The root cause of processing plastic parts size instability
When the injection molding machine starts to work, the plastic parts will be set in advance. But sometimes there are different sizes of plastic parts, sometimes slightly larger and sometimes slightly smaller. But whether it is large or small, there are differences with the pre-set size, so that the finished product will certainly not be satisfied by customers. Therefore, the injection molding machine manufacturers after analysis found that the plastic parts size instability is mainly related to the improper selection of molding raw materials and the injection molding machine fault.
- improper selection of molding raw materials
The shrinkage rate of forming material has great influence on the dimensional accuracy of plastic parts. If the precision of injection molding machine and mold is very high, but the shrinkage rate of molding raw materials is very large, it is difficult to ensure the dimensional accuracy of plastic parts. Under normal circumstances, the larger the shrinkage rate of forming raw materials, the more difficult to ensure the dimensional accuracy of plastic parts. Therefore, in the selection of molding resin, must give full consideration to the effect of raw material after molding shrinkage on the precision of plastic parts. For the selection of raw materials, the variation range of the shrinkage rate should not be greater than the requirements of the dimensional accuracy of plastic parts.
It should be noted that the shrinkage rate of various resins is different, according to the degree of crystallization of resin analysis. Usually, crystalline and semi-crystalline resin shrinkage rate than the non-crystalline resin, and the shrinkage rate range is also relatively large, and the corresponding plastic parts formed after the shrinkage rate fluctuation is also relatively large. For crystalline resin, high crystallinity, molecular volume reduction, plastic parts of the shrinkage, resin spherulite size also has an impact on the shrinkage rate. The spherulite is small, the gap between molecules is small, the shrinkage of plastic parts is small, and the impact strength of plastic parts is relatively high.
In addition, if the particle size of forming raw materials is uneven, poor drying, recycled material and new material mixing is not uniform, the performance of each batch of raw materials is different, it will also cause the fluctuation of plastic forming size.
- The injection molding machine is faulty
If the plasticizing capacity of the injection molding machine is insufficient, the feeding system is unstable, the screw speed is unstable, the stop action is abnormal, the check valve of the hydraulic system is out of order, the thermocouple is destroyed in the temperature control system, the heater is cut off, etc., all of these will lead to the instability of the molding size of the plastic parts. As long as these faults are found out, targeted measures can be taken to eliminate.
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