| 摘要 |
PURPOSE: A pipe forming apparatus of the type using bending rolls is provided which includes a plurality of rolls arranged on one side of a sheet material, and a counter roll arranged at the other side of the sheet material. CONSTITUTION: In a pipe forming process using bending rolls, load applied to an upper roll (34) is reduced to suppress the deflection of the upper roll, thereby suppressing the creation of a large end gap at the longitudinal center of the pipe, thus enabling the production of high-strength, thick-walled, elongated pipes. This is achieved either by: (i) setting the roll spacing L between lower rolls to a value greater than the sum of the diameter Dwu of the upper roll (34) and the diameter Dwl of each of the lower rolls (32) and setting the amount S of tightening of the upper roll (34) with respect to the lower rolls 32 to a value greater than the radius Rwl of each of the plural rolls; (ii) effecting pipe forming work on sheet material (10) such that the spacing L of the lower rolls (32) satisfies the following condition, (Dp + Dwl) ) L is greater than or equal 0.85 (Dp + Dwl), where Dp represents the outside diameter of the product pipe and Dwl represents the diameter of one of the plural rolls; (iii)preparing the sheet material having leading and trailing bent end regions bent beforehand over a length not smaller than 1/5 of the entire circumference of the pipe to be produced, and effecting bending by the bending rolls such that the length of the regions bent by the bending rolls is less than 3/5 the entire circumference of the pipe. |
