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Plastic molding process performance

by:CSSSLD     2021-01-23
Compatibility refers to two or more different varieties of plastic, in molten state don't separate production ability. If two plastic incompatibility, the mixed molten plastic injection processing parts surface defects such as delamination, peeling. The compatibility of plastic known as blending. By the properties of plastic, can be similar to the comprehensive performance of copolymer, is one of the important ways to improving the performance of plastic. Polycarbonate compatible with ABS plastic, for instance, to join in the polycarbonate ABS can improve its molding process.

plastic molding process refers to the plastic in the molding process of specific performance, influence the molding methods and the selection of process parameters and the quality of plastic parts. Thermoplastic plastic molding process performance include liquidity, shrinkage, thermal stability, moisture absorption and compatibility and so on. The plastic melt in a certain temperature and pressure under the action of filling cavity is called liquidity. The stand or fall of plastic liquidity, to a great extent, influences the molding process of many parameters, such as molding temperature, pressure, the size of the mould gating system and other structural parameters, etc. Size and wall thickness in the design of plastic parts, also want to consider the impact of liquidity.

according to the moisture absorption plastic can be roughly divided into two types: one kind is with wet or adhesion moisture absorption tendency of plastics, such as polyamide, polycarbonate, ABS, polyphenyl ether, polysulfone and so on. Another kind is hygroscopic or adhesion moisture tendency of tiny plastic, such as polyethylene, polypropylene, etc. Before processing molding, plastic is typically after drying, the moisture content control in 0. 2% - 0. Less than 5%. If polycarbonate, moisture content in 0. Below 2%, circulation drum wind drying oven, available at 110 ℃ drying over 12 hours, and will continue to heat preservation in the machining process, to prevent moisture absorption.

the molecular structure of the plastic melt liquid and plastic and additives. Add packing plastic will reduce the liquidity of resin, join plasticizer, lubricant can improve the liquidity. Illiquid plastic, not easy to full of cavity in injection molding, plastic parts produced lack of meat. When using multiple gate, stands at the junction of plastic melt ininjection mould can produce welding due to bad weld marks. These defects can lead to even plastic scrap. If, on the other hand, plastic liquidity is too good, easy to produce flow again when we do the injection delay and cause plastic overflow, molding plastic easy deformation. , therefore, should properly control the liquidity of plastic melt in the process of forming, has obtained satisfactory plastic parts.

the volume of a certain amount of plastic in the molten state than beneath the solid volume is large, to show that the plastic molding and cooling process of the volume contraction, this nature is called contractility. There are many factors which can affect the plastic shrinkage, basically have plastic composition and structure, molding process method, process conditions, plastic parts, geometry shape and the number of metal insert, the mold structure and gate shape and size, etc. Contractility has the size of the unit length of plastics shrinkage percentage, referred to as the shrinkage rate.

thermosetting plastic injection tooling can be made into a certain shape when heated parts. Continue to heat, when the temperature reached a certain degree, the molecules can present the reticular structure, will become not melt or insoluble resin body structure, fixed shape will no longer change. Such as heating again, also won't soften, no longer has the plasticity. Both the physical change in the change process, and there was a chemical change, thus changing process is not reversible. Bakelite, amino plastic, epoxy resin, silicone plastic, such as unsaturated polyester plastic as such.

thermal stability refers to the degree of plastic changes in performance when heated. Some plastic for a long time under a state of high temperature degradation happens, the phenomenon such as decomposition and change color, and make the performance change. Therefore, when this kind of plastic molding processing must be correct control temperature and cycle, choose the appropriate processing equipment or add stabilizer in plastics. Moisture absorption refers to the degree of closeness of plastics on the water.

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