1, The melt filling speed is too slow
Generally, too fast filling speed will cause problems such as overflow and white top. However, if the speed is too slow, it is also easy to cause such problems.
If the speed is too slow and the filling time is too long, it will be more difficult to fill the melt if the melt is cooled too much, and the injection pressure must be increased. As the pressure increases, the problems of overflow and top white are bound to arise.
At this time, the overflow of the product is usually concentrated in the area close to the flow channel, and the overflow caused by rapid injection is likely to be generated throughout the injection molded part.
Properly speeding up the injection speed can reduce the injection pressure and have a better effect on the problems such as top white overflow. But if it is added too fast, the overflow edge will come again. If you must use rapid injection, you can start two stages of slow speed and low pressure as the final filling and holding pressure when the cavity is about to fill, which can reduce or eliminate the overflow or top white.
Therefore, in general, it is better to use medium speed or a slightly faster speed for injection molding. The slow or super slow injection will only be used unless there are other problems due to the rapidity, such as gate position air lines, overflow, etc., or when slow speed is needed to solve certain problems.
2, Melt temperature is too low
If the temperature is too high, it is easy to produce overflow, which is easy to understand. However, if the temperature is too low, the problem of overflow may also occur.
The reason is the same as slow injection. It is difficult to fill the melt when it is frozen. It is necessary to increase the injection pressure to fill the filling part, but the overflow edge will also follow, and sometimes it has not been aligned, the injection molded part is already around the gate A large amount of overflow was generated.
In addition, the melt temperature is low, it will become difficult to adjust the machine, and other problems will also occur together.
Therefore, before starting to adjust the machine, it is necessary to develop a good habit of checking whether the temperature is sufficient, whether the melt flowability of the air shot is good (usually practice observation), if necessary, check whether the heating tube is normal (available pouring Mouth condensate inspection), and also pay attention to whether the temperature is too high (a lot of smoke will be generated or burnt, etc.). In this way, too many detours will not be taken when adjusting the machine, wasting too much time.
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