished products), soft boards for sound and thermal insulation (remember that such boards are not produced by Russian factories), as well as fiberboard used as a substrate for laying floor coverings are imported , for the manufacture of back walls of paintings and other products.
Currently, the share of fiberboard produced domestically and exported exceeds 30%. Most likely, this share is higher, since customs databases do not show supplies made to Kazakhstan and Belarus. But even without this data, it is clear that the share of exports from some factories is approaching 50%, that is, it turns out that factories already produce almost half of their products with the expectation of external sales. Moreover, among the recipients of export products are not only the closest neighbors in the CIS, but also Western European countries: Russian fiberboards are very successful in the markets of Poland, Germany, Sweden, Finland, Estonia, Hungary, Lithuania, Austria, Denmark, the Netherlands and other countries.
Competitive situation
Rice. 6. Dynamics of the ratio of market volumes of fiberboard and HDF boards in 2009-
2015 and forecast for 2016, %
But it is too early to call fiberboard an obsolete material. The performance properties of fiberboards, which have proven themselves over many years, combined with an affordable price, are the key to maintaining demand. From the point of view of chemical hazards, fiberboard boards are safer than, for example, chipboards from many domestic manufacturers. True, enterprises producing fiberboard using the wet method have problems with wastewater pollution, and therefore the issue of using boards (not only fiberboard) in the production of boards that contain binders that do not contain phenol, formaldehyde or any other harmful substances. Work on changing the composition of the mass for the production of boards is underway at many advanced factories, although it has not yet been possible to completely abandon synthetic binders.
However, the obvious cannot be denied: fiberboard is slowly but surely being replaced by other wood materials from the areas in which they were usually used. Fibreboard is difficult to compete with, for example, MDF and HDF boards. Now the cost of HDF boards with a thickness of 3 mm from some suppliers is quite comparable to the cost of a sheet of fiberboard with a thickness of 3.2 mm, which is especially important in 2015-2016, when new Russian manufacturers of HDF boards (almost all with foreign capital) are aggressively competing and reducing prices in hoping to conquer the market through expansive methods. Thus, low cost ceases to be a key competitive advantage of fiberboard.
Some experts believe that this type of slab will gradually become a thing of the past. But, most likely, this is true for those areas where decorated boards are used, because fiberboard is not well suited for veneering, in addition, fiberboard is a looser material compared to MDF and HDF boards, and not as smooth. When veneering, unglued areas and blisters can form on fiberboard, while HDF boards have a more uniform and dense structure, they are characterized by high dimensional stability, so they are readily veneered (usually on both sides). Double-sided veneered HDF boards are most often used for the manufacture of furniture fronts and back walls of furniture. HDF boards are an improved type of fiberboard and may soon completely replace fiberboard from furniture production.
Vera NIKOLSKAYA,
Research Director at ABARUS Market Research Agency
Fibreboard production is carried out using wet and dry methods.
Fiberboard production using the wet method
includes operations such as grinding wood chips, sizing the resulting fibrous mass, forming a carpet, pressing, impregnating slabs with oils, thermal-moisture treatment and cutting slabs.
The washed chips are subjected to two-stage grinding. The first grinding is carried out in defibrator mills, in which the chips are steamed and processed into large fibers. The second grinding is carried out in refiners, which make it possible to obtain thinner fibers with a thickness of 0.04 mm and a length of 1.5...2 mm. From such fibers an aqueous solution of wood fiber mass is prepared - pulp, which is stored in collection tanks or pools, stirring periodically to maintain a certain concentration of the mass, preventing the fiber from settling to the bottom.
The resulting wood fiber mass is then sent to a continuous sizing box, in which it is mixed with phenol-formaldehyde resin. Hydrophobic additives prepared in an emulsifier, strengthening substances and precipitants are also supplied there with a mixing pump at a temperature of no more than 60 ° C and in a volume at which the concentration of the resulting suspension for any ratio of the rock composition of the raw material fibers before casting is 0.9...1, 8%. The dosage of these components depends on the type of slabs, the composition of the fibers, the consumption of liquid, pressing modes, etc.
The operation of forming a wood-fiber carpet is performed on an endless mesh in casting machines. The final moisture content of the carpet for hard and super-hard boards with a thickness of 3.2 mm should be (72 ± 3)%, for soft boards with a thickness of 12 mm - ((61...63) ± 1)%. To form raw slabs, the pressed carpet is cut to a length and width that is 30...60 mm smaller than that of the finished slab.
For hot pressing of fiberboard, multi-story (20 floors) hydraulic presses are used. Loading and unloading of slabs is carried out using shelves. The fiberboard pressing cycle includes three phases, each of which is characterized by a certain pressure, holding time and moisture content of the boards.
The first phase is spinning. In 30 seconds, under the influence of a pressure of 4.2...5.5 MPa, water is removed from the fibrous carpet. In this case, the humidity is reduced to 45%, and the slab itself, as it warms up, becomes compacted.
The second phase is drying. The slabs are kept for 3.5...7 minutes at reduced pressure (0.65...0.85 MPa), at which the humidity of the slabs reaches 8%.
The third phase is hardening of the slabs, which promotes their compaction and increases their strength and hydrophobic properties. The plates are kept under pressure of 0.65...0.85 MPa for 2...3 minutes.
The resulting slabs must have a final moisture content of 0-.5... 1.5% and a bending strength of at least 35 MPa, which is ensured by compliance with the technological parameters of the process: the thickness of the fiberboard, the width of the press plates and the rock composition of the raw materials.
In addition to hot pressing, soft fiberboard is produced by drying fibrous carpets in continuous roller dryers, in which free moisture is removed. The dryer has 8-12 rows of roller conveyors, heated by saturated steam at a pressure of 0.9... 1.2 MPa. The air circulation speed is 5...9 m/s, drying time is 1.5...2 hours to a humidity of 2...3%.
To improve and stabilize the strength and hydrophobic properties of the slabs, they are subjected to heat treatment in batch chambers. The coolant in them is superheated water with a temperature of 190...210°C and a pressure of 1.8...2.2 MPa. Air movement speed is at least 5 m/s. The heat treatment time, taking into account the thickness of the plates, is 3...6 hours.
To give the slabs dimensional stability after heat treatment, they are cooled and then moistened in humidifying machines or batch chambers. Wet slabs are cut to size and then kept for at least 24 hours.
Superhard slabs are also subjected to the heat and moisture treatment procedure, but after they are impregnated with drying oils in an impregnation machine in order to increase strength and water resistance.
Dry fiberboard production much the same wet fiberboard production . But using the dry method it is possible to produce double-sided smooth slabs with a thickness of 5...12 mm and slabs with special properties (fire- and bio-resistant, profiled, etc.).
The production of fiberboard by the dry method is also different in that when grinding wood chips, the operations of steaming it, separating fibers for outer and inner layers and mixing them with additives and resin are included
The formation of a carpet is carried out from dried fibers by felting them and compacting them with a vacuum, and then pressing them with belt-roll and format presses. Hot pressing lasts 5...7 minutes and is carried out at a temperature of 200...230 °C with a single increase in pressure to 6.5 MPa for 15...25 s and a stepwise release of it first to 0.8...1 .0 MPa, and then to zero. Profiled fibreboards are secured to the press plates with special matrices.
Currently, MDF, which is more homogeneous in structure, which is much easier to cut and process, successfully competes with chipboard.
All slabs, regardless of the process of their production, after 24 hours of exposure are cut to size on circular saw format-edging machines according to their standard sizes.