Cross-Reference to Related Applications

[0001] This application claims the benefit of U.S Patent Application Serial No. 14/934,897 filed on November 6, 2015, which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

[0002] The present invention pertains to a floating draw plug for forming internal helical ribs in tubing and a method of using the same. More particularly, the present invention pertains to a draw plug having a rib forming portion that is axially tethered to but rotationally disjoined from the necking portion of the draw plug.

General Background

[0003] Floating draw plugs are commonly used to reduce the diameter of tubing. Float drawing, as opposed to rod or fixed plug drawing, allows for infinite lengths of tubing to be drawn since no tooling needs to extend axially out of the tubing. Depending upon the pull forces and angles of taper, pulling a tube between a draw plug and die can increase or decrease the wall thickness of tubing. In some cases it is desirable to form internal ribs/protrusions into tubing by floating draw plug methods. Such ribs/protrusions create grooves that can guide fluid through the tubing. Axially aligned ribs/protrusions also facilitate the manufacturing of tube-inside-tube (double-wall) products. Such products can serve well as heat exchangers. But internally ribbed tubing can also serve well as single-wall heat exchangers. However, tubing with axially aligned ribs/protrusions do not necessarily provide the optimal flow-path for fluids. In some cases, it is ideal to have tubing with helical internal ribs, but forming internal helical ribs using drawings methods has been a challenge. To form internal helical ribs into tubing using a draw plug, the draw plug or tubing necessarily needs to rotate about the tubing's lengthwise axis. When drawing long lengths of tubing, it is not practical to rotate the tubing (e.g., if it's coming off of a coil spool). However, the friction created by the radial forces of draw forming tubing inhibits the rotation of any draw plug.

[0004] The present invention allows helically ribbed tubing to be formed efficiently by draw plugs.

SUMMARY OF THE INVENTION

[0005] The invention allows for internally helically ribbed tubing to be formed efficiently by draw plugs by rotationally disjoining the forming of the helical ribs from the primary radial necking of the tubing via a multi-part draw plug. With the invention, the frictional forces suspending the necking body of the draw plug upstream of the die do not prevent the rotation of the rib forming member.

[0006] In one aspect of the invention, a floating draw plug for shaping tube comprises a necking body and a rib forming member. The necking body has an axis and a trailing end portion. The trailing portion has a cross-section that is symmetric about the axis and that converges toward the axis as it extends downstream. The rib forming member comprises helical protrusions and helical grooves. The helical protrusions and the helical grooves are aligned with the axis. The rib forming member is connected to the necking body in a manner such that at least a portion of the helical protrusions and at least a portion of the helical grooves extend downstream of the trailing portion of the necking body and such that the rib forming member is free to rotate about the axis relative to the necking body.

[0007] In another aspect of the invention, a method of drawing tube forms internal helical protrusions in the tube. The method includes floating a draw plug inside the tube. The draw plug comprises a necking body and a rib forming member. The necking body has an axis and a trailing end portion. The trailing end portion has a cross-section that is symmetric about the axis and that converges toward the axis as it extends downstream. The rib forming member has helical protrusions and helical grooves. The helical protrusions and the helical grooves are aligned with the axis. The rib forming member is connected to the necking body in a manner such that at least a portion of the helical protrusions and at least a portion of the helical grooves extend downstream of the trailing portion of the necking body and such that the rib forming member is free to rotate about the axis relative to the necking body. The method further comprises pulling the tube through a die and radially between the draw plug and the die in a manner forming the internal helical protrusions into the tube.

[0008] Further features and advantages of the present invention, as well as the operation of the invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0009] Figure 1 depicts a side view of a preferred embodiment of a draw plug in accordance with the invention, with the leading portion being oriented toward the right and the trailing end portion being oriented toward the left.

[0010] Figure 2 depicts an exploded assembly view of the draw plug shown in Figure 1 .

[0011] Figure 3 depicts a perspective partial cut-away view of the draw plug in use.

[0012] Figure 4 depicts a side view of the partial cut-away view shown in Figure 3.

[0013] Reference numerals in the written specification and in the drawing figures indicate corresponding items.

DETAILED DESCRIPTION

[0014] A floating draw plug 10 in accordance with the invention is shown in Figures 1 -4. The floating draw plug 10 comprises a necking body 12 and a rib forming member 14. The necking body 12 has an axial trailing end portion 16, an intermediate portion 18, and a leading end portion 20 that is symmetric about the axis of the draw plug 10. The trailing end portion 16 having a cross-section that is symmetric about the axis and that converges toward the axis as it extends downstream. The intermediate portion 18 is cylindrical and aligned with the axis. The leading end portion 20 diverges from the axis as it extends downstream. The necking body 12 also has an axial through-hole 22 and a counter-sunk axial recess 24 at its trailing end. The axial recess 24 extends partially into the trailing end portion 16.

[0015] The rib forming member 14 comprises helical protrusions 26 and helical grooves 28. The helical protrusions 26 and helical grooves 28 preferably have a constant radius about the axis. Like the necking body 12, the rib forming member 14 also comprises an axial through-hole 30.

[0016] The rib forming member 14 is operatively connected to the necking body 12 via a bolt 32 having a head 34, a shaft 36, and a threaded end 38. The bolt 32 extends through the through-hole 22 of the necking body 12 and the through-hole of the rib forming member 14. Preferably, a pair of nuts 40 threaded onto the threaded end 38 of the bolt 32 to thereby secure the necking body 12 and rib forming member 14 together in a manner such that the necking body and rib forming member aren't highly compressed against each other. As such, the necking body 12 and rib forming member 14 can easily rotate relative to each other, but are tied axially. Of course there are numerous other ways to achieve the same.

[0017] In use, the draw plug 10 is inserted into an end of tubing 42 and positioned upstream of a die 44 as the tube is drawn downstream sandwiched between the draw plug and die. The die 44 has a through-hole 46 that has a frustoconical leading portion 48 and a cylindrical trailing portion 50. The leading portion 48 of the through-hole 46 of the die 44 converges as it extends

downstream in a manner preferably concentric to the trailing end portion 16 of the draw plug 10 and has an upstream entry diameter slightly larger than the original outside diameter of the tubing 42 being drawn. The diameter of the intermediate portion 18 of the draw plug 10 is just slightly less than the original inside diameter of the tubing 42. Thus, axial friction between the floating draw plug 10 and the tubing 42 forces the draw plug toward the fixed die 44 as the tubing is drawn through the die. The frustoconical leading portion 48 of the through-hole 46 of the die 44 necks the tubing 42 down as the tubing passes through the die. The cylindrical trailing portion 50 of the through-hole 46 of the die 44 is slightly larger in diameter than the helical protrusions 26 of the rib forming member 14, but nonetheless is small enough to radially compress the tubing 42 against the helical protrusions 26 and into the helical grooves 28 of the rib forming member, thereby deforming the internal surface of the tubing in a manner such that internal helical ribs 52 are formed in the tubing. As the helical ribs 52 are formed, the rib forming member 14 rotates relative to the necking body 12. This decouples the large circumferential frictional forces acting on the necking body 12 due to the radial compressive forces between the necking body and the frustoconical leading portion 48 of the die 44 from the rib forming member 14. Thus, it is not necessary for the necking body 12 to rotate as the helical ribs 52 are formed in the tubing 42. This greatly reduces to rotational resistance acting on the rib forming member 14 and thereby forms very uniform and clean internal helical ribs 52 into the tubing 42.

[0018] In view of the foregoing, it should be appreciated that the invention has several advantages over the prior art.

[0019] As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.

[0020] It should also be understood that when introducing elements of the present invention in the claims or in the above description of exemplary

embodiments of the invention, the terms "comprising," "including," and "having" are intended to be open-ended and mean that there may be additional elements other than the listed elements. Additionally, the term "portion" should be construed as meaning some or all of the item or element that it qualifies.

Moreover, use of identifiers such as first, second, and third should not be construed in a manner imposing any relative position or time sequence between limitations. Still further, the order in which the steps of any method claim that follows are presented should not be construed in a manner limiting the order in which such steps must be performed, unless such an order is inherent or explicit.