Means and method for reducing radius expansion in the bending of elongated materials

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.

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.