Method for induction bend forming of a compression-resistant pipe having a large wall thickness and a large diameter, and induction pipe bending device

Abstract

A method for induction bend forming of a compression-resistant pipe ( 1 ) having a large wall thickness and a large diameter, in particular, for use in power plants and pipelines, comprises: horizontal placement of the unprocessed pipe ( 1 ); feeding the pipe ( 1 ) to the passage of a front pipe section through an annular inductor ( 20 ) of an electrical induction unit; clamping the front pipe section in a bending lock ( 31 ) that is mounted on a bending arm ( 30 ), which is pivotable around a vertical axis of rotation ( 32 ) arranged laterally to the pipe; current supply to the induction unit for heating a pipe section; and deflecting the bending arm ( 30 ) by longitudinal feeding of the pipe ( 1 ) until the completion of the pipe bend ( 3 ). The pipe ( 1 ) is compressed vertically in a pressing unit ( 50 ) prior to introduction into the inductor ( 20 ), such that a cross-section of the pipe ( 1 ) is forced into the shape of a lying oval, and a temperature profile with a lower temperature at an outer side of the bend ( 3.2 ) and with a higher temperature at an inner side of the bend ( 3.1 ) is set at least during a portion of the pipe bending process by means of a transverse movement of the inductor ( 20 ) relative to the pipe ( 1 ).

What is claimed is: 
     
         1 . In a method for induction bend forming of a compression-resistant pipe having a large wall thickness and a large diameter, in particular, for use in power plants and pipelines, said method comprising the following steps;
 horizontal placement of an unprocessed pipe;   feeding a front pipe section of the pipe through an annular inductor of an electrical induction unit;   clamping the front pipe section in a bending lock that is mounted on a bending arm, which is pivotable around a vertical axis of rotation arranged laterally to the pipe;   supplying current to the induction unit for heating a pipe section;   deflecting the bending arm by longitudinal feeding of the pipe until the completion of the pipe bend;   
       the improvement comprising the steps of
 compressing the pipe vertically in a pressing unit prior to introduction into the inductor, such that a cross-section of the pipe is forced into the shape of a lying oval, and 
 setting a temperature profile with a lower temperature at an outer side of the bend and with a higher temperature at an inner side of the bend at least during a portion of the pipe bending process by means of a transverse movement of the inductor relative to the pipe. 
 
     
     
         2 . Method as in  claim 1 , further comprising the step of continuously compressing the pipe during the longitudinal feed. 
     
     
         3 . Method as in  claim 2 , wherein the degree of the pipe compression is progressively increased from an initial tangent to the center of the pipe bend and then reduced again to an end tangent. 
     
     
         4 . Method as in  claim 1 , wherein the temperature profile is adjusted by an increased local energy supply at one side of the bend. 
     
     
         5 . Method as in  claim 4 , wherein the distance between the inductor and the inside of the bend is reduced and at the same time is increased at the outside of the bend, and wherein the absolute temperature level is adjusted by adapting the electrical current flowing in the inductor. 
     
     
         6 . Method as in  claim 1 , wherein the temperature profile is adjusted by an increased local energy removal at one side of the bend. 
     
     
         7 . Method as in  claim 6 , wherein the temperature at the inner side of the bend is reduced by means of a cooling device and wherein the absolute temperature level is adjusted by adaptation of the electrical current flowing in the inductor. 
     
     
         8 . Induction pipe bending device for compression-resistant pipes having a large wall thickness and a large diameter, in particular for use in power plants and pipelines, said device comprising, in combination:
 a machine bed for horizontal positioning of an unprocessed pipe;   a feed unit configured to act along the pipe axis;   an electrical induction unit with an annular inductor for heating a pipe section;   a bending arm that is pivotable around a vertical axis of rotation and has a bending lock for clamping the pipe as well as an adjustment device for adjusting the distance between the axis of rotation and the bending lock;   a pressing unit arranged upstream of the inductor in the feed direction having at least one punch acting vertically on the pipe and a counter support for the punch wherein the inductor is mounted such that it can be moved transversely to the feed direction, and   a control unit for adjusting the electrical power of the induction unit as a function of a transverse offset of the inductor or vice versa.   
     
     
         9 . Induction pipe bending device as in  claim 8 , wherein the pressing unit has at least two hydraulically driven punches that act upon the pipe in opposition to each other. 
     
     
         10 . Induction pipe bending device as in  claim 8 , wherein at least one punch and counter-support each have at least one pressure roller having the shape of a double cone or a rotational hyperboloid. 
     
     
         11 . Induction pipe bending device as in  claim 8 , wherein the at least one punch and counter support are arranged at the top and at the bottom in a closed rack, and wherein at least one lateral guide roller is arranged on both sides of the rack.