CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Repair of Continuous Casting Machine Pilot Rod Chain
Literature Overview and Industrial Background
This 2005 study published in Welding Technology by engineers from Shanghai Meishan Iron and Steel Company addresses a practical and economically significant problem in steelmaking: the repair of worn pilot rod chains used in continuous casting machines through weld overlay technology. The continuous casting pilot rod (also known as starter billet or pilot bar) is a critical component that initiates the casting process by being drawn into the mold to establish the initial solidification shell. The chain connecting the pilot rod is subjected to extreme conditions including high temperatures (up to 1500°C in the vicinity of the mold), thermal cycling, mechanical impact, and corrosive slag attack.
The research team from both the Technical Center and the Steelmaking Plant of Shanghai Meishan Iron and Steel Company conducted a systematic investigation into the weld overlay repair methodology, focusing on electrode selection, welding process parameters, preheating requirements, and post-weld inspection protocols.
Technical Methodology and Process Parameters
The pilot rod chain typically consists of high-carbon steel or alloy steel links that experience progressive wear at the engagement points. The repair methodology employed in this study involves the following key steps:
Pre-Weld Preparation
| Preparation Step | Specification | Purpose |
|---|---|---|
| Surface cleaning | Grit blasting to Sa 2.5 | Remove oxide scale, slag, and contamination |
| Weld preparation | V-groove, 60° included angle, 2 mm root gap | Ensure full penetration and bond strength |
| Preheating | 250–300°C, held for 30 min per 25 mm thickness | Reduce cooling rate, prevent cracking |
| Backing plate | Steel backing with flux | Ensure root reinforcement |
Weld Overlay Electrode Selection
The study evaluated multiple electrode types for the overlay application:
| Electrode Type | Composition | Hardness (HV) | Application |
|---|---|---|---|
| J507 | Low-carbon, basic flux | 180–220 | Base repair welds |
| D266 | Medium-carbon, high-hardness | 450–500 | Wear-resistant overlay |
| D397 | High-carbon, martensitic | 500–550 | Severe wear zones |
| A102 | Nickel-base | 200–250 | High-temperature zones |
The optimal strategy identified was a multi-pass approach: the first pass using J507 to repair the base metal structure, followed by 2–3 overlay passes using D266 or D397 to build up the wear-resistant surface layer.
Welding Process Parameters
| Parameter | Value | Notes |
|---|---|---|
| Welding current | 160–200 A | Adjusted per pass |
| Arc voltage | 25–28 V | Stable arc required |
| Travel speed | 150–200 mm/min | Controlled deposition rate |
| Interpass temperature | 250–300°C | Maintain throughout welding |
| Layer thickness | 3–5 mm per pass | Total overlay 8–15 mm |
| Pass number | 3–5 passes | Depends on wear depth |
Defect Analysis and Countermeasures
The study documented several common defects encountered during the pilot rod chain repair process and proposed corresponding countermeasures:
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Hot cracking | High carbon equivalent, rapid cooling | Increase preheat, reduce welding speed |
| Cold cracking | Hydrogen embrittlement in HAZ | Low-hydrogen electrode, post-weld heating |
| Porosity | Moist flux, contaminated surface | Dry electrode storage, thorough cleaning |
| Undercut | Excessive current, poor technique | Reduce current, optimize travel speed |
| Overlay delamination | Insufficient bond strength | Ensure proper preheat, clean interface |
The FMEA (Failure Mode and Effects Analysis) approach was implicitly applied in this study, with particular emphasis on the risk of hydrogen-induced cracking given the high carbon content of the base material and the high-temperature service environment.
Engineering Practice Integration
From an engineering practice perspective, this study demonstrates several important principles for weld overlay repair in harsh industrial environments:
- Thermal management is paramount — The combination of preheating (250–300°C) and controlled interpass temperature maintenance is critical for preventing cracking in high-carbon steel repair applications.
- Multi-layer strategy — Using a soft base layer followed by hard overlay layers provides both structural integrity and surface performance.
- Process discipline — Consistent execution of cleaning, preheating, and interpass temperature control directly correlates with repair success rate.
- Economic justification — The cost of weld overlay repair (typically 10–20% of new component cost) versus replacement makes this approach highly attractive for production continuity.
Inspection Protocol
The recommended inspection sequence for pilot rod chain repair includes:
- Visual inspection (VT) of all weld surfaces per GB/T 3323
- Magnetic particle testing (MT) of overlay surfaces per JB/T 6061
- Hardness verification at multiple points across the overlay layer
- Dimensional verification of repaired chain links
- Load testing before return to service
Study Insights and Practical Implications
This case study is valuable primarily for its demonstration of practical engineering problem-solving in a real industrial setting. The authors clearly understood the operating conditions and failure modes of the pilot rod chain, which informed their selection of repair methodology and materials.
One particularly insightful aspect is the recognition that the pilot rod chain operates in a unique environment where thermal cycling, mechanical impact, and corrosive slag exposure all act simultaneously. This multi-stress environment requires a repair strategy that addresses all degradation mechanisms rather than optimizing for a single failure mode.
The choice of D266 and D397 electrodes for the overlay layer reflects a practical understanding of the balance between hardness (for wear resistance) and toughness (for impact resistance). Purely maximizing hardness would compromise the ability of the overlay to withstand mechanical shock during casting operations.
The economic analysis implicit in this work is also significant: in a continuous casting operation, downtime for chain replacement can cost thousands of dollars per hour in lost production. The ability to perform rapid on-site repair through weld overlay technology provides substantial economic benefit.
In conclusion, this study exemplifies the practical application of weld overlay technology in a demanding industrial environment. The methodology presented — combining proper material selection, controlled thermal input, multi-pass deposition strategy, and rigorous quality control — represents a replicable approach for similar repair applications in steelmaking and foundry operations. Engineers facing similar challenges with worn components in high-temperature, high-stress environments should adopt this systematic approach to ensure reliable and economical repair outcomes.