Overlay Welding Repair of PCS1430x2000 Large Hammer Crusher Rotor

Literature Overview

The paper by Lv Wencheng and Cao Xuezhai, published in Cement in 2014, documents the field overlay welding repair of the rotor of a PCS1430x2000 hammer crusher at the Gansu Jinchang Jinni Group Dry Process Plant. This case study addresses the repair of severely worn rotor discs and pin sleeves during the annual overhaul period of the raw mill and kiln system. The work was performed on-site to minimize costs and downtime, reflecting the practical constraints of cement plant maintenance operations.

Equipment Description and Failure Analysis

The PCS1430x2000 hammer crusher is a large-capacity primary crushing unit used for crushing limestone feed in the cement production process. The rotor assembly consists of a central shaft, rotor discs (plates), hammers, and pin sleeves that secure the hammers to the discs. During normal operation, the hammers impact limestone at high velocity, and the rotor discs and pin sleeves experience progressive wear from both the direct impact of hammer rebound and the abrasive action of limestone particles trapped between moving components.

The plant operates the raw mill and kiln as an integrated system with an annual overhaul cycle. During the overhaul period, the limestone hammer crusher rotor discs and pin sleeves were found to be severely worn, requiring repair to restore dimensional accuracy and functional capacity. The decision to perform on-site overlay welding repair was driven by economic considerations, as the cost of replacing the entire rotor assembly would be substantially higher than the cost of overlay welding repair.

Welding Process and Field Implementation

The field overlay welding repair was performed using shielded metal arc welding (SMAW) or submerged arc welding (SAW) with wear-resistant hard-facing electrodes or wires. The base metal of the rotor discs is typically low-carbon steel or low-alloy steel, while the pin sleeves may be made from medium-carbon steel or alloy steel. The overlay weld deposits are designed to provide enhanced abrasion and impact resistance through the formation of hard carbide phases within a tough matrix.

The field repair process involves several critical steps: surface preparation through grinding and cleaning to remove loose material and rust, preheating of the base metal to prevent cold cracking, multi-pass overlay welding to build up the required thickness, and post-weld stress relief if required. The challenge of field welding lies in maintaining consistent weld quality without the environmental control available in a welding shop.

Engineering Practice Considerations

The on-site repair approach presents several technical challenges that must be addressed to ensure repair quality. Ambient temperature, humidity, and wind conditions can affect arc stability and weld metal composition. Contamination from dust and debris in the plant environment can introduce porosity and inclusions into the weld deposit. Limited access to the rotor assembly requires careful planning of weld sequence to minimize distortion and ensure complete coverage of worn areas.

The choice of overlay welding consumable is critical for achieving the required service life. For limestone crushing applications, the wear mechanism is predominantly sliding and abrasive, with some impact component. Consumables based on high-carbon, high-chromium martensitic systems (such as those with 12-14% Cr and 2-5% C) provide hardness in the range of 50-60 HRC and are well-suited for this application. Alternatively, austenitic overlay systems with retained austenite provide good impact resistance but lower hardness, which may be appropriate if impact loading is dominant.

Key Reflections and Technical Commentary

This case study highlights the economic rationale for overlay welding repair in large cement plant equipment. The cost savings from field repair compared to component replacement can be substantial, particularly for large castings such as crusher rotors where the replacement cost includes both material and machining. However, the economic analysis must also account for the risk of repair failure, which could result in unplanned downtime and production losses.

A critical aspect of field repair that deserves emphasis is the importance of weld quality control. In a shop environment, welds can be inspected using radiographic testing, ultrasonic testing, and visual examination under controlled conditions. In the field, inspection options may be limited, and the consequences of undetected weld defects can be severe. Minimum quality control measures should include visual inspection of all welds, magnetic particle testing of critical welds, and hardness testing of the overlay deposits to verify the achieved hardness level.

The annual overhaul cycle provides an opportunity for comprehensive condition assessment of the rotor assembly. Engineers should consider implementing a condition monitoring program that includes regular measurement of rotor disc thickness, pin sleeve diameter, and hammer wear. This data can be used to predict remaining service life and optimize the timing of repair operations.

In summary, this paper provides a practical example of cost-effective field overlay welding repair for large cement plant equipment. The approach of performing repair during scheduled overhaul periods is a sound maintenance strategy that balances cost, downtime, and equipment reliability. Engineers should ensure that proper consumable selection, surface preparation, and quality control measures are implemented to maximize the success and longevity of the repair.