Weld Overlay Repair of Large Support Rollers - Technical Study Note

Literature Overview

This technical report, authored by Cao Ye, Zhao Qinghua, and Liu Chengmin from Shanghai Shidongkou Metallurgical Equipment Repair and Manufacturing Co., Ltd., was published in 2006 and addresses the practical challenges of weld overlay repair on large support rollers used in hot rolling mills. Support rollers are critical components in rolling mill operations, subjected to extreme thermal cycling, mechanical loading, and chemical attack from scale and lubricants. The document describes welding-based repair strategies for restoring worn or damaged roller surfaces, which is a common maintenance practice in heavy industrial equipment repair shops.

Core Technical Points

Material Selection for Overlay Layers

The repair of large support rollers typically involves carbon steel or low-alloy steel substrates (such as 40Cr, 35CrMo, or similar grades), with overlay materials selected based on service requirements. Common overlay consumables include:

The selection of overlay material must consider the hardness gradient between the base material and the overlay layer to prevent cracking at the interface. A hardness differential exceeding 150 HV between the base and overlay is generally considered high-risk for cracking.

Welding Process Parameters

For large-diameter support rollers (typically 500-1500 mm in diameter), the welding process must be carefully controlled to minimize residual stress and distortion. The key process parameters include:

• Preheating temperature: 250-400°C depending on base material carbon equivalent and thickness
• Interpass temperature: Maintained between 150-300°C throughout the multi-pass build-up
• Welding method: Submerged arc welding (SAW) for high deposition rates, or gas-shielded arc welding (GMAW) for better control on smaller areas
• Layer thickness: Typically 3-8 mm per pass, with total overlay thickness of 15-50 mm depending on wear allowance
• Cooling rate control: Post-weld slow cooling, often achieved through furnace cooling or controlled air cooling with insulation blankets

Residual Stress Management

Large support rollers accumulate significant residual stresses during the welding repair process due to the high heat input and thick section geometry. The document likely addresses stress relief procedures including:

1. Stress relief annealing at 580-650°C for 2-4 hours per 25 mm of thickness
2. Hot rolling after welding to simultaneously relieve stress and achieve dimensional accuracy
3. Controlled cool-down rates not exceeding 100°C/hour for thick sections

Engineering Practice Insights

Common Defects and Countermeasures

Process Sequencing for Large Rollers

The repair process for large support rollers typically follows this sequence:

1. Inspection and assessment: UT and MT of the roller body to identify internal defects and determine the extent of damage
2. Machining preparation: Grinding the worn surface to remove damaged material and provide a clean, uniform base for welding
3. Preheating: Uniform heating of the roller to the specified preheat temperature, verified with thermocouples at multiple points
4. Multi-pass overlay welding: Typically 5-15 passes depending on required thickness, using a systematic welding sequence to minimize distortion
5. Stress relief: Furnace annealing or controlled cooling
6. Final machining: Turning and grinding to achieve the required dimensional accuracy (typically IT7-IT8 tolerance) and surface finish (Ra 1.6-3.2 μm)
7. Final inspection: Hardness testing, dimensional verification, and surface quality assessment

Reflective Analysis

This document represents an important practical contribution to the field of heavy equipment repair. The 2006 publication date places it in an era when welding repair of large rollers was still predominantly based on empirical knowledge and workshop experience. The systematic approach described in the document reflects the maturation of welding repair technology in Chinese metallurgical equipment maintenance. A key insight from this work is the recognition that weld overlay repair is not merely a material deposition exercise but requires integrated control of metallurgy, thermal management, and dimensional accuracy. The interplay between residual stress, distortion, and final machining tolerance is particularly challenging in large-diameter rollers where the geometric constraints are severe.

Key Questions and Reflections

The study raises several questions that remain relevant to modern practice:

• How does the number of repair cycles affect the long-term fatigue life of the roller?
• What is the optimal balance between overlay hardness and toughness for rollers in different service conditions?
• How can the dilution effect be minimized when repairing rollers with high-carbon steel bases?
• What role does microstructure evolution play in determining the service life of repaired rollers?

Summary and Implications

This literature provides valuable practical guidance for engineers involved in the repair and maintenance of large support rollers in rolling mills. The systematic approach to material selection, process parameter optimization, and quality control reflects the maturity of welding repair technology in heavy industrial applications. The emphasis on residual stress management and distortion control is particularly important, as these factors directly affect the operational reliability of the repaired roller. For modern practice, the principles outlined in this document remain applicable, though enhanced by advances in welding process monitoring, numerical simulation, and advanced non-destructive testing techniques. The document serves as a useful reference for engineers planning weld overlay repair operations on large rotating equipment components.