How does the material used affect the wear on the injection/extrusion screw?
The material used in plastic injection and extrusion applications can significantly affect the wear on the machine’s screw due to various factors such as abrasiveness, thermal properties, viscosity, chemical interactions, and more. Here are the most common issues and how they impact screw wear:
- Abrasiveness: Some materials, such as filled polymers (containing additives such as glass fibers, minerals, or other reinforcing agents) or those with high filler content, can be highly abrasive. These materials can cause increased wear on the screw surface due to the abrasive action during the plasticating process.
- Thermal Properties: Materials with high thermal conductivity or those that require high processing temperatures can cause thermal degradation of the screw surface. This degradation can lead to wear, erosion, or thermal fatigue over time.
- Viscosity: Materials with high viscosity or shear-thinning behavior may exert higher forces on the screw, leading to increased wear due to higher frictional forces between the polymer melt and the screw surface.
- Chemical Interactions: Some materials may chemically react with the metal surface of the screw, causing corrosion or degradation of the screw, which can accelerate wear and reduce the lifespan of the screw.
- Moisture Content: Materials that absorb moisture can lead to hydrolysis or degradation of the screw, especially if the processing temperatures are high. The higher temperature, coupled with the moisture, can weaken the screw structure and increase wear.
- Processing Conditions: Operating the machine under conditions of high pressure, high temperature, or high shear rates can exacerbate wear on the screw, regardless of the material being processed.
How can you mitigate wear on the screw?
Mitigating wear on the screw and thereby extending the life of the equipment while reducing downtime and maintenance costs in plastic injection and extrusion applications requires careful consideration and implementation of several strategies. A few practical ways to address wear include (but are not limited to):
- Wear-Resistant Screws: Select screws made from materials specifically designed to withstand abrasive wear such as hardened tool steels like CPM9-V, or bimetallic alloys such as Colmonoy 56 & 83 screws. These materials offer higher resistance to abrasion and extend the lifespan of the screw.
- Wear-Resistant Screw Coatings: Apply wear-resistant coatings or surface treatments to the screw to provide an additional layer of protection against wear. Common coatings include chrome plating, tungsten carbide, or other advanced coatings designed for high wear resistance.
- Wear-Resistant Screw Tips: In injection molding, using wear-resistant screw tips or mixing nozzles can be designed for optimizing valve life. Tips are an asset to enhancing throughput, but make sure they have a wear resistant substrate to assist with any wear issues, especially in relation to early check ring wear.
- Screw Design Optimization: Design the screw geometry to minimize abrasive wear. This can involve using lower compression designs, such as Posimelt low-shear design.
- Processing Parameters: Adjust processing parameters such as temperature, pressure, and screw speed to minimize abrasive wear.
- Maintenance and Monitoring: Regularly inspect the screw for signs of wear and degradation and perform preventive maintenance as needed. Implement a regular maintenance schedule that includes cleaning the screw and measuring the flight OD for wear. These periodic inspections can help detect wear early and prevent more severe damage to the screw.
- Material Quality: Ensure that the materials used in the process are of consistent quality and free from contaminants that could exacerbate wear on the screw. Proper handling and storage of raw materials can also help minimize the introduction of foreign particles into the processing equipment.
For both plastic injection and plastic extrusion applications, the choice of material significantly influences the wear on the machine’s screw. The material’s viscosity, abrasiveness, and thermal conductivity are crucial in determining the wear rate. It is essential for manufacturers to select materials compatible with their machine’s screw design carefully and to implement proper maintenance practices to mitigate wear and prolong the lifespan of the equipment.
A Family Tradition of Excellence For Over 100 Years! The doors have been open at Santa Fe Machine Works, Inc. since 1923, and for the past 45 years, we have been dedicated solely to manufacturing and supplying new & rebuilt injection & extrusion screws, barrels & valves to the plastics industry. We also offer custom-tailored screw, barrel, and valve combinations, allowing our customer’s production goals to be met in the best, fastest, and most cost-effective ways possible. Our employees have over 200 years of combined experience in the plastics industry and are eager to support your specific extrusion or injection needs. Have a question, need assistance, or looking for a quote? Contact us today!
