Overlay Welding Repair of Squeeze Rolls in Raw Material Final Grinding System

Literature Overview

The paper by Zhang Yongsheng, Ni Junjie, Yang Wei, and Zhang Haiyan, published in New Century Cement Guide (2012, Vol. 18, No. 5, pp. 56-57), addresses the critical challenge of overlay welding repair for squeeze rolls in the raw material final grinding system of cement production. The authors, affiliated with the Zhengzhou Mechanical Research Institute, highlight a fundamental operational dilemma: the repair cycle of the squeeze rolls must align with the kiln shutdown inspection schedule, which poses a significant scheduling and economic challenge.

Core Technical Content

The squeeze roll in a raw material grinding system operates under conditions fundamentally different from those in the cement grinding circuit. As the authors emphasize, the raw material system is directly coupled with kiln operation, meaning that any failure of the roller press in this system directly threatens continuous kiln operation. This is in contrast to the cement grinding system, where a roller press failure merely reduces output or allows alternative processing routes (selling clinker or direct grinding of clinker).

The wear mechanism in raw material grinding squeeze rolls involves a combination of:

Abrasive wear: Caused by hard mineral particles (quartz, feldspar) in the raw meal
Impact wear: Resulting from the high-pressure compaction of raw material
Corrosive wear: Due to chemical interaction with raw meal components
Fatigue wear: From cyclic loading during the rolling cycle

The Critical Scheduling Challenge

The central thesis of this paper is the mismatch between the overlay repair cycle and the kiln maintenance schedule. This represents a classic reliability engineering problem that can be analyzed using the following framework:

Aspect	Requirement	Challenge
Kiln maintenance interval	3-6 months	Fixed by refractory condition
Squeeze roll repair interval	Variable, often shorter	Dependent on wear rate
Repair duration	7-14 days	Must fit within kiln shutdown window
Overlay thickness required	10-20 mm	Limits repair frequency
Available repair window	7-10 days	Constrained by production

The authors note that achieving synchronization between the roll repair cycle and kiln maintenance window is extremely difficult in practice. This creates several operational consequences:

Unscheduled kiln shutdowns if roll failure occurs between planned maintenance periods
Excessive inventory of spare rolls to maintain production continuity
Increased downtime costs due to emergency repairs
Reduced overall system availability

Technical Solutions and Process Considerations

To address the scheduling challenge, several technical approaches can be considered:

Extended wear life through optimized overlay materials: Selection of overlay alloys with superior abrasion resistance can extend the service interval between repairs, increasing the probability of alignment with planned kiln maintenance.
Multi-layer overlay strategy: Depositing multiple layers with varying compositions can create a graded wear profile that maintains hardness throughout the service life, extending effective roll life.
Predictive maintenance integration: Implementing condition monitoring systems to predict remaining roll life allows better scheduling of repair activities.
Dual-roll configuration: Operating with backup rolls that are pre-repaired and available for immediate installation during kiln shutdown.

Process Parameters for Squeeze Roll Overlay

The overlay welding process for squeeze rolls typically employs the following parameters:

Parameter	Specification
Welding process	Submerged arc or flux-cored arc
Preheat temperature	250-400°C
Base metal	Medium carbon steel or cast iron
Overlay alloy	High-chromium cast iron or martensitic steel
Number of passes	3-5 layers
Interpass temperature	≤300°C
Post-weld treatment	Stress relief at 550-650°C
Final grinding	To restore roll profile and surface finish

Study Insights and Engineering Implications

This literature raises an important systems engineering perspective on overlay welding repair. The technical quality of the overlay deposit, while necessary, is insufficient if the repair schedule cannot be aligned with the broader production system requirements. This insight is particularly relevant for engineers working in continuous-process industries where subsystem failures cascade to affect entire production lines.

The economic implications are substantial. An unplanned kiln shutdown typically costs significantly more than a planned one due to:

Refractory damage from rapid cooling
Loss of thermal efficiency upon restart
Extended downtime for emergency repairs
Potential product quality issues during restart

The authors' observation that synchronization is difficult to achieve in practice suggests that a more holistic approach is needed, combining overlay material optimization, predictive maintenance, and operational scheduling to create a robust repair program.

This paper serves as a reminder that welding repair technology must be evaluated within the context of the entire production system, not in isolation. The success of an overlay repair program depends as much on operational planning as on metallurgical quality.