Patent ID: 6871774

Claim:
A method of providing a leak tight and structural connection between a core tube and an accommodating header plate in a tube and shell type heat exchanger, including the steps of: a. providing a header plate of a deformable metallic material with a core tube-accommodating through bore therein; b. providing a metallic material braze foil with a core tube accommodating through bore therein; c. providing a core tube of a deformable metallic material with an end having an outside diameter approximately the same as said header plate bore diameter; d. positioning said braze foil on top of said header plate so that said accommodating bore in said braze foil is aligned with said accommodating bore in said header plate; e. inserting said core tube end into the bore in said header plate so that it is received therein and said core tube end is substantially coplanar with said braze foil; f. installing a ferrule of a deformable metallic material into said inserted core tube end, said ferrule including a first cylindrical body portion having an outside diameter approximately the same as the inside diameter of said core tube and a second annular portion extending axially outwardly of said core tube end and having a radial extent greater than the wall thickness of said core tube; g. radially expanding said ferrule first cylindrical body portion so that cylindrical body portion is pressed against said core tube, thus in turn deforming said core tube into an area of intimate contact with said accommodating bore of the header plate; h. deforming said ferrule second annular portion into an area of deformation contact with an adjacent portion of said braze foil at said intimate contact area of said header plate and core tube; and i. brazing said core tube and header plate in a brazing furnace at a temperature and for a time sufficient for said braze foil to melt and flow from said deformation contact area towards and into said intimate contact area of said header plate and core tube, thus forming a leak tight seal in said intimate contact area.