In the roaring workshop of the machine, the boss brings the customer to the scene again, and all the faces on the scene are scratched with a nervous expression. Everyone gathered around an injection molding machine and talked to each other. The first mock exam is done. Then someone keeps pulling the safety door of the injection molding machine, taking out the plastic parts, checking the head, then shaking the head, discarding the plastic parts to the defective product box again, then brooding and brooding, observing the molding parameters on the screen, extending the fingers, popping, changing several parameters, and closing the safety door to continue the injection molding of the next mold. The first mock exam is a large round plastic lid, a 4 hole, because the functional part of the shrinkage part is not satisfied with the customer's acceptance. It becomes a tough problem at that time.
After a short time, the boss seemed to lose patience and said, "this shrinkage has been checked many times from the aspects of raw materials, molds and injection molding technology. Now it's nearly three days. It's strange, but it can't be solved completely. Now I announce, who can solve the problem of giving 1000 yuan cash reward on the spot? Let's have a rest and think about some ways. "
When everyone went to have a rest, an old engineer went to observe again. First of all, he ruled out all the abnormalities of the external conditions. He frowned and slapped his brow, increasing the back pressure value by nearly the normal set value 70%, and then injection molding several molds to see, his face does not feel a trace of joy, shrinkage is solved, but the measurement time is too long, the cycle is too long, and then reduce it appropriately, adjust to just shrink to solve, the measurement time is not the best balance point for a long time, this problem is solved.
Young people may encounter such situations: they often encounter a problem, all methods seem to have been tried, but the problem is that they can't solve it, and this problem is not necessarily a very difficult problem in normal work, but no matter "scratching ears" or "scratching cheeks", they just can't handle it. Therefore, there is a saying in the injection molding industry that there is no bull but a bull. It mainly depends on whether your thinking is divergent and comprehensive? Can you think of something other people can't think of? Often not not not, but did not think of that reason, will "card" in there "suffer".
The key to solve the above problems is to increase the back pressure value abnormally. It's thinking about what other people can't think and trying what other people can't try. Back pressure is an important parameter in injection molding. When it comes to back pressure, let's first make a basic understanding: what is back pressure and its principle and function.
What is the back pressure?
Back pressure, in a word, is the pressure on the back of the screw of the injection molding machine. The principle is to achieve the control purpose by adjusting the oil return throttle valve of the injection cylinder. The screw backward speed of the electric injection molding machine is controlled by AC servo valve.
What is the function of back pressure?
The back pressure is used to control the backward speed of the screw, so that the molten resin can be evenly stirred and compacted in the barrel, and the density is even, so as to improve the stability of the weight and the molding size of the plastic parts; at the same time, the gas in the molten resin and the barrel can be excluded, so as to avoid the defects of the plastic material flowers and bubbles and the internal shrinkage; improve the uniformity of the mixing of the color powder or the color masterbatch and the resin, and reduce the temperature Low or avoid color lines; increase the temperature of molten resin, improve the fluidity of resin; improve the shrinkage of plastic parts.
What is the effect of too small back pressure?
#The screw retreats too fast, the density of the melt resin is small, and there is much gas in it, which is easy to produce raw meal
#Large size and light weight of plastic parts
#The surface of plastic part is easy to shrink, the transparent part has bubbles, and the non transparent part will shrink
What are the effects of excessive back pressure?
#The nozzle is easy to salivate (glue overflow)
#Increase metering time and reduce molding efficiency
#When the molten resin stays in the screw for a long time, the colorant will change color or the resin will overheat and decompose due to heating, resulting in degradation
#Increase wear between screw and barrel of measuring equipment
