Abstract: A tube bending mandrel is provided, which is designed to avoid stress, fracture, and disassembly caused by forces exerted while a tube is bent. The mandrel includes mandrel links with a ball end, neck, and socket end, formed from two opposing and matching link sections. A radial tenon protruding from the face of one link section fits into a corresponding radial mortise formed in the face of the opposing link section. A detent mechanism includes a ball slot formed in the exterior of a ball end, a circular spring that fits into that ball slot, and a socket groove formed in the interior of an adjacent socket in which the ball end fits and rotates. By providing a ramp on one edge of the socket groove or the ball slot, the circular spring tends to move into the socket groove and ball slot, to assume a straight position after the mandrel has been removed from a bent tube. An external shoulder is provided on each socket, adjacent to the socket opening, to support a ball segment.

Abstract: Method and apparatus for bending serpentine heat exchanger tubes using a split bend die having a relatively short upper die section with a straight back end. After the tube is bent in conventional manner using a clamp die and a pressure die, the bend die is split along a shaft and rotated through a predetermined angle to position the straight back end substantially parallel to a straight segment of the tube at the output of the bend die. The input segment of the tube is then moved next to the shaft in preparation for rotating above the input segment to raise the output segment above the upper section of the bend die. Such lateral motion reduces the segment spacing required for clearance of the upper section. Other features for reducing the spacing are providing an indentation on the shaft, angling the back end with respect to the sides to provide a minimum length, and truncation an upper portion along the back end.

Abstract: A flexible tube-bending mandrel has a longitudinally-split shank link that is unthreaded, but recessed to receive a nut that threadedly engages the bolt for holding the link to a mandrel shank. The mandrel center links are longitudinally split for ease of assembly of their ball-and-socket interconnections and have their socket ends externally threaded to receive an internally-threaded ball segment that holds the center link sections in assembled condition and effectively restrains relative longitudinal motion of the two mating link sections.

Abstract: This invention relates to tube bending mandrels and, more particularly, to an improved version thereof characterized by a threaded connection between the tube-shaping ring and the necks of the ball-carrying links that functions in cooperation with an annular stop-forming rib and a retaining ring at opposite ends of the threaded link neck section to resist equally well both tension loads and compression loads while maintaining precise axial spacing between subassemblies in an assembly where, except for the links at opposite extremities, all parts remain fully interchangeable.

Abstract: This invention relates to an improved tube bending mandrel of the general type having fixed and bendable sections and wherein the latter comprises a chain of ball and socket elements linked together in end to end relation with each such element being encircled by a ring of the same diameter as the fixed section cooperating therewith and with one another to define limited movable universal connections therebetween. More specifically, the instant invention relates to an improved ball and socket assembly wherein the ball portion comprises two or more spherically-surfaced ring segments which cooperate with each other and with a spherically-concave head formed integral with the body in which the socket is formed on the opposite end of the link to form the ball.

Abstract: The present invention pertains to the treatment of a metal surface with a durable low-friction material in such a way as to greatly enhance the lubricant properties of the metal surfaces. The surface coating formed is a chromium plated surface containing microcracks so prepared as to permit injection or insertion of perfluorocarbon compositions such as polytetrafluoroethylene in a fused or nearly-fused state. In the method of forming the surface coating as described, the surface is plated by electrodeposition in a chromic acid bath followed by baking to oxidize the external plated surface. In this way, the surface may then be reverse etched to expand the microcracks without affecting the external surface, following which the plated surface may be heated to, or in excess of, the fusion point of the polytetrafluoroethylene material which is inserted preferably by application to the surface from a solid rod.