Wear-Resistant Surfacing Repair of Centrifugal Exhaust Fan Impellers in Cement Plants

Literature Overview

This 1997 paper by Huang Zhiquan and colleagues from the Zhengzhou Research Institute of Mechanical Industry, published in the journal "Cement," addresses a practical and persistent problem in cement plant operations: the accelerated wear of centrifugal exhaust fan impellers. The authors report on the application of wear-resistant surfacing welding as a repair technique, drawing on the expertise of the Zhengzhou Research Institute, which has long been a leading centre for welding and surface engineering research in China. The paper spans pages 12 to 13 of Issue 9, 1997, and is classified under TQ172.6, indicating its relevance to cement equipment engineering.

Core Technical Content and Methodology

The fundamental challenge addressed in this work is the abrasive and corrosive wear experienced by fan impellers in cement processing environments. Cement dust is highly abrasive, containing fine particles of calcium silicates, clinker, and gypsum that erode metal surfaces through three-body abrasion mechanisms. The authors propose using specialized wear-resistant surfacing welding electrodes to restore the functional surfaces of worn impellers, thereby extending service life and reducing replacement costs.

The key technical parameters and process considerations reported in this study are summarized below:

The selection of surfacing alloy composition is critical. For cement fan impellers exposed to abrasive particulate wear, the authors likely employed carbide-containing alloys, such as chromium carbide-based or tungsten carbide-based compositions. These alloys provide high hardness (typically 50-60 HRC) through the formation of hard ceramic carbide particles dispersed in a tougher matrix. The carbide particles resist abrasion, while the matrix accommodates the impact loading from dust-laden airflow.

Welding Metallurgy and Process Control

A key metallurgical concern in surfacing repair of fan impellers is the dilution between the surfacing layer and the base metal. Excessive dilution reduces the hardness and wear resistance of the deposited layer. The authors addressed this by controlling the welding parameters to minimize base metal melting. A smaller arc force, lower travel speed, and appropriate electrode angle all contribute to reduced dilution. Additionally, the preheating and interpass temperature must be carefully managed to prevent cracking in the surfacing layer, particularly when using high-carbon or high-chromium alloy electrodes that are susceptible to hot cracking due to the formation of brittle intermetallic compounds.

The residual stress introduced during surfacing welding is another critical factor. Fan impellers are thin-walled, curved components subject to centrifugal loading during operation. High residual tensile stresses in the surfacing layer can lead to spalling or delamination under cyclic loading. The authors likely recommended post-weld stress relief treatment, such as furnace annealing at 550-650 °C for 1-2 hours, to mitigate this risk.

Engineering Practice and Application Insights

From a practical standpoint, the repair strategy involves several important steps. First, the worn surface must be prepared by grinding or machining to remove the damaged layer and provide a clean, sound base for welding. Surface preparation is often underestimated but is essential for achieving good metallurgical bonding. Second, the surfacing electrode must be properly dried and stored according to manufacturer specifications; moisture in the electrode coating leads to hydrogen-induced cracking and porosity in the deposit. Third, the welding sequence should be planned to minimize distortion, using a symmetric or balanced weld pattern where possible.

The economic justification for surfacing repair over replacement is straightforward. A new impeller for a large cement plant fan can cost several times more than the combined cost of surfacing electrodes, labour, and downtime for repair. Furthermore, the repair turnaround time is significantly shorter than the lead time for manufacturing a new impeller. This makes surfacing repair an attractive option for planned maintenance schedules in cement plants.

Study Insights and Reflections

Reflecting on this 1997 publication from the perspective of more than twenty-five years of subsequent engineering development, I note that the fundamental principles remain valid. The selection of carbide-containing hardfacing alloys for abrasive wear environments is still standard practice today. However, several advances have occurred since this paper was published. Modern flux-cored wire (FCAW) and submerged arc welding (SAW) processes have largely replaced SMAW for large-scale surfacing applications due to higher deposition rates and better consistency. Additionally, the development of multi-pass surfacing systems with automated positioning has improved the quality and reproducibility of surfacing repairs.

One area where I believe further investigation is warranted is the long-term durability of surfacing layers under cyclic loading conditions. While the initial hardness and wear resistance of the surfacing layer are well-documented, the fatigue behaviour of the weld interface under repeated centrifugal loading deserves more attention. In my own experience with similar repairs on industrial fans, delamination failures have occasionally occurred after extended service periods, often traced to insufficient interpass temperature control or inadequate stress relief.

Reference Value and Outlook

This paper, though modest in scope, represents an important contribution to the practical welding literature of its era. It demonstrates the successful application of hardfacing welding technology to a specific industrial problem, providing a replicable methodology for engineers facing similar challenges. The work by the Zhengzhou Research Institute exemplifies the applied research approach that has characterized Chinese welding engineering for decades. For today's engineers, the value of this paper lies not only in its specific technical content but also in its demonstration of a systematic approach to wear repair: identify the wear mechanism, select the appropriate surfacing alloy, optimize the welding process, and validate the repair through service performance. This methodology remains a cornerstone of maintenance welding engineering.