CA1272187A - Copper radiator for motor cars excellent in corrosion resistance and method of manufacturing the same - Google Patents

Abstract

ABSTRACT
A copper radiator is disclosed, wherein fins are fitted to the outside of a plurality of tubes, through which a heat-exchanging medium flows, by bonding with solder, to form a copper core, and a seat plate is fitted to one or both ends of the core by bonding with solder to connect tanks thereto. The thickness of oxidized film on the surface of the fins after assembly is not more than 1200 .ANG.. Methods described therein include the soldering of the core being carried out in a nonoxidizing atmosphere and/or the core being submitted to a reduction treatment by heating in a reducing atmosphere during assembling the radiator after the formation of core. The core may also be submitted to a dipping treatment in a copper oxide-dissolvable or reducing solution during assembling the radiator after the formation of core and that, subsequent to the respective treatments aforementioned, a rust inhibitor can be adsorbed or adhered onto the surface of the fins in the process of the assembling of radiator after formation of the core.

Description

1~'7~

The present invent~on relates to a me~ho~ of manufactur~ng a copper radiator which is especially useful in motor cars. In partLcular, the corrosion reslstance of fins has bPen improved and the lightening in weight and hi8h performance of a radiator have been made possible by the invent~on.
In the drawing, Fig. 1 is a front ~levatlonal view of a typlcal radiator.
The radiator for a motor car is one to cool the heat-exchanging medlum by a stream of air. It is constructed generally as ghown ln Fi~. 1, wherein fins

(2) are provided between many flat tubes (1), at leazt onP ~urface of the tubes or fins being covered with brazing material, with the tubes and fins belng assembled temporarily. Then this temporary assemblags is dipped lnto a flu~
solution, or the ~lux solution is coated onto the surface theraof, and thereafter the assembla~e ls heated in the atmosphere. The brazing material is allowed to melt by this treatment and the molten brazing material is spread all over the contact places of tubes with fins. It then solidifies and the bonding o~ tubes with fins is made flrm to form the core S3)-The flux on the surface of the temporary assemblage has the function of removing the oxidized film produced on the surface thereof and lmproves the wettability of the brazing material w~en heating the temporary assemblage in the atmosphere.
Purthermore, the seat plates ~4~ and (4') are fitted to the ends of core

(3) by soldQring and the tanks (5) and (5') are connected to these seat plates.
In general, for the tubes, copper alloys such as brass, etc. are used; for the fins, thin plates made from high heat-conductive copper or copper alloys such as Cu-Sn, Cu-Cd, Cu-Zr, Cu-Ag, etc. and corrugated or louvered, are used; and for the seat plates, br~ss plates are used. Also, for the tanks, those made from brass have been used and connected by sol~ering, but reslnous tanks as recently used to achie~e a lightening in weight are connected by mechanical crimpin~.
Recently, from the requlrement for liKhtening in we1ght and incr,~aslng performance of the car, the lightening and the efficiency of the radistor for motor cars has also been examined. As a result, the thlnning and the high densification of fins are regarded as effective means and, for the flns, a number of thin plates (thic~ness: 0.02-0.05 mm) made from hi~h heat-conductive copper alloys aforementioned are used. Although copper and copper alloys are excellent in corrosion resistance, with the recent advent of the use of PAT 6369~

4 l- r chloride as a snow-melting ggent, the corrosion wastage ~ue to snow damage has b~come a serious pro~lem with the radiator. ~amely, the snow-meltlng ag~nt scattered in large quantities sticks to ~e radiator and corrode~ the fins a'c an extraordinarily high rate to decrease the effective radlation araa, so result~ng ln a drastic lowering in the performance of a radlator during a short psri~d.
Moreover, by the method as described above, since the temporsry assemblage is beated in the atmosphere, rslatively large amounts of oxidized film are prod~ced on the surface of the temporary assemblage for a ~hort time. Hareby, there ar~ses a problem that if the oxidized film ls produced ln large amounts, more flux becomes necessary and th~ mora the flux, the more the amount of flux is thermally decomposed, induc~n~ bad odors.
Horeover, it is also considared that when the molten brazing material is solidified and the bonding of tubes with fins has bean completed, this assemblage should be washed to wash out the flux remaining bshind on the surface thereof; but, as described above, if the amount of flux ~sed becomes large, the heavy metals in the flux flow out lnto the wash effluent at an incrQased rate, so producing effluent contamination.
In order to prevent thess problems, various methods have been investigated, but all of them have been insufficient. For example, coated fllm with a thickness of more than 0.01 mm becomes necessary to prevent corrosion, however, this is infer3Or bacause of an increasa in tha weight and a riss in the cost.
Moreover, if fins are formed with Cu-10% Ni alloy, known as a corrosion-resistant copper alloy, to make fins more corrosion-resistant, the radiation property decreases remarkably in 8 plate of the same thicknass. Namely, when comparin~ by the electroconductivity proportlonal to the thermal conductivity, the relation being known as the Wiedemann-Franz's law, Cu-10% Ni alloy shows less than 10% IACS to 90 to 80~ IACS with usual fin materials.
As a result of extensive investigations in view of the situatio~ methods of manufacturing an economical copper radiator for motor cars have been developed by the invention, wherein high performance is kept withstanding the wastage due to the snow damage, and it is poss~ble to comply wlth the request for llghtening and there are no bad odors and effluent contamination.
The heat-exchanger of this invention is characterlzed in that in a radiator wherein fins are fitted to the outsids of a plurality of tuba~ by bonding with solder to form a copper core, and a s~at plate is fitted to at least one end of said core by bonding wlth solder to connect a tan~ thereto, the thickness of oxidized fllm on ths surface of the fins i9 not more than 1200 A.
Uoreover, one of the manuacturing methods of the invent~on is characterlzed in that in the process aforementioned, the soldering for the formation of the core is carried out in a nonoxidizirlg atmosphere and/or the core is submltted to a rPduction treatment by heating in a reducing atmo~phere during assembling the radlator after soldering for the formation of core The thlckness of oxidized film on the surface of fins is not more than 1200 A after assembling the radiator.
~urthermore, another one of the manufacturing msthods of the invention is characterized ln that in the assembling of the radlator, the core is submitted to a dipping treatment in a copper oxide-dissolvable or reducing solution in the process for the assembling of the radiator after the formation of core, to mske the thickness of oxidized film on the surface of fins not more than 1200 A
after assem~llng the radiator.
Further, the third characterist~c of the inventlon lies in that following ths process aforementioned, rust inhibitor i8 adsorbed in, or adhered to the surface of fins.
In this invention, the reason why the thicknQ~s of oxidlzed film on the surface of fins was made not more than 1200 A after as~embling the radiator is due to the fact that as a result of overall diligent experimental analyses of the actual situation of corroqion due to salt damage aforementioned and various factors concerned therein, it has been known that the oxidized fllm produced on the surface of fins is a si~nificant factor in the promotion of corrosion. In consequence of further experlmentsl snalysis, it has become e~ident thst when the thickness of oxidized film exceeds 1200 A, the corrosion due to salt damage is accelerated and the extent thereof increaqes with an increase in the thickness of film.
Moreover, the fact that in the process of manufacturin~ the radiator aforementioned, the bonding wlth solder for the formation of the core is carried out in a nonoxidlzing atmosphere and~or the core is reduced by heatlng in a reducing atmosphere durinK assembling the radiator after soldering for the formation of core, or that the core is dipped into a copper oxide-dissolvable or reducing _olution is to maXe the thlckness of oxidized film on the surface ~q~

of fins not more than 1200 A after assem~lin~ the ra~lator.
Namely, in the manufacturin~ process, the temperature of tne hi~h-temperature furnace, where the soldering ~s done, is 300 to 400c and oxidized film wlth a thickness of 2000 to 10,000 R is produced. Although the in~ide of the urnace is dlluted somewhat with the vapor of flu~, etc., lt is a virtually atmospheric environment. Therefore, the ~ins are oxidized easily. The oxidation of fins is prevented by carryin~ out tho sol~ering ln a nonoxidizin~
atmosphere, and/or ~he oxidized film produced on the sur~ace of ~ins is r~duced by submittin~ the core to a reduction treatment by beating in a reducing atmosphere during assembling the radiator a~ter solderin~ for the formation of core. For the nonoxidlzin~ atmospheres, N2, H2, C0, C02, H20 or mixtures of these ~ases are used. For the reducing atmospheres, H2, C0 or ~ases having these as effectivo inKredien~s are used, ana the reduction is conducted by heating to hi8her than 150C.
The pravention of the oxide film can also be attalned by submitting the core to a dippin~ treatment for the dissolution of reduction into a solution of dissolvable or reducible copper oxlde durin~ assembling the radiator.
The copper oxide-dissolvable solutions can be such 28 dilute aqueous solutions of sulfuric acid, hydrochloric acid atc., or complex-formable aqueous solutions of ammonia, cyanides, ethylenedlaminetetrascetate (EDTA), methyl-aminenitrilotriacetate (NTA), etc. Also, the copper oxide-reducible solutions can be such as aqueous solutions of hydrazine, methylhydrazine, methyl alcohol, etc. The treatment is possible at normal ambient temperaturos, however, the treatment time can be shortened by warmine. In particular, at the time of the reduction treatment, it is preferable to warm the solution. ~oreover, the treatment time can also be shortened by raisln~ the tamperature of the coro or radlator by soldering. Through such treatment, the thickness of oxidized film on the surface of fins can be decr2ased to less than 100 A.
Moreover, since the build up of oxidized film on the surface of fins can be inhibited by submitting the surface of the fins to adsorption or aahèrence treatment by a rust inhlbltor, the corrosion of the fins due to salt dama8e can be more effectively reduced. Su,ch inhibitors can be benzotriazole (BTA), tolyltriazole (TTA) and ethylbenzotriazcle and reactlon products theroof wlth amines, carboxylic acids, etc., hi~her alkylamines ~uch a~ dodecylamine, stearylamine9 etc., mercaptobenzothiazole, and the like. Many various ~2~
compounded chemicals can also be obtained commercially. Moreover, these chemicals may be used in the form of an aqueous solution or in solution with an organic solvent.
With the radiator assembled by the manufactur~ng methods of the invention as described above, the corrosion due to the salt dama~e can be suppressed by about 20 to 50% compared with a conventlonal radiator. It is known that copper oxide has a protective proper~y agains~ atmospheric oxidation or sulfidizing corrosion, it promo~es corrosion due to a salt environment. Althou~h the raason for this is not clearly understood, it is con~idered that copper oxide has cracXs and pores, and these act as cathodes electrochemically a~ainst the copper ground. Accordin~ to the manufacturing methods of the invention, by makin~ the thickness of oxidized film on the surface of fins of the radiator not more than 1200 A, the corrosion due to ~alt has been prevented effectively.
Furthermore, lf using the manufact~ring method wherein the fo~nation of core is csrried out in a nonoxidlzin~ atmosphere, the thickness of oxidized fllm produced on the surfaces of the tubes and fins can be made thin and the quantity of flux required can be lowered. As a result, problems such as bad odors and effluent contamination, which are attributed to flux, can be avoided.
Moreover, since the oxidized fllm produced on the surface of tubes and fins is produced gradually in the air after soldering ln a nonoxidizing atmosphere, the oxidized film is a very dense thin film and it is posslble to make the surfaces of tubes and fins very ~mooth which contributes to the improvement in the corrosion reslstance.
The invention will now be illustrated in detail based upon the following examples.
Rxam~
Flst brass tubes (thickness of wall: 0.12 mm, width: lOmm, thicXness:
3mm) covered with solder, and fins, corrugated from thin plates tthicXness:
0.04 mm, width: 8.5mm) of Cu-0.15% Sn-0.01~ P alloy were superpose~ and bonded with solder by holding it with an iron frame snd keeping it for 10 minute~ at -310C in a nonoxidizin~ atmosphare consistin~ of ~2-1% H2. After bein~
Xept for a further 15 minutes ~t 120C in the same atmosphere, they were taken out to form the core.
Kx~:~
In Example 1, a nonoxidizin~ atmosphere of 100% N2 was used in place of N2- 1% H2 .
~Rmpl~ 3 The oore formed according to example 1 was aipped for 1 mlnute into a 0.25 aqueous solution of sTA and then drled.
l~xa~pl0 The core formed accordin~ to Example 1 was dipped for 1 minutes into a 0.57 alcoholic solution of mercaptobenzothiazole and then dried.
xampl~ 5 Flat brass tubes and corrugated flns were superposed ~imilarly to ~xample 1 10 and bonded with solder in the atmosphere by holdin~ i~ with an iron frame to form the core. Then the core was kept for 5 minutes at 180C in a reducin~
atmosphere consistin~ of H2-50~ C0 and, after bein~ Xept for a further 10 minutes at 120C in the same atmosphere, was taken out into the atmosphere for reducin~ treatment of the core.
~ample 6 The core formed according to Example 5 W~8 dipped for 1 minute into a 0.25 aqueous solution of BTA and then drled.
~xal~ 7 ~rom a comm~rcial radlstor manufactured by comblnin~ corrugated thin plates 20 of Cu-0.15~ Sn-0.01~ P alloy with a thickness of 0.04 mm, w~th brass tubes covered with solder, a piece of core havin~ a width of 10 cm and a length of 10 cm was cut off and dipped for 10 seconds at 40C lnto a 1% aqueous solution of H2S04. Then it was washed with water and dried.
xample 8 Following the treatment in Example 7, the core was dipped for 5 seconds at room temperature into a 0.25h slcoholic solution of BTA and then dried.
example 9 The core was dipped for 25 seconds at 40C into a 10~ aqueous solution (pH:
11.5) of EDTA, then washed with water and dried.
~xa~le 10 The core was dipped for 10 seconds at 40C lnto a 4% aqueous solution of NaCN, then washed with water snd dried.
exasnpl~ 11 Follow~n~ the treatment in Example 10, the core was dipped for 10 ~econds at 60C into a 0.1~ aqueous solutlon of dodecylamlne ana then dried.

Bxample 12 The core was dipped for 10 ssconds at ~0C into a 5% solutlon of NH2.NH2 and then dried.
ConvQntional ~ethod In Example 1, the bonding with solder was made in the air in place of non-oxidizing atmosphere consistin~ of ~2-1% H2 Of the respective cores thus manufactured, the thicknes~ of oxidized film on the surface of fins was measured. Then a spray test with a 5~ saline solution on the basis of the procedure JIS Z-2371 was conducted for 0.5 hours and a moistening test at 8 temperature of 60C and a humidity of 95% was conducted for 23.5 hours, 40 times. A portion of the fins was cut off and the amount of corrosion of the fin portion was determined. Moreover, cooling fluid was circulsted through the cores manufactured by the respective method~, while the spray test with saline solution was being carried out to evaluate the corrosion resistance of the tube by measuring the time until ths tube begins to lea~ fluid.
Results are shown in Table 1. The thickness of oxidized film on the surface of fin was measured by the cathodic reduction method, and the amount of corrosion was calculated from the difference of weights befors and after dipping when dipped for 1 minute into a S~ aqueous solution of H2S04 and applying ultrasonic waves to the llquid.

Table 1 Time until the Thickness of Amount of corrosion leakage of ~nufacturing method ¦ oxidized film Of fin fluid fron tube (R) (%) (hr) .. . _ _ Example 1 Nonoxidative 210 7.3 730 Soldering 2 390 7.2 500 " 3 Dipping, BTA 180 6.6 680 " 4 Dipping, Mercapto- 180 6 9 590 benzo~hiazole " 5 Postreduction 160 6.9 720 " 6 5 + Dipping, BTA 140 6.4 750 " 7 Acid pickling 80 7.2 640 " 8 7 + Dipping, BTA 50 6.6 710 " 9 Dipping, EDTA 60 7.0 560 " 10 Dipping, NaCN 80 7.4 630 " 11 10 + Dipping, 60 6.85 670 Dodecylamine " 12 Dipping, Hydrazine 60 7.0 590 Conventional method ' 4200 12.6 . . _ _ _ _ ~2~d2~87 Next, the cores in Example 1 aforementiong~ Were submltted to the oxldatlon treatment for 1 to 30 minutes zt 350C ln an alr bath and, th~reafter, the th~c~ness of oxldlzQd fllm and the amount o~ corroslon were measured s~mllarly to investl~ate the relatlonship between the thickness of oxidlz~d film an~ th~
amount of Corrosion. Results are shown ~n Table 2.

Table 2 j I Time kept ¦ 1 min 12 min 10 minl 30 m1n Thickness of oxidized film (R? ¦ 800 1 1400 3200 1 9800 Amount of corrosion (%) ! 8.1 9.9 ' 11.9 15.1 Furthermore, the cores manufaGtured accordln~ to Examples 1, 3, 4, 7, 8 and 11 and the conventional method were k~pt for 300 hour~ ln a molstened state at a temperature of ~0C and a humidity o~ 95~, and the thickness of oxidized fllm was measurQd. Then the spray test with sallne solutlon aforement~oned and the moistenln~ test were repeated 40 times to det0rmlno the amount o~ corroslon.
Results are shown in Table 3.
Table 3 ~ Thickness of , Amount of Manufacturing method oxidized film . corrosion (R) ¦ (%) ¦ Example 1 820 1 7,9 .. 3 350 6 9 "
! ~ 7 1100 1 8.8 , " 8 300 7,4 ~ 420 7.4 PAT 6369-1 . i Conventional method 4200 12.5 . . _ ~

~7 As e~ident from Table 1, it can be seen that in the case of the conventional method, ~he amount of corrosion of the fin 19 12.5~, whereas in the casss of ~xamples 1 throu~h 12 o~ the inventlon, it is as low as about 7 in all cases. Moreover, it is also recognlzed that the time until the fotmation of holes in a tube is as short as 180 hours according to the conventional method, whereas it amounts to more than 500 hours according to examples of the invention. ~Irthermore, in Examples 1 and 2, the amounts of flux could be decreased to less than abou~ half compared with that used in the conventional method.
Moreover, from Table 2, it can be seen that the amount of corrosion of the fin increases wlth increasing thickness of oxidized film on the fin and, in particular, it increases remarkably in the range wherein the thickness of oxidized film is more than 1400 R. Furthermore, as evident from Table 3, by following the manufacturing methods of the invention, the amount of corrosion becomes less, so that deterioration of the surface can be restrained under the environment from the shipment of the radiator to the end use. Besides, the effects shown by the foregoing examples are not conflned to Cu-Sn alloy, and the same thing can be said of Cu-Cd, Cu-Zn, Cu-Ag and others.
As described above, according to the invention, the corrosion due to the salt damage can be prevented effectively by suppressing the formation of oxidized film in the manufacturing process. Therefore, it has become possible to manufacture a high-performance radiator economically and lighten the car, so having a significant industrial effect.

Claims (15)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a copper radiator for motor cars comprising a plurality of tubes adapted for the flow of a heat-exchanging medium therethrough, fins bonded directly with solder to said tubes to form a copper core and wherein said core is bonded with solder to at least one seat plate, the improvement in that the surface of the fins of said copper radiator has an oxidized layer of a thickness of not more than 1200 .ANG..

2. The copper radiator of claim 1, further provided with a rust inhibitor adsorbed on or adhered to the oxidized layer.

3. A method of manufacturing a copper radiator wherein fins are fitted to the outside of each of a plurality of tubes, through which a heat-exchanging medium flows, by bonding with solder to form a copper core, and a seat plate is fitted to an end of said core by bonding with solder to connect a tank thereto, the soldering for the formation of the core being carried out in a nonoxidative atmosphere to limit the thickness of oxidized film on the surface of the fins to not more than 1200 .ANG..

4. A method of manufacturing a copper radiator wherein fins are fitted to the outside of each of a plurality of tubes through which a heat exchanging medium flows, by bonding with solder to form a copper core, and a seat plate is fitted to an end of said core by bonding with solder to connect a tank thereto, the core being submitted to a reduction treatment by heating in a reducing atmosphere after soldering for the formation of the core, to limit the thickness of oxidized film on the surface of the fins to not more than 1200 .ANG..

5. The method of claim 3, including submitting the core to a reduction treatment by heating in a reducing atmosphere after soldering for the formation of the core.

6. The method of claim 3, including submitting the core to a dipping treatment in a copper oxide reducible solution.

7. The method of claim 3, including submitting the core to a dipping treatment in a copper oxide dissolvable solution.

8. The method of any one of claims 3, 4 or 5, including submitting the core to adsorption of a rust inhibitor.

9. The method of either of claims 6 or 7, including submitting the core to adsorption of a rust inhibitor.

10. The method of any one of claims 3, 4 or 5, including submitting the core to adherence of a rust inhibitor.

11. The method of either of claims 6 or 7, including submitting the core to adherence of a rust inhibitor.

12. A method of manufacturing a copper radiator wherein fins are fitted to the outside of each of a plurality of tubes through which a heat-exchanging medium flows, by bonding with solder to form a copper core, and a seat plate is fitted to an end of said core by bonding with solder to connect a tank thereto, the core being submitted to a dipping treatment in a copper oxide reducible solution to limit the thickness of oxidized film on the surface of the fins to no more than 1200 .ANG. after assembly.

13. A method of manufacturing a copper radiator wherein fins are fitted to the outside of each of a plurality of tubes through which a heat-exchanging medium flows, by bonding with solder to form a copper core, and a seat plate is fitted to an end of said core by bonding with solder to connect a tank thereto, the core being submitted to a dipping treatment in a copper oxide dissolvable solution to limit the thickness of oxidized film on the surface of the fins to no more than 1200 .ANG. after assembly.

14. The method of either of claims 12 or 13, including submitting the core to adsorption of a rust inhibitor.

15. The method of either of claims 12 or 13, including submitting the core to adherence of a rust inhibitor.