Cladding Repair of Roller Press Squeeze Roll in Cement Industry

Literature Overview

The paper by Wei Jianjun, Huang Zhiquan, Pan Jian, Xu Jian, and Huang Shilin, published in the journal Cement in 1995 (No. 8, pp. 15-15), addresses the cladding repair of a Φ1000×260 roller press squeeze roll used in a bulk cement industry operation in Shantou, Guangdong Province. After approximately one year of service, the static roll experienced severe wear, and the authors investigated cladding repair as an alternative to complete roll replacement. The paper was contributed by researchers from the Zhengzhou Mechanical Research Institute (Ministry of Machinery Industry) and the Shantou Bulk Cement Industry Company. This case study is significant because roller presses are critical equipment in cement production, and their wear directly impacts production efficiency and cost.

Core Technical Content

Roller Press Operating Conditions and Wear Analysis

A roller press is a compression-based grinding machine used in cement production to reduce the particle size of clinker, limestone, or other feed materials. The Φ1000×260 designation indicates a roll diameter of 1000 mm and a roll length of 260 mm. The operating conditions are extremely severe:

• High compressive stress: The roll gap pressure can exceed 200 MPa, with localized contact stresses exceeding 2000 MPa.
• Abrasive feed material: Cement clinker contains hard particles (quartz, corundum) that cause severe abrasive wear.
• Thermal cycling: The roll surface experiences temperature variations from ambient to 100-200 °C due to friction and compression.
• Cyclic loading: The roll undergoes millions of loading cycles during operation.

The wear on the static roll after one year of service was likely caused by a combination of abrasive wear from the feed material, adhesive wear from metal-to-metal contact at the roll interface, and possibly some plastic deformation of the roll surface under high contact stress. The dynamic roll (the roll that rotates) typically wears less than the static roll because the relative motion between the rolls and the feed material distributes the wear more evenly.

Cladding Repair Strategy and Material Selection

The cladding repair strategy for the squeeze roll involved depositing a wear-resistant alloy layer on the worn roll surface to restore its dimensions and improve its wear resistance. The selection of the cladding material would be based on the following criteria:

1. Hardness: The cladding must be significantly harder than the feed material to resist abrasive wear. A hardness of 50-60 HRC is typically required for cement roller press applications.
2. Toughness: The cladding must have sufficient toughness to resist spalling under high contact stress. A purely hard material without toughness will spall prematurely.
3. Bond strength: The cladding must bond strongly to the base roll to prevent delamination.
4. Compatibility: The cladding must be compatible with the base roll material (typically 45# or 50Cr steel) in terms of thermal expansion and weldability.

Common cladding materials for roller press applications include high-chromium white iron (Cr20-Cr30), high-carbon martensitic steel (e.g., 5CrMnMo), and cobalt-based alloys. The choice depends on the specific wear conditions and the desired balance between hardness and toughness.

Welding Process and Repair Procedure

The cladding repair process for a large roller press roll typically involves:

1. Surface preparation: Machining the worn surface to remove damaged material and create a proper groove for cladding. The groove geometry (V-groove, U-groove, or J-groove) affects dilution and bond strength.
2. Preheating: The roll is preheated to 200-300 °C to reduce residual stress and prevent cracking.
3. Cladding deposition: Multiple passes of the wear-resistant alloy are deposited using SAW or GMAW. SAW is preferred for its high deposition rate and consistent quality.
4. Post-weld heat treatment: Stress-relief annealing at 550-650 °C for 2-4 hours to reduce residual stresses.
5. Machining: The cladding surface is machined to restore the original roll diameter and surface finish.
6. Inspection: NDT (MT or PT) is performed to detect surface cracks or other defects in the cladding.

The economic analysis presented by the authors highlights the cost savings of cladding repair compared to roll replacement. For a Φ1000×260 roller press roll, the replacement cost can be substantial, including the cost of the new roll, installation labor, and production downtime. Cladding repair typically costs 30-50% of the replacement cost and can be performed with minimal production disruption.

Engineering Practice Considerations

From my experience in heavy equipment maintenance, the repair of roller press rolls requires careful planning and execution. The key challenges are:

• Thermal distortion: The large mass of the roll and the intense heat input from welding can cause significant thermal distortion. The roll must be supported properly during welding, and the welding sequence must be planned to minimize distortion.
• Residual stress: The residual stress from welding can be as high as 300-400 MPa, which can cause the cladding to spall during service. Stress-relief heat treatment is essential to reduce these stresses to acceptable levels (typically below 100 MPa).
• Dilution control: The dilution from the base metal into the cladding layer can reduce the hardness below the required level. Multi-pass cladding with proper groove preparation is necessary to minimize dilution.
• Surface finish: The machined surface of the cladding must have a roughness value (Ra) of 0.8-1.6 μm to ensure proper operation of the roller press. A rough surface will increase friction and energy consumption.

The paper's focus on the cement industry is particularly relevant because cement plants operate continuously, and any downtime for roll replacement can result in significant production losses. The ability to perform cladding repair on-site, or at least with minimal disassembly, is a major advantage. In my experience, the most successful roller press repairs are those where the repair is planned during scheduled maintenance windows, allowing for thorough preparation and quality control.

Study Insights and Reflections

This 1995 paper provides a valuable case study of cladding repair in the cement industry, which is one of the most demanding applications for wear-resistant cladding. The paper demonstrates that cladding repair is a viable and cost-effective alternative to roll replacement, provided that the material selection and welding process are properly designed. However, the paper is relatively brief and does not provide extensive details on the welding parameters, microstructural analysis, or long-term performance data. A more comprehensive study would include:

• Wear testing: Laboratory wear tests (e.g., pin-on-disk, abrasion testing) to quantify the wear resistance of the cladding material under simulated roller press conditions.
• Field performance monitoring: Tracking the roll wear rate before and after repair to quantify the improvement in service life.
• Failure analysis: Examination of failed cladding areas to understand the failure mechanism and guide future improvements.

From a broader perspective, this paper highlights the importance of preventive maintenance and the economic benefits of extending the life of critical equipment through repair rather than replacement. In the cement industry, where margins are thin and production continuity is essential, the ability to perform effective cladding repair is a significant competitive advantage.

Conclusion

The cladding repair of the Φ1000×260 roller press squeeze roll is a practical and cost-effective solution to the problem of severe roll wear in cement production. The paper demonstrates that cladding repair can extend the service life of critical equipment at a fraction of the replacement cost, with minimal production disruption. The key lessons are the importance of proper material selection (balancing hardness and toughness), the necessity of stress-relief heat treatment, and the value of planning repairs during scheduled maintenance windows. Future work should focus on developing more durable cladding materials, optimizing the welding process for large rolls, and establishing predictive maintenance models based on wear rate monitoring to schedule repairs before failure occurs.