CLADDING TECHNOLOGY SHANXI CO., LTDManufacturing of Overlay Alloy Sealing Rings for Mechanical Seals
Literature Overview
This technical paper by Wang Min and Zeng Xingshao (1995) from Zigong Mechanical Seal Factory in Sichuan Province describes the manufacturing process for overlay alloy sealing rings used in mechanical seals for fluid machinery. Published in the journal Fluid Machinery, this work addresses the critical role of overlay welding in producing high-performance sealing rings that combine the toughness of a steel substrate with the wear resistance and corrosion resistance of an overlay alloy layer.
Core Technical Points
Mechanical seals are critical components in pumps, compressors, and other fluid handling equipment. The sealing ring (or seal face) experiences extreme operating conditions including high pressure, temperature, and chemical exposure. The overlay alloy layer on the sealing ring must provide:
- Excellent wear resistance under sliding contact
- Corrosion resistance against the sealed fluid
- Thermal stability at operating temperatures
- Dimensional stability during operation
- Compatibility with the mating seal face material
Common Overlay Alloy Compositions for Seal Faces
| Alloy Type | Composition | Hardness (HRC) | Application |
|---|---|---|---|
| Stellite 6 | Co-Cr-W | 40-45 | General service |
| Stellite 21 | Co-Cr-W (higher Cr) | 45-50 | High-temperature |
| Tungsten Carbide | WC-Co | 85-90 HV | Abrasive media |
| Silicon Carbide | SiC | 90-95 HV | Chemical service |
| Carbon-Carbon | C-C composite | 80-100 HV | High-temperature |
| Tungsten Alloy | W-Re | 300-400 HV | Nuclear service |
Manufacturing Process Steps
| Step | Operation | Key Parameters |
|---|---|---|
| 1 | Substrate preparation | Machining, cleaning, degreasing |
| 2 | Preheating | 200-400°C depending on alloy |
| 3 | Overlay welding | GTAW or plasma arc |
| 4 | Heat treatment | Solution + aging |
| 5 | Machining | Precision grinding |
| 6 | Surface finishing | Lapping or polishing |
| 7 | Inspection | Dimensional, hardness, NDT |
Overlay Welding Process Selection
For mechanical seal ring manufacturing, the selection of overlay process depends on the ring dimensions and required overlay thickness:
| Process | Overlay Thickness | Ring Diameter Range | Surface Quality |
|---|---|---|---|
| GTAW | 1-5 mm | 10-100 mm | Excellent |
| Plasma Arc | 1-3 mm | 5-50 mm | Very Good |
| Laser Cladding | 0.5-2 mm | Any | Excellent |
| Electroslag | 3-10 mm | 50-500 mm | Good |
| Powder Metallurgy | 1-5 mm | Any | Very Good |
Quality Control and Inspection
The quality of overlay alloy sealing rings is critical for the reliability of mechanical seals. Key quality assurance measures include:
- Bond Strength Testing: The overlay layer must have adequate bond strength to the substrate to prevent delamination during operation. Typical minimum bond strength requirements are 200-300 MPa.
- Hardness Verification: The overlay layer hardness must meet specifications, typically verified by micro-Vickers or Rockwell C testing. Hardness uniformity across the sealing surface is also important.
- Dimensional Accuracy: After overlay welding, the sealing surface must be machined to precise dimensional tolerances, typically within ±0.005 mm for flatness and concentricity.
- Non-Destructive Testing: Magnetic particle testing (MT) or liquid penetrant testing (PT) is used to detect surface cracks in the overlay layer. Ultrasonic testing may be used to verify bond integrity.
- Metallographic Examination: Cross-sectional examination verifies the absence of cracks, porosity, and incomplete melting at the overlay-substrate interface.
Engineering Practice Considerations
The manufacturing of overlay alloy sealing rings requires careful consideration of several factors:
- Thermal Distortion: The overlay welding process introduces thermal distortion that must be accounted for in the machining allowance. Preheating and controlled cooling rates help minimize distortion.
- Overlay Uniformity: The overlay thickness must be uniform across the sealing surface to ensure consistent contact pressure and wear rate. This requires skilled welder technique or automated processes.
- Residual Stress: Residual stresses from overlay welding can affect the dimensional stability of the seal ring during operation. Stress relief annealing is often performed after overlay welding and before final machining.
- Material Compatibility: The overlay alloy must be compatible with both the substrate material and the mating seal face material to prevent galvanic corrosion and ensure proper sealing performance.
Study Insights and Implications
This work demonstrates the critical role of overlay welding technology in the manufacturing of high-performance mechanical seals. The combination of a tough steel substrate with a hard, corrosion-resistant overlay layer provides an economical solution that would otherwise require expensive solid-state alloy materials. For engineers involved in fluid machinery design and maintenance, understanding the manufacturing capabilities and limitations of overlay alloy seal rings is essential for proper seal selection and specification. The continued development of overlay welding processes, particularly plasma arc and laser cladding, has expanded the range of achievable overlay compositions and surface qualities, enabling the use of exotic materials in seal face applications.