Ceramic sleeves and bushings take the wear between a shaft and its housing. They are specified where a bronze or polymer bearing would wear out, seize or contaminate the product.
Zirconia sleeves are used where a shaft deflects or runs misaligned, because the material tolerates the edge loading that would chip a brittle bore. They are also chosen for low friction against stainless steel in food and medical equipment.
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
| Inner diameter | 5-120 mm |
| Outer diameter | 8-150 mm |
| Length | up to 200 mm |
| Bore cylindricity | 0.005 mm |
| Bore finish | Ra 0.4 µm, honed Ra 0.2 µm |
| Outer diameter tolerance | ±0.01 mm |
| Fit | clearance matched to shaft material and duty |
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
Sleeves are ground on the outside and honed or internally ground to bore. We size the bore to the shaft you run rather than to a nominal dimension, because ceramic and steel expand at different rates and clearance at room temperature is not clearance at working temperature.
Where It Is Used
- Pump shaft sleeves and wear bushes in chemical and water service
- Insulating bushes through furnace walls and heated platens
- Guide bushes in food, pharmaceutical and textile machinery
- Bushings for high-temperature conveyors and kiln cars
- Electrical isolation sleeves in motor and generator assemblies
Frequently Asked Questions
How do you size the bore for a metal shaft?
We work from your shaft diameter and maximum working temperature, then calculate the clearance from the expansion coefficients of the two materials. A bore that fits at 20°C can grip at 300°C if it is sized purely nominally.
Can the sleeve be retained without adhesive?
Press fitting works where the housing is steel and the interference is modest. Where the housing is also ceramic or the duty involves thermal cycling, we prefer mechanical retainment or a compliant interlayer so differential expansion cannot crack the sleeve.