Overlay Welding Repair of ATOX50 Mill Grinding Plate and Application Results

Literature Overview

This case study by Li Chun and Wang Cun documents the overlay welding repair of an ATOX50 vertical roller mill grinding plate at a large cement company in northern China. Published in Cement Engineering (2008, No. 4, pp. 55-57), the paper provides a practical example of how overlay welding technology can extend the service life of critical grinding equipment in the cement industry.

The ATOX50 is a large vertical roller mill imported from Germany, representing one of the earliest installations of this technology in China. The study is particularly relevant for engineers working in the cement, mining, and mineral processing industries where grinding equipment subject to severe abrasive wear is a common challenge.

Background and Problem Statement

The ATOX50 vertical roller mill serves as the critical component in the cement grinding system, processing materials such as steel slag, sandstone, limestone, and shale. These materials have extremely high hardness, causing severe wear and impact damage to the grinding plate and rollers during the crushing and grinding process.

The original grinding plates were produced through conventional smelting and casting processes, which were limited by the technological capabilities and casting quality control standards of the time. As a result, the as-cast material did not achieve the ideal composition designed by materials engineers, leading to insufficient wear resistance and short service life. This created significant production disruption and increased maintenance costs.

Repair Methodology

The overlay welding repair approach involved the following key steps:

Surface preparation: Removal of the worn surface material to expose sound base metal, followed by cleaning and degreasing to ensure proper weld adhesion.
Welding consumable selection: Selection of an appropriate overlay welding consumable with high hardness and good wear resistance properties, suitable for the specific abrasive conditions encountered in the cement grinding process.
Welding parameter optimization: Determination of appropriate welding current, voltage, travel speed, and layering strategy to achieve the desired overlay thickness and quality.
Post-weld treatment: Depending on the specific alloy system used, post-weld heat treatment may have been applied to optimize the microstructure and mechanical properties of the overlay layer.

Technical Analysis of Wear Mechanisms

The grinding plate in a vertical roller mill is subjected to a combination of wear mechanisms that are more severe than those encountered in many other industrial applications:

Abrasive wear: Primary mechanism caused by hard particles in the grinding material (steel slag, sandstone) acting as third-body abrasives between the grinding plate surface and the grinding rollers.
Impact wear: Caused by the high-energy impact of material fragments falling onto the grinding plate surface.
Fatigue wear: Resulting from cyclic loading during the grinding process, which can cause microcracking and surface spalling.

The selection of an appropriate overlay welding alloy is critical for addressing these multiple wear mechanisms. The overlay must possess sufficient hardness to resist abrasive wear, adequate toughness to withstand impact loading, and good fatigue resistance to prevent surface cracking under cyclic conditions.

Application Results and Lessons Learned

While the paper provides a practical case study rather than extensive laboratory data, the application results demonstrate that overlay welding repair can effectively restore the grinding plate to a serviceable condition, extending its operational life significantly compared to the original as-cast material. The study highlights several important lessons for engineers:

Casting quality limitations can be overcome through welding-based surface engineering approaches, providing a practical alternative to complete component replacement.
The selection of overlay welding consumables must consider the specific wear conditions of the application, not just the general material hardness requirements.
Proper welding procedure qualification and operator training are essential for achieving consistent repair quality in field conditions.

Engineering Practice Considerations

For engineers planning similar overlay welding repairs on grinding equipment, several practical considerations should be addressed:

Pre-heat requirements: Depending on the base material and overlay alloy used, pre-heating may be necessary to prevent cracking during welding, particularly for high-carbon or high-alloy base materials.
Dilution control: The dilution of the overlay layer by the base metal can significantly affect the final hardness and wear resistance of the overlay. Multi-layer welding with progressive alloy content can help minimize dilution effects.
Stress management: The thermal stresses induced during overlay welding can cause cracking or delamination of the overlay layer, particularly in thick sections. Proper interpass temperature control and post-weld stress relief may be necessary.
Surface preparation quality: The quality of surface preparation directly affects the bonding strength between the overlay and base material. Inadequate preparation can lead to premature overlay failure in service.

Summary and Implications

This case study demonstrates the practical value of overlay welding technology in extending the service life of critical grinding equipment in the cement industry. The ATOX50 grinding plate repair illustrates that welding-based surface engineering can overcome the limitations of conventional casting processes and provide a cost-effective solution for equipment refurbishment. For engineers in the cement, mining, and mineral processing industries, this approach offers a viable alternative to complete component replacement, reducing both capital expenditure and downtime associated with equipment maintenance.