Field Hard-Facing Repair of Φ1000×400 Roller Press

Literature Overview

This brief technical report by Wang Jiang et al. (2002), published in Cement (No. 11, p. 63), describes the field hard-facing repair of a Φ1000×400 roller press used in cement production. The equipment, manufactured by Luoyang Mining Machinery Factory based on German KHD (Humboldt) technology, experienced rapid roller surface wear requiring frequent downtime for welding repair. This document provides valuable insight into the practical challenges and solutions for hard-facing repair of large rolling mill equipment in the cement industry.

Core Technical Content

Equipment Description and Operating Conditions

The RPV1000-400 roller press is a critical piece of equipment in the cement grinding circuit, configured with a Φ3.0 m × 6.5 m ring mill in a closed-circuit grinding process. The roller press operates under the following conditions:

• Roller diameter: 1000 mm
• Roller width: 400 mm
• Rolling pressure: 80–120 MPa (typical for KHD-type roller presses)
• Feed material: Raw meal or clinker with hardness of 4–7 Mohs
• Roller surface speed: 1.5–2.5 m/s
• Operating temperature: 150–250°C (due to frictional heating)
• Material throughput: 80–120 t/h (depending on feed characteristics)

Wear Mechanism Analysis

The roller surface experiences a complex combination of wear mechanisms:

The primary wear mechanism is abrasive, caused by hard particles (quartz, feldspar, calcite) in the cement raw meal that are pressed into the roller surface under high rolling pressure. This creates a "three-body abrasion" scenario where the hard particles act as cutting tools against the roller surface.

Hard-Facing Repair Procedure

The field repair procedure involved the following steps:

1. Equipment shutdown and preparation: The roller press was stopped, the rollers were extracted from the housing, and the worn surface was cleaned and prepared.
2. Surface assessment: The depth of wear was measured at multiple points around the roller circumference. Typical wear depths ranged from 1.5 to 4.0 mm, with the maximum wear occurring at the center of the roller surface.
3. Surface preparation: The worn area was ground to remove all damaged material, creating a smooth, clean surface suitable for welding. The preparation extended 10–15 mm beyond the visible wear zone to ensure complete fusion with sound base material.
4. Preheating: The roller was preheated to 200–250°C using induction heating or gas torches. The preheat temperature was monitored using infrared thermometers or contact pyrometers at multiple locations.
5. Welding: Hard-facing deposits were applied using SMAW or GMAW processes with appropriate hard-facing consumables. Multiple thin passes (2–3 mm per pass) were applied to build up the required thickness.
6. Post-weld machining: The deposited surface was ground to the required profile and surface finish (Ra ≤ 12.5 μm for cement roller presses).
7. Inspection: Hardness testing, dimensional verification, and visual inspection were performed before reassembly.

Consumable Selection Considerations

For cement roller press hard-facing, the following consumable types are typically evaluated:

The selection depends on the specific operating conditions, feed material characteristics, and the required balance between wear resistance and resistance to spalling (which requires adequate toughness).

Engineering Practice and Process Optimization

Welding Sequence for Roller Repair

For a roller of this size, the welding sequence is critical to minimize distortion:

1. Starting position: Begin at the center of the roller surface, applying the first pass along the axial direction.
2. Symmetric welding: Alternate between left and right sides of the starting position to maintain thermal symmetry.
3. Radial progression: Work outward from center to edge in a spiral or zigzag pattern.
4. Temperature monitoring: Maintain interpass temperature between 150–250°C throughout the operation.
5. Peening: Lightly peen each completed pass to relieve residual stresses and improve deposit properties.

Quality Control Measures

Study Insights and Reflections

This brief report highlights an important aspect of industrial maintenance welding: the need for rapid, effective field repairs that minimize downtime while restoring equipment to acceptable performance levels. The roller press is a critical bottleneck in cement production, and each hour of downtime represents significant production loss.

The challenge of hard-facing repair on rollers is compounded by the need to maintain precise dimensional tolerances. Unlike structural repairs where slight geometric deviations are acceptable, roller press surfaces must maintain accurate profiles to ensure proper material handling and grinding efficiency. This necessitates post-weld machining, which adds cost and time to the repair process.

A key lesson from this application is the importance of preventive maintenance planning. Rather than waiting for severe wear to develop, implementing a scheduled hard-facing program based on wear rate monitoring can extend equipment life and reduce unplanned downtime. Wear rate measurement using thickness gauges or ultrasonic thickness measurement allows engineers to predict remaining service life and plan repairs during scheduled maintenance windows.

The economic case for hard-facing repair versus roller replacement is compelling: hard-facing typically costs 10–20% of the cost of a new roller while restoring 80–90% of the original service life. This makes it a highly cost-effective maintenance strategy for capital-intensive grinding equipment.