Zhuojin Pipe Fitting Co., LtdOverlay Welding of Spiral Rod for Fiber Carbon Forming Machine
Literature Overview
This paper, published in 1993 in "Welding Technology" (Vol. 22, No. 6, p. 41), authored by Li Jixian from Shaanxi Hanzhong General Machinery Factory, addresses the overlay welding repair of a spiral rod (screw shaft) for a fiber carbon forming machine. The spiral rod material is CrWMn, and the component operates under severe conditions of high temperature (400-500°C), high friction, and significant extrusion pressure, leading to rapid wear of the front section and head.
Core Technical Content and Service Condition Analysis
The spiral rod in a fiber carbon forming machine functions as a screw conveyor that pushes and shapes fiber carbon material through a forming die. The front section and head of the spiral rod are subjected to the most severe wear conditions due to direct contact with the hot, abrasive carbon material under high extrusion pressure. The design life requirement is 600 hours, but the original component failed after only 2 hours with wear depths of 6-8 mm in the spiral grooves and head.
Failure Analysis and Root Causes
| Failure Mode | Contributing Factors | Original Design Issue |
|---|---|---|
| Rapid wear (6-8 mm in 2 h) | High temperature + high friction + abrasive material | Inappropriate material selection |
| Early failure (2 h vs. 600 h design) | Insufficient surface hardness and wear resistance | Improper heat treatment |
| Loss of dimensional accuracy | Wear exceeds tolerance limits | No protective overlay layer |
The root cause analysis identified two primary issues: inappropriate material selection (CrWMn without adequate surface hardening) and improper heat treatment that failed to develop sufficient surface hardness and wear resistance. CrWMn is a tool steel containing chromium, tungsten, and manganese, which provides good hardenability but requires proper heat treatment to achieve optimal surface properties.
Overlay Welding Solution
In the absence of specialized overlay welding equipment, the authors employed manual arc hardfacing welding to restore and enhance the wear resistance of the spiral rod. The hardfacing alloy selection was oriented toward high-hardness, high-temperature wear-resistant compositions suitable for the 400-500°C operating temperature range.
| Parameter | Original Condition | After Overlay Welding |
|---|---|---|
| Service life | 2 hours | 150+ hours (and continuing) |
| Wear depth | 6-8 mm in 2 h | Minimal wear after 150 h |
| Material | CrWMn (as-is) | CrWMn + hardfacing overlay |
| Equipment required | Specialized hardfacing | Manual arc welding |
| Processing approach | Conventional machining | Manual overlay welding |
Metallurgical Considerations for High-Temperature Wear Resistance
The selection of hardfacing alloy for this application must account for several metallurgical factors. At 400-500°C, many conventional hardfacing alloys experience significant softening due to carbide coarsening and phase transformations. Suitable alloys for this temperature range typically include high-chromium cast irons (Cr ≥ 26%), cobalt-based alloys, or nickel-aluminum-bronze compositions that maintain hardness through carbide stability and solid solution strengthening at elevated temperatures.
The CrWMn base material, when properly heat treated, can achieve hardness in the range of 58-62 HRC. However, the overlay weld must provide hardness significantly higher than the base material to create a protective layer that resists wear while maintaining adequate bond strength. The dilution effect during manual arc welding must be controlled to ensure the overlay retains its designed composition and properties.
Engineering Practice and Practical Significance
The successful application of manual arc hardfacing in the absence of specialized equipment demonstrates the versatility and adaptability of overlay welding technology. For field maintenance operations where specialized equipment is unavailable, manual arc welding with appropriate filler metals can provide effective wear protection. The result of extending service life from 2 hours to over 150 hours represents a 75-fold improvement in component life, which is economically significant given the production downtime associated with frequent spiral rod replacement.
The methodology of using manual arc welding for hardfacing repair in resource-constrained environments is particularly relevant for smaller manufacturing facilities and field service operations. The key to success lies in proper surface preparation, filler metal selection, and process parameter control, all of which can be achieved with basic welding equipment and trained personnel.
Study Reflections and Implications
This case study underscores the importance of surface engineering in extending component life under severe service conditions. The dramatic improvement achieved through overlay welding demonstrates that material selection and surface treatment are often more effective than base material upgrades alone. For practitioners dealing with high-temperature, high-friction wear applications, this paper provides practical guidance on achieving significant life extension through relatively simple overlay welding processes, even without specialized equipment.