Overlay Welding Maintenance and Care of Roller Compactor Roller Surfaces

Literature Overview

This 2006 publication by researchers from the Zhengzhou Machinery Research Institute and Sichuan Qimingxing Power Equipment Manufacturing Group addresses the practical challenges of overlay welding, maintenance, and preservation of roller surfaces in cement roller presses. Roller compactor rollers are subjected to extreme operating conditions in cement grinding circuits, where they experience continuous abrasive contact with cement clinker and raw meal particles. The overlay layer on the roller surface is the primary means of extending roller service life, and its proper application, maintenance, and care directly impact production efficiency and operating costs.

The paper adopts a practical engineering approach, combining metallurgical analysis with field experience to present a comprehensive guide for roller surface management. The authors draw upon extensive industrial experience to identify common failure modes and propose systematic maintenance procedures that can be implemented in cement plant operations.

Core Technical Content

Roller Operating Conditions and Wear Mechanisms

Cement roller press rollers operate under a complex combination of loading and environmental conditions:

The dominant wear mechanisms on roller surfaces include:

• Abrasive wear: Three-body abrasion by hard cement particles embedded in the contact zone, accounting for 60–80% of material removal
• Adhesive wear: Cold welding and tearing at contact asperities under high compressive stress
• Fatigue wear: Subsurface crack initiation and propagation under cyclic Hertzian contact stress
• Corrosive wear: Chemical attack by moisture and acidic compounds in cement materials

Overlay Material Selection

The selection of overlay material is the most critical decision in roller surface protection. The study evaluates several material systems:

For cement roller applications, the high-carbon chromium alloy system (such as Cr25Ni4Mo or Cr28Ni6Mo) is generally recommended due to its excellent combination of hardness, toughness, and resistance to both abrasive and adhesive wear. The retained austenite in these alloys provides inherent toughness and work-hardening capacity that prevents catastrophic failure.

Welding Process Selection

The choice of welding process depends on the roller geometry, available equipment, and production requirements:

For full roller surface overlay, submerged arc welding is the most economical choice due to its high deposit rate and consistent quality. However, for localized repairs and maintenance, GMAW or FCAW provides greater flexibility and accessibility.

Overlay Layer Design Considerations

The overlay layer design must account for several factors:

1. Thickness optimization: The overlay thickness should be sufficient to accommodate the expected wear life but not so thick as to introduce excessive residual stress. Typical thickness ranges from 3–8 mm for roller surfaces.
2. Profile geometry: A crowned or slightly convex profile (crown height 0.1–0.3% of roller diameter) helps distribute contact stress more uniformly and prevents edge loading.
3. Bond layer: A transition layer of medium-carbon steel may be applied between the substrate and the overlay to reduce dilution and improve bond quality.
4. Surface finish: The final surface roughness should be Ra 6.3–12.5 μm to balance wear resistance with lubrication film formation.

Maintenance and Care Procedures

Pre-Application Preparation

Proper surface preparation is essential for achieving good bond strength and overlay quality:

1. Surface cleaning: Remove all rust, scale, oil, and contamination using grinding, sandblasting, or chemical cleaning
2. Defect repair: Grind out existing cracks, pits, and loose material to sound metal
3. Surface profiling: Create a slight undercut or groove at the weld start/stop points to ensure good fusion
4. Preheating: Apply preheat of 150–250°C to reduce residual stress and prevent cold cracking
5. Temperature monitoring: Maintain interpass temperature below 250°C to avoid excessive grain growth

Overlay Application Procedure

The overlay welding procedure should follow these steps:

1. Apply the first pass at reduced current (70–80% of full current) to achieve good fusion with the substrate while controlling dilution
2. Apply subsequent passes at full current to build up the required thickness
3. Maintain a consistent travel speed and electrode angle throughout each pass
4. Overlap adjacent passes by 30–50% of the bead width to ensure uniform coverage
5. Apply the final pass at reduced current to achieve a smooth, dense surface finish
6. Allow natural cooling in still air (avoid forced cooling or water quenching)

Post-Weld Treatment

After overlay welding, the following post-weld treatments should be applied:

• Stress relief: Furnace treatment at 550–600°C for 2–4 hours to reduce residual stresses
• Machining: Machine the overlay surface to the required profile and finish
• Inspection: Perform magnetic particle inspection (MT) for surface cracks and ultrasonic testing (UT) for subsurface defects
• Hardness verification: Measure Vickers hardness at multiple locations to confirm uniformity

In-Service Maintenance

During operation, the following maintenance procedures should be followed:

1. Regular inspection: Inspect roller surface every 200–500 operating hours for wear patterns, cracks, and spalling
2. Wear measurement: Measure overlay thickness at regular intervals to predict remaining service life
3. Surface repair: Grind and re-weld localized wear areas before they become critical
4. Roller alignment: Verify roller parallelism and alignment to prevent edge loading and uneven wear
5. Lubrication: Maintain proper lubrication of roller bearings and guide mechanisms

Overlay Removal and Renewal

When the overlay layer is worn beyond acceptable limits, proper removal and renewal procedures must be followed:

• Mechanical removal: Use grinding wheels or milling cutters to remove the worn overlay without damaging the substrate
• Thermal removal: Apply controlled heating to the overlay surface to reduce hardness, then mechanically remove
• Substrate inspection: After overlay removal, inspect the substrate for cracks, grooves, or material loss
• Substrate repair: Weld repair any substrate defects before applying new overlay
• Re-overlay: Apply new overlay following the complete procedure outlined above

Engineering Practice Cases

Case Study: Roller Press in a Large Cement Plant

A large cement plant with a roller press of 1200 mm diameter and 400 mm width experienced frequent roller failures with overlay life of only 60–90 days. The root cause analysis identified several contributing factors:

1. Excessive dilution: The original overlay procedure used a dilution rate of 40–50%, resulting in an overlay hardness of only 400–450 HV
2. Inadequate thickness: The overlay thickness was only 2–3 mm, providing insufficient material for the expected wear rate
3. Poor surface preparation: Rust and scale on the substrate surface led to incomplete fusion and early delamination
4. No stress relief: High residual stresses from welding contributed to fatigue cracking

After implementing the improved procedures recommended in this study, the overlay life increased to 250–350 days, representing a 3–4 times improvement in service life. The key changes included:

• Reducing dilution to 15–20% by using a low-dilution wire and optimized parameters
• Increasing overlay thickness to 5–6 mm
• Implementing proper surface preparation with grinding and cleaning
• Adding a stress relief treatment after overlay welding
• Establishing a regular inspection and maintenance schedule

Common Failure Modes and Root Causes

Key Questions and Reflections

The study highlights several areas where further investigation is needed. The interaction between the overlay microstructure and the cement grinding process is complex and not fully understood. For example, the effect of particle size distribution on wear rate, the influence of material temperature on overlay performance, and the role of lubrication additives in modifying wear mechanisms all require further study.

Another important consideration is the economic optimization of the overlay maintenance strategy. The cost of overlay welding, including consumables, labor, downtime, and equipment, must be balanced against the cost of roller replacement. A life-cycle cost analysis should be conducted to determine the optimal overlay thickness, material selection, and maintenance interval.

The study also raises the question of whether advanced welding technologies such as laser cladding and cold spray could provide advantages for roller surface protection. While these technologies offer excellent dilution control and minimal heat input, their higher equipment costs and lower deposit rates may limit their practical application for large-scale roller overlay work.

Study Insights and Implications

This study provides a practical and comprehensive guide for the overlay welding, maintenance, and care of cement roller press surfaces. The systematic approach of addressing material selection, process optimization, quality control, and maintenance procedures offers a complete framework that can be adapted to other heavy-duty roller applications.

The key insight is that overlay performance is not determined by any single factor but by the integrated effect of material composition, process parameters, surface preparation, post-weld treatment, and maintenance practices. A holistic approach to overlay management is essential for achieving optimal performance and economic viability.

For engineering practice, the recommendation is to establish a documented overlay procedure that includes specific parameters for each step of the process, from surface preparation through to final inspection. Regular training of welding personnel and maintenance staff is essential to ensure consistent quality and to enable early detection of potential problems.