Testing method of plywood resistance to boiling water

Detection method of commercial plywood:

According to the classification of ordinary plywood, there are corresponding detection methods:

Type Ⅰ plywood: weather resistant plywood, used under outdoor conditions, can pass the boiling test;

Steps: boil in boiling water for 4 hours, dry at 63°C for 20 hours, boil in boiling water for 4 hours, dry, and test mechanically.

Type Ⅱ plywood: water resistant plywood, for use in humid conditions, can pass the 60℃±3℃ hot water immersion test;

Procedure: Boil in hot water at 60℃±3℃ for 3h, let it dry for 10min, and test it by mechanical machine.

Type Ⅲ plywood: that is plywood not moisture-resistant, for use under dry conditions, and can pass the dry test.


Analysis of common defects in the gluing process

In the commercial ply gluing process, some defects often appear, which may increase the trouble of rework and repair, or even reduce the commercial plywood 18mm and even become a waste product. The following lists several common glue defects, analyze their causes, and propose corresponding improvement measures.


① Low adhesive force, large area opening

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. In the process of commercial plywood application, various properties are better than flour, and the price is favorable.

Improvement measures: first is to replace the adhesive, choose a formula with less water content or add flour and soybean flour to absorb moisture; the second is to improve the quality of the veneer, and strictly control the moisture content of the veneer; the third is to adjust the hot pressing process to increase heat press temperature, extend the hot pressing time, and increase the pressure appropriately; fourth, check the equipment regularly to ensure the accuracy of the rotary cutting machine, and check the steam path and steam supply of the hot press plate.


② Bubbling and partial degumming

The main reasons are: too fast depressurization speed, too high moisture content of the veneer; insufficient hot pressing time or local temperature of the pressure treated plywood is too low; there are blank spots or inclusions or stickiness during gluing; the pine veneer plywood has poor air permeability and the hot pressing temperature is too high, turpentine vaporizes, causing cracking.

Improvement measures: first, adopt a 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; the fourth is to use pine species with poor air permeability. The hot pressing temperature is lower than 110°C; the fifth is to extend the hot pressing time appropriately; the sixth is to check the steam path and steam supply of the hot plate.


③The corners fall off

The main reasons are: the aging time is too long, the corner glue has dried up; the corner lacks glue; the large format press presses the small panel corner lack of glue; when the large format press presses the small panel, the loading position of each layer is shifted, causing Uneven pressure; warpage of the hot pressing plate; low temperature at the edges and corners of the pressing plate.

Improvement measures: First, shorten the aging time; second, pay attention to the glue application; third, the large press does not press the small plate, even if the small plate is pressed, the pressure position of each layer should be aligned; fourth, the plate can be warped and deformed when the small plate is small. Repair by planing the hot press plate; replace the press plate when the deformation is large; fifth, check the steam path and steam supply of the hot press plate.


④The lumber core plywood is stacked and the core is separated from the seam

The main reasons are: manual core discharging, inaccurate control of the expansion gap between the pieces of veneer; veneer core plywood misalignment when loading or moving; the pre-compression effect is not good, the veneer is not well bonded; the edge of the core plywood is not straight; There are ruffles and cracks on the edge of the core plywood.

Improvement measures: one is to realize the core plywood as a whole or to adopt a secondary gluing process; second, the opening and aging time of the rubber-coated core plywood should be appropriate; third, the slab is pre-pressed and then installed, and the slab is kept stable when moving the slab ; Four is to grasp the timing of pre-pressing; Fifth, the core plywood adopts the leveling process, the core plywood that is cut first and then dried should be flushed after drying; Sixth, the quality of core plywood peeling and drying should be improved.


⑤Panel surface through glue

The main reasons are: too thin glue and too much water; too much water; too deep cracks on the back of the veneer; too high moisture content of the veneer; insufficient slab aging time; excessive pressure during hot pressing.

Improvement measures: First, check the glue quality, increase the resin content of the glue, and choose a formula with less water content; second, reduce the amount of glue, replace the worn rubber roller; third, improve the quality of veneer peeling and adjust the pressure ruler Position, increase the rotary cutting press rate; fourth, reduce the moisture content of the veneer; fifth, increase the aging time, so that part of the water in the glue evaporates; sixth, reduce the heat pressure pressure, check the pressure gauge of the heat press.


⑥Warpage of plywood

The main reasons are: the assembly billet does not conform to the principle of symmetry; the front and back sides of the billet assembly are not correct; the veneer is made from the stressed wood section; the hot plate is warped and deformed; the quality plywood is not stacked flat.

Improvement measures: one is to make the corresponding layer symmetrical when assembling the billet; the other is that the face and the back plate should face outwards when assembling the billet; the third is that the veneer cut out by the rotary cutting should be leveled (softening treatment); the fourth is repair or replace the pressure plate; Fifth, the plywood should be stacked flat.


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