CA2032030C - Heat exchanger and method of assembly thereof - Google Patents

Abstract

A method of affixing a plurality of tubes into a plurality of corresponding openings in the header wall of a heat exchanger in which the wall has an inner, liquid-facing side and an outer, air-facing side. Ends of the tubes are welded to corresponding collar openings in the header wall, such that the tubes extend toward the air-facing side of the wall, to form a plurality of welded tube-to-header joints. Flux is applied by spraying or the like to the air-facing side of the tube-to-header joints. Thereafter, a lead/tin or other molten solder is applied to the liquid-facing side of the tube-to-header joint by dipping or wave solder techniques and flowed into any voids in the welded joints to substantially seal the joints against leakage of liquid.
Only those joints having potential liquid leaking voids receive the solder; sound, liquid-tight welded joints are not solder sealed.

Description

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HIE~T EXÇHANGER ANI:) METHOD OF ASSEMBI~ ?F

Back~round o~ the Invention This invention relates to heat ~r.h~ngers and, more part~cularly to motor vehicle heat exchangers or radiators and to a method of joining the members thereo~
Users of heat exchangers, particularly those used in automotive and truck engine~cooling radiators~ are interested in achieving longer life in units which they purchase. Truck manu~acturers are especially seeki n~ a longer li~e radiator which can withstand the extra stress and abuse in a truck environment for ~ignificantly longer mileage.
The joints between the tubes and header~ in heat exchangers in general, and automotlvQ type radiators in particular, hav~ recaived increa~ed ~crutiny in the goal to achlev~ longer ~ervice li~. Typically, the tube-to-headQr joint had been a ~imple tin/lead ~oldered joint between a thin walled bra~s tube and a thicker header which ha~ a collared hola to receive the tube.
Because o~ ~p~n~ion and contraction of the tube during the heating and cooling cycle pre~ent in operation, the joint~ between the tubes and the heA~er~ are placed in shear stress. Shock and vibra~ion in the ~otor vehicle environment add to this stress. In addition, chemical reactions between the coolant and any ~older which covers the header ~urface on it~ water side can cause corrosion produat~ which can flake off and clog the radiator tubes, thereby leading to engine overheating.

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Welding has been used to bond the tube~to-header joint in order to strengthen this portion o~ automotive radiators. However, current m~thods o~ welding do not provide a completely leak-free welded joint in every instance. To rectify this problem, it has been a practice ~o apply a coating of solder on the air side of all of the joint~ to seal any leak~ in th~ weld area between the tube and header. This operation requires the placement of ~r~n~i~e perforated solder foil or other lo prefabrlcated ~orms of solder over the tube~ on the radiator aore prior to assembly of the header to the core. After welding the tu~e~ to the header collars, the header is then dipped in flux and must be heated extensively to cau6e the soldsr foil to melt and form the sealant coating on the air ~ide of the header. During this operation, solder flows through the usually numerous tube-to-header joint leaks and con~iderabl~ ~older appears on the water side of the header. This operation is energy intensive, time consuming, and often causes the header ~o warp due to the high temperatuxe~ in the heating operation. Al~o, the core must normally ~till b~
tested to determine the int~grity of the tube-to-header joint~. In 5pite of the air side solder coat~ny, there may often A~pe~r several joints which remain un~ealed and leak coolant ~luid. The~e ~oints must then be repaired, usually by hand method6 such a~ u5ing a torch and wire solder on the air ~ide of the joint.
Alternative methods of s~al~ng the tube~to-header joints include applying flux to the liquid side of the bonded joint and then applyiny a coating o~ solder, for example, by dipping into a bath of molten solder or by tha use of wave soldering techniques. These methods result in lower header temperatures and thereby minimiza ~1~32~3~

warping and the need for repair. However, the increased amount of solder 1e~t on the water side sur~ace of the header cre~tes a potentia1 for the creation o~ solder corrosion products, a1so termed ~so1der b1Oom~.
Bearing in mind the problems and deficiencies of the prior art~ it is there~ora an object of the present invention to provide an improved tube-to-header joint for use in heat exchangers and, in particulax, automotive type radiatorsO
It is another object of the present invention to provide a heat ~chA~ger in which the tu~e-to-header heat exchanger joints are substantia11y leak-free.
It is a further object o~ the present invention to provide a tube-to-header heat exchanger joint which minimizes the need for post-production testing and repair for leaks.
It is yet another ob~ect of the present invention to provide a tube-~o-header heat exchanger joint which minimizes the amount of solder in contact with the heat exchanger liquid.
It is a further object of the present invention to provide a solder sealed tubs-to-he~er heat exch~ser joint which reduces the tota1 amount of so1der used, uti1izes 1ess expensive so1der, and minimizes the e~ort 25 needed to apply the ~older during the prodllctioll o~ the heat ~Y~-h~nger.
It is another object of the present invention to provide a welded so1dQr sea1ed tube-to-header heat exchanger j oint which can be readi1y manufactured by 30 mass-production techrliques and which results in an improved produat.

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summa~ o~ the Invention The above and other object~, which will be apparent to those skilled in the art, are achieved in the present 5 invention which provides a m~ths:~d of a:Efixing a pluralit~
of tubes to a plurality o~ corr~spondirlg ops~nin~ in the header wall o~ a heat exchanger in which the wall has an inner, liquid-facing side and an outer, air-fac~ g side by welding ends o~ thP tube~; to corresponding openings in 10 the header wall, such that the tubeE~ extend toward the air-facing side of the wall, to form a plurality of welded tube-to-header joints: applying flux to the air-facing 5~ de of the tube-to header joints; and thereafter applying a lead/tin or other solder to the 15 liquid-~acing ~ide of th~ ~ube-to-header ~oint and flowing said ~older into any voids in the welded joints to substantially ~eal the ~oint~ against leakage o~
liquid. Only those ~oints having potential liquid leaking voids receive the ~older; ~ound, liquid-tight welded joint3 are not ~older sealed.
PrePerably, the openings in the he~fler wall comprise collars drawn or ~orm~d from ~he header wall.
Non-ciraular tube~, ~or sxample oval ~haped, can be utilized and optionally, the tube end~ may he ~haped into a sub~tantially circular cros~-section for insertion into and through corre~po~ding circular collar opaning~ in the header. Flu~ may be sprayed onto the air-~acing side o~
the tube-to-header joint and thereafter the molten solder may be applied either by dipping the li~uid facing side 3 0 of the ; oint into a ba~h o~ mol~en solder or passing it through a molten solder wave. Following ~;olidification o~ the ~:;older, the liquid-~acing ~ide oî khe tube-to-haader joint~; should be ~ubstantially ~rae o~

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soldsr to minimize corroslon product~ insidQ the heat ch~nger during use.
Brief Desc~lption of the D~awin~

Fig. 1 i~ a side elevational view of the cross-section of a pair o~ ~u~e-~o-he~r jolnts on a heat eYçh~n~er header wall during the application of flux in accordance with the method o~ the pre~ent invention.
Fig. 2 is a cros~-sectional view of th~ end of a heat exchanger tube a~ seen along lines 2-2 in Fig. 1.
Fig. 3 is a side elevational cloee up view of a cro~-section of a welded tube-to-header joint having wQld voids.
Fig. 4 is a side elevational view showing a heat exchanger during the solder application step in accordance w~th the method of th0 pre~ent invention.
Fig. 5 is a cross-~ectional view of tube-to-header joints produced in accordance with the method of the present invent~o~.

Detailed De c~iption o~ the Invention ~efer~ncQ will be made herein to Fig~, 1 to 5 which ~5 detail var~ou~ portion~ of tha ~ethod and article of tAe pre~ent invention. Unless otherwise Rp~sified, the materials used to construct th~ heat eY~h~nger can be any conventional mater~al for such use, such as aluminum or the like. Like numerals refer to like features of the invent~on throughout the drawing~.
In Fig. 1 there is shown a portion of the heat exchanger made ln accordance with the present invention.
Heat exchanger tube~ lO are provided to carry the working ' ~320~c~

fluid o~ the heat ~c.h~n~er to any ~ins (not shown) and between opposed header~ a wall of which i5 shown as 16.
As ~een in Fig. 2 in an axial cross-section transverse to its longit~ n~l axis, the ma~n body portion o~ ~ube 16 has a generally oval or elliptical shape 12, the end portions 14 of which have been shap~d into a substantially circular cross-~ection~ Optionally, the tube body portions may have other cros~ sectional shapes and the tube end may be o~ any shape for which a corresponding opening in the header wall ~ay be made.
The header wall or plate 16 ~hown iB oriented with the air-facing side l~a ~acing upward and the liquid-facing side 16b facing downward~ as seen in Fig.
1. Header wall 16 includes a ~eries of openings in the form of in~egral drawn collars or ~lange~ 18 substantially con~orming to the shape of tube end portions 14. As ~hown in Fig. 1, circular tube ~nd portions 14 are received within and extending through circular collar openings 18 formed in wall 16. The tube body portions extend away and outward ~rom th~ joint on the air ~ide of the headar wall. Aftsr the tube ends are in~erted into the collar open;ncJs, they may be optionally sized to provide a tight comprQs~ion typa fit betwe~n the tube end. and the collar opening, ~or example, by the method taught in U.SO Patents 4,744,505 and 4,858,686, the disclosuras of which are herein incorporated by reference, wherein the tub~ and~ are sub~tantially coplanar with the end~ of collar 18 and the outermo~t tube end portion is ~r~n~P~ to ~orm a tight fit with the lip o~ the collar.
Following the tube in~Qrtion step, the tube ends are bonded to the header wall collar openings 18 by welding.
This proce~s may be performed by any known method, ~or '" 2~2~3~

example, ~y thos~ disclo6ed in the aforement.~on~d uos~
Patent~ or those methods di~c1O~2d in U.S. Patents 4,377,024 a~d 4,529,034, the disclosurQ~ of which are also incorporated by reference. The ~ini~h~d welded tube-to~header joints are shown as weld bead~ 20' and 20~.
In the course o~ produ~-ing a welded or otherwise bonded tube~to-header ~oint, voids may be present which present the possibility of liquid leakage from the liquid side of the header through the ~oint to the air side of the header. Typical void~ 22 are shown in welded joint 20'~' in the closeup of Fig. 3 wherein the voîd 22 comprises a narrow opening between the liquid and air sides o~ header wall 16. Void 22 iE~ shown a~ a 15 chann~l-like opening here only ~or purposes of convenience - such voi~s may be o~ numerou~ othar 6hapes such as gas pockets ~ormed in a wald bead, cracks formed upon heating or cooling of the w~ld bead, or area~ in which the welding or bonding ha~ bQen inaompletely made~
20 The term nvoid~ i8 intended to aover these and other potential liquid-le~k~ng op~nings in the joint. In any event, such voids 22 may or may not be present in every joint, as ~hown in Fig. 1 wh~rein void 22 is pre~ent in a fir6t welded joint 20', but absent from a second welded 25 joint 20N. It i5 common that at least a portion of, but not all, of thQ welded ~oin~; in ~ motor ~hicle type radiator may contain such void~. The pre~ent invention i~ directed to a method which result~ in a completed heat e~çh~nger in which only those welded joints having voids are sealed hy ~older, and those welded joints in which there are no leak cau~ing void~ ar~ nDt sealed by any solder.

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Re~erring back to Fig. 1, following the welding o~
the tube ends to the he~er wall, the heat exchanger is preferably positioned on its side so that the tube--to-header joints face downward, i.e., the haader wall 16 is usually horizontal and the tube bodie~ extend upward and vsrtically from the tube~to-header joints. A
solder flux type material iB shown being sprayed by nozzles 24 illtO the upward air side 26 of each tube-to-header joint. These fluxes may be any typ conventionally used in soldering which are capable of being applied in the manner contemplated by this invention . Each ; oint in a given heat exchanger is sprayed with flux in thi~; manner so that in those joints having voids which pre~ent the potential for liquid 15 leakage, the flux may thoroughly coat the area and flow ds~wnwar~ into the void it~elf either by gravity or capillary act~ on, or both. The usually limited ~ize o~
the voids which may be present in any of the tube-to-he~der ; oints prevents PYc~ive amounts o~ the 20 ~lux from running through or around to the water-faclng side of the he~rler plate., Subsequently, as illustrated in Fig. 4, the welded and fluxed tube-to he~r ~oints o~ the heat ~Ych~nger are ~ubjected to a ~oldering operation by c:ontacting the 25 liquid ~acing ide o~ the tube-to-header ~oint with solder, ~or example, by dipping into molten solder. The pre~erred method utilize~ a solder wave device 28 which employs a solder pump 30 to ~orm an upward directed molten solder wave 32. The header tu~e assembly 34 is shown on its side to present the downward facing ~oints 20 to the molten solder. Heat exchanger ~ins 40 are shown partially over heat exchanger tube array 36. Such ...... .... . .. . . . . .

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fin~, when they are employed, may be i~stalled over the entire fln array ei~her before or a~ter the 601dering method of the present invention.
~ uring the soldering process, header t~be assembly 34 5 iB moved to the right, as shown by the arrow in Fig. 4, to present thP downward ~acing joints ~or contact with the ~olten solder wave 32. ~he ends of the tube to-header joints 20 are immer~ed in the molten solder only to a degree sufficient to draw the solder up, by capillary action, through any voids pre~ent in those joints. A solder fillet may be formed o~ the air side of any ~uch join~. As practiced by the pra~ent invention, the ~oints are not exposed to any more heat than i~
necessary to apply the molten ~older in thi~ fashion.
Furthermore, because of the application ~ethod, the solder employed may be of the relatively inexpensive type u~ed in ~uch molten solder application device~, and need not be the more expensive Poil or wire type soldex utilized in the prior art. Joints which have no voids or 2 0 cracks do not draw up any solder an~, consequently, no solder fillets are formed on eikher the air or water side of any sound joints. Following solidificatiorl, the only solder which remains on the water side of the he~r is that which ac~ual~y seals ths vo:Lds in tho6e 25 tube-to~header ~ oints that have th~m. ~here i~
essentially no surfaca coYerage by ~older on the water side o~ the header wall because ~luxing is limited to lthe voids only, and therefora the water side of the header wall (aside from the voids themselve~) remains substantially solder free to prevent e~cessive solder bloom corrosion.

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Typical completed tube-to-header joint$ made in accordance with the pr~ ent invention are illustrated in Fig. 5 which ~hows a pair of tubes 10 and lOa joined to head~r wall 160 Tube 10 on the left is secured to the h~ r wall by welded joint 20' which initially included a pair of ~oids 22 through the joint fro~ the liquid ~o the aix side. As a result of the flux~g and soldering operation o~ the present invention, void~ 22 have been sealed by solder which has been drawn up through the ~0 voids by capillary action to eal not only vold 22 but also provide a fillet type seal 38 on the air facing side of the joint. Because the flux was initially applied to the air-facing side of thi6 ~oint, essentlally no solder ~ n~ on the liquid side o~ joint 20'. The othar tube lOa is shown as having been initially sealed to header wall 16 by a sound wslded ~oin~ 20~ which cont~neA no void6 which would provide potential points of leakage.
Although the welded joint 20~ also had flux applied on its air side and contacted with molten solder on it6 liquid side during ~he soldering opera~ion, the soundnes~
of the joint prevented any ~lux ~rom pa~sing through to the liquid sida. Thus, joint 20 is also ~ubstantially free of solder on both it8 air side and liguid side.
Following the solder application step o~ the present invQntion, the manu~acture o~ the heat ~Ych~nger may be continued and comple~ed by bon~n~ the header tank~ onto th~ respecti~e header walls and aecuring the ~ins over the tubeB ( if thi~ latter operation had not been done previously~ by any conventional methods such as ~hosa dQscrib~d in the a~oremen~ioned U.S. Patents.
~ he method of applying the flux and soldQr sealing of welding joints accordin~ to the present invention results in a welded radiator product which ha~ less ~older on the ~2~

water aide of the header than prior art ~ethods.
Furthermore, the mas~-produced heat exchangar which results from this m~thod is unigue in that soldar appears on the water side of the header only where void sealing 5 i8 reguired, and ~older appear~ on the air side of the header as a fillet around only thos~ tube-to-header joints which require th~ 6ealing of a void. ~hus the pr~sent invention result& in welded tube-to-header ~oints with greatly increa~ed strength over soldered joints with the advantage of minimizing the amount o f ~older in contact with the coolant and effectiYely eliminating the undesirable effects of solder bloom corrosion. The actual amount of solder coating is limited to tha location o~ actual leak~ and i~3 only a fraction of the 15 amount of solder employed in a solder dipped header.
This amount o~ solder is considerably less than the amount created on prior art welded he~er~; when ~~ealing solder i8 appliQd to the air side and ~lows through the le~k i ng welded joint~ to the water slde of ths h~er .
Furthermore, the C08t of the solder sealing u~ed in this invention i~ considerably 1~SB than the cost of prior art air soldering by the use o~ perforated fo~l or other specialty solder productB becauBe le68 solder i~
used, the solder i purchased in ;n~Y~n~ive form and no added shaping or perforation operation is re~uired, and thQ energy required to melt the solder for dipping and in particular ~or wave soldering ls less than that to melt the solder ~oil or other specialty solder product for air-~ide solder sealing.
Additionally, water side solder sealing according to the pres~nt invention is found to be almost completely effective in seal~ng ~ample cores, thereby eliminating the need ~or rework o~ the air side so~der which is 2~3~

usually required by hand performed torch and wirs solder operations. Typically, five to ten joints in every motor vehicle radiator core may require rework when utilizing prior art methods. The pre~ent invention which utilizes air side ~lux application and water side solder ~ealin~
reduces leaks to a level which provide the po~ibility of eliminating individual leak te~ting o~ the radiators.
Furthermore, the appearance of the welded cores wherein the solder is limited only to the lea~s on each collar is much more unlform and attractive than a core which has been sealed on the air ~ide and on whlch the ~older ha~
run through to the water side on many o~ the joints~
When utilized in the method o~ the present invention, wave ~oldering is significantly faster than the prior art air side oldering technique~ and reduces production costs along with the labor and cther expense o~ placing per~orated solder foil on the heat ~Y~h~nger.
While the invention ha~ be2n described wlth reference to specific embodimen~s, it will be reco~nized by those ~killed in the ar~ that variations are po~sible without departing from the ~pirit and scope of the invention, and that it is lntended ko cover all changes and modifications o~ the inven ion disclosed herein ~or the purpose~ o~ illustration which do not constitute departure from the ~pirit and scope o~ the invention, Having thu~ described the invention, what l claimed is:

Claims (15)

1. A method of securing and sealing a plurality of tube to a plurality of corresponding openings in the wall of a header in a heat exchanger wherein the wall has an inner, liquid-facing side and an outer, air-facing side comprising the steps of:
(a) welding ends of said tubes to corresponding openings in said header wall, such that said tubes extend outward from the air-facing side of said wall, to form a plurality of welded tube-to header joints;
(b) applying flux to the air-facing side of said tube-to header joints; and (c) applying solder to the liquid-facing side of said tube-to-header joint and flowing said solder into any voids in said welded joints to substantially seal said joints against leakage of liquid.

2. The method of claim 1 wherein said openings in said header wall comprise collars formed from the header wall prior to step (a).

3. The method of claim 1 wherein the ends of said tubes are inserted into and extend through the collar openings prior to step (a).

4. The method of claim 1 wherein the flux is applied in step (b) by spraying onto the air-facing side of said tube-to-header joints.

5. The method of claim 1 wherein the solder is applied in step (c) by dipping the liquid-facing side of the tube-to-header joint into molten solder.

6. The method of claim 1 wherein the solder is applied in step (c) by passing the liquid-facing side of the tube-to header joint through a molten solder wave.

7. The method of claim 1 wherein at least one of said welded tube-to-header joints contains a leak-sealing void following step (a), and wherein said leak-causing void is sealed following step (c).

8. The method of claim 1 wherein, following step (c), said tube-to-header joints are substantially free of solder on their liquid-facing side.

9. The method of claim 1 wherein said tubes are non-circular in cross-section and said openings are circular, and including the step of shaping the ends of said tubes into a substantially circular cross-section prior to step (a).

10. The method of claim 1 wherein said tube-to-header joints are positioned with the welded joints facing downward during flux application step (b).

11. The method of claim 1 wherein said tube-to-header joints are positioned with the welded joints facing downward during solder application step (c).

12 A method of producing tube-to-header joints in a heat exchanger comprising;
(a) preparing a header wall having a plurality of tube-receiving collar openings, said collar openings extending outward from a first side of said wall;
(b) preparing a plurality of tubes having end portions shaped to conform to said collar openings;
(c) fitting said tube end portions into said collar openings such that said tubes extend outward from a second side of said wall opposite said first side;
(d) welding said tube end portions to said collar openings to form a plurality of tube to-header joints whereby at least one, but not all, of said joints contains a void through which a working fluid for said heat exchanger may leak;
(e) applying solder flux to only the portion of said joint on said second side of said wall such that said flux flows into said voids; and (f) applying liquid solder to only the portion of said joint on said first side of said wall such that said solder flows into said voids; and (g) solidifying said solder to seal said void-containing joints against leakage of said working fluid whereby the surface of said joint on said second side of said header wall is otherwise substantially free of solder.

13. The method of claim 12 wherein said solder applying step (f) is by dipping said joint into molten solder.

14. The method of claim 13 wherein said solder applying step (f) is by passing said joint through a molten solder wave.

15. The method of claim 14 wherein said flux applying step (e) is by spraying.