Method for producing seamless pipe and method for determining length of billet for use in producing seamless pipe
View Patent ↗Seamless pipes are produced by using billets for which the length L of a parent billet, the lengths l of child billets and the number n B of the obtainable child billets are determined on the basis of predetermined tolerances and the conditions of a billet-heating furnace and billet-rolling facilities. In this way, energy saving in the production of seamless pipes can be realized and the productivity in the production of seamless pipes can also be improved.
1. A method for producing a seamless pipe comprising steps of a billet-heating process, a billet-cutting process, a piercing-rolling process and elongation-rolling process, wherein:
the method using the billets satisfying the following formulas (1) to (3):
l min ≦l≦l max (1)
L min L≦L max (2)
F≧F min (3)
wherein L is the length (m) of the parent billet and is represented by the following formula (4), and F is the billet-heating-furnace filling factor (%) and is represented by the following formula (5):
L=l×n B + k ×(n B −1) (4)
F= 100× L / L max (5)
wherein in the above-described formulas, the meanings of the individual symbols are as follows:
L min : The minimum length (m) of the parent billet allowed on the basis of the conditions of the billet-heating furnace
L max : The maximum length (m) of the parent billet allowed on the basis of the conditions of the billet-heating furnace
l: The length (m) of the child billet
l min : The minimum value (m) of the length of the child billet allowed on the basis of the predetermined tolerances and the rolling conditions
l max : The maximum value (m) of the length of the child billet allowed on the basis of the predetermined tolerances and the rolling conditions
k: Billet cutting margin (m)
n B : The number (number of pieces) of the child billets obtainable from one piece of parent billet
F min : The allowable minimum value (%) of the heating-furnace filling factor
wherein, the method adopts the following respective values in the following respective cases (A) to (C) in each of which the relation between the number-of-obtainable-billet indexes I 0 and I l calculated respectively from the following formulas (6) and (7) is specified:
(A) A case where I 0 =I l :
L obtained by substituting n B =I 0 and l=l max into the above-described formula (4) is adopted as the length L of the parent billet, l max is adopted as the length l of the child billet, and I 0 is adopted as the number n B of the obtainable child billets
(B) A case where I 0 <I i , and F satisfies the above-described formula (3) wherein F is obtained by substituting, into the above-described formula (5), L obtained by substituting n B =I 0 and l=l max into the above-described formula (4):
L obtained by substituting n B =I 0 and l=l max into the above-described formula (4) is adopted as the length L of the parent billet, l max is adopted as the length l of the child billet, and l 0 is adopted as the number n B of the obtainable child billets
(C) A case where I o <I i , and F does not satisfy the above-described formula (3) wherein F is obtained by substituting, into the above-described formula (5), L obtained by substituting n B =I 0 and l=l max into the above-described formula (4):
L max is adopted as the length L of the parent billet,(L max −k×n B −l))/n B is adopted as the length l of the child billet, and I 0 +l is adopted as the number n B of the obtainable child billets
I 0 =Int(( L max+ k )/( l max+ k )) (6)
I l =Int(( L max+ k )/( l min+ k )) (7)
wherein Int(X) means the maximum integer that does not exceed the specified numerical value X.
2. A method for cutting a billet for use in a seamless pipe, comprising cutting the billet to a length determined so as to satisfy the following formulas (1) to (3):
l min ≦l≦l max (1)
L min ≦L≦L max (2)
F≧F min (3)
wherein L is the length (m) of the parent billet and is represented by the following formula (4), and F is the billet-heating-furnace filling factor (%) and is represented by the following formula (5):
L =l×n B +k×(n B −l) (4)
F= 100× L / L max (5)
wherein in the above-described formulas, the meanings of the individual symbols are as follows:
L min : The minimum length (m) of the parent billet allowed on the basis of the conditions of the billet-heating furnace
L max : The maximum length (m) of the parent billet allowed on the basis of the conditions of the billet-heating furnace
l: The length (m) of the child billet
L min : The minimum value (m) of the length of the child billet allowed on the basis of the predetermined tolerances and the rolling conditions
l max : The maximum value (m) of the length of the child billet allowed on the basis of the predetermined tolerances and the rolling conditions
k: Billet cutting margin (m)
n B : The number (number of pieces) of the child billets obtainable from one piece of parent billet
F min : The allowable minimum value (%) of the heating-furnace filling factor
wherein the method adopts the following respective values in the following respective cases (A) to (C) in each of which the relation between the number-of-obtainable-billet indexes I 0 and I l calculated respectively from the following formulas (6) and (7) is specified.
(A) A case where I 0 =I l :
L obtained by substituting n B =and I 0 and l=l max into the above-described formula (4) is adopted as the length L of the parent billet, l max is adopted as the length l of the child billet, and I 0 is adopted as the number n B of the obtainable child billets
(B) A case where I 0 <I l , and F satisfies the above-described formula (3) wherein F is obtained by substituting, into the above-described formula (5), L obtained by substituting n B =I 0 and l=l max into the above-described formula (4):
L obtained by substituting n B =I 0 and l=l max into the above-described formula (4) is adopted as the length L of the parent billet, l max is adopted as the length l of the child billet, and l 0 is adopted as the number n B of the obtainable child billets
(C) A case where I 0 <I l , and F does not satisfy the above-described formula (3) wherein F is obtained by substituting, into the above-described formula (5), L obtained by substituting n B =I 0 and l=l max into the above-described formula (4):
L max is adopted as the length L of the parent billet, (L max − k ×(n B −l))/n B is adopted as the length l of the child billet, and I 0 + l is adopted as the number n B of the obtainable child billets
I 0 =Int(( L max + k )/(l max + k )) (6)
I l =Int(( L max + k )/(l mim + k )) (7)
wherein Int(X) means the maximum integer that does not exceed the specified numerical value X.