Overlay Welding Repair of Sintering Car Body

Literature Overview

This 2005 paper published in Hot Working Technology (Vol. 34, No. 12, pp. 85-85) documents the overlay welding repair of sintering car bodies at Baogang (Baotou Steel). Authored by Cheng Jun and Guo Changqing from Inner Mongolia University of Science and Technology, the study presents a practical case study of using multi-layer multi-pass overlay welding to restore worn sintering car bodies to service condition. The paper is concise but addresses a common industrial maintenance challenge in the iron and steel industry.

Core Technical Content

Sintering cars are used in iron ore sintering plants to transport sinter mix through the sintering machine. The car body is subjected to severe wear from the abrasive sinter mix, thermal cycling from the hot sinter cake, and mechanical loading. The car body is typically fabricated from pearlite heat-resistant steel, which provides adequate strength and thermal stability but limited wear resistance.

The repair approach involves multi-layer multi-pass overlay welding with a wear-resistant alloy to restore the worn surfaces of the car body. The key findings are:

Failure Analysis and Process Selection

The study begins with a failure analysis of the sintering car body to determine the primary wear mechanism and the appropriate repair strategy. The wear pattern on the car body is typically characterized by:

• Abrasive wear on the bottom surface and side walls where the sinter mix slides
• Thermal fatigue cracking from repeated heating and cooling cycles
• Mechanical deformation from impact loading during loading and unloading
• Possible oxidation and scaling on surfaces exposed to hot sinter cake

The selection of multi-layer multi-pass overlay welding is based on the following considerations:

1. First layer (transition layer): A low-dilution transition alloy is deposited to ensure good metallurgical bonding with the base steel and to reduce the dilution of subsequent layers.
2. Intermediate layers: Additional passes with the wear-resistant alloy are deposited to build up the required thickness while maintaining good composition control.
3. Surface layer: The final pass provides the wear-resistant surface with the desired hardness and microstructure.

The multi-layer approach allows for better control of the weld pool composition, reduced residual stress, and improved mechanical properties compared to single-layer overlay welding.

Quality Verification

The study reports comprehensive quality verification of the repaired car body, including:

The fact that the repaired car body achieves service life comparable to a new car body is a strong validation of the repair process. This finding has significant economic implications for steel plants that can extend the service life of expensive sintering cars through overlay welding repair rather than complete replacement.

Engineering Practice Considerations

The repair of sintering car bodies presents several practical challenges:

• Geometry constraints: The car body has complex geometry with corners, weld seams, and reinforcement ribs that make overlay welding challenging. The welder must maintain good access and avoid excessive heat input on thin sections.
• Preparation requirements: The worn surfaces must be thoroughly cleaned to remove scale, rust, and contaminated material before overlay welding. Incomplete cleaning leads to poor bonding and potential delamination.
• Distortion control: The sintering car body is a large structural component, and excessive heat input during overlay welding can cause distortion that affects the car's alignment on the sintering machine tracks.
• Welding sequence: The welding sequence must be carefully planned to minimize distortion and residual stress. Symmetrical welding from the center outward is a common approach for large flat surfaces.

Key Questions and Reflections

• The paper does not specify the exact overlay alloy used, which limits the ability to evaluate the selection rationale. The choice of overlay alloy should be based on the specific wear mechanism and operating conditions of the sintering car.
• The study does not address the long-term performance of the overlay weld layer under thermal cycling. In sintering applications, the car body is exposed to temperatures up to 900-1000°C, and the overlay layer must maintain its properties under these conditions.
• The paper is very brief (only 1 page) and does not provide detailed process parameters such as welding current, voltage, travel speed, or number of passes. This limits the practical value for engineers seeking to replicate the repair process.
• The study does not compare the overlay welding repair with alternative repair methods such as metal spray, thermal spray, or complete replacement. A comparative analysis would provide a more complete economic evaluation.

Study Insights and Implications

This case study demonstrates the practical application of multi-layer multi-pass overlay welding for the repair of heavily worn industrial components. The key insight is that a properly designed overlay welding process can restore worn surfaces to their original service condition, providing a cost-effective alternative to component replacement.

For maintenance engineers in the iron and steel industry, this paper reinforces the importance of systematic failure analysis before selecting a repair strategy. The multi-layer multi-pass approach provides better control of composition, residual stress, and mechanical properties compared to single-layer overlay welding, and is particularly suitable for thick repair builds. The achievement of service life comparable to new components validates the overlay welding approach as a viable maintenance strategy.