Claims
- 1. In an apparatus for hot bending elongated materials having an annular heating means for locally heating a limited portion of the material, an arm freely pivotable about an axis in the plane of the heating means, a clamp carried by said arm for engaging a leading portion of the material, and means for continuously advancing the material through said heating means and guiding the trailing, unbent portion of the material, the improvement wherein said advancing and guiding means is operative to maintain the longitudinal axis of the unbent portion of the elongated material at an acute angle with respect to a perpendicular to the plane of the heating means during the bending of the pipe by the pivotable arm, said angle being selected to compensate for the spring back material when the material is unclamped so that the material has the desired bending radius when the material is unclamped.
- 2. The apparatus of claim 1 further comprising means for detecting change in the radius of curvature of the material and moving the heating means a suitable distance to compensate therefor.
- 3. The apparatus of claim 2 further comprising means for detecting change in the radius of curvature of the material and for turning the unbent portion of the material a suitable angle to maintain the bending radius constant.
- 4. An apparatus for hot bending, elongated metal materials such as metal pipes of circular cross section comprising:
- heating means for heating a limited area of the metal material to a high temperature;
- cooling means for cooling the heated area immediately after the heating thereof;
- an arm which is freely pivotable about an axis located within the plane of said heating means, said arm being also adapted to clamp a portion of the metal material to guide the portion in its bending direction;
- means for applying pressure to the material from the direction generally parallel to the axis of pivoting of said arm, at a suitable location behind said cooling means;
- means for continuously advancing a metal material to be bent; and,
- means for guiding the metal material so that the unbent portion of the material is advanced toward the heating means while maintained in a position where it has turned a suitable angle from the point of intersection of the line connecting the center of bend and the heating means and the line crossing said line at right angles thereto during the bending of the pipe by the pivotable arm, said angle being selected to compensate for spring back of the material when the material is unclamped so that the material has the desired bending radius when the material is unclamped.
- 5. In a hot bending method for bending elongated material in which the material to be worked passes through a heating device such as a high frequency inductor capable of effecting high temperature heating on a limited area, with the leading end or a suitable middle part of said material being clamped to an arm pivotable about an axis within the plane of the heating device, the arm having a length that matches the bending radius of the material, and then continuously and straightforwardly advancing the material while heating the material locally by the heating device to a plastic deformation inducing temperature and thereafter immediately followed by cooling with the application of a bending moment to the material to cause continuous plastic deformation in the heated area of the material, the improvement wherein change of the bending radius of the material through spring back of the material after unclamping is reduced by maintaining the material in a position while bending, such that the longitudinal axis of the unbent portion of the material at the point of intersection of the material and a first line connecting the center of the bend with the heating means is turned a suitable angle with respect to a second line at right angles to said first line to compensate for spring back of the material when the material is unclamped, so that the material has a bending radius approximately equal to the length of the arm when the material is unclamped.
- 6. The method of claim 5, wherein the heating means is disposed on a straight line in the direction of advancement of the unbent material and at a position in the path of the advance of the material, a suitable distance from a line perpendicular to said straight line and passing through the center of the bend to compensate for the springback of the material when the material is unclamped.
- 7. The method of claim 5 wherein the heating means is moved responsive to change in the curvature of the bent portion of the material to maintain the bending radius constant.
- 8. The method of claim 5 wherein the unbent portion of the material is turned through a suitable angle responsive to change in the radius of curvature of the bent portion of the material to maintain the bending radius constant.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 50-64956 |
May 1975 |
JPX |
|
RELATED APPLICATION
This is a divisional application of pending prior application No. 593,961 filed on July 8, 1975, U.S. Pat. No. 4,062,216.
There are known two general methods for accomplishing bending work on metal pipes, rods, or the like. In cold bending the desired bending work is performed by giving to the work piece a bending moment that exceeds the elastic limit of the work piece at normal temperature. In hot bending the bending work is accomplished by giving a bending moment to the work piece by heating it to a temperature that induces plastic deformation of the work piece. Cold bending is suited for relatively small diameter metal pipes or the like of which no high product precision is required, but it is not suited for relatively large diameter metal pipes or the like of which high product precision is required. On the other hand, hot bending is suited for relatively large diameter metal pipes or the like of which high product precision is required, but fairly large-scale equipment and heating apparatus is required. Also, as work efficiency is poor, the working cost is high.
Attempts have been made to overcome these problems, and there have been recently developed and put to practical use an improved method and apparatus for effecting bending work by hot bending, according to which a metal pipe or the like to be worked is first passed through a heating device such as for example a high frequency inductor which is capable of effecting high temperature heating over a limited area, with the end or a suitable middle part of said pipe being clamped to an arm which is freely swingable and whose axis of the revolution is located within the plane of said heating device, the arm also having a length that matched the bending radius of said pipe. Then, with the pipe being continuously driven straight forward, it is subjected to local heating to a plastic deformation inducing temperature by said heating device, which is immediately followed by cooling so as to effect continuous plastic deformation in said heated area of said pipe while giving a bending moment to said pipe, thereby to accomplish the desired bending.
Referring first to FIG. 1, there is shown such a conventional bending apparatus. In the figure, reference numeral 1 designates a steel pipe to be bent, a support block 2 is adapted to support the pipe end and is formed integral with the means for continuously and straightforwardly propelling the steel pipe 1, also provided are a pair of guide rolls 3 and 4, a heating device 5 such as an annular high frequency inductor which is capable of heating a limited area of the steel pipe 1 sidewise to a high temperature, and a cooling device 6 integral with said heating device. A rocker arm 7 is mounted on the pivotal shaft 8 arranged such that its center resides within the plane of the heating device 5, and a clamp 9 fixed to the arm 7.
In operation of the apparatus just described, steel pipe 1 is first passed between guide rolls 3 and 4 and then further passed through heating device 5 as shown in the drawing. The pipe end is supported by support block 2 of the propelling means, and in certain applications, in end or a suitable middle portion of the steel pipe 1 is fastened to the arm 7 by the clamp 9. The steel pipe 1 is continuously fed straightforwardly by the propelling means while subjected to local heating by heating device 5 to a plastic deformation inducing temperature, and this treatment is immediately followed by cooling so as to effect continuous plastic deformation of the steel pipe 1 in its heated area while giving a bending moment to the pipe by the thrust of the propelling means under the guidance of the arm 7, thereby to accomplish the desired bending. Thus, according to this apparatus, the desired bending of steel pipe can be performed at high efficiency without requiring any elaborate thermal works. The same effect can be obtained by using this apparatus for bending of other types of metal pipes or metal strips. It is to be particularly noted that no bending mold is required and it is possible to bend the pipe at any desired radius of curvature.
According to this method and apparatus, the desired bending can be accomplished on elongated materials very efficiently with some precision, but when the clamp is released upon completion of the bending, there may occur so-called spring back to cause expansion of the bending radius (hereinafter referred to "R expansion"). Known bending means and methods do not avoid "R expansion".
Therefore, it has been attempted heretofore to carry out the bending with a bending radius that makes allowance for possible spring back. This measure, however, is still unsatisfactory.
In a known method performed as shown in FIG. 2, a pipe 1 to be worked is passed between guide rolls 3, 3' and 4, 4' and then through heating device 5 and fastened to clamp 9 at the end of arm 7. Thus, the pipe 1, while moved forwards by thrust P, is heated locally by heating device 5 to a plastic deformation inducing temperatures and then immediately cooled by a cooling device (not shown), so as to induce continuous plastic deformation in said heated area of said pipe while giving bending moment thereto. The axis of the unbent pipe portion is rectilinear. The position of the vertical line extending down to the center .theta. of bend as well as the distance of shift of the heating point A from the axial line XX' is slightly changed by change of the bending angle .theta., so that when clamp 9 is loosened to release the pipe upon completion of the bending work, the fastened portion, or the clamp portion CD, may not only spring back to the position of CD, and consequently, the bending radius does not stay uniform with respect to the bending angle resulting in increased bending radius at the termination of bending.
In recent years, pipelines are popularly used for the transportation of fluids, and the number of steel pipes used for such pipelines is increasing at a high rate. Also, more and more high precision is required for bending such pipes.
Thus, demand has been voiced in the industries for development of a method and apparatus wich are capable of effecting bending metal pipes such as steel pipes with higher precision than is attainable with the presently available techniques.
In view of the above, the present invention has for its object to provide a method and apparatus which are capable of bending long metal materials such as pipe, bar and rod with high efficiency and high precision.
It is another object of the present invention to provide a method and apparatus which are capable of bending steel pipes used for constructing pipelines for fluid transport without causing any undesirable phenomenon such as R expansion.
These and other objects and features of the invention will become apparent from the claims and from the following description when read in conjunction with the appended drawings.
US Referenced Citations (6)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 541,032 |
Sep 1921 |
FRX |
Divisions (1)
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Number |
Date |
Country |
| Parent |
593961 |
Jul 1975 |
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Patent Grant
4122697
