What Repair Methods Are Available for Worn Barrels and Screws?
Repairing worn barrels and screws requires adhering to the principle of "tiered intervention": for minor wear, grinding and polishing are the preferred methods; for moderate wear, thermal spraying or alloy hardfacing is employed; and for severe wear-or when the clearance exceeds permissible limits-boring out the barrel to fit a new screw, or replacing the bimetallic liner, becomes necessary. Blindly attempting repairs not only wastes resources but may also lead to reduced output or material degradation due to improper operational clearances.
Drawing upon your previous inquiries regarding maintenance and replacement protocols, I have compiled the following systematic guide for repairing worn components. This framework is designed to assist you in making the most cost-effective decisions when weighing the options between "repair" and "replacement."
Screw Repair Strategies: Categorized by Damage Severity
As the active rotating component, screw wear typically manifests as a reduction in diameter. Depending on the depth of the wear, the following three strategies may be adopted:
Minor Wear and Surface Scratches (Restoring Surface Finish)
If the screw surface exhibits only minor scratches or negligible dimensional changes, extensive thermal processing (involving high heat) is unnecessary.
Procedure: Manually grind and polish the surface using oilstones or fine emery cloth to remove burrs and eliminate stress concentration points, thereby restoring surface smoothness.
Applicable Scenarios:Non-structural damage discovered during routine maintenance, or as a preparatory step for other, more extensive repair processes.
Moderate Wear (Dimensional Restoration and Surface Hardening)
When the screw diameter has diminished but the core structural integrity remains intact, the objective is to restore the original dimensions while simultaneously enhancing surface hardness.
Thermal Spraying Technology: Employ High-Velocity Oxy-Fuel (HVOF) spraying to deposit a wear-resistant alloy (such as tungsten carbide) onto the screw surface, followed by precision grinding to restore the standard dimensions. This method offers high efficiency and strong bonding strength, significantly enhancing the screw's resistance to wear.
Wear-Resistant Alloy Hardfacing: Deposit a layer of specialized alloy (containing elements such as C, Cr, Co, and W)-typically 1 to 2 mm thick-onto the screw threads, followed by machining to the required dimensions. This method provides excellent resistance to both corrosion and wear; however, it entails higher costs and is therefore best suited for high-value screws. Hard Chrome Plating: The chrome layer offers high hardness and corrosion resistance; however, if the layer is excessively thick, it becomes prone to peeling. Consequently, this method is suitable only for applications involving minor wear where corrosion resistance is a primary requirement.
Severe Wear or Fracture (Remanufacturing)
If the screw has twisted off or suffered wear severe enough to create an excessive clearance between the screw and the barrel, repairing the screw is no longer economically viable.
Remanufacturing: It is necessary to remanufacture the screw by redesigning its outer diameter based on the actual inner diameter of the barrel (taking into account its dimensions after wear), ensuring the proper operational clearance is restored.
Note: In such cases, merely repairing the screw without addressing the barrel will result in an excessive operational clearance, leading to increased backflow and a significant decline in output.
