The Defects of Plywood and the Principle

(1) Gluing defects

Low glue strength-The glue strength of plywood is lower than the standard value. The reason is that the quality of the adhesive is not good; the hot pressing conditions are not well controlled, such as low hot pressing temperature, insufficient pressure or short hot pressing time, low moisture content of the veneer, insufficient glue, poor veneer quality, and improper aging time Wait.

Low wood breakage rate-The wood breakage rate of plywood is lower than the standard value. The reason is that the bonding strength is low, and the quality of the adhesive used does not meet the requirements. Sometimes the hot pressing temperature is low, the pressure is insufficient or the hot pressing time is short, the veneer has a low moisture content, poor quality, and improper aging time will also make the wood breakage rate low.

Bubbling or Gluing-Bubbling means that the steam in the slab destroys the structure of the plywood when the pressure is reduced, forming raised bubbles on the surface of the board, sometimes accompanied by a loud sound. If the failure of the slab is entirely in the glue layer, it can be regarded as glue opening. Sometimes two kinds of defects are difficult to separate exactly. The reasons for this kind of defects are that the pressure drop is too fast and the hot pressing time is insufficient; the moisture content of the veneer is too high or the amount of glue applied is too large; there are blank spots or inclusions and stains on the veneer during glue application; pine with poor air permeability The hot pressing temperature of the plywood is too high.

Gluing the corners-The corners of the plywood are not glued together, and the glue is split. The reasons for this defect are: the aging time of the glued veneer is too long, the corners have dried up and lost activity; the corners are lack of glue; the quality of the glue milling agent is low, and the bonding strength is poor; the quality of the veneer is poor and the thickness is uneven; The edges and corners of the slabs in every single compartment are not aligned, and the slabs are placed skewed and unevenly when the plate is installed; the corners of the pressing plate are worn and the pressure is insufficient, the pressing plate is deformed, and the temperature of the pressing plate surface is uneven.

(2) Structural defects

Plywood warpage-Plywood production warps and deforms. If the board surface is not flat, if the board is placed horizontally, the degree of warpage can be observed through the diagonal. The reason is that the moisture content of the surface and the backboard are inconsistent; the veneer of different tree species is unreasonably matched and violates the principle of symmetry; the veneer has torsion patterns; the temperature of individual hot press boards is not enough; the stacking place is uneven.

Core plate lamination gap-The edge strips of the core board of the plywood are stacked together or separated from a large gap, and obvious streaks and unevenness appear on the board surface. The reasons for this defect are: the reserved gap is too large or too small when the core is manually used for the core; the core plate is misaligned when the plate is installed; the parts are uneven, cracked, or ruffled, etc.

Missing edges and less meat-The plywood case back and core board are insufficient in size, and there are missing edges. The reasons are: the glued assembly of blanks did not achieve "one side and one end"; the table and back panels were small in size and arranged incorrectly; the edges of the plywood were glued or the backing board was glued.

(3) Appearance defects

Adhesive penetration-The adhesive penetrates the plywood, and the defect of glue marks appears on the surface of the board. The reason is; the glue is too thin; the amount of glue applied 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 is insufficient; the slab is too large.

Discoloration of the board-Surface of the plywood has an abnormal color. The reasons are: the glue is too alkaline or acidic, and the wood contains high tannins; the wet veneer is not dried in time in summer, and the surface of the board is moldy; the hot press board leaks.

The information is provided by the plywood factory.