US3363043A - Aluminum brazing furnace - Google Patents

Description

Jan. 9, 1968 v c. R. FOX I 3,363,043

ALUMINUM BRAZING FURNACE Filed March 9, 1965 I A 11 j I 4; I; d I,

3 z'. j L a c a 7 INVENTOR. d'fflr/es W 72 X Unite ABSTRACT OF THE DISCLOSURE An aluminum brazing furnace comprising a furnace housing having inner and outer housing sections and defining a molten salt reservoir; cover means on the housing defining an opening communicable'with the reservoir; the cover means extending over the opposite ends of the reservoir and defining a pair of spaced electrode alcove compartments therewith; a pair of vertically extending cylindrical electrodes supported on the portions of the cover means adjacent said alcove compartments and comprising lower portions extending into the reservoir and upper portions extending above the upper surface of the cover means; an aluminum protective jacket covering the upper ends of each of the electrodes; the jackets extending partially below the surface of the molten aluminum bath; the upper ends of the jackets having a cylindrical terminal mounting surface formed thereon; a sleeve shaped terminal mounted on each of the surfaces, each of the sleeves being communicable with a source of electric current, and cooling means on each of the terminals including means defining a serpentine cooling fluid passageway circumjacent the outer peripheries of the terminals, whereby cooling fluid may be transmitted adjacent said terminals.

This invention relates generally to electrically heated furnaces and, more particularly, to a new and improved aluminum brazing furnace.

It has been the practice in the construction of aluminum brazing furnaces to utilize two or more spaced electrodes which are connected to a suitable source of electric power and are at least partially submerged within a molten bath of aluminum fluxing salt or the like. It has frequently been the case in such type furnaces to incorporate electrodes constructed of nickel or nickel alloys; however, this type of electrode construction has been found to be dbjectionable due to the fact that the electrodes decompose and introduce metallic nickel into the salt bath in the form of a black sludge and as blue nickel fluoride that de posits on the work stock or purging sheets as a looseblack smut. Also, the nickel deposits result in deleterious contamination of the braze fillets on the work stock and occasional surface attack of the alloy being brazed. Although these undesirable characteristics may be overcome by proper slud'ging and sheeting, these operations are expensive, time consuming and interfere to some appreciable extent with the production schedule of the factory.

It has heretofore been proposed in the construction of aluminum brazing furnaces to substitute graphite electrodes for the aforesaid nickel electrodes; however, even though the graphite electrodes provide highly desirable heating characteristics, they have been objectionable be cause they tend to oxidize or burn and decompose quite rapidly above the surface of the molten bath due to the substantially high temperatures of the baths. This, of course, requires frequent replacement of the electrodes, an obviously expensive and therefore undesirable feature.

It is a general object of the present invention to provide an aluminum brazing furnace which overcomes the aforediscussed undesirable features of similar type furnaces heretofore known and used.

It is a more particular object of the present invention rates J] area-t to provide a new and improved aluminum brazing furnace of the above character which is provided with a plurality of graphite electrodes whose surfaces that are normally exposed to the atmosphere are covered with a protective coating or jacket which prevents the heat of the molten salt bath from deleteriously attacking the electrodes.

It is another object of the present invention to provide a new and improved brazing furnace of the above character wherein the electrodes are mounted in the furnace such that they may be conveniently removed without bailing out the molten bath of the furnace.

It is still another object of the present invention to provide a new and improved aluminum brazing furnace of the above character wherein the electrodes are mounted in a manner such that the molten bath is readily accessi=ble.

It is yet another object of the present invention to provide an aluminum brazing furnace of the above character wherein the electrical terminals communicating electric current to the electrodes are provided with cooling means to maintain the temperature of the terminals at a minimum level, thereby preventing the highly corrosive salt of the molten bath from attacking the electrodes between the outer peripheries therof and the electrical terminals.

It is a further object of the present invention to provide a new and improved aluminum brazing furnace of the above character which is of a simple design and thus may be easily assembled and economically manufactured.

The foregoing and other related objects and advantages of the present invention are achieved through the provision of a novel aluminum brazing furnace construction which includes a plurality of elongated cylindrical graphite electrodes that are each provided with a protective coating or jacket which extends slightly below the bath line and entirely encloses the portions of the electrodes normally exposed to the atmosphere, whereby to prevent the heat of the associated molten salt bath from burning orsimilarly attacking the upper ends of the electrodes. Accordingly, the electrodes will have a long and effective operational life, thus minimizing electrode replacement costs to the extreme.

A more complete understanding of the present invention and other objects and features thereof will be obtained from the following detailed description taken in conjunc tion with the accompanying drawing, wherein:

FIGURE 1 is a top elevational view of an aluminum brazing furnace embodying the principles of the present invention;

FIGURE 2 is a transverse cross-sectional view taken alone the line 2-2 of FIGURE 1;

FIGURE 3 is a fragmentary cross-sectional view taken along the line 33 of FIGURE 1;

FIGURE 4 is a horizontal cross-sectional view taken along the line 4--4 of FIGURE 3; and

FIGURE 5 is an elevated perspective view of the structure illustrated in FIGURE 3.

Referring now to the drawing, an aluminum brazing furnace 1t constructed in accordance with the principles of the present invention, is shown as comprising a furnace housing, generally designated 12, that defines an elongated bath reservoir 14 within which is located a molten bath of aluminum fluxing salt or the like. The furnace housing 12 comprises an inner housing 16 that is preferably constructed of a relatively dense fire brick and whichis surrounded by a layer of castable refractory concrete 18 that is preferably 2 /2 to 4 /2 inches thick. The inner housing 16 and concrete 18 are enclosed within an outer housing 20 that is also preferably fabricated of fire brick, although this brick may be of a lower quality than that constituting the inner housing 16. The housing 12. extends inwardly over the opposite ends of the reservoir 14 and defines. a generally rectangular shaped access opening 22, the

opposite ends of the reservoir 14 forming a pair of trapezoidal shaped electrode alcove compartments 24 and 26 within which suitable heating electrodes may be operatively mounted, as will be described; It will be seen from this construction that the reservoir 14 may be easily replenished and that Work stock may be conveniently trans ferred to and from the interior of the furnace through the opening 22 Without interfering to any extent with the operation or mounting of the aforesaid electrodes. Also, the electrodes may be easily removed from the housing 12 without bailing out the molten salt bath Within reservoir 14. Mounted on the top of the housing 12 is a flat or planar, horizontally extending cover member 28 that is preferably constructed of a strong heat-resistant material such as Transite board or the like. The entire furnace housing 12 is preferably mounted on a support structure (not shown) that includes a pair of spaced parallel I-beams or the like which are adapted to support the housing 12 off the floor and allow transporting the furnace 10 with a conventional fork-lift truck.

Referring now in detail to the heating electrodes that are incorporated in the furnace construction 10 and which are constructed in accordance with the principles of the present invention, as best seen in FIGURE 1, mounted on the housing 12 are two pair of spaced parallel and vertically extending electrodes, generally designated by the numeral 30, which extend through and are supported one within each of four circular openings 32 that are formed in the housing 12 and cover member 28 above the alcove compartments 24 and 26. Each of the electrodes is identical in size and construction, as best illustrated in FIGURES 3 through 5, each comprises an elongated cylindrical, solid graphite rod which is preferably about 2 inches in diameter and long enough to extend from approximately six inches above the upper surface of the cover member 28 to approximately one inch above the bottom of the reservoir 14. Due to the fact that the portions of the graphite electrodes 30 that are exposed to the atmosphere oxidize or burn at a temperature of approximately 700 to 800 degrees Fahrenheit, and since the operating temperature of the molten salt bath in the reservoir 14 is approximately 1100 to 1120 degrees Fahrenheit, the upper end of each of the electrodes 30 is provided with a protective coating or jacket 34 which functions to prevent the hereinbefore described oxidation 'or burning of the upper ends of the electrodes. In a preferred construction of the present invention, the jackets 34 consist of commercially pure aluminum which covers the entire upper ends, including the tops, of the electrodes 30 and is preferably approximately one quarter of an inch thick. The aluminum jackets 34 may be applied to the ends of the electrodes 30 by any of a variety of well known methods, i.e., casting, dipping, etc.; however, one method that is preferable and which is incorporated herein is to spray molten aluminum onto the ends of electrodes with an oxyacetylene gun, whereby an effective air-tight bond is achieved between the jackets 34 and the outer peripheries of the upper ends of the electrodes 30. As seen in FIGURES 2 and 3, the jackets 34 extend downwardly around the electrodes 30 to a position approximately one inch below the surface of the molten bath, and thereby assure that the heat of the molten salt bath will not come into peripheral contact with the portions of the electrodes 30 which extend above the surface of the bath.

After the aluminum jackets 34 have been provided on the electrodes 30, the upper ends of the jackets 34 are machined, for example, on a suitable lathe apparatus or the like, to provide accurate and symmetrical cylindrical surfaces on the upper ends of the electrodes, as seen at 36 in FIGURE 3. Mounted 'circumjacent the machined surfaces 36 of each of the electrodes 30 is a cylindrical terminal sleeve 38 which serves to communicate electric current to the electrodes 30, as will later be described. The terminal sleeves 38 are preferably constructed of a low carbon steel, as opposed to conventional copper terminals, due to the fact that the aforesaid copper terminals tend to deteriorate quite rapidly in the corrosive environment above the molten bath. As best seen in FIGURES 4 and 5, the terminal sleeves 38 are formed with radially outwardly projecting flange sections 40 and 42 upon which suitable draw bolts 44 and nuts 46 are mounted to firmly secure the sleeves 38 on the upper ends of the electrodes 39. Each of the terminal sleeves 38 comprises a radially outwardly projecting connecting plate 48 which is adapted to be secured to one end of one of a plurality of buss bars 39 by suitable bolts 52 and nuts 54, the opposite ends of the buss bars 50 being connected to a power transformer or the like of a type well known in the art and which is adapted to provide electric power to operate the furnace 10. It will be noted that the buss bars 50 are preferably flat and thin to provide for maximum air cooling and thus avoid transferring heat from the molten bath back to the aforesaid transformer.

Mounted on the outer periphery of each of the terminal sleeves 38 is a serpentine configured cooling coil 56 through with a suitable fluid coolant, such as water or the like, is adapted to be transmitted to minimize the operating temperature of the upper ends of the electrodes 30. The cooling coils 56 are preferably constructed of stainless steel and are brazed or similarly secured to the terminal sleeves 38, as best illustrated in FIGURES 3 through 5. The opposite ends of each of the coils 56 are connected to suitableinlet and outlet conduits 58 and 66 which are adapted to be communicable with a suitable fluid coolant reservoir, pump or the like. In an alternate construction of the present invention, the coolant fluid may be transmitted through suitable water jackets that may be secured to the outer peripheries of the terminal sleeves 33, such jackets also being preferably constructed of stainless steel and being communicable with a suitable reservoir and/or pump through associated inlet and outlet conduits.

In operation of the furnace construction 10 of the present invention, electric current is transmitted to the electrodes 30 through the plurality of buss bars 50, resulting in the molten salt bath being heated to a predetermined temperature level. If for any reason the furnace 10 has been inoperative or shut down for any appreciable length of time, the furnace bath will be in a solid or frozen condition. Under such conditions, a suitable starting coil (not shown) may be initially placed withlri the reservoir 14, which coil may be connected to the aforementioned transformer or equivalent source of electric power. It may be noted that in the event the furnace is to be made inoperative due to a scheduled shut down, the aforesaid starting coil may be submerged within the molten salt bath prior to shutting the furnace 10 off, hence the starting coil will be frozen in the bath during the shut down. After the coil has been energized for a predetermined amount of time, depending upon the capacity of the coil and the size of the reservoir 14, the bath will begin to transmit electric current between the pair of electrodes 30 located adjacent the starting coil. At such time as the one pair of electrodes 3!} begins to operate, the starting coil may be removed from the bath, the pair of electrodes 30 at the opposite end of. the reservoir 14 becoming effective in heating the bath at such time as the portion of the bath that has become molten envelopes them. During the operation of the furnace 10, the protective jackets 34 covering the upper ends of each of the electrodes 30 prevent the heat of'the molten bath from burning or oxidizing the upper ends of the cylindrical graphite rods so that the electrodes 30 will have a long and effective operational life.

It will be seen'from the foregoing construction that the present invention provides a new and improved aluminum brazing furnace which is of an extremely simple design and is adapted to be constructed of readily available materials. Accordingly, the furnace construction 10 of the present invention may be easily assembled and econom ically manufactured. Furthermore, due to the provision of a plurality of electrodes that are protected from both the heat and corrosive materials of the molten furnace bath, the operating expenses, i.e., electrode replacement, will be minimized to the extreme.

While it will be apparent that the preferred embodiment herein illustrated is well calculated to fulfill the objects above stated, it will be appreciated that the furnace construction of the present invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. In an electrically heated aluminum brazing furnace comprising a molten salt bath,

at least one pair of elongated graphite electrodes, each of said electrodes having a first portion submerged below the salt bath and a second portion extending above the bath,

.a metallic jacket covering the upper ends of said electrodes and extending below the surface of the salt bath to prevent the heat of the bath from attacking said electrodes, and electrical conductor means connected to said jackets to supply electrical current to said electrodes.

2. An electrically heated aluminum brazing furnace comprising a molten salt bath,

a graphite electrode for heating the bath,

a metallic jacket covering at least a portion of said electrode extending below the surface of the salt bath for providing a substantially gas-tight enclosure for said portion of said electrode, whereby to prevent the heat of the bath from attacking said electrode means, and electrical conductor means mounted adjacent the upper end of the electrode for supplying electric current thereto.

3. An electrically heated furnace having a molten salt bath,

at least one pair of fixedly mounted elongated graphite electrodes, each of said electrodes having a first portion submerged below the molten bath and a second portion extending above the bath,

a metallic aluminum jacket covering at least a portion of said electrodes extending below the surface of the salt bath and providing a gas-tight and heat-resistant barrier to prevent the heat of the furnace bath from oxidizing said electrodes, electrical conductor means mounted on said jackets for communicating electrical current to said electrodes, and cooling means mounted on said jackets for cooling the upper ends of said electrodes.

4. In combination in an electrically heated metallic brazing furnace adapted to braze two or more workpieces together,

electrode means for heating a molten bath in the furnace,

a protective jacket covering at least a portion of means, said jacket extending below the surface of the bath and providing a gas tight seal around the periphery of said electrode means and being composed of the same material as the brazing material used to braze the workpieces together, and electrical conductor means mounted on said jacket for supplying electrical current to said electrode means.

5. In combination in an aluminum brazing furnace,

a furnace housing containing a molten salt bath,

a pair of elongated cylindrical and vertically extending graphite electrodes supported in said housing and adapted to communicate electric current to said bath,

each of said electrodes having a portion extending below the surface of the bath and a portion extending above the surface of the bath,

an aluminum jacket covering the portions of said electrodes extending above the surface of the bath, said jackets extending below the surface of the salt bath and forming an air tight seal around the periphery of said electrodes,

terminal means mounted on the outer peripheries of said jackets for communicating electric current to said electrodes through said jackets, and

means adjacent said electrodes for cooling said terminal means.

6. The invention as set forth in claim 5 wherein said cooling means comprises a serpentine configured cooling coil fixedly secured to the outer peripheries of said sleeves.

7. The invention as set forth in claim 5 wherein said furnace housing defines a vertically extending access opening communicable with said bath and wherein said electrodes are arranged on said furnace at a position spaced away from the opposite sides of said opening and extend vertically downwardly into said bath.

8. In an aluminum brazing furnace,

a furnace housing comprising inner and outer housing sections and defining a reservoir containing a molten salt bath,

cover means on said housing defining an opening communicable with said reservoir,

said cover means extending over the opposite ends of said reservoir and defining a pair of spaced electrode alcove compartments therewith,

a pair of vertically extending cylindrical electrodes supported on the portions of said cover means adjacent said alcove compartments and comprising lower portions extending into said reservoir and upper portions extending above the upper surface of said cover means,

an aluminum protective jacket covering the upper ends of each of said electrodes,

said jackets extending partially below the surface of the molten bath and forming an air tight seal with the outer peripheries of said electrodes,

the upper ends of said jackets having a cylindrical terminal mounting surface formed thereon,

a. sleeve shaped terminal mounted on each of said surfaces,

each of said sleeves being communicable with a source of electric current, and

cooling means on each of said terminals including means defining a serpentine cooling fluid passageway circumjacent the outer peripheries of said terminals, whereby cooling fluid may be transmitted adjacent said terminals.

References Cited UNITED STATES PATENTS 1,811,754 6/1931 Hultgren 13-1 2,290,961 7/1942 Heuer 13-23 2,315,725 4/1943 Moller 117-51 2,419,383 4/1947 Ames 13-23 2,512,206 6/1950 Holden 13-23 2,526,241 10/1950 La Burthe et al. 13-6 2,697,130 12/1954 Korbelak 13-23 X 2,701,269 2/1955 Holden 13-23 2,768,277 10/1956 Buck et a1 13-25 2,798,892 7/1957 Penberthy 13-17 2,933,545 4/1960 Keefer 13-17 2,953,613 9/1960 Keefer 13-17 2,966,537 12/1960 Witucki 13-25 2,978,526 4/1961 Olson 13-14 3,059,093 10/1962 Norcross et al. 219-74- FOREIGN PATENTS 526,677 6/1956 Canada.

RICHARD M. WOOD, Primary Examiner.

VLADIMAR Y. MAYEWSKY, Examiner.

Attest:

H Edward M. Fletcher, Jr.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,363,043 January 9, 1968 Charles R. Fox

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 58, cancel "at least"; same line 58, before "means insert said electrode I Signed and sealed this 9th day of September 1969.

(SEAL) Attesting Officer Commlssloner of Patents WILLIAM E. SCHUYLER, JR.

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