Strip Cladding Repair of Continuous Casting Machine Guide Rollers

Literature Overview

This 2007 publication by Zhang Xiangfu from the Machinery Manufacturing Company of Jinan Iron and Steel Group Corporation addresses a practical and economically significant problem in the continuous casting industry: the repair of worn guide rollers using strip cladding (also known as flash butt welding or explosive cladding) technology. Continuous casting machine guide rollers are subjected to extreme conditions including high temperatures (up to 1500°C from molten steel), severe mechanical loading, thermal cycling, and abrasive wear from scale and slag. When these rollers wear beyond service limits, replacement is prohibitively expensive, making repair through cladding or overlay a cost-effective alternative.

Core Technical Content

Service Environment and Wear Mechanisms

Continuous casting guide rollers operate in an exceptionally harsh environment. The primary wear mechanisms include:

The typical service life of a guide roller in a slab caster ranges from 3 to 12 months depending on casting speed, steel grade, and roller material. The roller surface hardness typically degrades from an initial 28-32 HRC to below 20 HRC after significant wear, at which point repair or replacement is required.

Strip Cladding Process Description

Strip cladding, as applied to guide roller repair, involves the bonding of a wear-resistant alloy strip to the worn roller surface through a controlled welding or bonding process. The most common approach for roller repair is the use of submerged arc welding (SAW) or electroslag welding (ESW) to deposit a wear-resistant overlay layer, or alternatively, the application of a pre-fabricated cladding strip through flash butt welding or explosive cladding.

For guide roller applications, the repair typically involves:

1. Removal of the worn surface layer by grinding or machining to expose sound base material
2. Surface preparation including cleaning and preheating
3. Application of the cladding layer using the selected process
4. Post-weld machining to restore dimensional accuracy
5. Heat treatment to achieve required hardness and relieve residual stresses

Material Selection for Roller Cladding

The selection of cladding material for guide roller repair depends on the specific service conditions:

For continuous casting guide rollers, high chromium cast iron or specialized hardfacing alloys are commonly selected based on the balance between wear resistance and the roller's structural requirements.

Process Parameters and Quality Control

Welding Process Selection

The choice of welding process for roller repair is influenced by the roller geometry, required cladding thickness, and production requirements. For cylindrical rollers, SAW overlay with multiple passes is the most common approach due to its high deposition rate and good penetration characteristics.

Quality Assurance Requirements

Quality control for cladding repair of guide rollers includes dimensional inspection, hardness verification, and NDT examination. The repaired roller must meet the original dimensional specifications within tolerance (typically ±0.1 mm for diameter and ±0.05 mm for runout). Hardness testing should verify uniform coverage of the required hardness range across the entire cladded surface.

NDT requirements typically include magnetic particle testing (MT) of the cladding surface to detect surface cracks, and ultrasonic testing (UT) to detect subsurface defects such as lack of fusion at the cladding-base interface. For critical applications, radiographic testing (RT) of weld joints may be required.

Engineering Practice and Cost Analysis

Economic Justification

The economic case for strip cladding repair versus replacement is compelling. A new guide roller for a slab caster can cost 50,000-200,000 RMB depending on diameter and material, while cladding repair typically costs 10,000-30,000 RMB. The repair extends roller life by 1-3 years in most cases, providing a significant return on investment.

Field Experience and Lessons Learned

From extensive field experience, several key lessons emerge regarding guide roller cladding repair:

• Preheating to 200-300°C is essential to prevent cracking in the base material, particularly for cast iron rollers
• The transition zone between base metal and cladding should be examined for cracks after repair, as thermal mismatch can cause cracking during subsequent thermal cycling
• Multiple thin passes produce better results than single thick deposits in terms of crack resistance and dimensional accuracy
• Post-weld stress relief at 550-650°C for 2 hours is recommended to prevent delayed cracking

Summary and Conclusions

This literature provides practical guidance for the repair of continuous casting guide rollers through strip cladding technology. The systematic approach to material selection, process parameter optimization, and quality assurance presented in the study is directly applicable to similar wear repair applications in heavy industry. The economic benefits of repair over replacement are substantial, and the technical challenges associated with thermal cycling and mechanical loading in the service environment require careful attention to process quality. Engineers involved in continuous casting equipment maintenance should adopt the systematic approach outlined in this study to ensure reliable and cost-effective roller repair operations.