AU619191B2

AU619191B2 - Mesabi tube reconditioning

Info

Publication number: AU619191B2
Application number: AU18233/88A
Authority: AU
Inventors: David Thomas Fenn
Original assignee: Markhill Investments Pty Ltd
Current assignee: Markhill Investments Pty Ltd
Priority date: 1987-06-22
Filing date: 1988-06-22
Publication date: 1992-01-23
Anticipated expiration: 2008-06-22
Also published as: AU1823388A

Description

To the Coxmissioner of Patents, Commonwealth of Australia.

4 COMMONWEALTH OF AUSQ IL Patents Act 1952 COMPLETE (Original FOR OFFICE US1E Application Number: Lodged: Class Int. Class tt 44 4.4 4 @4 o o O0o too 0 0O 00 0 00 0 o~ 00 o o 00 o o.j 00 0 0) 00 00 0 0 00 00 4 0 0 4 0 o~ Complete Specification Lodg~ed: Accopted: Pu;.lifshed: Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Invjcntor: AMd'ress for Service:- David Thomas FENN 9 Murrena Street, Wedgefield, in the State of Western Australia, Commonwealth of Aitstralia.

David Thomas FENN Wray Associates Primary Industry House 239 Ad..laide Terrace Perth Weste~rn Australia 6000.

Complete Specification for the invention entitled: "WABI TUBE RECONDITIONING" P0012 1 2O' The following statement is a full description of thi-, invention, including the best method of performing it knc~wti to me: 1 In particular, this invention relates to an apparatus and method for manufacture and/or for reconditioning mesabi tubes.

Tubes containing heat transfer elements such as cooling fins are most often used in radiator assemblies wherein a number of hollow tubes are provided in a spaced relationship with each other and wherein the tehs conduct 00 o*10 a fluid which is to be cooled or heated through heat transfer with the environment. To maximise heat transfer between the fluid in the tubes and the environment the 000°0 tubes are normally provided with a number of heat transfer Sa oelements extending along the outside of each tube which increases the surface area of the tube and thus the heat transfer between the fluid inside the tube and the 0 o environment. Typically such heat transfer elements are in 6 the form of a continuous thermally conductive ripple 0 2 shaped sheet material which is formed separately from the 0 o 20 tube and then subsequently attached. In most instances, each tube is provided with a pair of such ripple shaped s 0 sheet heat transfer elements in opposed relationship to o° each other.

0 0a Tubes containing the above mentioned heat transfer elements are also referred to as mesabi tubes and throughout the speciicatior the term mesabi tubes will include this definition.

A disadvantage with the current manufactuare of mesabi tubes lies in the fact that the ripple shaped cooling fins are difficult to properly apply onto the outsied surface of the tubes resulting in premature separation of the fins from the tube and thus a lower efficiency of heat transfer between the fluid in the tubes ii the environment.

''"*incl de t is d fini ion jijli l~ 3 Hitherto, mesabi tubes have been manufactured by applying solder and flux to either or both faces of the surface of the fins and the tube followed by clampiing together of the fins and the tube and subsequent heating to melt the solder and bond the fins and the tubes together. Bonding of this type is generally unsatisfactory as the bonding between the contact areas of the component parts is not maximised and the component pa cs are not stress relieved prior to bondi.g.

The present invention is being devised with the general f r, object of overcoming this and other disadvantages by providing an improved method and apparatus for attaching Sheat transfer elements to tubes.

I I: In one form the invention resides in a method of formin heat exchange elements comprising securing a heat transfer element in the form of a length of strip material to an elongate tube to provide a finned extension extending along said tube, said method further comprising applying a flux to surfaces of the tube and the heat transfer element which are to be in abutting engagement, locating the heat exchange element and tube in abutting relationship to form an assembled unit, locating said assembled unit in a restraining means comprising a pair of elongate members wherein said assombled unit is located between said, t t t A> elongate members, the opposed faces of the elongate members having a recessed configuration to receive the assemnbled unit, applying a clamping force between the elongate members to clamp the heat transfer element and tubes together, applying molten solder to at least the abutting surfaces of the tube and heat transfer element, applying a flux to at least the junction between the abutting surfaces of the tube and heat transfer element, heating the tube and 4heat transfer element, allowing the assembled unit to cool and the solder to solidify and removing the heat transfer element from the restraining means.

The above method results in a greatly improved bond between the heat transfer elements and the tube and which is more resistant to fatigue due to thermal stress.

In a further preferred form, t s tube is provided with a pair of heat transfer elements disposed on opposite sides of the tube.

o0 o o 0 In yet a further preferred form, the heat transfer elements and tube are pretreated with an alkaline solution to remove 0' undesirable matter, followed by contact with an aqueous acidic solution, followed by contact with an aqueous solution.

In another aspect of the invention, there is provided a heat exchange element restraining means for use in the method as described above where said restraining means comprises a pair of elongate members having substantially parallel opposed faces which are each formed with a longitudinal recess to accommodate the assembled unit and being connected by a clamping means adapted to cause relative movement of the elongate members towards and away from each other.

II

r i-~~opl 5 The invention will be better understood by reference to the following description of one specific embodiment thereof as shown in the accompanying drawings in which:- Figure 1 is an end view of a pair of mesabi tubes restrained by a restraining means; Figure 2 is an end perspective, view of elongate members of the restraining means of Figure 1; and Figure 3 is an end view of a clamp means containing the restrained mesabi tubes of Figure 1.

I 10 The embodiment is directed to method of an apparatus for manufacturing mesabi tubes. A mesabi tube comprises a tube 13 with a pair of opposed heat transfer elements in the form of fins 14a, 14b (see Fig. 1) wherein each fin is formed from a sheet of material configured to a ripple shape and extending along the length of the tube. The fins may be partially attached to the tube as with mesabi tubes which are to be reconditioned or may be separate from the tube as with mesabi tubes which are to be newly manufactured. The fins and tubes are washed with a 20 caustic solution comprising 50 grams of caustic, to a litre of water to remove paint, grease, scale and other foreign matter. The cleaned fins and tubes are then washed with water and thereafter washed with a 30% aqueous solution of hydrochloric acid followed by further washing in water. Finally the fins and tubes are immersed into a prepared flux solution comprising 100 grams of flux in 1 litre of water. The fins and tubes are then roughly assembled by placing a fin on each opposed side of the tube and restraining the fins onto the tube by a restraining means (see Figure The restraining means as disclosed in Figure 1 allows two mesabi tubes to be restrained but the restraining means need not be limited to this particular embodiment. The restraining means comprises three spaced elongate members 1Oa, 10b, 1Oc 6 between which are positioned the two mesabi tubes lla, l1b. The elongate members are of a length to allow only a slight projection of the tube of the mesabi tubes from each end thereof. The two outer elongate members 10a, Sare provided with a recess on the inner face thereof 12a, 12c. These recesses are configured to at leat partially receive the fins of the mesabi tubes 14b. The inner elongate member 10b is provided with an identical recess as described above on each face thereof to accept one set of fins from each mesabi tube (see Fig. A biassing r 0means 15 in the form of a modified vice grip urges the two r «outer elongate members together resulting in restraining of the fins and tube to each other. The assembly comprising the restraining means and the mesb'i tubes is then immersed into a hot solder bath at 360 0 C 'or 1 to 3 minutes. The solder typically comprises a 40 to mixture of tin and lead. After immersion in the solder bath, excess solder is removed from the assembly and the

S'

L assembly is subsequently transferred to a clamping means.

20 The clamping means (see Figure 3) comprises a first fixed face 20 provided with spaced positioning pins or ilanges t l 21 and 21b, and a second movable member 23 also provided with positioning pins or flanges 22a, 22b. In use, the assembly is positioned between face 20 and member 23 so Sthat the positioning pins or flanges 21a and 21b, 22a, 22b are disposed on each side of the Lube 13. Upon movement of member 23 to face 20, thr positioning pins or flanges centralise the tube with respect to the fins. The clamp means also functions to straighten any bent tubing or fins, or the shape of the tubing and fins in other configurations. Subsequent to centralisinc! and/or straightening the tubes and fins, the assembly is brushed over with flux and heated with an oxy-acetylene welding torch to ensure complete bonding between the tube and the fins, 7 The clamping means need not be limited to that disclosed above, the only requirements being that the tubes and fins are able to be centrally positioned and straightened if necessary while still being restrained by the restraining means. Thus in a further preferred embodiment, an aligning tool in the form of an elongate member with a U shaped cross section can be used to centralise the tubes and the fins. In this embodiment, the side walls of the aligning tool are spaced to correspond with the distance between the tubes of the two mesabi tubes. By positioning the peripheral edge of each side wall of the aligning tool along the length of each mesabi tube, and subsequent hammering of the aligning tool, the fins and the tubes of each mesabi tube will be correctly aligned. Additionally, the aligning tool will also allow bent tubes or fins to be straightened.

Subsequent to heating with the oxy acetylene welding torch, the assembly is cooled, the restraining means os a removed and the bonded mesabi tubes are washed in an °I 20 aqueous alkaline solution to neutralise any remaining flux or acid and then finally rinsed with water and dried.

A further advantage of immersing the mesabi tubes into the molton solder is that all surfaces of the mesabi tube are coated with the solder which provides an excellent ,corrosion barrier.

It should be appreciated that various alterations, changes and modifications may be made to the restraining means and clamping means to accommodate various sizes, lengths and numbers of mesabi tubes and that various other changes and modifications may be made to the embodiments described without departing from the present invention.

Claims

3. A method as claimed at claim 1 or claim 2 wherein the heat transfer element has a corrugated profile where the axes of said corrugations are substantially transverse to the longitudinal axis of the heat transfer element.
4. A method as claimed in any one of claims 1, 2 or 3 wherein a pair of heat transfer elements are located in opposed relationship at opposite sides of the tube. i ie~_l_ i r~ i- i S9 A method as claimed at any one of claims 1-4 comprising cleaning the surface of the heat transfer elements and or the tubes prior to the application of flux.
6. A method as claimed at claim 5 wherein said cleaning comprises cua'ting the surfaces with an alkaline solution, washing the alkaline solution from the surface and applying an acidic solution to the surfaces.
7. A method as claimed in any one of the preceding claims wherein the application of flux comp:cises immersion of the heat transfer element and tube in a flux solution.
8. A method as claimed in any one of the preceding claims wherein the application of molten solder comprises immersion of "he assembled unit in molten solder.
9. A method as claimed in any one of the preceding claims wherein the method further comprises aligning the tube in relation to the heat transfer element subsequent to the application of molten solder, and heating he assembled unit but prior to allowing the assembled unit to cool. A method of forming heat exchange elements as substantially herein described with reference to the accompanying drawings.
11. A heat exchange element restraining means for use in the method as claimed in any one of the preceding claims where said restraining means comprises a pair of elongate members having substantially parallel opposed faces which are each formed with a longitudinal recess to accommodate the assembled unit and being cco-t.', rdteed by a clamping means adapted to cause relative movement of the elongate members towards and away from each other. ~i:i i I i L;iii l-i 10
12. A heat exchange element restraining means as claimed at claim 11 comprising a plurality of intermediate elongate members each having opposed faces formed with said longitudinal recesses, said intermediate elongate members being intended to be interposed between the elongate members to accommodate assembled units between the pair of opposed faces of opposed elongate members.
13. A heat exchange element restraining means as claimed at claim 11 or.12 further comprising a support adapted to receive a set of elongate members having assembled units clamped therebetween, said support being provided with a *o Oo set of guides which are to be received between the opposed 0 o faces of the elongate members to engage the tubes of the assembled units. 9 a
14. A heat exchange element restraining ,-eans as claimed SooOE at claim 13 wherein two opposed sets of guides are provided 9 0 on said support said sets of guides being movable towards each other whereby said guides will engage opposite sides Of the tubes of the assembled heat exchangers. 0 0
15. A heat exchange element restraining means used in the forming of heat exchange elements substantially as herein poo described with reference to the accompanying drawings. ooo DATED this TWENTY SECOND day of OCTOBER 1991 o a 9 4 b0 DAVID THOMAS FENN Applicant. Wray Associates Perth, Western Australia, Patent Attorneys for the Applicant. At LYLL