Hey there! As a supplier of extruder bimetallic screws, I've seen my fair share of these screws in action and also witnessed the different ways they can fail. In this blog, I'll be talking about the common failure modes of an extruder bimetallic screw.
1. Wear and Tear
One of the most common failure modes of an extruder bimetallic screw is wear and tear. When the screw is in operation, it constantly rubs against the plastic material being extruded. Over time, this friction can cause the surface of the screw to wear down.
The bimetallic design of the screw is supposed to help with this, as the outer layer is usually made of a more wear - resistant material. However, even with this protection, the constant abrasion can still take its toll. For example, in applications where the plastic contains abrasive fillers like glass fibers or mineral powders, the wear rate can be significantly higher.
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2. Corrosion
Corrosion is another major issue for extruder bimetallic screws. Depending on the type of plastic being processed, there could be chemicals present that can react with the screw material. For instance, some plastics release acidic or alkaline by - products during the extrusion process. These substances can corrode the surface of the screw, especially if the protective layer is damaged.
The bimetallic construction can sometimes create a situation where galvanic corrosion occurs. This happens when two different metals in the bimetallic screw are in contact with an electrolyte (like the corrosive chemicals in the plastic). The less noble metal in the pair will corrode preferentially. To avoid this, proper material selection and surface treatments are crucial.
3. Fatigue Failure
Fatigue failure is more likely to happen in screws that are subjected to cyclic loading. During the extrusion process, the screw experiences repeated stress as it rotates and pushes the plastic through the extruder. Over time, these cyclic stresses can cause small cracks to form on the surface of the screw.
These cracks start off tiny, but as the screw continues to operate, they can grow and eventually lead to a complete failure of the screw. Factors like the design of the screw, the operating speed, and the type of plastic being processed can all affect the likelihood of fatigue failure. If you're looking for smaller extruder screws that might have different fatigue characteristics, Small Extruder Screw is a great resource.
4. Erosion
Erosion is similar to wear but is usually caused by the high - velocity flow of the plastic material. When the plastic moves through the extruder at a high speed, it can act like a sandblaster on the surface of the screw. This is especially true in areas where the flow of the plastic is turbulent, such as near the screw flights or in the feed section.
The bimetallic screw can be more prone to erosion in areas where the bond between the two metals is not perfect. If there are any voids or weak spots in the bond, the high - velocity plastic can penetrate and cause damage.
5. Melting and Deformation
In some cases, the extruder bimetallic screw can experience melting and deformation. This usually happens when the temperature in the extruder is too high. If the temperature control system fails or if the screw is running at a speed that generates too much heat, the screw material can start to melt.
Once the screw starts to melt, its shape can change, and it won't be able to function properly. Deformation can also occur due to mechanical overload. If the screw is forced to push a plastic material that is too viscous or if there is a blockage in the extruder, the excessive force can cause the screw to bend or twist.
6. Bond Failure in Bimetallic Screws
Since we're talking about bimetallic screws, bond failure is a unique failure mode. The two metals in a bimetallic screw are joined together through a bonding process. If this bond fails, the screw can lose its intended properties.
There are several reasons why the bond can fail. Improper bonding during the manufacturing process is one factor. If the surface preparation before bonding was not done correctly or if the bonding parameters were not optimized, the bond strength will be weak. Thermal cycling during the operation of the extruder can also cause the bond to fail over time, as the two metals expand and contract at different rates.
How to Prevent These Failures
Now that we've talked about the common failure modes, let's discuss how to prevent them. First of all, proper material selection is key. You need to choose a bimetallic screw with the right combination of metals based on the type of plastic you'll be processing.
Regular maintenance is also crucial. This includes cleaning the screw after each use to remove any residual plastic or chemicals. Inspecting the screw for signs of wear, corrosion, or cracks on a regular basis can help you catch problems early.
Proper temperature and speed control during the extrusion process can prevent melting, deformation, and fatigue failure. Make sure your extruder's temperature control system is working properly and that you're running the screw at the recommended speed.
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Conclusion
As you can see, there are several common failure modes for extruder bimetallic screws, including wear and tear, corrosion, fatigue failure, erosion, melting and deformation, and bond failure. But with the right knowledge and preventive measures, you can extend the lifespan of your screws and ensure smooth operation of your extruder.
If you're in the market for high - quality extruder bimetallic screws or have any questions about the failure modes and how to prevent them, don't hesitate to reach out. We're here to help you find the best solution for your extrusion needs. Whether you're a small - scale manufacturer or a large industrial operation, we can provide you with the right screw for your specific requirements. Contact us to start a procurement discussion and find out how we can improve your extrusion process.
References
- Smith, J. (2020). Handbook of Extrusion Technology. New York: Wiley.
- Johnson, R. (2018). Plastic Extrusion: Principles and Practice. London: Elsevier.