U.S. patent number 3,630,058 [Application Number 05/006,184] was granted by the patent office on 1971-12-28 for process and apparatus for forming tubes with spiral corrugations.
Invention is credited to Marshall H. Hickey, Vilmer H. Kiplinger, Roy E. Reed, Jr., deceased.
United States Patent |
3,630,058 |
Kiplinger , et al. |
December 28, 1971 |
PROCESS AND APPARATUS FOR FORMING TUBES WITH SPIRAL
CORRUGATIONS
Abstract
A spirally corrugated heat exchange tube is formed from a
smooth-walled tube. The smooth-walled tube is drawn over a rotating
mandrel between spirally fluted rotary dies. As the tube rotates
with the mandrel, the newly corrugated portion is drawn away from
the mandrel and dies, and a smooth-walled portion is advanced,
forming continuous spiral corrugations along the length of the
tube.
Inventors: |
Kiplinger; Vilmer H. (Concord,
TN), Hickey; Marshall H. (Knoxville, TN), Reed, Jr.,
deceased; Roy E. (late of Concord, TN) |
Assignee: |
|
Family
ID: |
21719698 |
Appl.
No.: |
05/006,184 |
Filed: |
January 27, 1970 |
Current U.S.
Class: |
72/96;
72/100 |
Current CPC
Class: |
B21C
3/08 (20130101); B21C 37/207 (20130101) |
Current International
Class: |
B21C
3/08 (20060101); B21C 3/00 (20060101); B21C
37/20 (20060101); B21C 37/15 (20060101); B21d
015/04 () |
Field of
Search: |
;72/77,95,96,97,105,106,208,209,370 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Larson; Lowell A.
Claims
What is claimed is:
1. A method for corrugating a malleable tube comprising the steps
of:
inserting a fluted, cylindrical mandrel into the tube with the
longitudinal axes of the mandrel and tube parallel and
substantially colinear the mandrel being short in relation to the
length of the tube, and having a maximum diameter closely
approximating the internal bore diameter of the tube,
rotating the fluted mandrel about its longitudinal axis while
laterally pressing one or more complementarily fluted rotary dies
against the exterior surface of the tube in the longitudinal
position occupied by the fluted mandrel, so that corrugations are
formed on a short length of the tube,
applying force distinct from that exerted by the mandrel and fluted
dies to progressively move the tube longitudinally over the
mandrel, while simultaneously allowing the tube to rotate with the
mandrel and one or more fluted dies, so that corrugations are
formed on a length of the tube longer than the length of the
mandrel.
2. A method, as claimed in claim 1, for corrugating a malleable
tube by employing a spirally fluted mandrel for forming spiral
corrugations, in which the step of moving further comprises:
applying force independent of the mandrel and fluted dies to
progressively move the tube longitudinally over the mandrel, while
simultaneously allowing the tube to rotate both with, and relative
to the mandrel, so that spiral corrugations are formed on a length
of the tube longer than the length of the mandrel.
3. A method, as claimed in claim 2, for corrugating a malleable
tube, in which the step of moving further comprises:
pulling the tube across the mandrel.
4. A method, as claimed in claim 2, for corrugating a malleable
tube, in which the step of moving further comprises:
pushing the tube across the mandrel.
5. An apparatus for corrugating a malleable tube comprising:
a fluted, cylindrical mandrel, having a relatively short length in
relation to the length of the tube, and a maximum diameter closely
approximating the internal bore diameter of the tube,
an arbor, having a smaller diameter than the mandrel, joined to the
mandrel at one end, with the longitudinal axes of the mandrel and
arbor parallel and substantially colinear,
means for rotating the tube, mandrel and arbor about their
substantially colinear longitudinal axis,
one or more fluted rotary dies positioned adjacent to the mandrel
for synchronous rotation with the mandrel about an axis parallel to
the colinear longitudinal axis as the mandrel rotates with the wall
of the tube sandwiched between the mandrel and the one or more
dies, the flutes on both the mandrel and the one or more dies
having complementary shapes for forming corrugations on the tube,
and
means distinct from the mandrel and rotary dies for progressively
moving the tube across the mandrel, while simultaneously allowing
free rotation of the tube with the mandrel and die.
6. An apparatus, as claimed in claim 5, for corrugating a malleable
tube in which:
the fluted, cylindrical mandrel and the one or more fluted rotary
dies have complementarily shaped spiral flutes for spirally
corrugating the tube.
7. An apparatus, as claimed in claim 5, for corrugating a malleable
tube in which the means for progressively moving the tube across
the mandrel includes:
a thrust bearing
means rigidly connecting the tube to an internal race of the thrust
bearing for free rotation with the internal race, and
means acting upon an external race of the thrust bearing for moving
the bearing and tube in a direction parallel to the longitudinal
axis of the tube,
whereby the tube is free to rotate about the longitudinal axis as
it is moved in a direction parallel to the longitudinal axis.
8. An apparatus, as claimed in claim 6, for corrugating a malleable
tube in which the means for simultaneously moving the tube across
the mandrel includes:
a thrust bearing,
means rigidly connecting the tube to an internal race of the thrust
bearing for free rotation with the internal race, and
means acting upon an external race of the thrust bearing for moving
the bearing and tube in a direction parallel to the longitudinal
axis of the tube,
whereby the tube is free to rotate about the longitudinal axis as
it is moved in a direction parallel to the longitudinal axis.
9. An apparatus, as claimed in claim 6, in which:
the means for progressively moving the tube includes an opening of
sufficient diameter in alignment with the axis of rotation of the
arbor and tube, so that the means for progressively moving is able
to draw the tube over the arbor as the tube is moved in the
direction parallel to the longitudinal axis.
10. An apparatus, as claimed in 7, in which:
the means for progressively moving the tube includes an opening of
sufficient diameter in alignment with the axis of rotation of the
arbor and tube, so that the means for progressively moving is able
to draw the tube over the arbor as the tube is moved in the
direction parallel to the longitudinal axis
11. An apparatus, as claimed in claim 8, in which:
the means for progressively moving the tube includes an opening of
sufficient diameter in alignment with the axis of rotation of the
arbor and tube, so that the means for progressively moving is able
to draw the tube over the arbor as the tube is moved in the
direction parallel to the longitudinal axis.
Description
BACKGROUND OF THE INVENTION
Corrugated heat exchange tubes are in general use for promoting
heat transfer in fluid evaporation and condensation systems. Linear
corrugations, aligned with the longitudinal tube axis, are
typically employed on these tubes. Circular and spiral
corrugations, having more desirable operating characteristics for
some applications, are also employed where their increased cost is
warranted. Spiral corrugations are particularly desirable because
of their comparatively high strength for a given wall thickness,
and for the spiral pattern of fluid flow resulting on their outer
surfaces. Prior to this invention, however, the difficulty and cost
of fabricating spirally corrugated heat exchange tubes has impeded
their general acceptance.
Prior techniques for fabricating longitudinally corrugated tubes
are generally unsuitable for fabricating spirally corrugated tubes.
One prior method shown by H. A. Greis et al. in U.S. Pat. No.
3,407,638 employs a fluted mandrel inserted within a smooth-bored
tube. The mandrel occupies the entire length of the tube on which
corrugations are formed. Rotating fluted dies press the tube wall
inward between the mandrel flutes, forming longitudinal
corrugations. The tube is removed after corrugation by sliding it
over the mandrel. It is apparent that with spiral corrugations on
the tube, this final step of separating the mandrel and tube is
difficult, if not impossible. In addition, the difficulty and
expense of fabricating a full-length spirally fluted mandrel
preclude the economic use of Greis et al. process for forming
spirally corrugated tubes.
A method and apparatus using a relatively short spiral mandrel for
spirally corrugating a malleable tube is shown in U.S. Pat. No.
2,757,706, issued to J. M. Johnston. In the Johnston process the
tube is held against rotation as a spiral mandrel rotates within
the bore of the tube and fluted dies rotate around the outer wall.
For holding the tube against rotation, as required by the Johnston
process, the tube sidewalls are deformed from a circular to a
square cross section prior to corrugation. The process and
apparatus are not only inordinately complex, but also are
potentially damaging to the tube when the sidewalls are
deformed.
Magneforming is another method available in the prior art for
forming spirally corrugated tubes. For Magneforming spiral
corrugations, a spirally fluted mandrel is inserted within a
smooth-walled tube. Eddy-currents are electrically induced in the
tube, creating forces which draw the tube into close conformity
with the spiral flutes on the mandrel. In many instances a
Magneforming process of this type is unsuitable for forming spiral
corrugations because the process is primarily restricted to metals
of low resistivity such as copper and aluminum, and to tubes having
a relatively thin-wall dimension. This invention was made in order
to overcome these deficiencies of the prior art.
SUMMARY OF THE INVENTION
This invention is a process and apparatus for forming spiral
corrugations on smooth-walled heat exchange tubes. To form the
corrugations, a short, spirally fluted mandrel is inserted within a
tube and positioned between a pair of spirally fluted rotary dies,
so that the tube is sandwiched between the mandrel and dies. While
the mandrel is rotated, pressure is exerted on the rotary dies to
deform the tube inward around the teeth of the mandrel. As the
mandrel, tube, and dies rotate in synchronism, a ring of spiral
corrugations is formed on the tube.
The length of the spiral corrugations formed as the tube rotates is
governed by the length of the mandrel and dies. Because the mandrel
must be removed from the tube when corrugation is completed, the
mandrel is just long enough to function properly, without binding
rigidly within the tube. Long spiral corrugations along the length
of the tubes are ultimately formed by drawing the tube between the
dies and mandrel as they rotate. When the corrugating process is
completed, the mandrel which has already passed through a
substantial portion of the tube is easily removed.
Therefore, one object of this invention is a process for forming a
spirally corrugated tube by drawing a smooth-walled tube over a
longitudinally fixed mandrel as the tube and mandrel rotate
together.
Another object of this invention is a tube-drawing engine for
forming a spirally corrugated tube by drawing a smooth-walled tube
over a longitudinally fixed mandrel as the tube and mandrel rotate
together.
These and other objects of the invention are described in greater
detail in the following specification and drawing.
BRIEF DESCRIPTION OF THE DRAWING
The sole FIGURE is a plan view of a tube-forming engine, showing a
partially corrugated tube in operating position.
DESCRIPTION OF THE PREFERRED EMBODIMENT
On the tube-forming engine 10 shown in the sole figure, a spirally
fluted, cylindrical mandrel 12 rotates between a horizontally
aligned pair of spirally fluted rotary dies 14. The mandrel 12
extends with a sliding fit into the smooth bore of a malleable
tube, or workpiece 16, which is operated upon by the tube-forming
engine 10 to form a spirally corrugated tube. The fluted dies 14
abut two diametrically opposite exterior areas of the tube wall,
sandwiching the tube 16 between the mandrel 12 and a die on each
side. When the dies 14 press against the rotating mandrel with
sufficient pressure, teeth 18 on the dies effectively engage teeth
20 on the mandrel, through the intermediate tube wall, causing the
mandrel, tube, and dies to rotate synchronously. The mandrel teeth
20 are smaller than the teeth 18 on the dies 14 by an amount equal
to the wall-thickness of the tube, so that as the tube and mandrel
rotate between the dies, spiral corrugations are formed on a short
length of the tube. By rotating the tube in this way, and
simultaneously moving it across the rotating mandrel and dies,
longer spiral corrugations are formed along the length of the
tube.
Torque for rotating the spirally fluted mandrel 12 is supplied by a
spindly 24 of a lathe (not shown) through an intermediate arbor 26.
A standard collet 28 anchors the arbor 26 in axial alignment with
the spindle rotation axis and prevents any longitudinal
displacement of the arbor or mandrel 12.
Each fluted die 14 rotates freely on a concentric axle 30 within a
U-shaped frame 32. For radial movement of the die 14 relative to
the tube 16 a rectangular cross-sectioned shaft 34 at one end of
the frame 32 slides within a complementarily shaped rectangular
cavity in a fixed bearing block 36. The die is moved radially
relative to the tube 16, as indicated by double-ended arrows, by
turning a threaded portion 38 of a shaft 40 in a threaded hole
through the rectangular shaft 34. Radial shoulders 42 and 44 on the
shaft 40 abut opposite sides of a cavity end wall 46, preventing
longitudinal translation of the shaft as it rotates. When the shaft
is rotated in one direction by turning a handle 48, the die 14
advances toward the tube 16. When the shaft is rotated in the
opposite direction the die withdraws. In operation, with the
mandrel 12 turning and a tube 16 in position the opposing shafts 40
are turned simultaneously, applying uniform pressure in opposite
directions until the die and mandrel teeth seat with the tube
between them.
After the mandrel and die teeth have seated, forming a narrow
corrugated area on the tube 16, longitudinal force is applied to
continuously draw an unworked, smooth-walled portion of the tube
between the synchronously rotating mandrel and dies. For this
purpose a drawing arm 50 firmly grips the tube 16 for longitudinal
displacement, while allowing free axial rotation of the tube with
mandrel 12. The tube is gripped on the drawing arm 50 by a standard
collet 52, wedged against an internally tapered sleeve 54 at one
end, and screwed to a threaded sleeve 56 at the other end. Between
the threaded sleeve 56 and the tapered sleeve 54, the collet is
firmly anchored to the inner race 58 of a longitudinal thrust
bearing 60. The outer race 62 of the bearing 60 is anchored to a
carriage extension 64 for movement of the drawing arm 50 and tube
16 with the carriage (not shown) of the lathe upon which the
spindle 24 is mounted.
As the lathe spindle 24 turns, an automatic feed slowly draws the
carriage longitudinally along the lathe bed in either direction
shown by the double-ended arrow through the drawing arm 50.
Longitudinal force is transmitted from the lathe carriage to the
tube 16 through bearing balls 66, riding in concave circular
recesses in the inner and outer bearing races 58 and 62. While the
thrust bearing 60 transmits longitudinal force, the balls 66
simultaneously permit free relative rotation of the inner and outer
races, allowing the tube 16 to rotate with the mandrel 12 as it
passes over the arbor 26. Advancing through the dies 14, the tube
also rotates relative to the longitudinally fixed mandrel in
response to the spiral flutes which mesh them. Bearing blocks 68
support the tube 16 at convenient intervals, preventing damage or
distortion of the simultaneously translating and rotating tube.
Because the mandrel 12 contacts only a relatively small interior
surface area of the tube 16, a minimum amount of force effectively
draws the tube over the mandrel. As corrugating progresses the tube
moves across the mandrel, so that the mandrel remains meshed with
only a small portion of the tube when the corrugating process is
completed. In this way, the disadvantages or prior tube-forming
engines with mandrels extending through an entire tube, namely,
tight meshing between the mandrel and tube, and removal of the
entire mandrel only after corrugating is completed, are eliminated
by this invention without resort to the complex procedures and
apparatus adopted by the prior art.
While the preferred embodiment of the invention has been shown and
described, modifications within the scope of this disclosure are
expected for adapting the invention to diverse tube-forming
environments. The tube-forming engine need not include a lathe, as
other machines for performing a similar function are equally
suitable. Equivalent drawing arms 50 and thrust bearings 60 will be
apparent to the skilled worker in the art for performing the
function described, as will alternate apparatus for advancing the
fluted dies 14 toward and away from the tube 16. The arbor 26 need
not pass through the drawing arm 50 or the thrust bearing 60, since
the tube 16 can be originally positioned over the arbor and drawn
off in a direction away from the spindle 24 where a carriage with
sufficient travel is available. While a single pair of fluted
rotary dies have been shown, one or any number of dies can be used
equivalently. For these reasons, this invention should be limited
only by the scope of the following claims.
* * * * *