Views: 31 Author: Site Editor Publish Time: 2021-04-07 Origin: Site
In the process of plastic injection molding, custom plastic injection molds will encounter common problems such as oil stains, drape, and whitening in the custom plastic parts produced in China. So how to control the production of these defective products? This requires our technicians to be familiar with the temperature of various raw materials, and at the same time adjust and control the injection molding tooling temperature accordingly according to the characteristics of the raw materials. So, what are the precautions when adjusting the mold temperature?
How to control the temperature of injection molding tooling
The temperature of injection molding tooling is the most important variable in injection molding. No matter what kind of plastic is injected, the mold surface must be basically moist. A hot mold surface keeps the plastic surface liquid for a long time, enough to be in the cavity Build up pressure. If the cavity is filled and before the frozen skin hardens, the cavity pressure can press the soft plastic against the metal, then the surface replication of the cavity is high. On the other hand, if the plastic entering the cavity under low pressure is suspended, no matter how short the time is, then its slight contact with the metal will cause stains, sometimes called gate stains.
For every type of plastic and plastic parts, there is a limit to the surface temperature of the mold. If this limit is exceeded, one or more adverse effects may occur (for example, components can overflow with burrs). Higher mold temperature means less flow resistance. On many injection molding machines, this naturally means faster flow through the gate and cavity, because the injection flow control valve used does not correct this change, and faster filling will cause a higher efficiency in the runner and cavity Pressure may cause flash burrs. Since the hotter model does not freeze the plastic that enters the flash side area before the high pressure is formed, the melt can flash burrs around the ejector rod and overflow into the gap of the dividing line. This shows the need for good injection rate control, and some modern flow control programmers can indeed do this.
Generally, the increase in mold temperature will reduce the condensation layer of the plastic in the cavity, and make the molten material flow more easily in the cavity, resulting in greater part weight and better surface quality. At the same time, the increase in mold temperature will increase the tensile strength of the parts.
Matters needing attention in controlling the temperature of injection molding tooling
1. The temperature of each part of the forming mold after heating should be uniform to ensure that the melt has a better filling quality, so that the molding quality of the injection molded product is guaranteed, and the qualified rate of the injection molded product is improved.
2. The process temperature adjustment of the mold body should be determined by the viscosity of the melt. When the higher viscosity melt is injected into the mold, the temperature of the mold body should be adjusted slightly higher; while the lower viscosity melt is used to fill the mold. The temperature of the mold body can be appropriately lowered. When preparing for injection production, the temperature of the mold body must be within the range of process requirements. In order to ensure the uniform temperature of the mold body, the mold body heated to the temperature required by the process should be kept at a constant temperature for a period of time.
3. When injection molding large plastic products, due to the large amount of molten material used for molding, the melt flow channel is relatively small, and the large mold body must be heated and moisturized at the melt flow channel to prevent the melt flow due to the long melt flow channel. When the temperature is lowered, the viscosity of the melt is increased, which slows down the material flow, affects the quality of the melt injection and mold filling, and even causes the melt to cool and solidify in advance, making the injection work of the injection molding machine impossible.
4. In order to reduce the temperature of the melt due to the long melt flow path and increase the heat energy loss, a heat insulation and moisture-retaining layer should be added between the low temperature part of the mold cavity and the high temperature part of the melt flow path.
The correct control of the injection molding tooling temperature directly affects the output quality of this product. Therefore, it also emphasizes that in addition to advanced machinery and equipment, we also need to find a group of good technical adjusters. It is equally important to fully coordinate the equipment and talents, and deliver the products according to quality and quantity on time. This is a plastic injection molding. Manufacturer's long-term sustainable development plan.