What are the forming techniques for Reaction Bonded Silicon Nitride?
What are the forming techniques for Reaction Bonded Silicon Nitride?
A number of factors are considered before choosing the most suitable forming technique. These include complexity of geometry, overall size of the component, quantity required, surface finish and component tolerance. Table 1 below lists some of the typical factors considered with determining the most suitable forming techniques. Note that, although prototype parts cannot be made via the ‘Injection Moulding’ and ‘Die Pressing’ route, prototypes can be made by the ‘Green Machining’ route.
Table 1: - Comparison of forming techniques for Reaction Bonded Silicon Nitride
|
| Green Machining | Injection Moulding | Die Pressing | Freeze Casting |
| Part Complexity | High | High | Medium | Low |
| Tolerance | High | Medium | Medium | Low |
| Suitable Volumes | Low - Medium | Medium – High | Medium – High | Low - Medium |
| Prototyping | Yes | No | No | Yes |
| Tooling Cost | Very Low | Very High | High | Medium |
| Part Cost | Higher | Low | Low | Medium |
Note: cross-section thickness should be no greater than 20mm for green machining, pressing and freeze casting and 6mm for injection moulding.
Hot Pressed Silicon Nitride (HPSN)
Hot Pressed Silicon Nitride (HPSN) is a fully dense Silicon Nitride (i.e. 0% porosity), which is made via a more classical ceramic manufacturing route. Hot Pressed Silicon Nitride is a mixture of fine grain Si3N4 and sintering additives, but is formed under high pressure and temperature in a graphite mould to produce a ‘Hot Pressed Billet’. This is then ground to the desired geometry and surface finish. HPSN exhibits the highest mechanical properties of the Silicon Nitride family due to reduction of residual porosity, removed during the Hot Pressing stage.
The choice of material for the specific application is dependant on cost and properties of components required. RBSN is the lowest cost material of the Silicon Nitride family, followed by HPSN. HSPN gives the best mechanical properties, compared to RBSN (follow links below to material datasheets).
Typical Applications of Silicon Nitride:
- Molten metal handling (including crucible / wear plates)
- Brazing jigs
- Induction heating coil supports
- Reinforcement phase for composites
- Welding jigs, fixtures and weld location pins
- Dental heat treatment supports
- TIG / Plasma welding nozzles
- Thermocouple sheaths
- Bearings and rollers
- Glow plugs
- Cutting tools
Download the Silicon Nitride data sheets
