Influence Of Injection Temperature And Speed On Product Shrinkage

1. Two temperature standards that are not conducive to solving shrinking difficulties

1) The temperature of the abrasive tool is too low, which is not conducive to solving the problem of shrinkage

The shrinkage problem of hard plastic products (surface shrinkage and internal shrinkage) is caused by the fact that when the melt is refrigerated and folded, the indoor space left by the centralized folding cannot be fully filled by the melt from the position of the water inlet. Therefore, the factors that are not conducive to feeding are endangering us to solve the problem of shrinking.

Most people know that the temperature of the abrasive tool is too high, which is very easy to cause shrinkage problems. Generally, they like to reduce the temperature of the abrasive tool to solve the problem. But sometimes if the temperature of the abrasive tool is too low, it is not conducive to solving the problem of shrinkage, which is not noticed by many people.

The temperature of the abrasive tool is too low, the melted glue is refrigerated too fast, and the slightly thicker glue position is far from the water inlet. Because the middle part is cooled too fast, the safe passage for feeding is blocked, and it is far more convenient to obtain sufficient melted glue. Filling, making the shrinkage problem more difficult to solve, especially the shrinkage problem of thick and large injection molding products.

Secondly, the temperature of the abrasive tool is too low, which is not conducive to improving the overall shrinkage of the injection molded product, which increases the centralized shrinkage, and the shrinkage problem is more serious and significant.

Therefore, when solving the more difficult shrinkage problems, it is beneficial to also remember to check the mold temperature. Professional and technical personnel with work experience will generally touch the surface of the mold concave mold with force. Each raw material has its suitable mold temperature. For example, the shrinkage problem of PC material, if the credit hole is properly improved, the s hole will be improved, but if the mold temperature is too high, the injection molding product will have the problem of shrinkage.

2) Too low melt temperature is not conducive to solving the problem of shrinkage

It is also known to most people that the melt temperature is too high, and the injection molding product is very likely to cause shrinkage problems. If the temperature is moderately reduced by 10~20°C, the shrinkage problem will be improved.

However, if there is shrinkage in a thicker part of the injection molded product, adjust the melt temperature too low, for example, when it is close to the lower limit of the melt temperature for injection molding, it is not conducive to solving the problem of shrinkage, and even more comparisons will continue. Seriously, the thicker the injection molded product, the more obvious the situation is.

The reason is similar to that of the mold temperature being too low. The melted glue is too cold, and there is no great temperature difference between the shrinking part and the water part, which is beneficial to feeding. The feeding safety channel of the shrinking part will be blocked too early. The solution to the problem is getting more and more difficult. It can also be seen that the faster and faster the melting rate of glue is not conducive to solving the shrinkage problem. PC material is a very fast raw material, so its shrinkage problem can be said to be a big difficulty in injection molding processing. .

In addition, too low melting temperature is also not conducive to increasing the amount of overall shrinkage, resulting in an increase in the amount of centralized shrinkage, which in turn aggravates the problem of shrinkage.

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

2. Too fast injection rate is not beneficial to solve the problem of serious shrinkage

To solve the problem of shrinkage, the first thing that comes to mind is to increase the working pressure of the injection and increase the injection time. But if the injection rate has been adjusted quickly, it is not conducive to solving the shrinkage problem. Therefore, sometimes when the shrinkage cannot be removed, it should be solved by reducing the injection rate in cooperation with each other.

Reducing the injection rate can cause a large temperature difference between the molten glue walking in front and the water entry part, so it is beneficial to the sequential condensation and feeding of the molten glue from far to near, and it is also beneficial to the shrinking part far from the water part. Being filled with higher work pressure will be very helpful in solving difficult problems.

Because the injection rate is reduced, the temperature of the melted adhesive in the front is lower, and the rate has slowed down, and the injection molding product is not easy to cause a sharp edge, and the injection pressure and time can be increased and longer, which is even more It is beneficial to solve the problem of serious shrinkage.

In addition, the actual effect may be more significant if the final stage end filling with slower speed, higher working pressure and longer time and the curing method of gradually slowing down and filling the pressure are used. Therefore, when it is impossible to use a slower rate of injection from the beginning, it is also a very good rescue method to use this method from the middle and late stages of injection.

But it is worth reminding that, the filling is really too slow, but it will not be conducive to solving the problem of shrinking. Because the melt has been completely refrigerated until the die is filled, just like the temperature of the melt is too low, there is simply no ability to compensate for the shrinkage in the distance.