IE51520B1

IE51520B1 - Sealing flat metal tube ends

Info

Publication number: IE51520B1
Application number: IE307/86A
Authority: IE
Original assignee: Mooney Brian F
Priority date: 1984-02-16
Filing date: 1984-02-16
Publication date: 1987-01-07
Also published as: EP0153138A3; EP0153138A2; DE3569894D1; EP0153138B1; BE901760A

Abstract

A method of manufacturing heat exchangers comprises holding two lengths of header piping in mutually parallel relationship and advancing the header piping step-by-step through a series of work stations to enable operations to be performed at the work stations, locating heat exchange elements relative to the header piping so that an aperture at each end of each heat exchange element is aligned with an aperture in each length of header piping, welding the apertured heat exchange elements to the header piping and subsequently cutting the assembly of header piping and heat exchange elements to form radiators of predetermined size. The invention also provides apparatus for carrying out the method and radiators made by the method. The invention further provides a method of closing the open ends of a flat metal tube using a pair of grooved rollers, each of which is alternately pressed down on and moved across the open end of the tube, causing the material of the tube to be pressed inwardly, thereby closing the open end of the tube.

Description

The present invention relates to heat exchangers and in particular to heat radiators of the kind in which a plurality of mutually parallel flat heat exchange tubes are connected between a pair of header pipes. The invention is concerned with a novel method of and apparatus for closing the ends of the flat metal tubes used in the manufacture of such radiators.

The invention provides a method of closing the ends of flat metal tubes. By flat tubes is meant tubes which have two flat parallel closely spaced apart side walls. Flat tubes have a large surface to volume ratio and are thus useful in heat exchangers, for example in central heating radiators.

In such applications, a heat exchange element is formed by cutting a length of flat tubing, closing and sealing the two ends of the length, and providing a small aperture or apertures adjacent each end of the length as an entry and exit for the heat exchange fluid. When the heat exchange element is intended for a column radiator, the apertures are generally provided on the curved part of the sidewall or on the folded over end of the element. When the heat exchange element is intended for a panel radiator the apertures are generally provided on the flat part of the sidewall.

The method of closing an open end of a metal tube 51530 - 3 having two mutually parallel side walls joined by a pair of curved ends, comprises the use of a roller having a shaped circumferential groove to fold inwardly the curved ends and then the side walls of the open end of the tube while the roller is passed across the open end of the tube from one end towards the other and pressed into engagement with the tube so that the tube end is within the groove, two roller passes being made one after the other and in opposite directions, one starting from beyond each corner. The folded in end is preferably sealed by tungsten inert gas welding.

Advantageously, the first roller pass extends less than half the length of the end of the tube and the second roller pass extends more than half the length and overlaps the first roller pass.

The roller employed should ideally have a profile such that a clearance is left between the cheek of the roller and the side walls of the tube.

Advantageously, two pairs of rollers are employed, one at each end of the tube, so that the tube may be sealed in an automatic or semi-automatic fashion, the distance between the pairs of rollers being finely adjustable.

The invention also provides apparatus for closing an open end of a flat metal tube having two mutually parallel side walls joined by a pair of curved ends, the - 4 apparatus comprising a roller having a shaped circumferential groove to fold inwardly the curved ends and then the side walls of the open end of the tube while the roller is passed across the open end of the tube from one end towards the other and pressed into engagement with the tube so that the tube end is within the groove, and means for pressing the roller into engagement with the end of the tube and for driving the roller along the end of the tube. .

The invention further provides a heat exchange element comprising a flat metal tube the ends of which have been closed and/or sealed by the method or by the apparatus referred to above.

The invention will now be described more particularly, by way of example, with reference to the accompanying drawings, in which: Figures la to Id illustrate successive stages in the method of closing and sealing the ends of a flat metal tube, and each show a view of the end of the tube together with a partial view of the side wall, near the end; - 5 Figures 2a to 2d are sections taken on II-IX of Figures la to Id respectively; Figures 3a to 3f are partial sectional elevation views showing the rollers at successive stages of closing over the edges of one end of the tube; Figures 4a and 4b are side elevations and end elevations respectively of a roller, illustrating the shape and dimensions (in millimetres) thereof; Figures 5a and 5b illustrate the dimensions (in millimetres) of the end of a flat tube, and are respectively views of the end and of the part of the side wall near the end; Figures 6a and 6b illustrate rollers closing the ends of a tube, and are respectively a sectional view on a flat side wall of the tube and a view of the end of the tube; Figures 7a and 7b are plan and sectional side elevations respectively of apparatus for making heat exchange elements, including closing and sealing flat metal tubes by the above method, the heat exchange elements being suitable for column radiators; Figures 8, 9, 10 and 11 are each end elevation views of work stations in the apparatus of Figures 7a and 7b, namely rolling, punching, welding and cleaning stations; - 6 Figures 12a and 12b are views similar to Figures 7a and 7b respectively of apparatus for making heat exchange elements suitable for panel radiators; Figure 13 is a view of a flat side wall of one end 5 of a flat metal tube whose side walls have been depressed in the region around the fluid apertures so that the fluid apertures stand proud for resistance welding purposes, while Figures 13a to 13c are sectional views thereof; Figure 14a is a sectional side elevation, as seen from one end of a flat metal tube, showing the forming tool for depressing the side walls, while Figures 14b and 14c are sectional views thereof.

The method of preparing the heat exchange elements will now be described in more detail. Referring to Figure 1 of the drawings; Figure la shows the open end of the flat metal tube before the commencement of the method; Figure lb shows the end of the tube after the first roller pass; Figure lc shows the end of the tube after the second roller pass, and shows the seam 100; and Figure Id shows the end of the tube after the seam 100 has been sealed by TIG welding. Figures 2a to 2d are sections on Figures la to Id respectively.

Referring to Figure 3, which shows one end of the tube only, the method is carried out in automated - 7 fashion by four rollers, two at each end of the tube. The first roller 101 at each end is moved across the end, thereby making a pass (Figure 3b) and is then withdrawn (Figure 3c), and the second roller 102 at each end ia moved across the end, thereby making a pass (Figure 3e), and is then withdrawn (Figure 3f).

The seam 100 may be sealed in any one of a number of ways, for example, by welding, brazing, soldering, or sealing with an adhesive or sealing compound. The preferred method is TIG welding which gives a very neat finish.

As will be noted from Figure 3c, the seam 100 lies in a single straight line in one plane, and thus lends itself to being sealed in a simple and automated fashion.

It has been found that each roller has a tendency to form a bulge in the tube material as the roller operates to close the end of a tube. It is desirable to prevent a noticeable bulge or blemish on the finished tube where the two roller passes meet. It has been found advantageous, when using the roller profile and dimensions shown in Figure 4 and the tube dimensions shown in Figure 5, that the first roller pass should extend less than halfway and preferably about one third of the way along the length of the end of the tube, and 51530 - a that the second roller pass should then extend about three quarters of the way along the length of the end of the tube in the opposite direction. Thus any bulge created by the first roller pass is pushed towards one end of the tube end by the second roller pass. The bulge of the second pass meets the bulge of the first pass not at the centre of the end of the tube where collapse or distortion of the side walls might take place but, instead, sufficiently close to the end to take advantage of the relatively high strength of the formed end.

The rollers have a profile very similar to that desired on the finished closed tube end, but a tapered clearance is desirable between the tubes and the side cheeks of the roller to prevent rubbing between them, and to allow easy access of the roller onto the tube end.

The diameter of the roller is also important in producing a good finish. Too large a diameter will produce too much downward pressure under the roller relative to the necessary forward pressure and may cause collapse of the tube side walls. The roller diameter shown in Figure 4 has been found suitable for the mild steel tube profile shown in Figure 5.

The pressure exerted by the rollers on the ends of - 9 the tubes is also important in giving a neat finish.

Too high a pressure may cause the walls of the tube to collapse, but too low a pressure may not fully close over the edges of the tube. Too low a pressure, in some instances, may be sufficient to close over the edges of the tube but not sufficient to prevent the excess metal on the inwardly rolled corners from distorting backward in a direction opposite to that of the roller pass, causing the end of the rolled tube to be wider than its original dimension.

Because the roller is free to rotate on its axis, the pressure exerted by the roller on the tube will mainly be determined by the distance from the path of the roller pass to the end of the tube which will lie parallel to it. The pressure can thus be finely adjusted by altering this distance. In the example of the mild steel tube and roller depicted in Figures 5 and 4, a suitable distance between roller paths, when both ends are rolled simultaneously, has been found to exist where the unrolled tube length (L) is reduced by 5mm in length during rolling, as depicted in Figure 6.

It has also been found that the lengths of batches of tubes to be rolled should be controlled within a tolerance of + 0.1mm to ensure a good finish when rolled. - 10 The method has been found successful for steel tubes of the dimensions shown in Figure 5. Tests have indicated that the method may also be used on tubes of various dimensions but that the ratio of the material thickness to the overall thickness of the flat tube should lie between about 0.1 to 0.2 (e.g. the tube shown in Figure 5 has a ratio of 1.5 : 11.0 = 0.136).

The method has also been found successful for tubes where the corners have been other than the simple semi-circle shown in Figure 5.

Where TIG welding is used to seal the element ends it may usefully be applied in either of the following ways:(a) Orienting the flat tube such that the seams to be welded are vertical, and then carrying the TIG weld from the top of the seam downwards to the bottom by vertical descent of the welding torch. (b) Orienting the flat tube such that the seams to be welded are horizontal, and moving the torch horizontally from one end of the seam to the other.

The horizontal welding method has the advantage that the seam weld is less likely to be affected by gravity and will thus be neater and more even, whereas the vertical welding method may exhibit a slight bulging at the lower end of the weld. The horizontal welding - 11 method is particularly suitable for elements used in panel radiators, where the elements lie one against the other, and a small uneveness would be noticeable. Horizontal orientation of the flat tubes also facilitates provision of waterway apertures in the tubes in a production line or apparatus in which tube orientation is maintained, as these apertures will normally be punched or drilled on the flat faces of the flat tubes.

The vertical welding method may be found more convenient for column radiators, where the slight uneveness will be less noticeable and where the waterway apertures are provided on the curved part of the sidewalls of the tube.

Apparatus for preparing heat exchange elements suitable for a column radiator will now be described with reference to Figures 7 to 11.

Flat metal tubing is cut into lengths, in batches with a length tolerance of + 0.1mm. One side of the apparatus shown in Figure 7a is movable to enable batches of elements of different lengths to be made.

One of the tube lengths from the batch may be used as a direct measure for setting the width of the apparatus.

The cut tube lengths are introduced to the 51320 apparatus either by individual loading or by automatic feeding from a manually loaded stack of cut tubes. The tubes are automatically moved through the work stations of the apparatus, all of the tubes in the apparatus being advanced simultaneously one step at a time. This may be achieved by various known methods of multiple component transfer such as a conveying surface or by means of loading the tubes into holders mounted on a pair of parallel endless chains which run between the two halves of the apparatus.

The first work station 104 is an end rolling station, where the ends of the tube are closed over by rolling as described above. The tube is positioned and held by a fixed rest 105 underneath and a powered movable forked clamp 105a which descends on the tube from above. Both the upper and lower rollers, which are free to rotate, are mounted in a single carriage 103 which can slide in a vertical direction only and is powered down and up by means of either a hydraulic cylinder or a mechanical screw (not shown).

The second work station 106 is an aperture punching station. When preparing heat exchange elements for a column radiator, a single aperture is required, for fluid entry and exit, at each end of the curved part of the side wall of the tube. These apertures should be at - 13 least 5 mm in diameter. The tube is clamped similarly to the first work station 104. A bottom punch die is not used. An angled punch 107 is used to reduce the punching force. The slug is not fully punched from the tube but is retained by a small tag and bent through ninety degrees into the tube, to prevent problems of loose slugs rattling in the heat exchange element at a later stage.

The flat tube is then carried to the third work station 108. In this work station the closed tube ends are sealed by TIG welding. Linear movement devices 109 automatically cause the TIG welding torches 110 to traverse the seams at the closed over ends of the tubes, thereby sealing the tubes. The tubes are clamped similarly to the first station 104. The time required to TIG weld one element end is many times greater than any of the other operations carried out in the apparatus being described. Thus where production capacity is important it will be found advantageous to equip the apparatus with more than one pair of TIG welders. The apparatus shown in the drawings has three pairs of TIG welders and these are all moved by single linear movement devices on each side of the apparatus. Welding occupies three workstation positions on the apparatus, and the automatic apparatus feeding cycle is arranged such that the welding process is carried out only on - 14 every third cycle of the apparatus, whereas the other processes are carried out on every cycle of the apparatus.

The heat exchange elements are then carried to the 5 fourth workstation 111 where the area adjacent the fluid apertures is cleaned in preparation for subsequent resistance welding. Cleaning is carried out by means of a rotating wire brush 112 which descends onto the curved part of the sidewall of the element when the element is positioned in the work station.

The heat exchange elements are now complete and are discharged from the apparatus.

Apparatus for preparing heat exchange elements suitable for a panel radiator will now be described with reference to Figures 12a and 12b.

The preparation of cut tube lengths and the setting of the distance between the two halves of the apparatus are similar to that described for the apparatus shown in Figures 7 to 11.

The cut tube lengths are fed from a manually loaded magazine 113 into the apparatus. The tubes are automatically moved through the workstations of the apparatus, one step at a time, and carried by some suitable means such as a conveying surface, or by an endless chain and supporting horizontal tracks for the tubes. - 15 The first workstation 114 is an aperture punching station. In the ease of a panel radiator, two apertures are provided on the flat faces at each end of the tube. These apertures should be at least 5mm in diameter.

When punching is used, it is necessary to insert a bottom die into the tube to support it. This die is not shown in the drawings. The die is inserted and retracted automatically from the tube by the apparatus. Alternatively, the apertures can be drilled.

The second work station 115 is used only when the heat exchange element is to be subsequently resistance welded, in which case it is advantageous that the tube parts which support the fluid apertures, should project above the level of the tube material surrounding those tube parts.

Figures 13 to 13c illustrate a tube end formed at the second work station 115.

Figures 14a, 14b and 14c illustrate a forming tool set to carry out the operation. The Figures show an upper forming tool 116, a lower forming tool 117, a tube support block 118 and the tube end 119. The tube end 119 is supported underneath by support block 118. The lower forming tool 117 is inserted into the tube end 119, and has raised projections underneath where the raised portions of the tube are desired. The upper forming tool 116, having complementary depressions - 16 corresponding to the raised projections of the lower forming tool 117, descends on the tube, with sufficient force to form projections on it by permanently deforming downwards the surrounding metal of the tube.

The projection forming work process may be carried out before or after formation of the fluid apertures, or, with special tooling may be carried out simultaneously. It may also be performed as a separate operation, distinct from the element making machine.

The third work station 120 is a tube end rolling station and is similar to that previously described with reference to Figures 7 to 11. However, because the tube is moved in the apparatus with its flat face horizontal, it cannot enter the throat of the rolling device as simply as in the previously described apparatus. Instead the tube is moved into the throat by an elevating device 121, which lowers the tube to its former position when rolling is completed.

The fourth work station 122 is the TIG weld end sealing station and is similar to that previously described with reference to Figures 7 to 11 except that the welding carriage moves horizontally instead of vertically along the tube seams.

At the final workstation 123 the area of tube adjacent the fluid apertures is cleaned by wire brushes. This station 123 is similar to that previously described - 17 with reference to Figures 7 to 11 except that the apertures lie on a different part of the tube.

Work stations 123 are only provided when the heat exchange element is to be subsequently resistance welded to headers.

Two pairs of wire brushing stations are provided in the apparatus illustrated in Figures 12a and 12b because each tube end has two fluid apertures.

The heat exchange elements are now complete and are 10 discharged from the apparatus.

Heat exchangers may sometimes include one or more dummy elements, that is elements through which no water flows and which are provided for purely aesthetic reasons. In making these dummy elements, the punching operation may be omitted from the method by rendering the punching station of the apparatus inoperative.

Claims

1. A method of closing an open end of a flat metal tube having two mutually parallel side walls joined by a pair of curved ends, the method comprising the use of a roller having a shaped circumferential groove to fold inwardly 5 the curved ends and then the side walls of the open end of the tube while the roller is passed across the open end of the tube from one end towards the other and pressed into engagement with the tube so that the tube end is within the groove, two roller passes being made one after the 10 other and in opposite directions, one starting from beyond each corner.

2. A method according to Claim 1, in which the folded in end of the tube is sealed by tungsten inert gas welding.

3. A method according to Claim 1 or Claim 2, in which 15 the first roller pass extends less than half the length of the end of the tube and the second roller pass extends more than half the length and overlaps the first roller pass.

4. A method according to any one of Claims 1 to 3, in 20 which the roller employed has a profile such that a clearance is left between the cheek of the roller and the side walls of the tube.

5. A method according to any one of Claims 1 to 4 in which a pair of rollers are employed at the end of the 25 tube, one to make each pass.

6. A method according to Claim 5, in which two pairs of rollers are employed, one at each end of the - 19 tube, so that the tube may be sealed in an automatic or semi-automatic fashion, the distance between the pairs of rollers being finely adjustable.

7. Apparatus for closing an open end of a flat metal 5 tube having two mutually parallel side walls joined by a pair of curved ends, the apparatus comprising a roller having a shaped circumferential groove to fold inwardly the curved ends and then the side walls of the open end of the tube while the roller is passed across the open end of 10 the tube from one end towards the other and pressed into engagement with the tube so that the tube end is within the groove, and means for pressing the roller into engagement with the end of the tube and for driving the roller along the end of the tube. 15

8. A heat exchange element comprising a flat metal tube the ends of which have been closed and/or sealed by the method according to Claim 1 or by the apparatus according to Claim 7.

9. Apparatus for sealing the end of a flat metal tube, 20 substantially as herein described with reference to and as shown in the accompanying drawings.

10. A method of closing and sealing an end of a flat metal tube, substantially as herein described with reference to the accompanying drawings.