Zhuojin Pipe Fitting Co., LtdExperimental Study on Carbon Arc Surfacing of Scraper Conveyor Middle Sled
Literature Overview
This paper by the Zhangjiakou Coal Mine Machinery Factory and the Harbin Welding Research Institute, published in "Coal Science and Technology" in 1983, presents an experimental study on carbon arc surfacing of the middle sled of a scraper conveyor. The study focuses on the application of carbon arc surfacing for repairing wear-prone areas at the four corners of the middle sled, using pre-made wear-resistant alloy powder blocks. The resulting surfacing layer is a high-carbon, high-chromium, boron-containing alloy with high hardness, suitable for the severe wear conditions encountered in coal mining operations.
Core Technical Content
The scraper conveyor middle sled is a critical component in underground coal mining operations, subjected to intense abrasive wear from coal and rock material. The four corners of the middle sled are particularly vulnerable to wear due to the concentrated loading from the scraper chain and the abrasive action of the transported material. Traditional repair methods often involve replacing the entire middle sled, which is costly and time-consuming in underground mining environments.
Carbon arc surfacing offers an alternative repair approach that is well-suited to field conditions. The process involves placing pre-made wear-resistant alloy powder blocks on the wear-prone areas and using a carbon arc to melt the powder and fuse it with the 16Mn base material, forming a high-hardness surfacing layer.
| Process Parameter | Specification |
|---|---|
| Base Material | 16Mn low-alloy steel |
| Surfacing Alloy | High-carbon, high-chromium, boron-containing |
| Welding Process | Carbon arc surfacing |
| Powder Block Form | Pre-made alloy powder compact |
| Application Area | Four corners of middle sled |
| Key Property | High hardness wear resistance |
Carbon Arc Surfacing Process Characteristics
The carbon arc surfacing process described in the paper has several distinctive characteristics that make it suitable for mining field applications:
- Simple equipment: The process requires only a carbon arc welding power source, a carbon electrode holder, and basic safety equipment. This simplicity makes it feasible for use in underground mining environments where complex equipment is impractical.
- Easy operation: The process is relatively straightforward and can be mastered by trained operators with minimal specialized training. This is important in mining operations where skilled welders may be limited.
- Low cost: The use of pre-made powder blocks and basic carbon arc equipment results in low material and equipment costs, making the repair economically attractive compared to component replacement.
- High dilution rate: The carbon arc process produces deep penetration, which results in a higher dilution rate between the surfacing layer and the base metal. While this may reduce the hardness of the surfacing layer compared to processes with lower dilution, it ensures a strong metallurgical bond between the surfacing layer and the base material.
- Deep penetration: The deep penetration of the carbon arc ensures good fusion with the base material, creating a strong bond that can withstand the severe mechanical loading in mining operations.
Comparison with Plasma Surfacing
The paper includes a comparison with plasma surfacing (plasma spraying/welding) as an alternative repair method. Both processes can achieve similar chemical compositions in the surfacing layer, but they differ in several important aspects:
| Comparison Factor | Carbon Arc Surfacing | Plasma Surfacing |
|---|---|---|
| Equipment complexity | Simple | Complex |
| Field applicability | Excellent | Limited |
| Dilution rate | High | Low |
| Penetration depth | Deep | Shallow |
| Surface hardness | Moderate (due to dilution) | High (low dilution) |
| Bond strength | Strong | Good |
| Cost | Low | High |
| Operator skill required | Moderate | High |
The trade-off between carbon arc and plasma surfacing is primarily between dilution rate and equipment complexity. Carbon arc surfacing accepts a higher dilution rate (and consequently lower surface hardness) in exchange for simpler equipment and better field applicability. For the mining application described, the carbon arc approach is preferred because the repair must be performed in underground conditions where equipment simplicity and operator accessibility are paramount.
Metallographic Analysis and Performance
The study includes metallographic examination of the surfacing layer to characterize the microstructure and bonding quality. The high-carbon, high-chromium, boron-containing alloy forms a hard, wear-resistant microstructure that includes carbides and borides. The boron addition is particularly important for enhancing hardness and wear resistance in the alloy system.
The dilution between the surfacing layer and the 16Mn base material creates a transition zone with gradually changing composition and microstructure. This transition zone is critical for ensuring a strong metallurgical bond and preventing delamination under mechanical loading. The deep penetration of the carbon arc helps create a well-bonded interface, although it also means that the surface hardness is lower than it would be with a low-dilution process.
Engineering Practice Implications
For mining engineers and maintenance personnel, this paper provides a practical solution for extending the service life of scraper conveyor middle sleds. The carbon arc surfacing method is particularly valuable for underground mining operations where:
- Equipment must be portable and simple to operate.
- Skilled welders may be limited in number.
- Repairs must be performed quickly to minimize production downtime.
- The cost of replacement components is high due to transportation and logistics constraints.
The pre-made powder block approach also offers advantages in terms of quality control, as the alloy composition is predetermined and consistent, reducing the variability associated with on-site powder mixing. The method can be standardized and documented as a repair procedure, facilitating quality assurance in mining operations.
The study also highlights the importance of considering the operating environment when selecting a surfacing process. While plasma surfacing may offer superior surface properties, its complexity and cost make it impractical for many field applications. The carbon arc approach demonstrates that process selection must balance technical performance with practical constraints.
Summary
This paper presents a practical and cost-effective solution for repairing wear-damaged scraper conveyor middle sleds using carbon arc surfacing with pre-made alloy powder blocks. The process is well-suited to the demanding conditions of underground coal mining, where equipment simplicity, operator accessibility, and low cost are critical factors. The resulting high-carbon, high-chromium, boron-containing surfacing layer provides adequate wear resistance for extending component service life, and the deep penetration of the carbon arc ensures a strong metallurgical bond with the 16Mn base material. The study demonstrates the value of selecting appropriate surfacing processes based on the specific operating environment and practical constraints of the application.