Abstract: In the manufacture of tubing, and particularly finned tubing, for use by the heat transfer industry in the manufacture of heat exchangers, annealed ends and lands are desirable in certain applications to facilitate the assembly of the tubes to headers and baffles by expanding techniques. Such spot-annealed portions can be produced on a continuous basis by the described apparatus and method in which the moving tube is passed through a heating chamber which reciprocates on a carriage in the direction of tube movement. The heating chamber has a pair of power-actuated, current-carrying clamps which grip spaced portions of the tube so as to resistance-heat the tube portion between the clamps. The heating chamber and carriage move with the tube while it is clamped to provide sufficient heating time. The carriage then returns to its starting position. If desired, an inert gas can be supplied to the heating chamber to prevent oxidation and/or discoloration.

Abstract: In the manufacture of tubing, and particularly finned tubing, for use by the heat transfer industry in the manufacture of heat exchangers, annealed ends and lands are desirable in certain applications to facilitate the assembly of the tubes to headers and baffles by expanding techniques. Such spot-annealed portions can be produced on a continuous basis by the described apparatus in which the moving tube is passed through a heating chamber which reciprocates on a carriage in the direction of tube movement. The heating chamber has a pair of spaced, power-actuated clamps which grip the tubing at the ends of a discrete length portion. The heating chamber and carriage are moved with the tube while it is clamped to provide sufficient heating time to anneal the discrete length portion. The carriage then returns to its starting position. Heating of the discrete clamped tubing portion can be by a resistance technique through the clamps or by other techniques such as induction heating or gas radiant heat.

Abstract: An improved drawing die apparatus is disclosed for reducing the wall thickness of a thin wall metal tube in cooperation with a floating pin or a fixed mandrel. At least three, and preferably four, wall thickness sensors are positioned in the die body in angular relationship around the outer periphery of a carbide draw die nib for indicating the wall thickness, and thus the eccentricity, of the tubing as it is being produced. Preferably, the sensors are contact type ultrasonic transducers which are acoustically coupled with a viscous couplant to flats formed on the draw nib in regions overlying a land region of the die. The acoustic coupling between the draw nib and tube is achieved through the O.D. drawing lubricant.