Extending Wear Life for Barrels and Screws

Barrels and screws play a critical role in polymer processing applications. Achieving high throughput and maintaining product quality hinges on the performance and durability of the screw and barrel. However, while wear and tear is inevitable due to the nature of the materials processed, excessive wear creates serious processing issues that impact quality and costs. Below, we’ll explore strategies to extend the wear life of barrels and screws, ensuring optimal functionality and efficiency in your plastic manufacturing operations.

Careful operation is critical to extending the life of screws and barrels. This includes ensuring proper alignment and straightness of the screw during installation. Even a straight, brand-new barrel can be misaligned, which will result in premature wear.

Optimal temperatures must be maintained during processing. Excessive heat can accelerate wear and degrade the materials being processed. Avoid processing abrasive materials like glass-filled or mineral-filled polymers, which can rapidly increase wear for barrels and screws made from materials incompatible with abrasives.

Regular maintenance is also necessary and includes regularly inspecting and cleaning the screws and barrels to prevent the accumulation of degraded material, which can increase wear. Ensure that operators are well-trained in best practices for machine use. This includes understanding the importance of maintaining consistent processing conditions and recognizing early signs of wear.

Wear in screws and barrels can manifest in several forms, notably adhesive, abrasive, and corrosive wear. Understanding these wear types is crucial for implementing the right strategies.

• Adhesive wear occurs due to metal-to-metal contact, often leading to damage on the screw flights or the barrel’s interior surface that appears as burrs or groves.
• Abrasive wear results from processing resins with fillers, additives, or contaminants can cause grooving, galling, roughing, or smoothing.
• Corrosive wear is typically observed when processing polymers like PVC, which can aggressively attack metal surfaces and cause pitting.

There are many reasons why excessive screw and barrel wear happen, including processing incompatible or abrasive materials, uneven heating of the cylinder, improper alignment, a bent barrel or screw, etc.

The choice of materials for screws and barrels is pivotal in preventing premature wear. Selecting materials compatible with your application will assist in achieving maximum wear resistance. Additionally, the compatibility of screw and barrel materials can significantly affect wear rates.

Common barrel materials include:

• Xaloy X-102 — For general purpose, unfilled resins
• Xaloy X-220 — For general-purpose use with some corrosion resistance
• Xaloy X-306 — For very corrosive resins
• Xaloy X-800 — For highly filled resins that require extreme abrasion resistance.

Common screw materials include:

• AISI 4140 — Most common screw material used for general-purpose unfilled resins
• AISI 4340 — Most beneficial for screws that have very deep flights and smaller diameter screws where strength is more critical
• 17-4 PH Stainless — Provides corrosion resistance and is an excellent selection for smaller screws where strength is important
• D2 and H13 Tool Steel — Primarily used for abrasive applications and offers a good degree of corrosion resistance
• CPM Tool Steel — Used with highly abrasive materials such as resins filled with fiberglass.
• Hastelloy C-276 — offers outstanding chemical resistance
• Inconel — used with highly corrosive materials and high temperatures

The design of the screw and barrel plays a critical role in the performance and longevity of plastic processing equipment. A well-designed screw and barrel will efficiently convey plastic material, melt it evenly, and produce high-quality products with minimal wear.

Some elements of the screw and barrel to consider optimizing to prevent premature wear include:

• Barrel surface finish — The surface should be smooth and defects-free to minimize friction and wear. A polished surface can also help to prevent material buildup.
• Flight clearance — Flight clearance is the distance between the screw flight and the barrel wall. Proper flight clearance is essential for efficient material conveying and to prevent excessive wear. Too little clearance can cause material drag and wear, while too much clearance can lead to material slip and reduced mixing.
• Root diameter— The root diameter is the diameter of the screw core. A larger root diameter provides greater stability and wear resistance. However, it also increases the shear stress on the material, which can be detrimental for certain resins.
• Helix angle — The helix angle is the angle between the screw flight and the axis of the screw. A steeper helix angle increases the mixing efficiency but also increases the shear stress on the material. A shallower helix angle reduces shear stress but also decreases mixing efficiency.

With extensive process and application knowledge, our team can design an optimized barrel and screw system that meets your application and polymer processing needs. If you are experiencing unexplained premature wear, we can provide a comprehensive injection molding or extrusion process analysis and a complete solution focused on process optimization.

Contact us to get started and see how your optimized components can increase productivity, improve product quality, and prolong lifespan.