Patent ID: 6385837
Filing Date: 2002-05-14
Classification: B23P,B25B,E21B,G05D,Y10T

Abstract:
A method of fixedly connecting together an externally threaded tube and an internally threaded tube by tight engagement of an externally threaded portion of said externally threaded tube and an internally threaded portion of said internally threaded tube, comprising: performing a wrenching operation in which said externally and internally threaded tubes are rotated relative to each other with said externally and internally threaded portions engaging each other while an axial force is applied so as to act between said tubes;detecting a wrenching torque being applied to rotate said tubes relative to each other; obtaining a physical quantity relating to a coefficient of friction between said tubes, on the basis of the detected wrenching torque and said axial force; determining a terminating condition for terminating said wrenching operation, on the basis of the obtained physical quantity; and terminating said wrenching operation when said terminating condition has been satisfied, wherein said axial force is applied to said externally and internally threaded tubes for forcing said tubes toward each other, and wherein said step of detecting a wrenching torque comprises detecting at least one of an initial value of said wrenching torque in an initial phase of said wrenching operation in which shoulder surfaces of said externally and internally threaded tubes are not in contact with each other while thread surfaces of said tubes are in contact with each other, and an intermediate value of said wrenching torque in an intermediate phase of said wrenching operation in which said shoulder surfaces are in substantial contact with each other while said thread surfaces of said tubes are not in substantial contact with each other, so that said physical quantity is obtained on the basis of said at least one of said initial value and said intermediate value.