A solid performer

Molybdenum-disulfide lubricant helps stop galling of stainless-steel tube fittings exposed to hostile environments. Half-section diagrams of a Parker Hannifin CPI singleferrule and an A-LOK two-ferrule compression tube fitting. Turning the nut drives the ferrule(s) into contact with the body seat and tubing surface. The ferrule and tubing do not rotate with the nut, but instead slide axially. This action is critical to forming a leak-free tubing connection during the first makeup and subsequent remakes. Sliding takes place at high pressure between the back of the ferrule and nut flange, and in the threads. These locations need lubricants with exceptional lubrication and anti-galling properties, such as molybdenum disulfide. Electroplated silver with wax lubricant is another option. ) is a solid that has exceptional lubricating properties under conditions of high temperature and pressure, vacuum, and corrosive environments. There are several ways to apply MoS to sliding surfaces, from vacuum sputtering to sprinkling it on as a loose powder. The most common technique mixes the powder with a binder and carrier to form a bonded coating. Molybdenum disulfide owes its exceptional lubricity to a crystal structure of weakly bonded lamellae. These lamellae shear under low force to provide lubrication with an extremely low (about 0.025) coefficient of friction. The lamellae also strongly resist forces perpendicular to them and therefore don't squeeze out from between mating surfaces under extreme pressure, as do liquid lubricants. This combination of properties builds a boundary layer that effectively prevents pairs of lubricated surfaces from touching. Objects still touch along small contact regions or asperities, however. These contact regions have considerably less area than that of the bulk surface, typically about 0.5 to 0.001% for a machined metal surface. Consequently, the stresses at contact points are significantly higher than those calculated for the bulk surface area and may be sufficient