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.
Alumina sleeves are the standard wear bush for pumps handling water, chemicals and mild slurries. They outlast bronze by a wide margin in abrasive service and, unlike metal, they will not corrode or gall onto the shaft.
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
| 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 |
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
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.