1. Judge the melting temperature of engineering plastics
As we all know, when engineering plastics are processed by injection molding, choosing the right melting temperature is very important for product quality. Generally, the tolerance of melting temperature of engineering plastic injection molding is stricter than that of molding amorphous resin, which shows that the molding conditions of the machine directly affect the final quality of the product.
2.Second, the molding problem caused by the wrong melting temperature
Generally, the melting temperature of engineering plastics is not allowed to be too high or too low. The correct melting temperature of engineering plastics should be within the material's melting temperature distribution range.
It should be known that if the temperature is too high, the polymer will be degraded or decomposed, and the polymer polymer chain will be destroyed. At the same time, additives in the melt glue, such as pigments, impact agents, etc., will also be decomposed together. As a result, the physical and mechanical properties of the product are reduced, various obvious defects appear in the appearance, and an unpleasant odor is produced.
In addition, if the temperature is too low, the material cannot be fully melted, and the polymer structure cannot complete the required homogeneity of the molding, which seriously reduces the impact strength of the product and causes other physical properties of the product to decrease.
In addition, the residence time of the polymer in the tube also plays an important role. Under normal circumstances, the residence time of the polymer in the tube should be 2 to 9 minutes. If the residence time is extended, thermal decomposition may occur even if the melting temperature is set correctly. If the dwell time is too short, the melt glue usually cannot completely reach homogeneity.
3. Product defects caused by incorrect setting of melting temperature
For POM, extreme thermal stress can cause product decomposition. When cleaning the barrel of the injection molding machine, the formation of air bubbles in the melt can be clearly observed. There are other symptoms such as mold mold scale and unpleasant odor.
For PA, discoloration occurs at extreme melting temperatures, and overheating of the nozzle can also cause this result. The thermal decomposition of various PAs reduces the mechanical properties of the product. In the laboratory, thermal decomposition can be confirmed by measuring the melt viscosity, but it should be noted that this method cannot be applied during injection molding.
PBT and PET react more strongly to overheating, which can easily lead to a reduction in product strength. It is difficult to identify whether the melting temperature is appropriate or not based on the appearance of PBT and PET products during molding. Without proper quality control measures, defects are manifested only during the assembly phase or when the part is used. Discoloration of the product indicates a severe defect. Generally, random samples can be tested to confirm the relative strength of the product.
4. Correctly set melting temperature
1) It is not reliable to determine the optimal plastic melting temperature only through the heating temperature setting of the barrel of the injection molding machine, because in addition to the heating ring to increase the melting temperature, the screw friction also generates heat. The amount of heat generated by this depends on the screw shape, speed and back pressure, which affects the melting of the plastic.