Strengthened graphite-metal threaded connection

In a threaded connection between a graphite shaft with a female thread and a metal shaft having a male thread, adapted so that the joint between said shafts is tightened upon the driving of said metal shaft, said graphite shaft having an end surface a portion of which comes into contact with a seating surface of a flange portion of said metal shaft upon the fastening of the shafts through said threaded connection, the improvement comprising a coating on said portion of the end surface of the graphite shaft that is positioned to contact said seating surface of the metal shaft flange, said coating comprising a powdered material with individual particles that do not melt, disintegrate or break up under the conditions of operation, together with a liquid binder phase capable of holding the particles together and bonding them to said graphite surface only, with limited absorption of the liquid binder phase into the graphite porosity, said coating serving to substantially increase the friction between the graphite surface to which said coating is bonded and the metal contacting surface upon the fastening of the shafts through said threaded connection as compared with the friction between the comparable uncoated graphite and metal contacting surface,

• whereby the increased friction between the contacting surfaces upon completion of the connection between said coated graphite shaft and said metal shaft results in an increase in torque strength of the threaded connection such as to enable said threaded connection to have a greatly increased ability to transmit driving torque from the metal shaft to the graphite shaft.

A process for improving the threaded connection between a graphite shaft with a female thread and a metal shaft having a male thread driven so as to tighten the joint between the shafts, wherein said graphite shaft has an end surface, a portion of which comes into contact with a seating surface of a flange portion of said metal shaft upon the fastening of the shafts through said threaded connection, said improvement comprising applying a coating on said portion of the end surface of the graphite shaft that is positioned to contact said seating surface of the metal shaft flange, said coating comprising a powdered material with individual particles that do not melt, disintegrate, or break-up under the conditions of operation, together with a liquid binder phase capable of holding the particles together and bonding them to said graphite surface, with limited absorption of the liquid binder phase into the graphite porosity, said coating serving to substantially increase the friction between the graphite surface to which said coating is bonded and the metal contacting surface upon fastening of said coated graphite shaft with the metal shaft as compared with the friction between the comparable uncoated graphite and metal contacting surfaces,

• whereby the increased friction between the contacting surfaces upon completion of the connection between said coated graphite shaft and said metal shaft results in an increase in the torque strength of the threaded connection such as to enable said threaded connection to have a greatly increased ability to transmit driving torque from the metal shaft to the graphite shaft.