Title:
METHOD OF FORMING SPIRAL RIDGES ON THE INSIDE DIAMETER OF EXTERNALLY FINNED TUBE
United States Patent 3768291
Abstract:
Helical external fins and helical internal ridges are formed simultaneously on a tube by rolling the fins up out of the tube with inclined rotating discs, and pressing the tube onto a rotatable spirally or helically grooved portion of a multiple part internal pin.
US Patent References:
Method of forming internally ribbed tubes
Hill - December 1966 - 3292408
Process of producing seamless internally-ribbed tubes
Davis - August 1923 - 1465073
METHOD AND APPARATUS FOR MANUFACTURING FINNED PIPES
Luea - May 1971 - 3580026
Method of forming internally ribbed tubes
Hill - December 1966 - 3292408
Process of producing seamless internally-ribbed tubes
Davis - August 1923 - 1465073
METHOD AND APPARATUS FOR MANUFACTURING FINNED PIPES
Luea - May 1971 - 3580026
Application Number:
05/224095
Publication Date:
10/30/1973
Filing Date:
02/07/1972
View Patent Images:
Export Citation:
Assignee:
Universal, Oil Products (Des Plaines, IL)
Primary Class:
Other Classes:
165/179, 72/96, 165/133, 72/98
International Classes:
B21C37/20; F28F1/42; B21C37/15; F28F1/10; B21H3/12
Field of Search:
72/78,96,97,98,100,209,370
Primary Examiner:
Larson, Lowell A.
Claims:
What I claim as my invention is
1. Apparatus for simultaneously forming external helical fins and internal helical ridges which comprises means for supporting a tube for axial advance including internal tube support structure having a first part provided with a smooth cylindrical exterior surface and a second part provided with a helically grooved exterior surface, means for retaining said tube support structure at a fixed rolling zone longitudinally of the tube through which the tube advances, a plurality of circumferentially spaced fin rolling tools at said zone, each of said tools comprising a plurality of axially spaced groups of fin rolling discs, means supporting said tools for rotation with their axes crossed in space with respect to the tube axis, means supporting said first part of the tube support structure within the tube in registration with a first one of said groups of discs of said tools and supporting said second part of the tube support structure within the tube in registration with a second one of said group of discs of said tools positioned to act on the tube subsequent to the action thereon of said first one group of discs, means for effecting relative motion between said tools and tube equivalent to revolving said tools about the axis of the tube at said rolling zone and rotating said groups of discs about their own axes whereby to advance the tube through the rolling zone, and means providing for relative rotation between said first and second parts of said tube support structure.
2. Apparatus as defined in claim 1 in which said internal tube support structure comprises a mandrel, and said second part of said tube support structure comprises an externally grooved sleeve rotatably supported on said mandrel.
3. Apparatus as defined in claim 2 in which said first part of said tube support structure comprises a sleeve having a smooth cylindrical surface rotatably supported on said mandrel for rotation independent of said second part of said tube support structure.
4. Apparatus as defined in claim 3 in which the means for retaining the tube support structure at said fixed rolling zone comprises means providing for rotation of said mandrel about its axis.
5. Apparatus as defined in claim 2 in which said first part of said tube support structure comprises an integral part of said mandrel, and in which the means for retaining the tube support structure at said fixed rolling zone comprises means providing for rotation of said mandrel about its axis.
6. Apparatus for simultaneously forming external helical fins and internal helical ridges on a tube comprising a plurality of fin forming tools positioned circumferentially around a tube at a rolling zone, a tube support member within the tube at said rolling zone, means supporting said tube support member at said zone against axial movement and for rotation relative to the tube, said tube support member having helical grooves in its exterior surface into which said tools press material of the tube incident to the pressure applied to the tube in the fin forming operation, said grooves in normal cross-section having side walls which are essentially straight throughout their major width, the included angle between the side walls of said grooves being obtuse.
7. Apparatus as defined in claim 6 in which the included angle between the side walls of said grooves is between 90°-120°.
8. Apparatus as defined in claim 6 in which the side wall of said groove facing in the direction from which the tube advances over the tube support member intersects the plane tangent to the tube support member thereat at a larger angle than does the opposite side wall.
9. Apparatus as defined in claim 6 in which said member is provided with grooves which extend therein at a helix angle in excess of 30°, an angle measured between the tube axis and a tangent to the helix curve.
10. Apparatus as defined in claim 6 in which the tube support member is formed of a hard, wear-resistant material such as tungsten carbide.
1. Apparatus for simultaneously forming external helical fins and internal helical ridges which comprises means for supporting a tube for axial advance including internal tube support structure having a first part provided with a smooth cylindrical exterior surface and a second part provided with a helically grooved exterior surface, means for retaining said tube support structure at a fixed rolling zone longitudinally of the tube through which the tube advances, a plurality of circumferentially spaced fin rolling tools at said zone, each of said tools comprising a plurality of axially spaced groups of fin rolling discs, means supporting said tools for rotation with their axes crossed in space with respect to the tube axis, means supporting said first part of the tube support structure within the tube in registration with a first one of said groups of discs of said tools and supporting said second part of the tube support structure within the tube in registration with a second one of said group of discs of said tools positioned to act on the tube subsequent to the action thereon of said first one group of discs, means for effecting relative motion between said tools and tube equivalent to revolving said tools about the axis of the tube at said rolling zone and rotating said groups of discs about their own axes whereby to advance the tube through the rolling zone, and means providing for relative rotation between said first and second parts of said tube support structure.
2. Apparatus as defined in claim 1 in which said internal tube support structure comprises a mandrel, and said second part of said tube support structure comprises an externally grooved sleeve rotatably supported on said mandrel.
3. Apparatus as defined in claim 2 in which said first part of said tube support structure comprises a sleeve having a smooth cylindrical surface rotatably supported on said mandrel for rotation independent of said second part of said tube support structure.
4. Apparatus as defined in claim 3 in which the means for retaining the tube support structure at said fixed rolling zone comprises means providing for rotation of said mandrel about its axis.
5. Apparatus as defined in claim 2 in which said first part of said tube support structure comprises an integral part of said mandrel, and in which the means for retaining the tube support structure at said fixed rolling zone comprises means providing for rotation of said mandrel about its axis.
6. Apparatus for simultaneously forming external helical fins and internal helical ridges on a tube comprising a plurality of fin forming tools positioned circumferentially around a tube at a rolling zone, a tube support member within the tube at said rolling zone, means supporting said tube support member at said zone against axial movement and for rotation relative to the tube, said tube support member having helical grooves in its exterior surface into which said tools press material of the tube incident to the pressure applied to the tube in the fin forming operation, said grooves in normal cross-section having side walls which are essentially straight throughout their major width, the included angle between the side walls of said grooves being obtuse.
7. Apparatus as defined in claim 6 in which the included angle between the side walls of said grooves is between 90°-120°.
8. Apparatus as defined in claim 6 in which the side wall of said groove facing in the direction from which the tube advances over the tube support member intersects the plane tangent to the tube support member thereat at a larger angle than does the opposite side wall.
9. Apparatus as defined in claim 6 in which said member is provided with grooves which extend therein at a helix angle in excess of 30°, an angle measured between the tube axis and a tangent to the helix curve.
10. Apparatus as defined in claim 6 in which the tube support member is formed of a hard, wear-resistant material such as tungsten carbide.
Description:
BRIEF SUMMARY OF THE INVENTION
It has heretofore been suggested that external helical fins and internal helical ridges may be provided simultaneously on a metal tube by rolling the tube with external finforming discs on an internally positioned externally helically grooved mandrel or pin. Australian Pat. No. 111,528 to Lenk makes such a disclosure.
However, it has been found that certain changes in apparatus as suggested in the prior art are necessary, particularly where the internal ridges are provided with multiple-starts and have a high helix angle or short lead, and internal ridges must be dimensionally controlled.
Specifically, the internal support structure which has the additional function of forming the internal helical ridges must be formed of a plurality of relatively rotatable members.
Where the fin-forming discs are arranged in a plurality of axially spaced groups, the internal pins, which may in fact be sleeves supported for rotation on a mandrel, may be positioned to cooperate with a selected one or more of the groups of discs.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged elevational view, partly in section of an internally ribbed externally finned tube of the present invention.
FIG. 2 is an elevational view showing the apparatus for forming the tube of FIG. 1.
FIG. 3 is a greatly enlarged fragmentary sectional view showing the engagement between tube, discs, and mandrel pins.
FIG. 4 is an enlarged elevational view at the dotted circle 4 of FIG. 2.
FIG. 5 is a view similar to FIG. 4, showing a modified construction.
FIG. 6 is a view similar to FIG. 2 showing a different embodiment of the invention.
FIG. 7 is an enlarged sectional view on line 7--7, FIG. 3.
DETAILED DESCRIPTION
The present invention relates to the production of an externally finned tube 10, as seen in FIG. 1, in which helical external fins 12 are provided, and in which the interior of the tube is provided with helical ridge convolutions 14.
In accordance with the present invention, the internal ridges may extend at substantially any required helix angle and may be single or multiple start as necessary to provide the desired fluid flow conditions in the tube.
The formation of the internal ridge convolutions is produced by the action of fin-forming roll assemblies, one of which is indicated generally at 16 in FIG. 2. Usually, three such rolls are provided, spaced uniformly around the axis of the advancing plain tube. The rolls comprise, as illustrated herein, axially separated groups 18, 20 and 22 of discs, the individual discs being indicated at 24. The discs of each group are of the same thickness, and are assembled in tightly abutting relation on an arbor 26. Due to tube elongation during rolling, the discs of successively acting groups 20 and 22 are of slightly increased thickness. The groups 18, 20 and 22 are separated by spacers 28 and 30 and are clampled between washers 32 and flanges 34 on arbor 26 by nut 36.
In practice the rolls 16 may revolve about the axis of tube 18, while rotating on their own axes, or the tube may rotate. In any case the successively acting groups of discs, and the discs of each group are generally of increasing diameter and may be of like shapes or progressively changing shape so as to force the metal of the tube up into the helical fins 12 as seen in FIG. 1.
The support structure at the interior of the tube comprises a mandrel 40 which is held against longitudinal travel and may either rotate about its axis or be restrained against rotation. The mandrel has a reduced cylindrical end portion 42 on which are rotatably received hollow pins or sleeves, the first sleeve 44 having a smooth exterior surface, and the second sleeve 46 having one or more helical grooves 48. The sleeves are retained on the reduced portion of the mandrel by nut 50 threaded to the end of the mandrel.
As most clearly seen in enlarged FIG. 3, the inner surface of the tube beneath the groups 18 of discs is pressed into engagement with the smooth cylindrical surface, as indicated at 52. The formation of fins by the action of the discs not only causes relative rotation between the but also and tube also causes positive axial advance of the tube. Accordingly, where the tube engages the smooth outer surface of the first sleeves 44, in the zone indicated at 52 in FIG. 3, the tube slides longitudinally to the right as seen in this Figure. If the tube is rotating about its axis at this zone, then sleeve 44 will rotate on mandrel rod 40, or the mandrel itself will rotate. The action of the first group 18 of discs is to form the incipient fins 54 without starting the formation of internal ridges which would be shaved off due to the elongation of tube between disc groups 18 and 20. Due to springback or resilience of the tube, clearance will exist between the interior surface of the tube and the sleeves 44, 46 as indicated at 56. However, the action of the second group 20 of discs will again press the tube into contact with the adjacent sleeve, which in this case is the sleeve 46, the zone of contact being seen in FIG. 3 at 58.
The action of the several groups 20 of discs is to further penetrate the tube material and reduce the width of the partially formed fins as indicated at 60. The pressure exerted by the groups 20 is sufficient to displace metal into the helical groove or grooves 48, as clearly seen at 62. Since the tube is continuously advanced axially by reason of the engagement between the inclined discs and the helical fins, and since the sleeves, including the helically grooved sleeve 46, is restrained against axial movement, the tube slides axially over the sleeve 46. However, since metal is displaced by the disc group 20 into the helical grooves 48, this relative axial movement must be accompanied by a relative rotation as determined by the sliding of the incipient ridge 62 along the helix of the groove 48.
As a result of the foregoing, the relative sliding between the tube and cylindrical sleeve 44 will be limited to an axial direction, the sleeve 44 rotating with the tube. However, the relative sliding between the tube and the grooved sleeve 46 will be limited by engagement between helical grooves 48 and ridges 62 to a helical direction. Therefore, relative rotation is required between sleeves 44 and 46.
It is further to be observed in FIG. 3 that due to springback, the inner surface of the tube again moves into clearance with respect to the cylindrical surface of sleeve 46, as indicated at 64, this clearance may be increased by increasing the diameter of sleeve 44, and is again pressed strongly against the sleeve beneath the disc group 22, where fins 66 are finished to full height, tube wall thickness reduced to its final dimension as indicated at 68, and ridges formed to their final shape as indicated at 70.
The exact shape of grooves 48 in cross-section transverse to the groove, as seen in FIG. 7, may vary for different materials, different helix angles, and different desired operations with particular fluids flowing through the tube. However, in general the grooves are relatively wide and shallow, having an obtuse included angle between the sides, preferably between 90° and 120°. Ordinarily, the sides of the groove, as seen in FIG. 7 are composed of straight line elements interconnected at the bottom of the groove by a small fillet. The sides 72,74 of the grooves 48 may be equally inclined as seen in FIG. 7. However, to provide the most effective turning force to the sleeve, the side of the groove facing the direction from which the tube moves (the side 72 in FIG. 7) will have a greater inclination than the opposite side. For example, with an included angle of 100°, the steeper angled side 72 may be inclined at an angle of 50° while the other side is inclined at an angle of 30° to the tangent plane 75. This provides a more effective thrust tending to rotate the sleeve 44.
In FIG. 4 there is an enlarged elevation showing the adjacent ends of sleeves 44 and 36. It will be noted that the end of sleeve 44 is beveled at 76 and the adjacent end of grooved sleeve 46 is similarly beveled as seen at 78.
In FIG. 5 there is shown an alternate construction in which the end of the smooth sleeve, here designated 44a is flat except for a rounded end corner 79 which has an extremely small radius in cross-section, as for example about 0.005 inch. The end of the grooved sleeve, here designated 46a, is chamfered as seen at 80, at an angle of about 30° as shown.
Referring now to FIG. 6 there is shown an arrangement in which the plain sleeve 82 extends to underlie both disc groups 18 and 20, while the grooved sleeve 84 is relatively short and underlies only the final forming disc group 22. Since sleeve 82 is smooth, the relative sliding movement between it and the tube is axial, while that between the grooved sleeve 84 and the tube is helical. Accordingly, there is relative rotation between sleeves 82 and 84, which is provided for by mounting them on the reduced portion 86 of the mandrel.
It is recognized that the tube rolling operation has the effect of elongating the tube and twisting it as the fin formation takes place. The use of separate relatively rotatable sleeves 44, 46 or 82,84 accommodates the twisting or average circumferential displacement of the portions of the tube pressed into engagement with the grooved sleeve with respect to the portions pressed into engagement with the smooth sleeve.
The forces tending to produce elongation of the tube may be opposed by the discs and sleeve grooves, so that actual elongation for the most part takes place only after the tube passes beyond the last disc of each group and the grooved sleeve. On the other hand, the inclination of the grooves 48 may be gradually varied to accommodate tube elongation, the lead of the groove being increased or its helix angle decreased for this purpose.
While the smooth sleeve 44 or 82 is shown as rotatable on a mandrel 40, it will be understood that where the mandrel is freely rotatable, it may include an enlarged pin portion integral therewith which will perform the function of plain sleeve 44 or 82, and that only the grooved sleeve 46 or 84 may be rotatably mounted thereon. It will also be understood that plain sleeves 44 or 82 may be of slightly larger diameter to permit additional metal forming (sinking) to provide sufficient material for the internal ridges.
The apparatus herein permits the formation of multiple start short pitch ridges internally of the tube. For a specific example a grooved sleeve producing a ridge formation of six ridges has a pitch (axial spacing between adjacent groove convolutions) of 0.387 inch and an outside diameter of 0.690 inch.
The present apparatus permits the production of internal ridges which extend at a greater helix angle than has heretofore been feasible, this meaning the angle measured between the axis of the tube and a line tangent to the helix curve. Moreover, it permits the production of tubing having multiple start ridges. By way of example ridges of satisfactory cross-sectional dimensions have been produced in tubing having an internal diameter of about 0.785 inch, with a helix angle in excess of 45°, and with a six-start pattern of helical ridges. In general, the apparatus makes production of multiple start ridges with helix angles in excess of 30° entirely satisfactory.
Preferably, the sleeves are formed of a hard wear-resistant material such as tungsten carbide.
It has heretofore been suggested that external helical fins and internal helical ridges may be provided simultaneously on a metal tube by rolling the tube with external finforming discs on an internally positioned externally helically grooved mandrel or pin. Australian Pat. No. 111,528 to Lenk makes such a disclosure.
However, it has been found that certain changes in apparatus as suggested in the prior art are necessary, particularly where the internal ridges are provided with multiple-starts and have a high helix angle or short lead, and internal ridges must be dimensionally controlled.
Specifically, the internal support structure which has the additional function of forming the internal helical ridges must be formed of a plurality of relatively rotatable members.
Where the fin-forming discs are arranged in a plurality of axially spaced groups, the internal pins, which may in fact be sleeves supported for rotation on a mandrel, may be positioned to cooperate with a selected one or more of the groups of discs.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged elevational view, partly in section of an internally ribbed externally finned tube of the present invention.
FIG. 2 is an elevational view showing the apparatus for forming the tube of FIG. 1.
FIG. 3 is a greatly enlarged fragmentary sectional view showing the engagement between tube, discs, and mandrel pins.
FIG. 4 is an enlarged elevational view at the dotted circle 4 of FIG. 2.
FIG. 5 is a view similar to FIG. 4, showing a modified construction.
FIG. 6 is a view similar to FIG. 2 showing a different embodiment of the invention.
FIG. 7 is an enlarged sectional view on line 7--7, FIG. 3.
DETAILED DESCRIPTION
The present invention relates to the production of an externally finned tube 10, as seen in FIG. 1, in which helical external fins 12 are provided, and in which the interior of the tube is provided with helical ridge convolutions 14.
In accordance with the present invention, the internal ridges may extend at substantially any required helix angle and may be single or multiple start as necessary to provide the desired fluid flow conditions in the tube.
The formation of the internal ridge convolutions is produced by the action of fin-forming roll assemblies, one of which is indicated generally at 16 in FIG. 2. Usually, three such rolls are provided, spaced uniformly around the axis of the advancing plain tube. The rolls comprise, as illustrated herein, axially separated groups 18, 20 and 22 of discs, the individual discs being indicated at 24. The discs of each group are of the same thickness, and are assembled in tightly abutting relation on an arbor 26. Due to tube elongation during rolling, the discs of successively acting groups 20 and 22 are of slightly increased thickness. The groups 18, 20 and 22 are separated by spacers 28 and 30 and are clampled between washers 32 and flanges 34 on arbor 26 by nut 36.
In practice the rolls 16 may revolve about the axis of tube 18, while rotating on their own axes, or the tube may rotate. In any case the successively acting groups of discs, and the discs of each group are generally of increasing diameter and may be of like shapes or progressively changing shape so as to force the metal of the tube up into the helical fins 12 as seen in FIG. 1.
The support structure at the interior of the tube comprises a mandrel 40 which is held against longitudinal travel and may either rotate about its axis or be restrained against rotation. The mandrel has a reduced cylindrical end portion 42 on which are rotatably received hollow pins or sleeves, the first sleeve 44 having a smooth exterior surface, and the second sleeve 46 having one or more helical grooves 48. The sleeves are retained on the reduced portion of the mandrel by nut 50 threaded to the end of the mandrel.
As most clearly seen in enlarged FIG. 3, the inner surface of the tube beneath the groups 18 of discs is pressed into engagement with the smooth cylindrical surface, as indicated at 52. The formation of fins by the action of the discs not only causes relative rotation between the but also and tube also causes positive axial advance of the tube. Accordingly, where the tube engages the smooth outer surface of the first sleeves 44, in the zone indicated at 52 in FIG. 3, the tube slides longitudinally to the right as seen in this Figure. If the tube is rotating about its axis at this zone, then sleeve 44 will rotate on mandrel rod 40, or the mandrel itself will rotate. The action of the first group 18 of discs is to form the incipient fins 54 without starting the formation of internal ridges which would be shaved off due to the elongation of tube between disc groups 18 and 20. Due to springback or resilience of the tube, clearance will exist between the interior surface of the tube and the sleeves 44, 46 as indicated at 56. However, the action of the second group 20 of discs will again press the tube into contact with the adjacent sleeve, which in this case is the sleeve 46, the zone of contact being seen in FIG. 3 at 58.
The action of the several groups 20 of discs is to further penetrate the tube material and reduce the width of the partially formed fins as indicated at 60. The pressure exerted by the groups 20 is sufficient to displace metal into the helical groove or grooves 48, as clearly seen at 62. Since the tube is continuously advanced axially by reason of the engagement between the inclined discs and the helical fins, and since the sleeves, including the helically grooved sleeve 46, is restrained against axial movement, the tube slides axially over the sleeve 46. However, since metal is displaced by the disc group 20 into the helical grooves 48, this relative axial movement must be accompanied by a relative rotation as determined by the sliding of the incipient ridge 62 along the helix of the groove 48.
As a result of the foregoing, the relative sliding between the tube and cylindrical sleeve 44 will be limited to an axial direction, the sleeve 44 rotating with the tube. However, the relative sliding between the tube and the grooved sleeve 46 will be limited by engagement between helical grooves 48 and ridges 62 to a helical direction. Therefore, relative rotation is required between sleeves 44 and 46.
It is further to be observed in FIG. 3 that due to springback, the inner surface of the tube again moves into clearance with respect to the cylindrical surface of sleeve 46, as indicated at 64, this clearance may be increased by increasing the diameter of sleeve 44, and is again pressed strongly against the sleeve beneath the disc group 22, where fins 66 are finished to full height, tube wall thickness reduced to its final dimension as indicated at 68, and ridges formed to their final shape as indicated at 70.
The exact shape of grooves 48 in cross-section transverse to the groove, as seen in FIG. 7, may vary for different materials, different helix angles, and different desired operations with particular fluids flowing through the tube. However, in general the grooves are relatively wide and shallow, having an obtuse included angle between the sides, preferably between 90° and 120°. Ordinarily, the sides of the groove, as seen in FIG. 7 are composed of straight line elements interconnected at the bottom of the groove by a small fillet. The sides 72,74 of the grooves 48 may be equally inclined as seen in FIG. 7. However, to provide the most effective turning force to the sleeve, the side of the groove facing the direction from which the tube moves (the side 72 in FIG. 7) will have a greater inclination than the opposite side. For example, with an included angle of 100°, the steeper angled side 72 may be inclined at an angle of 50° while the other side is inclined at an angle of 30° to the tangent plane 75. This provides a more effective thrust tending to rotate the sleeve 44.
In FIG. 4 there is an enlarged elevation showing the adjacent ends of sleeves 44 and 36. It will be noted that the end of sleeve 44 is beveled at 76 and the adjacent end of grooved sleeve 46 is similarly beveled as seen at 78.
In FIG. 5 there is shown an alternate construction in which the end of the smooth sleeve, here designated 44a is flat except for a rounded end corner 79 which has an extremely small radius in cross-section, as for example about 0.005 inch. The end of the grooved sleeve, here designated 46a, is chamfered as seen at 80, at an angle of about 30° as shown.
Referring now to FIG. 6 there is shown an arrangement in which the plain sleeve 82 extends to underlie both disc groups 18 and 20, while the grooved sleeve 84 is relatively short and underlies only the final forming disc group 22. Since sleeve 82 is smooth, the relative sliding movement between it and the tube is axial, while that between the grooved sleeve 84 and the tube is helical. Accordingly, there is relative rotation between sleeves 82 and 84, which is provided for by mounting them on the reduced portion 86 of the mandrel.
It is recognized that the tube rolling operation has the effect of elongating the tube and twisting it as the fin formation takes place. The use of separate relatively rotatable sleeves 44, 46 or 82,84 accommodates the twisting or average circumferential displacement of the portions of the tube pressed into engagement with the grooved sleeve with respect to the portions pressed into engagement with the smooth sleeve.
The forces tending to produce elongation of the tube may be opposed by the discs and sleeve grooves, so that actual elongation for the most part takes place only after the tube passes beyond the last disc of each group and the grooved sleeve. On the other hand, the inclination of the grooves 48 may be gradually varied to accommodate tube elongation, the lead of the groove being increased or its helix angle decreased for this purpose.
While the smooth sleeve 44 or 82 is shown as rotatable on a mandrel 40, it will be understood that where the mandrel is freely rotatable, it may include an enlarged pin portion integral therewith which will perform the function of plain sleeve 44 or 82, and that only the grooved sleeve 46 or 84 may be rotatably mounted thereon. It will also be understood that plain sleeves 44 or 82 may be of slightly larger diameter to permit additional metal forming (sinking) to provide sufficient material for the internal ridges.
The apparatus herein permits the formation of multiple start short pitch ridges internally of the tube. For a specific example a grooved sleeve producing a ridge formation of six ridges has a pitch (axial spacing between adjacent groove convolutions) of 0.387 inch and an outside diameter of 0.690 inch.
The present apparatus permits the production of internal ridges which extend at a greater helix angle than has heretofore been feasible, this meaning the angle measured between the axis of the tube and a line tangent to the helix curve. Moreover, it permits the production of tubing having multiple start ridges. By way of example ridges of satisfactory cross-sectional dimensions have been produced in tubing having an internal diameter of about 0.785 inch, with a helix angle in excess of 45°, and with a six-start pattern of helical ridges. In general, the apparatus makes production of multiple start ridges with helix angles in excess of 30° entirely satisfactory.
Preferably, the sleeves are formed of a hard wear-resistant material such as tungsten carbide.