Patent ID: 7121131

Claim:
A bending method for producing a coil having return sections bent at 180° comprising the steps of: providing a metallic pipe; setting up a tangency point where a bend will occur; pre-heating the pipe where the bend will occur at a temperature of between 570° F. to 2200° F. for a time of between 30 seconds to 60 minutes; pre-bending the pre-heated pipe at 180° taking as bending reference point the tangency point in order to obtain a “U” shaped piece having two straight tube sections depending from a bent section; heating the bent section at a temperature of between 570° F. to 2200° F. for a time between 1 to 60 minutes; forming a final bending radius by applying a lateral pushing force along a straight section respectively and a pushing force on the tangency point perpendicular to the lateral pushing forces; and applying a compression force to the entire “U” shaped piece in order to round the sections until the required roundness is obtained.