Overlay Welding Treatment Technology for Ball-less Mill Rotor Discs

Literature Overview

This paper by Li Kunshan from the School of Mechanical Engineering, University of Jinan, published in Materials Protection in 2002 (Vol. 35, Issue 8, p. 60), presents overlay welding treatment technology for ball-less mill rotor discs. The work addresses the wear problem in ball-less grinding mills (also known as vertical mills or roller mills) used in cement and mineral processing industries, where rotor discs are subjected to severe abrasive wear from grinding media and material particles.

Technical Context and Wear Mechanism

Ball-less mills (粉磨机) are used for fine grinding applications where conventional ball mills are inefficient. The rotor disc in such mills is subjected to extreme abrasive wear from the interaction between grinding media and material particles. The wear mechanism is primarily three-body abrasion, where hard particles are pressed against the rotor surface and removed material through ploughing and cutting mechanisms.

The service conditions are characterized by:

High contact pressure between grinding elements and rotor surface
Continuous sliding contact with abrasive particles
Variable temperature conditions depending on mill operation
Potential for impact loading during material feed fluctuations

Overlay Welding Approach

The paper describes the application of overlay welding as a surface treatment technology to extend the service life of ball-less mill rotor discs. The approach involves depositing wear-resistant alloy layers on the rotor surface to provide enhanced abrasion resistance compared to the base material.

Key technical considerations for this application include:

Parameter	Consideration
Overlay Material	Must provide superior abrasion resistance to base material
Bond Strength	Overlay must resist spalling under impact and sliding loads
Layer Thickness	Must balance wear life against cost and dimensional constraints
Surface Finish	Must be compatible with mill operation requirements
Thermal Effects	Welding heat must not distort or weaken the rotor structure

Engineering Considerations for Rotor Disc Repair

In my engineering practice, the overlay welding of rotor discs presents several unique challenges:

Geometric constraints — the curved surface geometry of rotor discs requires careful weld sequencing to minimize distortion
Rotational balance — overlay material addition can affect dynamic balance, requiring careful mass distribution
Service accessibility — field repair conditions may differ significantly from workshop conditions
Cost-benefit analysis — the cost of overlay repair must be compared against rotor replacement costs and downtime costs
Surface preparation — existing wear patterns and surface contamination must be addressed before overlay application

The selection of overlay material is critical. For abrasive wear applications in grinding mills, common choices include:

High chromium cast irons (12-28% Cr) for severe abrasion
Manganese steels for impact-abrasion combined conditions
Carbide-containing alloys for extreme wear resistance
Hardfacing alloys with specific carbide formers for targeted wear resistance

Process Development and Implementation

The paper, though brief, addresses the fundamental aspects of overlay welding process development for this application. Successful implementation requires:

Proper surface preparation through grinding or shot blasting
Selection of appropriate welding process (typically SAW, FCAW, or plasma arc)
Development of qualified welding procedure with controlled heat input
Implementation of multi-pass welding with controlled interpass temperatures
Post-weld machining to achieve required surface finish and dimensional accuracy
Quality verification through hardness testing, macrographic examination, and possibly wear testing

Study Insights and Practical Value

This paper, while concise, addresses a practically important application of overlay welding technology. The ball-less mill rotor disc is a critical component in mineral processing operations, and its wear directly impacts production efficiency and operating costs. The overlay welding approach offers a cost-effective alternative to complete rotor replacement, particularly when the base structure remains sound.

From a broader perspective, this application exemplifies the value of overlay welding as a remanufacturing and life extension technology. Rather than discarding worn components, overlay welding enables restoration of functional surfaces while preserving the structural integrity of the base material. This approach aligns with modern sustainability principles by reducing material consumption and waste generation.

For engineers working in cement and mineral processing industries, the key takeaways from this paper are: overlay welding is a viable technology for rotor disc wear protection; process development must account for the specific wear mechanism and service conditions; and systematic approach to material selection, process optimization, and quality verification is essential for successful implementation. The paper serves as a foundation for more detailed process development work that would address specific equipment configurations and operating conditions.