Precautions for molding injection-grade TPR soft rubber
Source：德創(chuàng)化工Time：2021-01-06Hits：2723
Before the newly purchased TPR injection molding machine is used for the first time, or when it is necessary to change products, raw materials, colors or plastic decomposition in production, the injection molding machine needs to be cleaned or taken out. The heating barrel cleaning method is generally used when cleaning the injection molding machine. Cleaning materials usually use plastic raw materials. For TPR materials, transitional cleaning materials can be replaced by newly processed materials.
The molding temperature of injection grade tpr injection is the key to determine the appearance and performance of products in the process of processing TPR molding. The following are some suggestions on temperature setting in tpr process of injection molding. The temperature in the feeding area should be set very low, so as not to block the feeding inlet and escape the entrained air. In order to improve the mixing state when using masterbatch, the temperature of transition zone should be set above the melting point of masterbatch. The temperature of the area closest to the nozzle should be set close to the required melting temperature. Therefore, after testing, the general temperature setting range of injection-molded tpr products in each area is 160℃ to 210℃ for the barrel and 180℃ to 230℃ for the nozzle.
Generally, the injection pressure control of injection TPR is divided into primary injection pressure, secondary injection pressure (holding pressure) or more than three injection pressures. Whether the timing of pressure switching is appropriate is very important to prevent excessive pressure in the mold, flash or lack of materials. The specific volume of the molded product depends on the melt pressure and temperature when the gate is closed during pressure.
When switching from maintaining pressure to cooling stage, if the pressure and temperature are the same every time, the specific volume of the product will not change. At a constant molding temperature, packing pressure is an important parameter to determine product size, and packing pressure and temperature are important variables to influence product size tolerance. For example, after filling the mold, the holding pressure will decrease immediately, and when the surface layer has a certain thickness, the holding pressure will increase again. In this way, larger thick-walled products can be formed with lower clamping force, thus eliminating shrinkage cavity and flash.
The cooling time mainly depends on the melt temperature, product wall thickness and cooling efficiency of injection TPR. In addition, the hardness of injection TPR material is also a factor. Compared with the very soft varieties, the harder varieties cure faster in the mold. If cooling is performed from both sides, the cooling time per 0.100 inch wall thickness is usually about 10 to 15 seconds. Encapsulated products require a longer cooling time because they can be cooled effectively with a smaller surface area.
