Note: Descriptions are shown in the official language in which they were submitted.
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FINNED HEAT_TRANSFER DEVICE_AND METHOD FOR MAKING SAME
Field of the_Invention
The present invention relates to an improved heat
transfer fin for a finned heat transfer device, and to an
improved process and apparatus for making and applying the same
to a tube.
Background of the Invention
In refrigeration and air conditioning applications it
is common to utilize a refrigerant-carrying tube as the means by
which heat is removed from a chamber or areas to be cooled, and
to flow air across the refrigerant-carrying tube to assist in
transferring heat to or from the tube wall as imparted by the
heat of vaporization or condensation of the refrigerant within
the tube. In the applications just mentioned, the refrigerant
carrying tubes usually constitute either a condenser or an
evaporator.
The refrigerant has a significantly greater ability to
transfer heat to the tube in which it is carried than does the
air which flows across its exterior. As a result, it is an
accepted practice in the refrigeration art to substantially
increase the surface area provided on the outside, or airside,
of the tube. Most often, the increased surface area is provided
in the form of some sort of extended cooling surface or fin
extending from the tube outer surface. Many types of finned
tubing are commercially available for use in refrigerant-to-air
heat exchangers (both evaporators and condensers). One type of
extended surface fin is that known as a "spine fin", as
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disclosed in my prior U.S. Patent 2,983,300. The spine fin has
a disadvantage in that it is mechanically weak and has a low
resistance to bending and compressive forces. Therefore, to
permit its practical utilization the spine fins are spaced very
closely on the refrigerant tube. Other types of extended
surface fins are disclosed or example in U.S. Patent No.
4,143,710, issued to LaPorte et al; these latter fins are
complex geometric shapes, which are difficult to fabricate and
have a higher degree of waste material in relation the heat
transfer capacity provided~
These prior art fins have been used successfully for
many years to increase the surface area of the air side of
refrigerant carrying tubes in home refrigerators and air
conditioning units, where the operating temperature of the air
lS flowing across the air side of the tube is above the freezing
point of water. However, they have not been so successful in
environments where the air temperatures are below freezing,
primarily for two reasons:
(l) because the moisture in the freezing air condenses
out and forms a ~frost bridge" between the closely spaced spine
fins or portions of the geometric fins, which materially
inhibits the air flow across and between the fins, and which in
turn reduces the heat transfer capability and
(2) if the fins are spaced far enough apart to prevent
this frost bridging, the resulting structure is mechanically
weak.
Objects and Summary of the Invention
The present invention provides a new form of fin
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structure which addresses the dual problems of frost bridging
and insufficient mechanical strength.
Accordingly, an object of the present invention is to
provide a fin structure which will minimize frost bridging and
which will function in an environment where the convection air
forced across the fins is below the freezing point of water,
while at the same time maintaining sufficient mechanical
strength to permit pragmatic utilization.
It is also an object of the present invention to
provide a method of manufacturing a chain of looped fins in
which the looped fin stock is applied to refrigerant-carrying
tube stock immediately after its formation, so as to minimize
the number of steps required in the manufacturing process.
It is a further object to provide an apparatus for
carrying out the method.
According to the present invention there is provided a
finned heat transfer device providing heat transfer to and from
a tube for containing a heat transfer fluid and comprising an
integrally formed chain of separate heat conductive fins wound
helically around said tube so that the fins extend generally
longitudinally of the tube, characterized in that:
the chain includes a pair of continuous mounting
flanges extending outwards along opposed edges of the chain;
the chain is wound in tension around the tube so that
the mounting flanges snugly engage the tube continuously
therealong in heat transferring relation therewith; and
each fin comprises two transversely spaced leg members
each extending outwardly from a respective mounting flange and
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connected at their outer ends by a bridge member of a minimum
dimension for inhibition of frost bridgingO
Also according to the invention there is provided a
method of making a finned heat transfer device providing heat
transfer to and from a tube for containing a heat transfer fluid
comprising the steps of:
(a) providing an elongate strip of thermally
conductive material;
and characterized byO
(b) transversely lancing said strip and forming it
into an intermediate configuration having a pair of imperforate
opposed side mounting flange portions interconnected by a lanced
web portion;
(c) stretch preforming said intermediate configuration
to reform the same into a subsequent configuration comprising an
integrally formed chain of a plurality of looped fins between
said mounting flanges, each of said fins comprising leg members
extending outwardly from each of said mounting flanges and a
bridge section connecting said leg members at the distal end of
said leg members; and
(d) helically winding said chain under tension onto
the exterior surface of a tube with the fins extending
longitudinàlly of the tube.
Further according to the invention there is provided
apparatus for making a finned heat transfer device, comprising,
in combination:
(a) means for feeding an elongate strip of thermally
conductive material;
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characterized by:
(b) means for transversely lancing said strip into an
intermediate configuration having a pair of imperforate opposed
side mounting portions interconnected by a lanced web portion;
(c) means for stretching and reforming said
intermediate configuration into a subsequent configuration
comprising ~n integrally formed chain of a plurality of looped
fins, said chain having a respective mounting flange formed from
each of said imperforate opposed side portions, and each of said
fins comprising two vertical leg members extending outwardly
from a respective one of said mounting flanges and a bridge
portion connecting said leg members to one another at the distal
end of said leg member;
(d) means for feeding a tube; and
(e) means for winding the said chain about the tube in
the form of a helix with the fins extending longitudinally of
the tube.
Description of the Drawings
Particular preferred embodiments of the invention will
now be described, by way of example, with reference to the
accompanying diagrammatic drawings, wherein:
FIGURE 1 is a schematic perspective view of a first
embodiment of apparatus of the invention for fabricating a
looped fin structure and mounting it on a cylindrical tube, and
also illustrates the corresponding method of the invention;
FIGURE 2 is a perspective view to a larger scale and
showing the stage at which the looped fin structure is mounted
on the tube;
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FIGURE 2A is a cross section on the line 2A-2A in
Figure 2;
FIGURE 2B is an end elevation of the assembled
structure of Figure 2;
FIGURE 3A is a cross section through the looped fin
structure of Figures 1 and 2, while Figures 3B through 3D are
similar cross sections illustrating alternative structures of
the invention;
FIGURE 4 is a plan view of lancing cutting work station
A of Figure 1, at whi-ch thin metal strip stock is lanced and
changed to channel form;
FIGURE 5 is a side elevation of the work station A;
FIGURE 6 is a perspective view of the lanced and
channel-formed thin metal strip after it emerges from work
station A;
FIGURE 7 is a plan view of combined stretch forming and
U-shape forming work station B of Figure l;
FIGURES 7C, 7D and 7E are cross sections on the lines
C-C, D-D and E-E of Figure 7 to show the progressive pre-forming
of the lanced stock in the work station B;
FIGURE 8 is a side elevation of the work station B;
FIGURE 9 is a perspective view of the "looped fin"
strip after it emerges from work station B;
FIGURE 10 is a perspective view of an alternative
apparatus for forming the U-shape corresponding to station B of
Figure 1, or station F of Figure 11, or station J of Figure 12;
FIGURE 11 is a perspective view of an alternative
apparatus of the invention, and also illustrates a corresponding
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alternative method of the invention;
FIGURE 12 is a perspective view of a further
alternative apparatus of the invention, and also illustrates a
further alternative method of the invention,
FIGURE 13 is a perspective view of the flat lanced thin
metal strip that emerges from station E of the apparatus of
Figure 11, or station H of the apparatus of Figure 12;
FIGURE 14a shows the preferred angular relation
(angle C~ ) between a line through the lance roll centers and
another line through the form roll centers;
FIGURE 14b shows the possible range of size of the
angle C~;
FIGURE 15 shows a transverse cross section of a loop
fin of the invention and the manner in which if moisture is
retained it is retained therein; and
FIGURE 16 shows a similar cross section o~ a prior art
fin structure and the manner in which moisture is retained
therein.
Description of the Preferred Embodiments
Referring particularly to Figure 1, the looped fin
chain 3 of the present invention is fabricated in a unitary
process employing apparatus that combines several work stations
which cooperate to produce and apply the formed looped fin chain
3 immediately to a tube 4. In this embodiment a coil 1 of thin
sheet metal 2 (fin stock), for example, aluminum of the 3003 or
1100 alloy type, is disposed horizontally around a series of
work stations A through D arranged generally vertically over a
table 15 and within the core of the coil 1, all of which rotate
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in the direc~ion shown by arrow 16 around the tube 4, which is
fed vertically longitudinally along its own axis at
approximately the center of the coil 1 in the direction shown by
arrow 5. An apparatus of this kind is described in U.S. Patent
No. 3,134,166 issued to Venables.
The stock 2 is drawn from the coil 1 by its engagement
between two lance cutter rolls 6 and 7 which comprise work
station A and which cooperate in their rotation to pull the fin
stock 2 therethrough. The equipment and processes for producing
a series of slits through a moving thin metal strip are
generally known, and in this embodiment the cutter rolls 6 and 7
are both equipped with radial cutting teeth 18 which intermesh
as the fin stock 2 is fed therebetween, as is shown in more
detail in Figure 5. The lance cutter 7 is equipped with flanges
of selected vertical dimension and constitutes a "female"
cutter, while the lance cutter 6 engages in the space between
the flanges and constitutes a "male" cutter. The width of the
fin stock 2 is greater than that of the lance cutters 6 and 7,
so that it is formed into a shallow lanced generally channel
shaped form shown in Figure 6, with the unlanced portions 8 and
9 of the fin stock extending perpendicularly to the lanced
central portion, which has a series of closely spaced transverse
fin preforms 10 formed therein by a series of parallel
transverse slits 11 produced by the intermeshing teeth 18.
The lanced and channeled fin stock is then drawn
between matched cooperating forming rolls 12 and 13 of selected
dimension located at work station B, which stretch preform and
final-U-form the fin preforms 10 to the required "looped fin"
configuration. ~s discussed in more detail below, stretch
preforming enables the lanced channel to be formed into the
required deep U-form in a single processiny step. This may be
compared, for example, with the process described in U S. Patent
No. 4,224,984, issued to Sharp K. K., in which multiple forming
steps are required to produce its shaped heat transfer fin.
The center line through the axes o~ the form rolls 12
and 13 of work station B is oriented at preselected angle ~ in
relation to the center line through the axes of lance cutters 6
and 7 of work station A, with the result that the lanced channel
2 is placed in tension as it is pulled around the male forming
roll 12 before being pulled through the interface of the two
forming rolls. By placing work station B at this preselected
angle in relation to work station A, and by operating the form
rolls 12 and 13 of work station B at a slightly higher
peripheral speed than the lance cutters 6 and 7 of station A,
tension is applied to the unlanced mounting flange tips 8 and 9
between the stations A and B, and this tension urges the
mounting flange tips to move toward each other in a direction to
be disposed parallel to the corresponding peripheral face of
form roll 12. This causes the stock to stretch and begin, prior
to the point of its tangentlal contact with form roll 12, to
form into a general U-shape which is finalized between the form
rolls 12 and 13. The stretch preforming function and U-forming
sequence is discussed in more detail below and is shown in
Figures 7 to 9, and particularly in the progressive Figures 7C,
7D and 7E.
As the U-shaped fin stock emerges from work station B
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the product is now in its final configuration as shown in Figure
9, namely an integrally formed chain of looped fins separated by
slits 11, each of which fins comprises a pair of generally
vertical leg members lOa and lOb connected by a bridge portion
lOc, and having relatively short mounting flanges 8 and 9
substantially parallel to the bridge portion lOc extending
perpendicularly from each vertical leg member. The integral
chain is then fed around guide roll 11 at work station C,
preparatory to being helically wound under tension around the
tube 4 at work station D in an inverted fashion, the base
flanges 8 and 9 of the looped fins being applied in contact with
the outer periphery 4a of the tube 4, the looped fins being
disposed generally longitudinally of the length of the tube, and
the bridge portions lOc of the looped fins being disposed
generally circumferentially and outwardly in relation to the
tube periphery 4a. As the chain 3 is wound on the tube the fins
separate from one another with a progressively increasing
circumferential spacing as the radial distance increases from
surface 4a of the tube. The chain is wound so that the
immediately adjacent portions of base flanges 8 and 9 of
successive turns butt as closely as possible tightly against one
another, so as to minimize the space between them. The tension
applied to the chain 3 as it is wound around the tube assures
adequate contact between the base flanges of the looped fin
stock and the outer periphery of the tube stock which promotes
mechanical contact providing a good heat transfer relationship
between the looped fin and the tube. Guide roll 11 is disposed
with its rotation axis at a selected angle ~ which permits the
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looped fin structure to approach the tube stock at the selected
helix angle ~. For example, the angle e is 19 when wrapping at
a pitch of 1 looped fin per centimetre (2 1/2 looped fins per
inch).
Referring now to Figures 2 and 3, in order to provide
the most resistance to frost bridgingr the looped fin chain 3 is
made to preselected dimensions and is helically wound around the
refrigerant tube 4 at a preselected pitch ox distance between
adjacent rows, so that the fins are spaced far enough apart in
all three directions, namely radially from the mounting flange
tips 8 and 9 to the bridge portion lOc, circumferentially
between the generally parallel vertical members lOa and lOb and
longitudinally between successive helical wraps (spaces 14 in
Figures 2 and 2A). For example, when 0.018 cm (0.007 inch)
thick aluminum strip 2 of 2.5 cm (1 inch) width is used for the
fin stock, the lancing of such stock with slits 11 that are 2 cm
(0.80 inch) long and spaced 0.076 cm (0.030 inch) apart results
in unlanced mounting flange tips 8 and 9 each of 0.25 cm (0.100
inch) width. The resultant fins are very narrow, and this close
spacing of the slits results in an increase in available
air-contacting area of about 20~ to 25%, because the height of
the vertical edges thus generated when the fins are formed is
added to the area of the top and bottom of the initial strip.
This may be contrasted with prior art methods in which metal is
removed during the forming process with consequent loss of
available air-contacting area. In this example, when such a
lanced channel is stretch preformed and worked into the final
looped fin chain configuration 3, the bridge portion lOc will be
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approximately 0.5 cm (0.200 inch) wide, while the vertical
members lOa and lOb will ea~ch be approximately 0.75 cm (0.300
inch) in length. In this example, the resultant element is to
be used for a domestic refrigerator or air conditioner and the
diameter of the tube 4 employed is 0.94 cm (0.375 inch), the
fins being wound at a pitch of 2 per cm (5 per inch). In
another example employed with the same size tube 4, but with the
fins wound at a pitch of 3 per cm (8 per inch), the length of
each flange 8 and 9 is 0.16 cm (0.0625 inch), the length of each
leg member is 0.95 cm (0.375 inch), while the bridge member
reduces to 0.32 cm (0.125 inch). The distance from the exterior
surface 4a of the tube to the outermost part of the bridge
member lOc can be characterized as about equal to the tube
diameter. The distance 14 (Figures 2 and 2A) between the
helical rows is generally controlled by the width to which the
mounting flange tips 8 and 9 have been formed, the pitch of the
rotation of fin stock 2 and the rate of longitudinal feed of the
tube stock 4 being arranged so that the tips 8 and 9 of adjacent
turns are contiguous to each other; the distance between
adjacent helical rows 14 will therefore be nominally double the
length of each connecting flange, namely 0~5 cm (0.200 inch) and
0.32 cm (0.125 inch) in these examples. These dimensions, which
are exemplary only, have been found effective to prevent frost
bridging with a refrigerant tube, while providing sufficient
mechanical strength to permit pragmatic industrial use.
Alternative materials for the fin stock are copper and steel.
In commercial practice a refrigerator or air
conditioner heat exchanger assembly will comprise a
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predetermined length of the pipe 4 having a corresponding length
of the chain 3 mounted thereon while straight and then bent to
the required shape. The tensioned chain is fastened to the pipe
at least at its two ends by any suitable means, such as
mechanical clamps, welding, or a suitable glue or cement. The
chain can also be retained under tension on the tube by
fastening the butting mounting flanges 8 and 9 to one another by
any of these means so as to prevent relative longitudinal
movement between them, at least at the two ends of the chain,
and perhaps also at intermediate points.
It is found that the lancing of the strip produces a
small stretch of the unlanced side portions 8 and 9, but to an
extent of less than about 0.5% of the strip length. A much
greater extension is produced during the stretch forming between
the form rolls 12 and 13, and the amount of tension that is
required usually is such as to produce an extension of about 1
to 2.5% in length of the flanges 8 and 9, usually in the range
2~ to 2.5~.
Another extension is produced by the wrapping tension
of the order of 1~ to 1.5% in length. The total extension
produced by the process must of course be within the yield limit
of the material, and for a hard aluminum (or alloy) this will be
about 4%, while for softer aluminum (or alloy) this will be of
the order of 5% to 6%. The extension produced by the lancing is
due to the spreading action of the cutting blades, irrespective
of their speed, and appropriate forming and wrapping tensions
may be maintained by adjusting the respective drive to feed out
the required s~aller length of lanced fin stock than would be
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required in the absence of tension, or by utilizing tension
sensing devices controlling variable speed mechanisms between
the lance cutter drive, the forming roll drive, and the tube
rotating drive.
It is preferred that the fin leg members lOa and lOb be
essentially parallel to each other as shown in Figure 3A to
provide optimum distance between fin members to minimize frost
bridging. The bridge portion lOc is optimum when it is
essentially flat and substantially parallel to the mounting
flange tips 8 and 9, again as shown in Figure 3A, but variations
to this optimum configuration can be tolerated with only slight
degradation in performance, as measured by resistance to frost
bridging promotion and resistance to deformation during
fabrication and application. For example, a slight radius lOr
at the intersections of portions lOa and lOb with portion lOc,
as shown in Figure 3A, will have only a slight effect in
reducing resistance to frost bridging. Extending that radius to
one half the distance between portions lOa and lOb to form an
arch shaped bridge section lOs, as shown in Figure 3B, will also
permit only slightly increased frost bridging. Fin members in
which the portions lOa, lOb and lOc merge smoothly with one
another to constitute a general semi-circle (not shown) would
also be effective in preventing frost bridging. When the looped
fins each comprise geometric shapes such as shown in Figures 3C
and 3D, of a dimension approaching that of fin pitch spacing 14,
the propensity to form frost bridging begins to increase. In
addition, geometric shapes such as shown in Figures 3C and 3D
offer less resistance to deformation. Decreasing the length of
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cross portion lOc as shown in Figures 3C and 15 decreases the
resistance to frost bridging, and when cross portion lOc is
reduced to zero to form an inverted V-shape as shown in Figure
16, which is the structure disclosed in U.S. Patent No.
4,184,544, issued to Ullmer, the resulting vertex tips provide a
nucleating site or focal point which promotes frost formation,
which in turn accelerates frost bridging, and shapes with such
highly reduced bridge portions lOc are accordingly not effective
in minimizing frost bridging. Decreasing the length of portion
lOc, for example as shown in Figure 3C by utilizing angular leg
portions lOd, and as shown Figure 3D by inclining the leg
portions lOa and lOb toward one another, results in shapes which
have a greater tendency to hold defrost water by surface energy
within the shortened dimension. The water is held in the form
of a meniscus 17, which shields the fin legs and bridge portion
and thereby reduces the effective fin surface area available for
effective heat transfer as shown by the cross-hatched area of
Figures 15 and 16. In practice the dimension of the bridge lOc,
or the equivalent dimension between the leg portions is
correlated with the fin pitch, or the number of turns per unit
length of tube. For refrigerator and air conditioning
applications the practical maximum is about 3 turns per cm
(about 8 turns per inch). Thus, with the particular examples
described, it is preferred that the approximate minimum
dimension of portion lOc to prevent such water meniscus
retention and frost bridging should not be reduced below 0.32 cm
(0.125 inch). Such dimensions, of course, are exemplary only.
Stretch preforming as employed in this invention is a
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novel process whereby the lanced channel produced ~rom the strip
2 is progressively formed into an approximate ~-shape in a
single forming step as the lanced channel progresses around the
circumference of male roll 12 in its approach to the tangent
contact point with female roll 13. Stretch preforming is
accomplished in this embodiment by providing the two rolls with
complementary shoulders 12s and 13s between which the flange
tips 8 and 9 pass and are gripped thereby, and by operating the
work station B form rolls 12 and 13 at approximately 1~ to 2.S%
higher peripheral speed than the rate at which the lanced
channel is fed out of the lance cutters 6 and 7 at work station
A. This tension acts to progressively bend the lanced center
strips 10 into a sufficiently preformed U-shape appropriate for
entering the intermesh of form rolls 12 and 13 where the final
U-shape is produced at their point of tangency. A distance C D
(Figure 8) between the centers of the form rolls 12 and 13 is
selected which provides sufficient contact friction of the rolls
to mounting flange tips 8 and 9 to provide sufficient tension in
preforming the U-shape, but which allows adequate slippage to
prevent exceeding the elastic limit of the selected fin material.
An alternative method of providing adequate frictional
drive without exceeding the elastic limit of the selected fin
material involves spring loading the bearing support of either
roll 12 or 13 to provide a floating or variable center distance
C D, such spring loading accommodating minor variations in the
thickness of the fin stock 2 and the imperforate unlanced
mounting flange tips 8 and 9. A second alternative to
accomplish the same result can be the provision of a slip clutch
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in the drive shaft of the drive to the form rolls 12 and 13.
Other methods generally known in the art could also be employed
to provide the needed tension and, if needed, slippage of the
generally U-shaped fin stock as it passes through form rolls 12
and 13.
Figure 10 shows an alternative arrangement of forming
rolls for employment at station B to provide final U-forming
after stretch preforming, in which the single female form roll
13 is replaced by two angular rolls 13a, 13b, which respectively
engage the side portions 10a and 10b, and back up roll 13c which
engages cross portion 10c and maintains it flat.
Reference to Figures 7 and 14a shows that, when the
angle C~ is approximately 90, stretch preforming of the lanced
channel is accomplished through an arc ~ of the circumference
of the forming roll 12, the preforming being substantially
completed at cross section E-E, before the actual intermesh
between the rolls. Where ~ is approximately 90, the stretch
preforming is accomplished through an arc ~ of approximately
85 when proper tension is maintained. The stretch preforming
of the lanced channel commences at a leading angle ~ (Figure
14a) prior to intersection of the lanced channel with a line 20
through the axis of forming roll 12 at cross section C-C, which
line 20 is parallel to a line 19 through the axes of lance
cutters 6 and 7. By the time the lanced channel has progressed
around male form roll 12 to point C-C, the imperforate unlanced
mounting flange tips 8 and 9 are already upwardly disposed, as
shown in Figure 7C. As the lanced channel continues to be
pulled around the forming roll 12 the flange tips 8 and 9 move
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continuously toward one another, as illustrated by sections D-D
and E-E, so that final forming of the lanced channel may be
accomplished by a single pass through the intermesh of rolls 12
and 13. In the preferred arrangement, as shown in Figure 14a,
when angle C~ is approximately 90, stretch preforming occurs
throughout an arc o ~ of between 80 and 90, preferably
approximately 85, and the corresponding leading angle ~ is
between 20 and 30, with a preferred value of approximately
25. Figure 14b shows that angle C~ may range from a minimum
60 to a maximum of at least 180 when the two lines are
parallel so as to accommodate work stations in other
arrangements besides that described above.
Alternative machinery arrangements for different
methods of making the looped ~in chain 3 of the present
invention are disclosed in Figures 11 and 12. In the apparatus
of Figure 11 both the rotational and the directional motions are
provided to the refrigerant tubing 4. In this apparatus and
with this method there are only two work stations, E and F,
before the looped fin 3 is helically applied to the tubing 4.
This provides more working or maintenance space between work
stations. The required helix approach angle 0 with respect to
the tubing 4, determined by the rotational and longitudinal feed
rate of tube 4, is provided by appropriate angular placement of
the stations E and F with respect to the plane of travel of the
tubing 4. It would also be possible to maintain all axes of
rotation in parallel orientation by adding an idler roll
oriented to the helix angle such as the idler roll 11 of station
C in the apparatus of Figure 1.
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LZ~2~
Another alternative apparatus and method oE making the
loop fin of the present invention is shown in Figure 12. In
this embodiment, a lance station ~ performs only the lancing
function and all final loop fin forming is performed at a
forming station J. Lance station H is similar to that described
earlier in relation to Figures 4 and 5 except that the flanges
have been removed from "female" lance cutter 7. Since the width
of the fin stock 2 is greater than the width of the lance
cutters 6 and 7, it emerges from lance station H as a flat
center lanced strip with fin preforms lOa, the imperforate
unlanced portions 8a and 9a extending on each side of the slits
11, as shown in Figure 13.
An idler roll 20 at station I is located in such a
manner as to guide the flat center lanced stock and cause it to
approach form roll 12 at the required approach angle ~ prior
to contact therewith. As the stock contacts form roll 12 it is
stretch preformed around an arc ~ of the roll until stretch
preforming is complete prior to the intermesh between the two
rolls, where any remaining final U-forming is accomplished, and
the stock emerges in the loop fin configuration 3 as shown in
Figure 9.
In the apparatus of Figure 12 it will be seen that the
employment of an idler roll 20 allows parallel alignment of the
lance and form stations. Idler roll 20 aids in the critical
step of stretch preforming in the process depicted in Figure 12
by providing an adequate angle of approach ~ . As with the
apparatus of Figure 1, the tension on imperforate unlanced
portions 8a and 9a is provided by operating the cooperating
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forming rolls 12 and 13 or work station J at a slightly higher
peripheral speed than the cooperating lance cutters 6 and 7 of
work station H. For example, sufficient stretch preforming
occurs if work station J is operated at a peripheral speed
approximately 1% greater than work station H. Work station J
functions and operates essentially the same as work station s of
Figure 1 to provide the final looped fin configuration 3. After
exiting from work station J the looped fin chain 3 is wound onto
the tubing 4 at work station K, with the helix angle controlled
by the longitudinal speed of the tube 4 along the line of arrow
5 and the rate of rotation of tube 4 as it travels in that
direction.
The above description and drawings should not be
construed as limiting the ways in which this invention may be
practiced, but should be inclusive of many other variations that
do not depart from the broad scope and intent of the invention.
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LIST OF REFERENCE NUMBERS
1. Coil
2. Thin metal strip (fin stock)
3. Looped fin chain structure
4. Tube; particularly refrigerant tube
4a. Tube outer surface
5. Direction arrow of movement of tube 4
6. Male lance cutter
7. Female lance cutter
8. Lanced fin stock mounting flange tip (Figure 6)
8a. Lanced fin stock mounting flange tip (Figure 13)
9. Lanced fin stock mounting flange tip (Figure 6)
9a. Lanced fin stock mounting flange tip (Figure 13
10. Fin preforms
10a. Fin vertical leg member
10b. Fin vertical leg member
10c. Fin bridge portion
11. Guide roll at station C
12. Male forming roll
12s. Strip gripping surface of forming roll 12
13. Female forming roll
13a. ~
13b. ~ Replacement rolls for female forming roll 13 (Figure 10)
13c. J
13s. Strip gripping surface of forming roll 13
14. Longitudinal space between looped fins
15. ~pparatus table
16. Direction arrow of movement of apparatus (Figure 1)
17. Water meniscus (Figures 15 and 16)
18. Intermeshing teeth of lance cutters 6 and 7
19. Line between lance roll centers (Figure 14a)
20. Idler roll at station I (Figure 12)
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