The moldtemperature is too low to solve the shrinkage problem
The shrinkage problem of hard rubber parts (surface shrinkage and internal shrinkage) is due to the defect that the space left by concentrated shrinkage can not be fully supplemented by melt adhesive from the direction of water inlet when the melt glue is cooled and shrinked. Therefore, unfavorable factors will affect us to solve the problem of shrinkage.
Most people know that the mold temperature is too high, easy to produce shrinkage problem, 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 solve the problem of shrinkage, which is a lot of people do not pay attention to.
The mold temperature is too low, the melt glue is cooled too fast, and the feeding channel is blocked because of the middle part cooling too fast, which makes the shrinkage problem more difficult to solve, especially for the thick injection molding parts.
Moreover, too low mold temperature is not conducive to increase the overall shrinkage of the injection molding parts, so that the concentrated shrinkage increases, and the shrinkage problem is more serious.
Therefore, when solving the difficult shrinkage problem, remember to check the mold temperature will be beneficial. Experienced technicians usually touch the surface of the mold cavity with their hands. Each material has its proper mold temperature. For example, the shrinkage problem of PC material can be improved if the holes are filled properly. However, if the mold temperature is too high, the injection molding parts will shrink again.
2. Too low melt temperature is not conducive to solve the problem of shrinkage
It is also known to most people that if the melt temperature is too high, the injection molding parts are prone to shrinkage problems. If the temperature is properly reduced by 10 ~ 20 ℃, the shrinkage problem will be improved.
However, if the injection molding part shrinks in a relatively thick part, and then adjust the melt temperature too low, for example, when it is close to the lower limit of the injection molding melt temperature, it is not conducive to solve the shrinkage problem, and even more serious. The thicker the injection molding part is, the more obvious the situation is.
The reason is similar to the mold temperature is too low, the melt glue condenses too fast, and there is no large temperature difference between the shrinkage position and the nozzle which is conducive to feeding. The feeding channel at the shrinkage position will be blocked too early, and the solution to the problem becomes more difficult. It can also be seen that the faster the melt condensation speed is, the less conducive to solve the shrinkage problem. PC material is a raw material with rapid condensation, 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 increase the amount of overall shrinkage, leading to an increase in the amount of concentrated shrinkage, thus aggravating the problem of shrinkage.
Therefore, when adjusting the machine to solve the difficult shrinkage problem, it is very important to check whether the melt glue temperature is set too low. In addition to looking at the thermometer, it is more intuitive to check the temperature and fluidity of the melt glue by air shooting.
3. Too fast glue injection speed is not conducive to solve the problem of serious 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 solve the shrinkage problem. Therefore, when shrinkage is difficult to eliminate, it is necessary to reduce the injection speed.
As a result, the higher melt distance between the nozzle and the nozzle is helpful to solve the problem of glue shrinkage.
As a result of reducing the injection speed, the temperature of the melt in front is lower and the speed has slowed down, so it is not easy for injection molding parts to produce batch front, and the injection pressure and time can be increased and lengthened, which is more conducive to solving the problem of serious shrinkage.
In addition, the effect will be more obvious if the last stage end filling mode with slower speed, higher pressure and longer time is adopted, and the pressure maintaining mode of gradually slowing down and pressurizing is adopted. Therefore, it is also a good remedy to use this method from the later stage of injection when it is not possible to use a slower speed at the beginning.
However, it is worth reminding that filling is too slow, which will not help solve the problem of shrinkage. Because when the cavity is filled, the melt glue has been completely frozen, just like the melt temperature is too low, there is no ability to further shrinkage in the distance.
