When compression molding of thermosetting plastics in cemented carbide molds, they must be maintained at a certain temperature and pressure for a certain period of time in order to fully cross-link and solidify them into plastic parts with excellent performance. This time is called compression time. The compression time is related to the type of plastic (resin type, volatile matter content, etc.), the shape of the plastic part, the process conditions of compression molding (temperature, pressure), and operating steps (whether to exhaust, pre-pressure, preheating), etc. As the compression molding temperature increases, the plastic solidifies faster and the required compression time decreases. Therefore, the compression cycle will also decrease as the mold temperature increases. The impact of compression molding pressure on molding time is not as obvious as molding temperature, but as the pressure increases, the compression time will also decrease slightly. Since preheating reduces the plastic filling and mold opening time, the compression time is shorter than without preheating. Usually the compression time increases as the thickness of the plastic part increases.
The length of compression time of cemented carbide mold has a great influence on the performance of plastic parts. If the compression time is too short and the plastic is not hardened enough, the appearance and mechanical properties of the plastic parts will deteriorate, and the plastic parts will be easily deformed. Properly increasing the compression time can reduce the shrinkage rate of plastic parts and improve the heat resistance and other physical and mechanical properties of carbide molds. However, if the compression time is too long, it will not only reduce productivity, but also increase the shrinkage rate of the plastic part due to excessive cross-linking of the resin, resulting in stress, resulting in a decrease in the mechanical properties of the plastic part, and in severe cases, the plastic part may rupture. For general phenolic plastics, the compression time is 1 to 2 minutes, and for silicone plastics, it takes 2 to 7 minutes.
What are the principles for selecting cemented carbide mold materials?
1) The performance requirements of the carbide mold should be met. It must have sufficient strength, hardness, plasticity, toughness, etc. to meet the working conditions, failure modes, life requirements, reliability, etc. of the carbide mold.
2) The selected materials should have good processing properties according to different manufacturing processes.
3) The market supply situation should be taken into consideration. Market resources and actual supply situation should be considered. Try to solve the problem domestically with less import, and the varieties and specifications should be relatively concentrated.
4) Carbide molds should be economical and reasonable, and try to use low-priced materials that meet performance and usage conditions.
Post time: Aug-02-2024
