FORM 02
Ceramic Crucibles
Shallow and tall crucibles for melting, firing and holding aggressive media at temperature.
View ceramic cruciblesDUTY 04
Ceramic parts for furnaces, kilns and molten metal
Above a certain temperature the question stops being "which metal" and becomes "which ceramic, and what happens when it cools".
Every high-temperature design fails in one of two ways: the part creeps and sags under its own load at temperature, or it survives the heat and cracks on the way down. Metals handle the first badly and the second worse. Ceramics invert the trade-off — they hold shape far higher, but they have no ductility to absorb a thermal gradient.
That is why the useful specification work is about thermal history rather than peak temperature. How fast the part heats, how unevenly it cools, whether it is supported at temperature, and what it touches — a setter, a refractory, a molten bath — decide the grade more than the maximum number on the data sheet.
Why ceramic
What changes when the part is ceramic
No creep at temperature
A ceramic support holds its section at temperatures where metal would sag and take a permanent set.
Chemically inert against the load
Alumina and silicon carbide resist reaction with most molten metals and glasses, so the part does not become part of the melt.
Thermal shock is a design choice
Silicon carbide and silicon nitride tolerate rapid gradients far better than alumina, which is why cyclic furnaces use them.
Material fit
Which system suits this duty
Ratings follow the comparison published for the four systems. The grade is confirmed against the duty at quotation.
| Material | Choose it when |
|---|---|
| Silicon carbide | Kiln furniture, beams and parts that see fast cycles and heavy load at temperature. |
| Silicon nitride | Repeated thermal cycling with mechanical load — supports, rollers, fixtures. |
| Alumina | Crucibles, tubes and insulators in steady furnaces, and the widest range of shapes. |
| Zirconia | Chemical resistance to a specific melt, and where toughness matters more than peak temperature. |
Part forms
Forms supplied for this duty
Each form page carries the dimensional call-outs and ordering route for that shape.
FORM 01
Ceramic Tubes
Straight and stepped tubes for high-temperature process lines, sensor protection and electrical isolation.
View ceramic tubesFORM 03
Ceramic Rods
Solid rods and ground pins for structural, insulating and wear duty in tight assemblies.
View ceramic rodsFORM 04
Ceramic Plates
Flat plates and substrates where flatness, insulation and wear resistance decide the part.
View ceramic platesFORM 07
Ceramic Insulators
Insulating bodies, spacers and supports for equipment that runs hot and live at the same time.
View ceramic insulatorsFORM 12
Ceramic Structural Parts
Blocks, brackets and spacers that locate, support or isolate inside equipment.
View ceramic structural partsOn the drawing
What this duty needs pinned down
- The full thermal cycle: heating rate, hold temperature, cooling rate, and how often per week.
- What the part rests on and what rests on it, since support geometry drives sag and cracking.
- The atmosphere — air, inert, vacuum, reducing — and any vapour that will condense on the part.
- What the part touches: the melt composition, the refractory, or the charge, and whether wetting is acceptable.
Inspection
What gets checked
- Wall thickness and bore on crucibles, checked for the taper the drawing calls for.
- Straightness on tubes and rods measured over the full length, because sag shows up there first.
- Surface condition on the load-bearing face — a repair that looks cosmetic can seed a crack under cycling.
Inspection points are agreed at quotation and recorded, so the first article and the tenth are judged the same way.
Questions
Asked about this duty
Which ceramic survives thermal shock best?
Silicon carbide and silicon nitride tolerate rapid gradients much better than alumina, which is the usual reason a cyclic furnace moves away from alumina furniture. Zirconia is tough but its shock resistance is only moderate, so it is chosen for chemical duty rather than fast cycling.
Can a crucible be used for molten aluminium?
Alumina and silicon carbide are both used in aluminium contact, but wetting and dross build-up differ between grades, and the flux chemistry matters as much as the metal. The melt and the flux are normally stated together when the grade is quoted.
Why do parts crack on cool-down rather than at temperature?
Because that is when the gradient is steepest and the part is least able to accommodate it. Support geometry, wall uniformity and the cooling rate usually matter more than the maximum service temperature claimed for the material.
Continue
Other pages in this catalogue
The same catalogue, filed by material and by shape.