Causes and Prevention Measures of Plywood Bubbling in China
In the plywood production process, hot pressing is a very important process, which is an important process to finalize the product. It is irreversible. Once quality problems occur, especially bubble will bring great losses to the company. Therefore, it is necessary to understand and master the causes and prevention methods of blistering during hot pressing to avoid this phenomenon.
Causes and preventive measures of blisters during hot pressing
- Water content of medium plate:
The water content of the medium plate exceeds the process standard, which is the main reason for bubbling. The moisture content of eucalyptus medium plate is required to be controlled at 8-12% for the base material plate. If it reaches above 15% and the hot pressing operator does not take measures, it is easy to produce blisters. Therefore, the first priority of plywood production is to strictly control the moisture content of the middle board, which must meet the requirements of the process regulations.
- Pressing plate temperature:
The high and low temperature of hot press pressing plate is also the main reason for producing blisters. The higher the temperature is, the easier it is to produce blisters. However, in order to ensure the bonding strength or immersion peeling strength of plywood, and to fully cure the glue solution, a certain temperature must be reached. For example, the temperature of the triamine adhesive should not be lower than 105 ℃, which will lead to conflicts. Therefore, the temperature control is very important in the production process. It is necessary to ensure the bonding strength and not produce foam board. Generally, the production of base plate should be controlled between 105 ℃ and 120 ℃ to achieve the effect of double harvest. In addition, due to manufacturing and other reasons, it is difficult for hot press platen to reach the same temperature of upper, lower, left and right platens, and there is a certain temperature difference. Therefore, during the operation, pay attention to the adjustment of the steam inlet and drainage of the hot press to make it meet the requirements of the hot pressing process.
- Pressure relief time:
Because there is some water in the middle plate, plus the water in the glue solution, there is still a lot of water in the plate embryo. It is not easy to discharge the water during the closed hot pressing of the pressing plate, so as the slab temperature increases, the high-pressure water vapor formed in the middle of the slab cannot be discharged. When the pressure is released, once the pressing plate is quickly removed, the water vapor will burst through the rubber layer and release due to the sudden drop of external pressure, resulting in foam plate. Therefore, the press operator must control the pressure relief speed, slowly lower the pressure plate, so that the moisture in the plate embryo is gradually discharged, so as not to damage the adhesive layer, so as to avoid blistering. It is better to use manual pressure relief.
