CLADDING TECHNOLOGY SHANXI CO., LTDWear-Resistant Overlay Welding on Brick Machine Spiral Cutters
Literature Overview
This study by Zhang Hongjian, Gao Diankui, Zhang Hai, Zhang Changyi, and Sun Zhongxiao was published in 1990 in the journal Welding Technology. The work was a collaborative effort between Northeast Heavy Machinery Institute and the Qiqihar No. 9 Brick Factory, combining academic research with industrial application. The study addresses the wear-resistant overlay welding of spiral cutters used in brick-making machines, which are subjected to severe abrasive wear during the continuous cutting of clay and brick mixtures. The work represents an early example of systematic approach to wear-resistant overlay technology in heavy machinery applications.
Service Conditions and Wear Mechanisms
Spiral cutters in brick-making machines operate under extremely harsh conditions. The cutter is in continuous contact with abrasive clay material containing silica particles, quartz fragments, and other hard mineral constituents. The primary wear mechanism is abrasive wear, with a secondary contribution from adhesive wear during the cutting process. The operating speed of the cutter, the hardness of the clay material, and the moisture content of the mixture all influence the wear rate. The following table presents the key service parameters and wear characteristics:
| Parameter | Typical Value | Effect on Wear |
|---|---|---|
| Cutter rotational speed | 150–300 rpm | Higher speed increases wear rate |
| Clay hardness | 30–60 MPa (unconfined) | Harder clay increases abrasive wear |
| Cutting depth | 50–150 mm | Deeper cuts increase contact stress |
| Service life (uncoated) | 200–500 operating hours | Baseline for comparison |
| Desired overlay life | 3000–5000 operating hours | 6–10× life extension target |
| Wear rate (uncoated) | 0.5–1.5 mm/1000 h | Depends on clay composition |
The wear pattern on the spiral cutter is not uniform. The leading edge of the cutter blade experiences the highest wear rate due to direct contact with the clay material, while the trailing edge experiences less wear. The root of the blade, where it joins the cutter body, is also susceptible to wear and fatigue cracking due to the combination of mechanical loading and stress concentration.
Overlay Material Selection and Process Development
The researchers evaluated several overlay materials for this application, including high-carbon martensitic steels, cobalt-based alloys, and nickel-based alloys with carbide-forming elements. The selected overlay material was a high-carbon, high-chromium alloy containing approximately 12–14% chromium and 3–5% carbon, with additions of tungsten and vanadium to promote the formation of hard carbides. This composition provides a good balance of hardness, wear resistance, and toughness for the application.
The overlay process employed was submerged arc welding (SAW) with a specially formulated flux-cored wire. SAW was selected for its high deposition rate, which is important for covering the large surface area of the spiral cutter blade. The process parameters were optimized as follows:
- Welding current: 350–500 A
- Arc voltage: 28–35 V
- Travel speed: 150–250 mm/min
- Wire feed rate: 3.5–5.5 m/min
- Flux type: Low-hydrogen, high-alkalinity
- Preheat temperature: 100–150°C
- Number of passes: 3–5 depending on required thickness
The multi-pass approach was used to build up the overlay layer gradually, with each pass providing a controlled dilution rate and a refined microstructure. The first pass (root pass) was deposited at a lower current to ensure good fusion with the base material, while subsequent passes were deposited at higher currents to increase deposition rate.
Microstructural Characterization and Wear Performance
Metallographic examination of the overlay revealed a microstructure consisting of a martensitic matrix with dispersed hard carbides. The carbides were primarily M7C3 and M23C6 type carbides, with some M6C carbides containing tungsten and vanadium. The carbide size was in the range of 2–10 μm, and the carbide volume fraction was approximately 20–30%, which provides adequate wear resistance without compromising toughness excessively.
The hardness of the overlay layer was measured at 600–700 HV, which is significantly higher than the 200–250 HV of the base carbon steel cutter body. Hardness profiling across the overlay showed a gradual transition from the overlay hardness to the base material hardness over a distance of approximately 0.5–1.0 mm, indicating a well-bonded interface without brittle intermetallic formation.
Wear testing was conducted using a pin-on-disk tribometer with a clay-silica composite disk to simulate actual service conditions. The overlay-protected cutter blade exhibited a wear rate that was 8–12 times lower than the uncoated base material. In field trials at the brick factory, the overlay-protected cutters achieved a service life of 3500–4500 operating hours, compared to 300–500 hours for uncoated cutters. This represents a 7–10 times improvement in service life, which translates to significant economic benefits in terms of reduced downtime and replacement costs.
Process Optimization and Defect Control
The study identified several critical process factors that influence overlay quality. The most important factor was the preheat temperature, which must be sufficient to prevent cold cracking in the HAZ but not so high as to coarsen the base material grain structure. A preheat of 100–150°C was found to be optimal. Another critical factor was the flux coverage, which must be maintained continuously to prevent oxide inclusion and porosity. Inconsistent flux coverage was identified as the primary cause of porosity in the overlay layer.
A systematic approach to defect prevention was developed, including the following measures:
- Visual inspection of the base material surface before welding to detect cracks or inclusions
- Preheat temperature verification using thermocouples or infrared pyrometers
- Continuous monitoring of flux coverage and wire feed consistency
- Post-weld stress relief at 550–600°C to reduce residual stresses
- Final grinding and dressing of the overlay surface to achieve required geometry
The stress relief treatment was found to be particularly important for preventing delayed cracking in the overlay layer. Without stress relief, some overlay specimens exhibited cracking after 50–100 hours of service, which was attributed to residual stress relaxation during the first thermal cycle in service.
Engineering Practice and Economic Analysis
The economic analysis conducted in this study demonstrated that the overlay welding process provides substantial cost savings despite the additional processing steps. The cost of overlay application was approximately 15–20% of the cost of manufacturing a new cutter, while the service life extension was 7–10 times. This results in a cost per operating hour that is reduced by 80–85% compared to using uncoated cutters.
The process was successfully implemented in production at the Qiqihar No. 9 Brick Factory, where it became a standard maintenance practice for spiral cutter replacement. The overlay work was performed in the factory's own workshop using standard welding equipment, which made the process accessible and practical for industrial implementation. Welder training was conducted to ensure consistent process execution, with emphasis on preheat control, flux management, and post-weld inspection.
Key Technical Insights
This study, despite being published in 1990, provides enduring principles for wear-resistant overlay technology. The systematic approach to material selection, process optimization, and performance validation remains relevant today. The emphasis on microstructural characterization to understand the relationship between microstructure and wear performance is particularly valuable, as it provides a scientific basis for process optimization rather than relying solely on empirical trial and error.
The use of SAW for large-area overlay applications is well justified by the economics of the process. The high deposition rate of SAW makes it suitable for covering large blade surfaces efficiently, while the flux provides excellent protection against atmospheric contamination. The multi-pass approach with controlled dilution demonstrates good engineering judgment in balancing deposition rate with microstructural quality.
Summary
This literature presents a comprehensive approach to wear-resistant overlay welding of brick machine spiral cutters, combining fundamental research on microstructure and wear mechanisms with practical industrial implementation. The selected high-carbon, high-chromium overlay material with carbide-forming alloying elements provides excellent abrasive wear resistance, while the SAW process with optimized parameters ensures reliable and economical application. The demonstrated 7–10 times improvement in service life and the associated economic benefits make this technology highly attractive for heavy machinery applications involving abrasive wear. The systematic approach to process development, quality control, and economic evaluation provides a valuable template for engineers tackling similar wear-resistant overlay challenges in other industrial sectors.