1. The mold temperature is too low to solve the shrinkage problem

The shrinkage of hard plastic parts (surface shrinkage and internal shrinkage) are all defects caused by the lack of sufficient space left by the concentrated shrinkage of the melt from the direction of the water inlet when the melt cools and shrinks. Therefore, factors that are not conducive to shrinkage will affect us to solve the shrinkage problem.

Most people know that too high mold temperature can easily cause shrinkage problems, and they usually like 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 shrinkage problem, which is not noticed by many people.

The mold temperature is too low, the melted glue is cooled too fast, and the thicker glue position far away from the water inlet, because the middle part of the cooling is too fast, the feeding channel is sealed, and the melted glue cannot be fully replenished far away , Which makes the shrinkage problem more difficult to solve, especially the shrinkage problem of thick and large injection molded parts.

Moreover, the mold temperature is too low, it is not conducive to increase the overall shrinkage of the injection molded parts, so that the concentrated shrinkage increases, and the shrinkage problem becomes more serious.

Therefore, it is beneficial to remember to check the mold temperature when solving the more difficult shrinkage problem. Experienced technicians usually touch the surface of the mold cavity with their hands. Each raw material has a suitable mold temperature. For example, the shrinkage of PC material, if the mold temperature is too high, the injection molded part will shrink again.

2. Too low melt temperature is not conducive to solving shrinkage problems

Most people also know that if the melt temperature is too high, the injection molded parts are prone to shrinkage. If the temperature is appropriately lowered by 10-20°C, the shrinkage problem will be improved.

But if the injection molded part shrinks in a thicker part, adjust the melt temperature too low, for example, when it is close to the lower limit of the injection melt temperature, it will not help to solve the shrinkage problem, and it will even be more serious. The thicker the piece, the more obvious the situation.

The reason is similar to that the mold temperature is too low. The melt condenses too quickly, and a large temperature difference conducive to feeding cannot be formed from the shrinking position to the nozzle. The feeding channel at the shrinking position will be sealed prematurely, and the problem is solved It becomes more difficult. It can also be seen that the faster the condensation speed of the melt is not conducive to solving the shrinkage problem. PC material is a material that condenses quite quickly, so its shrinkage problem can be said to be a big problem in injection molding.

In addition, too low melt temperature is also not conducive to increasing the amount of overall shrinkage, resulting in an increase in the amount of concentrated shrinkage, thereby exacerbating the shrinkage problem.

Therefore, when adjusting the machine to solve the more difficult shrinkage problem, it is also extremely important to check whether the melt temperature is adjusted too low. In addition to looking at the thermometer, it is more intuitive to check the temperature and fluidity of the melt by air injection.

3. Too fast injection speed is not conducive to solving the problem of serious shrinkage

To solve the shrinkage problem, the first thing that comes to mind is to increase the injection pressure and extend the injection time. But if the injection speed has been adjusted very fast, it will not help to solve the shrinkage problem. Therefore, when the shrinkage is difficult to eliminate, it should be solved by reducing the injection speed.

Reducing the injection speed can make a larger temperature difference between the molten glue walking in front and the water inlet, which is conducive to the solidification and feeding of the molten glue from far to near, and it is also conducive to the shrinkage position far away from the nozzle Obtaining a higher pressure supplement will greatly help solve the problem.

Due to the reduction of the injection speed, the temperature of the leading melt is lower, and the speed has been slowed down, the injection molded parts are not easy to produce front, the injection pressure and time can be increased and longer, which is more beneficial Solve the problem of serious shrinkage.

In addition, the effect will be more obvious if the last-stage end filling with slower speed, higher pressure and longer time and the pressure holding method of slowing down and increasing step by step is adopted. Therefore, when it is not possible to shoot at a slower speed from the beginning, it is also a good remedy to use this method from the later stage of the injection.

However, it is worth reminding that filling is too slow, but it will not help solve the shrinkage problem. Because when the cavity is filled, the melt has been completely frozen, just like the temperature of the melt is too low, there is no ability to feed the shrinkage in the distance.