Application of RMD-01 Overlay Welding Electrode on Single-Roller Crusher

Background and Operational Challenges

The 2003 study by Zhou Xianwu, Lü Yingguang, and Wang Yipu from the Sintering Plant of Tongling Steel Co., Ltd. addresses a common industrial problem: the rapid wear of single-roller crusher components in iron ore sintering operations. Single-roller crushers are used to break down sintered iron ore into uniform particle sizes for blast furnace feeding. The crusher's working surfaces—particularly the roller shell and the chamber walls—undergo severe abrasive wear from iron ore particles, with service life often limited to only 200–500 hours before replacement or repair is required. The RMD-01 overlay welding electrode was developed and applied to extend the service life of these critical components.

RMD-01 Electrode Characteristics

The RMD-01 electrode is a specialized overlay welding consumable designed for high-abrasion applications. Its design incorporates the following features:

Parameter	Specification	Purpose
Electrode classification	RMD-01 (wear-resistant overlay type)	Designated for medium-to-high abrasion applications
Core wire composition	High-carbon high-chromium alloy (C 3.0–4.0%, Cr 20–25%, Mo 2–3%)	Produces hard carbide matrix with high wear resistance
Flux type	Basic flux with added Cr2O3 and V2O5	Promotes chromium carbide formation and slag deoxidation
Deposit hardness (as-welded)	60–65 HRC	Provides high abrasion resistance
Deposit hardness (after tempering)	55–60 HRC	Balances hardness with toughness for impact resistance
Recommended welding current	150–220 A (DCEN)	Ensures proper penetration and dilution
Maximum deposit thickness per pass	3.0 mm	Thicker deposits require multiple passes with grinding

Application Methodology

The application of RMD-01 to the single-roller crusher followed a systematic approach:

Surface preparation — The worn roller shell and chamber walls were ground to remove all loose material and oxide scale, exposing clean base metal. The grinding pattern was designed to provide mechanical keying for the overlay.
Pre-heating — The component was pre-heated to 250–350 °C using induction heating or gas torch to prevent cold cracking in the base metal HAZ, particularly important for the medium-carbon steel roller shell.
Overlay welding — Multiple passes of RMD-01 were applied in a herringbone pattern to ensure uniform coverage. The first pass was applied with slightly lower current to minimize dilution, and subsequent passes used the full current range to build up thickness.
Post-weld treatment — The overlay was tempered at 250–300 °C for 2 hours to relieve residual stress and transform brittle martensite to tempered martensite, improving toughness while maintaining hardness above 55 HRC.
Machining and finishing — The overlay was ground to the required dimensional tolerance and surface finish. The grinding also removed any surface defects and ensured uniform hardness distribution.

Performance Results

The field application results demonstrated significant improvements in component life:

Component	Original Life (hours)	Life with RMD-01 Overlay (hours)	Improvement Factor
Roller shell (wear band)	300–400	1,200–1,800	3–4.5×
Crusher chamber wall	200–300	800–1,200	3–4×
Feed plate	150–250	600–900	3–3.6×

The overlay hardness was measured at 58–62 HRC after tempering, with good uniformity across the deposit. Metallographic examination revealed a microstructure of tempered martensite with dispersed M7C3 and M23C6 chromium carbides, providing excellent abrasion resistance against the iron ore particles. No cracks, porosity, or delamination were observed at the overlay-base metal interface after extended service.

Defect Analysis and Countermeasures

Despite the overall success, several defect patterns were encountered during the application:

Defect	Frequency	Root Cause	Countermeasure
Surface cracks in overlay	Occasional	Excessive cooling rate on thin sections, or high carbon content in first pass	Increase pre-heat temperature, use lower current for first pass, apply multiple thin passes
Undercut at overlay edge	Occasional	Welding speed too high, or electrode angle incorrect	Reduce welding speed by 20%, maintain electrode angle at 10–15° from vertical
Excessive dilution (>30%)	Rare	Base metal too thin, or welding current too high	Reduce current, increase travel speed, or apply a separate transition layer
Overlay spalling during service	Rare	Insufficient bond strength due to inadequate pre-heating or surface contamination	Ensure thorough surface preparation, maintain pre-heat at minimum 250 °C, clean between passes

Economic Analysis

The economic benefit of RMD-01 overlay application was substantial. The cost of overlay welding (including electrode, labor, and equipment) was approximately 15–20% of the cost of replacing the entire worn component. Given the 3–4× life extension, the cost per hour of service was reduced by 70–75%. Additionally, the reduced frequency of component replacement decreased unplanned downtime, which was estimated to save an additional 30–40% in production losses. The total economic benefit justified the investment in overlay welding equipment and training.

Study Reflection

This case study illustrates the practical value of overlay welding in extending the life of worn industrial components. The RMD-01 electrode, with its high-carbon high-chromium composition, is particularly effective in abrasive wear environments where iron ore particles cause severe material removal. The key success factors were proper surface preparation, adequate pre-heating, and appropriate post-weld tempering. The study also highlights the importance of field validation—laboratory tests alone cannot predict the actual performance of an overlay in a real operating environment. The 2003 timeframe of this work reflects the growing maturity of overlay welding technology in Chinese heavy industry, where the focus has shifted from basic process development to systematic application optimization. For modern applications, the RMD-01 concept can be extended to automated welding processes (GMAW, FCAW) with appropriate wire consumables, enabling further improvements in productivity and consistency.