It is very common for the shrinkage of PP ( Polypropylene) plastic profiles due to the various external reasons during plastic extrusion manufacturing. However, this defective rate can be minimized with appropriate cooling temperature and post-treatment process. There are three main manifestations of the shrinkage of pp plastic profiles.
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1. Plastic extrusion dies design: For multi-gate molds, the filling speed of each gate should be adjusted, and it is better to open gates symmetrically. The key parts of the mold should be effectively set with cooling water channels to ensure that the cooling of the mold has a good effect on eliminating or reducing shrinkage. The entire mold should be free of burrs and have mold-closing sealability, which can withstand high-pressure, high-speed, and low-viscosity melt filling.
2. Plastic extruder equipment: insufficient material supply. The screw or plunger is severely worn, and the molten material leaks duringextrusion and pressure holding, which reduces the filling pressure and material volume, resulting in insufficient molten material. The nozzle hole is too large or too small. If it is too small, it is easy to block the feed channel, and if it is too large, the injection force will be small and mold filling will be difficult.
3. Extrusion technology- Increase injection pressure, hold pressure, and extend injection time.
For plastics with high fluidity, high pressure will produce flash and cause collapse. The material temperature should be appropriately lowered as well as the front section of the barrel and the nozzle. So that the volume of the molten material entering the cavity is reduced, and it is easy to freeze. For high-viscosity plastics, we should increase the barrel temperature to make the fast filling. When shrinkage occurs in the gate area, the dwell time should be extended. Increasing the injection speed can more easily fill the pp plastic profile and eliminate most of the shrinkage.
Thin-walled pp plastic profiles should increase the mold temperature to ensure smooth material flow; Thick-walled parts should reduce the mold temperature to accelerate the curing of the skin.
Low-precision products should be removed from the mold as soon as possible and allowed to cool slowly in the air or hot water so that the shrinkage and depression can be smooth without affecting the use.
4.Thermalresin raw materials: raw materials are too soft and prone to dents. An effective method is to add a nucleating agent to accelerate crystallization.
Dongguan H.D. plastic products are specialized in the production of extruded plastic profiles and tubing. We can customize and process a variety of plastic profiles, PVC profiles, abs profiles, pp profiles, PC lampshades, transparent plastic profiles.