The cooling time of the selected parts of the thermosetting injection molding machine accounts for approximately 80% of the production time of the entire injection molding process. Poor cooling often leads to product warping, deformation, or surface defects, which affect the dimensional stability of the product. Scientific allocation of injection and cooling time can improve product quality and productivity.
The cooling time of a workpiece usually refers to the time from when the plastic solution fills the injection mold cavity to when the workpiece can be removed. The Time standard of the parts can be taken out from the mold, usually based on the fact that the parts have been dry and cured enough, have a certain strength and stiffness, and will not deform and crack when the mold is ejected.
Even if the same kind of plastic is used for forming, its cooling time varies with the thickness, the temperature of molten plastic, the temperature of molded parts and the temperature of Injection mold construction. The formula for cooling time has not been clearly calculated in all situations, and is calculated based on appropriate assumptions. The definition of cooling time for thermosetting injection molding machine manufacturing also varies.
At present, the following three standards are generally used as reference for cooling time:
1. The temperature of the central layer at a thick wall of a plastic injection molded part, and the time required to cool to below the thermal expansion temperature of the plastic;
2. The average temperature within the cross-section of plastic injection molded parts, and the time required to cool the product demolding temperature;extrustion blow molding machine.
3. The temperature of the central layer on the wall of crystalline plastic molded parts is relatively thick, and it takes time to cool to below its dissolution point or reach the specified crystallization percentage.
When solving formulas, the following assumptions are generally made:
1. Inject plastic into Injection mold construction and transfer heat to Injection mold construction for cooling;
2. The plastic in the molding cavity is in close contact with the mold core and will not separate due to cooling shrinkage. The heat transfer and flow between the solvent and the mold wall have no resistance, and the temperature at which the melt contacts the mold wall becomes the same. That is to say, when plastic is filled into the mold core, the surface temperature of the part is equal to the mold wall temperature;
3. During the cooling process of plastic injection parts, the temperature of the cavity surface of the Injection mold construction is always uniform;precision core parts
4. The heat conduction level on the surface of the mold processed by the thermosetting injection molding machine is constant; (The melt forming process is regarded as a Isothermal process, and the material temperature is uniform).household plastic mold.
The direction of plastic and the influence of thermal stress on part deformation can be ignored, and part specifications do not affect the condensation temperature.
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