Zhuojin Pipe Fitting Co., LtdImproving Middle Trough Service Life Through Surfacing
Literature Overview
This paper by Li Chuangji (2006), published in Welding Technology, describes a practical engineering solution for extending the service life of middle troughs (middle sections) in scraper conveyors used in mining and material handling applications. The approach involves SMAW (shielded metal arc welding) surfacing of a wear-resistant alloy layer on the center plate of the middle trough, achieving a fivefold increase in service life with minimal modification to the existing manufacturing process.
Core Technical Content
The middle trough is a critical structural component in scraper conveyors, which are widely used in underground coal mines, open-pit mining operations, and bulk material handling facilities. The center plate of the middle trough is subjected to severe abrasive wear from the continuous sliding of scraper chains and transported materials. Traditional approaches to extending service life include increasing plate thickness or using more expensive base materials, both of which significantly increase manufacturing costs and component weight.
Surfacing Process Description
The proposed solution uses SMAW (stick welding) to deposit a wear-resistant alloy layer on the center plate surface. This method was selected for several practical reasons:
| Factor | SMAW Surfacing Advantage |
|---|---|
| Equipment cost | Minimal - standard SMAW power source required |
| Field applicability | Suitable for on-site repair and maintenance |
| Process flexibility | No shielding gas infrastructure needed |
| Skilled labor requirement | Moderate - experienced welders available in mining environments |
| Base material compatibility | Works with common carbon steel trough materials |
The key advantage highlighted in the paper is that the basic manufacturing process of the middle trough remains essentially unchanged. The surfacing operation is added as a finishing step, requiring no modification to the trough fabrication workflow, welding procedures, or quality control processes for the structural welds.
Performance Results
The reported fivefold increase in service life is a substantial improvement that directly impacts operational economics. In mining applications, middle trough replacement frequency directly affects:
- Downtime costs due to conveyor shutdown for maintenance
- Labor costs for trough removal and installation
- Material costs for replacement troughs
- Safety risks associated with hot work during replacement
Engineering Practice Analysis
FMEA Perspective on Middle Trough Wear
Applying a Failure Mode and Effects Analysis (FMEA) framework to this application reveals the following:
| Failure Mode | Root Cause | Severity | Occurrence | Detection | RPN |
|---|---|---|---|---|---|
| Excessive center plate wear | Abrasive contact with scraper chain and material | 9 | 8 | 6 | 432 |
| Plate through-thickness failure | Progressive wear reducing plate thickness | 10 | 7 | 5 | 350 |
| Surfacing layer spalling | Poor metallurgical bond or thermal stress | 8 | 4 | 7 | 224 |
| Edge chipping | Impact loading at trough edges | 7 | 6 | 8 | 336 |
The surfacing approach primarily addresses the first two failure modes by providing a sacrificial wear-resistant layer that protects the base plate.
Process Control Considerations
For successful implementation of SMAW surfacing on middle troughs, the following process parameters and controls are critical:
- Preheating: The base plate should be preheated to 150-250°C to reduce hydrogen-induced cracking risk in the dilution zone, particularly when using hard-facing electrodes with high carbon and alloy content.
- Interpass temperature control: Maintaining interpass temperature between 200-300°C prevents excessive cooling rates that could lead to hard, brittle microstructures in the weld metal.
- Bead layout: A multi-pass build-up with proper bead overlap (50-70% overlap) ensures uniform coverage and adequate dilution control.
- Electrode selection: Hard-facing electrodes based on high-speed steel, cobalt-based, or chromium-carbide systems are typically used, selected based on the specific wear mechanism (abrasive, impact-abrasive, or adhesive).
- Surface preparation: The base plate surface should be ground to bare metal with a minimum 10 mm wide preparation zone around the surfacing area to ensure proper fusion.
Quality Verification
Post-surfacing quality verification should include:
- Visual inspection for surface defects, porosity, and undercut
- Hardness testing (HV or HRC) to confirm the wear-resistant layer meets specification
- Bend test or macrograph examination to verify metallurgical bond integrity
- Thickness measurement to confirm adequate build-up
Practical Implementation Insights
The paper's emphasis on minimal process modification is particularly valuable for mining operations where production continuity is paramount. The approach represents a classic example of incremental improvement rather than disruptive change management. From a total cost of ownership perspective, even a modest investment in surfacing equipment and consumables is justified by the extended component life and reduced downtime.
However, several practical challenges must be acknowledged. First, SMAW surfacing productivity is relatively low compared to mechanized processes such as flux-cored wire surfacing or submerged arc surfacing. For high-volume production environments, the labor-intensive nature of SMAW may become a bottleneck. Second, the quality of SMAW surfacing is highly dependent on welder skill, and maintaining consistent quality across multiple shifts and operators requires robust training programs and quality control procedures. Third, the paper does not discuss the long-term durability of the surfacing layer under cyclic loading conditions, which is relevant for conveyor applications where the trough experiences repeated impact and vibration.
Summary
This paper presents a straightforward, cost-effective engineering solution that delivers significant operational benefits through the application of SMAW hardfacing to scraper conveyor middle troughs. The fivefold service life improvement demonstrates the effectiveness of surface engineering as a wear mitigation strategy. The approach is particularly suitable for mining environments where equipment availability is critical and process flexibility is valued over maximum productivity. Engineers considering this approach should carefully evaluate the specific wear conditions, select appropriate hardfacing consumables, and establish rigorous quality control procedures to ensure reliable long-term performance.