In the plywood production process, hot pressing is a very important process, and the process of shaping the product is irreversible. Once there is a quality problem, especially the bubbling will bring great losses to the company. Therefore, it is necessary to understand and master the causes and prevention methods of the opening and blowing of the rubber during the hot pressing process in order to guide the production and avoid this phenomenon.
Causes and preventive measures for bubble plate generation during hot pressing
1. Medium plate moisture content:
The water content of the middle plate exceeds the process standard and is the main cause of bubbling. The substrate board requires that the moisture content of the eucalyptus medium board is controlled at 8~12%. If it is more than 15%, the hot pressing operator will not take measures, and it is easy to produce the bubble board. Therefore, the first priority in the production of plywood is to strictly control the moisture content of the middle plate, and must meet the requirements of the process.
2, platen temperature:
The temperature of the press plate of the hot press is also the main reason for the bubble plate. The higher the temperature, the more likely the bubble plate is generated. However, in order to ensure the bonding strength or the immersion peel strength of the plywood, a certain temperature must be reached in order to fully cure the glue. For example, triamine gel can't be lower than 105 °C, which creates contradictions. Therefore, temperature control is very important in the production process, and it is necessary to ensure the bonding strength and the bubble board. Generally, the production of the substrate plate should be controlled between 105 ° C and 120 ° C to achieve the double harvest effect. In addition, it is difficult to achieve the same temperature of each of the upper, lower, left and right press plates due to manufacturing and the like, and there is a certain temperature difference. Therefore, in the operation, it is necessary to check the most heat-prone and heat-prone, even if the steam inlet and the drainage of the hot press are adjusted to meet the requirements of the hot pressing process.
3. Pressure relief time:
Since the middle plate contains a certain amount of water, and the water in the glue, the slab still contains a lot of water. The water is not easily discharged during the hot pressing of the pressure plate, so that as the temperature of the slab increases, the high-pressure water vapor formed in the middle of the slab cannot be discharged. When the pressure is released, once the pressure plate is quickly removed, the water vapor will be released due to the sudden drop of external pressure, and the bubble plate will be released. Therefore, the press operator must control the pressure relief speed, slowly lower the pressure plate, so that the water vapor in the blank is gradually discharged, so as not to damage the rubber layer, to avoid the bubble plate, it is best to use manual when unloading.
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