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Parting Surface in Injection Mould Design

To meet the needs of demoulding of the plastic part and the condensed material in gating system and the need of inserts installation, the mould cavity can be appropriately divided into two or more parts, these touch surfaces that can be separated is called parting surface. In the case of poor mould making and insufficient clamping force, the molten plastic in the injection mould will be extruded through the parting surface to form rather thick flash. Although modified, there will be still obvious marks. Parting surface has various types, and the common ones are horizontal parting surface, step parting surface, oblique parting surface, and special parting surface. The parting surface is generally flat, but sometimes it is necessary to use curved surface and stepped surface for the purpose of convenient demoulding. Although the parting surface processing is complicated, the processing of cavity will be easy.

The quality of parting surface in injection mould has great influence on the plastic part quality and processing process performance. So the following principles should be considered comprehensively when selecting the injection mould parting surface.
  1. Convenient demoulding of plastic parts not only requires the parting surface won’t make plastic parts be stuck in cavity and can’t take out, but also requires the plastic part leave on the side of moving mould when mould opening, so as to convenient for demoulding mechanism design. Therefore, generally the main core is mounted on the side of moving mould to make plastic parts is wrapped on the main core after shrinking, so that the cavity can mounted on the side of fixed mould. If there is insert with hold on the plastic part, or there is no hole on it, the cavity can be designed on the side of moving mould making use of the adhesion of the complex shape to the mould cavity, so as to the plastic parts can be leave on the side of moving mould after mould opening.Injection mould parting surface
  2. The injection mould structure is as simple as possible: If the shape of plastic part is special, designing the parting surface to be flat, the cavity bottom won’t be easy to process. If the parting surface is designed to be bevel or curved surface to make cavity bottom to be horizontal surface, it will be easy to process.
  3. Can make gas in the mould cavity vent smoothly: The main venting method is setting vent slot on the parting surface. So the parting surface should be at the end of melt flow. If the parting surface is too close to the gate, it is easy to cause poor vent. 
  4. Can guarantee the quality of plastic parts: The position of parting surface should be conducive to ensuring the coaxiality of the plastic part, and also to ensuring the dimensional accuracy of plastic part, thereby ensuring the quality of plastic part.
  5. Will not damage the appearance of the product.
  6. The equipment can be fully and reasonably used, and the parting surface should avoid long-distance core pulling: The lateral core pulling of the typical injection mould is achieved by the movement of the mould opening. When the core is pulled by the mould core pulling mechanism, the distance to complete the core pulling is limited within a limited opening stroke. Therefore, for plastic parts with holes or grooves in both directions perpendicular to each other, long-distance core pulling should be avoided.

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