In most cases carbon graphite vs silicon carbide is the preferred seal face material combination. However, in some applications, carbon graphite is not suitable as a face material, so a combination of hard materials such as silicon carbide or tungsten carbide is required instead. This is usually determined by the characteristics of the sealed product or to meet the requirements of stringent contamination standards. Reasons to select two hard faces include.
- The sealed product includes abrasives and will wear the carbon face rapidly, e.g. gypsum slurry, sea water, crude oil, etc.
- The sealed product has a high viscosity and will tend to bond faces together, e.g. bitumen.
- On applications where no contamination from carbon wear debris is acceptable, e.g. pharmaceutical, food, make up, etc.
- On some de-ionised water applications the carbon can ‘wear’ rapidly.
- The duty temperature is higher than that tolerated by carbon graphite.
- When the carbon face will be attacked by the product e.g. acids.