Overlay Welding Repair of Roller Press Roller Surface in Cement Industry

Literature Overview

This paper by Wang Xin and colleagues from the Zhengzhou Machinery Research Institute, published in Cement Engineering in 2004, addresses the practical challenge of roller surface repair for roller presses used in cement grinding operations. Roller presses are critical equipment in modern cement grinding circuits, where two large rollers compress clinker and other cementitious materials to reduce particle size. The roller surfaces are subjected to severe abrasive wear from the hard cement particles, and periodic repair through overlay welding is essential to maintain production efficiency and product quality. This study introduces a series of newly developed welding materials and processes that can completely replace imported materials for roller surface overlay repair.

Wear Mechanism Analysis and Material Selection

The wear mechanism on roller press surfaces is primarily abrasive in nature, with contributions from adhesive wear and possible impact damage from large hard particles. The cement grinding process subjects the roller surface to continuous sliding contact with hard clinker particles, creating a three-body abrasion environment. The roller surface material must therefore possess high hardness, good abrasion resistance, and adequate toughness to resist crack initiation and propagation under repeated impact loading.

The researchers developed a series of welding materials designated ZD1, ZD2, ZD3, and ZD310, available as submerged arc welding (SAW) seamless flux-cored wire, CO2 gas-shielded wire, and ZD3, ZD310, and TM65 electrodes. This product range covers the full spectrum of welding processes available for roller repair, allowing selection based on the specific repair scenario, equipment availability, and performance requirements.

Comparison of Available Repair Materials and Processes

Welding Process Development and Performance Results

The study identifies two primary repair scenarios: shop repair with the roller removed from the press, and field repair performed in situ. The performance results clearly demonstrate that shop repair using automatic SAW produces the best outcomes, with roller service life exceeding 6000 hours. Field repair, when appropriate welding processes and materials are selected, can also achieve satisfactory results, though with somewhat reduced service life.

The automatic SAW process offers several advantages for roller surface repair. The process provides consistent arc stability, uniform bead geometry, and precise control over travel speed and wire feed rate, all of which contribute to consistent overlay properties. The flux in SAW welding provides excellent protection against atmospheric contamination and promotes favorable dilution characteristics. For large-diameter rollers with extensive surface areas requiring repair, the high deposition rate of SAW significantly reduces repair time compared to manual processes.

Process Parameters and Welding Strategy

The selection of welding parameters is critical to achieving the desired overlay performance. Key parameters include:

• Current and voltage: Must be optimized to achieve full penetration of surface defects while maintaining acceptable dilution rates. Excessive current leads to high dilution and reduced overlay hardness, while insufficient current results in poor fusion and incomplete defect repair.
• Travel speed: Directly affects bead geometry, dilution rate, and cooling rate. Faster travel speeds produce narrower beads with lower dilution but higher cooling rates that can promote cracking in high-carbon overlay materials.
• Wire feed rate: In SAW with flux-cored wire, the wire feed rate must be synchronized with the travel speed to maintain consistent arc length and deposition rate.
• Interpass temperature: Must be controlled to prevent excessive grain growth in the overlay layer while avoiding cold cracking in the base metal.

For field repair, the CO2 gas-shielded process offers a good balance between deposition rate and flexibility. The ZD3 and ZD310 CO2 wires are specifically designed for this application, providing adequate arc stability and spatter control in the CO2 atmosphere. The SMAW option with ZD3, ZD310, and TM65 electrodes provides maximum flexibility for difficult access areas, though the lower deposition rate means longer repair times.

Engineering Practice and Quality Control

From a practical standpoint, the success of roller surface repair depends on several factors beyond material selection and welding process. Surface preparation is critical: the worn roller surface must be ground to expose sound base metal, and any surface defects such as cracks, pits, or indentations must be completely removed. The surface roughness after preparation directly affects the dilution rate and bonding quality of the overlay layer.

The roller base metal, typically a high-manganese steel or similar wear-resistant alloy, presents specific welding challenges. High-manganese steels are susceptible to cracking during welding due to the formation of brittle martensite in the heat-affected zone. Preheating and post-weld heat treatment may be necessary to control hydrogen-induced cracking and to temper the hard, brittle phases in the HAZ. The overlay welding process itself acts as a post-weld heat treatment for the previous weld pass, so proper interpass temperature control is essential.

Quality control for roller surface overlay repair should include:

• Visual inspection of all weld beads for proper geometry and absence of surface defects
• Hardness testing of the overlay layer to verify specification compliance
• Penetrant testing (PT) or magnetic particle testing (MT) of the overlay surface to detect surface-breaking defects
• Dimensional verification to ensure the overlay thickness meets specifications for the intended service life

The 6000-hour service life achieved with automatic SAW repair is a significant improvement over previous repair practices that relied on imported materials. This demonstrates that domestically developed welding materials and processes can achieve international competitive performance for this critical industrial application. The economic implications are substantial, as roller press repair is a recurring maintenance activity in cement production facilities, and the cost of imported welding materials represents a significant portion of repair expenses.

Study Insights and Implications

This study contributes to the broader effort of developing domestic alternatives to imported welding materials for heavy industrial applications. The ZD series materials represent a complete product line that covers all common welding processes used in roller repair, providing engineers with flexible options depending on the specific repair scenario. The systematic approach of developing materials for multiple processes ensures that the right tool is available for each application, whether it is large-scale shop repair or confined-space field repair.

The emphasis on practical applicability is commendable. The study does not merely present laboratory results but provides guidance on process selection based on repair scenario, which is directly useful for maintenance engineers in cement plants. The demonstration that field repair can achieve acceptable results when proper materials and processes are used is particularly valuable, as it reduces the need for roller removal and associated downtime.

One area for further development is the optimization of overlay layer microstructure through advanced welding techniques such as multi-layer welding with compositionally graded materials. By depositing a transition layer between the base metal and the final overlay, it may be possible to further improve bonding quality and reduce the risk of overlay spalling under severe service conditions. Additionally, the incorporation of ceramic particles or carbide reinforcements in the overlay material could potentially extend service life beyond the current 6000-hour benchmark.

In summary, this study presents a comprehensive solution for roller press surface repair in cement industry applications. The ZD series welding materials, combined with appropriate process selection, provide a reliable and cost-effective alternative to imported materials. The demonstrated service life of over 6000 hours with automatic SAW repair establishes a new benchmark for roller maintenance in cement grinding operations.