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Compression molding process parameters

by:CSSSLD     2021-01-23
When compared with the compression molding, injection molding, plastic before entering the cavity is plasticizing, therefore can produce complex shape, thin wall or wall thickness change is very big, injection molding processing parts with fine insert. Because of the plastic in the mold pressure-keeping hardening time is shorter, so can shorten the molding cycle, improve production efficiency, the density of plastic parts and strength are improved. Before due to the plastic molding mold closed completely, the parting surface flash is very thin, and plastic parts to ensure accuracy, surface roughness value is low.

in a certain temperature range, mold temperature, shorten the molding cycle, improve production efficiency. If the mold temperature is too high, will make the resin and organic matter decomposition, on the surface of the plastic color will be dark. Because of the influence of outer plastic hardening first, the flow of material, will cause the molding, especially the moulded complex shape, thin wall and deep plastics is most obvious. At the same time, because of moisture and volatile matter is difficult to eliminate, plastic stress is big, the mold opens, prone to swelling and cracking, warp, etc.

also known as transfer molding, injection molding is developed on the basis of the compression molding of a kind of thermosetting plastic molding method. Injection molding, the thermosetting plastic raw material into a closed mold of indoor feeding, in the charging indoor heated plasticizing. Under the action of stress, the plastic melt through the loading chamber bottom gating system, into a closed cavity. Plastic inside the cavity continue to heat, pressure and curing, and then open the mold to take out the plastic parts.

if the mold temperature is too low, the long cycle of hardening and hardening is insufficient, will light on the surface of the plastic, its physical performance and mechanical performance degradation. Thermosetting plastic compression molding, want to keep some time under a certain temperature and pressure, can make its full of crosslinking curing, become a good performance of plastic parts, this time become a compression of time. Compression time and the types of plastic, plastic pieces of shape, compression molding technological conditions and operating steps and so on.

compression molding temperature, plastic curing speed, the compression time is reduced, thus the compression cycle mould temperature increase will also decrease. Compression molding pressure for moulding time less than the influence of moulding temperature, but with the increase of pressure, the compression of time will be reduced slightly. Because the preheating can reduce the time of plastic molding and mould, so the compression time is shorter than when no preheating, usually compressed time will increase with the increase of the thickness of the plastic parts.

compression molding temperature affect the plastic melt in the molding whether smoothly, also affect the forming of hardening speed, then the quality of the injection molding processing. Gradually with the increase of temperature, the plastic solid powder melting, viscosity from big to small, start crosslinking reaction, when its liquidity there was a peak along with the rise of temperature, increases the molding pressure, make plastic when temperature is not high and liquidity larger parts of cavity.

the length of the compression time had a great influence on the performance of the molded parts. Compression time is too short, plastic hardening is insufficient, will enhance the appearance of plastic parts performance, mechanical performance, easy to deformation. Appropriate increase the compression time, can reduce the plastic shrinkage rate, improve its heat resistance and other physical and mechanical properties. But if the compression time is too long, not only reduce the productivity, but also because of excessive shrinkage plastic resin crosslinking increased, to produce stress, resulting in a decline in plastic mechanics performance, serious when broken plastic. General bakelite, compression time is 1 - 2-2 min, organic silicon plastic 7min。

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