Focus on extrusion, granulation screw barrels design and manufacturing
What are the hardware problems of the screw barrel of the injection molding machine
2022.03.02
If screw slip is due to conical twin screw barrel for extrusion 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 about wear, you can measure the width of the gap between the screw and barrel, and if it does not meet the specified tolerances, it should be replaced or repaired.
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 highest compression ratio for their material. The cause of screw slippage can also be a non-return valve (one-way valve) that is not working properly. When the screw is rotated to prepare for injection, the retaining ring should be at the front (open position), in contact with the tab of the retaining ring holder.
If the retaining ring is at the end (i.e. closed position), or halfway 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 fast compression section (i.e. abruptly tightened at the bottom) is more suitable for processing uniform raw meal, but not regrind. Due to the wide particle size distribution of the recycled material, it will affect the uniformity of the feed, which means that the screw cannot transport the melt uniformly under 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.
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 highest compression ratio for their material. The cause of screw slippage can also be a non-return valve (one-way valve) that is not working properly. When the screw is rotated to prepare for injection, the retaining ring should be at the front (open position), in contact with the tab of the retaining ring holder.
If the retaining ring is at the end (i.e. closed position), or halfway 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 fast compression section (i.e. abruptly tightened at the bottom) is more suitable for processing uniform raw meal, but not regrind. Due to the wide particle size distribution of the recycled material, it will affect the uniformity of the feed, which means that the screw cannot transport the melt uniformly under 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.
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