Alumina Ceramic Rods are cylindrical parts used to locate, guide, space or insulate. The geometry is simple; the tolerance requirements rarely are.
Alumina rods are the general-purpose choice for insulating and locating duty. They carry the best balance of hardness, electrical insulation and cost, and where a rod runs in sliding contact against a mating bore, the 1500-1700 HV surface resists the wear that would quickly groove a steel pin.
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
| Diameter range | 1-60 mm |
| Length | up to 500 mm |
| Diameter tolerance | ±0.01 mm standard, ±0.002 mm ground |
| Straightness | 0.02 mm per 100 mm |
| Surface finish | Ra 0.4 µm as ground, Ra 0.05 µm polished |
| End configuration | chamfered, radiused, flat, stepped or threaded |
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
Rods are centreless ground from extruded or isostatically pressed stock, then lapped or polished to finish. Straightness is the hardest requirement on long parts, and we check it along the full length rather than at the two ends, because a bowed rod can measure in tolerance at both ends and still bind in service.
Where It Is Used
- Guide and locating pins in fixtures and assembly equipment
- Insulating shafts in furnaces, heaters and analytical instruments
- Plunger stems and valve push rods in metering pumps
- Wear rollers and thread guides in textile and wire machinery
- Spacers and standoffs in high-voltage and vacuum assemblies
Frequently Asked Questions
How straight can a ceramic rod be made?
Straightness is held to 0.02 mm per 100 mm as a working standard. We measure along the full length rather than at the two ends, because that is the condition that decides whether the rod will bind in a bore.
Can you put a shoulder, a thread or a cross hole on a ceramic rod?
Yes. Steps, shoulders and cross holes are ground into the blank. Sharp internal corners are avoided in the design because they concentrate stress in a brittle material, so a radius is always used instead.