CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay of Roller Press Squeeze Rollers for Final Slag Grinding
Literature Overview
This 2012 publication from the Zhengzhou Machinery Research Institute, authored by Zhang Xiubao and published in New Century Cement Herald, addresses a critical maintenance challenge in cement and clinker grinding operations: the weld overlay repair of roller press squeeze rollers used in final grinding of slag. Roller presses have become increasingly prevalent in modern cement grinding circuits, replacing or supplementing traditional ball mills due to their superior energy efficiency. However, the severe abrasive and impact loading conditions in slag grinding service demand robust surface protection strategies, and weld overlay remains one of the most effective repair and refurbishment methods available to plant engineers.
Core Technical Content
The roller press operates by compressing material between two counter-rotating rolls, where the working surfaces are subjected to simultaneous abrasion from hard mineral particles and impact from material compaction. In slag grinding applications, the material is particularly challenging because slag particles tend to be angular, hard, and sometimes sticky, leading to accelerated roll surface degradation. The authors describe a systematic approach to weld overlay repair that encompasses surface preparation, consumable selection, welding process parameters, and post-weld treatment.
Material Selection for Overlay
The selection of overlay material is the most consequential decision in this repair scenario. The following table summarizes the typical material options considered:
| Overlay Material Type | Hardness (HV) | Abrasion Resistance | Impact Resistance | Typical Application |
|---|---|---|---|---|
| Medium-carbon martensitic steel | 400-500 | Moderate | Good | General grinding service |
| High-carbon martensitic steel | 500-600 | High | Moderate | Severe abrasion service |
| High-chromium white iron | 550-700 | Very High | Poor | Extreme abrasion, no impact |
| Medium-chromium iron alloy | 450-550 | High | Moderate | Combined abrasion/impact |
| Austenitic manganese steel | 250-350 (as-welded) | High (work-hardened) | Excellent | Heavy impact service |
For slag grinding roller presses, high-carbon martensitic steel or medium-chromium iron alloy overlays are typically preferred because they offer the best balance between abrasion resistance and impact tolerance. The authors emphasize that the overlay material must be compatible with the base steel of the roll, which is generally a medium-carbon or low-alloy steel with yield strength in the range of 300-500 MPa.
Welding Process and Parameters
The welding process described involves multi-pass overlay welding, typically using submerged arc welding (SAW) or gas metal arc welding (GMAW) with flux-cored wire. The key process parameters include:
- Preheat temperature: 150-250 °C to reduce hydrogen-induced cracking susceptibility
- Interpass temperature: maintained below 250 °C to ensure proper martensitic transformation in the overlay
- Weld bead height: 3-5 mm per pass, with a total overlay thickness of 15-30 mm
- Travel speed: 200-400 mm/min depending on the process
- Shielding gas (for GMAW): 80% Ar + 20% CO₂ or pure CO₂
A critical aspect discussed is the removal of the entire worn surface before overlay application. The authors advocate for complete machining of the damaged surface down to sound material, followed by thorough cleaning to remove oil, rust, and scale. Any residual contamination can lead to porosity and lack of fusion defects at the weld interface.
Post-Weld Treatment
Post-weld heat treatment is essential for martensitic overlay materials to relieve residual stresses and improve toughness. The recommended procedure involves:
- Tempering at 500-600 °C for 2-4 hours, followed by air cooling
- Monitoring of dimensional changes during heat treatment to prevent roll distortion
- Final machining to restore the roll profile to original specifications
The authors note that without proper tempering, the overlay hardness may exceed 600 HV, making subsequent machining extremely difficult and increasing the risk of cracking during the grinding operation.
Engineering Practice Integration
From my experience with roller press maintenance programs, the weld overlay approach described in this literature aligns well with industry practice. However, several additional considerations deserve emphasis:
- Roll geometry restoration: The overlay must not only restore the surface but also correct any profile deviations that have developed during service. This often requires more overlay material on certain sections of the roll surface, necessitating careful planning of weld pass sequences.
- Thermal distortion control: Roller presses are precision-machined components with tight tolerances on roll diameter and profile. Weld overlay introduces significant thermal input, and without proper constraint or symmetric welding sequences, distortion can exceed acceptable limits.
- Service life prediction: A well-executed overlay repair should extend the service life of the roll by 2-3 times compared to the original surface. The actual life depends on the material feed composition, roll pressure settings, and the quality of the overlay.
Key Defects and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking at weld interface | Excessive cooling rate, hydrogen pickup | Increase preheat, use low-hydrogen consumables, control interpass temperature |
| Porosity | Contaminated surface, improper gas shielding | Thorough surface preparation, verify gas flow rate and nozzle condition |
| Lack of fusion | Insufficient heat input, poor surface preparation | Increase current, ensure complete removal of oxide and coating |
| Excessive hardness | Over-tempered or under-tempered overlay | Strict control of heat treatment parameters, verify with hardness mapping |
| Spalling | Thermal fatigue, poor bond strength | Ensure proper base metal preparation, consider bonding layer between base and overlay |
Study Insights and Implications
This literature provides a practical, field-oriented perspective on roller press repair that is valuable for maintenance engineers. The emphasis on consumable selection matched to service conditions, combined with rigorous process control, reflects the fundamental principle that weld overlay success depends on the synergy between material, process, and application. The 2012 publication date means that some of the specific consumable recommendations may have evolved, but the underlying engineering principles remain valid. I would recommend that engineers supplement this reference with more recent studies on hot-wire TIG cladding and laser cladding for roller surfaces, as these newer technologies offer improved bond strength and reduced dilution compared to traditional arc welding methods.