1.4.3 Detection method of plywood:
According to the classification of ordinary plywood, there are corresponding detection methods:
Class I plywood: weather resistant plywood, used in outdoor conditions, and able to pass the boiling test;
Steps: boiled in boiling water for 4 hours, dried at 63°C for 20 hours, boiled in boiling water for 4 hours, air-dried, and mechanically tested.
Class II plywood: that is water resistant plywood, which can pass the 60°C±3°C hot water immersion test under humid conditions
Steps: Boil in hot water at 60°C±3°C for 3 hours, dry for 10 minutes, and test mechanically.
Class III plywood: that is plywood that is not moisture-resistant, used under dry conditions, and can pass the dry test.
1.4.4 Analysis of common defects in gluing process
There are often some defects in the plywood gluing process, which increases the trouble of rework and repair, reduce the gluing or even become a waste product. The following lists several common gluing defects, analyzes their causes, and proposes corresponding improvement measures.
①Low adhesive force, large area of glue
The main reasons are: the quality of the adhesive is not good, such as deterioration and excessive moisture; the moisture content of the veneer is too high, and the surface quality is poor; the bonding conditions are not well controlled, such as the hot pressing temperature is too low or part of the temperature is uneven, and the pressure is insufficient , the hot pressing time is too short and the adhesive layer is not fully cured; insufficient or too long aging time will also reduce the adhesive force.
Improvement measures: First, replace the adhesive, choose a formula with less water content or add flour appropriately to absorb water; Second, improve the quality of veneer and strictly control the moisture content of the veneer; Third, adjust the hot pressing process to increase the heat; Fourth, check the equipment regularly to ensure the precision of the rotary cutting machine, and check the steam passage and steam supply of the hot pressing board.
②Bubbling and local degumming
The main reasons are: the depressurization speed is too fast; the moisture content of the veneer is too high; the hot pressing time is insufficient or the local temperature of the pressing board is too low; there are blank spots or inclusions and sticky stains during gluing; the pine veneer has poor air permeability and the hot pressing temperature is too high, turpentine vaporization, resulting in open glue.
Improvement measures: one is to use multi-stage depressurization process to strictly control the depressurization speed; the second is to reduce the moisture content of the veneer; the third is to increase the glue concentration or reduce the amount of glue applied; the fourth hot pressing temperature is lower than 110°C; the fifth is to appropriately extend the hot pressing time; the sixth is to check the steam passage and steam supply of the hot pressing board.
③The corners fall off
The main reasons are: the aging time is too long, and the corner glue has dried up; the corner glue is lacking; the large-format press presses the small-format panel without the corner glue; when the large-format press presses the small-format panel, the loading position of each layer is shifted, resulting in uneven pressure; warping deformation of the hot pressing board: the temperature of the corners of the pressing board is too low.
Improvement measures: First, shorten the aging time; Second, pay attention to the gluing operation; Third, the large press does not press the small plate, even if the small plate is pressed, the pressure positions of each layer should be aligned; Fourth, the warping deformation of the pressing plate is small. Repair by planing the hot pressing plate; when the deformation is large, the pressing plate needs to be replaced; Fifth is to check the steam passage and steam supply of the hot pressing plate.
④The core board stacking core is separated from the seam
The main reasons are: manual core arrangement, inaccurate control of the expansion gap between the veneer; The edge of the core board has ruffles and slits.
Improvement measures: First, to realize the whole core board or adopt the secondary gluing process; Second, the aging time of the opening of the glued core board should be appropriate; Third, the slab should be pre-pressed and then installed, and the slab should be moved smoothly; The fourth is to master the timing of pre-pressing; The fifth is to use the leveling process for the core board, and the core board that is cut first and then dried should be flushed after drying; The sixth is to improve the quality of the core board rotary cutting and drying quality.
Sixth, improve the quality of core plate rotary cutting and drying quality. Plate peel quality and drying quality.
⑤The board surface is permeable
The main reasons are: the glue is too thin and the water is too much; the amount of glue is too large; the cracks on the back of the veneer are too deep; the moisture content of the veneer is too high; the aging time of the slab is insufficient; the pressure during hot pressing is too large.
Improvement measures: First, check the quality of the glue, increase the resin content of the glue, and choose a formula with less water content; second, reduce the amount of glue applied and replace the worn glue roller; third, improve the quality of veneer rotary cutting, adjust the pressure gauge The fourth is to reduce the moisture content of the veneer; the fifth is to increase the aging time to evaporate part of the water in the glue; the sixth is to reduce the hot pressing pressure and check the pressure gauge of the hot pressing machine.
⑥Plywood warping
The main reasons are: the principle of symmetry is not met when the billet is assembled; the front and back directions of the face and back plate are wrong when the billet is assembled; the veneer is made from the stressed wood segment; the hot-pressed plate is warped and deformed; the plywood is not stacked flat.
Improvement measures: first, the corresponding layers should be symmetrical when assembling the blank; second, the face and back plate should face outward when assembling the blank; third, the veneer cut out by rotary cutting should be leveled (softening treatment); fourth, repair or replace the pressure plate; Fifth, the plywood should be stacked flat.
