The Effect of Injection Temperature and Speed on Product Shrinkage

1. Too low mold temperature is not conducive to solving the shrinkage problem
The shrinkage problem of hard adhesive parts (surface shrinkage and internal shrinkage) is caused by defects where the space left by concentrated shrinkage cannot be fully replenished by the melt from the water inlet direction during the cooling shrinkage of the melt. So, factors that are not conducive to shrinkage will affect our ability to solve the shrinkage problem.
Most people know that too high a mold temperature can easily cause shrinkage problems, and they usually prefer to lower the mold temperature to solve the problem. But sometimes if the mold temperature is too low, it is not conducive to solving the problem of shrinkage, which is something many people do not pay much attention to. The mold temperature is too low and the melt cools too quickly. The slightly thick glue position far from the water inlet is blocked due to the rapid cooling of the middle part, which prevents sufficient replenishment of the melt in the distance, making it more difficult to solve the shrinkage problem. The shrinkage problem of thick and large injection molded parts is particularly prominent. Furthermore, if the mold temperature is too low, it is not conducive to increasing the overall shrinkage of the injection molded parts, resulting in an increase in concentrated shrinkage and a more severe shrinkage problem. Therefore, when solving difficult shrinkage problems, it is beneficial to remember to check the mold temperature. Experienced technicians usually touch the surface of the mold cavity with their hands. Each raw material has its appropriate mold temperature. For example, the shrinkage problem of PC materials can be improved if the holes are properly sealed, but if the mold temperature is too high, the injection molded parts may experience shrinkage problems.
2. Low melting temperature is not conducive to solving the shrinkage problem
Most people also know that if the melt temperature is too high, injection molded parts are prone to shrinkage problems. By appropriately lowering the temperature by 10-20 ℃, the shrinkage problem will be improved. But if there is shrinkage in a thicker part of the injection molded part, setting the melt temperature too low, such as approaching the lower limit of the injection molded melt temperature, is not conducive to solving the shrinkage problem, and even more serious. The thicker the injection molded part, the more obvious the situation. The reason is similar to the mold temperature being too low. The molten adhesive condenses too quickly, making it difficult to form a large temperature difference between the shrinkage position and the water inlet that is conducive to shrinkage. The shrinkage channel at the shrinkage position will be sealed prematurely, making it even more difficult to solve the problem. From this, it can also be seen that the faster the condensation speed of the melt adhesive, the less conducive it is to solving the shrinkage problem. PC material is a raw material that condenses quite quickly, so its shrinkage problem can be said to be a major problem in injection molding. In addition, too low a melt temperature is also not conducive to increasing the overall shrinkage, leading to an increase in concentrated shrinkage, thereby exacerbating the problem of shrinkage. Therefore, when adjusting the machine to solve the difficult shrinkage problem, it is extremely important to check whether the temperature of the melt adhesive has been adjusted too low. In addition to checking the temperature gauge, it is more intuitive to check the temperature and fluidity of the melt adhesive using air injection method.
3. Excessive glue injection speed is not conducive to solving the problem of severe shrinkage
To solve the shrinkage problem, the first thing to think of is to increase the injection pressure and extend the injection time. But if the injection speed has been adjusted very fast, it is not conducive to solving the shrinkage problem. Therefore, sometimes when shrinkage is difficult to eliminate, it should be solved by reducing the injection speed. Reducing the injection speed can create a significant temperature difference between the molten adhesive walking in front and the water inlet, which is conducive to the sequential solidification and shrinkage of the molten adhesive from far to near. At the same time, it is also conducive to obtaining higher pressure replenishment at the shrinkage position far from the water inlet, which will be of great help in solving the problem. Due to the decrease in injection speed, the melt temperature ahead is lower and the speed has slowed down, making it difficult for injection molded parts to produce batch edges. The injection pressure and time can be further increased and extended, which is more conducive to solving the problem of severe shrinkage. In addition, if the last stage end filling with slower speed, higher pressure, and longer time is used, and the pressure maintaining method of gradually slowing down and pressurizing is adopted, the effect will be more obvious. Therefore, when it is not possible to use a slower speed for glue injection from the beginning, using this method from the later stage of glue injection is also a good remedy. However, it is worth reminding that filling too slowly can actually be detrimental to solving the problem of shrinkage. Because by the time the mold cavity is filled, the melt has completely frozen, just like the melt temperature is too low, there is no ability to compensate for the shrinkage in the distance anymore.