CLADDING TECHNOLOGY SHANXI CO., LTDOverlay Welding Repair of Sugar Mill Roller Journal Wear - Process Development and Industrial Application
Literature Overview
The paper by Pang Sixiong, Feng Chuanshan, Hu Lifang, Yang Zhongjian, and Liang Shaolu (1997), published in the Journal of Guangxi University (Natural Science Edition), documents a practical overlay welding repair process for worn journals of cane sugar mill rollers. This work was conducted in collaboration with sugar mills in Guangxi Province, China, specifically the Pumiang Sugar Mill and the Dongjiang Sugar Mill. The study represents an important early application of overlay welding technology in the sugar processing industry, where roller journals experience severe abrasive wear from cane fibers and sugar crystals during the crushing process.
Core Technical Content
The roller journals in cane sugar mills are subjected to continuous sliding contact with the feed roller and gear teeth, leading to progressive wear that reduces the journal diameter below tolerance. Traditional repair methods such as machining and re-hardening are often insufficient for restoring dimensional accuracy and surface hardness simultaneously. The authors developed an overlay welding repair process that involves the following key steps:
- Surface preparation: The worn journal surface is ground to remove loose material, oxide scale, and contaminated zones. The surface is cleaned with acetone or a similar solvent to remove oil and grease.
- Preheating: The journal is preheated to 200 to 300 degrees Celsius to reduce thermal stress and prevent cracking during welding.
- Overlay welding: Multiple layers of hardfacing alloy are deposited using shielded metal arc welding (SMAW) or submerged arc welding (SAW), depending on the available equipment and the size of the journal.
- Post-weld machining: The overlay layer is machined to the required dimensional tolerance and surface finish.
- Heat treatment: A tempering treatment is applied to relieve residual stress and optimize hardness.
Overlay Alloy Selection and Parameters
| Parameter | Specification | Rationale |
|---|---|---|
| Base material | Medium carbon steel journal (typically 45 steel or similar) | Standard mill roller material |
| Overlay alloy | High-carbon chromium steel or cobalt-based alloy | Provides wear resistance and hardness |
| Electrode type | Hardfacing electrode (e.g., D415, D507 equivalent) | Suitable for SMAW overlay |
| Preheat temperature | 200–300 degrees Celsius | Reduces cooling rate, prevents cracking |
| Interpass temperature | Below 300 degrees Celsius | Controls microstructure, prevents grain growth |
| Welding current | 120–180 A (SMAW) | Adequate penetration without excessive dilution |
| Post-weld treatment | Temper at 550–650 degrees Celsius | Relieves residual stress, stabilizes microstructure |
| Target hardness | HRC 50–60 after tempering | Ensures wear resistance |
Process Development and Industrial Application
The authors report that the developed process was successfully applied to repair worn journals at the Pumiang and Dongjiang sugar mills. The overlay layer achieved a hardness of HRC 50 to 60 after tempering, which is comparable to or exceeds the original journal surface hardness. The wear life of the repaired journals was reported to be significantly extended compared to the original condition, with service life approaching that of new rollers.
A critical aspect of the process development was the selection of the overlay alloy composition. The authors considered several factors:
- Compatibility with base metal: The overlay alloy must have a coefficient of thermal expansion compatible with the base steel to prevent cracking during thermal cycling.
- Weldability: The overlay alloy must be weldable without excessive cracking susceptibility, particularly in the presence of carbon and alloying elements in the base metal.
- Hardness after tempering: The overlay must retain adequate hardness after the tempering treatment required to relieve residual stress.
- Machinability: The overlay layer must be machinable to achieve the required dimensional tolerance and surface finish.
Defect Analysis and Countermeasures
During the development process, several defects were encountered and addressed:
| Defect | Cause | Countermeasure |
|---|---|---|
| Cracking at fusion boundary | High carbon content in base metal, rapid cooling | Increase preheat temperature, use low-hydrogen electrode |
| Porosity in overlay layer | Surface contamination, insufficient shielding | Improve surface cleaning, ensure adequate gas shielding |
| Excessive dilution | High welding current, large electrode diameter | Reduce current, use smaller electrode, increase layers |
| Undercut at bead edge | Excessive travel speed, improper electrode angle | Reduce travel speed, maintain proper electrode angle |
| Hardness below specification | Insufficient alloy content, excessive dilution | Increase number of layers, use higher alloy content electrode |
Engineering Practice Integration
The practical implementation of this repair process in the sugar industry highlights several important considerations for field welding operations:
- Equipment availability: Sugar mills may not have access to specialized welding equipment. The process must be adaptable to standard SMAW or SAW equipment available at the mill.
- Logistics and scheduling: Mill downtime is expensive. The repair process must be designed for rapid execution, ideally allowing the journal to be repaired in-situ or with minimal disassembly.
- Quality control: Field conditions make it difficult to perform comprehensive non-destructive testing. The process must be designed to minimize defect susceptibility, and visual inspection combined with hardness testing should be used as primary quality control methods.
- Cost-effectiveness: The repair cost must be significantly lower than replacement cost. The authors implicitly address this by demonstrating that the overlay welding process extends service life to near-new condition at a fraction of the replacement cost.
Key Questions and Reflections
One significant question is the long-term durability of the overlay repair under cyclic loading conditions. Sugar mill rollers experience continuous vibration and impact loading during operation. The overlay layer must withstand not only abrasive wear but also fatigue and thermal cycling. The authors do not provide long-term field data, which limits the ability to fully assess the reliability of the repair process.
Another reflection concerns the scalability of the process to other industrial applications. The principles of overlay welding repair for worn journals are directly applicable to other rotating equipment such as pump shafts, crusher rolls, and conveyor rollers. The key is to adapt the overlay alloy selection and welding parameters to the specific wear mechanism and loading conditions of each application.
Study Insights and Implications
This paper represents a valuable example of applied overlay welding technology in the sugar processing industry. The practical nature of the study, with direct collaboration between academic researchers and industrial practitioners, is commendable. The process development approach, which iteratively addresses defects and optimizes parameters based on field feedback, is a model for applied engineering research. The study also highlights the importance of considering the entire repair cycle, from surface preparation through post-weld machining and heat treatment, rather than focusing solely on the welding process itself. For future work, the authors should consider conducting tribological testing of the overlay layer under simulated sugar mill operating conditions and performing long-term field trials to validate the service life predictions.