CA1077690A - Apparatus for forming serpentine heat exchangers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A machine for forming a serpentine heat exchanger having a predetermined length from a continuously formed spine fine tubing. A supply of continuously formed spine fin tubing is directed to a forming and bending head in predetermined increments where it is bent in alternate directions about a central axis to form the serpentine heat exchanger. Prior to the bending action the portion to be bent is deformed into a cross section having its major axis parallel to the plane of the tube. The following bending operation causes the tube diameter across the major axis to decrease as the wall in the area of the outer curve migrates radially inwardly due to its failure to elongate sufficiently, in effect, the cross sectional area in the completed bent portion is substantially equal to the cross sectional area of the tube before the deforming and bending operation.

Description

~7690 This invention relates generally to a machine for forming a serpentine heat exchanger having a preselected length from a continuous supply of tubing. The machine includes a feed mechanism that advances tubing in preselected increments to a forming and bending heat which deforms the section of tubing to be bent prior to successively bending each of the increments in alternative directions.
The tubing is deformed in the bend area into an elliptical or oval configuration having its major axis paralle to the plane of the tube. During the bending operation the wall in the area of the outer curve moves radially inwardly to decrease the dimension of the major axis due to its inability to elongate sufficiently, while the dimension of the minor axis increases so that a tube passageway having a predetermined design area is maintained. After a pre~
determined number of successive bending operations have been completed the serpentine heat exchanger formed by the present invention is severed or cut off from the continuous tube at a precise design point to eliminate any need for successive cutting operations and in effect the elimination of scrap and waste is realized.
In the manufacture of serpentine heat exchangers it has been common practice to provide a length of tubing which was bent either between a wheel or shoe with the inside of the tube occupied by a mandrel to maintain the round-ness of the tube passageway during the bending operation.

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~077690 In actual practice it is extremely difficult to provide the exact length of tubing for a particular ser-pentine heat exchanger to be formed, and, in fact, the length of tubing provided is usually longer than the design length of the completed heat exchanger. This practice is necessary to allow for variations due to stretch and size of bend radiuses. Accordingly the heat exchanger as formed must then be trimmed to the exact length needed for a par-ticular application which, results in a certain amount of waste or scrap.
The practice of employing internal mandrels has many disadvantages, for example, the length of the tubing in the heat exchanger is limited by the length of the man-drel. In practice when using tubes having a .375 inch diameter, the maximum practical length of the mandrel has been found to be about 25 feet. As a result, in many in-stances, several heat exchangers so formed must be joined to provide some of the volume requirement when they are used in refrigeration systems. Other disadvantages arise when the mandrel scores the inner wall surface of the tubing which may lead to undesirable refrigerant flow character-istics. The use of internal mandrels also in some instances allows contaminants to be present in the final heat exchanger.
These contaminants, when present and if not removed, may lead to blockage in the refrigerant system, especially in re-stricted areas such as capillary tubes and could result in compressor failure.
SUMMARY OF THE INVENTION
; The present invention provides a machine for forming a serpentine heat exchanger having a predetermined length from :-. .

a continuous tubing, wherein a forming and bending head is adapted to successively bend increments of the continuous tube in alternate directions about a central axis.
The continuous tube is received in a support structure from a supply of continuous tubing with its longitudinal axis in a plane substantially perpendicular to the central axis of the forming and bending head. Prior to advancing the increments of tubing to be bent about the central axis, the tube is shifted laterally so that the successive increments to be bent are arranged on alternate sides of the central axis diametric to the direction of the bending.
The tube is fed longitudinally in predetermined increments past the head so that a selected portion of the increment, generally the trailing portion to be bent, is arranged between shaping members or forming portions associated with the forming and bending head. The head is driven longitudin- -ally along its central axis so that the shaping member deforms the selected portion of the increment into an elliptical or oval cross section having its major axis lying parallel to the plane of the tubing. A wall portion of a subsequent increment diametric to the direction of the bending operation is held against lateral movement to insure that a parallel relationship between the increments is attained by the bending operation.
With the selected portion arranged between the ; shaping members, the head is rotated or oscillated in one direction 180 about the central axis so as to bend the selected portion about the central axis and in effect bring the increment into substantially parallel relationship with the subsequent continuous tube. When the serpentine heat exchanger reaches a predetermined configuration in length it is then severed from the continuous tubing, and the 1~77690 machine then recycles and another serpentine heat exchanger is started from the continuously fed tubing.
In forming the serpentine heat exchanger of the present invention from a continuous tubing, the use of an internally applied mandrel is not possible. Accordingly by the present invention a serpentine heat exchanger is in fact fabricated without employing an internally applied mandrel by deforming the tubing in the area to be bent to allow bending of the tube 1~0 without collapsing the tube ~n the bend area.
It is an object of the present invention to fab-ricate a serpentine heat exchanger from a continuously supplied tube by bending preselected increments of tubing about a central axis.
Another object of the invention is to deform the tube in the bend area into a cross sectional configuration that will cause the resulting stretching of the wall in the area of the outer curve to reshape the tube walls.
BRIEF DESCRIPTION OF T~E DRAWINGS :
Figure 1 is a`plan view showing a typical serpen-tine spine fin heat exchanger formed by the apparatus of the present invention;
Figure 2 is a schematic view of another heat ex-changer formed by the apparatus of the present invention;
Figure 3 is a schematic view of still another heat exchanger formed by the apparatus of the present invention;
Figure 4 is an elevational view of the apparatus of the present invention;
Figure S is an enlarged elevational view of the heat exchanger forming machine of the present invention;

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~o77690 Figure 6 is similar to Figure S with parts in a second position;
Figure 7 is an enlarged sectional view taken along lines 7-7 of Figure 6 showing details of the advancing mechanism;
Figure 8 is a plane view taken along lines 8-8 of Figure 7 showing further details of the advancing mechanism;
Figure 9 is an elevational view partly in section showing the indexing portion of the advancing mechanism;
Figure 10 is similar to Figure 9 with parts in a second position;
Figure 11 is a partial elevational view of the ad-vancing mechanism of Figure 7 with the holding member in a second position;
Figure 12 is an elevational view taken along lines 12-12 of Figure 6 showing the aligning and shifting mech-anism of the present invention;
Figure 13 is a partial elevational view of the head in the active position;
Figure 14 is a schematic view of the tube in its deformed state;
Figure 15 is a schematic similar to Figure 14 with ; the parts moved to provide clearance;
Figure 16 is a sectional view taken along lines 16-16 of Figure 6 showing the cutoff mechanism of the present invention; and : Figure 17, 18, and 19 are schematic views showing different stages in forming the heat exchanger of the present invention.

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`` 1~77690 DETAILED DESCRIPTION OF THE INVENTION
Referring to Figure 1, there i9 illustrated a typical heat exchanger 10 fabricated by the apparatus of this invention wherein increments of spine fin tubing are bent about a central axis A of Figure 4. While the heat exchanger 10 illustrated includes five return bends joined by tubes of equal lengths it should be understood that hy the machine of ~he present invention a heat exchanger h~ving any number of configurations can be fabricated and Figures 2 and 3 illustrate some of the typical vàriations that may be formed.
With reference to Figure 4, the preferred apparatus for carrying out this invention may be conveniently divided into components 12, 14, 16 and 18 for ease of description.
Component 12 represents a machine 12 for producinq continuous spine fin tubing 13 as shown and described in U.S. Patent 3,688,375-Venables III, assigned to General Electric Company, assignee of the present invention. Com-ponent 14 represents a tube feed compensating means which, as will be expl~ined hereinafter, regulates the flow of tubing between the continuous feed of the spine fin forming machine 12 to the increment feed requirements of the heat exchanger 10. Component 16 is utilized to straighten the tube 13 as it enters component 18 which, as will be described in detail, is the serpentine heat exchanger forming machine 18 of the present invention.
The spine fin tubing ma~ be made continually in machine 12 from a rotatably supported stock roll 15 that may contain 2,000 and sometimes as much as 10,000 linear feet of tubing.

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- ~ ' - ' - , , `` ` ~07~7690 Within the present embodiment the heat exchanger 10 is made in conjunction with the spine fin tubing 13 as it is received continuously from the spine fin wrapping machine 12. It should be noted that the completed spine fin tubing 13 may be stored on rolls and the heat exchanger 10 may then be fabricated from material supplied from the rolls.
When, for continuous automatic operation, the spine fin material is received directly from the forming machine 12, means must be provided to compensate between the continuous feed rate of the spine fin forming machine 12 and the inter-mittent feed requirement of forming machine 18. ~o this end the feed compensating means 14 includes a holding frame 20 wherein a predetermined length of tubing 13 received from machine 12 may be stored, Switch or control means are pro-vided to regulate between a predetermined minimum and maximumlensth of tubing 13 stoxed in frame 20. To this end a con-trol 21 is emplo~ed to interrupt the operation of the ~Irapping machine 12 when the maximum length is 5ensed and a control 22 to terminate operation of the forming machine 18 when the tubing 13 stored in frame 20 reaches a predetermined minimum length. ~r, The component 16 as mentioned hereinbefore is the tube straightening portion of the apparatus for carrying out the present invention and includes a plurality of spaced rollers 24 arranged on either side of the longitudinal axis of the tube 13 so that axis of the tube 13 as it leaves the final rollers is arranged in a substantially straight line as it enters the forming machine 18. :
Referring now to Figures 4-11 of the dra~ings, an advanciny. mechanism 26 arranged in a support structure or :

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1(377690 frame 28 of the machine 18 is effective in advancing the tube 13 in preselected increments relative to the central axis A. The tube 13 is received in a tubular guide member 25 supported on brackets 23 forming a part of the advancing mechanism 26, The tube guide member 25 is positioned to locate the longitudinal axis of the tube 13 so that it lays in a plane C perpendicular to the central axis A. The ad-vancing mechanism 26 includes guide means or slide frame 30 and a tube ad~ancing portion 31 which is arranged for longi-tudinal movement on frame 30 relative to the central axisA. The frame 30 includes parallel spaced guide rails 32 (Figures 7 and 8) which includes recesses or tracks 34 for slidably receiving a support plate 35 of tube advancing portion 31. Arranged on the support plate 35 are a pair of tube holding or gripping members 36 which are movable laterally xelative to each other on a bracket 38 secured to plate 35, The lower portion of members 36 includes holding portions 39 which are positioned so as to be arranged diametrically of the longitudinal axis of the tube ~3.
Secured to the portions 39 are gripping fingers or plates 40 which project radially toward the axis of tube 13 and . are adapted to engage tube 13 as shown in Pigure 7. The fingers 40 are spaced so as to extend between the spi.ne fin and engage the tube wall without unduly deforming the fins which could result in loss of heat exchange efficiency. A
pair of actuators 41 in the form of actuators or air cylin-ders arranged on bracket 38 are operable at a selected time to move members 36 relative to each other to cause fingers 40 to engage tube 13 and alternatively to disengage from tube 13. -.

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~77690 Mounted on the upper surface of support plate 35 (Figures 9 and 10) are a series of dampers 42 which are arranged to engage stop members 43 which are selectively mounted on the stationary frame 30 relative to the central axis. Referring to Figures 9 and 10, it will be seen that the stop members 43 are arranged for vertical travel on a support structure 44 which is adjustably mounted on the frame 30. In operation a selected stop 43 is moved by an operating member 46 into the path of a cooperating damper 42 to control and index the tube advancing portion 31 in its retracted position relative to the central axis as shown in Figures S and 9. The cooperating dampers 42 and stops 43 are arranged axially relative to longitudinal travel of the tube 13 as will be explained hereinafter to provide pre-selected increments of travel of the tube advancing portion 31. To prevent movement of the stop 43 relative to the frame 30 in impact with the damper 42, a gear rack segment 48 movable with stop 43 engages a cooperating rack 50 secured to the stationary frame 30, As shown in Figures 9 and 10, the retracted posi-tion of the advancing portion 31 relative to the central axis, and the length of the tube increment B advances, is determined by the position of the stop members 43 on the frame 30. It should be noted that a selectively located stop 43 must be provided for each desired increment of tube movement to engage a cooperating damper 42. For example, the heat exchanger configuration shown in Figures 2 and 3 require that the length of tubing between return bends be -different and, accordingly, the advancing portion 31 must ba positioned a selected retracted position for each length of increment required.

1~77690 As the advancing mechanism is retracting to its , preselected position relative to the central axis A, the actuators 41 are in their retracted positions as shown in Figure 11 and accordingly maintain the fingers 40 out of engagement with the tube 13. At the preselected time in . .
the forming operation while the advancing portion 31 is in its selected retracted position against an appropriate : stop 43, the actuators 41 are energized and as shown in Figure 7, the fingers 40 move to engage and grip the tube -' 13 securely therebetween.
Means are provided to move the advancing portion 31 longitudinally relative to the frame 30. To this end with the tube 13 securely held by the fingers 40, an actu- -ating ram or member (not shown) is energized to move and ', 15 advance the portion 31,on the frame 30 from the retracted - position against a preselected stop 43 as shown in Figures , 5 and 9, to the advanced position as shown in Figures 6 and 10 against a fixed stop 51 secured to frame 30. In this . position the selected increment of tubing B has been movéd ' 20 to an advanced position relative to the central axis A.
~ The advanced increment of tubing is supported on a suitable .' table or support surface 45.
'` As mentioned hereinbefore, to form the serpentine :
' heat exchanger 10 in accordance with the present invention, the spine fin tubing 13 is bent in alternate directions about the central axis A. Accordingly means are provided for positioning the advanced increment B of tubing on l alternate sides of the central axis A.
-~'' To this end a shifting mechanism 52 as shown in 5 ~ 30 Figures 5, 6, and 12 is arranged on the support 28 for :~, ~ .

` 1077690 lateral movement relative to the longitudinal axis of the tube 13. The mechanism 52 is mounted on stationary plate 54 which has rails 56 supported therefrom. Slidably mounted on the rails 56 is a platform 58 which is connected to an actuator 60. The slide frame 30 is pivotally connected at 57 to the rParward end of platform 58 so that lateral movement of the platform 58 on rails 56 by the actuator 60 causes the advancing mechanism 26 to shift laterally. This lateral movement of the advancing mech-anism 26 carries with it the guide member 25 which con-centrically supports the tube 13 and, accordingly, the tube 13 is shifted to a selected side of the central axis A to be in position for the following alternate bending operation.
Associated with the central axis A (Figures 4, 5, 6, and 13) is a forming and bending head 65 having forming portions or shaping members which comprise cooperating upper and lower portions 62, 63 respectively. The portions 62, 63 are mounted for synchronous rotational oscillations in alternate directions about a central A and for reciprocal axial movement relative to each other. To this end the portions 62, 63 are ; mounted for reciprocal movement on guides 62' and 63' respectively. The guides are adapted to be moved axially relative to each other by a cooperating mechanism 68. A drive means 71 associated with guide 63' of portion 63 is effective when the portions 62 and 63 are engaged to rotate the he~d 65 in alternate directions about the central axis A.
Referring now to Figure 13 it will be seen that the portions ~ -62, 63 including the forming or shaping surfaces 66 thereon are diametrically arranged about plane~ and aligned along central axis A. At the propex time in the sequence - ~ .

1()77690 of operation the portions 62, 63 are moved axially toward each other by mechanism 68 so that the surfaces come to-gether and meet substantially in the plane C to clamp the tube 13 between the surfaces 66.
With the tube 13 held between the surfaces 66, the head 65 is rotated approximately 180 about a cam 67 centrally arranged on axis A in one direction until the -- advanced increment B of tube 13 is arranged substantially parallel to the following or subsequent portion 70 of tube 13.
In bending a tube having a diameter of .375 inches and a wall thickness of between .035 and .020 lnches wherein the radius of the tube axis in the bend is approximately .565, means must be provided to prevent the movement or collapse of the tube wall in a radial direction to the bend due to the inability of the wall in the area of the outer curve to stretch an amount sufficient to maintain its radial position relative to the wall in the area of the inner curve.
This collapsing of the tube walls is of course not acceptable in that it effects the design flow characteristics of re- -frigerant and means must be provided to prevent the collap-sing of the tube 13 in the bend area 69.
Accordingly by the present invention, the portion ~-69 of the increment B that, as shown in Figure 1, repre-sents the return bend area in the completed heat e~changer 10 is deformed prior to bending operation. The portion 69 of spine fin tube 13 is deformed as shown in Figures 13 and 14 by the portions 62, 63 as they are brought together and accordingly only the spine fins in the return bend area are ~0 unduly deformed. To this end the surfaces 66 when brought -12- .

together with sufficient pressure to deform the portion 69 are so dimentioned that the tube 13 will assume a cross sectional configuration resembling an oval or ellipse having a major axis D.
The major axis D of the deformed cross sectional configuration is parallel to the plane C. As can easily be understood with the deformed portion 69 positioned between the surfaces 66, the subsequent rotational movement of head 65 will cause the wall in the area of the outer curve to try to stretch to form the outer circumference of the completed bend. As mentioned hereinbefore during the bending operation the outer wall in its inability to stretch sufficiently to maintain its radial position relative with the inner wall, will move radially inwardly while at the same time the tube diameter along the minor axis expands so that the tube cross sectional configuration will tend to reform to substantially the original round configuration thereby maintaining a clear unobstructed design passageway. After the deforming operation the surfaces 66 are so spaced (Figure 14) that they will allow the reshaping of the tube portion 69.
In the bending operation as increment B is bent about the central axis, the subsequent or following increment 70 of tube 13 adjacent the head 65 tends to move laterally from the longitudinal axis of the tube in a direction diametric to the bending operation.
Accordingly, with reference to Figures 5, 6, and 12, it will be seen that in fabricating the heat exchanger 10 in accordance with the present invention, means are pro-vided to prevent movement of the portion 70 during the bending operation of increment B. A tube aligning mech-anism 72 is mounted for lateral movement with the shifting mechanism 52 and more particularly to the plate 58. The aligning mechanism 72 includes a frame member 74 mounted on guide rods 80 which are slidably arranged in support blocks 82 secured to plate 58. Pivotally mounted on the frame 74 are a pair of arms 76 including tube holding blades or members 77. The arms 76 are pivoted at 79 on frame 74 at a position above the guide member 25 and tube 13. The arms 76 are moved alternatively by a pair of actuators 78 so that the members 77 engage the tube 13.
Since lateral movement of tube 13 occurs in a direction diametric to the bending operation, the actuators 78 are energized alternatively so that the arm 76 and holding member 77, moved, engages a portion of subsequent increment ; s of the stationary tube side wall that in fact is an ex-tension of the wall of the outer curve. It should be noted that members 77 are fabricated from relatively thin metal so that a minimum number of spine fins are deformed. ~:
Referring to Figure 6, .in order to be effective in preventing lateral movement of tube 13 in portion 70, the member 76 should engage the tube wall portion adjacent the head 65 and in effect, during the bending operation the mechanism 72 is allowed to move forward on guide rcds ~0 from the position shown in Figure 5 ~o that of Figure 6.
After the bending operation and prior to the next bending operation, the aligning mechanism 72 is positively retrzcted relative to the forming head 65 by an actuzto~ 83. Prior to a banding operation the mechanism 72 is in its retracted position as shown in Figure 5 and both holding members 76 . -14-' ~ 77690 are rotated or pivoted away from the tube 13, Immediately prior to the bending operation the appropriate members 76 are pivoted into engagement with the tube 13 in increment 70.
After a predetermined number of alternate bending operations the heat exchanger 10 is cut from the continuous tube 13 so that another heat exchanger can be fabricated from the continuous tube 13. To this end a cutoff mech-anism 85 is provided (Figure 16) wherein a cutter 86 is located below the plane C of tube 13 and a cooperating cutter 87 is arranged above tube 13. Both o~ the cutters 86 and 87 are arranged for vertical movement on guides B8 formed in blocks 89. It should be noted that cutter 87, which is mounted on plate 54, is shifted laterally by the shifting mechanism so that upper cutter 87 moves laterally with, and is always properly positioned, over tube 13 and accordingly a single U-shaped cutting area 91 is provided.
The lower stationary cutter 86 is provided with two cutting areas 92 so that the tube 13 is aligned with one of the cutting areas in either of its shifted positions relative ' 20 to the central axis A. In operation, an actuator 93 effec-tively drives cutter 87 vertically downwardly whi].e cutter 86 is driven upwardly by actuator 94 so that the cutting area 91 and the cooperating cutting areas 92 are driven through the tube 13.
Referring now to Figures 17-19, there are shown the steps in fabricating the heat exchanger illustrated.
In progressing through the forming of the heat exchanger, it will be assumed that to start with, the free end of a continuous spine fin tubing is located at a point adjacent the head 65 and more specifically at the point, a previously fabricated heat exchanger may have been cut off.

,' ~ -15-In operation, with the advancing portion 31 located longitudinally at a preselected location by an appropriate stop 43, the holding portion 39 is actuated to engage the tube and move it forward a preselected in-crement by action of the advancinq mechanism 26. Thisforward movement of tube 13 is selected so that the trailing end or portion 69 of increment B forming the return bend is arranged between the shaping surface 66. The shifting mech-anism 52 is then actuated to laterally arrange its assoc-iated mechanism including increment B of tube 13 and morespecifically portion 69 to one side of the central a~is A.
The holding member 76 moves to engage the side wall of the subsequent tube portion to prevent movement of the stat-ionary tube portion in a direction diametric to the bending direction. The advancinq mechanism retracts to a preselected distance to engage an appropriately arranged stop. The head members 62, 63 move axially toward each other until the surfaces 66 engage portion 69 with sufficient pressure to deform the tubing into the generally oval configuration so that it has its major axis D arranged parallel with the plane C and perpendicular to the central axis A. The head 65 then rotates in one direction to form the first return bend of the heat exchanger. The rotation of head 65 in each direction is substantially 180 so as to locate in-crement B parallel to the subsequent increment 7~ of tube13 to be bent. The above described steps are repeated until the desired number of return bends and length of heat exchanger 10 is attained, at which time the cutoff mech-anism 85 is actuated and the heat exchanger 10 severed from the continuous tubing 13.

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1~77690 In adapting the apparatus to be used in an auto-.
matic production operation, the table portion 45 that supports the severed heat exchanger 10 is pivoted at 96 and rotated downwardly by an actuator 97 so that the com-pleted heat exchanger 10 may slide down onto a conveysystem 100.
It should be apparent to those skilled in the art that the embodiment described heretofore is considered to be the presently preferred form of this invention. In accordance with the patent statutes, changes may be made in the disclosed apparatus and the manner in which it is used without actually departing from the true spirit and scope of this invention.

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Claims (4)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:
1. An apparatus for forming a serpentine heat exchanger having a predetermined length from a continuous tubing including a forming and bending head means for successively bending incre-ments of said continuous tubing in alternate directions about a central axis comprising:
a) tube supply means for receiving said continuous tubing;
b) support means associated with said supply means for receiving said tubing with its longitudinal axis in a plane substantially perpendicular to said central axis;
c) tube shifting means arranged on said support means for lateral movement relative to said central axis for successively placing the increments of said tubing to be bent on alternate sides of said central axis, including holding means being movable alternatively into engagement with opposite side walls of said continuous tube diametric to the rotational direction of said forming head to prevent lateral movement of said continuous tubing during the bending operation while said increment is positioned substantially parallel with said continuous tube;
d) tube feed means arranged on said support means for advancing said tubing along its longitudinal axis in predetermined increments relative to said head so that a selected portion of said increment to be bent in said plane is arranged in cooperative relationship with said head means, including an advancing member slidably mounted on a guide member for longitudinal movement in a path parallel to said plane, tube holding means mounted on said advancing member being movable into engagement with said tubing when said feed means is in its retracted position relative to said central
1. Claim 1 continued:
   axis, stop means adjustably arranged longitudinally on one of said members positioned to cooperatively engage damping members on the other of said members when said feed means is in said retracted position to regulate the length of said increment advanced longitudinally relative to said central axis by said advancing member;
   e) said head means including a pair of shaping members arranged on said central axis on either side of said plane being dimensioned to deform said selected portion into an oval cross section having its major axis lying parallel with said plane;
   f) drive means associated with said head means being operable when said selected portion is in the advanced position between said shaping members for moving said head means longitudinally along said central axis to move said shaping members into engagement with said selected portion of said tube with sufficient pressure to deform said portion into said oval cross section; and means for imparting a successive rotational oscillation to said head means in one direction while the shaping members are in engagement with said selected portion to bend said increment in said selected portion substantially 180°
   about said central axis so that said increment is substantially parallel to said continuous tubing;
   g) cutoff means positioned relative to said continuous tubing being movable radially through said longitudinal axis including a first cutter on one side of said plane arranged for cooperatively engaging a second cutter on the other side of said plane, said first cutter is mounted for lateral movement with said shifting means and said second cutter includes a plurality of cutting area so that said first cutter is aligned with one of said cutting areas, means for moving said cutters perpendicular to said plane and through said tubing to sever said heat exchanger from said continuous tube after a predetermined number of successive bending operations.
2. 2. The apparatus of claim 1 wherein said tube supply means includes a receiving area for holding a variable predetermined length of said tubing and to direct said tubing to said support means as it is advanced in increments by said tube feed means;
   control means arranged in said receiving area to regulate the length of tubing in said receiving area to maintain said tubing in said receiving area within said variable predetermined length.
3. 3. The apparatus of claim 2 wherein a guide means is arranged in the path of travel of said tubing intermediate said supply means and said support means including a plurality of diametrically positioned rollers located so that the longitudinal axis of the tubing is arranged in a substantially straight line as it passes through successive rollers.
   4. A method of forming a serpentine spine fin heat exchanger having a predetermined length by successively bending increments of a spine fin tubing formed at a continuous feed rate including the steps of:
   receiving said continuously formed spine fin tubing at its feed rate in a feed compensating means;
   feeding a predetermined increment of spine fin tubing from said feed compensating means with its longitudinal axis lying in a plane substantially perpendicular to the central axis of a bending head so that a selected portion to be bent is arranged between forming portions of said head while said spine fin tubing is being continuously received into said feed compensating means;
   shifting the axis of said spine fin tubing laterally relative to the central axis of said bending head prior to said successive bending to position said selected portion to be bent
4. Claim 4 continued:
   on one side of the said central axis diametric to the direction of the bending;
   deforming said spine fin tubing in the selected portion to provide a substantially oval cross-sectional area having its major axis parallel to said plane;
   bending said selected portion in said head substantially 180° about the central axis of said head until said predetermined increment of tubing is substantially parallel to said subsequent portion of tubing;
   cutting off said serpentine heat exchanger from said continuously formed tubing after a predetermined number of successive bending operations.