US3530932A - High strength heat exchange assembly - Google Patents

Description

United States Patent [56] References Cited UNITED STATES PATENTS 1,405,534 2/1922 Merritt 29/197 3,021,804 2/1962 Simbelaar l65/153X 3,180,022 4/1965 Briggs 29/197.5X 3,226,808 1/1966 Thomas 29/197.5X FOREIGN PATENTS 1,462,160 1 1/1966 France 165/164 Primary Examiner- Robert A. OLeary Assistant ExaminerTheophil W. Streule Anorneys- Robert H. Bachman, Richard S. Strickler and George S. Koeser ABSTRACT: The present invention relates to a composite metallurgically bonded fin stock material and a heat exchange assembly including same wherein said fin stock material has an aluminum base alloy core clad on both sides with copper.

Pat ented Sept. 29, 1970 3,530,932

lt. w ll? ALUMINUM ALLOY COPPER L ALLOY v I MENTOR:

H6 3 BY ZCY ATTORNEY HIGH STRENGTH HEAT EXCHANGE ASSEMBLY This application is a division of copending application Ser. No. 611,018, filed Jan. 23, I967, now U.S. Pat. No. 3,480,41 l.

The present invention relates to a fin stock material for use in heat exchangers. More particularly, the present invention resides in a highly advantageous composite fin stock material for use particularly in automotive radiators.

Huge quantities of copper are consumed annually as fin stock material, particularly in automotive radiators. Fin stock material must be highly solderable and have excellent thermal conductivity. Essentially unalloyed copper has the advantage of being highly solderable and has the excellent thermal conductivity required in fin stock applications.

Unfortunately, however, essentially unalloyed copper suffers from the significant disadvantage that during soldering of the copper fins to the tubes of the heat exchanger, a very significant softening of the cold worked copper occurs. This significantly detracts from the strength of the overall assembly.

The use of copper alloys with a higher softening point has been suggested. These alloys do exist; but unfortunately they are generally quite costly and/or lack the excellent solderability and workability of unalloyed copper.

Accordingly, it has been suggested that aluminum alloys be used as fin stock material. Unalloyed aluminum has only about two-thirds the thermal conductivity of copper. However, its much lower density makes aluminum basically attractive for fin stock applications. Wide spread use of aluminum into the automotive and fin stock field has, however, been severely limited because of the extremely poor solderability of this metal.

In order to find a fin stock material satisfying the diverse necessary requirements the use of composite materials has been suggested. Thus, certain composites of copper clad on commercial purity aluminum have been used on a limited basis for fin stock material. However, those composite materials with acceptable thermal conductivity suffer from the same disadvantage of copper in that the soldering operation itself will serve to anneal the commercial purity aluminum and copper thereby reducing the strength to unacceptably low values. By the same token, those aluminum alloys with high annealed temper yield strength and which show good strength after soldering, likewise possess unacceptably low thermal conductivity.

Accordingly, it is a principal object of the present invention to provide an improved composite material.

lt is a particular object of the present invention to provide an improved composite fin stock material.

It is an additional object of the present invention to provide a material as aforesaid which has the requisite high solderability and thermal conductivity required in fin stock applications.

It is a still further object of the present invention to provide a material as aforesaid which does not significantly soften during soldering.

Further objects and advantages of the present invention will appear hereinafter.

In the drawings:

FIG. I is a front view, with portions cutaway, of an automobile radiator illustrating one use of the composite, metallurgically bonded fin stock of the present invention;

FIG. 2 is a partial perspective view of the composite, metallur ically bonded fin stock of the present invention in the folsed or corrugated state; and

FIG. 3 is a schematic partial sectional view of the composite, metallurgicallybonded fin stock of the present inventron.

In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily obtained. The composite metallurgically bonded fin stock of the present invention consists essentially of a core of an aluminum base alloy containing over 90 percent aluminum clad on both sides'with a high conductivity solderable copper base alloy, with the thickness of the claddings being less than one third of the total composite thickness, per side, said composite having:

A. a thermal conductivity of at least 233 B.t.u./ft2/ft/ hour/F. based on an equal weight of copper;

5 B. a yield strength at room temperature after 30 percent cold rolling from the annealed condition of at least 47,000 p.s.i. at equal weight to copper at maximum cladding thickness; and

C. a yield strength, after cold rolling 30 percent from the annealed condition and heating at 600F. for 1 hour and cooling to room temperature of at least 19,000 p.s.i. at equal weight to copper and at maximum cladding thickness.

In particular, the foregoing composite alloy may be used as corrugated fin stock material having a total thickness less than 0.030".

The composite metallurgically bonded fin stock of the present invention provides numerous advantages over conven- 2 tional fin stock material. The composite material may be processed in a manner essentially identical to that of aluminum or copper itself. In addition, it may be readily formed into cold worked, corrugated fins suitable for insertion into various heat exchange devices.

Unlike other solid or composite metals, the composite material of the present invention will not greatly soften within the temperature range of normal soldering operations, for example, a treatment of l hour at 600F. simulates this operation. Furthermore, the loss of strength of the core of the present invention by recovery below its recrystallization temperature is essentially non-existent. Accordingly, essentially all of the original cold worked strength of the core can be retained after a soft soldering operation in which the fin is joined to the appropriate heat exchange tube or tubes.

The surface layers of solderable copper alloys metallurgically bonded to the aluminum core provide the premium solderability that is required in this application.

The core material may be any aluminum base alloy containing from to 1.0 percent iron plus silicon and from 0.1 to 0.5 percent zirconium, with the zirconium preferably essentially precipitated as finely divided zirconium aluminide. In addition, the aluminum alloy of the core may contain various impurities or alloying additions, with one or more of the following materials being preferred: chromium from 0.05 to 0.5 percent; manganese from 0.1 to 1.0 percent; vanadium from 0.05 to 0.5 percent; and molybdenum from 0.05 to 0.5 percent, with all percentages being weight percentages. A particularly preferred core material is alriminum alloy X8040 containing the foregoing requisite quantity of zirconium.

The aluminum core material has a thermal conductivity of greater than 90 B.t.u./ft2/ft/hour/F., a yield strength after 30 percent cold reduction from the annealed condition of no less than 19,000 p.s.i. and a yield strength after 30 percent cold reduction from the annealed condition followed by heating for l hour and cooling to room temperature of no less than 13,500 p.s.i.

The zirconium addition to the alloy of the core material has the particular advantage that it does not significantly decrease the thermal or electrical conductivityof the aluminum base alloy which is thereby maintained at a high and acceptable value.

The cladding material may be any copper or copper base alloy having a thermal conductivity of at least 210 B.t.u./ft2/ft/ hour/F. The copper cladding-material should have a total Development Association designation) containing 99.90 percent minimum copper, oxygen 0.05 percent maximum, silver 0.034 to 0.0476 percent, with the minimum copper content including silver.

The manner of bonding the core and cladding is not particularly critical and any desired process may be readily employed. It is only necessary that the cladding be firmly bonded to the core so that the composite will withstand the severe forming operations involved in manufacturing conventional fin stock material.

The characteristics of the composite are as follows:

A. a thermal conductivity of at least 233 B.t.u./ft2/ft/ hour/F. based on an equal weight of copper;

B. a yield strength at room temperature after 30 percent cold rolling from the annealed condition of at least 47,000 p.s.i. at equal weight to copper at maximum cladding thickness; and

C. a yield strength, after cold rolling 30 percent from the an nealed condition and heating at 600F, for l hour and cooling to room temperature of at least l9,000 p.s.i. at equal weight to copper and at maximum cladding thickness.

It is well known in electrical power transmission technology that the electrical conductivity and strength of aluminum on an equal thickness basis is greatly inferior to that of copper. However, the density of aluminum is less than one-third that of copper. Therefore, when the two metals are compared on an equal weight basis, aluminum is substantially superior to copper and so has substantially displaced copper from this field of use.

Accordingly, what has been done in the present specification is to calculate what characteristics pure copper would have at an equal weight with the composite of the present invention. This illustrates the advantages of the composites of the present invention.

In the characteristics of the composites of the present invention, 30 percent cold rolled is used since the bulk of copper fin stock applications lie between 2040 percent cold rolled.

In accordance with the present invention a high strength heat exchange assembly may be readily prepared utilizing the fin stock material of the present invention, as shown in the appended drawings. Referring to FIG. 1, the radiator assembly includes a heat dissipating unit or core 11 having at opposite ends a top tank or inlet header 12, and a bottom tank or outlet header 13, adapted for connection, respectively, with the or connecting members 17. The strips 15, therefore, extend between adjacent walls to the adjoining tubes to divide the space into a number of relatively small air cells or conduits 18. Ordinarily, the opposite edges or front and rear faces of the core assembly are dipped first in a flux and then in molten solder to seal the margins of the walls of the water tubes where necessary and to join the fin strips to the walls. 1f the passageways and fin strips are evenly formed so as to make possible continuous contact from edge to edge, there will be an inward capillary flow of solder toward the center of the core, and a positive bond will result throughout substantially the entire depth of the core to insure the free flow of heat into the fins.

The present invention will be more readily apparent from a consideration of the following illustrative examples.

EXAMPLE! The composite fin stock of the present invention was prepared in the following manner. All components were cleaned and rolled together cold in one pass taking a total reduction of percent. The aluminum core had a thickness of 0.050 going into the mill, to be clad on both sides with a copper alloy having a thickness of 0.050" on each side. Thus, the components had a total thickness of 0.150" going into the mill and the bonded composite exiting from the mill was 0.045" thick, with the core 0.015" clad on each side with 0.015" copper alloy.

The composite was then cold rolled to 0.007" gage followed by a flash anneal at 950F, for 30 seconds. The material was then rapidly cooled to room temperature and cold rolled 30 percent to 0.005 gage.

EXAMPLES ll-X in accordance with these examples physical properties were determined on composite materials prepared in accordance with example I. The properties are listed in the table I, below, wherein in all cases the cladding material was copper alloy 110 (Copper Development Association designation) and wherein all physical properties are expressed on an equal weight basis for pure copper. in the following table the aluminum alloy core materials are Aluminum Association designations. Examples lX-X represent the comparative properties of copper alloys 110 and 114. it is noted that examples ii, iii, iv and V do not meetthe required properties of the composite ofthe present invention.

TABLE I.YIELD STRENGTH K 5.1.

30% Cold rolled heated 600 F. Thermal 1 hr. conduccooled tivity, to B.t.u./ room ftJ/IL/ 30% Cold temperhour/ Material rolled ature Q F.

Example:

II Aluminum alloy 1100 core, copper alloy 110 c1ad 46 11. 7 250. 2 III Aluminum alloy 3003 core, copper alloy 110 clad--. 49 15. 6 233. 0 IV- Aluminum alloy 5050 core, copper alloy 110 clad 50. 5 16. 5 241. 9 V- Aluminum alloy 5052 core, copper alloy 110 clad... 53. 5 18. 2 227. 4 VI Aluminum alloy 8040 (0.6 Fe, 0.06 Si, 0.17 Zr) core, 50. 5 20. 8 250. 2

copper alloy 110 clad. VII Core of aluminum alloy containing 0.23 Zr, 0.46 49.5 22. 6 236. 3

Cr, 0.1 Fe, 0.05 Si, copper alloy 110 clad. VIII Core of aluminum alloy containing 0.4 Zr, 0.25 50. 5 23. 5 233. 0

Cr, 0.3 Mn, 0.4 Fe, 0.1 Si, copper alloy 110 clad. IX Copper alloy 110 45 9 226. 2 X Copper alloy 114 46 15 discharge and intake conduits of a cylinder block cooling 70 I jacket. For the flow of cooling medium from one tank to the other the core 11 is made up of a number of fluid passageways or water tubes 14, spaced apart by fin strips 15 of the present invention. The fin strip shown in the drawing is of folded or EXAMPLES Xl-XIX in accordance with these examples physical properties were determined on aluminum alloy core materials given the treatcorrugated outline providing a series of fins 16 between fold ment Outlined in example I, without having been formed into a tin stock material having a core of an aluminum base alloy containing over 90 percent aluminum clad on both sides with copper, with the thickness of the claddings being less than one-third of the total composite thickness,

per side, said composite having: v

l. a thermal conductivity of at least 233 B.t.u./ft/

ft/hour/F, based on an equal weight of copper;

TABLE II.-YIELD STRENGTH K 5.1.

30% Cold rolled heated Thermal 600 F. conduc- 1 hr. tivity cooled 30% cold to rolled, room B.t.u. 30% Cold temper- L /[12.] Material rolled ature hourl F.

Example:

XI Aluminum alloy 1100 17 5 129, 9 21 6 91.8 24 8 112 30 12 78.4 24 18 129.9 0.1 Fe, 0.05 s: 22 22 98.6 .3 Mn, 0.4 Fe, 0.1 51---- 24 24 91. s Copper alloy 110 45 9 226. 2 X Copper alloy 114 46 224 This invention may be embodied in other forms or carried 2. a yield strength at room temperature after percent out in other ways without departing from the spirit or essential cold rolling from the annealed condition of at least characteristics thereof. The present embodiment is therefore 47,000 psi. at equal weight to copper at maximum to be considered as in all respects illustrative and not restric- 30 cladding thickness; and V tive, the scope of the invention being indicated by the ap- 3. a yield strength, after cold rolling 30 percent from the pended claims, and all changes which come within the meanannealed condition and heating at 600F, for 1 hour ing and range of equivalency are intended to be embraced and cooling to room temperature, of at least 19,000 therein. psi. at equal weight to copper and at maximum I claim: 3 cladding thickness. 7

l. A high strength heat exchange assembly comprising:

A. at least one header;

B. connected by at least one tube;

C. corrugated fin stock material soldered to said tube, said 2. A high strength heat exchange assembly according to claim 1 including two parallel headers connectedby a plurali- V ty of tubes perpendicular therewith.

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