Plywood QC Inspection Checklist : Part 21 How to identify the quality of plywood
The quality of a plywood has a direct impact on its use and use value. Therefore, if we want to do a good job of checking the product quality, we must carry out according to the national standards, so as to achieve a unified understanding. Plywood can be inspected from three aspects: size, appearance quality and physical and mechanical properties.
1. Dimension: Check whether the thickness, length and width of the board, the two diagonals and warpage meet the requirements of the state, especially the length and width. The size of the board can only have positive tolerance, and negative tolerance is not allowed.
2. Appearance quality: According to the national standard, ordinary plywood is divided into four grades according to material defect and processing defect: special grade, first grade, second grade and third grade. The last three grades are the main grades of ordinary plywood. Each grade is determined by visual inspection according to the allowable defects on the panel, and the allowable defects and processing defects of the backplane and inner veneer are limited.
3. Physical and mechanical properties. The national standard stipulates moisture content and bonding strength, which are the two most important items. The national standard stipulates that when using resin adhesives, the moisture content should be controlled in the range of 6-14%, and the bonding strength should be controlled in the range of 0.7-0.8 Mpa.
When inspecting defects, some defects will affect the appearance, such as live joints, cracks, decay, patches, edge defects, etc. According to the occurrence of more or less, as long as within the allowable scope of the standard, it is only product degradation. However, some defects directly affect the strength of products such as bubbling, stratification and so on, which is not allowed in any grade. Some bubbles and layers, if the area is large, can be easily observed by visual observation, but the area is small, not easy to observe, you can use a small stick to beat anywhere on the board, if the board echoes crisp and loud, you can judge that there is no bubbles or layers. If the echo is silent or mute, it indicates that there are bubbles or stratification.
Therefore, the quality of plywood must be judged from the above three aspects.