Patent ID: 8033018

Claim:
A method for manufacturing a tube and fin heat exchanger comprising the steps of: providing a supply of non-skin-hardened tubing having a nominal outer diameter; and reducing the outer diameter of said non-skin-hardened tubing to a value significantly smaller than said nominal outer diameter so as to produce a supply of skin-hardened tubing from said non-skin-hardened tubing; wherein said step of reducing the outer diameter further comprises the step of rolling said non-skin-hardened tubing between first and second pre-size rollers; whereby said step of rolling creates an ovality in said skin-hardened tubing; cutting said skin-hardened tubing to plurality of predetermined lengths; bending said plurality of predetermined lengths of tubing 180 degrees into hairpin tubes; lacing said plurality of hairpin tubes through a plurality of apertures in a stack of fins sandwiched between first and second endplates; and expanding the outer diameter of said laced hairpin tubes to create an interference fit between said hairpin tubes and said plurality of apertures.