Overlay Welding Maintenance Experience for Roller Press Surfaces in Cement Production

Literature Overview

This paper by Wang Mingwan from Baoshan Kungang Jiahua Cement Building Materials Co., Ltd. was published in the journal "Cement" (水泥) in 2015 (Issue 1, pages 32–33). The article presents practical experience and lessons learned from the overlay welding maintenance of roller press surfaces in cement production. Roller presses are critical equipment in cement grinding circuits, where they reduce the particle size of clinker and other raw materials through compression and crushing. The operating conditions are extremely severe, with high contact pressures, abrasive material, and continuous operation, making surface protection through overlay welding essential for equipment longevity.

Core Technical Content

The paper emphasizes that roller press surfaces must be pre-protected at the manufacturing stage through wear-resistant overlay welding to extend service life. The overlay welding is not merely a repair operation but a preventive maintenance strategy that determines the overall productivity and downtime of the grinding circuit. The key factors influencing overlay life include the wear resistance of the deposited material, the characteristics of the material being ground, and the timeliness of maintenance interventions.

Typical Operating Conditions

Parameter	Typical Range	Impact on Overlay
Contact pressure	10–30 MPa	High compressive stress causes plastic deformation and fatigue
Material being ground	Clinker, limestone, gypsum, fly ash	Abrasive particles cause wear and spalling
Operating temperature	50–150 °C	Thermal cycling affects residual stress and coating integrity
Roller speed	30–60 rpm	Dynamic loading conditions
Throughput	200–500 t/h	Determines material removal rate

Analysis of Failure Modes

The roller press surface is subject to multiple degradation mechanisms simultaneously. Understanding these failure modes is essential for selecting appropriate overlay materials and designing maintenance strategies.

Wear Mechanisms

Abrasive wear: Hard particles in the feed material (particularly quartz-bearing limestone and certain types of clinker) scratch and gouge the overlay surface. This is the dominant wear mechanism in cement grinding applications.
Adhesive wear: Under high contact pressure, localized cold welding occurs between the roller surface and the material being processed, followed by tearing and material transfer.
Fatigue spalling: Cyclic loading causes subsurface crack initiation and propagation, leading to spalling of the overlay material. This is particularly critical for hard, brittle overlay deposits.
Corrosive wear: In some cement plants, moisture and sulfur compounds in the feed material can cause corrosive degradation of the overlay surface.

Spalling and Delamination

One of the most challenging failure modes is spalling, where the overlay material separates from the substrate in large patches. This is typically caused by:

Excessive hardness of the overlay deposit, which reduces its ability to accommodate plastic deformation
High residual tensile stress in the overlay, which promotes crack initiation
Poor adhesion between the overlay and the substrate due to inadequate surface preparation or improper welding parameters
Thermal mismatch between the overlay and the roller body material

Overlay Material Selection and Design

The paper does not provide specific alloy compositions but discusses the general principles of overlay material selection for roller press applications. The following considerations are critical:

Hardness Gradient Design

A single-layer overlay with uniform hardness is generally not optimal for roller press surfaces. A multi-layer approach with a hardness gradient from the substrate to the surface is preferred:

Layer	Function	Typical Hardness (HRC)	Material Type
Transition layer	Reduce thermal mismatch and residual stress	25–35	Low-carbon or medium-alloy steel
Buffer layer	Absorb plastic deformation and prevent crack propagation	35–45	Medium-alloy steel with ductility
Hard face layer	Provide wear resistance	50–60	High-carbon, high-chromium, or carbide-containing alloy
Pattern layer (optional)	Improve material retention and reduce slip	45–55	Medium-hardness alloy with surface profile

Material Categories

Common overlay materials for roller press surfaces include:

High-carbon martensitic steels: Hardness of 50–58 HRC, good balance of wear resistance and toughness. Suitable for moderate abrasion conditions.
High-chromium white iron: Hardness of 60–65 HRC, excellent wear resistance but brittle. Suitable for severe abrasion but prone to spalling.
Carbide-reinforced alloys: Contain WC, Cr7C3, or TiC carbides for enhanced wear resistance. Hardness can exceed 65 HRC.
Composite coatings: Combine a ductile matrix with hard carbide particles for improved spalling resistance.

Maintenance Experience and Best Practices

The practical experience discussed in this paper highlights several key lessons:

Surface Preparation

The roller surface must be thoroughly cleaned and prepared before overlay welding. Oxide scale, rust, and previous overlay remnants must be completely removed by grinding or shot blasting.
Surface roughness should be controlled to 3.2–6.3 μm Ra for optimal adhesion.
Preheating of the roller to 200–300 °C is recommended to reduce residual stress and prevent cracking.

Welding Process Selection

Submerged arc welding (SAW): Preferred for large-scale overlay application due to high deposition rate and good penetration. Suitable for transition and buffer layers.
Flux-cored arc welding (FCAW): Flexible and adaptable to various positions. Commonly used for hard face layers.
Gas metal arc welding (GMAW): Used for repair and touch-up operations. Lower deposition rate but good controllability.
Laser cladding: Increasingly used for precision overlay with low dilution and fine microstructure control.

Residual Stress Management

Welding residual stress is a critical factor in overlay performance. High tensile residual stress at the overlay-substrate interface promotes crack initiation and spalling. The following measures are recommended:

Control the welding sequence to minimize thermal distortion and residual stress concentration.
Apply a multi-pass welding strategy with controlled interpass temperatures.
Consider post-weld stress relief heat treatment at 550–650 °C for 2–4 hours, if compatible with the roller body material.
Use peening or shot peening after overlay welding to introduce compressive residual stress at the surface.

Maintenance Strategy

The paper emphasizes the importance of proactive maintenance:

Regular visual inspection of the roller surface to detect early signs of wear, spalling, or cracking.
Measurement of overlay thickness using ultrasonic testing or magnetic thickness gauges.
Scheduled re-overlay when the remaining overlay thickness falls below the minimum acceptable level (typically 3–5 mm).
Avoidance of emergency repairs, which often result in poor quality and premature failure.

Engineering Practice Implications

The experience presented in this paper is highly relevant to engineers managing roller press maintenance in cement plants. The key takeaway is that overlay welding is not a one-time operation but a systematic maintenance program that requires careful planning, material selection, process control, and ongoing monitoring. The hardness gradient design principle—transitioning from ductile at the substrate to hard at the surface—is a fundamental concept that should be applied in all roller press overlay applications.

A practical FMEA (Failure Mode and Effects Analysis) approach can be applied to roller press overlay maintenance:

Failure Mode	Severity	Occurrence	Detection	RPN	Mitigation
Abrasive wear	7	9	6	378	Select harder overlay material
Fatigue spalling	8	6	5	240	Reduce overlay hardness, improve adhesion
Delamination	9	4	3	108	Improve surface preparation, control residual stress
Cracking	8	5	4	160	Preheat, control thermal input, PWHT
Excessive dilution	6	5	4	120	Use low-dilution process, multiple layers

Summary

The experience presented in this paper underscores that successful roller press surface protection through overlay welding requires a holistic approach that integrates material selection, process design, surface preparation, residual stress control, and preventive maintenance. The hardness gradient concept is a cornerstone of effective overlay design, ensuring that the surface provides wear resistance while maintaining sufficient toughness to resist spalling. Engineers managing roller press maintenance should adopt a systematic approach based on documented procedures, regular inspection, and data-driven decision-making to maximize equipment availability and minimize downtime. The practical lessons learned from this experience are directly transferable to similar heavy-duty grinding and crushing applications across various industries.