Plug for cold drawing and method for manufacturing of metal pipe
View Patent ↗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 D 1 . The second columnar portion 40 has an outside diameter D 2 which is larger than the outside diameter D 1 . 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 D 1 and D 2 , and the axial direction length L meet the following expressions (1) to (4): 0.25≦ρ≦2.00 (1), 0.06≦ L/D 2≦0.8 (2), L/D 2≦0.3×ρ+0.575 (3), and L/D 2≧0.1×ρ (4) where ρ=( D 2− D 1)/ D 1×100. 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.
1. A plug for use in cold drawing of a metal pipe, comprising:
a first columnar portion having an outside diameter D 1 ;
a second columnar portion formed coaxially with the first columnar portion and having an outside diameter D 2 larger than the outside diameter D 1 ; and
a tapered portion formed between the first columnar portion and the second columnar portion and having a tapered surface provided with an outside diameter gradually increasing from the first columnar portion to the second columnar portion and an axial direction length L,
the outside diameters D 1 and D 2 , and the axial direction length L meeting the following expressions (1) to (4):
0.25≦ρ≦2.00 (1),
0.06 ≦L/D 2≦0.8 (2),
L/D 2≦0.3×ρ+0.575 (3), and
L/D 2≧0.1×ρ (4)
where ρ=( D 2 −D 1)/ D 1×100.
2. The plug for cold drawing of claim 1 , wherein
a connection portion of the tapered surface that is connected with an end edge of the first columnar portion is smoothly curved in a concave shape.
3. A method for manufacturing of a metal pipe, comprising the steps of:
preparing a plug for cold drawing including a first columnar portion having an outside diameter D 1 ; a second columnar portion formed coaxially with the first columnar portion and having an outside diameter D 2 larger than the outside diameter D 1 ; and a tapered portion formed between the first columnar portion and the second columnar portion and having a tapered surface provided with an outside diameter gradually increasing from the first columnar portion to the second columnar portion and an axial direction length L, the outside diameters D 1 and D 2 , and the axial direction length L meeting the following expressions (1) to (4), and a die for cold drawing:
0.25≦ρ≦2.00 (1),
0.06 ≦L/D 2≦0.8 (2),
L/D 2≦0.3×ρ+0.575 (3), and
L/D 2≧0.1×ρ (4)
where ρ=( D 2 −D 1)/ D 1×100;
inserting one end of a hollow shell into the die;
inserting the plug for cold drawing into the hollow shell from the second columnar portion toward the direction of drawing; and
drawing the hollow shell while holding the plug for cold drawing at a predetermined position.
4. The method for manufacturing of a metal pipe of claim 3 , wherein
a connection portion of the tapered surface of the plug for cold drawing that is connected with an end edge of the first columnar portion is smoothly curved in a concave shape.