GB2128915A

GB2128915A - Method of making heat exchange elements

Info

Publication number: GB2128915A
Application number: GB08224726A
Authority: GB
Inventors: Richard Walker Kritzer
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-27
Filing date: 1982-08-27
Publication date: 1984-05-10
Also published as: GB2128915B

Abstract

In a method of making an elongate heat exchange element 1 having outwardly projecting fins 4 cut or gouged by cutters 14 and 15 from a tubular member 2, the cutters 14 and 15 and the tubular member 2 are vibrated relative to each other to afford roughened surfaces on the cutter-adjacent faces 21 of the fins. <IMAGE>

Description

SPECIFICATION Method of making heat exchange elements This invention relates to a method of making a heat exchange element, and, more particularly, to a method of making a heat exchange element having outwardly projecting fins spaced longitudinally therealong, and wherein both of the longitudinally facing surfaces of the fins are roughened.

The making of spined heat exchange elements by cutting or gouging the spines from outwardly projecting ribs on a tubular member has been heretofore known in the art, being shown, for example in my U.S. Patent No.

3,202,212 and in U.S. Patents Nos.

3,866,286, 3,886,639 and 3,947,941.

Also, the making of spined heat exchange elements wherein the spines are formed as integral parts of a larger fin member by cutting or gouging the spines from outwardly projecting ribs and cutting or gouging the remainder of the fin members from material underlying the ribs has been heretofore known in the art, being shown, for example, in U.S. Patent No. 3,692,105.

It is known that in the making of finned and/ or spined heat exchange elements in accordance with the teachings of all the aforementioned U.S. patents, the faces of the fins, facing in the direction of travel of the cutting tool in the making of the cuts, are substantially roughened. Such roughening commonly is in the nature of bubbles having a thickness of from 0.025 to 0.050 mm on fins having an overall thickness of 0.23 mm. This, in spite of the fact that the reverse sides of such fins, and the underlying surfaces of the workpiece, from which the fins have been cut or gouged, are shiny-smooth in nature.It is my opinion that such roughening of the one side of such fins is caused by the thickening and foreshortening of the fins during the gouging action; for example, a cut of 0.076 mm thickness and a length of 28.6 mm typically produces a fin having a thickness of about 0.23 mm and a length of about 10 mm.

It has been found that even having the one roughened surface on such fins is advantageous in a heat transfer member, affording a greater heat-transfer surface area, assisting in breaking up laminar flow past the fins, creating turbulence in the working fluid passing between the fins, and tending to break up the boundary layers of working fluid disposed immediately adjacent to such roughened surfaces.

It is an important aim of the present invention to provide a method of forming fins on the surface of a heat exchange element which results in both sides of the fins being roughened.

According to the invention, a method of forming fins on the surface of a heat exchange element comprises the steps of feeding an elongate tubular body member longitudinally past a cutter, reciprocating said cutter forwardly and rearwardly toward and away from said surface at an acute angle and cutting into said surface during the forward movement thereof in a skiving action, thereby to form an upstanding fin, one end of which is integral with said body member, and imparting relative vibration between said cutter and said body member during forward movement of said cutter, thereby to produce a roughened surface on the cutter-adjacent side of the fin thus formed.

The relative vibration between said cutter and said body member may be caused by vibrating said body member and/or said cutter. The relative vibration may be in a direction transverse to the reciprocatory movement of said cutter.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a somewhat diagrammatic side view of apparatus adapted to perform the presently preferred form of the method in accordance with the invention, Figure 2 is a fragmentary plan, on an enlarged scale, of a portion of the apparatus shown in Fig. 1, looking in the direction of the arrows 2-2 in Fig. 1, Figure 3 is a sectional view taken on the line 3-3 in Fig. 2, Figure 4 is a fragmentary sectional view, similar to a portion of Fig. 1, but on an enlarged scale and showing the cutter at the end of a cutting or gouging stroke, Figure 5 is a rear elevational view of a work-holder adapted to perform a modified form of the method in accordance with the invention, the view being in the direction of the arrows 5-5 in Fig. 1 if the work-holder, shown in Fig. 5, were embodied in the apparatus of Fig. 1, and Figure 6 is a fragmentary sectional view taken along the line 6-6 in Fig. 5.

Referring to Figs. 1 to 4, in the preferred practice of the present invention a heat exchange element 1 is formed from a suitable length of tubular stock, such as the tubular member 2 (Fig. 1), working from one end portion A of the member 2 toward the other end B thereof, and severing the heat exchange element 1 from the remainder B-C of the tubular member 2 upon completion of the forming of the desired length of the heat exchange element, such as the length A-C.

The heat exchange element 1 embodies, in general, an elongate tubular body portion 3 having elongate fins 4 projecting outwardly therefrom, each of the fins 4 embodying an elongate base portion 5 having a plurality of spines 6 projecting outwardly from one longitudinal edge thereof (Figs. 1 and 2). Preferably, the fins are of the general type of the spined fins shown in the aforementioned U.S.

Patent No. 3,692,105.

Preferably, the tubular member 2 is substantially rectangular in transverse cross-section, as shown in Fig. 5 with respect to a modified form of the invention. The tubular member 2 shown in Fig. 5 has a top wall 7 and a bottom wall 8 disposed in substantially parallel relation to each other, and two oppositely disposed side walls 9 and 10 extending between respective sides of the side walls 7 and 8 in substantially perpendicular relation thereto. A plurality of openings 11 extend longitudinally through the tubular member 2.

As will be appreciated by those skilled in the art, the tubular member 2 is shown herein as being rectangular in transverse cross-section and having a plurality of openings 11 extending longitudinally therethrough merely by way of illustration and not by way of limitation, and tubular members having shapes other than rectangular and having a single opening extending longitudinally therethrough may be employed without departing from the purview of the present invention.

In the heat exchange element 1 shown in Fig. 1, the fins 4 project outwardly from the outer faces of two walls 7a and 8a corresponding to, and, in fact, formed from the walls 7 and 8 of the tubular member 2, as will be discussed in greater detail presently.

The fins 4 extend longitudinally across the respective walls 7a and 8a in a direction transverse to the length of the tubular member 2, and each of the fins 4 embodies one of the aforementioned base portions 5 having a lower longitudinal edge portion 12 integral with the respective wall 7a or 8a to which it is attached. Each base portion 5 projects outwardly from the respective one of the walls 7a and 8a, preferably in substantially perpendicular relation thereto, with the spines 6 thereon spaced along and projecting outwardly from the longitudinal edge of the base portion 5 remote from the wall 7a or 8a.

The tubular member 2, from which the heat exchange element is made, may be made of any suitable material, such as, for example, aluminium, and embodies a plurality of elongate outwardly projecting ribs 1 3 (Fig. 5) on the outer face of each of the side walls 7 and 8, the ribs 13 extending longitudinally of the tubular member 2 in parallel spaced relation to each other.

In making the heat exchange element 1, a tubular member such as the tubular member 2, and embodying the ribs 13 extending the full length thereof, may first be formed. Thereafter, the fins 4 may be successively formed on each of the side walls 7 and 8 from one end portion of the tubular member 2, such as the end portion A, toward the other end B thereof (Fig. 1). The fins may each be cut or gouged from the walls 7 and 8 by means of suitable reciprocatable cutting tools such as the cutters 14 and 15, which first cut into the ribs 13 lengthwise of the latter, from left to right, as viewed in Fig. 1, to form surfaces 16 which terminate at their lower ends, as viewed in Fig. 1, at the base 17 of the ribs 13. The cutters then continue to cut into the portion 18 of the wall 7 or 8 underlying the ribs 13 to form the surface 19 (Fig. 1).The fins 4, which have been cut or gouged in this way from the walls 7 and 8 of the tubular member 2, are then bent outwardly preferably to a position approximately perpendicular to the planes of the walls 7 and 8 on which they are formed.

After thus forming the fins 4 along the desired length of the tubular member 2, such as the length A-C, the tubular member 2 may be severed transversely to its length at the point C, thereby to afford a finished heat exchange element having fins 4 spaced along substantially the whole length thereof. As will be appreciated by those skilled in the art, if desired, the formation of the fins 4 may be commenced inwardly of the end portion A of the tubular member 2, and the tubular member may be severed outwardly to the left, as viewed in Fig. 1, of the last formed fin 4, thereby to afford end portions which project outwardly from the outermost fins 4 to afford connecting members at each end of the finished heat exchange element.In such last mentioned construction, not shown, the ribs 13 of the tubular member 2 disposed outwardly of the aforementioned outermost fins, preferably are removed by suitable means, such as, for example, grinding, thereby to afford a smooth-walled end portion for the completed heat exchange element.

The method of making finned heat exchange elements thus far described herein, by cutting or gouging them from opposite sides of a tubular member, has been heretofore known in the art, being shown, for example, in the previously mentioned U.S. patents.

However, as previously mentioned, only the faces of the fins of such heretofore known heat exchange elements, corresponding to the faces 20 of the fins 4, which face to the right as viewed in Fig. 1, are roughened, while the faces of the fins, corresponding to the faces 21 of the fins 4 which face to the left, as viewed in Fig. 1, are shiny-smooth, as are the surfaces of the tubular member 2 from which these last-mentioned faces are lifted. As will be discussed in greater detail hereinafter, in the practice of the method of the present invention, the faces 21 of the fins 4, as well as the faces 20 thereof are roughened, thereby to afford the previously mentioned advantageous performances of the fins 4.

In accordance with the principles of the preferred form of the method in accordance with the invention, the roughening of the faces 21 of the fins 4 is accomplished by vibrating the cutters 14 and 15 with respect to the tubular member 2, during the formation of the fins 4, as will be discussed in greater detail hereinafter.

In the apparatus shown in Figs. 1 to 4, each of the cutters 14 and 15 is operatively connected to a suitable mechanism 22 and 23, respectively, for forming the fins 4 in accordance with the method of the present invention. The mechanisms 22 and 23 are identical in construction, except that they are mirror images of each other and, therefore, parts of the mechanism 23, which are identical to corresponding parts of the mechanism 22 are designated with the same reference numerals as the corresponding parts of the mechanism 22.

The mechanism 22 embodies an elongate, substantially rectangular-shaped cutter slide 24 slidably mounted in the bottom portion of a substantially inverted U-shaped, stationarily mounted cutter guide 25, for longitudinal reciprocation therethrough. The cutter guide 25 has a plurality of pins 26 mounted in the opposite side walls thereof and projecting into elongate grooves 27 formed in the respective opposite sides of the cutter slide 24, and extending the length thereof, for mounting the slide 24 in the cutter guide 25 for the aforementioned longitudinal reciprocation therethrough, only one side of the guide 25 and one groove 27 being shown here.

The mechanism 22 also includes a substantially inverted U-shaped cross-head 28 movably mounted therein for vertical reciprocation relative to the cutter slide 24. The cross-head 28 embodies two vertically extending side walls 29 and 30 (Fig. 1) disposed on opposite sides of the slide 24, the side walls 29 and 30 each having cam slots 31 disposed therein. Pins 32, one of which is shown in Fig. 1, are mounted in the opposite sides of the slide 24 and project outwardly through respective ones of the cam slots 31 in such position that vertical reciprocation of the cross-head 28 is effective to reciprocate slide 24 longitudinally through the guide 25 by reason of the engagement of the pins 32 with the side walls of the cam slots 31.

The slide 24 of the mechanism 22 has a rectangular-shaped recess 33 formed in the front end portion thereof and extending transversely across the full width thereof (Figs.

2 and 3). The cutter 14 is of rectangular, cross-sectional shape, and is of such size that it will fit into the recess 33, with the top 34 of the cutter disposed in abutting engagement with the top wall 35 of the slide 24; the rear face 36 of the cutter 14 disposed in abutting engagement with the rear wall 37 of the recess 33; the bottom 38 of the cutter 14 disposed in uniplanar relation to the bottom 39 of the slide 24; and the cutting edge 40 of the cutter 14 projecting outwardly beyond the front end 41 of the slide 24. The length of the cutter 14 is somewhat less than the lateral width of the slide 24, the ends 42 and 43 of the cutter being disposed in inwardly spaced relation to the sides 44 and 45 of the slide 24, when the cutter 14 is disposed in operative position in the latter (Fig. 2).

The slide 24 has two elongate slots 46 and 47 (Fig. 2) extending vertically through the top wall 35 of the recess 33, in substantially longitudinal alignment with each other, along the longitudinal centre line of the top wall 35, and two bolts 48 and 49, having heads 50 and 51, respectively, resting on top of the top wall 35, project downwardly through the slots 46 and 47, respectively, and are screwthreaded into the cutter 14 for slidably securing the latter in the recess 33 for longitudinal reciprocation therein. Preferably, the cutter 14 is secured to the slide 24 by the bolts 48 and 49 with a relatively snug, but freely slidable fit, so that it is firmly held in the recess 33 but is free to slide longitudinally therein.

A vibrator 52 is mounted on the slide 24 for movement therewith by suitable supporting means, such as a mounting bracket 53 (Fig. 2) and embodies a vibratory shaft 54 suitably secured to the cutter 14, such as, for example, by being screw-threaded into one end thereof. The vibrator 52 may be of any suitable type readily available on the market, but, preferably, is of such type that it will longitudinally vibrate the cutter 14 at a rate of from 12,000 to 15,000 vibrations per minute, for a purpose that will be discussed in greater detail presently.

From the foregoing it will be seen that vertical reciprocation of the cross-head 28 is effective through the engagement of the pins 32 with the side wall of the cam slots 31 therein to reciprocate the cutter slide 24 longitudinally through the cutter guide 25 and thus correspondingly reciprocate the cutter 14 through the cutting or gouging motions, heretofore mentioned, for forming fins, such as the fins 4.

The apparatus also includes a guide 55 (Fig. 1) for longitudinal movement of the tubular member 2 therethrough. The guide 55 is disposed in position effectively to support the tubular member 2 in position for the aforementioned cutting or gouging operations of the cutters 14 and 15 on the tubular member 2.

It will be remembered that in forming the fins 4, the cutter 14 moves through a stroke of substantial length, such as, for example, a length of 28.5 mm, at a relatively narrow depth of cut, such as, for example, a depth of 0.08 mm, to produce a fin of substantially less length than the length of cut, such as, for example, a length of 10 mm and having a thickness substantially greater than the depth of cut, such as, for example, a thickness of 0.23 mm. As previously mentioned, it has been found that such skiving operations form a roughened or bubbled surface on one side of the fins 4, namely the faces 20 thereof, while leaving the other faces 21 of the fins shiny-smooth.In the practice of the method of the present invention, at all times during the reciprocation of the slide 24 of the mechanism 22, the vibrator 52 is energised thereby to cause the shaft 54 to vibrate longitudinally at a relatively rapid rate, such as, for example, at the aforementioned rate of 1 2,000 to 15,000 vibrations per minute. Such vibration of the cutter 14 is for the purpose of causing roughening of the faces 21 of the fins 4 to a depth in the nature of 0.025 mm, and with the roughened portions spaced from each other, between the edge portions 12 of the fins 4 and the free edges thereof, in the nature of thirty-five to forty-five, and preferably forty roughened areas per fin.

With the fins 4 formed in the aforementioned manner, it will be seen that both faces 20 and 21 thereof are roughened. This roughening of the faces 21 of the fins 4 is effective to afford a heat-transfer area which is greater than that of the shiny surfaces heretofore known in the art; affords a surface which assists in breaking up laminar flow past the fins 4; creates increased turbulence in the working fluid passing between the fins 4; and tends to break up the boundary layers of working fluid disposed immediately adjacent to the faces 21.

The operation of the mechanism 23 is the same as that of the mechanism 22, except that the mechanism 23 is disposed below the tubular member 2, and operates on the lower face thereof, and, of course, both mechanisms 22 and 23 are operated simultaneously on the member 2 passing through the guide 55.

In Figs. 5 and 6, which show a modified form of apparatus for performing the method in accordance with the invention, parts which are the same as parts shown in Figs. 1 to 4 are designated with the same reference numerals as the corresponding parts shown in Figs. 1 to 4, and parts which are similar to, but are different from, corresponding parts shown in Figs. 1 to 4 are designated with the same reference numerals with the suffix "b" added thereto.

In the apparatus shown in Figs. 5 and 6, the tubular member 2 and the cutters are vibrated relative to each other during the aforementioned fin-forming operations, but rather than the cutters, such as the cutters 14 and 15 of the apparatus shown in Figs. 1 to 4, being vibrated relative to the tubular member 2, the tubular member 2 is vibrated relative to the cutters during the fin4orming operations.

In Figs. 5 and 6, the guide 55b for the tubular member 2 is slidably mounted by a pin or rod 56 extending through and slidably mounted in a passageway 57 in the upper portion 58 of a mounting base 59. The rod 56 is mounted in and secured to two ears 60 and 61 on the guide 55b, the ears 60 and 61 being disposed in outwardly spaced relation to opposite sides of the upper portion 58 of the base 59, so that the rod 56 may be longitudinally reciprocated relative to the latter.

A vibrator 52b is mounted on the base 59 and has a vibratory shaft 54b extending therefrom and secured to the guide 55b by suitable means such as being screw-threaded thereinto. In the operation of the apparatus illustrated in Figs. 5 and 6, the tubular member 2 passes through an opening 62 in the guide 55b, and is disposed therein with a relatively snug, but freely slidable fit. During such passage through the guide 55b, the vibrator 52b is effective, through its connection to the guide 55b by the shaft 54b, to vibrate the guide 55b longitudinally of the rod 56 and thereby cause vibration of the tubular member 2 relative to the cutters, performing the cutting or gouging operations thereon.

If desired, the cutters used with the apparatus shown in Figs. 5 and 6 may be vibrated, in the same manner as heretofore discussed with respect to the apparatus shown in Figs. 1 to 4, but it is presently preferred that, when the relative vibration between the tubular member and the cutters is afforded by vibration of the tubular member, such as, for example, by the apparatus shown in Figs. 5 and 6, the cutters operating on the tubular member should not be vibrated simultaneously therewith. This, of course, may be readily accomplished when using apparatus of the type shown in Figs. 1 to 4 in cooperation with the apparatus shown in Figs. 5 and 6 merely by eliminating the vibrators 52 and securing the cutters 14 and 15 on their respective slides 24 with a snug, non-slidable fit, by suitably tightening the bolts 48 and 49.

From the foregoing it will be seen that the present invention affords a method of making heat exchange elements having improved heat-transfer characteristics between the fins thereof and the working fluid passing therebetween, which method is practical and efficient in operation and which may be readily and economically accomplished.

Claims

1. A method of forming fins on the surface of a heat exchange element which comprises the steps of feeding an elongate tubular body member longitudinally past a cutter, reciprocating said cutter forwardly and rearwardly toward and away from said surface at an acute angle and cutting into said surface during the forward movement thereof in a skiving action, thereby to form an upstanding fin, one end of which is integral with said body member, and imparting relative vibration between said cutter and said body member during said forward movement of said cutter, thereby to produce a roughened surface on the cutter-adjacent side of the fin thus formed.

2. A method according to claim 1, wherein the relative vibration between said cutter and said body member is caused by vibrating said body and/or said cutter.

3. A method according to claim 1 or 2, wherein the relative vibration between said cutter and said body member is in a direction transverse to the reciprocatory movement of said cutter.

4. A method according to claim 1 or 2, wherein the relative vibration between said cutter and said body member is in a direction transverse to the feed direction of said body member.

5. A method of forming fins on the surface of a heat exchange element, substantially as herein described with reference to, and as illustrated in, Figs. 1 to 4, or Figs. 1 to 4 as modified by Figs. 5 and 6, of the accompanying drawings.

6. A heat exchange element when made by the method claimed in any of the preceding claims.