Mold temperature and the relation of plastic molding
Plastic resin to plastic injection moulds and the natural convection heat into the air die mold heat, radiation heat to the air and the mold to the injection molding machine heat difference, is the diffusion of mold heat with cooling water.
If the plastic resin in the mould all the heat released from cooling water conduction, heat transfer factors, namely ignore other then the mould cooling water volume flow formula available as needed.
the thermoplastic melt injection into the mold, must be within the mold cooling solidification can be referred to as the plastic parts, so the mould temperature must be lower than injection into the mold cavity of the temperature of the molten resin, which meet the following a certain temperature range.
In order to improve the efficiency of molding, usually by shorten the cooling time of the methods to shorten the molding cycle.
Because the performance characteristics of the resin itself is different, so different plastics have different mold temperature.
the design of the cooling circuit should be medium flow in circuit system can fully absorb heat conduction with molding plastic parts, keep the molding temperature on the surface of the stable at the required temperature range, and to make the cooling medium in open loop system flows, without the stranded part.
Determining the diameter of the cooling hole should be paid attention to, no matter how much the mold, the diameter of the hole is not greater than 14 mm, otherwise the cooling water is difficult to be turbulent state, to reduce the heat exchange efficiency.
Generally the diameter of the hole according to the average wall thickness of plastic parts to determine.
for low viscosity, liquid plastic, such as polyethylene, polystyrene, polyamide, due to the molding process requirement temperature is not too high, so common room temperature of mould cooling water, sometimes in order to further shorten the cooling time in mould, and the condensation of cold water after processing can be used for cooling.
For plastic high viscosity, poor liquidity, in order to improve the filling performance, considering the molding process requires a higher mold temperature, so often need to heat the mold.
for viscous flow temperature or low melting point plastic, generally need to use cold water or cold water to the mold cooling, temperature and high melting point for the viscous flow of plastic, use warm water to mold temperature control.
Asked in 150 - for thermosetting plastics, mould
200 ℃, the mould must be heated.
For long process, wall thickness smaller parts, or viscous flow temperature and melting point though is not high, forming a very large area of plastic parts, in order to ensure that the plastic melt in the molding process of filling, not too much temperature drop and influence can be installed heating device for mould preheated.
the mold temperature is to point to the surface temperature of the mold cavity and core.
Mold temperature is appropriate, uniform and stable, molding of plastics melt flow, curing and finalize the design, production efficiency and the shape of the injection molding processing, appearance and dimensional accuracy has important influence.
Mold's purpose is to through the set temperature control system control the temperature of the mold, the injection molding plastic parts with good quality and high production efficiency.
for the small thin wall plastic parts, and molding technological requirements when the temperature is not too high, can not set the cooling device and rely on natural cooling.
After the set temperature control device, sometimes will bring some problems to the production of injection molding, for example, use cold water to adjust mould temperature, condensation of moisture in the atmosphere are easy in mold cavity wall, affect surface quality of plastic parts, and after heating measures, die within some clearance fit of the parts may be due to inflation and make the gap decrease or disappear, causing stuck or unable to work, when the design should be pay attention to these problems.
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