Regenerative Surfacing Repair of Φ1700×1800 Roll Press Squeezing Rolls at Jiangxi Yadong Cement Plant

Literature Overview

This technical report by Xu Jian, Zhang Yongsheng, Wang Xin, and Li Junwei, published in New Century Cement Herald (Vol. 14, No. 6, 2008, pp. 44-46), documents the regenerative surfacing repair of Φ1700×1800 roll press squeezing rolls at Jiangxi Yadong Cement Co., Ltd. The facility operates three advanced dry-process cement production lines using German KHD (Humboldt) technology, with a total annual cement production capacity of 8 million tons. The plant is equipped with five Φ1700×1800 roll presses, the largest of their type in Asia at the time of publication, with two units in the clinker grinding system and three units in the raw material final grinding system.

Component Description and Service Conditions

Roll presses are critical components in modern cement production, used for the pre-grinding or final grinding of cement clinker and raw materials. The Φ1700×1800 designation indicates a roll diameter of 1700 mm and a roll length of 1800 mm, representing a large-scale industrial component with significant material volume and manufacturing cost.

The service conditions for these squeezing rolls are severe:

The primary failure modes of roll press squeezing rolls are surface wear (abrasive material removal), surface fatigue (rolling contact fatigue leading to spalling and cracking), and edge chipping at the roll shoulders. These failure modes are interrelated and often occur simultaneously, leading to progressive degradation of the roll surface profile and eventual loss of grinding efficiency.

Regenerative Surfacing Repair Process

The regenerative surfacing repair process involves the removal of the worn surface material through grinding, followed by the application of a new hardfacing layer to restore the roll surface to its original or improved specification. This approach is significantly more economical than complete roll replacement, which would require the manufacture or procurement of new rolls at a cost of hundreds of thousands of dollars per roll.

The repair process follows a systematic sequence:

1. Assessment and preparation: Measure the remaining roll diameter and assess the extent of surface damage (wear, spalling, cracking). Determine the required surfacing thickness to restore the roll to specification.
2. Surface preparation: Grind the worn surface to remove all damaged material, including the affected subsurface region. The ground surface must be clean, free of oxide and contaminants, and machined to a finish of Ra ≤ 3.2 μm to ensure proper weld metal fusion.
3. Substrate preheating: Preheat the roll to 200-300°C to reduce the cooling rate and prevent thermal cracking. The preheating is typically accomplished using induction heating or gas heating, with temperature monitoring at multiple points around the roll circumference.
4. Surfacing welding: Apply the hardfacing layer using a multi-pass technique. The first pass serves as a transition layer to ensure metallurgical compatibility with the roll substrate, while subsequent passes build up the wear-resistant composite layer to the required thickness.
5. Post-weld treatment: Control the cooling rate to prevent thermal stress cracking. Post-weld stress relief at 500-600°C may be applied if the residual stress levels are expected to be significant.
6. Machining and finishing: Machine the surfaced surface to the final diameter and profile specification. The finished surface must meet the required dimensional accuracy (typically IT8-IT9) and surface finish (Ra ≤ 1.6 μm) for proper roll press operation.

Surfacing Alloy Selection and Performance

The selection of the surfacing alloy for roll press squeezing roll repair is critical and depends on the specific service conditions and material being ground:

The surfacing deposit must achieve a hardness of at least 50 HRC to provide adequate wear resistance against the abrasive cement clinker and raw meal. However, excessive hardness (above 60 HRC) can increase susceptibility to rolling contact fatigue and spalling, which is particularly problematic for large-diameter rolls operating at high pressures.

Economic Analysis

The economic advantage of regenerative surfacing repair over complete roll replacement is substantial:

The economic savings are further enhanced by the reduced downtime associated with repair compared to replacement, as the surfacing repair can be performed at the plant or at a nearby service facility, whereas new roll procurement requires international shipping and extended lead times.

Quality Control and Verification

The quality of the surfacing repair is verified through a comprehensive inspection protocol:

• Visual inspection: Examination of the entire surfaced surface for cracks, porosity, undercuts, and incomplete fusion.
• Magnetic particle testing (MT): Detection of surface and near-surface cracks in the surfacing deposit and heat-affected zone.
• Ultrasonic testing (UT): Detection of subsurface defects including lack of fusion, slag inclusions, and internal porosity.
• Hardness testing: Verification of hardness uniformity across the surfaced surface, with acceptable variation of ±3 HRC.
• Metallographic examination: Examination of cross-sections to verify the quality of the substrate-surfacing interface and the microstructure of the deposit.
• Dimensional verification: Measurement of the final roll diameter, runout, and surface profile using precision measuring instruments.

Key Technical Insights and Reflections

This case study demonstrates the practical application of regenerative manufacturing principles in the cement industry, where large, expensive components can be economically restored to service through surfacing welding. The key insight is that the surfacing repair process must be carefully designed to address not only the immediate surface wear but also the underlying causes of premature failure, including rolling contact fatigue and edge chipping.

One important consideration is the cumulative effect of multiple surfacing repairs on the roll substrate. Each repair cycle introduces a new thermal cycle that can affect the substrate microstructure and residual stress state. Over multiple repair cycles, the substrate may experience progressive softening, embrittlement, or cracking, which can eventually limit the total number of viable repair cycles. Engineers should establish a maximum number of repair cycles based on the specific roll material, surfacing alloy, and service conditions.

Additionally, the quality of the surfacing repair is highly dependent on the skill and experience of the welding operator. The large diameter and length of the roll, combined with the need for uniform surfacing coverage and controlled thermal input, present significant challenges to the welding process. Automated or mechanized welding systems are strongly recommended for large-diameter roll surfacing to ensure process consistency and quality.

Study Insights and Implications

This documentation of the regenerative surfacing repair of large roll press squeezing rolls provides valuable practical guidance for engineers in the cement industry and related heavy industries. The systematic approach to repair — from assessment and preparation through surfacing welding, post-weld treatment, and quality verification — establishes a clear protocol for component restoration. The economic analysis demonstrates that surfacing repair can reduce component costs by 85-90% compared to complete replacement, making it a highly attractive option for large, expensive components where the failure is localized to the surface. For engineers managing maintenance and repair operations in cement plants, mining operations, and other heavy industries, the principles demonstrated in this case study are directly applicable to the extension of component life through surface engineering and regenerative manufacturing.