The surface failure and wear of graphite seals

Exfoliated graphite rings are now the most common form of die-formed seal for valve stems, and other stuffing box applications. However, there is very little fundamental knowledge of what determines their friction and wear. In earlier papers, it was shown that the mechanical properties of this material could be represented approximately by a geotechnical model designed for soils or rocks. In this paper, a simple test is described for measuring the friction and wear of seals against steel sliders in a controlled atmosphere. The results, which are rather surprising, can be explained by applying the geotechnical model referred to above, to the case of sliding.