Offline Surfacing Device for Vertical Mill Roller Sleeve

Literature Overview

This paper, published in Cement (No. 12, 2020, pp. 34-35) by Luan Jiangtao, Luan Chenchen, and Gan Aijun from Nanyang Zhonglian Cement Co., Ltd. and Sichuan University, presents the design and application of an offline surfacing rotation fixture for the roller sleeve of vertical mill rollers in cement production. Vertical mills are critical equipment in cement grinding operations, and the roller sleeves are subjected to severe abrasive wear from the continuous grinding of cement clinker and raw materials. The offline surfacing device enables the roller sleeve to be removed from the mill and refurbished through surfacing, extending its service life and reducing maintenance costs.

Core Technical Content

The offline surfacing rotation fixture described in the paper is a relatively simple but effective mechanical device designed to facilitate the surfacing of roller sleeves outside the mill. The device consists of the following components:

Component	Description	Function
Shaft	Main rotating shaft	Supports the roller sleeve and provides rotation
Inner clamp plate	Fixed inner plate	Secures the roller sleeve to the shaft
Outer clamp plate	Movable outer plate	Provides additional clamping force
Bearings	Support bearings	Support the shaft and allow smooth rotation
Bearing housing	Bearing support structure	Houses and supports the bearings
Fixed clamp plate	Welded fixed plate	Provides rigid connection to the fixture frame
Movable clamp plate	Two-part (inner + outer ring)	Allows quick roller sleeve change without removing bearing housing

Design Features and Engineering Considerations

The key design innovation of this fixture is the two-part movable clamp plate (inner ring and outer ring), which allows the roller sleeve to be quickly removed and replaced without disassembling the bearing housing. This design feature significantly reduces the time required for roller sleeve changeover, which is a critical consideration in cement plant maintenance operations where downtime is costly.

The fixture is designed for offline surfacing, meaning the roller sleeve is removed from the mill and transported to a dedicated surfacing station. This approach offers several advantages over in-situ surfacing:

Better accessibility — The roller sleeve can be positioned in an optimal orientation for surfacing, allowing uniform coverage of the entire surface.
Improved quality control — Offline surfacing allows for careful preparation, process parameter optimization, and thorough quality inspection.
Reduced downtime — Multiple roller sleeves can be prepared and refurbished in advance, minimizing the time the mill is offline for maintenance.

Process Analysis

The surfacing of vertical mill roller sleeves is a demanding application due to the severe operating conditions:

Abrasive wear — The roller sleeve is in continuous contact with abrasive cement clinker particles.
Impact loading — The grinding action involves significant impact forces from the clinker particles.
Thermal loading — The grinding process generates significant heat, which can cause thermal fatigue of the surfacing layer.
Chemical attack — The cement clinker contains various chemical compounds that can cause corrosion of the surfacing layer.

Surfacing Process Requirements

Requirement	Specification	Rationale
Surfacing hardness	HRC 50-60	Adequate wear resistance for cement grinding
Surfacing thickness	3-5 mm	Sufficient overbuild for machining to final dimensions
Dilution rate	<30%	Preserve alloy content in surfacing layer
Crack resistance	High	Resist cracking under thermal and impact loading
Adhesion strength	High	Prevent delamination of surfacing layer from base material

Recommended Surfacing Processes for Roller Sleeves

Process	Advantages	Limitations
FCAW	High deposition rate, good wetting, low cost	Higher dilution than low-heat-input processes
GMAW with flux-cored wire	Good deposition rate, moderate dilution	Requires shielding gas, sensitive to wind
Submerged arc welding (SAW)	Very high deposition rate, excellent protection	High heat input, not suitable for thin sections
HVOF	Very low dilution, excellent adhesion	High equipment cost, limited to thin coatings

Engineering Practice Integration

The implementation of an offline surfacing program for vertical mill roller sleeves requires careful planning and coordination:

Removal and transport — The roller sleeve must be carefully removed from the mill and transported to the surfacing station without damage.
Surface preparation — The roller sleeve surface must be thoroughly cleaned and prepared for surfacing, including removal of any existing surfacing layer or coating.
Surfacing operation — The surfacing must be performed using optimized process parameters to achieve the required hardness, thickness, and adhesion.
Post-weld treatment — The surfacing layer may require stress relief treatment to minimize residual stresses.
Machining — The surfacing layer must be machined to the required dimensional tolerances and surface finish.
Quality inspection — The refurbished roller sleeve must undergo thorough quality inspection before being returned to service.

Quality Control Plan

Inspection Stage	Method	Acceptance Criteria
Pre-surfacing	Visual inspection, MT	No cracks, no loose material
Post-surfacing	Hardness test, thickness measurement	Hardness within specification, thickness adequate
Post-machining	Dimensional inspection, surface finish measurement	Within tolerance, surface finish acceptable
Final	NDT (MT or UT), dimensional verification	No defects, all dimensions within specification

Key Questions and Reflections

The paper provides a practical description of the offline surfacing fixture but does not extensively discuss the surfacing process parameters or the metallurgical considerations for the specific roller sleeve application. Engineers working on similar applications should pay particular attention to the following:

Base material compatibility — The base material of the roller sleeve (typically low-carbon or medium-carbon steel) must be compatible with the selected surfacing consumable.
Thermal stress management — The large diameter of the roller sleeve can lead to significant thermal stresses during surfacing, which must be managed through careful process parameter control.
Uniformity of surfacing — The rotation fixture must provide smooth, consistent rotation during surfacing to ensure uniform surfacing layer thickness and hardness.

Study Insights and Implications

This paper demonstrates the practical application of offline surfacing technology for cement mill roller sleeves. The key insight is that offline refurbishment offers significant advantages over in-situ repair in terms of quality, efficiency, and cost. The simple but effective design of the rotation fixture highlights the importance of practical engineering solutions that address real-world maintenance challenges. For engineers working on similar applications, the paper provides a valuable reference for fixture design and offline refurbishment program planning.