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.
Zirconia rings are chosen for seals and bearings exposed to impact or cavitation. The 900-1200 MPa strength tolerates the pressure spikes and vibration that would crack a harder but more brittle ring.
Yttria-stabilised zirconia is the toughest of the engineering oxides, with 8-10 MPa·m½ fracture toughness and flexural strength to 1200 MPa. It absorbs the impact and side loads that would crack alumina, and it carries the lowest thermal conductivity of the structural ceramics here.
Two limits apply. Continuous service above roughly 800-1000°C destabilises the metastable tetragonal phase, and moisture between 200 and 300°C can trigger low-temperature degradation, so stabiliser grade is matched to the duty.
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 |
Zirconia Properties
| Composition | Yttria-stabilised zirconia (Y-TZP) |
| Density | 6.00-6.05 g/cm³ |
| Vickers hardness | 1200-1350 HV |
| Flexural strength | 900-1200 MPa |
| Fracture toughness | 8-10 MPa·m½ |
| Max. service temperature | 800-1000°C |
| Thermal conductivity | 2-3 W/m·K |
| Thermal expansion (20-1000°C) | 10.0 ×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.
