Patent Application
20160082493
This invention relates generally to methods and devices used for forming elongate wire, rod, tubing and the like into shapes, in particular forming wire or tubing into helical shapes.
As disclosed in U.S. patent application Ser. No. 13/864,018, the contents of which are incorporated herein by reference, a heat exchanger in which the heat exchanger tubes are formed into helical tube bundles has significant advantages over straight-tube heat exchangers in terms of durability, size and thermal efficiency.
Apparatus and methods for forming a single rod of wire or tube into a helical shape are well known. U.S. Pat. No. 4,402,205 to Yakovlev et al. discloses various methods for forming helical springs by winding a resilient rod around a rotating mandrel. U.S. Pat. No. 4,606,209 to Eisinger discloses a disk roller mechanism for forming a wire into a helical shape in which the wire is drawn through a plurality of staggered disk-shaped forming rollers while the wire is also being rotated about its own axis. Although the prior art discloses numerous methods of forming a single wire into a helix, or multiple thin strands into wire rope, the prior art does not disclose a method and apparatus for simultaneously forming a plurality of tubes into a helical bundle.
The present invention comprises an apparatus and method for forming a plurality of rigid or semi-rigid elongate members, for example a plurality of stainless steel tubes, into a helical bundle. According to an illustrative embodiment, a pair of bending die assemblies are mounted on a moveable carriage, the moveable carriage itself being supported by a frame. The bending dies each have a plurality of grooved rollers that engage the sides of the tubes to apply a bending force while allowing the tubes to move longitudinally through the die assemblies. The die assemblies can be rotated independent of each other or in unison by means of stepper motors. A collet, attached to the frame, holds the ends of the tubes during the bending operation.
With the tubes firmly held by the collet, the first bending die assembly is rotated about the axis of the tube bundle until the lead angle of the helix is established, taking into account the elastic recovery of the tubes. Thereafter, both bending die assemblies are rotated in unison as the carriage is advanced along the axis of the tube bundle. The pitch (helical angle) of the tube bundle can be varied by varying the spacing of the bending die assemblies, the angular orientation between the two bending die assemblies and/or by varying the speed of advancement of the carriage relative to the rotation of the die assemblies. The helical radius of the tube bundle can be adjusted by altering the depth of the grooved rollers.
The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which:
The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention.
With reference to the figures and in particular
Each of bearing blocks 18 has a central bore 22 which supports a ball bearing 24 retained in central bore 22 by a snap ring 26. A bending die comprising a grooved roller 28 is disposed in central bore 22 supported at one end by ball bearing 24 and the other end by a needle roller bearing 30. A die retaining screw 32 secures grooved roller 28 to bearing block 18. Collectively the grooved rollers 28 form guideways that exert a lateral force for bending tubes 42 while allowing tubes 42 to pass through bending die assembly 14. Although the illustrative embodiment discloses grooved rollers supported by ball bearings and needle roller bearings, other art-recognized equivalents may be substituted without departing from the scope of the invention, for example a non-roller supported forming die may be used, provided sufficient lubrication is applied to prevent galling of the surfaces of the tubes being formed. Accordingly, it is not intended that the invention be limited to the particular method of supporting the bending dies disclosed in the illustrative embodiment.
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Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the invention. For example, although in the illustrative embodiment, the angular orientation between rear bending die assembly and front bending die assembly remain constant the angular orientation between rear bending die assembly 14 and front bending die assembly 12 can be varied, and the rotational velocity of the bending die assemblies relative to the speed of the carriage imparted by lead screw 128 can be varied if a variable pitch helical tube bundle is desired. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law. Additionally, as used herein, references to direction such as “up” or “down” are intend to be exemplary and are not considered as limiting the invention and, unless otherwise specifically defined, the terms “generally,” “substantially,” or “approximately” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater, and as used herein, a step of “providing” a structural element recited in a method claim means and includes obtaining, fabricating, purchasing, acquiring or otherwise gaining access to the structural element for performing the steps of the method.
