One or two temperature conditions that are not conducive to solving the shrinkage problem
1) The mold temperature is too low to solve the shrinkage problem
The problem of shrinkage of hard rubber parts (surface shrinkage and internal shrinkage) is due to the fact that the space left by the concentrated shrinkage does not get enough to be fully replenished from the direction of the water inlet when the melt is cooled and contracted. Therefore, factors that are not conducive to supplementation will affect us to solve the problem of shrinking. Most people know that mold temperatures are too high to cause shrinkage problems, and it is often desirable 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 problem of shrinkage, which is not noticed by many people.
The mold temperature is too low, the melt cooling is too fast, and the slightly thicker glue position farther from the water inlet is blocked because the middle part is cooled too fast, and the melt is not enough in the distance. Supplementation, making the shrinkage problem more difficult to solve, the shrinkage of thick injection molded parts is particularly prominent.
Moreover, the mold temperature is too low, which is not conducive to increasing the overall shrinkage of the injection molded parts, so that the concentration shrinkage is increased, and the shrinkage problem is more serious. Therefore, when solving the difficult shrinkage problem, it is good to check the mold temperature. Experienced technicians typically touch the surface of the mold cavity by hand, each material having its proper mold temperature.
2) The temperature of the melt is too low, which is not conducive to solving the shrinkage problem.
Similarly, most people know that the temperature of the melt is too high, and the injection molded parts are prone to shrinkage. When the temperature is lowered by 10 to 20 Â°C, the shrinkage problem will be improved. However, if the injection molded part shrinks at a relatively thick part, and then adjusts the temperature of the melt too low, such as close to the lower limit of the temperature of the injection melt, it is not conducive to solving the shrinkage problem, and even more serious, injection molding. The thicker the piece, the more obvious it is.
The reason is similar to the mold temperature is too low, the melt condensation is too fast, and there is no large temperature difference between the shrinking position and the nozzle, which is conducive to the shrinkage. The shrinkage channel of the shrinkage position will be blocked prematurely, and the problem is solved. It has become more difficult. It can also be seen that the faster the melting rate of the melt is, the more difficult it is to solve the shrinkage problem. The PC material is a relatively fast condensing raw material, so its shrinkage hole problem can be said to be a big problem of injection molding.
In addition, too low a melt temperature is also unfavorable for increasing the amount of overall shrinkage, resulting in an increase in the amount of concentrated shrinkage, thereby exacerbating the problem of shrinkage. Therefore, when adjusting the machine to solve the difficult problem of shrinkage, it is extremely 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-jet method. .
Second, the speed of injection is too fast to solve the problem of serious shrinkage
To solve the problem of shrinkage, the first thing that comes to mind is to raise the pressure of the shot and extend the shot time. However, if the speed of the glue is adjusted quickly, it is not conducive to solving the problem of shrinkage. Therefore, sometimes it is difficult to eliminate the shrinkage, it should be solved with the reduction of the injection speed.
Reducing the speed of injection can make a large temperature difference between the melted glue and the water inlet, which is beneficial to the solidification and feeding of the melt from far to near, and also facilitates the shrinking position far from the nozzle. Get a higher pressure to supplement, will help a lot of problems.
Due to the lowering of the injection speed, the temperature of the melted rubber in the front is lower and the speed has been slowed down. The injection molded parts are not easy to produce the front, and the pressure and time of the injection can be increased and lengthened, which is more beneficial. Solve the problem of serious shrinkage.
In addition, if you use the slower, higher pressure, longer time, the last stage of the end filling and the step-down and pressure-holding method, the effect will be more obvious. Therefore, when it is not possible to use a slower speed shot at the beginning, it is also a good remedy to use this method from the beginning of the shot.
However, it should be reminded that the filling is too slow, but it will not help solve the problem of shrinking. Because when the cavity is filled, the melt is completely frozen, just like the temperature of the melt is too low, and it is impossible to replenish the shrinkage in the distance.
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