EP0099737A2

EP0099737A2 - Forming helical grooves in tubes

Info

Publication number: EP0099737A2
Application number: EP83304117A
Authority: EP
Inventors: Ronald Albert Pain
Original assignee: Heat Transfer Pty Ltd
Current assignee: Heat Transfer Pty Ltd
Priority date: 1982-07-15
Filing date: 1983-07-15
Publication date: 1984-02-01
Also published as: AU1690083A; EP0099737A3

Abstract

A method and apparatus for forming helical grooves (6) in the outer surface of stainless steel tubes (2). The technique utilizes a forming roller (16), which forms the groove and a shoe (22) follows in the groove which has just been formed a short distance behind the roller so as to eliminate buckling of the tube.

Description

This invention relates to a method and apparatus for forming helical grooves in the outer surfaces of metallic tubes. Such tubes are useful in heat exchangers of the type disclosed in Australian Patent No. 402788.
One technique for forming the helical grooves involves providing a die which is preferably stationary and arranging for the tube to be moved longitudinally through the die whilst simultaneously being rotated. The die includes a roller which is forced radially inwardly so as to engage and deform the outer surface of the tube so as to form the helical groove as the tube is drawn through the die. It is possible to support the interior surface of the tube by means of a mandrel but this is cumbersome when long tubes are to be grooved. Further,difficulties are encountered when welded tubes are used since frequently these have a weld bead remaining on their internal surface and this interferes with the mandrel. It is therefore usually most convenient to have the inner surface of the tube unsupported in the die.
The die includes a circular opening which is the same as the outer diameter of the tube so as to have a snug fit therewith, the circular opening supporting the tube during the deformation process. Whilst this technique is reasonably satisfactory, it makes the tube more difficult to pass through the die because of the snug fit. Further, problems may occur where the tube departs from its nominal outer diameter and thus can be too tight in the die or alternatively to slack in the die. In the latter case, there is a tendency for the tube to buckle just after having the groove formed therein, the buckled tube remaining plastically deformed and quite useless for use in a heat exchanger. It is thought that the tendency to buckle is related to the slackness in the die and also is more prone to occur when deeper grooves are impressed into the tube. The characteristics of the buckling are also thought to be related to the tube diameter and tube thickness, and generally speaking, the buckling tends to occur closer to the point of contact of the forming roller in smaller diameter tubes and further from the point of contact in larger diameter tubes.
An object of the present invention is to provide a new method and apparatus for forming helical grooves in tubes which substantially avoid the problem of buckling as indicated above.
According to the present invention there is provided a method of forming a helical groove on the outer surface of a tubular element, said method comprising thesteps of causing simultaneous axial and circumferential relative velocity between the tubular element and a forming roller, supporting in a die the outer surface only of the tubular element adjacent to the forming roller, and applying a generally inwardly radial force to said tubular element in or adjacent to the groove formed therein at a predeteremined spacing from the roller.
The invention also provides apparatus for forming a helical groove in a tubular element, said apparatus comprising a die having a forming roller and a support for supporting the outer periphery of the tubular element, said apparatus including means for causing simultaneous, axial and circumferential relative velocity between the die and the roller whereby the forming roller depresses a helical groove into the outer surface of the tubular element as it passes through the die, said apparatus being characterized by the provision of a force applying member which applies a force having radially inwardly directed components relative to the tubular element, said force being applied in or adjacent to said groove at a predetermined spacing from the forming roller.
The invention will now be further described with reference to the accompanying drawings, in which:

Figure 1 is a schematic plan view of a die for forming helical grooves in accordance with the invention,
Figure 2 is a cross-sectional view taken along the line 2-2, and
Figure 3 is a fragmentary sectional view taken along the line 3-3.

Figure 1 illustrates a stainless steel tube 2 passing through a forming die 4 for forming a helical groove 6 on the tube. In the preferred arrangement, the die 4 is stationary and the tube 2 is moved axially through the die whilst simultaneously being rotated. The mechanism for causing rotation and axial movement of the tube is not shown. It may however simply comprise an arrangement which is similar to a gear cutting lathe with the end of the tube being mounted in the chuck of the lathe, the chuck being rotated'and moved axially along the bed of the lathe.
The die comprises a supporting plate 8 which is stationary with respect to the bed (not shown) of the apparatus. A cylindrical tube support cylinder 10 is carried by the plate 8, the support cylinder 10 having an internal cylindrical surface 12 which snuggly engages the outer surface of the tube 2. The cylinder 10 includes an opening 14 which provides access for a forming roller 16 which bears against the outer surface of the tube 6. The roller 16 is carried by a yoke 18 the position of which is controlled by a pressure applying member 20 which may comprise the push rod of an hydraulic or pneumatic ram mounted on the plate 8. Alternatively, the member 20 may comprise the lower end of a screw threaded member which passes through a threaded nut affixed to the plate 8. As seen in Figure 1, the axis of the roller 16 is inclined relative to the axis of the tube 2 such that the axis of the roller is transverse to the direction of the groove 6 at the point of contact with the tube.
The arrangement described above has been found to perform satisfactorily with grooves up to a depth of 0.12 inches. Difficulties are, however, encountered when attempting to form deeper grooves or when the tubes 2 do not bear snuggly against the support surface 12. In such cases, it has been found that there is a tendency for the tube to buckle in the region of the groove which has just been formed by the roller 16. It has further been found that this problem can be substantially avoided altogether by applying a radial force to the tube in the region where buckling is most likely to occur. In particular, it has been found that very satisfactory results can be obtained by providing a force applying member 22 just behind the roller 16 so that it applies a force in the groove 6 which has just been formed. The force has substantial radial components relative to the tube 2 and will also have significant tangential components due to frictional contact with the tube. The member 22 may comprise a roller but best results have been obtained with the use of a hardened polished shoe having a lower surface 24 which is of complementary configuration to the profile of the groove 6, as best seen in Figure 3. The member 22 is preferably carried by an arm 6 which is pivotally mounted on a shaft 8 projecting from the plate 8. The pivotal axis of the arm 26 is parallel to the axis of rotation of the roller 16. The radially inwardly directed force transmitted via the shoe is determined by means of a force applying member 30 which is generally radially directed relative to the tube 2 and bears against the upper face of the arm 26. The member 30 may comprise the push rod of an hydraulic or pneumatic ram mounted on the support plate 8 or alternatively may comprise a purely mechanical member extending from the plate 8. The arrangement' is such that the circumferentially directed forces generated by the contact of the shoe with the tube are taken by the arm 26 so that these forces are not transmitted to the force applying member 30.
The spacing of the shoe relative to the roller 16 depends to some extent upon the diameter of the tube being grooved, the larger the tube, the bigger the spacing. Further, the optimum spacing depends also on the clearance between the outer surface of the tube and the inner surface 12 of the cylinder 10, the bigger the gap the further should be the spacing between the shoe and the roller. Still further, the spacing depends on the depth of the groove being formed, the deeper the groove, the larger the spacing between the shoe and the roller. It is preferred therefore that the apparatus be adjustable so as to give optimum results. It is thought however that the force applying member 22 should be spaced through between say 30° and 60° relative to the roller as seen axially of the tube (0.4445 to 0.508 cm).
A prototype of the invention has been tested and found to perform satisfactorily with groove depths of up to 0.175 to 0.200 inches.
Many modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A method of forming a helical groove (6) on the outer surface of a tubular element (2), said method comprising the steps of causing simultaneous axial and circumferential relative velocity between the tubular element and a forming roller (10), supporting in a die (4) the outer surface only of the tubular element adjacent to the forming roller, and applying a generally inwardly radial force to said tubular element in or adjacent to the groove formed therein at a predetermined spacing from the roller.

2. A method as claimed in claim 1 wherein the roller is forced radially inwardly relative to the tubular element by a fluid actuated ram (18) and wherein said inwardly directed fluid is applied by means of a shoe (22) which is forced radially inwardly by a fluid actuated ram (30).

3. A method as claimed in claim 1 or 2 wherein the inwardly directed force is applied between 30° and 60° downstream from the roller when viewed axially of the tubular element.

4. A method as claimed in claim 1, 2 or 3 wherein the tubular element comprises a stainless steel tube the outer diameter of which is in the range of 25 mm to 200 mm and the roller produces a groove depth in-the range 0.175 to 0.200 inches (0.4445 to 0.508 cm).

5. Apparatus for forming a helical groove (6) in a tubular element (2), said apparatus comprising a die (4) having a forming roller (16) and a support (10) for supporting the outer periphery of the tubular element, said apparatus including means for causing simultaneous, axial and circumferential relative velocity between the die and the roller whereby the forming roller depresses a helical groove into the outer surface of the tubular element as it passes through the die, said apparatus being characterized by the provision of a force applying member (22) which applies a force having radially inwardly directed components relative to the tubular element, said force being applied in or adjacent to said groove at a predetermined spacing from the forming roller.

6. Apparatus as claimed in claim 5 wherein the force applying member comprises a shoe having a surface (24) which in use is engaged in the groove formed in the tubular member by the roller, said surface being complementary to the profile of the groove.

7. Apparatus as claimed in claim 5 wherein the die includes a support plate (8) and a hollow cylindrical member (10) connected thereto, said cylindrical member having an opening (12) therethrough and through which the tubular member passes said cylindrical member having an opening (14) or openings in which the roller and force applying member are located so as to enable engagement with the outer surface of the tubular member.

8. Apparatus as claimed in claim 7 wherein the forming roller is mounted on a fluid actuated ram (18), the cylinder (20) of which is mounted on the support plate (8) and the shoe (22) is mounted on an arm (26) which is pivotally connected to the support plate.

9. Apparatus as claimed in claim 8 wherein the axis of rotation of the forming roller is off-set relative to the axial direction of the tubular element such that it maintains rolling contact with the tubular element as the latter moves axially and rotationally through the cylindrical member and wherein said arm is pivotally mounted relative to the support plate about an axis which is parallel to the rotation axis of the forming roller. to the axis of rotation of the roller 16. The radially inwardly directed force transmitted via the shoe is determined by means of a force applying member 30 which is generally radially directed relative to the tube-2 and bears against the upper face of the arm 26. The member 30 may comprise the push rod of an hydraulic or pneumatic ram mounted on the support plate 8 or alternatively may comprise a purely mechanical member extending from the plate 8. The arrangement is such that the circumferentially directed forces generated by the contact of the shoe with the tube are taken by the . arm 26 so that these forces are not transmitted to the force applying member 30.

The spacing of the shoe relative to the roller 16 depends to some extent upon the diameter of the tube being grooved, the larger the tube, the bigger the spacing. Further, the optimum spacing depends also on the clearance between the outer surface of the tube and the inner surface 12 of the cylinder 10, the bigger the gap the further should be the spacing between the shoe and the roller. Still further, the spacing depends on the depth of the groove being formed, the deeper the groove, the larger the spacing between the shoe and the roller. It is preferred therefore that the apparatus be adjustable so as to give optimum results. It is thought however that the force applying member 22 should be spaced through between say 30° and 60° relative to the roller as seen axially of the tube.

A prototype of the invention has been tested and found to perform satisfactorily with groove depths of up to 0.175 to 0.200 inches (0.4445 to 0.508 cm).

Many modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.