This application claims priority to Canadian Patent Application No. 2,420,273 filed Feb. 27, 2003.
The invention relates to methods for manufacturing plates for heat exchangers, particularly to methods in which generation of scrap is reduced, and to heat exchanger plates made by these methods.
Heat exchangers are commonly made from multiple stacked plate pairs which define coolant flow passages extending between a pair of headers. As shown in
The individual plates making up such a heat exchanger are usually formed by a process known as “progressive stamping” in which the plates are progressively formed by successive stamping operations performed on a coil of sheet metal. As explained above, the end bosses must be of a sufficient height to allow insertion of cooling fins. The bosses must also be of a specific diameter or area to allow sufficient coolant flow through the headers. Thus, the strip width required for each plate is generally determined by the width of strip material required for formation of the bosses.
In many cases, the width of strip material required to form the bosses is greater than a desired width of the plate pairs. This results in the need to trim excess material along the edges of the plates, particularly between the end portions in which the bosses are formed. The amount of scrap material generated by conventional progressive stamping of heat exchanger plates can be as high as 35 percent.
Thus, there is a need for improved methods of forming heat exchanger plates in which generation of scrap is reduced or eliminated, and in which plates of varying lengths may be produced without excessive tooling costs.
In one aspect, the present invention provides a method for forming a plate for a heat exchanger, the plate having a length and a width, the length defining a longitudinal axis, the method comprising: (a) providing a flat, sheet metal strip having elongate, longitudinally extending side edges, the strip having a width substantially the same as the width of the plate; (b) forming a fluid flow channel extending along the side edges of the strip, the fluid flow channel being raised relative to the side edges; and (c) forming a pair of raised bosses in the strip, the bosses being raised relative to the side edges and the fluid flow channels, wherein a longitudinal dimension of the bosses is greater than a transverse dimension of the bosses.
In another aspect, the present invention provides a heat exchanger plate, comprising: (a) a central portion defining an elongate fluid flow channel; (b) a pair of end portions separated by the central portion; (c) a raised boss provided in each of the end portions, each raised boss having an interior and an upper surface provided with a fluid flow aperture, wherein the interiors of the bosses are in communication with the fluid flow channel; (d) a planar flange extending continuously about an entire periphery of the plate and surrounding the fluid flow channel and the raised bosses; and (e) a plurality of tabs, each of which is integrally formed with the flange and extends from the flange, each of the tabs being located in one of the end portions of the plate.
In yet another aspect, the present invention provides A heat exchanger, comprising a plurality of plate pairs formed from the heat exchanger plates according to the invention, each of the plate pairs being formed by sealing the flanges of the plates together with the interiors of the bosses of one plate communicating with the interiors of the bosses of the other plate and so that the central portions of the plates combine to form a fluid passage in communication with the interiors of the bosses, the plate pairs being stacked with the apertures of the bosses in registry, the bosses of the plate pairs forming a pair of headers.
The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
The plate 10 has an upper surface 18 and an opposed lower surface 20, with elongate side edges 22 extending along the entire length of plate 10 and terminating at end edges 24. Extending along the side edges 22 of plate 10 are a pair of shoulders 26, these shoulders 26 defining a longitudinally extending fluid flow channel 28 extending along the lower surface 20 of plate 10. The fluid flow channel 28 preferably extends along substantially the entire central portion 12 of plate 10, and may preferably extend beyond dotted lines 16 into the end portions 14 of plate 10. The shoulders 26 are spaced from the side edges 22 so as to form flat peripheral side flanges 30 between the side edges 22 and the shoulders 26. The side flanges 30 extend longitudinally along the side edges 22 between the end portions 14.
Located in the end portions 14 of plate 10 are a pair of raised bosses 32. The bosses 32 are raised relative to the side edges 22 and relative to the fluid flow channel 28, having a height sufficient such that when a heat exchanger is formed by stacking plate pairs formed from plates 10, each plate pair formed by joining a pair of plates 10 with their lower surfaces facing one another, sufficient space exists between the plate pairs for insertion of cooling fins.
The bosses 32 can be of any desired shape, including circular. Preferably, the bosses 32 each have a major diameter extending in the longitudinal direction which is greater than a minor diameter extending in the transverse direction. Most preferably, the bosses are of an oval shape. As used herein, the term “oval” refers to any non-circular shape having a generally smoothly curving periphery, such as an ellipse, a rectangle with rounded corners, or other oblong or egg shape. In the preferred embodiment shown in the drawings, the bosses 32 are oval in plan view, having substantially straight longitudinally extending sides 34 extending between smoothly curved ends, a proximal end 36 located at or near the dotted line 16 between the central portion 12 and end portions 14, and a distal end 38 located proximate the end edge 24 of the plate 10.
As shown in
In order to provide fluid communication through the headers after assembly of the heat exchanger, the upper surface 44 of each boss 32 is provided with an aperture 42. The area of the aperture 42 is sufficiently large to provide adequate fluid flow throughout the header, while maintaining an annular sealing surface 46 on the upper surface 44. During assembly of the heat exchanger, adjacent plate pairs are joined to one another, for example by brazing, along the annular sealing flanges 46. As shown in the preferred plate 10, the aperture 42 may preferably be centred on upper surface 44 and may generally follow the shape of the raised bosses 32, although this is not essential.
As best seen in the bottom plan view of
As mentioned above, the plate pairs formed from plates 10 may be provided with turbulizers such as the expanded metal turbulizers disclosed in the above-mentioned patent to So et al., which is incorporated by reference herein in its entirety. The turbulizers are preferably rectangular in shape and are received between the plates 10 of the plate pairs, preferably extending throughout substantially the entire central portions 12 of the plates 10. As well as enhancing heat transfer, turbulizers provide support for the central portions 12 of plates 10, preventing collapse or narrowing of the fluid flow channels 28. In a heat exchanger constructed from pairs of plates 10, the ends of the turbulizers preferably overlap the proximal curved ends 36 of the bosses 32, so that the turbulizers provide support along the entire length of the fluid flow channels 28. The inward tapering of the side flanges 30 functions as an integral turbulizer stop so as to prevent longitudinal sliding of the turbulizer between the plate pairs. A preferred position of the end of a turbulizer (not shown) is indicated by dotted line 51 in FIG. 3.
Having now described the preferred heat exchanger plate 10 according to the invention, the following is a description of a preferred method for manufacturing a heat exchanger plate 10 according to the invention.
One preferred method of the invention begins by providing a sheet metal strip 52, preferably comprised of a brazeable material, which is preferably selected from the group comprising aluminum, an aluminum alloy, and aluminum or aluminum alloy coated with a brazing filler metal. The strip 52 as defined herein is of indefinite length, having longitudinally extending side edges 54, an upper surface and an opposed lower surface (not shown). The width of strip 52, measured in the transverse direction, is substantially the same as the width of the plate 10 described above.
A plurality of strips 52 may be formed by longitudinally slitting a coil of sheet metal (having a width greater than the width of strip 52) at one or more points across its width, with the longitudinal direction of the strip 52 being parallel to the direction of slitting. Alternatively, strips 52 may be formed by dividing a coil into sheets which are then slit longitudinally or transversely into strips 52.
During the method of the invention, the strip 52 is severed in the transverse direction at one or more points to form a plurality of blanks 53, each of which has a length, measured in the longitudinal direction, which is substantially the same as the length of plate 10.
Another preferred method of the invention begins by providing a sheet metal blank 53 having a width the same as that of strip 52 and having a length which is substantially the same as that of plate 10. The blanks 53 may preferably be formed as described above by transversely severing strips 52 of indefinite length. Where the length of the blank 10 is the same as the width of the sheet metal coil, the blanks 53 may be formed by cutting transversely across the width of the coil. Where the length of the blank 53 is somewhat greater than the width of the coil, the blanks 53 may be formed by slitting the coil diagonally, that is with the side edges 54 of the strip 52 being angled relative to the transverse direction of the coil.
Except as otherwise indicated, the method now described below begins with a blank 53 having a length and a width which are substantially the same as the length and width of the plate 10. However, to indicate that the method may begin with the provision of either a strip 52 or a blank 53,
The next step in the method comprises the formation of the fluid flow channel 28, preferably by formation of shoulders 26 along the side edges 54 of the blank 53. Preferably, as shown in
It will be appreciated that the formation of shoulders 26 provide each plate 10 with a single, longitudinally extending flow channel 28, with side flanges 30 extending along either side of the flow channel 28. The plates 10 may, however, be of more complex configuration and may be formed with more than one flow channel, although all configurations would be formed with flanges adjacent the side edges 54, and a raised central portion forming the flow channel(s).
As mentioned above, the width of strip 52 or blank 53 is substantially the same as the width of plate 10. As used herein with reference to the width of plate 10, the term “substantially the same” is intended to mean that the width of strip 52 or blank 53, measured transversely across the central portion 12 thereof, after formation of flow channel 28, is the same as the width of the plate 10, measured transversely across the central portion 12 thereof, such that no edge trimming of the plate 10 is required. It will be appreciated that the width of the strip 52 or blank 53, prior to formation of the flow channel 28, will be slightly greater than the width of plate 10 since the material required for formation of the shoulders 26 will be drawn from the width of the strip 52 or blank 53.
It will be appreciated that, where the method begins by provision of a strip 52 of indefinite length, the shoulders 26 may be roll-formed prior to severing the strip 52 into individual blanks 53. Of course, the shoulders 26 may also be formed by stamping the strips 52 or blank 53 with an appropriate die.
The next step in the method comprises formation of the raised bosses 32 in each of the end portions 14 of strip 52 or blank 53. The bosses 32 are formed by a plurality of successive stamping operations, with the degree of boss formation in each successive stamping operation being illustrated in
In the most preferred embodiments according to the invention, it is preferred that the strips 52 are severed into blanks 53 prior to formation of bosses 32, and that the bosses 32 are formed by successive stamping operations by pairs of dies. The dies are preferably mounted in an apparatus in such a manner that the distance between the dies can be adjusted, thereby permitting the formation of plates having various lengths, which is not possible in progressive stamping dies.
It will be appreciated that the length, width and height of the bosses 32 are selected such that the heat exchanger formed by pairs of plates 10 will have a desired flow through its headers, such that a desired spacing will be maintained between the plate pairs to allow insertion of cooling fins, and such that the bosses 32 may be formed within the width dimension of the strip 52 or blank 53, thereby avoiding the need to trim excess material from the edges of the plate 10.
After formation of the bosses 32, the next step in the method comprises the formation of apertures 42 in bosses 32, for example using a cutting die.
As shown in
Although not essential, some of this material may be removed by trimming, for example to provide smoothly rounded edges 62 as shown in
As mentioned above, the length of the blank 53 is substantially the same as the length of plate 10. As used herein with reference to the length of plate 10, the term “substantially the same” is intended to mean that the total length of blank 53, measured longitudinally between end edges 56, after formation of bosses 32, is the same as the total length of plate 10, before end trimming as described in relation to FIG. 10. It will be appreciated that the length of the blank 53, prior to formation of the bosses 32, will be slightly greater than the length of plate 10, before end trimming, since the formation of bosses 32 will somewhat reduce the length of the blank 53.
As can be seen from
In the preferred embodiment of the invention, in which the bosses 32 and apertures 42 are oval in shape, the apertures 64 are preferably also elongated in the longitudinal direction. In the particularly preferred embodiment shown in
Rather than trimming the end flange 40 as shown in
When the plate pairs 74 are stacked to form a heat exchanger, the tabs 72 will extend into the space between the plates 10. In some preferred embodiments, the tabs 72 of adjacent plate pairs 74 are of sufficient height to abut one another, and may become connected to one another during brazing of the heat exchanger, thus providing an additional brazed connection between the plates 10. In other preferred embodiments, the tabs are of lesser height, such that the tabs 72 of adjacent plate pairs do not contact one another. Where the tabs 72 of adjacent plate pairs do not engage one another, they serve to provide a plurality of surfaces to which a heat exchanger mounting bracket may be secured. Of course, a mounting bracket can also be secured to the tabs 72 in the embodiment where the tabs of adjacent plate pairs 74 abut one another.
Although the method according to the invention has been described as including formation of the flow channel prior to formation of the bosses, it is to be appreciated that this sequence of steps is preferred, but not essential. In other preferred embodiments, the bosses may be formed prior to formation of the flow channel. However, it may be preferred to form the flow channel first since the channel form improves the rigidity of the blank, thereby reducing its tendency to bend or twist, and possibly resulting in improved accuracy of the boss stamping operation.
Although the invention has been described in relation to certain preferred embodiments, it is not limited thereto. Rather, the invention includes all embodiments which may fall the scope of the following claims.
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