Process for locating the ideal screwing position of bolts of large dimensions

Process for locating the ideal screwing position of bolts of large dimensions, especially for fastening the cover of a vessel having tapped orifices, including the steps, subsequent to fastenign the bolt (10) to a screwing/unscrewing device (20), of

• (a) making a check to ascertain that the bolt (10) is vertical and is aligned with the axis of the tapped orifice (5);
• (b) lowering the bolt (10) under control, until it engages in a tapping recess of the orifice (5);
• (c) rotating the bolt (10) in the direction opposite to screwing;
• (d) detecting the point of engagement of the threads (11) of the bolt (10) in the threads of the tapped orifice (5);
• (e) arresting the rotation of the bolt (10) in the opposite direction and controlling the start of screwing by rotating the bolt in the normal direction by a few turns, if possible, and at a low speed;
• (f) arresting the rotation of the bolt (10) if, during this screwing, a first seizure of the bolt (10) in the tapped orifice (5), when the screwing torque becomes greater than a specific disengaging torque, is detected;
• (g) locating the ideal screwing position of the bolt (10) according to a circular or square spiral path, as soon as said first seizure is detected;
• (h) detecting said ideal screwing position at the moment when the screwing torque again becomes less than the disengaging torque, and recording the coordinates of a new ideal screwing center;
• (i) continuing screwing at a reduced speed for a few turns, and, if possible, increasing the screwing speed;
• (j) detecting each new seizure during this screwing and af ter each seizure locating the ideal screwing position by means of a suitable path from the center corresponding to the preceding stop previously recorded, the paths of the succeeding location of the ideal screwing positions being either flattened or rectangular spirals, if there is a preferred direction of seizure, or circular or square spirals if there is not;
• (k) resuming screwing after each detection of the new ideal screwing center;
• and
• (l) continuing the screwing of the bolt (10) at high speed until the end of screwing is detected.