Difficult to fill raw materials and injection parts with larger and thinner sizes usually need to be filled with a faster injection speed to fill the cavity. However, many injection-molded parts will produce obvious ridges or gas lines around the gate, and problems such as scorching after injection of the injection parts. Especially when spraying silver paint, even very slight air lines that are not easily noticeable to the naked eye can cause scorching problems in the injection molded parts. This situation often occurs in production.
After observation, the gas lines or shot lines around the gate are caused by the turbulence caused by the rapid injection when it enters the cavity. Therefore, it is necessary to use a slower injection speed that cannot produce gas lines or jet lines as the first-level injection, but this will inevitably lead to difficulty in subsequent filling.
Therefore, when a relatively slow injection enters a small part of the cavity, after the gas lines or the injection temperature have been eliminated, it is necessary to immediately return to the second rapid injection, and also give the foot pressure to ensure that the rapid filling is started, so that it can be successive Solve two conflicting problems.
It’s just that the starting point of this second level needs to be adjusted more accurately. Because it is too early to solve the problem of air lines or jet lines, it will cause difficulty in filling late, so it takes a little patience to adjust the position.
If the mold flow channel is too long, you can add a higher level of injection before this level of slow injection, or increase the size of the cross flow channel or gate to avoid premature freezing of the melt and affect the subsequent filling process .
In addition, if there is a structure such as a concave cavity or a boss in a part of the middle of the injection molded part, then when the rapid injection passes through this position, the injection molded part will also have the problems of gas lines and fuel injection. Therefore, when the fast injection reaches this point, it is required to switch back to the slow injection. After the melt flows through these positions and the gas lines are eliminated, then switch back to the fast injection.
Finally, in the rapid injection stage, if it is always allowed to shoot the cavity so quickly, the injection molded part is likely to produce a lot of overflow. At this time, when the rapid injection is about to fill the cavity (usually after 90% full), it should be immediately switched to low and medium speed and pressure for filling. When the pressure is maintained at a lower pressure and speed after being filled, the overflow problem can be avoided. In addition, you can use the “positioning injection” method to prevent the occurrence of overflow.
When solving the above problems, it is best to increase the mold temperature and the material temperature appropriately to ensure that the filling can proceed smoothly at each stage.
In order to find the transition points of slow speed and fast speed, learn how to use the “mold transparency method” to help you find, you can find fast and accurate. Therefore, it is an inevitable guarantee for the application of multi-stage injection technology.
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