| 摘要 |
PURPOSE:To stably maintain the thickness of a lubricating film by providing grooves of a specific depth continuously on the surface of a mandrel bar body in the circumferential direction. CONSTITUTION:The mandrel bar 1 is rotated and while the bar is progressed at a specified velocity in an axial direction, the spiral or annular grooves 3 are formed by grinding wheels 2 on the surface of the mandrel bar 1 continuously in the circumferential direction or at prescribed intervals. The grinding wheels of proper grain size are used to make 10-30mu the depth of grooves. The number of the grinding wheels 2 may be properly increased or decreased by taking workability into consideration. The grooves which are recognized as the roughness of ruggedness in the axial direction of the mandrel bar and are recognized as the continuous recesses in the circumferential direction of the mandrel bar are provided. The holdability of the lubricating agent of the mandrel bar surface during rolling is enhanced in this way and the low coefft. of friction is stably attained. In addition, a seizure property is improved and the life of the mandrel bar extended. The improvement in product quality is attained as well. |
