Apparatus for bending a straight tube into a serpentine tube

Apparatus for producing a serpentine tube for use with a heat exchanger or the like by bending a straight tube comprising:

• bending head means movable both longitudinally and transversely for forming bends in the straight tube;
• and
• drive means for moving said bending head means longitudinally and transversely;
• motor means associated with said drive means to drive dies in the direction of a center axis of the straight tube and, at the same time, in a direction intersecting said axis at a different speed,
• wherein the improvement resides in that said bending head means comprises
• a fixed die provided with an arcuate surface for forming a bent portion of the serpentine tube by bending the straight tube, and
• a pair of wings associated with said fixed die to hold the straight tube between the die and the two wings and push the tube to the arcuate surface of the die during a bending operation, said two wings moving symmetrically to right and left respectively from the apex of the arcuate surface to said die, and
• means actuating both of said two wings to rotate 90.degree. against and around the arcuate surface of each die for effecting bending of said serpentine tube without producing excess material by maintaining a dimensional relationship between the straight tube and the serpentine tube which satisfies following equation:
• ##EQU4## where:
• PQ:
• half length of straight tube portion during a bending operation of the tube;
• L:
• length of straight portion on completion of bending operation;
• R:
• the radius of bent portion of tube;
• .theta.:
• bending angle of bent portion of tube.