Knowledge points about wooden based board and plywood, series five.
- Briefly describe the pollution of the plywood industry.
Air pollution: (1) exhaust gas from the veneer dryer (2) harmful gas produced in the process of gluing and hot pressing (3) emission from the sanding process the dust.
Water pollution: ① waste water generated by water stripping of wood section ② waste water generated by water heat treatment of wood section ③ Washing waste water of glue mixing and glue coating equipment and veneer dryer.
Noise pollution: The noise of most equipment in plywood production has exceeded the expected value
Brief introduction of the harmfulness and long-term nature of free formaldehyde in plywood. The harmfulness of wood-based panel free formaldehyde is reflected in its seriousness and long-term nature.
(1) Severity causes serious impact on human health, causing serious harm to eyes, respiratory system, hematopoietic system and nervous system, especially in infants and young children.
(2) Long-term the release peak is 3 years, and the decay period is 12 years, a total of 15 years. - What is the advanced finishing of plywood? The requirement of plywood base material for advanced processing is briefly described. Deep processing: all kinds of wood-based panels are used as substrates and processed in different ways to meet different requirements. Requirements: it should have certain strength and water resistance. The moisture content of the base material should be uniform, generally required in the range of 8~10%. The thickness deviation of the substrate shall be less than plus or minus 0.2 mm. The surface of the substrate shall be smooth and clean. Base material structure should be symmetrical, no warping deformation.
- What is a joinery board? Describe the principles of its composition.
Definition: one or two layers of veneer or plywood glued together on both sides of a solid or square core board consisting of strips of wood plywood of a special structure, called joinery board. Constitution principle:
(1) Symmetry principle
The veneer on both sides of the symmetrical center plane of the joinery board should be symmetrical and consistent in thickness, layer number, manufacturing method, fiber direction and moisture content, so as not to produce stress, ungluing and warping deformation.
(2) Odd number layer principle
The middle layer of the joinery board is usually wood core board, and the two sides are respectively glued to the veneer with the same number of upper layers. If the number of layers is even, the joinery board cannot achieve symmetry, so the number of layers of the joinery board must be odd. Because only in this way can ensure the structure symmetry, so that the symmetrical center plane and the middle layer of the core board of the plane overlap, not by bending the maximum stress falls on the rubber layer and the rubber layer damage.
(3) texture interlacing principle
The wood fiber direction of the adjacent layer inside joinery board should be perpendicular to each other, in order to ensure its vertical and horizontal direction strength tends to be consistent, make the anisotropy of wood is transformed into isotropy, use intensity rises somewhat. - What are the features of the joinery board compared to the solid wood board? Compared with the third board?
(1) Comparison between joinery board and three boards:
(a) Lower material requirements compared to plywood. The manufacture of veneer requires better logs, and the veneer in the joinery only accounts for the board
20-40 % of the material, a large number of cores. Core strip is not tall to raw material requirement, can use small path material, low qualitative material, sapwood and small mastow to wait, and the raw material of plywood wants better log.
(b) Superior quality in comparison with particleboard and fiberboard. Joinery board surface has beautiful natural wood grain and color, the board structure is reasonable, easy to process, light weight, nail holding force, good strength, a certain degree of elasticity, board edge characteristics and bonding strength is better than particleboard and fiberboard.
(c) Less glue is used compared with plywood and particleboard. Joinery boards require less glue, about half as much as plywood or particleboard of the same thickness. The amount of glue is less than that of plywood because the thin plate has less glue layer; Less glue is used than particleboard because joinery boards are less dense.
(d) Simple equipment and low investment.
(e) Simple process, low energy consumption.
(2) Comparison between joinery board and solid wood board:
(a) The structure is stable in size and not easy to crack and deformation. The size and shape of solid wood panel are very unstable with the change of environmental equilibrium moisture content when it is used. Easy to produce dry shrinkage wet tension, will gradually warpage deformation, and even dry shrinkage cracking. The joinery board, due to its structure and material factors, has good stability and minimal expansion and contraction deformation; In general, warping deformation and cracking will not occur in the process of use.
(b) Conserving quality wood and using sapwood knits. The joinery board is made of high-quality wood only on its face, which only accounts for the entire board thickness about 5-10%, the back plate, the middle plate can be used other wood. Core panel can use sapwood small material, which is all made of high quality wood compared with the solid wood board (with the same specification), the high quality wood consumed by joinery rice is only the solid wood board
1/10-1/20. Not only use sapwood small material, improve the utilization rate of wood, but also save high quality precious tree species.
(c) The surface texture is beautiful, without natural defects. The face plate of joinery board can use plane to cut thin wood or turn to cut veneer adornment, easy purify natural defect, because this the grain of board face is more beautiful, colour and lustre is more uniform and consistent.
(d) High transverse strength and large plate stiffness. Joinery boards have much higher transverse static bending strength and better rigidity than solid wood boards.
(e) The plate is wide and the surface is smooth and consistent. - Briefly describe the composition and technical requirements of the joinery board.
(1) The symmetrical layer veneer on both sides of the core plate shall be of the same thickness, same tree species or similar material;
(2) the surface should be tightly facing outward;
(3) the core strip of the same joinery board should be the same thickness, the same tree species or similar material species;
(4) Jointing non-porous tape is not allowed to be used in the interior of the joinery board;
(5) the width of the core strip of the joinery board should not be greater than 3.5 times its thickness;
(6) along the length direction of the plate, the distance between the joints at both ends of the adjacent two rows of core strip is not less than 50mm, that is, the length of the core strip is not less than 100mm;
(7) The side gap of the core strip shall not exceed 1mm, and the end gap of the core strip shall not exceed 3mm;
(8) Core panels are allowed to be processed with strips, blocks and veneers. Request a Quote - What are the forming processes of joinery boards?
(1) one pressing molding process; (2) pre-pressing repair secondary hot pressing process; (3) prepressing repair once hot pressing process. - Briefly describe the advantages and disadvantages of the secondary hot pressing process of prepressing repair. Advantages:
① Two repairs and sanding greatly improved the surface smoothness. The cold repair after slab prepressing basically takes out the high part that fold core in plank or bulges up, the hot repair after hot pressing basically fills in plank groove with putty ash or the low concave part that leaves seam. The defects on the slab surface were well corrected in two repairs.
(2) After the hot pressing dressing slab is aged for two days and then sanding, the residual stress of the plate is released, and the normal rebound is completed, which is conducive to the stability of the plate size.
The constant thickness sanding ensures the flatness of the plate surface and the allowable thickness deviation.
(4) is conducive to improving the appearance of the plate quality, such as covering the surface, the back plate before the slab with concealed agent cover processing, then the plate disorderly pattern or color will not be exposed on the table, the back plate, the product surface pattern and color remain consistent. Disadvantages: the process is more complex, covers an area of large, sanding increases material loss, energy consumption is greater than a hot pressing process. - What is laminated veneer? What is the difference between it and ordinary plywood?
Veneer laminated material (LVL) is a board made of 2.5~3.2mm veneer with a thickness of 2.5~3.2mm and a parallel group of blanks along the grain direction. Its length direction is consistent with the grain.
The difference with multilayer plywood: ①Veneer along the grain group blank.
② The length is large. It is generally 2.4 to 18.3m long.
Number of layers and thickness of veneer. The thickness of LVL is generally 19~89mm, and the width is 600~1200mm. - Briefly describe the characteristics of laminated veneer.
(1) Not only retains the natural characteristics of wood, but also removes defects such as nodes and insect eyes.
(2) The allowable stress increases when the coefficient of variation of strength decreases.
(3) The dimensional stability is improved, and the deformation is very small (only 1/8 of the square deformation).
(4) Large area structure boards can be produced by small diameter wood, which broadens the application field of plantation wood.
(5) LVL waterproof adhesive for structure, PF and MF modified, coniferous veneer; Non-structural LVL generally use plastic UF, broadleaf veneer (low strength, beautiful). Request a Quote
