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Temperature Control Of Injection Mold
Jul 09, 2018

The design of injection mold cooling systems is often considered a secondary issue. No attention has been paid to the size and structural design of the cooling system. The design of the cooling system is unreasonable, and internal stress will be generated for small plastic parts. For large plastic parts with thin walls, deformation or even stress cracking will occur. Moreover, insufficient cooling can result in prolonged molding cycles, thereby reducing production efficiency. In the following, in some simplified forms, the complex cooling process of the injection mold is studied, practical formulas are derived, and methods for determining the size of the cooling system are discussed based on these formulas. Determining the size of the cooling system is certainly not a simple task. In general, mold designers are still unfamiliar with certain aspects. This kind of work is very complicated, and even in the technical literature, it is difficult to find a satisfactory answer to some problems. Some of the heat transfer equations are known, and computers and pocket programmable calculators can now be used to solve these equations. Despite this, the situation encountered in practical problems often brings difficulties to the solution of the problem. For example, the cavity walls are periodically heated by the injected high temperature plastic melt. As a result, the temperature difference between the mold and the cooling water is increased, and the cooling effect becomes stronger. After the mold is opened and the plastic part is ejected, the cavity is cooled by the surrounding air. Therefore, the temperature of the surface of the cavity changes periodically. The solution to the problem becomes more difficult because the injected high temperature plastic melt only contacts the cavity of the mold, while the entire mold is cooled by the cooling water of the cooling passage. Further, the cooling water is heated while passing through the cooling passage of the mold, thereby changing the temperature difference between the mold and the cooling water. The structural composition of the injection molding die can be divided into the following parts: the molding part, the mold guiding part, the product pushing part, the core drawing part, the heating and cooling part of the mold body, the supporting part of the mold body, and the pouring melt channel and row Stomata, etc. (1) Forming part. That is, the mold assembly directly forms a cavity part of the plastic product, and has a punch, a die, a core, a rod or an insert. (2) Clamping guide part. It is a component that is set to correctly align the center axis when clamping the movable and fixed molds, and has a guide post, a guide hole sleeve or a beveled tapered member, etc. (3) The product push-out portion. It is the component used to push the molded injection product out of the molding cavity, including the ejector rod, the fixing plate, the push plate and the spacer. (4) Core extraction part. When the plastic product with the pit or the side hole is injection-molded, the core mechanism parts for the pit and the side hole forming are first extracted, such as the inclined guide column which is frequently used, and 5) the heating and cooling portion of the mold body. It refers to the control system that adapts to the temperature of injection molding process of plastic products, such as resistance heating plate, rod and its electronic control components; circulating cooling water pipe for cooling part. (6) The support portion of the mold body. Refers to the auxiliary parts to ensure the correct working of the mold body, such as moving, fixed mold pad, positioning ring, lifting ring and various fastening screws. (7) Casting the melt channel. It refers to the flow path that can guide the molten material injected through the nozzle to the cavity of the molding die, and can be generally divided into a main channel, a branching channel, a bushing port (gate) and a cold trough. (8) Vent hole. It refers to the part that can discharge the air in the mold cavity. In general, small products may not have a dedicated vent hole, and the air in the cavity may be discharged from the gap of each fitting; for a mold for a large injection product, a vent hole must be provided.


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