Abstract: Provided is a method for producing a double-wall tube with braided wires at its interface in which the braided wires are interposed between an outer-wall and inner-wall blank tubes and then a drawing process is applied so as for the braided wires to be brought into close contact with the inner surface of the outer-wall tube and the outer surface of the inner-wall tube, the method comprising: polishing the inner surface of the outer-wall blank tube and the outer surface of the inner-wall blank tube so that a surface roughness thereof satisfies Ra<1.0 ?m, followed by interposing the braided wires between the outer-wall and inner-wall blank tubes; performing a sinking drawing process so that the difference of the outer diameter of the resulting double-wall tube relative to a die bore diameter is 0.1 mm to 0.3 mm; and subsequently performing heat treatment. The double-wall tube produced is suitable as a heat-transfer tube.

Abstract: Provided is a method for producing a double-wall tube with braided wires at its interface in which the braided wires are interposed between an outer-wall and inner-wall blank tubes and then a drawing process is applied so as for the braided wires to be brought into close contact with the inner surface of the outer-wall tube and the outer surface of the inner-wall tube, the method comprising: polishing the inner surface of the outer-wall blank tube and the outer surface of the inner-wall blank tube so that a surface roughness thereof satisfies Ra<1.0 ?m, followed by interposing the braided wires between the outer-wall and inner-wall blank tubes; performing a sinking drawing process so that the difference of the outer diameter of the resulting double-wall tube relative to a die bore diameter is 0.1 mm to 0.3 mm; and subsequently performing heat treatment. The double-wall tube produced is suitable as a heat-transfer tube.

Abstract: A reducing mill includes a plurality of stands disposed along a rolling direction line. The stands each include n rolls (n?3) disposed around the rolling direction line, the n rolls are shifted by 180°/n around the rolling direction line from n rolls included in a preceding stand. The n rolls included in each of the stands excluding the last stand each have a groove having an arch shape. The bottom of the groove has a circular arc shape around the rolling direction line having a first radius in cross section. The distance between the surface of a roll flange portion between the bottom and the edge of the groove and the rolling direction line is longer than the first radius. The distance between the edge of the groove and the rolling direction line is longer than the first radius in the groove of a roll included in the preceding stand.

Abstract: The plug is for expanding the inside diameter of the end portion of a metal pipe. Its cross section is a circle, and includes a taper portion and a parallel portion connected to the tail end of the taper portion. The diameter of the taper portion gradually increases from the head end of the taper portion to the tail end of the taper portion where the diameter is D1. The axial distance LR from the point where the diameter D2=D1×0.99 to the tail end where the diameter is D1 satisfies the Expression 22?LR/((D1?D2)/2)?115. The taper angle on the surface where the diameter is D2 is larger than or equal to the taper angle on the tail surface of the taper portion following the point where the diameter is D2. The diameter of the parallel portion is D1.

Abstract: A plug 1 includes a first columnar portion 20, a tapered portion 30, and a second columnar portion 40. The first columnar portion 20 has an outside diameter D1. The second columnar portion 40 has an outside diameter D2 which is larger than the outside diameter D1. The tapered portion 30 is formed between the first columnar portion 20 and the second columnar portion 40. The tapered portion 30 has a tapered surface 31 provided with an outside diameter which is gradually increased from the first columnar portion 20 to the second columnar portion 40, and an axial direction length L. The outside diameters D1 and D2, and the axial direction length L meet the following expressions (1) to (4): 0.25???2.00??(1), 0.06?L/D2?0.8??(2), L/D2?0.3×?+0.575??(3), and L/D2?0.1×???(4) where ?=(D2?D1)/D1×100. Therefore, the cold drawing plug according to the present invention can reduce the tensile residual stress on the outer surface of a metal pipe after the cold drawing.

Abstract: An apparatus for sizing a pipe end comprising: a plug 3 for sizing the pipe end; a chuck 2 for clamping the pipe; and shifting means for shifting the position of the plug 3 and/the chuck 2, which are placed successively from the end of the pipe 2, and the plug 3 has a circular cross section, and is constituted by a taper portion 31 and a diameter equivalent portion 32 continuously formed from the tip of the plug in succession. The outer diameter of the taper portion 31 is gradually expanding from the tip toward the rear end while satisfying the following formulas (1) and (2). The chuck 2 is capable of changing clamping position of the pipe 1. This apparatus makes it possible to size the inner diameter of a pipe end with superior dimensional precision 22?LR/(D1×0.01/2)?115 ??(1) R2?R1 ??(2).

Abstract: The present invention provides a mechanical pipe-end expander comprising a cone and a die having tapered wedge bodies whose outer radius is larger towards a flangeless end direction from a flange end, wherein a pipe-end zone is expanded by a wedge effect of the die, which results from a procedure that the cone and the die are inserted together into the pipe-end zone to be expanded, and that then only the cone is axially drawn outwards leaving the die within the pipe-end zone. A seamless steel pipe with an expanded pipe-end zone is manufactured by applying a mechanical pipe-end expander comprising a die having tapered wedge bodies whose outer radius is larger towards a flangeless end direction from a flange end. The resulting seamless steel pipe has satisfactory pipe-end dimensional accuracy, and exhibits characteristics with excellent field welding workability.

Abstract: A plug 1 includes a first columnar portion 20, a tapered portion 30, and a second columnar portion 40. The first columnar portion 20 has an outside diameter D1. The second columnar portion 40 has an outside diameter D2 which is larger than the outside diameter D1. The tapered portion 30 is formed between the first columnar portion 20 and the second columnar portion 40. The tapered portion 30 has a tapered surface 31 provided with an outside diameter which is gradually increased from the first columnar portion 20 to the second columnar portion 40, and an axial direction length L. The outside diameters D1 and D2, and the axial direction length L meet the following expressions (1) to (4): 0.25???2.00??(1), 0.06?L/D2?0.8??(2), L/D2?0.3×?+0.575??(3), and L/D2?0.1×???(4) where ?=(D2?D1)/D1×100. Therefore, the cold drawing plug according to the present invention can reduce the tensile residual stress on the outer surface of a metal pipe after the cold drawing.

Abstract: An apparatus for sizing a pipe end comprising: a plug 3 for sizing the pipe end; a chuck 2 for clamping the pipe; and shifting means for shifting the position of the plug 3 and/the chuck 2, which are placed successively from the end of the pipe 2, and the plug 3 has a circular cross section, and is constituted by a taper portion 31 and a diameter equivalent portion 32 continuously formed from the tip of the plug in succession. The outer diameter of the taper portion 31 is gradually expanding from the tip toward the rear end while satisfying the following formulas (1) and (2). The chuck 2 is capable of changing clamping position of the pipe 1. This apparatus makes it possible to size the inner diameter of a pipe end with superior dimensional precision. 22?LR/(D1×0.

Abstract: The present invention provides a mechanical pipe-end expander comprising a cone and a die having tapered wedge bodies whose outer radius is larger towards a flangeless end direction from a flange end, wherein a pipe-end zone is expanded by a wedge effect of the die, which results from a procedure that the cone and the die are inserted together into the pipe-end zone to be expanded, and that then only the cone is axially drawn outwards leaving the die within the pipe-end zone. A seamless steel pipe with an expanded pipe-end zone is manufactured by applying a mechanical pipe-end expander comprising a die having tapered wedge bodies whose outer radius is larger towards a flangeless end direction from a flange end. The resulting seamless steel pipe has satisfactory pipe-end dimensional accuracy, and exhibits characteristics with excellent field welding workability.

Abstract: A reducing mill according to the invention includes a plurality of stands disposed along a rolling direction line, in which a tube is rolled through the plurality of stands along the rolling direction line. The stands each include n rolls (n?3) disposed around the rolling direction line, and the n rolls are disposed shifted by 180°/n around the rolling direction line from n rolls included in a preceding stand. The n rolls included in each of the plurality of stands excluding the last stand each have a groove having an arch shape in cross section.

Abstract: The plug is for expanding the inside diameter of the end portion of a metal pipe. Its cross section is a circle, and includes a taper portion and a parallel portion connected to the tail end of the taper portion. The diameter of the taper portion gradually increases from the head end of the taper portion to the tail end of the taper portion where the diameter is D1. The axial distance LR from the point where the diameter D2=D1×0.99 to the tail end where the diameter is D1 satisfies the Expression 22?LR/((D1?D2)/2)?115. The taper angle on the surface where the diameter is D2 is larger than or equal to the taper angle on the tail surface of the taper portion following the point where the diameter is D2. The diameter of the parallel portion is D1.

Abstract: A die through hole has an inside surface including a bell portion, an approach portion, and a bearing portion from the entrance side. The diameter of the approach portion is D1 on its entrance side and D2 on its exit side and gradually decreases from the entrance side to the exit side. The diameter satisfies Equation (1): 0.7?D2/D1<0.97. The die half angle of an inside surface where the diameter D3 is D2/0.97 is not less than the die half angle R2 of an inside surface nearer to the approach portion exit side than the inside surface where the diameter is D3. The axial distance LR from the inside surface where the diameter is D3 to the inside surface where the diameter is D2 satisfies Equation (2): 20?LR/((D3?D2)/2)?115. The through hole diameter at the bearing portion is fixed at D2, and the length is LB and satisfies Equation (3): 0.3?LB/D2?10.

Abstract: The through hole of a die has an inside surface including a bell portion, an approach portion, and a bearing portion from the entrance side formed in a continuous manner. The diameter of the approach portion is D1 on the entrance side of the approach portion and D2 on the exit side of the approach portion and gradually decreases from the entrance side to the exit side. The diameter satisfies Equation (1): 0.7?D2/D1<0.97. The die half angle of an inside surface where the diameter D3 is D2/0.97 is not less than the die half angle R2 of an inside surface nearer to the exit side of the approach portion than the inside surface where the diameter is D3, and the axial distance LR from the inside surface where the diameter is D3 to the inside surface where the diameter is D2 satisfies Equation (2): 20?LR/((D3?D2)/2)?115. The diameter of the through hole at the bearing portion is fixed at D2, and the length is LB and satisfies Equation (3): 0.3?LB/D2?10.

Abstract: A die through hole has an inside surface including a bell portion, an approach portion, and a bearing portion from the entrance side. The diameter of the approach portion is D1 on its entrance side and D2 on its exit side and gradually decreases from the entrance side to the exit side. The diameter satisfies Equation (1): 0.7<D2/D1<0.97. The die half angle of an inside surface where the diameter D3 is D2/0.97 is not less than the die half angle R2 of an inside surface nearer to the approach portion exit side than the inside surface where the diameter is D3. The axial distance LR from the inside surface where the diameter is D3 to the inside surface where the diameter is D2 satisfies Equation (2): 20?LR/((D3?D2)/2)?115. The through hole diameter at the bearing portion is fixed at D2, and the length is LB and satisfies Equation (3): 0.3?LB/D2?10.

Abstract: A steel tube hot-finished by the Mannesmann tube-making method is subjected to a simple grinding process for the inner surface, and thereafter to a cold drawing, so that the depth d of the concave portion in the concavo-convex profile forming the inner surface of the steel tube, the surface roughness Ra and the width w of the entrance in the concave portion are specified, or similarly the depth d of the concave portion in the concavo-convex profile, the Vickers hardness Hv of the inner surface layer and the width w of the entrance in the concave portion are specified, hollow parts for a drive shaft, which have an excellent fatigue strength and which is optimal to reduce the weight of a car body, can be produced. Accordingly, the application of the manufacturing method according to the present invention allows drive shafts for automobiles to be efficiently produced in a reduced manufacturing cost, thereby providing a significant advantage in the industry.