CLADDING TECHNOLOGY SHANXI CO., LTDPlasma Transferred Arc Cladding Application in Guide Strip Manufacturing
Literature Overview
This 1997 publication by Wang Long from a military-affiliated department addresses the application of plasma transferred arc (PTA) welding in the manufacturing of guide strips. Guide strips serve as critical functional components in metallurgical rolling mills, power generation equipment, and precision machinery, where they require exceptional surface hardness, wear resistance, and dimensional stability. The work represents an early Chinese contribution to understanding the advantages of PTA cladding over conventional arc welding methods for precision strip production.
Core Technical Points
PTA cladding differs fundamentally from conventional gas metal arc welding (GMAW) overlay in its ability to produce extremely thin, homogeneous overlay layers with minimal dilution. For guide strip applications, the following process parameters are critical:
| Parameter | Typical Range | Function |
|---|---|---|
| Arc current | 80-200 A | Controls deposition rate and dilution |
| Shielding gas flow | 10-25 L/min (Ar) | Protects molten pool and powder |
| Powder feed rate | 50-200 g/min | Controls deposition thickness per pass |
| Travel speed | 50-300 mm/min | Affects dilution and layer uniformity |
| Preheat temperature | 150-250°C | Reduces residual stress and cracking tendency |
| Interpass temperature | <300°C | Prevents excessive grain growth |
The key advantage of PTA for guide strips lies in the precise control of dilution rate, which can be maintained below 5-10% depending on powder composition and process settings. This low dilution ensures that the overlay layer retains its designed hardness and wear properties without significant alloying element depletion.
Powder Selection and Metallurgical Considerations
For guide strip applications, typical powder compositions include Cr-Co alloys (such as Stellite-type), Cr-Mo-V hardfacing powders, or Ni-based solid solution strengthening alloys. The selection depends on the specific wear mechanism encountered in service.
- Abrasive wear environments: Cr-Co alloys with 60-70% Cr provide excellent hardness (HRC 40-50 in as-deposited condition) due to the formation of hard M₇C₃ carbides.
- Corrosive-wear environments: Ni-Cr-Mo alloys (such as Inconel 625-type powders) offer superior corrosion resistance combined with adequate hardness.
- High-temperature wear: Co-Cr-W alloys maintain hardness at elevated temperatures due to their high melting point and thermal stability.
The metallurgical microstructure of PTA deposits typically shows a columnar-to-equiaxed transition when properly controlled. Excessive heat input leads to excessive columnar grain growth, which can compromise mechanical properties and increase susceptibility to cracking.
Process Analysis and Engineering Practice
The manufacturing of guide strips by PTA cladding typically follows a multi-pass deposition strategy. The first pass establishes a sound metallurgical bond with the substrate, while subsequent passes build up the required overlay thickness. A typical deposition sequence involves:
- Substrate preparation: grinding to remove scale and contamination, followed by dimensional verification
- First pass: low current, high travel speed to minimize dilution
- Intermediate passes: optimized parameters for deposition rate
- Final pass: controlled parameters to achieve surface finish requirements
Common defects encountered in PTA cladding of guide strips include:
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Cracking | Excessive heat input, rapid cooling | Preheat, reduce current, use lower-carbon powders |
| Porosity | Inadequate shielding, powder moisture | Increase gas flow, dry powder thoroughly |
| Incomplete bonding | Contamination, insufficient current | Thorough cleaning, increase first-pass current |
| Uneven thickness | Travel speed variation | Use CNC-controlled deposition equipment |
In engineering practice, the dimensional accuracy of PTA-cladded guide strips can be maintained to ±0.05 mm per 100 mm when using computer-controlled deposition systems. This level of precision is essential for applications where the guide strip interfaces with moving components under tight tolerances.
Study Insights and Implications
This work highlights a critical principle in weld overlay engineering: the selection of cladding process must be driven by the functional requirements of the final component, not merely by cost considerations. PTA cladding, while more expensive than GMAW overlay, offers superior control over dilution, deposition thickness, and surface quality—attributes that are indispensable for precision guide strips. The military-affiliated nature of this research suggests that the guide strips in question served demanding applications where component reliability was paramount.
For modern engineers, this work serves as a reminder that process selection in cladding must consider the full spectrum of requirements: metallurgical bond quality, dimensional accuracy, surface integrity, and long-term service performance. The principles established in this 1997 publication remain valid today, with modern PTA systems offering even greater process control through real-time monitoring and closed-loop parameter adjustment.