Influence of injection temperature and speed on product shrinkage

Table of Contents

The injection temperature and speed have an important effect on the shrinkage of the product. If the injection temperature is too low, the shrinkage of the product will be too high. If the injection temperature is too high, the shrinkage of the product will be too low. 

The same is true for the injection speed. If the injection speed is too low, the shrinkage of the product will be too high. If the injection speed is too high, the shrinkage of the product will be too low. Therefore, it is important to control the injection temperature and speed to achieve the desired product shrinkage.

Influence of injection temperature on product shrinkage

The injection temperature has a great influence on the shrinkage rate of the product. The higher the injection temperature, the lower the shrinkage of the product. 

The effect of injection temperature on product shrinkage is due to the different crystallinity of the polymer at different temperatures. At lower temperatures, the polymer has a higher crystallinity, which leads to higher product shrinkage. 

On the other hand, at higher temperatures, the polymer has lower crystallinity, which leads to lower product shrinkage. Therefore, it can be said that the injection temperature plays an important role in determining the shrinkage of the product.

Effect of injection speed on product shrinkage

The speed of injection affects the size of the product in various ways. In general, the faster the injection speed, the smaller the size of the product. The main reason for this is that faster injection speeds result in shorter cooling times and therefore less time for crystallization to occur. 

This results in smaller, more amorphous products. In addition, the faster injection may also lead to a higher degree of molecular orientation, which further reduces the size of the product. Finally, a rapid injection may lead to voids or defects in the product, which can also reduce its size. 

Therefore, it is generally preferable to use a slower injection rate to avoid product shrinkage. However, in some cases, faster injection speeds may be necessary to achieve the desired degree of crystallization or orientation.

How can the injection process be optimized to achieve the desired level of shrinkage?

The injection molding process is complex and requires precise control to achieve the desired level of shrinkage. To optimize the plastic injection molding process, it is important to understand the factors that affect shrinkage. 

These factors include melt temperature, cooling rate, mold temperature,ure, and gate size. By controlling these variables, it is possible to achieve the desired level of shrinkage. 

It is also important to use a high-quality release agent to prevent sticking and to ensure consistent surface quality of the finished product. By following these tips, it is possible to optimize the injection molding process and achieve the desired level of shrinkage.

The mold temperature is too low to solve the problem of shrinkage

The problem of shrinkage of hard plastic parts (surface shrinkage concave and internal shrinkage hole) is caused by the defect that the space left by the concentrated shrinkage is not adequately replenished by the melt from the direction of the water inlet when the melt is cooled and shrunk. 

Therefore, the factors that are not conducive to shrinkage replenishment will affect us to solve the shrinkage problem.Most people know that the mold temperature is too high to produce shrinkage problems, and usually like to reduce the mold temperature to solve the problem. 

However, sometimes if the mold temperature is too low, it is also not conducive to solving the problem of shrinkage, which is not very much noticed by many people.

If the mold temperature is too low, the melt glue will be cooled too fast, and the thicker glue position far away from the water inlet will be blocked by the middle part of the cooling too fast, so the distant part will not be fully replenished by the melt glue, which makes the shrinkage problem more difficult to solve, especially for thick and large injection molded parts.

Moreover, the mold temperature is too low, which is not conducive to increasing the overall shrinkage of the injection molded parts, so the number of concentrated shrinkage increases and the shrinkage problem becomes more serious and obvious.

The melt temperature is too low and is also not conducive to solving the problem of shrinkage

Again, most people know that if the melt temperature is too high, the injection molded parts will be prone to shrinkage problems, and if the temperature is properly lowered by 10~20℃, the shrinkage problem will be improved.

However, if the shrinkage occurs in a thicker part of the injection molded part, and then the melt temperature is adjusted too low, such as close to the lower limit of the melt temperature, but not conducive to solving the shrinkage problem, and even more serious, the thicker the injection molded parts, the more obvious the situation.

The reason is similar the mold temperature is too low, the melt condenses too quickly, and the temperature difference between the shrinkage position and the water outlet cannot be formed to facilitate the shrinkage, the shrinkage channel will be closed prematurely, and the problem becomes more difficult to solve.

It can also be seen that the faster the melt glue condensation rate is not conducive to solving the shrinkage problem, PC material is a fast condensing raw material, so its shrinkage problem can be said to be a big problem for injection molding. 

In addition, the melt temperature is too low and is also not conducive to increasing the overall amount of shrinkage, increasing the amount of concentrated shrinkage, thus exacerbating the problem of shrinkage. 

Therefore, when adjusting the machine to solve the more difficult shrinkage problem, you should also check whether the melt temperature is adjusted too low is extremely important, in addition to looking at the temperature table, using the empty shot method to check the temperature and fluidity of the melt is more intuitive.

Too fast injection speed is not conducive to solving the problem of severe shrinkage 

To solve the problem of shrinkage, 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 is not conducive to solving the problem of shrinkage. Therefore, when shrinkage is difficult to eliminate, it should be solved by lowering the injection speed.

Reduce the injection speed, so that the melt in front of the melt and the water inlet forms a larger temperature difference, and therefore conducive to the melt from far to near the order of solidification and shrinkage, but also conducive to the water inlet far from the shrinkage position to obtain a higher pressure supplement, the solution to the problem will be of great help.

As a result of reducing the injection speed, the melt in front of the lower temperature, the speed has been slowed down, the injection molding parts will not be easy to produce batch front, injection pressure and time can be raised and put longer, which is also more conducive to solve the problem of severe shrinkage.

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

However, it is worth reminding that too slow a filling is not conducive to solving the shrinkage problem. Because by the time the mold cavity is filled, the melt is completely frozen, just as the too low melt temperature, there is no ability to make up for the distant shrinkage.

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