Injection molding machine screw barrel hardware problem

If the screw slip is due to equipment rather than process setup, screw and barrel wear 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 delivers it to the front end. If the screw and barrel are worn, it is difficult for the screw to effectively convey the material to the front end. If you are not sure whether it has suffered wear, you can measure the gap width between the screw and barrel, and if it does not meet the specified tolerance, it should be replaced or repaired.

The screw design, especially the compression ratio design, plays an important role in plasticizing. A feeding section that is too short, that is, a compression ratio that is too small, will result in reduced throughput and screw slippage. Resin suppliers will recommend the best compression ratio for their material.

The reason for the slippage of the screw may also be that the check valve (one-way valve) is not working properly. When the screw is rotated to prepare for injection, the retaining ring should be at the front end (open position), in contact with the convex buckle of the retaining ring holder. If the retaining ring is at the end (ie closed position), or midway between the tail and the retaining ring frame, it will be difficult for the polymer melt to pass through this gap. If there is any 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. Proper design of the hopper is the key to uniform feeding, but this is often overlooked. A square hopper with a rapid compression section (that is, abruptly tightened at the bottom) is more suitable for processing uniform raw meal, but not for processing recycled material. Due to the wider particle size distribution of the recycled material, it will affect the uniformity of the feed, which means that the screw cannot deliver the melt uniformly at the same pressure, which will eventually lead to slippage. To solve this problem, use a round hopper with a tapered compression section (that is, a tapered taper at the bottom) to handle materials with a wide particle size distribution.