Influence of temperature on injection mold and control principle

What effect does temperature have on injection molds? Why does temperature affect the molding of injection molds? How to choose the temperature of the mold reasonably? This article will answer the effect of temperature on mold forming and several principles of temperature control, please read below:

1. The effect of temperature on injection molding

The temperature of the injection mold is a very major variable in the injection molding process. When the mold temperature is too low, the melt fluidity will be reduced, and under injection may occur; the mold temperature affects the crystallinity of the plastic. For ABS, if the mold temperature is too low, the product finish will be low. Compared with plastics and fillers, plastics are more likely to migrate to the surface at high temperatures. Therefore, when the temperature of the injection mold is high, the plastic component will be closer to the surface of the injection mold, the filling will be better, and the brightness and gloss will be higher. However, the temperature of the injection mold should not be too high. If it is too high, it is easy to stick to the mold, and there will be obvious bright spots in the part of the plastic part. If the temperature of the injection mold is too low, it will also cause the plastic part to be held too tightly, and it is easy to strain the plastic part when demoulding, especially the pattern on the surface of the plastic part. For every plastic and plastic part, over one mold surface temperature, one or more adverse effects occur.
                                                                          

On the contrary, when the temperature of the injection mold is too high, the melt will be thermally decomposed, the shrinkage rate of the product in the air will increase, and the product size will become smaller. If the part size becomes larger at low temperature, it is usually due to the low surface temperature of the injection mold. This is because the surface temperature of the mold is too low, and the shrinkage rate of the product in the air is also low, so the size is large. The reason is that the low temperature of the injection mold will accelerate the "freeze orientation" of the molecules and increase the thickness of the melt frozen layer in the mold cavity, while the low mold temperature will hinder the growth of crystals, thereby reducing the molding shrinkage of the product. On the contrary, the injection mold temperature is high, the melt cooling is slow, the relaxation time is long, and the orientation degree is low, which is conducive to crystallization, and the actual shrinkage of the product is large.

 
Because the hotter mold cavity does not freeze plastic that entered the flash edge area before high pressure builds, the melt can flash around the ejector pin and spill into the parting line gap. This shows the need to have good injection rate control, which some modern flow control programmers do. So higher mold temperatures mean less flow resistance, which means faster flow through gates and cavities. Because the injection flow control valve used does not correct for this change, faster filling will cause higher effective pressures in the sprue and cavity, possibly causing flash burrs due to hotter mold cavities that do not freeze those Plastic that enters the flash edge area before high pressure builds up, the melt can flash around the ejector pin and spill into the parting line gap. This shows the need to have good injection rate control, which some modern flow control programmers do. In general, an increase in mold temperature reduces the condensation layer of plastic in the cavity, allowing the molten material to 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 also increase the tensile strength of the part. After reading the effect of temperature on mold forming, let's see how to control the temperature reasonably.

Second, the principle of mold temperature control
In order to ensure the production of plastic parts with high appearance quality requirements, stable dimensions and small deformation within an effective time, the basic principles of mold temperature control should be clearly understood during design.


1. Different rubber materials require different mold temperatures, and molds with different surface qualities and different structures require different mold temperatures, which requires targeted design of the temperature control system.
2. The mold temperature should be balanced, and there should be no local overheating or overcooling. If the temperature of the front mold is higher than the temperature of the rear mold, the temperature difference is generally about 2~3o.
3. The temperature of the front mold with fire pattern requirements is higher than that of the general smooth surface. When the front mold needs to pass hot water or hot oil, the general temperature difference is about 40o.
4. When the actual mold temperature cannot reach the required mold temperature, the mold should be heated up. Therefore, when designing the mold, it should be fully considered whether the heat brought by the rubber into the mold can meet the mold temperature requirements.
5. The heat brought into the mold by the rubber material is consumed by heat radiation and heat conduction, and most of the heat needs to be brought out of the mold by the circulating heat transfer medium.