Injection Molding Process of PPS Material
Polyphenylene sulfide (PPS) is a high-performance engineering plastic, renowned for its excellent heat resistance, chemical resistance, and electrical insulation properties. It finds extensive applications in electronics, automotive, and aerospace industries. However, due to its high melting point and rapid crystallization rate, injection molding of PPS presents certain challenges.
Key Points in PPS Injection Molding Process
Drying Treatment: PPS is highly sensitive to moisture, which can reduce the melt flow and lead to defects like bubbles and voids in the molded parts. Therefore, PPS raw materials must be thoroughly dried before injection. Vacuum drying at around 170°C for 4-6 hours is commonly used.
Temperature Control: PPS has a high melting point, typically between 285-295°C. During injection molding, the barrel temperature should be set between 290-340°C, and the mold temperature is usually between 140-170°C. Too low a temperature will result in poor melt flow and short shots, while too high a temperature can cause material degradation.
Injection Pressure: The injection pressure for PPS is generally between 80-150 MPa, or even higher. A higher injection pressure helps fill the mold cavity and improve the density of the molded part.
Injection Speed: The injection speed should not be too fast, as excessive speed can lead to weld lines and shrinkage. A moderate injection speed is generally recommended.
Holding Pressure: The holding time and holding pressure significantly affect the dimensional stability of the molded part. Insufficient holding time can cause shrinkage and deformation, while excessive holding pressure can cause internal stress.
Screw Speed: The screw speed should not be too high, as excessive speed can generate shear heat and cause material degradation.
Mold Design: Mold design should consider the shrinkage rate and flow characteristics of PPS. The location of the gate and the design of the cooling system also have a significant impact on the quality of the molded part.
Common Problems and Solutions in PPS Injection Molding
Rough Surface: Possible causes: rough mold surface, excessive injection speed, and low material temperature. Solutions: improve the surface finish of the mold, reduce injection speed, and slightly increase the material temperature.
Shrinkage: Possible causes: insufficient holding time, improper gate location, and low material temperature. Solutions: extend the holding time, optimize the gate location, and slightly increase the material temperature.
Voids: Possible causes: insufficient drying of the material, excessive injection speed, and low mold temperature. Solutions: enhance drying, reduce injection speed, and increase the mold temperature.
Advantages of PPS Injection Molding
Excellent Dimensional Stability: PPS has a low coefficient of linear expansion, resulting in excellent dimensional stability of the molded parts.
Superior Heat Resistance: PPS exhibits excellent heat resistance and can be used in high-temperature environments for extended periods.
Excellent Chemical Resistance: PPS is resistant to corrosion by various chemicals and has good chemical stability.
Excellent Electrical Properties: PPS has excellent electrical insulation and arc resistance.
