Wear-Resistant Hardfacing of Vertical Roller Mill Rollers and Tables

Literature Overview

The paper by Zhang Kunmou, Zheng Guoliang, and Peng Xinqiao (2005), published in New Century Cement Bulletin, examines wear-resistant hardfacing technology for vertical roller mill rollers and grinding tables. Vertical roller mills have been widely adopted in cement grinding circuits for their significant energy savings compared to traditional ball mills. However, the authors highlight that irregular wear of rollers and tables, combined with increased clearance due to material loss, leads to declining equipment efficiency, rising energy consumption, and ultimately unplanned shutdowns for repair.

Core Technical Analysis

Wear Mechanisms in Vertical Roller Mills

Vertical roller mills operate under conditions of sustained high pressure between the grinding rollers and the table, with compressive forces typically in the range of 800–1200 kN per roller for a mill of 100 t/h capacity. The wear environment is characterized by a combination of abrasive action from hard mineral particles trapped between the rolling surfaces, adhesive transfer of material between roller and table, and fatigue damage from cyclic compressive loading. The irregular nature of the wear pattern—often showing center-heavy or asymmetric profiles—is a consequence of uneven material distribution, hydraulic system asymmetry, and the complex kinematics of the grinding action.

The authors identify three critical consequences of progressive wear: first, the grinding gap increases, reducing the pressure per unit area and lowering grinding efficiency; second, the material throughput decreases as the effective grinding surface diminishes; and third, the energy consumption per ton of product increases as the mill operates less effectively. These effects create a negative feedback loop that accelerates the need for repair.

Hardfacing Technology and Process Optimization

The paper discusses the application of wear-resistant hardfacing alloys to restore roller and table surfaces to original dimensions. The following table presents the key technical parameters and considerations:

The authors emphasize that the surface preparation step is critical: any residual oxide, scale, or contaminated metal must be completely removed to ensure proper fusion between the base metal and the hardfacing deposit. Incomplete preparation leads to poor bond strength and premature spalling of the deposit under operational loading.

Impact on Production and Maintenance Costs

A key contribution of this paper is the economic analysis linking hardfacing quality to production performance. The authors note that poor hardfacing practices—such as insufficient preheat, excessive cooling rates, or improper alloy selection—result in cracking and spalling of the deposit within weeks of operation, leading to repeated repair cycles and extended downtime. Conversely, properly executed hardfacing extends the service interval between repairs by 2–4 times, significantly reducing maintenance costs and improving plant availability.

Engineering Practice and Standards Considerations

The hardfacing technology described in this paper has direct relevance to pipe manufacturing operations, particularly for mill roll hardfacing in tube and pipe mills. In seamless pipe manufacturing, the plug mill rolls, piercing rolls, and finishing mill rolls all experience severe wear conditions that require periodic hardfacing repair. The principles of alloy selection based on wear mechanism, controlled thermal input to prevent base metal degradation, and post-weld dressing to restore dimensional accuracy are universally applicable.

From a quality control perspective, the hardfacing repair of critical equipment should be governed by documented procedures that include welder qualification, consumable traceability, preheat and interpass temperature monitoring, and post-weld inspection including visual examination, magnetic particle testing for surface cracks, and hardness profiling. Standards such as ASME B31.3 for pressure piping systems and relevant welding procedure qualification standards (such as ISO 15614 or AWS D1.1) provide the framework for qualified hardfacing procedures, and these should be adapted for equipment repair applications.

Key Reflections and Implications

The literature underscores that hardfacing is not merely a welding operation but a system-level engineering solution that requires integration of metallurgical knowledge, process control, and operational management. The economic argument presented by the authors—that proper hardfacing practice reduces total maintenance costs despite higher initial repair expenses—provides a compelling case for investing in qualified welding procedures, skilled personnel, and quality assurance systems. For engineers managing heavy equipment in any industry, the lesson is clear: the quality of the hardfacing process is a direct determinant of equipment availability and production efficiency, and shortcuts in this area inevitably lead to higher total costs.