1、 Two temperature conditions that are not conducive to solving the shrinkage problem
1) The mold temperature is too low, which is not conducive to solving the shrinkage problem
The shrinkage problem of hard rubber parts (surface shrinkage and internal shrinkage) is a defect caused by the space left by concentrated shrinkage not being fully supplemented by molten rubber from the water inlet direction when the molten rubber is cooled and shrunk.
Most people know that the temperature of the injection mold is too high, which will easily lead to shrinkage. They usually like to reduce 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. The mold temperature is too low, the melt cools too fast, and the slightly thick glue position far from the water inlet is sealed because the middle part cools too fast, so that the melt cannot be fully replenished at a distance, which makes it more difficult to solve the shrinkage problem, especially the shrinkage problem of thick injection parts.
Therefore, when solving the difficult shrinkage problem, it is beneficial to remember to check the mold temperature. Experienced technicians usually touch the mold cavity surface with their hands. Each material has its proper mold temperature. For example, the shrinkage of PC material products, but if the mold temperature is too high, the injection part will shrink.
2) Too low melt temperature is not conducive to solving the shrinkage problem
It is also known to most people that if the melt temperature is too high, the shrinkage problem of injection molded parts is easy to occur. If the temperature is properly reduced by 10 ~ 20 ℃, the shrinkage problem will be improved.
However, if the injection molded part shrinks at a relatively thick part, then the melt temperature is adjusted too low. For example, when it is close to the lower limit of the injection molded melt temperature, it is not conducive to solving the shrinkage problem, and even more serious. The thicker the injection molded part, the more obvious the situation is.
Therefore, when adjusting the machine to solve the difficult shrinkage problem, it is also very important to check whether the temperature of the melt is 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.
2、 Too fast injection speed is not conducive to solving the problem of serious shrinkage
To solve the shrinkage problem, the first thing you will think of is to increase the injection pressure and prolong the injection time. However, 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 form a large temperature difference between the melt in front and the water inlet, which is conducive to the solidification and feeding of the melt from far to near, and also conducive to the higher pressure supplement at the shrinking position far from the water inlet, which will be very helpful to solve the problem.
In addition, if the last stage end filling with slower speed, higher pressure and longer time is adopted, and the pressure maintaining mode of gradually slowing down and pressurizing is adopted, the effect will be more obvious. Therefore, when it is impossible to shoot at a slower speed at the beginning, it is also a good remedy to use this method from the later stage of shooting.
Post time: Sep-02-2022