Field Overlay Welding Repair of Metal Matrix Composite Ceramic Grinding Discs

Literature Overview

The paper by Ni Junjie and Yang Wei, published in New Century Cement Bulletin (2013, Vol. 19, No. 5, pp. 80-81), documents the field repair of RM57/28 type metal matrix composite ceramic grinding discs using ZD903-O welding wire through three intermittent overlay welding passes. The authors are affiliated with the Zhengzhou Research Institute of Mechanical Engineering. This case study addresses a critical maintenance challenge in the cement industry: the repair of large, expensive grinding disc components that incorporate ceramic inserts for enhanced wear resistance.

Core Technical Content

Component Description and Failure Analysis

The RM57/28 raw material vertical roller mill grinding disc is a large component used in cement grinding operations. The disc incorporates metal matrix composite (MMC) technology, where ceramic inserts (typically alumina or silicon carbide) are embedded in a metallic matrix to provide superior abrasion resistance against cement clinker and raw meal.

Welding Material Selection

The ZD903-O welding wire was selected for this repair application. The selection criteria included:

1. Metallurgical compatibility: The wire must form a metallurgical bond with the metallic matrix of the composite surface.
2. Thermal expansion matching: The thermal expansion coefficient of the weld metal should be compatible with both the metallic matrix and the ceramic inserts to minimize thermal stress during welding and service.
3. Wear resistance: The overlay must provide abrasion resistance comparable to or exceeding the original composite surface.
4. Weldability: The wire must be suitable for field welding conditions with available equipment.

Repair Process and Results

The repair was executed through three intermittent overlay welding passes. The key process features included:

The results demonstrated:

• Weld bead quality: Good bead formation with uniform profile across all three passes.
• Bond integrity: No delamination or spalling observed at the interface between the overlay weld and the composite surface.
• Wear resistance: The repaired surface exhibited superior abrasion resistance compared to the original disc surface.
• Thermal effects on ceramic inserts: The welding heat input did not significantly affect the ceramic inserts, indicating that the thermal management was effective in limiting the temperature rise in the ceramic zones.

Engineering Practice Analysis

Thermal Management Strategy

The success of this repair case hinges on the thermal management strategy. The intermittent (discontinuous) welding approach is a critical technique for managing heat input when repairing components with heterogeneous materials. By welding discrete sections and allowing cooling between passes, the thermal gradient is minimized, reducing the risk of:

• Thermal cracking in the ceramic inserts
• Delamination at the ceramic-metal interface
• Excessive distortion of the disc geometry
• Residual stress buildup that could lead to premature failure

This approach is analogous to the "skip welding" technique used in pipe welding, where welds are not completed sequentially around the circumference but are instead executed in a pattern that minimizes cumulative distortion.

Interface Metallurgy

The formation of a metallurgical bond between the ZD903-O weld metal and the metallic matrix of the composite surface is essential for repair integrity. The absence of delamination indicates that:

1. The welding parameters produced sufficient heat to achieve complete melting and mixing at the interface.
2. The cooling rate was appropriate to form a sound metallurgical bond without excessive grain growth or brittle phase formation.
3. The thermal expansion mismatch between the weld metal and the composite surface was managed through controlled heat input.

Quality Verification

For field repair applications, the following quality verification steps are recommended:

Study Insights

This case study demonstrates the feasibility of field repair of metal matrix composite components through overlay welding, which is a significant finding given the complexity of repairing heterogeneous materials. The use of intermittent welding passes to manage heat input is a practical and effective strategy that can be applied to other composite component repairs.

The finding that the repaired surface exhibited superior wear resistance to the original disc is particularly interesting. This could be attributed to several factors: the overlay weld material may have a harder microstructure than the original composite surface, the welding process may have refined the grain structure at the interface, or the repair may have eliminated surface defects that initiated wear in the original component.

For engineers working in the cement, mining, and power generation industries, this paper provides valuable evidence that overlay welding repair is a viable alternative to replacement for expensive composite surface components. The key to success lies in proper material selection, thermal management, and process control.

Summary

This field repair case study provides practical evidence that metal matrix composite ceramic grinding discs can be successfully repaired through overlay welding using ZD903-O wire with intermittent passes. The absence of delamination, good weld bead quality, and superior wear resistance of the repaired surface demonstrate the effectiveness of the approach. The thermal management strategy of intermittent welding is a key technique that should be adopted for similar repair applications involving heterogeneous materials. This work contributes valuable field experience to the growing body of knowledge on composite component repair through welding.