Claims
- 1. A pipe formed by a pipe forming method using a pipe forming apparatus having bending rolls including a pair of rolls arranged on one side of a sheet material, and a counter roll arranged at the other side of the sheet material, said pipe forming method comprising:effecting pipe forming work on said sheet material such that the spacing L of the pair of rolls satisfies the following expression: (DP+Dwl)>L≧0.85(Dp+Dwl) wherein Dp represents the outside diameter of the product pipe and Dwl represents the diameter of one of the pair of rolls.
- 2. The pipe according to claim 1, wherein the pipe comprises a high strength, thick walled steel pipe having a strength of at least 40 kgb/MM2 and a thickness of at least 20 mm.
- 3. A pipe formed by a pipe forming method using a pipe forming apparatus having bending rolls including a pair of rolls arranged on one side of a sheet material, and a counter roll arranged at the other side of the sheet material, said pipe forming method comprising:effecting pipe forming work on said sheet material such that the spacing L of the pair of rolls satisfies the following expression: (DP+Dwl)>L≧0.85(Dp+Dwl) wherein Dp represents the outside diameter of the product pipe and Dwl represents the diameter of one of the pair of rolls; and further comprising the steps of effecting correction of the bend by effecting roll bending to provide a curvature change which is not greater than 10% of the final curvature.
- 4. The pipe according to claim 3, wherein the pipe comprises a high strength, thick walled steel pipe having a strength of at least 40 kgb/mm2 and a thickness of at least 20 mm.
- 5. A pipe formed by a pipe forming method using a pipe forming apparatus having bending rolls including a pair of rolls arranged on one side of a sheet material, and a counter roll arranged at the other side of the sheet material, said pipe forming method comprising:effecting pipe forming work on said sheet material such that the spacing L of the pair of rolls satisfies the following expression: (DP+Dwl)>L≧0.85(Dp+Dwl) wherein Dp represents the outside diameter of the product pipe and Dwl represents the diameter of one of the pair of rolls; further comprising the steps of effecting correction of the bend by effecting roll bending to provide a curvature change which is not greater than 10% of the final curvature; and wherein, when no bend correcting work is executed, the forming method is applied to the final pass of the bending by the bending rolls.
- 6. A pipe formed by a pipe forming method using a pipe forming apparatus having bending rolls including a pair of rolls arranged on one side of a sheet material, and a counter roll arranged at the other side of the sheet material, said pipe forming method comprising:effecting pipe forming work on said sheet material such that the spacing L of the pair of rolls satisfies the following expression: (DP+Dwl)>L≧0.85(Dp+Dwl) wherein Dp represents the outside diameter of the product pipe and Dwl represents the diameter of one of the pair of rolls; further comprising the steps of effecting correction of the bend by effecting roll bending to provide a curvature change which is not greater than 10% of the final curvature; and wherein, when a bend correcting work is executed subsequent to a tack welding, the forming method is applied to said bend correcting work.
- 7. A pipe formed by a pipe forming method using a pipe forming apparatus having bending rolls including a pair of rolls arranged on one side of a sheet material, and a counter roll arranged at the other side of the sheet material, said pipe forming method comprising:effecting pipe forming work on said sheet material such that the spacing L of the pair of rolls satisfies the following expression: (DP+Dwl)>L≧0.85(Dp+Dwl) wherein Dp represents the outside diameter of the product pipe and Dwl represents the diameter of one of the pair of rolls; further comprising the steps of effecting correction of the bend by effecting roll bending to provide a curvature change which is not greater than 10% of the final curvature; and wherein, when a bend correcting work is executed subsequent to a tack welding, the forming method is applied to the final pass of the pending by the bending rolls and to said bend correcting work.
- 8. A pipe formed by a pipe forming method using a pipe forming apparatus using bending rolls including 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, said pipe forming method comprising:providing a sheet of feed material having leading and trailing bent end regions each bent beforehand over a length not smaller than ⅕ of the entire circumference of the pipe to be produced; and effecting roll bending such that the length of the regions bent by the bending rolls is less than ⅗ the entire circumference of the pipe to be produced.
- 9. The pipe according to claim 8, wherein the pipe comprises a high strength, thick walled steel pipe having a strength of at least 40 kgb/mm and a thickness of at least 20 mm.
- 10. A pipe formed by a pipe forming method using a pipe forming apparatus using bending rolls including a plurality of rolls arranged on one side of a sheet material, and a counter roll arranged at the other end side of the sheet material, said pipe forming method comprising:providing a sheet of feed material having leading and trailing bent end regions each bent beforehand over a length not smaller than ⅕ of the entire circumference of the pipe to be produced; and effecting roll bending such that the length of the regions bent by the bending rolls is less than ⅗ the entire circumference of the pipe to be produced; wherein operation of the bending rolls is suspended during passage of each of said bent end regions so as to avoid deformation of the bent end regions by the bending rolls, thereby ensuring that the length of the region bent by the bending rolls is less than ⅗ the entire circumference of the pipe to be produced.
- 11. A pipe formed by a pipe forming method using a pipe forming apparatus using bending rolls including 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, said pipe forming method comprising:providing a sheet of feed material having leading and trailing bent end regions each bent beforehand over a length not smaller than ⅕ of the entire circumference of the pipe to be produced; and effecting roll bending such that the length of the regions bent by the bending rolls is less than ⅗ the entire circumference of the pipe to be produced; wherein the roll spacing of said plural rolls is in increased, thereby ensuring that the length of the region bent by the bending rolls is less than ⅗ the entire circumference of the pipe to be produced.
Priority Claims (3)
Number |
Date |
Country |
Kind |
10-313206 |
Nov 1998 |
JP |
|
10-313207 |
Nov 1998 |
JP |
|
10-313208 |
Nov 1998 |
JP |
|
Parent Case Info
This application is a division of U.S. Ser. No. 09/433,968 filed Nov. 4, 1999 now U.S. Pat. No. 6,339,946.
US Referenced Citations (7)
Foreign Referenced Citations (1)
Number |
Date |
Country |
743485 |
Jan 1956 |
DE |