Take Nissei injection molding machine as an example: Injection pressure: 85-98% Holding pressure: 50-80% Injection speed: 60-80% Holding speed: 10-30% Screw speed: 30% Barrel temperature (from nozzle to feeding port): 290, 310, 300, 290°C Mold temperature: 160°C
1. Range of molding conditions
Generally, when molding large parts, the time of each cycle becomes longer, and the residence time of the resin in the barrel also increases, and if it is held for too long at high temperature, the color of the resin will be blacker and the fluidity will be slightly reduced, but it will not have too long effect on the characteristics of the resin. Generally, for the molding of large parts, the barrel should use a lower temperature, while the molding of small parts should use a higher barrel temperature. In order to prevent the weight of the molded product from changing from time to time, adding a certain back pressure (about 5kgs/cm°) is helpful to obtain molded products with stable quality. However, if the resin is placed in the barrel for a long time, it may harden in the barrel, so be sure to avoid this phenomenon, and be sure to wash the resin out after molding.
2. NOZZLE
Molding can be performed using an open nozzle, but in order to prevent nozzle overflow, it is recommended to use a closed nozzle, and the heater of the nozzle is more convenient for molding with a separate controller. The mouth of the nozzle at the beginning should be inverted with an inverted cone of 2-3°, and the diameter should be 3-6φ. The valve is difficult to clean and must be disassembled to remove resin, so it is recommended to use a special nozzle.
3. Drying
The recommended drying temperature is 150-160 ° C for 2-3 hours. If a hot air dryer is used, the height of the raw materials placed in the dish should not be higher than 50mm. If a dehumidification dryer is used, the inlet temperature is -40°C dew point.
4. Injection speed
The injection speed is different, the surface light of the product is different, the faster the speed, the better the surface gloss, but it is easy to warp the product and burn, which must be paid attention to. Generally, medium speed, high injection pressure conditions are used for molding.
Since PPS resin is a crystalline resin, the cooling time is usually extended to improve crystallinity during thick-wall molding, but in thin-wall molding, even if the number of molding at a time is large, 10-30 seconds per cycle is sufficient.
The screw speed during molding is generally 40-100RPM, and although more than 200RPM can be used for high-cycle molding, the resin is easy to heat up at this time, and the barrel temperature must be set lower.
5. Loss of barrel and screw
The loss of barrel and screw can be divided into chemical and physical. PPS does not have chemical corrosion. In terms of physical properties, because the glass fiber contained in it (like other engineering plastics containing glass fiber) causes loss to ordinary barrels and screws, it is necessary to use wear-resistant barrels and screws recommended by forming machine manufacturers, and this kind of barrel and screw are specially designed for processing glass fiber engineering materials. If the temperature of the barrel under the hopper is too high, it will easily lead to an increase in the wear of the barrel and screw.
6. Cleaning after molding
Polyethylene with a low melting index (about 0.2-0.5) is usually used for cleaning of molding, but in order to shorten the cleaning time, polysulfone with high molding temperature is used, polycarbonate (preferably glass fiber reinforced) is effective, and even if recycled products are used, they have sufficient effects. After cleaning with glass fiber reinforced resin, in order to ensure the barrel and screw of the molding machine, it should be cleaned with resin without filling.
