AU633164B2 - Heat exchanger and method of assembly thereof - Google Patents

Description

COMMONWEALTH OF AUSTRALIA Patents Act 1952

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0 Name of Applicant(s): Address of Applicant(s): Actual Inventor(s): Address for Service: THE ALLEN GROUP INC.

100 Gando Drive, New Haven Connecticut 06508, U.S.A.

LONNIE E. WINSTON DUDLEY HARRISON KEN RAWSON CULLEN Patent 240 Queen Brisbane, Australia

COMPANY,

Trade Mark Attorneys, SStreet, Qld. 4000, C C 0S. S

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o 5 COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: HEAT EXCHANGER AND METHOD OF ASSEMBLY THEREOF The following statement is a full description of the invention including the best method of performing it known to us: -la- HEAT EXCHANGER AND METHOD OF ASSEMBLY THEREOF Background of the Invention This invention relates to heat exchangers and, more particularly to motor vehicle heat exchangers or radiators and to a method of joining the members thereof.

10 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 manufacturers are especially seeking a S.longer life radiator which can withstand the extra stress 15 and abuse in a truck environment for significantly longer mileage.

The joints between the tubes and headers in heat exchangers in general, and automotive type radiators in 6666 Sparticular, have received increased scrutiny in the goal to achieve longer service life. Typically, the tube-to-header joint had been a simple tin/lead soldered joint between a thin walled brass tube and a thicker .6666.

S header which has a collared hole to receive the tube.

Because of expansion and contraction of the tube during the heating and cooling cycle present in operation, the joints between the tubes and the headers are placed in shear stress. Shock and vibration in the motor vehicle environment add to this stress. In addition, chemical reactions between the coolant and any solder which covers the header surface on its water side can cause corrosion products which can flake off and clog the radiator tubes, thereby leading to engine overheating.

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I_ -2- Welding has been used to bond the tube-to-header joint in order to strengthen this portion of automotive radiators. However, current methods of welding do not provide a completely leak-free welded joint in every instance. To rectify this problem, it has been a practice to apply a coating of solder on the air side of all of the joints to seal any leaks in the weld area between the tube and header. This operation requires the placement of expensive perforated solder foil or other 1~ 0 prefabricated forms of solder over the tubes on the radiator core prior to assembly of the header to the core. After welding the tubes to the header collars, the header is then dipped in flux and must be heated extensively to cause the solder foil to melt and form the sealant coating on the air side of the header. During this operation, solder flows through the usually numerous tube-to-header joint leaks and considerable solder "i appears on the water side of the header. This operation is energy intensive, time consuming, and often causes the 20 header to warp due to the high temperatures in the heating operation. Also, the core must normally still be tested to determine the integrity of the tube-to-header too e S" joints. In spite of the air side solder coating, there may often appear several joints which remain unsealed and 25 leak coolant fluid. These joints must then be repaired, .gog•: S usually by hand methods such as using a torch and wire solder on the air side of the joint.

Alternative methods of sealing the tube-to-header joints include applying flux to the liquid side of the bonded joint and then applying a coating of solder, for example, by dipping into a bath of molten solder or by the use of wave soldering techniques. These methods result in lower header temperatures and thereby minimize

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-3warping and the need for repair. However, the increased amount of solder left on the water side surface of the header creates a potential for the creation of solder corrosion products, also termed "solder bloom".

Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved tube-to-header joint for use in heat exchangers and, in particular, automotive type radiators.

1 0 It is another object of the present invention to ooo: provide a heat exchanger in which the tube-to-header heat S. exchanger joints are substantially leak-free.

It is a further object of 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 object of the present invention to provide a cube-to-header heat exchanger joint which Sminimizes the amount of solder in contact with the heat exchanger liquid.

It i a further object of the present invention to provide a solder sealed tube-to-header heat exchanger S* joint which reduces the total amount of solder used, utilizes less expensive solder, and minimizes the effort needed to apply the solder during the production of the heat exchanger.

It is another object of the present invention to provide a welded solder sealed tube-to-header heat exchanger joint which can be readily manufactured by mass-production techniques and which results in an improved product.

i -4- Summary of the Invention The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention which provides a method of affixing a plurality of tubes to 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 by welding ends of the tubes to corresponding 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; applying flux to the air-facing side of the tube-to header joints; and thereafter applying a lead/tin or other solder to the 15 liquid-facing side of the tube-to-header joint and flowing said solder into any voids in the welded joints to substantially seal the joints against leakage of liquid. Only those joints having potential liquid 20 leaking voids receive the solder; sound, liquid-tight 20 welded joints are not solder sealed.

Preferably, the openings in the header wall comprise collars drawn or formed from the header wall.

e Non-circular tubes, for example oval shaped, can be utilized and optionally, the tube ends may be shaped into 25 a substantially circular cross-section for insertion into ee -I S and through corresponding circular collar openings in the header. Flux may be sprayed onto the air-facing side of the tube-to-header joint and thereafter the molten solder may be applied either by dipping the liquid facing side of the joint into a bath of molten solder or passing it through a molten solder wave. Following solidification of the solder, the liquid-facing side of the tube-to-header joints should be substantially free of

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i solder to minimize corrosion products inside the heat exchanger during use.

Brief Description of the Drawings Fig. 1 is a side elevational view of the cross-section of a pair of tube-to-header joints on a heat exchanger header wall during the application of flux in accordance with the method of the present invention.

10 Fig. 2 is a cross-sectional view of the end of a heat exchanger tube as seen along lines 2-2 in Fig. i.

SFig. 3 is a side elevational close up view of a cross-section of a welded tube-to-header joint having weld voids.

Fig. 4 is a side elevational view showing a heat exchanger during the solder application step in accordance with the method of the present invention.

Fig. 5 is a cross-sectional view of tube-to-header joints produced in accordance with the method of the 20 present invention.

S Detailed Description of the Invention Reference will be made herein to Figs. 1 to 5 which detail various portions of the method and article of the Spresent invention. Unless otherwise specified, the materials used to construct the heat exchanger can be any conventional material for such use, such as aluminum or the like. Like numerals refer to like features of the invention throughout the drawings.

In Fig. 1 there is shown a portion of the heat exchanger made in accordance with the present invention.

Heat exchanger tubes 10 are provided to carry the working

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_I 1_~ -6fluid of the heat exchanger to any fins (not shown) and between opposed headers, a wall of which is shown as 16.

As seen in Fig. 2 in an axial cross-section transverse to its longitudinal axis, the main body portion of tube 16 has a generally oval or elliptical shape 12, the end portions 14 of which have been shaped into a substantially circular cross-section. Optionally, the tube body portions may have other cross sectional shapes and the tube end may be of any shape for which a S 10 corresponding opening in the header wall may be made.

The header wall or plate 16 shown is oriented with Sthe air-facing side 16a facing upward and the liquid-facing side 16b facing downward, as seen in Fig.

1. Header wall 16 includes a series of openings in the form of integral drawn collars or flanges 18 substantially conforming to the shape of tube end portions 14. As shown in Fig. 1, circular tube end **portions 14 are received within and extending through oo circular collar openings 18 formed in wall 16. The tube body portions extend away and outward from the joint on the air side of the header wall. After the tube ends are inserted into the collar openings, they may be optionally sized to provide a tight compression type fit between the tube end and the collar opening, for example, by the method taught in U.S. Patents 4,744,505 and 4,858,686, the disclosures of which are herein incorporated by reference, wherein the tube ends are substantially coplanar with the ends of collar 18 and the outermost tube end portion is expanded to form a tight fit with the lip of the collar.

Following the tube insertion step, the tube ends are bonded to the header wall collar openings 18 by welding.

This process may be performed by any known method, for L -7example, by those disclosed in the aforementioned U.S.

Patents or those methods disclosed in U.S. Patents 4,377,024 and 4,529,034, the disclosures of which are also incorporated by reference. The finished welded tube-to-header joints are shown as weld beads 20' and In the course of producing a welded or otherwise bonded tube-to-header joint, voids may be present which present the possibility of liquid leakage from the liquid 1 0 side of the header through the joint to the air side of the header. Typical voids 22 are shown in welded joint in the closeup of Fig. 3 wherein the void 22 comprises a narrow opening between the liquid and air a sides of header wall 16. Void 22 is shown as a channel-like opening here only for purposes of convenience such voids may be of numerous other shapes such as gas pockets formed in a weld bead, cracks formed upon heating or cooling of the weld bead, or areas in ~which the welding or bonding has been incompletely made.

20 The term "void" is intended to cover these and other potential liquid-leaking openings in the joint. In any event, such voids 22 may or may not be present in every S joint, as shown in Fig. 1 wherein void 22 is present in a first welded joint 20', but absent from a second welded joint 20". It is common that at least a portion of, but not all, of the welded joints in a motor vehicle type radiator may contain such voids. The present invention is directed to a method which results in a completed heat exchanger in which only those welded joints having voids are sealed by solder, and those welded joints in which there are no leak causing voids are not sealed by any solder.

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Referring back to Fig. i, following the welding of the tube ends to the header wall, the heat exchanger is preferably positioned on its side so that the tube-to-header joints face downward, the header wall 16 is usually horizontal and the tube bodies extend upward and vertically from the tube-to-header joints. A solder flux type material is shown being sprayed by nozzles 24 into the upward air side 26 of each tube-to-header joint. These fluxes may be any type 1 0 conventionally used in soldering which are capable of being applied in the manner contemplated by this 6 invention. Each joint in a given heat exchanger is sprayed with flux in this manner so that in those joints having voids which present the potential for liquid leakage, the flux may thoroughly coat the area and flow downward into the vci.d itself either by gravity or capillary action, or both. The usually limited size of the voids which may be present in any of the .449 20 tube-to-header joints prevents excessive amounts of the flux from running through or around to the water-facing side of the header plate.

Subsequently, as illustrated in Fig. 4, the welded S and fluxed tube-to-header joints of the heat exchanger are subjected to a soldering operation by contacting the liquid facing side of the tube-to-header joint with solder, for example, by dipping into molten solder. The preferred method utilizes a solder wave device 28 which employs a solder pump 30 to form an upward directed molten solder wave 32. The header tube assembly 34 is shown on its side to present the downward facing joints to the molten sol&;r. Heat exchanger fins 40 are shown partially over heat exchanger tube array 36. Such L fins, when they are employed, may be installed over the entire fin array either before or after the soldering method of the present invention.

During the soldering process, header tube assembly 34 is moved to the right, as shown by the arrow in Fig. 4, to present the downward facing joints for contact with the molten solder wave 32. The ends of the tube-to-header joints 20 are immersed in the molten solder only to a degree sufficient to draw the solder up, by capillary action, through any voids present in those joints. A solder fillet may be formed on the air side of any such joints. As practiced by the present invention, the joints are not exposed to any more heat than is necessary to apply the molten solder in this fashion.

5 Furthermore, because of the application method, the solder employed may be of the relatively inexpensive type used in such molten solder application devices, and need not be the more expensive foil or wire type solder utilized in the prior art. Joints which have no voids or cracks do not draw up any solder and, consequently, no S. solder fillets are formed on either the air or water side of any sound joints. Following solidification, the only oe•, solder which remains on the water side of the header is that which actually seals the voids in those a 25 tube-to-header joints that have them. There is S essentially no surface coverage by solder on the water side of the header wall because fluxing is limited to the voids only, and therefore the water side of the header wall (aside from the voids themselves) remains substantially solder free to prevent excessive solder bloom corrosion.

rl Typical completed tube-to-header joints made in accordance with the present invention are illustrated in Fig. 5 which shows a pair of tubes 10 and 10a joined to header wall 16. Tube 10 on the left is secured to the header wall by welded joint 20' which initially included a pair of voids 22 through the joint from the liquid to the air side. As a result of the fluxing and soldering operation of the present invention, voids 22 have been sealed by solder which has been drawn up through the voids by capillary action to seal not only void 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 this joint, essentially no solder remains on the liquid side of joint 20'. The other tube 10a is shown as having been initially sealed to header wall 16 by a sound welded joint 2 0 N which contained no voids 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 its liquid side during the soldering operation, the soundness S.of the joint prevented any flux from passing through to the liquid side. Thus, joint 20 is also substantially free of solder on both its air side and liquid side.

Following the solder application step of the present invention, the manufacture of the heat exchanger may be continued and completed by bonding the header tanks onto the respective header walls and securing the fins over the tubes (if this latter operation had not been done previously) by any conventional methods such as those described in the aforementioned U.S. Patents.

The method of applying the flux and solder sealing of welding joints according to the present invention results in a welded radiator product which has less solder on the y, -11water side of the header than prior art methods.

Furthermore, the mass-produced heat exchanger which results from this method is unique in that solder appears on the water side of the header only where void sealing is required, and solder appears on the air side of the header as a fillet around only those tube-to-header joints which require the sealing of a void. Thus the present invention results in welded tube-to-header joints with greatly increased strength over soldered joints with 0 the advantage of minimizing the amount of solder in contact with the coolant and effectively eliminating the undesirable effects of solder bloom corrosion. The actual amount of solder coating is limited to the location of actual leaks and is only a fraction of the amount of solder employed in a solder dipped header.

This amount of solder is considerably less than the amount created on prior art welded headers when sealing solder is applied to the air side and flows through the leaking welded joints to the water side of the header.

20 Furthermore, the cost of the solder sealing used in this invention is consid i bly less than the cost of prior art air solderjiLng by tue use af perforated foil or other specialty solder products because less solder is used, the solder is purchased in inexpensive form and no added shaping or perforation operation is required, and S the energy required to melt the solder for dipping and in particular for wave soldering is less than that to melt the solder foil or other specialty solder product for air-side solder sealing.

Additionally, water side solder sealing according to the present invention is found to be almost completely effective in sealing sample cores, thereby eliminating the need for rework of the air side solder which is i -12usually required by hand performed torch and wire solder operations. Typically, five to ten joints in every motor vehicle radiator core may require rework when utilizing prior art methods. The present invention which utilizes air side flux application and water side solder sealing reduces leaks to a level which provide the possibility of eliminating individual leak testing of the radiators.

Furthermore, the appearance of the welded cores wherein the solder is limited only to the leaks on each collar is 1 0 much more uniform and attractive than a core which has been sealed on the air side and on which the solder has run through to the water side on many of the joints.

When utilized in the method of the present invention, wave soldering is significantly faster than the prior art air side soldering techniques and reduces production costs along with the labor and other expense of placing perforated solder foil on the heat exchanger.

While the invention has been described with reference *.to specific embodiments, it will be recognized by those skilled in the art that variations are possible without departing from the spirit and scope of the invention, and that it is intended to cover all changes and modifications of the invention disclqed herein for the purposes of illustration which do not constitute departure from the spirit and scope of the invention.

Having thus described the invention, what is claimed is: d

Claims (7)

1. A method of securing and sealing a plurality of tubes 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: 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; applying flux to the air-facing side of said tube-to header joints such that said flux flows into any voids in said welded joints; and i: applying solder to the liquid-facing side of said tube-to-header joint and flowing said solder into said voids in said welded joints to substantially seal said joints S against leakage of liquid. 10 2 :0 •go "'20 *o

7. The metl welded tube-t following ste sealed followii

8. The meth tube-to-heade: their liquid-f.

9. The me non-circular i and including a substantiall

10. The meth are positionec flux applicati

11. The met are positionec solder applica a 2. The method of claim 1 wherein said openings in said header wall comprise collars formed from the header wall prior to step 3. The method of claim 2 wherein the ends of said tubes are inserted into and extend through the collar openings prior to step 4. The method of claim 1 wherein the flux is applied in step 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 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 by passing the liquid-facing side of the ii tube-to-header joint through a molten solder wave. 1 ft. 3 S 12. A metho( exchanger com 25 E tube-receivinc outward from a r portions shape 30 1 openings sucl side of said v (d) openings to f

35.. i -C -~i~XI 14 7. The method of claim 1 wherein at least one of said welded tube-to-header joints contains a leak-causing void following step and wherein said leak-causing void is sealed following step 8. The method of claim 1 wherein, following step 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 s- d tube-to-header joints eeee• are positioned with the welded joints facing downward during S solder application step 12. A method of producing tube-to-header joints in a heat exchanger comprising: preparing a header wall having a plurality of tube-receiving collar openings, said collar openings extending outward from a first side of said wall; preparing a plurality of tubes having end portions shaped to conform to said collar openings; 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; welding said tube end portions to said collar openings to form a plurality of tube-to-header joints whereby uii Y i 15 at least one, but not all, of said joints contains a void through which a working fluid for said heat exchanger may leak; 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 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 solidifying said solder to seal said void-containing joints against leakage of said working fluid whereby the surface of said joint on said first side of said S header wall is substantially free of solder. 13. The method of claim 12 wherein said solder applying step is by dipping said joint into molten solder. 14. The method of claim 13 wherein said solder applying step is by passing said joint through a molten solder wave. S 15. The method of claim 14 wherein said flux applying step is by spraying. 16. A heat exchanger having the tube-to-header joints produced in accordance with the method of claim 1. 17. A heat exchanger having tube-to-header joints produced in accordance with the method of claim 12. 18, A heat exchanger having a plurality of tubes joined to a plurality of corresponding openings in the wall of a header wherein the wall has an inner, liquid-facing side and an outer, air-facing side to form a plurality of tube-to-header welded joints, at least some but not all of said joints having potentially leak-causing weld voids therein, said air-facing 16 side of said joints being coated with a flux such that said flux flows into said voids, said liquid-facing side of said joints being contacted with a solder sealant such that, except for the void locations themselves, said liquid-facing side of all said tube-to-header joints are substantially free of solder, and said air-facing side of the void-free joints are free of solder. 19. The heat exchanger of claim 18 further including solder sealant on only said air-facing side of the void-containing joints. o;0 20. A method of securing and sealing a plurality of tubes 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 3ide, substantially as herein described with reference to the accompanying drawings. DATED this 19th day of November 1992 THE ALLEN GROUP INC. By their Patent Attorneys CULLEN CO. o i