Silicon carbide (sic)
SILICON CARBIDE (SiC) S052
The most common mechanical seal face material being used at this writing.
Reaction Bonded Silicon Carbide
- Provided the advantages of lower porosity, higher elastic modulus (stiffness) and improved thermal conductivity and tribological behavior.
- This material required extensive grinding and the free silicon in the structure was susceptible to highly caustic or acidic environments.
- This family of materials quickly gained acceptance in a variety of applications as contact pressures could be increased with less face deflection than that of metallic materials.
- A normal application was to run a high duty, hard, mechanical carbon-graphite against the reaction bonded silicon carbide.
Sintered Silicon Carbide
- Because of its chemical resistance in virtually all corrosive environments sintered (aka, self-sintered, direct sintered or pressure less sintered) silicon carbide seaal faces dominated the process industry.
- It could be formed into specific shapes and then sintered to, or nearly to, the finished size, limiting the amount of expensive grinding for the finished item.
- This reduction in production cost, coupled with the homogeneous nature of the material, enabled its use in highly corrosive environments and higher volume applications.
- Figure 1. Graphite-loaded sintered SiC structure
Graphite-Loaded Silicon Carbide
- The marriage of silicon carbide and graphite was a normal progression. Graphite initially was added to reaction-bonded silicon carbide and quickly exhibited an increase in the performance capabilities of hard face combinations.
- Strength is reduced somewhat and the ability to handle abrasives is not as good as that of pure silicon carbide. tribological behavior is improved significantly.
- Graphite-loaded sintered silicon carbide has the benefits of sintered silicon carbide while incorporating a second, abradable phase that provides pockets or reservoirs for the “storage” of fluid.
Because of the uniformity of these composites, their characteristic performance will not change during operation,
Unlike previous ceramics, these silicon carbides have excellent thermal conductivity characteristics, but like all ceramics they are very hard and can fracture easily in use, if molded in thin cross sections.
If you want to run a SiC face against another SiC face in your mechanical seal applicaion, you will probably be better of running two seperate grades against each other to avoid galling or damage between the lapped faces.
- On February 17, 2018