Wear-Resistant Overlay Welding Repair of Centrifugal Exhaust Fan Impellers in Cement Industry

Literature Overview

This paper, authored by Huang Zhiquan, Wei Jianjun, Pan Jian, and Xu Jian from the Zhengzhou Research Institute of Machinery Industry (Ministry of Machinery Industry), was published in the journal "Cement" in 1997 (Issue 9, pp. 12-13). The work addresses a long-standing operational problem in cement production: the rapid wear of centrifugal exhaust fan impellers caused by abrasive cement dust and particulate matter. The authors propose a systematic approach to extending impeller service life through the application of wear-resistant overlay welding electrodes, providing practical guidance for maintenance engineers in the cement and bulk material handling sectors.

Core Technical Approach

The centrifugal exhaust fans used in cement kiln systems are subjected to continuous erosion from high-velocity gas streams carrying fine cement particles, fly ash, and other abrasive contaminants. The impeller blades, particularly the leading edges and suction surfaces, experience severe abrasive wear that can reduce equipment availability and increase unplanned shutdowns. The authors selected appropriate wear-resistant overlay welding electrodes—typically classified under GB/T standards for high-chromium cast iron or cobalt-based hardfacing compositions—to deposit a protective layer on the critical wear zones of the impeller.

The overlay welding process employed was SMAW (Shielded Metal Arc Welding), which is well-suited for field repair conditions where portability and equipment simplicity are essential. The selection criteria for the hardfacing electrode included hardness (targeting 50-60 HRC for high-chromium martensitic compositions), wear resistance against abrasive particles, thermal shock resistance to withstand temperature fluctuations in the exhaust gas stream, and adequate ductility to prevent catastrophic spalling of the overlay layer.

Process Parameters and Practical Considerations

The following table summarizes the typical process parameters used in the overlay welding repair of impeller blades:

Parameter	Recommended Value	Rationale
Base material	Carbon steel Q235 or 16Mn impeller	Common fan construction material
Electrode type	High-Cr martensitic hardfacing (e.g., D407, D427 series)	Hardness > 50 HRC, good abrasion resistance
Electrode diameter	3.2-4.0 mm	Suitable for thin blade sections
Current range	100-180 A	Prevents excessive heat input into thin sections
Interpass temperature	< 150°C	Minimizes residual stress and cracking risk
Number of overlay layers	2-3 passes	Ensures adequate thickness (2-3 mm) for wear life
Preheating	100-150°C (for thicker sections)	Reduces hydrogen cracking susceptibility

The key challenge identified by the authors is the thin cross-section of impeller blades, which limits the allowable heat input and increases the risk of distortion and thermal cracking. To mitigate this, the authors recommended low-current, multi-pass welding with careful interpass temperature control. The use of short arc length and weaving technique was emphasized to ensure uniform deposition and adequate fusion with the base metal.

Engineering Practice Insights

From a practical standpoint, this work highlights several important principles that remain relevant in modern maintenance welding:

Wear analysis first: Before selecting the overlay material, a thorough analysis of the wear mechanism (abrasive, adhesive, erosive, or combined) is essential. In cement exhaust fans, the dominant mechanism is two-body and three-body abrasion from cement particles embedded in the gas stream.
Layer design: A single hardfacing layer may not be optimal. The authors implicitly suggest that a graded layer approach—starting with a softer, ductile transition layer followed by harder wear-resistant layers—can improve bonding strength and reduce spalling risk.
Post-weld treatment: Stress-relief annealing at 550-650°C for 1-2 hours is recommended after overlay welding to reduce residual stresses that could cause delayed cracking or distortion.
Inspection and acceptance: Visual inspection for undercut, porosity, and incomplete fusion should be supplemented by hardness testing (minimum 45 HRC in the overlay layer) and, for critical applications, dye penetrant testing (PT) to detect surface cracks.

Key Defects and Countermeasures

Defect	Cause	Countermeasure
Cracking in overlay	High cooling rate, hydrogen pickup	Preheat, low-current welding, post-weld stress relief
Spalling/delamination	Poor fusion, thermal mismatch	Ensure adequate penetration, use graded layer design
Excessive distortion	High heat input on thin sections	Multi-pass low-current, back-up copper plate support
Inadequate hardness	Dilution with base metal	Minimum 2-3 passes, proper electrode composition selection

Study Insights and Implications

This 1997 publication, while modest in scope, represents a practical engineering solution to a real industrial problem. The approach is straightforward and cost-effective, requiring only standard SMAW equipment and commercially available hardfacing electrodes. The methodology described—selecting appropriate hardfacing composition based on wear mechanism, controlling heat input for thin sections, and verifying results through hardness and visual inspection—remains a valid framework for overlay welding repair work today.

For modern engineers, the key takeaway is that overlay welding repair is not merely about depositing a hard layer; it requires careful consideration of the metallurgical compatibility between the overlay and base material, the thermal constraints imposed by the component geometry, and the service conditions that the repaired component must withstand. The cement industry's experience with impeller repair has direct parallels in other bulk material handling applications, including mining, power generation, and chemical processing, where centrifugal fans and similar rotating equipment are exposed to abrasive wear.