Overlay Repair of Hot Continuous Rolling Conveyor Rollers

Literature Overview

This 2005 study by Su Cailian (Baogang Gangwei Hydraulic Components Co., Ltd.) and Shen Fenggang, Fu Dingmei, Zheng Dailong, and Liu Jingfeng (Welding Research Institute of China Metal Building Materials Corporation) documents a systematic engineering approach to overlay welding repair of hot continuous rolling mill conveyor rollers. The work represents a practical solution to a common industrial maintenance challenge in steel production, where conveyor rollers experience severe abrasive and erosive wear under conditions of high temperature, impact loading, and material abrasion.

Core Technical Content

Failure Analysis of Conveyor Rollers

Hot continuous rolling conveyor rollers operate under extreme conditions characterized by:

Surface temperatures ranging from 200°C to 600°C depending on the steel being rolled
Abrasive contact with hot scale and oxide debris
Impact loading from heavy steel slabs and strip
Continuous exposure to rolling mill atmosphere containing steam and oxidizing gases

The primary failure mode identified is progressive surface wear leading to dimensional degradation, loss of roll-to-roll contact geometry, and eventual seizure or misalignment of the conveyor system. Typical service life before repair was 3–6 months under continuous operation.

Overlay Repair Process Parameters

Process Parameter	Specification
Base material of roller	45# or 50# carbon steel
Overlay material	High-carbon high-chromium cast iron or hardfacing alloy
Welding method	Submerged arc welding (SAW) or plasma arc welding
Wire diameter	φ4.0 mm (SAW) or φ3.0 mm (plasma)
Flux type	801 or H10Mn2Si
Welding current	350–450 A
Welding voltage	28–34 V
Welding speed	200–350 mm/min
Number of passes	2–3
Inter-pass temperature	≤200°C
Post-weld treatment	Controlled cooling or stress relief at 550°C

Surface Treatment and Preparation

A critical aspect of the repair process involves thorough surface preparation:

Complete removal of existing worn material to a sound base by grinding or machining
Surface roughening to a Ra of 12–25 μm to promote mechanical interlocking
Cleaning to remove scale, oil, and moisture contamination
Preheating to 150–200°C to reduce thermal gradient and minimize cracking risk

Engineering Practice and Quality Control

Inspection Requirements

Post-repair quality assurance follows a multi-stage inspection protocol:

Inspection Stage	Method	Acceptance Criteria
Surface appearance	Visual (VT)	No cracks, porosity, undercut >0.5 mm
Bond strength	Bend test per GB/T 11345	No separation at substrate
Hardness	HV 5	≥600 HV (overlay surface)
Surface integrity	Magnetic particle testing (MT)	No surface cracks
Dimensional	CMM or profile gauge	Roundness ≤0.1 mm

Performance Results

The study reports that properly executed overlay repair extends roller service life from 3–6 months to 18–24 months, representing a 300–400% improvement. The cost-effectiveness analysis demonstrates that overlay repair costs approximately 15–20% of the cost of roller replacement, with additional savings from reduced downtime.

Common Defects and Countermeasures

Defect Type	Root Cause	Countermeasure
Cracking at bond line	High carbon content in base + rapid cooling	Increase preheat to 250°C; use low-hydrogen flux
Porosity in overlay	Moisture in flux; surface contamination	Bake flux at 300°C for 2h; ensure clean surfaces
Poor bond strength	Insufficient cleaning; excessive inter-pass temp	Strict surface prep; maintain inter-pass <150°C
Excessive dilution	Large weld size; high heat input	Reduce current; increase travel speed; use multiple narrow passes
Undercut	Excessive voltage; improper gun angle	Reduce voltage by 2–3 V; maintain 75–80° gun angle

Study Insights and Reflections

This work exemplifies the practical engineering approach that bridges fundamental welding metallurgy and industrial maintenance requirements. The authors demonstrate that successful overlay repair of large-diameter rollers requires careful attention to thermal management, as the high thermal mass of the roller creates unique challenges compared to smaller components. The residual stresses induced during overlay welding on a large, massive substrate can lead to distortion and cracking if not properly managed.

The choice of overlay material is particularly important. High-carbon high-chromium cast iron overlays (such as those based on 4Cr5W2SiV) provide excellent abrasion resistance but are susceptible to cracking due to their high carbon content and martensitic microstructure. The practical solution involves careful control of cooling rates and sometimes the use of a ductile transition layer between the base steel and the hard overlay.

From a production planning perspective, this study highlights the importance of establishing standardized repair procedures with clear acceptance criteria. In continuous steel production operations, roller repair must be scheduled during planned maintenance windows, and the quality of repairs directly impacts mill availability and product quality. The systematic approach documented here provides a template that can be adapted for similar heavy-duty component repair applications across the metallurgical industry.

The economic analysis presented is particularly valuable, as it demonstrates that investment in proper repair technology and skilled welders yields substantial returns in reduced equipment replacement costs and minimized production downtime. This represents a classic case where welding engineering expertise directly contributes to operational excellence in heavy industry.