Boron Nitride Ceramic Rods are cylindrical parts used to locate, guide, space or insulate. The geometry is simple; the tolerance requirements rarely are.
Boron nitride rods serve as release and insulating elements rather than as load-bearing parts. They are chosen for molten metal contact, where almost nothing wets the surface, and for vacuum furnace standoffs that need to be machined to fit after firing.
Hot-pressed boron nitride is the softest ceramic here at roughly Mohs 2, and the one that can be machined with ordinary carbide tooling. It is chemically inert to molten metals that barely wet it, stays stable to 1000°C in air and 2000°C in inert atmospheres, and remains an electrical insulator.
Its hot-pressed form carries low flexural strength of 60-100 MPa and it is slowly attacked by moisture, so it is used where release, insulation or vacuum compatibility matter more than load carrying.
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 |
Boron Nitride Properties
| Composition | Hot-pressed hexagonal boron nitride |
| Density | 2.00-2.20 g/cm³ |
| Vickers hardness | 200-300 HV (Mohs approx. 2) |
| Flexural strength | 60-100 MPa |
| Fracture toughness | 2-3 MPa·m½ |
| Max. service temperature | 1000°C in air, 2000°C inert |
| Thermal conductivity | 30-60 W/m·K (in-plane) |
| Thermal expansion (20-1000°C) | 1-3 ×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.