Heat exchanger core assembly construction and methods of making the same

A heat exchanger core and header of the fin and tube type characterized by improved resistance to stress failure between tubes and header comprising a plurality of tubes disposed in generally axially parallel and spaced apart relation, a fin assembly between adjacent tubes, a header plate at one end of said tubes, said header plate having a series of openings therein adapted to receive said tubes and generally uniformly spaced from the sidewalls of said tube ends, said openings in the header being upset to form a flange extending away from the fin assembly on one side of the header plate and a curved entry into the opening on the other side of the header plate facing the fin assembly, an elongate ferrule in each said opening substantially filling the area between said openings and said tubes and extending axially along said tubes from said header on the side opposite the fins, said ferrule being provided at one end facing the fin assembly with a generally curved radial flange generally matching and overlaying the curved entry to the openings in the header plate, a metallurgical bond between the ferrules and tubes and between the ferrules and header over substantially their entire contacting areas.