Silicon Nitride Ceramic Rods are cylindrical parts used to locate, guide, space or insulate. The geometry is simple; the tolerance requirements rarely are.
Silicon nitride rods are used where a rod carries load at speed and temperature, such as welding pins and locating elements in hot fixtures. The 700-900 MPa strength and 6-8 MPa·m½ toughness tolerate the contact and thermal cycling that would break alumina or glass in the same duty.
Silicon nitride pairs high strength of 700-900 MPa with 6-8 MPa·m½ toughness at only 3.2 g/cm³. It survives the thermal shock that cracks most ceramics, resists molten non-ferrous metals, and its fine grain allows bearing-grade finishes.
It is among the more expensive options, and unlike SiC its thermal conductivity is a modest 25-35 W/m·K, so it is specified for mechanical reliability rather than heat spreading.
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 |
Silicon Nitride Properties
| Composition | Gas-pressure sintered silicon nitride |
| Density | 3.20-3.25 g/cm³ |
| Vickers hardness | 1500-1600 HV |
| Flexural strength | 700-900 MPa |
| Fracture toughness | 6-8 MPa·m½ |
| Max. service temperature | 1000°C (1200°C short term) |
| Thermal conductivity | 25-35 W/m·K |
| Thermal expansion (20-1000°C) | 3.2 ×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.