Method and apparatus for fixedly connecting threaded tubes, and recording medium storing control program for practicing or controlling those method and apparatus

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 externally and internally threaded portions are tapered threaded portions, and said wrenching torque is detected while a radial tightening force is not generated between said tapered threaded portions.

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 wrenching torque is detected in an initial phase of said wrenching operation in which leading flanks of said externally threaded portion of said externally threaded tube contact leading flanks of said internally threaded portion of said internally threaded tube.