Ceramic rings and seal rings serve as wearing seats, seal faces, spacers and bearing races. Most are simple in outline and extremely demanding on the two flat faces.
Alumina rings are the default for mechanical seal faces in clean water and general chemical service. The 1500-1700 HV surface is hard enough to run against carbon for years, and the material is unaffected by most process fluids.
Alumina is the default engineering ceramic. It combines high hardness (1500-1700 HV) with good electrical insulation and chemical inertness at a lower cost than most technical ceramics, and in 99.8% purity it holds strength to 1700°C while resisting most acids, alkalis and solvents.
It is not the toughest option. At 3-4 MPa·m½ fracture toughness, sharp impact or point loading will chip an edge, so chamfers and radii belong in the drawing from the start.
Specifications
| Outer diameter | 5-200 mm |
| Inner diameter | 3-180 mm |
| Height | 2-40 mm |
| Wall thickness | 1-20 mm |
| Face flatness | 0.005 mm |
| Parallelism | 0.01 mm |
| Seal face finish | Ra 0.05-0.1 µm lapped |
Alumina Properties
| Composition | Aluminium oxide, 96% / 99.5% / 99.8% |
| Density | 3.70-3.95 g/cm³ |
| Vickers hardness | 1500-1700 HV |
| Flexural strength | 300-400 MPa |
| Fracture toughness | 3-4 MPa·m½ |
| Max. service temperature | 1500°C (99.8%: 1700°C) |
| Thermal conductivity | 25-35 W/m·K |
| Thermal expansion (20-1000°C) | 8.0 ×10⁻⁶/K |
Machining and Tolerances
Rings are cut from pressed or extruded tube stock or pressed individually, then both faces are ground and lapped together so they stay parallel. Seal faces are lapped to Ra 0.05-0.1 µm, and we inspect flatness under monochromatic light rather than with a dial indicator.
Where It Is Used
- Mechanical seal faces and mating rings in pumps and mixers
- Wear rings and throttling discs in valve trim
- Insulating spacers in high-voltage stacks
- Bearing races for corrosive or high-temperature service
- Precision spacers and shims in optical and metrology assemblies
Frequently Asked Questions
How flat can a seal face be made?
Lapped seal faces are held to 0.005 mm flatness or better, verified under monochromatic light. Below about 0.3 light bands the result depends more on the lapping method than on the material.
Do you supply matched seal pairs?
Yes. A rotating ring and its stationary seat are lapped as a pair so the two faces are matched, which shortens run-in and reduces the risk of initial leakage.