PURPOSE: To prevent the thinning of the coating layer at the welded bead sections on the pipe surface by adjusting the rotational speed of the intended pipe in winding a half-melted plastic strip around the pipe, having welded beads on its longitudinal direction, by the T die method.
CONSTITUTION: A steel pipe having welded beads 3 on the outer surface is on its longitudinal direction coated is coated with a half-melted plastic strip 6 by spirally winding thereof on the outer surface of the pipe being transferred turning in the axial way. In this process, the welded beads 3 are detected with detectors 7 and 7' so that the rotational speed of the pipe is temporarily decelerated while they are passing the section to be coated with the strip. In this manner, the thinning of the coating layer at the welded beads 3 after the coating can be avoided.
OKADA HIROSHI
KAYA KAZUAKI
| JPS5236782A | 1977-03-22 |