Causes and control measures for warping and deformation of thin particleboard produced by continuous press

With the increasing pursuit of personalization and the diversification of residential apartment types, traditional pre-made furniture is no longer able to meet consumer needs. Custom furniture is gaining popularity. Reducing particleboard thickness or directly using thin particleboard to produce panel furniture components is a major way for custom furniture companies to reduce particleboard consumption. This reduction in the thickness of custom furniture components places higher demands on the quality of the various particleboard specifications used to ensure structural stability and strength.

This paper focuses on analyzing the main quality problems of thin particleboard (hereinafter referred to as thin board) with a thickness of less than 10 mm and their causes, and proposes improvement measures, in order to provide useful reference for particleboard companies to improve product quality.

1. Causes of warping and deformation of thin plates

Particleboard warping refers to the phenomenon that the surface of the board is uneven and deformed in various ways. The problem of warping is particularly prominent during the production and use of thin boards, and its causes are multifaceted.

1) Asymmetric slab paving structure. When the thin plate is laid, the slab structure is asymmetric. After being pressed into the plate, the density difference is too large. The density deviation causes the internal stress of the plate to increase, and eventually causes warping and deformation.

2) Unreasonable hot pressing parameters. Different hot pressing process parameters produce different cross-sectional densities of thin plates. The hot pressing temperature and pressure in the high-pressure zone of the continuous press are too high, resulting in an excessively large cross-sectional density gradient in the thickness direction of the thin plate. The peak of the cross-sectional density curve is too sharp and narrow, making it difficult to ensure symmetry of the cross-sectional density in the thickness direction after sanding, resulting in deformation.

3) Inadequate cooling treatment. After the sheet is hot-pressed, there is uneven stress inside it. If it is immediately stacked without cooling treatment or if the cooling is insufficient, it is easy to cause warping and deformation.

4) Uneven surface sanding. Conventional particleboard has a saddle-shaped cross-sectional density distribution. If the sanding amount on the upper and lower surfaces is inconsistent, the cross-sectional density curve in the thickness direction of the sanded board will be asymmetrical, and the peak deviation between the upper and lower surfaces will be too large, causing the board to warp.

5) Improper stacking and storage: When thin plates are stacked and stored, if the number of pads placed under the plate stack is too small, the distribution is uneven, the spacing is too large, or the pads on the upper and lower stacks are not aligned, the thin plates will become wavy.

2. Measures to control the warping deformation of thin plates

1) Control the symmetry of slab paving. To ensure the dimensional stability of the thin plate, the principle of structural symmetry should be followed when paving the thin plate slab. That is, the size, density, thickness, etc. of the shavings in the corresponding layers on both sides of the symmetrical center plane of the thin plate should be the same or similar.

2) Use a reasonable hot pressing curve. When using a continuous press to produce thin plates, the zone temperature and pressure gradient should be set appropriately. The temperature and pressure in the high-pressure zone should not be set too high to avoid excessive density gradients in the thickness direction of the thin plate.

3) Ensure sufficient cooling of the sheet material. After hot pressing, thin sheets require cooling to blunt the temperature and moisture gradients in the sheet's surface and core layers, reducing internal stress. Due to the rapid production of thin sheets and the limited number of storage compartments in the cooling plate turning machine, the cooling time for thin sheets is limited. To ensure sufficient release of internal stress in the thin sheets, finished thin sheets should be naturally stacked and cooled for at least 2-3 days before sanding.

4) Control the surface sanding amount to be consistent. To ensure uniform thickness and smooth surface of the finished thin plate, the thickness tolerance of the rough plate should be controlled during hot pressing. When sanding, the sanding amount of the upper and lower surfaces should be consistent to ensure that the cross-sectional density curve of the plate in the thickness direction after sanding is symmetrical.

5) Properly stack and store boards. When stacking and storing thin boards, increase the number of pads under the stack and reduce the spacing between them. The pads under each stack should be evenly distributed and aligned. Add a thicker board at the bottom and top of each stack to prevent deformation during storage.