US2162693A - Method of making a heat exchange element - Google Patents

Description

June 20, 1939. A BEE; AL METHOD OF MAKING A HEAT EXCHANGE ELEMENT- Filed Aug. 4, 19:57

FEEL laf ll i I llc l INMENTOR ALFRED, J. BERG F25; OHN. HUSE 7 ed to form the rib or Patented June 20, 1939 UNITED STATES PATENT OFFICE Alfred J. Berg,

Huse,

Portsmouth, N. IL, and John 0.

United States Navy Application August 4, 1931, Serial No. 157,378

7 Claims.

(Granted under the a amended April 30,

Our present invention relates to a new and useful heat or cold exchanging element and method of making the same, which element may be otherwise usefully employed.

l'his invention is a continuation in part of and an improvement upon our application, Serial No.

63,894, series of.1935, entitled Heat exchanging element and process of making the same, filed February 14, 1936. In said filed application the ribs or fins of heat exchanging elements were machined or cut as a shaving from a bar of metal. Our present invention substantially improves the helical shaving cut from a bar of metal having a central longitudinal hole therethrough and adaptfin of a heat exchanging element which may be hollow. Ourpresent invention furthermore substantially improves the cutter by which such shaving may be formed.

The objects of our invention are to improve the strength and stability of the shaved rib or fin; to avoid the liability of breaking the shaved fin as it passes over the thicker part of the cutter immediately after it is severed from the bar of metal, as well as to avoid the liability of breaking the fin while it is being installed upon and secured to its tube and/or in handling the finished tube; also to providean improved cuttingtool for more efiiciently and economically shaving such improved fin from a bar of metal and which cutter will maintain its edge for protracted periods without stopping the machine and resharpening the same or liability of breaking the rib or fin formed by said cutting tool. Other objects of the invention will hereinafter be made apparent.

In the drawing illustrating our invention, Fig. 1 is a top plan view of a cutter for lathes and the like for cutting our improved heat exchanger rib or fin from a bar of metal;

Fig. lais an end view thereof;

Fig. 1b is a side elevation view of the cutter shown in Fig. 1;

Fig. 1c is aview of a cutting tool similar to Figs. 1 and 11) but having a different-shearing cutting edge;-

Fig. ld is a view'in side elevation embodiment of the cutter;

Fig. 1e a view in end bodiment; and

- Fig. If is a view in plan thereofx I Fig. 2 is a top plan view of a bar of metal with the cutter of Fig. 1 cutting a helical shaving from the end face thereof to form a helical rib for a heat exchanger tube.

Fig. 2a is a view showing a preferred relation of the shearing edge to the bar.

of a further elevation of this emdistortion of the (ol. 29-' 157.s)

ct of March a, 1883, as 1928; 370 o. G. 157) Fig. 3 is an end view of a bar of metal mounted for rotation in the chuck of a lathe or like tool with the cutter of Fig. 1b positioned to cut a shaving from the end face of such bar adapted to form a, rib or fin for a heat exchanger tube.

Fig. 4 is a view similar to Fig. 3 but employing the cutter illustrated in Fig. 1d;

Fig. 5 is a cross-sectional end view of a portion of the shaving adapted to form the'rib or fin of a heat exchanger tube, the section being taken upon a plane passing through the center and one side of the helically turned shaving.

Fig. 6 is a central vertical cross-sectional view of a portion of a heat exchanger tube or element provided with ribs or fins formed of the shaving llb.

lll diagrammatically represents the chuck of a lathe or like tool adapted to rigidly hold a relatively long bar ll of metal concentric with spindle l2, Fig. 2, of the lathe or like tool. .l3 represents a portion of the usual lathe carriage to which tool post I4 is rigidly attached. Post I4 is usually bifurcated to receive the shank of cutting tool A5 which is secured in said bifurcation by screw it. The cutting edge I! of the cutting tool l5 extends across the end of bar II from a point within the central -longitudinal opening Ila extending through bar II to a point beyond the diameter of bar ll so as to cut a shaving of the required thickness from the end of bar I I as the same is turned in the lathe while the carriage I3 is progressively moved not shown, to progressively move the cutting edge longitudinally of the bar I It is such longitudinal movement of the cutting edge I! relative to the rotation of bar II that fixes and maintains the thickness of the shaving severed from the bar ll which forms the helical fin of a heat exchanger tube or element.- v I When using a cutting tool having a straight cutting edge to sever the shaving 1 lb from bar ll we have found that the shaving is liable to break as it is being severed and simultaneously bent at the wide angle necessary for it to pass over the bevelled portion of the utting tool 55 which supportsits cutting edge I]. This we have found is due to a number of factors, including the cold worked forming of bar I l with the resulting grain metal of bar-l I, together. with the further grain distortion due to the cutting of the shaving l lb. Such breakage is contributed .-to. by the line of breakage usually being radial relative to bar ll and that such line coincides with the straight cutting edge of the tool so that the severance and simultaneous ,bending of the by the usual feed screw,

. and appearance of the finished product. Said provided means include the following: Normalizing or annealing the metal of bar I I is one such remedy, but it adds to the time and expense required for such operation. For more economical and eflicient results weprefer to form bar H by extruding hot metal to the required length through a die forming the required external and internal diameter and then normalizing by reducing to atmospheric temperature the hot drawn metal of bar II.

We further provide a cutting tool having its cutting' edge disposed otherwise than upon a straight line extending substantially radially relative to bar II, and preferably upon an un-uniform or generated line which will form a shearing cutting edge which is disposed at an angle, or at a varying angle relative to a radial line passing through the bar II.

A further provision tending to avoid such dimculty is that the shaving IIb is formed more or less cambered, as shown in Fig. 5, that is of uniform thickness thereof curved with the high point of the curve occurring in the center or at a point intermediate the width of the shaving. Such cambered shaving affords additional initial strength to the severed shaving and necessitat'es no waste of the. metal of bar Ii. The different cutting tools I5 'whi h we have provided for the severance of our im eved shaving IIb, which is essentially adapted to form a helical heat exchanger rib or ribs upon a heat exchanging tube or element will now be described.

The tool shown in Figs. 1b, 1c, and 3 has its cutting edge Il, as will more. clearly appear in Fig. 3, disposed at an angle to a line which is radial relative to bar II. The point of the tool of the cutting edge Il extends within the bore IIa of bar II and terminates outside of the diameter of bar II and near the highest point of such cutting edge, relative to the light radial line shown in Fig. 3. Such highest point of cutting edge I1 is in the instance shown in Fig. 3 near the outer diameter of bar BI.- One advantage of such disposition of cutting edge ll is that its greatest shearing action upon the metal of bar II occurs in the smaller tion of bar II where the relative cutting speeds are substantially less that the relative cutting speeds of the metal in the larger Ediametered portions of bar I I. This form of shearing cut, shown in Figs 11) and 3, have been found eilective ,and eflicient as well as to obviate the liability of the breakage of the shaving hereinbefore described.

The cutting edge Ila of the cutting tool I5 shown in- Figs. 1d and 4, provides a difierent shearing action upon the metal of the, bar I I than disclosed by the cutting edge Ilb in Figs. 1 and 3.

The cutting edge Ila shown in Figs. M and 4 hasits highest point at 'Ilrc or adjacent the center. of the width of the shaving IIb. ,From, this high point the cutting" edge Ila progres sively lowers as it extends in opposite directions from said high point. The high point of the cutting edge Ila may be the apex of angular diametered poroppositely extending straight portions of the cutting edge Ila, but in the instance shown in the drawing said cutting edge is curved. The high point of cutting edge Ila being at a point intermediate the sides of the shaving IIb tends to obviate all, or at least the major portion, of the end thrust upon the cutter I5 as well as the resulting lateral thrust upon the bar II from while the opposite sides of the shaving IIb are still an integral part of the bar II. These unsevered lateralportions of shaving III; are severed by the cutting edge Ila while its high point is continuing its advanced severance of the central portion of the width of theshaving IIb. This shearing cut of the shaving IIb aiforded by this'cutting edge Ila furthermore results in the forming of substantially the cambered shaving IIb shown in Fig. 5, due to the fact that the high point of the cutting edge Ila severs the central portion of the shaving IIb from the end of bar II and forces the same progressively over the thicker bevelled portion of the cutter I5 upon the upper edge of which the cutting edge Ila is formed. This severance in forcing over the central bevelled portion of cutter I5 of the central portion of the severed shaving IIb while its lateral edges are still integral with the'bar II causes the central portion of the shaving III) to be curved outwardly, and such curvature progressively lessens as the lateral edges of the shaving I Ib are approached. This is true because a radial line passing from the center of the bar II through the points of intersection of the inner and outer diameters of the bar I I with the cutting edge Ila will also pass through progressively thicker portions of the bevelled edge of cutter I5 .whose apex forms the cutting edge Ila. Such progressively thicker portions will be passed through by said radial line until the high point of the cutting edge Ila is reached, and from this point to the outer diameter of bar II this radial line will pass through progressively thinner portions of the cutter I5. It is these progressively thicker and then thinner portions of the cutter I5 over which the shaving is passed as it is being sheared from bar II that results in such camber-of shaving IIb as is substantially indicated in Fig. 5.

To enable a straight cutting edge of a cutter I 5, or even the cutter of Figs. 1b and 3 to cut a cambered shaving IIb, substantially as shown in Fig.

.5,,f rom the bar II a transversely arched cutting edge llb is formed at and beneath the actual cutting edge of the cutter I5. This arched cutting edge Ilb severs the cambered shaving IIb di-' rectly from the bar II.

- The-vertical surface m directly beneath each of the several cutting edges I I, Ila and Ilb extended -at a-downward and outward angle from their respective cutting edges so as to afford substantial clearance between the end of bar II and portions of the cutter I5 below the cutting edge of each of the cutters that may be em-.

ployed. in severing the shaving MD from the bar I I.

It will be appreciated by those skilled in the art that the cambered shaving 'IIb aifords greater than normal strength to the shaving llb, as well as contributes to the avoidance of the liability of the breakage of the shaving llb, at any point in its length as the same is being severed and bent over the thicker portion of the cutter supporting the cutting edge which separates the shaving from the bar I I'. It will furthermore be appreciated by those skilled in the art that the shearing cutting edges I! or Ila substantially contribute to the severance of the shaving I Ib from the bar II more efliciently and with less power; that said shear cutting edge or edges efliciently cut for longer periods than non-shearing cutting, edges; that said shearing cutting edges substantially contribute to the avoidance ofthe breaking of even the thinner shavings llb even of the unnormalized or un-annealed bar II, and make a .more 'efiicient as well as stronger shaving from the normalized or extruded bar I I; that the longer service enduring shearing cutting edges I1,

IIa, also require less stoppage of the shaving cutting for the purpose of sharpening or changing the cutter I5, which sharpening or change also necessitates a careful re-adjustmentofthesharpened or replaced cutter I in order to continue without flaw precisely the path of the former cut in order to maintain the uniform thickness of this shaving llb; that the shear cutting of the shaving llb cold works the shaving by distorting one portion of the grain of the metal'of the shaving llb while an adjacent portion or portions of the grain of the metal of the shaving remains for the instance an integral portion or portions of the bar I l and which contributes to the avoidance of the liability of the breakage of the shaving IIb in the plane of such grain of the metal of the shaving, and that such cold working increases the surface density as well as the heat exchang ing capacity and efli'ciency of the shaving llb; and that the cold working and other advantages of said shear cut are'increased by the cutting aswell as by the progressive forming while shaving of the cambered shaving llb from the bar II.

In turning or cutting the shaving llb helically from the end of the bar I I the central opening Ila longitudinally through the center of bar ll enables the helical shaving llb to be formed with the central opening therethrough Ilaa, Fig. 2, which substantially conforms to the external diameter of the heat or cold exchanging tube or body 20, Fig. 6. A suitable length of the helical shaving l Ibmay be placed about the tube or body 20 with one end of said shaving secured at a desirable point upon tube or body 20 by a drop of solder 2|. The shaving llb may be uniformly spaced throughoutthelen'gth of tube or body 20 by pressure applied to the unsecured end of the shaving I lb which is then adapted'to be secured to the, tube or body 20 by another portion of solder 2| our application,

entitled Heat and cold exchanging element and or other securing means and the shaving severed at the outer end of said last securement 2|, The size of the bore I la in bar II is such that the resulting diameter of central opening Ila in shaving I lb will be a snug fit'upon and about the exterior surface of the tube or body 20 and afford a firm and efficient'engagement of high thermal conductivity between the surface of tube or element 20 and the helical-shaving llb.

It will be understood by those 'skilledin the art that the helical shaving disclosed in Figs. land 12 as well as 13, 14, 15 and 16 of the'drawlng of Serial No. 63,397, series of 1935,

method of making the same, filed February 14, 1936; may be made in accordance with our apas the method of making the herein disclosed shaving together with the making of the bar from which the shaving is made; that the extrusion of the bar from which the shaving is made as well as the production of the shaving IIb may be performed by any one of a number of existing machines and that thefinal production of the ribbed or finned heat exchanging element may be done by hand or by a number of existing apparatus with'or without substantial modification; that the practice of said method results in the more economical and efiicient production of a thinner, wider, stronger, lighter, cheaper and more eflicient heat exchanger element of greater capacity per unit of length and weight than has been heretofore commercially producible; that a heat exchanging rib or fin, either circular or helical for a heat exchanger tube or body of greater thinness, width and strength may be more cheaply and efliciently produced by our present meth- Wor than has been heretofore possible of productherib or fin, represented by the width of the strip, could not approximately exceed one-half the diameter of the tube or body to be provided with such ribs or fins and that such height or width could be slightly increased by pre-coiling the strip to an intermediate diameter before finally coiling the same about the tube or body; that by the method disclosed in our said application No. 63,894, serlesof 1935, the height of the rib or fin represented by the width of the shaving could be substantially increased by shaving a helical shaving from the end of a tubular bar and employing such shaving as the rib or fin of the heat exchanger element; and that a substantially wider, thinner, stronger and more eflicient shaving of greater strength and heat or cold exchanging capacity per unit of weight and length of substantially less liability of flexure may be formed of the generic as well as the specific shearing disclosed in our present application. It will be understood by those skilled in this art that there are substantial problems in the making-of heat exchanger ribs or fins from a shaving cut from one end of a tubular bar of metal, and that applicants have solved said problems in and bytheir present invention. The major-one of said problems appears to be that the shaving when severed from the bar substantially upon a radial line passingthrough its axis of r0; tation'compels the simultaneous severance and substantial lateral bending of the shaving along said radial line which is the shortest distance across the width of the shaving and hence the weakest point in such shaving. This liability of breakage of the shaving is overcome by the following contributory factors arising from applicantspresent shearing line of cleavage ofthe shaving from the bar substantially departing from said radial line;

1. This shearing cleavage line increases in angularity as the cutting speed decreases toward the center of rotation of the bar from which the heat exchanger ribs are turned.

2. While the metal toward the periphery of the bar is being sheared through a point in a radial line passing through the axis of rotation of the bar, some metal of the bar toward its center of rotation and extending beyond the cleavage line is below said radial line and still unsheared from the bar and supports the sheared part of the shaving from liability of breakage while being laterally bent over the outer side of the cutting tool.

3. The shearing or cleavage line of the shaving from the bar is curved in the plane of rotation and substantially longer than a radial line extending through the axis of rotation of the bar. This renders the shaving wider and stronger along such curved line of cleavage which consequently increases the bendability of the shaving and substantially decreases the liability of breakage of the shaving while being bent laterally over the outer surface of the cutting tool.

4. The angular line of cleavage of the shaving from the end of the bar of metal causes a flowage of metal along the line of cleavage as well as angularly across the cleaved surfaces. This results in a smoother, more burnished and cold worked shaving-pn each of its opposite cleaved surfaces which increases the stability, surface.

density and heat transfer properties of the shaving. This also reduces the liability of the accumulation of dust, sediment and other insulating mediums upon the surfaces of the shaving. The cutter illustrated in Fig; 3 affords a greater rate of such flowages to equalize the lesser cutting speed as the center of bar II is approached. The cutter illustrated in Fig. 4 at its inner end affords the same flowage equalizing advantages but increases the rate of flowage along the outer portion of the shaving to afford the highest degree of burnishing and cold worked characteristics toward the periphery of. the fin where the maximum heat exchanging takesplace and where the resistance to flow of ,the' medium to be heated or cooled is .greatest.

5. The above 'stated flowage of metal may be better understood when characterized as being a deflection of very smallportions of metal of the outer portions of the sheared surfaces. Such deflections occur in a direction at an angle to a radial line passing through the center of rotation of the tubular bar whose end is being shaved.

Such direction, when the shearing edge lowers "as it approaches the inner bore of the tubular bar occur at an inward angle, while when the shearing edge drops as it approaches the periphery such deflection occurs in an outward direction. At the high point of the shearing edge, whether such edge drops only in one or in two'opposite directions, affords no angular deflection, ina sense, bends a small outer portion of-the metal o t metal spinning in which a blunt tool deflects or flows metal from there to different points of the surface upon which it acts. In applicants case, the relativity of the axis of rotation of the metal bar (from the end of which the shaving is sheared) and the shearing edge occasions the, in effect, spinning, deflection or flowage simultaneously with the shearing of'the shaving from the end of the bar.

A preferred relativity of the shearing edge i'i, i'la, or llb, with the bar ii is shown in Fig. 2a in which the inner tip-of such cutting edge, which extends slightly within the bore Ila of tubular bar ii is approximately closer to the chuck or face plate ii] of the lathe than is the adjacent side of cutter i5 at approximately the center of the tool post it. This forms a slightly dished end surface 'of the bar M as indicated in Fig; 2a.

This also tends to produce a helical shaving which is slightly thinner at its periphery than at the inner edge of the central longitudinal opening therethrough.

A further preferred relativity of the shearing edge if, ila or i'lb is that the high point Hz of the shearing surfaces shown in Figs. 3 and 4 is slightly above a horizontal line passing through the axis of rotation of the bar ii, while the other portions of' such shearing edges drop, toward and/0r below said line as such shearing edge extends across the thickness of the wall of tubular bar ii. We have obtained very satisfactory results with said high point approximately above such horizontal line.

The arched shearing edge llb of cutting tool [5 of Fig. 1- also produces a correspondingly curved end wall of the tube il, so that only the thinner small initial portion of the shaving is required to be broken ofi, which represents that initial portion until the shearing edge llb heli cally attains the required thickness of the shaving.

' In Figs. 2, 3 and 4, we provide a rod lic which extends into opening iia throughout the length of bar ii and projects beyond the outer end of bar Ha to receive and hold concentric with bar i i the helical shaving i lb as the same is cut from the end of said bar I i. This steadies the severed portions of the helices lib and materially tends to prevent their being broken from the bar Ii, as well as prevents the free, end of the severed helix I lb from being whipped about by the turning of, the lathe to the menace of the operator.

The surface ilc extending downward from the cutting edge I1, "a, "b shapes away from said cutting edge about three degrees in order to afford clearance: between said surface Ho and the unsevered end of'bar ii. i

The beveled surface, opposite surface We, extends downward from said cutting edge at a wide angle in order to afford substantial strength of metal supporting said cutting edge. As the severed portion of helix llb flows over this beveled surface its surface in contact therewith is highly burnished while its opposite surface assumes a frosted appearance at the point where it bends sharply away from the unsevered metal comprising the end of bar' II. This frosted appearance extends uniformly, in many instances, throughout the outer surface of the seve'redportion of ,the'h'elices I lb and seems to be occasioned 7 llb are separated from the end of bar II, and is certainly polished substantially by its sliding contact over the beveled surface of the cutting tool l5. Such cold working of the opposite major surfaces of the helices Hb increase the resistance to breakage as well as the capacity of said surfaces of the helices to transfer heat or cold. Such cold working also increases the thinness of said helices Nb and the heat or cold exchanging efilciency and lightness of the heat exchanger element 20 with which the same may be provided by increasing the number of such helices llb per unit of length of element 20 without impairing the upright stability of the helices D by reason of their increased strength and greater freedom from breakage and deformation provided by said cold working.

This invention may be made and used by or for the Government of the United States for governmental purposes without the payment of any royalty thereon or therefor.

Having now so fully described our invention that others may therefrom make and use the same, what we claim is:

1. The method of making a helical fin of relatively wide, thin metal having a longitudinal "opening through its center and the helix cam-- bered in cross-section comprising separating from the end of a tubular bar of metal a central initial portion of the helix and stretching the same to form the camber, and then separating from the bar the inner and outer edges of the separated and stretched-portion of the helix.

2. The method of making a helical fln of relatively wide, thin metal having a longitudinal opening through its center and the helix cambered in cross-section comprising separating from the end of a tubular bar of metal a central initial portion of the helix and stretching the same to form the camber, and then separating from the bar the inner and outer -edges of the separated and stretched portion of the helix while a further advanced central portion of the helix is being severed from the bar and stretched, and

progressively continuing said operations until the desired length of helix is obtained.

3. The method of making a helical rib for a heatexchanging element having a longitudinal opening through 'its center and helices of wide, thin metal cambered in cross-section by shearing progressive portions of, the helix from the end of a tubular bar of metal with the line of shear being of substantially the camber required in the helices.

4. The method of making a helical heat exchange fin comprising progressively cutting a bar of high heat conductivity metal continuously at its end along a non-radial line thereof and in the direction of its length to directly form by the cutting operation a helical heat exchange fin.

5. The method of making a. helical heat exchange fin comprising progressively cutting a bar of high heat conductivity metal continuously at its end and in the direction of its length to directly form by the cutting operation a helical heat exchange fin, and concurrently with the aforesaid cutting operation imparting a camber to the helical heat exchange fin.

6. The method of making a helical-heat. exchange 'fln comprising progressively cutting a bar of high heat conductivity metal continuously at its end along a non-radial line thereof and in the direction of its length to directly form by the cutting operation a helical heat exchange fin and concurrently with the aforesaid cutting operation imparting a camber to the helical heat exchange fin.

7. The method of making an apertured helical heat exchange fln comprising progressively cutting a longitudinally aperturedbar of high heat conductivity metal continuously at its end and in the direction of its length to directly form by the cutting operation an apertured helical heat exchange fln and supporting the apertured helical heat exchange fin at its inner periphery during the cutting operation.v

JOHN 0. HUSE. ALFRED J. BERG.

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