Zhuojin Pipe Fitting Co., LtdOverlay Welding Repair of ATOX50 Mill Grinding Disc and Application Performance
Literature Overview
This paper by Li Chun and Wang Cun, published in Cement Engineering (2008, Issue 4), documents the practical application of overlay welding technology for the repair and performance enhancement of ATOX50 vertical roller mill grinding discs in cement production. The ATOX50 is one of the earliest large-scale vertical mills imported into China, representing a critical piece of equipment in the cement grinding system. The paper bridges the gap between metallurgical research on wear-resistant overlay materials and their practical implementation in heavy industrial maintenance.
Problem Statement and Background
The ATOX50 vertical roller mill processes extremely abrasive materials including iron slag, sandstone, limestone, and shale. These materials have high hardness values and create severe abrasive and impact wear conditions on the grinding disc and roller surfaces. The original cast components suffer from limited wear resistance due to constraints in metallurgical processing technology and casting quality control. The result is short service life and frequent production interruptions for component replacement.
Root Cause Analysis of Wear Failure
The wear mechanism in this application involves multiple damage modes:
- Abrasive wear: Hard particles in the grinding media plow and cut the surface material
- Impact wear: Repeated loading from the grinding rollers creates subsurface fatigue
- Thermal fatigue: Localized heating during grinding cycles creates thermal cycling stresses
- Chemical wear: Interaction between grinding media and the base metal surface
The traditional approach of replacing worn grinding discs with new cast components is economically inefficient and causes significant production downtime. Overlay welding provides a viable alternative by restoring dimensions and dramatically improving surface wear resistance.
Overlay Welding Repair Solution
The repair process involves the following key steps:
| Process Step | Technical Parameter | Purpose |
|---|---|---|
| Surface preparation | Grinding and cleaning | Remove oxide, ensure base metal integrity |
| Preheating | 150-250°C (typical for cast iron/steel) | Reduce thermal stress, prevent cracking |
| Overlay welding | Multi-pass hardfacing with high-carbon alloy | Build wear-resistant surface layer |
| Post-weld heat treatment | Stress relief at 500-600°C | Reduce residual stress, prevent delayed cracking |
| Machining | Precision grinding to final dimensions | Achieve surface finish and dimensional accuracy |
The selection of overlay welding consumables is critical. For this application, high-carbon chromium iron or nickel-based hardfacing alloys are typically selected to provide hardness in the range of HRC 55-65 while maintaining adequate impact toughness to resist spalling under impact loading.
Application Results and Performance Assessment
The overlay welding repair approach demonstrated significant improvements in grinding disc service life compared to the original cast condition. The hardfaced surface provides a hard, wear-resistant layer while the ductile base metal maintains structural integrity and impact resistance. The combined effect is a synergistic improvement in overall component durability.
Key performance indicators include:
- Extended service life between maintenance intervals
- Reduced production downtime for component replacement
- Improved grinding efficiency due to maintained surface geometry
- Cost savings from repair versus full component replacement
Engineering Practice Reflections
This case study exemplifies the practical value of overlay welding in heavy industry maintenance. The economic analysis strongly favors repair over replacement when the base component retains structural integrity. Engineers should consider overlay welding as a first-line maintenance strategy for worn surfaces before resorting to component replacement.
The paper also highlights an important consideration: the quality of the base casting directly affects the success of overlay welding repair. Poor casting quality, including internal porosity, segregation, and cracks, can compromise the weld interface and lead to premature failure. Therefore, pre-repair inspection of the base component is essential.
From a process optimization standpoint, the choice between single-pass and multi-pass overlay welding depends on the required thickness of the wear-resistant layer. Multi-pass welding allows for better control of dilution between the base metal and overlay material, ensuring the overlay retains its designed hardness and microstructure. The dilution rate should be monitored through hardness profiling across the overlay depth.