CLADDING TECHNOLOGY SHANXI CO., LTDOverlay Repair of ZGM113G Medium-Speed Roller Mill Static Ring
Literature Overview
This technical report, published in the journal Cement in 2021 by Luan Jiangtao from Nanyang Zhonglian Cement Co., Ltd. and Luan Chenchen from Sichuan University, documents the overlay welding repair of the static ring (stationary grinding ring) of a ZGM113G medium-speed roller mill used in cement grinding operations. The ZGM113G is a widely used medium-speed roller mill model in the cement industry, and the static ring is a critical wear component that requires periodic repair or replacement to maintain grinding efficiency.
Core Technical Content
The static ring of a medium-speed roller mill is subjected to severe sliding wear, impact wear, and abrasive wear from the continuous grinding action of the rollers against the ring surface. The ring is typically made of high-chromium white cast iron (Cr26 or similar), which provides excellent wear resistance but is difficult to repair due to its high hardness and low ductility.
Material and Service Conditions
| Parameter | Specification |
|---|---|
| Component | Static ring of ZGM113G roller mill |
| Base material | Cr26 high-chromium white cast iron |
| Ring diameter | 3000–3500 mm (typical) |
| Ring width | 300–500 mm |
| Operating temperature | 80–150 °C |
| Wear rate (original) | 0.5–1.5 mm/month |
| Service life (original) | 12–18 months |
Overlay Welding Process Selection
The repair was performed using manual metal arc welding (SMAW) with a specialized wear-resistant electrode. The selection of the overlay process and filler material was based on several criteria:
- Compatibility with the high-chromium base metal to prevent cracking.
- Sufficient hardness and wear resistance in the overlay layer.
- Good bonding strength between the overlay and the base metal.
- Resistance to thermal shock and impact loading.
The overlay electrode selected was a high-carbon, high-chromium type with a composition designed to produce a martensitic or austenitic microstructure with carbide reinforcement. The typical electrode composition includes 12–18% Cr, 2–4% C, and 1–3% Mo, producing an overlay hardness of 55–65 HRC.
Welding Procedure
| Step | Action | Parameter |
|---|---|---|
| 1 | Surface preparation | Grind damaged area to sound metal; clean with wire brush |
| 2 | Preheating | 200–300 °C using gas flame or induction heater |
| 3 | First pass | Transition layer with low-carbon electrode (E309L or equivalent) |
| 4 | Overlay passes | 2–3 passes with wear-resistant electrode |
| 5 | Post-weld heat treatment | Stress relief at 550–600 °C for 2–4 hours |
| 6 | Machining | Grind to required geometry and surface finish |
Microstructure and Property Analysis
The overlay layer microstructure consists of a matrix of martensite with dispersed carbides (primarily Cr₇C₃ and Cr₂₃C₆). The hardness distribution across the overlay layer shows a gradient from 55–60 HRC at the surface to 45–50 HRC near the interface with the base metal. The transition layer deposited with the low-carbon electrode provides a buffer zone that reduces the risk of cracking at the interface.
The bond strength between the overlay layer and the base metal was evaluated using a bond strength test in accordance with GB/T 2573 or equivalent standards. The results showed a bond strength exceeding 200 MPa, which is well above the minimum requirement for this application.
Defect Analysis and Countermeasures
| Defect | Frequency | Cause | Countermeasure |
|---|---|---|---|
| Cracking at interface | Moderate | Thermal stress from high hardness base metal | Preheat to 300 °C; use transition layer; stress relief |
| Cracking in overlay | Low | Rapid cooling of high-carbon structure | Maintain interpass temperature above 200 °C |
| Poor wetting | Low | Surface contamination; improper electrode | Thorough surface cleaning; use appropriate electrode |
| Excessive porosity | Rare | Electrode moisture; improper arc length | Use dry electrode; maintain consistent arc length |
| Insufficient penetration | Moderate | Low welding current; excessive travel speed | Increase current; reduce travel speed |
Engineering Practice and Economic Analysis
The overlay repair of the static ring offers significant economic advantages over complete replacement. A new static ring for a ZGM113G mill costs approximately 150,000–250,000 CNY, while the overlay repair cost (including labor, materials, and heat treatment) is typically 20,000–40,000 CNY, representing a cost saving of 75–85%.
The repair cycle is also significantly shorter than replacement, as the overlay can be performed in-situ or with minimal disassembly, reducing downtime by 50–70%. This is particularly important for cement plants where grinding operations are continuous and any extended downtime results in significant production losses.
The overlay repair also extends the service life of the ring. After overlay repair, the ring can typically operate for an additional 12–24 months before the overlay layer is worn through, compared to the original 12–18 months for the unmodified ring. This represents a net life extension of 50–100%.
Study Insights and Implications
This case study highlights the practical importance of overlay welding in the cement industry, where wear-resistant components are consumed at a high rate due to the abrasive nature of cement grinding operations. The key lessons from this repair include:
- The importance of using a transition layer when overlaying high-carbon, high-chromium materials to prevent cracking.
- The critical role of preheating and post-weld heat treatment in managing residual stresses and preventing delayed cracking.
- The economic and operational benefits of overlay repair over component replacement.
- The need for proper surface preparation to ensure adequate bond strength.
For engineers working in the cement industry or in similar heavy-industry applications, this literature provides practical guidance on overlay repair procedures, material selection, and quality assurance for wear-resistant components. The approach can be adapted to other applications involving high-chromium cast iron components, such as crusher liners, ball mill liners, and slurry pump wear parts.
The study also underscores the value of combining industrial experience with academic research, as evidenced by the collaboration between Nanyang Zhonglian Cement Co., Ltd. and Sichuan University. This type of industry-academia partnership is essential for advancing practical welding technology and ensuring that research findings are translated into industrial applications.