Novel Online Weld Overlay Repair Device for Grinding Table Crushing Rollers

Literature Overview

This 2012 research by Wang Minsheng, Cheng Zhiguo, Liu Jianwei, Zhao Chunyan, Wu Zaimin from the Harbin Welding Research Institute of the Chinese Academy of Engineering, in collaboration with Li Xiaoping from Yushan Wannianqing Cement Co., Ltd., presents an innovative engineering solution for the in-situ repair of grinding table crushing rollers in cement mills. The study addresses a practical industrial problem: the frequent wear and damage of grinding rollers in cement production, which traditionally requires complete removal, transport to an off-site workshop, repair, and reinstallation—a process that causes significant production downtime and logistical costs.

Problem Statement and Engineering Context

In modern cement production, vertical roller mills are widely used for grinding clinker and raw materials. The grinding rollers are subjected to severe abrasive wear from the cement material and periodic impact loading from feed material variations. Over time, the roller surface develops wear grooves, spalling, and localized damage that must be repaired by weld overlay to restore dimensional accuracy and surface integrity.

Traditional repair procedures involve:

• Removing the roller from the mill (typically 8–24 hours depending on access).
• Transporting the roller to a welding workshop (logistical challenge for large rollers weighing several tons).
• Performing weld overlay repair in a controlled environment.
• Reinstalling and aligning the roller (another 8–24 hours).

The total downtime for a single roller repair can exceed 48 hours, which is economically unacceptable in high-capacity cement plants operating at continuous production rates.

Device Design and Operating Principle

The novel online repair device is designed to be mounted directly on the grinding roller while it remains installed in the mill. The key design features include:

• A compact welding head that can be positioned at any angular location around the roller circumference.
• A support arm that accommodates the roller diameter and provides stable positioning.
• Integrated shielding gas delivery to ensure adequate protection in the confined space of the mill housing.
• A portable power supply and control unit that can be connected to the mill's existing electrical infrastructure.
• A rotation mechanism that allows the roller to be slowly rotated during welding to ensure uniform overlay coverage.

Process Considerations for In-Situ Repair

Welding on a roller that remains installed in the mill introduces several challenges that are not present in a workshop environment:

• Limited access for torch positioning and manipulation.
• Restricted ventilation, which can lead to accumulation of welding fumes and shielding gas depletion.
• Potential contamination from cement dust and moisture in the mill environment.
• Difficulty in achieving uniform interpass temperature control due to the large thermal mass of the roller and surrounding structure.
• Limited space for post-weld inspection and grinding.

The study addresses these challenges through careful process parameter selection and the use of consumables that are tolerant of environmental contamination. The use of flux-cored wire is particularly advantageous because the flux provides slag protection that reduces sensitivity to ambient oxygen and moisture.

Overlay Material Selection

For cement mill grinding rollers, the overlay material must resist abrasive wear from cement clinker particles while maintaining sufficient toughness to resist impact from feed material variations. Common overlay materials include:

Quality Control and Inspection

In-situ repair requires adapted inspection procedures. Conventional ultrasonic testing may be limited by the curved geometry and confined access. The recommended inspection sequence includes:

• Visual examination of the weld surface for porosity, undercut, and incomplete fusion.
• Magnetic particle testing (MT) for surface and near-surface crack detection.
• Hardness testing at multiple locations around the roller circumference to verify overlay uniformity.
• Dimensional verification using a calibrated gauge or laser measurement system.

Engineering Practice Integration

The practical impact of this online repair device is substantial. By eliminating the need to remove and transport the roller, the total repair time is reduced from 48+ hours to approximately 8–12 hours, representing a 75–80% reduction in downtime. For a cement plant with multiple grinding mills, this translates into significant annual production gains and reduced maintenance costs.

The study also highlights the importance of operator training for in-situ welding. Unlike workshop repair, where the welder has full control of the environment, in-situ welding requires the operator to adapt to changing conditions—such as variations in ambient temperature, ventilation, and access constraints. Standard operating procedures and qualification testing are essential to ensure consistent repair quality.

Key Reflections

This research exemplifies the principle that engineering innovation is often driven by practical necessity rather than theoretical advancement. The online repair device does not introduce new welding physics or novel materials; instead, it creatively applies existing welding technology to overcome a logistical constraint. The lesson for engineers is that process innovation—finding new ways to apply established technology in new contexts—can be as impactful as material or equipment innovation. The study also demonstrates the value of close collaboration between research institutions and end-user companies: the Harbin Welding Research Institute provided the technical expertise, while the cement company provided the practical requirements and test environment. This partnership model is a template for industry-academia collaboration that engineers should emulate.