CLADDING TECHNOLOGY SHANXI CO., LTDLarge-Area Pattern Hardfacing on Scraper Conveyor Middle Plates
Literature Overview
This 1994 publication by Xu Guodong and Liu Zhuguo from Datun Coal Electric Company Comprehensive Machinery Rental Station addresses the hardfacing of large-area patterns on the middle plate of a scraper conveyor system. Scraper conveyors are critical components in underground coal mining operations, where the middle plates are subjected to extreme abrasive wear from coal, rock fragments, and continuous mechanical impact. The concept of "pattern hardfacing" refers to applying hardfacing deposits in a specific geometric arrangement rather than covering the entire surface, optimizing material usage and cost while providing adequate wear protection at critical locations.
Core Technical Content
The scraper conveyor middle plate typically has a flat or slightly contoured surface with wear zones concentrated at specific locations: the scraper contact area, the chain engagement zone, and areas where material impact is most severe. Pattern hardfacing involves applying hardfacing in strips, blocks, or rows at these critical zones, leaving the non-critical areas unprotected to reduce weight and cost.
The key technical challenges include:
- Achieving uniform hardness across large areas with multiple weld passes
- Managing heat input to prevent distortion of the large flat plate
- Ensuring consistent bond strength across the entire pattern
- Controlling interpass temperature during multi-pass welding on large surfaces
Welding Process and Parameters
For large-area pattern hardfacing on scraper conveyor middle plates, submerged arc welding (SAW) and flux-cored arc welding (FCAW) are commonly employed due to their high deposition rates and good penetration characteristics. The following table summarizes typical process parameters:
| Parameter | SAW (Single Wire) | FCAW |
|---|---|---|
| Wire Diameter | 1.6–2.0 mm | 1.2–1.6 mm |
| Current | 400–600 A | 250–350 A |
| Voltage | 28–35 V | 28–32 V |
| Travel Speed | 300–500 mm/min | 200–400 mm/min |
| Shielding Gas (FCAW) | CO₂ or Ar+CO₂ mix | — |
| Flux Type | Acidic or basic | Self-shielded or gas-shielded |
| Target Hardness | 45–55 HRC | 45–55 HRC |
| Overlay Thickness | 4–8 mm per pattern zone | 3–6 mm per pattern zone |
Pattern Design Considerations
The pattern design must account for the wear mechanism and the direction of material flow. Key design principles include:
- Directional alignment: Hardfacing strips should be oriented perpendicular to the primary wear direction to maximize resistance against abrasive sliding.
- Spacing optimization: The gap between hardfacing strips should be 10–20 mm to allow for thermal expansion and to prevent crack propagation from one strip to another.
- Edge reinforcement: Additional hardfacing passes at the plate edges provide protection against edge chipping and corner wear.
- Transition zones: Gradual transitions between hardfaced and unhardfaced areas reduce stress concentrations at the pattern boundaries.
Defect Prevention and Quality Control
| Defect Type | Cause | Prevention |
|---|---|---|
| Cracking | High residual stress, hydrogen | Preheat 200°C, stress relief PWHT |
| Excessive dilution | High heat input, thin first pass | Use lower current for first pass |
| Distortion | Asymmetric heat input | Symmetric welding sequence, clamping fixtures |
| Incomplete fusion | Poor surface preparation | Grinding to bare metal, flux cleaning |
| Hardness variation | Parameter drift | Monitor parameters, periodic hardness checks |
Engineering Practice and Economic Analysis
The pattern hardfacing approach offers significant economic advantages over full-surface hardfacing. By covering only 30–50% of the plate surface area with hardfacing material, the cost of expensive alloy filler metals is reduced while still providing adequate wear protection. For a typical scraper conveyor middle plate measuring 1000 mm × 400 mm, pattern hardfacing can reduce alloy consumption by 50–60% compared to full coverage.
The welding sequence should follow a symmetric pattern to minimize distortion. Starting from the center and working outward, or using a staggered sequence, helps distribute heat input evenly across the plate. For large plates, segmental welding with periodic stress relief may be necessary to maintain dimensional accuracy within tolerances of ±1.0 mm per meter.
Study Insights and Reflections
This study exemplifies the engineering philosophy of targeted protection: applying expensive wear-resistant materials only where they are most needed. The pattern hardfacing approach demonstrates that effective engineering solutions do not always require maximum material usage. The economic efficiency of this method makes it particularly suitable for mining equipment where large quantities of wear parts are consumed annually. Engineers should consider pattern design as a critical design variable that directly impacts both performance and cost. The key insight is that the pattern geometry must be tailored to the specific wear mechanism of the application, not applied generically.