PC characteristics and injection molding process
PC the outstanding performance, high transparency, impact toughness, good creep, using temperature range wide, PC technological characteristic is: melt viscosity shear rate of the sensitivity of the smaller, and the sensitivity of temperature, no significant melting point, molten body viscosity, high temperature resin easily hydrolyzed, products easy to crack. According to these characteristics, we special attention should be paid to differentiate between the: to increase the melt flow, not by increasing injection pressure and improve injection temperature should be adopted to achieve. Requirements of mould flow, gate short and thick, to reduce the pressure of fluid loss, and at the same time higher injection pressure. Resin in forming to fully before the dry processing, make its water content control under 0.02%, in addition, in the machining process of resin insulation measures should be taken to, in case to moisture absorption. Need not only reasonable products design, still should correctly master the molding process, such as improving mould temperature, the products for post-treatment can reduce or eliminate stress. Depending on the product of the different situations timely reset process parameters.
Here's molding process
1, injection temperature must be integrated products shape, size, die structure. Products performance, requirements and so on various aspects of the situation into consideration to make. General use in molding temperature in 270 ~ 320 ℃, and between the high temperature of the material such as more than 340 ℃, the PC will appear decomposition, products dark, the surface appear silver article, dark, black spots, bubble, defects, and physical and mechanical properties also significantly.
2, injection pressure to the PC products of the physical and mechanical properties, stress, molding shrinkage rate, etc have certain effect to the appearance of the products and stripping sex have a major influence, too low or too high injection pressure will make products appear some defects, general injection pressure control in the 80-120 MPa between the thin wall, long process, complex shape, gate of smaller products, in order to overcome the resistance of the melt flow, for timely full of cavity, just choose higher injection pressure (120-145 MPa). To get a complete and smooth surface of products.
3, holding pressure and the holding time holding pressure of the size and the length of time the pressure of the internal stress of PC products have great influence, holding pressure is too small, small shrinkage effect to fill a vacuum bubble or surface appear shrink concave, holding pressure is too large, gate to produce larger internal stress around, in actual processing, often in high temperature material, low pressure solution to. The holding time choice should inspect the thickness of the products, gate size, mold temperature, etc and decide, general small and thin goods does not need a long the holding time, on the contrary, large, thick products the holding time should be long. The pressure the length of time can be through the gate sealing the test time to identify.
4, injection speed on the performance of the PC products without obvious effects, in addition to thin, small runner, deep hole, long process products outside, generally USES the medium speed or slow processing, the best is the multi-level injection, general use a slow-fast-slow multilevel injection mode.
5, mold temperature general control in the 80-100 ℃ can, to complex shape, thinner, demand higher products, but also can be increased to 100-120 ℃, but no more than die heat distortion temperature.
6, screw speed and back pressure due to melt viscosity PC larger, from favorable plasticizing, favorable exhaust, favorable machine maintenance, prevent screw overload, to screw speed requirements cannot too tall, general control in 30 to 60 r/min advisable, and back pressure control in the injection pressure between 10-15% of advisable.
7, PC in injection molding process to strictly control the release agents use, at the same time, the use of raw again no more than three times, use should be 20% or so.