1. Cause
If the slab surface is uneven after paving, the slab after hot pressing will show an asymmetric structure. In this way, the density difference after pressing into a plate is too large, which causes an increase in the internal stress of the plate, and finally produces warpage deformation.
2. Solutions
In order to ensure the dimensional stability of particleboard, the principle of structural symmetry should be followed during slab paving, that is, the particles on both sides of the symmetrical center plane of the particleboard should be made of materials with similar tree species, thickness, density and size as possible. When setting the parameters of the paving process, the proportion of shavings on the upper surface should be appropriately increased.
Second, the moisture content of the board
1. Cause
In board production, if the particleboard is partially dried or sizing is uneven, the moisture content of the shavings in the surface and core layer of the particleboard will be unstable, which will cause the warpage of the board.
2. Solutions
In order to stabilize the moisture content of the shavings after sizing, raw materials with similar moisture content should be selected to keep the surface of the board smooth and flat, and the gluing should be kept as uniform as possible.
If the slab surface is uneven after paving, the slab after hot pressing will show an asymmetric structure. In this way, the density difference after pressing into a plate is too large, which causes an increase in the internal stress of the plate, and finally produces warpage deformation.
2. Solutions
In order to ensure the dimensional stability of particleboard, the principle of structural symmetry should be followed during slab paving, that is, the particles on both sides of the symmetrical center plane of the particleboard should be made of materials with similar tree species, thickness, density and size as possible. When setting the parameters of the paving process, the proportion of shavings on the upper surface should be appropriately increased.
Second, the moisture content of the board
1. Cause
In board production, if the particleboard is partially dried or sizing is uneven, the moisture content of the shavings in the surface and core layer of the particleboard will be unstable, which will cause the warpage of the board.
2. Solutions
In order to stabilize the moisture content of the shavings after sizing, raw materials with similar moisture content should be selected to keep the surface of the board smooth and flat, and the gluing should be kept as uniform as possible.
Three, hot pressing process problems
1. Cause
During hot pressing, the heat transfer is from the inside to the outside, so there is a high-to-low temperature gradient from the surface layer to the core layer of the slab. Therefore, if the upper and lower platens use the same temperature under the same pressure, the heat of the upper and lower surfaces of the same platen will be inconsistent, resulting in inconsistent curing strength of the two surface layers of the particleboard, resulting in unbalanced internal stress, which will cause the particleboard to warp. warp deformation.
2. Solutions
To correctly grasp the hot pressing process and the temperature change of the platen, it is necessary to adjust the temperature of the platen according to the actual production situation, so that the upper and lower surface layers of the slab have the same degree of curing and similar strength, and avoid different internal stresses. In addition, the slab can be processed by high-frequency preheating and steam spraying before hot pressing to increase the temperature of the core layer, so that the cross-sectional density of the slab tends to be uniform.
Fourth, the surface sanding problem
1. Cause
The profile density distribution of conventional particleboard is "saddle-shaped". If the sanding amount of the upper and lower surfaces is inconsistent, the profile density curve in the thickness direction of the board after sanding is asymmetrical, and the upper and lower peak deviations are too large, and the board will warp and deform.
3. Solutions
The thickness tolerance of the rough board should be controlled during hot pressing. When sanding, try to make the sanding amount of the upper and lower surfaces the same, so that the profile density curve in the thickness direction of the board after sanding is symmetrical. This can ensure that the thickness of the board is uniform, and the board surface is smooth and clean.
1. Cause
During hot pressing, the heat transfer is from the inside to the outside, so there is a high-to-low temperature gradient from the surface layer to the core layer of the slab. Therefore, if the upper and lower platens use the same temperature under the same pressure, the heat of the upper and lower surfaces of the same platen will be inconsistent, resulting in inconsistent curing strength of the two surface layers of the particleboard, resulting in unbalanced internal stress, which will cause the particleboard to warp. warp deformation.
2. Solutions
To correctly grasp the hot pressing process and the temperature change of the platen, it is necessary to adjust the temperature of the platen according to the actual production situation, so that the upper and lower surface layers of the slab have the same degree of curing and similar strength, and avoid different internal stresses. In addition, the slab can be processed by high-frequency preheating and steam spraying before hot pressing to increase the temperature of the core layer, so that the cross-sectional density of the slab tends to be uniform.
Fourth, the surface sanding problem
1. Cause
The profile density distribution of conventional particleboard is "saddle-shaped". If the sanding amount of the upper and lower surfaces is inconsistent, the profile density curve in the thickness direction of the board after sanding is asymmetrical, and the upper and lower peak deviations are too large, and the board will warp and deform.
3. Solutions
The thickness tolerance of the rough board should be controlled during hot pressing. When sanding, try to make the sanding amount of the upper and lower surfaces the same, so that the profile density curve in the thickness direction of the board after sanding is symmetrical. This can ensure that the thickness of the board is uniform, and the board surface is smooth and clean.
