Mold Tech

Polystyrene PS Injection Molding

• 2021-08-13

Polystyrene (PS, GPS) is commonly known as ordinary styrene hard plastic which is transparent and belongs to translucent plastic (with greater density than water, fragility).

The properties of PS include good optical performance 88%-92%, excellent electrical performance, easily molding and processing and good colorability. Its disadvantages include fragility, low temperature of heat-resisting, high requirements for processing and molding conditions (distinct Aging and great sensitivity to heat) weak acid resistance, easy to burn. If there is no fire source and it will burn continually with yellow color, thick black charcoal, blistering, and monosomy.

Viscosity is sensitive to the velocity of shear. With the increase of pressure, melt viscosity decreases. Therefore, considering internal stress factors which are easy to produce, which means injecting into the cavity with high speed in the ideal molten state, the pressure should not be overloaded.

The processing temperature ranges from 176-260 Celsius degree and the melting point is 225 Celsius degree. Injection temperature of molding should not be too high, and the temperature of feed cylinder is distributed as low in the entrance, less high in the middle and the highest in the outlet, as well as twice high at the nozzle.

Time of mold opening can be a little early and adjust dwell time appropriately (Big gate products) as its solidification speed is faster than other plastics.

When demoulding, it should pay attention to clean the gate wire and should not drag out it in the way of mould closing by violence. For the production of usual internal stresses, it can be immersed in the sink (65-80 Celsius degree) for 1-3 hours after demoulding.

HIPS or IPS is commonly known as unbroken PVC, unbroken hard rubber or unbroken rubber.
Raw materials of MPS are not transparent, which are yellow or milky white and easy to be processed and colored. It has strong tenacity and greater impact strength of flexibility, similar to the high elastic rubber (injection pressure and molding temperature should be high).

SAN is commonly known as transparent and unbroken plastic, which has high softening temperature and shock temperature, high resistance to stress. Cracking, wear resistance, chemical stability, dry resistance, heat resistance, corrosion resistance, oil resistance are better, with stable size and easy molding.

Modified polymethyl methacrylate plastics have similar transparency with polymethyl methacrylate, good toughness and some certain impact-resistance temperature, abrasive resistance, poor chemical stability, dry resistance, heat resistance, corrosion resistance, oil resistance, stable size, and easy molding.

For the cooling rate, HIPS is slower than PS. It requires enough dwell pressure and dwell time, intensifying the heat exchange of mold and providing enough cooling condition.

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