Mold is the key to obtaining precision plastic products that meet the quality requirements. Whether the mold design is reasonable will directly affect the quality of plastic products.
Since the size of the mold cavity is obtained from the required size of the plastic product and the shrinkage rate of the material used, the shrinkage rate is often a value within a range recommended by the plastic manufacturer or the engineering plastics manual. It is not only related to the gate form of the mold. , The location of the gate is related to the distribution, and is related to the crystal orientation (anisotropy) of the engineering plastic, the shape and size of the plastic product and the distance and position from the gate.
The main factors affecting plastic shrinkage include thermal shrinkage, phase transition shrinkage, orientation shrinkage, compression shrinkage and elastic recovery, etc., and these influencing factors are related to the molding conditions or operating conditions of precision injection molded products.
Therefore, the designer of the mold must have rich experience in design and injection molding, and must consider the relationship between these influencing factors and injection conditions and their apparent factors, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature. , mold structure and gate form and distribution, as well as the influence of gate cross-sectional area, product wall thickness, the content of reinforcing fillers in plastic materials, and the crystallinity and orientation of plastic materials.
The influence of the above factors is also different due to different plastic materials, or other molding conditions such as temperature, humidity, continuous crystallization, and changes in the injection molding machine after molding.
Because the injection molding process is a process of transforming plastics from solid (powder or pellet) to liquid (melt) and back to solid (product). From the pellets to the melt, and then from the melt to the product, the temperature field, flow field and density field must be affected in the middle.
Under the combined action of these fields, different plastics (thermosetting or thermoplastic, crystalline or amorphous, reinforced or non-reinforced, etc.) have different polymer structure morphology and rheological properties.
All factors that affect the above "field" will definitely affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products.
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