US2438568A - Method and apparatus for making composite strip material - Google Patents

Description

March 30,1948. C. A., MAM; y 2,438,568

METHOD AND APPARATUS FOR MAKING COMPOSITE STRIP MATERIAL Original Filed Jan. 29, 1941 2 Sheets-Sheet 1 la lll/l I g Y//IIIIIIIIIIIIIIIII/y 4 II/IIIIIIIIIIIIIII 4 ATTORNE March 30, 1948. c. A. MANN 2,438,568

METHOD AND APPARATUS FOR MAKING COMPOSITE STRIP MATERIAL Original Filed Jan. 29, 1941 2 Sheets-Sheet 2 "La i? ATTORN Patented Mar. 30, 1948 METHOD AND APPARATUS FOR MAKING COMPOSITE STRIP MATERIAL Cecil A. Mann, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original application January 29, 1941, Serial No. 376,512. Divided and this application April 3, 1944, Serial No. 529,325

Claims.

This invention relates to a method and apparatus for conditioning the surface of a metal strip for subsequent casting operations thereon and is particularly concerned with the conditioning of the surface of a strip wherein another metal is cast on to the surface thereof to make a bimetallic strip.

This invention is a division of my co-pending application, Serial No. 376,512, for Method and apparatus for applying molten metal on strip stock, iiled January 29, 1941, and which application has matured into Patent No. 2,405,220, issued August 6, 1946.

An object of this invention is to thoroughly condition strip material by means of a reactive gas under suitable temperature conditions whereby the surface of the strip is partially cleaned, and fluxed.

It is another object of the invention to heat the strip electrically, for example, by resistance or induction heating.

It is a further object to utilize a bath of the molten metal to be cast upon the surface of said strip as one electrode in the electrical heating operation.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred forms of embodiment are shown.

In the drawings:

Fig. 1 is a View in perspective showing a gas heated type of fluXing apparatus;

Fig. 2 is a View taken onthe line 2-2 of Fig. 1;

Fig. 3 shows a fragmentary sectional View of the apparatus wherein resistance heating is utilized to heat the surface of the strip while the same is conditioned by means of a suitable atmosphere; and

Fig. 4 shows a fragmentary sectional View of another embodiment of the invention wherein an inductive heating apparatus is utilized.

In my prior Patent No. 2,405,220, referred to above, an apparatus and method for casting a layer of lower melting point metal on metallic strip stock is disclosed. This apparatus may be used in connection with steel or the like having a porous metal layer bonded thereto, which layer is impregnated with babbitt andincludes a pre'- determined thickness of babbitt overlay thereon.

The overlay thickness is regulated by means of a casting gate included with the apparatus. It is manifestfthat the casting operation may be carried out on strip stock without the porous metal layer if a simple cast layer of predetermined thickness is desired.

In all cases in order to obtain a satisfactory alloy bond between the strip stock and the lower melting point metal, it is necessary that the surface of the strip stock be conditioned so that the molten metal will flow evenly thereover and bond thereto after cooling. This conditioning step is required for a number of reasons. One of these reasons is that the surface of steel, iron, nickel, copper or alloy strips usually includes some volatile material thereon. Obviously, when low melting point metal, such as lead, tin or alloys thereof, various babbitts, aluminum, bronze, brass or the like are cast thereon, this material if not removed, forms an integral layer and actual contact of the molten metal is not obtained with backing metal, whereby the bond is made weak and the babbitt layer is easily detached.

Second, it is a known fact that most metallic strips after manufacture contain a submicroscopic layer of oxide at the surface thereof. This oxide likewise is very detrimental to the bonding operation and in fact a strip will not, as a rule, bond readily to a lower melting point metal unless this oxide layer is removed. This may be accomplished to a degree of success by scratch brushing, acid pickling, sand blasting or the like, but it is best accomplished by a reaction between the oxide and a reducing gas.

In order to eliminate these past dilculties, I utilize a fluxing apparatus at the entrance to the main casting apparatus. This fluxing apparatus, as shown in my co-pending application, includes a heating means, positioned beneath the strip prior to its entry into the babbitt, which has sucient heating capacity to bring the moving strip to a suitable elevated temperature considerably less than the melting point of the strip. In most cases Va temperature of 600 to 800 F. contingent on the material is satisfactory. In this connection the strip is preferably preheated to a temperature approximating the temperature of the molten metal. This heating step under a controlled atmosphere, conditions the strip by volatilizing any volatile material on the surface of the strip and thereby cleans the surface of the strip of these materials. While at an elevated temperature, the strip passes under a hood wherein a reducing gas is present, for example, incompletely burned hydrocarbon gas including hydrogen and carbonmonoxide or hydrogen, carbon monoxide mixtures thereof and the like.

The reducing gas reacts with the oxide von the strip to reduce the same. In its reduced state the surface of the strip is highly reactive as it is in what may be termed nascent condition which is highly desirable for the bonding operation. The strip after conditioning immediately enters the castingapparatus whereby the surface of the strip is covered with -r'nolten casting metal prior to exposure to atmospheric air andprior to cooling of the strip. In this condition, the lower melting point metal readily attaches itself by means of an alloy bond to the surface of the strip and when cast to the desired thickness and cooled, a strong bond is apparent between the cast metal and the surface of the strip.

The drawings show three embodiments of the conditioning apparatus each utilizing a different heating means. In all cases, however, the cleaning action on the surface of. the strip is the same; that is, the surface of the strip is deoxidized and cleanedof any volatile material through the action of a suitable atmosphere reacting with the undesirable material on the surface of the` strip while the strip is maintained at an elevated temperature. u i

Referring particularly to Fig. 1, one very satisfactory type of apparatus is shown at 240. This fluxing equipment includes a gas burner 2M which comprises a cored out block` 242 which carries therein a plurality of blast burners 24d. The block 262 is connected to an air-gas supply through a pipe 265. Additional outlets in the block, such as 22MB,r are also provided soY that when varying width strips are used additional burners may be inserted. These openings N8,V maybe plugged when not in use. The strip, 33 passes over the burner 24| and is heated to a suitable elevated temperature but below its melting point. Prior to its entry into the apparatus throughL the throat 876, a hood 250 is provided which is hollowed out as noted in Fig. 2 yand is connected by means of the pipe 252 to a source of avreducing atmosphere. Thus as the strip 3i]Y in the heated condition passes beneath hood 2 5!! it is subjected to the action of a reducing atmosphere, such as; hydrogen, carbon monoxide, 4mixtures thereof, incompletely. lburned natural gas, or any other suitable reducing atmosphere. Thus, the action of the atmosphere on theA oxides at the surface of the strip causes the reduction thereof which is hastenedby the heated condition of the strip. In this manner the strip 30 is preheated and likewise is cleaned and deoxidized and is in a iiuxed condition as it enters the molten babbitt that is contained in tank apparatus 24.

v Another type of fluXing equipment is shown in Fig. 3 wherein resistance heating of the strip is utilized. n L

In this instance the strip 3S, as shown in lg. 3, passes between Va pair of pinch rolls 215V. and 2H which are spring pressed by meansfof, springs 2@ and are carried byblock 2li) whichris supr-` ported by and insulated'from a support 2&4. VThe block 21B is connected to one side of a` suitable electrical current source by means of a conduit 283. YThe hood, 25% is similar to the hood shown in Fig. 2 and is supplied with reducing gas through tube 252. 'Ifhe strip 36 passes into the babbitt designated at 285A which is Carried within chamber 2d. The babbitt and chamber are com nectedy to the other side of the current sourceby means of the conduit 287. Thus a,k complete circuit is set up through conduit 283g, block E pinch rolls 21,5 and Z'F'Lstrip 3Q, babbitt and conduit Z'STwhereby the portion of the strip betweenthe pinchrolls 215 and 211 and thebabbitt ZBisheated bymeans of the resistancethereof 4. to a suitable temperature. This temperature can be Varied by either changing the current input,

or by increasing the distance between the pinch rolls andthe babbitt 285. In this manner, the strip is heated to a temperature approximating the temperature obtained when using the apparatus as shown in Fig. 2 and reducing gas is held thereover by hood 25E). Thus, Vthe apparatus Iiiuxes the surface of the strip and cleans the same of any oxidation while the temperature attainedremoves volatile impurities. After passing into the babbitt 285, the strip passes out of the babbitt tank Ythrough an opening 310 into a? casting gate Y3ll2 (shown in part) the strip 30 nowV has a lbabbitt layer 3|4 therein held in place by. side -rails 3M until the babbitt is solidified byk Silit `and fluxes lthe strip in the same manner aspreviously described in connection with Figsfl, 2 and 3. Resistance and inductive heating are well-known in the a-rt and, therefore, speciiic currents, etc., will not be designated other vthan' the single example hereinafter noted since vthese factors are best arrived at by trial and in accordance with the width, thickness, speed and length of the strip used.

An example of the oon-trol factors utilized in flu-Xing a strip of the character described will be given vwith respect to the resistance heating of one type of strip. In this instance a strip 5 inches wide is moved at a rate oi 20-25 feet per minute through the pinch rolls 215 and 277. 'Ihese rolls are 30 inches from the babbitt'Zil in chamber 24. The strip utilized is .056 Yinch thick. In order to heat the strip to 750'o F.-a current of 8900 amperes at 8.8 Volts is utilized. Obviously, these currents and voltages change with varying widths and thickness ofthe strip aswell as speed of the feed of the strip,l all of these variables being interrelated. -I-Iowever, the example given is one satis-` factory set of conditions to ux properly a strip when using a reducing 'atmosphere of incompletely burned natural gas in the hood 250. In this instance the hood ZES-is 2) inches lon-g. The babbitt utilized is a lead base babbitt maintained at a temperature olf-2750i F. l

The samev conditions vare existing when using any other of' the uXi-ng apparatus disclosed. That is to say, the strip should be raised to a temperature of 750 F. according tothe temperature of the babbitt prior to itsI entry intov the molten babbittand should be adequately exposed -to reducing gas in order that the surfaceY of the strip is properly cleaned. In eachA instance, as ynoted heretofore, best `results can be obtained by rriaking. severalY trial runsin order to denitely de.- termine thatzthe resultsobtained are entirely4 sat,- isiactory since it is apparent that metals, other than the babbitt noted in the example, may require slightly higlfier` or lower temperatures to induce the4 best :wetting action. However, all of these variables. can be Veasily determined by one Vskilled in the art.

After the strip haspassed into the chambery 24 .in its .cleaned andheated condition the babbitt readily wetsA the surface of the strip. whether or not a porous metal strip is utilized and the babbitt will cling tenaciously to the surface thereof. In each case after complete wetting is obtained the strip passes out of the babbitt and through a casting gate, not shown, wherein a predetermined thickness of the babbitt layer is chilled into a solid condition on the surface of the strip. Due to the clean condition of the strip surface this chilled cast babbitt or other cast metal will be completely and satisfactorily bonded to the surface of the strip by a metallurgical bond.

It is to be noted that in the rst two examples given herein that the back of the strip is oxidized by the action of the flame and/or air so that the babbitt does not adhere thereto. With particular respect to Fig. 4 the babbitt will wet both surfaces of the strip if both surfaces are fluxed. However, if it is desirable only to flux one surface only of the strip, it is possible to oxidize the under surface of the strip just prior to its entry into the babbitt by directing a stream of an oxidizing gas thereon. This will prevent adherence of the babbitt. The very fact that the babbitt does not adhere to the back surface of the strip as conditioned in the apparatus shown in Figs. 1 and 3, is adequate proof of the importance of the herein described operation since it is very obvious that babbitt or other metal will not adhere to an oxidized surface and, therefore, even if cast thereon would have an unsatisfactory bond of no strength which would readily crack olf or peel during subsequent operations.

The invention described herein has proved highly successful commercially and produces a clean and conditioned surface that may readily be operated upon in the casting tank and subsequent casting apparatus.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. An apparatus for continuously fluxing on surface only of metallic strip material that is to be subsequently babbitted on one surface only, comprising in combination, heating means for progressively heating a portion of the strip at both sides thereof, and iluxing means consisting of a confining hood adapted to be :filled with reducing atmosphere and disposed adjacent one surface only of the strip so that said atmosphere aifects the heated portion of the strip for deoxidizing said one surface only thereof, and means for babbitting the surface of the strip immediately after the strip has been uxed and before it has been exposed to atmospheric air.

2. The apparatus as claimed in claim 1 wherein the heating means consists of a gas burner.

3. The apparatus as dei-ined in claim 1 wherein the heating means consists of two terminals spaced from one another and contacting the strip and adapted to pass an electric current through the strip whereby the strip is heated due to its resistance.

4. In a method for continuously casting a lower melting point metal on one surface only of metallic strip stock, the steps comprising, progressively heating a portion of the stock in the atmosphere as it is moving toward a casting tank containing the metal to be cast thereon in the molten state, progressively supplying a reducing atmosphere to one surface only of the heated strip for cleaning that surface of the strip and for iiuxing the same, and then continuously immersing the strip in the molten metal in its heated and cleaned condition prior to exposure to atmospheric air, and nally casting a predetermined thickness of the lower melting point metal on said one surface only of the strip.

5. In a continuous method for conditioning the surface of a metallic strip for subsequent casting operations of a lower melting point metal on one surface only thereof, the steps comprising; heating the surfaces of said strip in the atmosphere by causing a current to pass from a point remote from said molten metal through said strip and into said molten metal, heating the strip by its own resistance to a suitable temperature, simultaneously reducing oxides at one surface only of the strip by means of a reducing atmosphere adjacent said one surface of the heated strip and prior to its introduction into said molten metal whereby the said one surface of the strip is cleaned and placed in a nascent condition for facilitating the casting operation thereon and nally immediately casting molten metal onto the clean surface of said strip.

CECIL A. MANN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Re. 20,673 Meyers Mar. 15, 1938 789,215 Goodson May 9, 1905 1,496,309 Girvin June 3, 1924 1,942,025 Frost Jan. 2, 1934 2,110,893 Sendzimir Mar. 15, 1938 2,203,606 Whiteld et al June 4, 1940 2,216,519 Quarnstrom Oct. 1, 1940 2,294,750 Harris Sept. 1, 1942 2,320,129 I-Iarris May 25, 1943

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