If the screw slip is caused by equipment rather than process settings, the wear of the screw and barrel may be the culprit. The resin melts in the transition section and sticks to the barrel wall, just like the feed section. As the screw rotates, it shears the melt down and transports it to the front end. If the screw and the barrel are worn, it is difficult for the screw to effectively convey the material to the front end. If it is not sure whether it has been worn, the gap width between the screw and the barrel can be measured. Once the specified tolerance is not met, it should be replaced or repaired. Screw design, especially compression ratio design, plays a role in plasticizing
If the screw slip is caused by equipment rather than process settings, the wear of the screw and barrel may be the culprit. The resin melts in the transition section and sticks to the barrel wall, just like the feed section. As the screw rotates, it shears the melt down and transports it to the front end. If the screw and the barrel are worn, it is difficult for the screw to effectively convey the material to the front end. If it is not sure whether it has been worn, the gap width between the screw and the barrel can be measured. Once the specified tolerance is not met, it should be replaced or repaired.
Screw design, especially compression ratio design, plays an important role in plasticization. The feeding section is too short, that is, the compression ratio is too small, which will cause the conveying capacity to decrease and the screw to slip. Resin suppliers will recommend the best compression ratio for their materials.
The cause of the screw slip may also be the check valve (one-way valve) does not work properly. When the screw is rotated to prepare for injection, the retaining ring should be located at the front end (open position), and the protruding buckle of the retaining ring frame should be connected. If the retainer ring is at the end (I. e., closed position), or intermediate the tail and retainer frame, it will be difficult for the polymer melt to pass through this gap. If there is a problem with the retaining ring, it should be replaced in time.
In addition, the resin feed hopper may also be one of the factors that cause the screw to slip. The correct design of the hopper is the key to uniform feeding, but this is often overlooked. A square hopper equipped with a rapid compression section (I. e., a sharp tightening at the bottom) is more suitable for processing uniform raw materials, but not for processing recycled materials. Because the particle size distribution of the recycled material is wide, it will affect the uniformity of the feed, which means that the screw can not transport the melt uniformly under the same pressure, which will eventually lead to slippage. To solve this problem, a circular hopper equipped with a progressive compression section (I. e., tapering in a cone at the bottom) is used to process materials with a wide particle size distribution.
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