Ceramic tubes protect, isolate and carry. They serve as thermocouple sheaths, furnace muffles, insulating bushes and fluid paths where metal would corrode, creep or conduct.
Mullite tubes serve in kilns and in hot gas sampling to 1400°C, where thermal cycling is constant and load is low. They cost less than alumina at these temperatures and their 5 ×10⁻⁶/K expansion keeps them stable through repeated cycles.
Mullite bridges alumina and fused silica. It offers good creep resistance and thermal-shock behaviour to 1400°C with expansion near 5 ×10⁻⁶/K, making it a standard for kiln furniture, thermocouple sheaths and hot-gas components under constant cycling.
Room-temperature strength of 150-200 MPa is well below alumina, so it is chosen for high-temperature stability rather than load-bearing or wear duty.
Specifications
| Outer diameter | 3-150 mm |
| Inner diameter | 1-120 mm |
| Length | up to 600 mm |
| Minimum wall thickness | 0.5 mm |
| Concentricity | 0.02 mm |
| Bore finish | Ra 0.4 µm, honed Ra 0.2 µm |
| Ends | square cut, chamfered, flanged or closed one end |
Mullite Properties
| Composition | Mullite (3Al₂O₃·2SiO₂) |
| Density | 2.80 g/cm³ |
| Vickers hardness | 1000-1200 HV |
| Flexural strength | 150-200 MPa |
| Fracture toughness | 2-3 MPa·m½ |
| Max. service temperature | 1400°C |
| Thermal conductivity | 3-4 W/m·K |
| Thermal expansion (20-1000°C) | 5.0 ×10⁻⁶/K |
Machining and Tolerances
Tubes are extruded, isostatically pressed or slip cast depending on size and quantity, then ground on the outside and honed internally. Long thin-wall tubes are the most distortion-prone parts we make, so we rough grind, allow the part to relax, then finish grind.
Where It Is Used
- Thermocouple protection sheaths and furnace muffles
- Insulating bushes through heated panels and vacuum chambers
- Fluid and slurry transport in corrosive or abrasive service
- Lamp, laser and UV equipment bodies
- High-voltage insulators and standoffs
Frequently Asked Questions
What is the thinnest wall you can produce?
0.5 mm is the practical floor for most materials and lengths. Below that, yield drops sharply during firing and grinding, so we review the drawing and usually suggest thickening the wall or shortening the tube.
Can you supply closed-end tubes?
Yes. Closed one end, hemispherical closed ends and reduced-tip ends for thermocouple sheaths are all produced, either formed during shaping or ground after firing.