US3094752A - Dip forming tubing - Google Patents

Description

Inventor- /Qobez- M )Cdr-ke b Mw United States Patent ce 3,094,752 Patented June 25, 1963 3,094,752 DIP FORMING yTUBING YRobert M. Parke, Schenectady, N.Y., assignor to General kElectric Company, a corporation of New York 'FiledDem 1, `1960,'Ser."No. 73,069 .'1`Claim. (Cl. 22-203) This'inventionrelates to dip forming tubing `and more `particularly to an improved method lof dip forming a tubing about a central'core with subsequent removal of the core.

Variousmethoda'such vaswelding, casting or extruding,'are utilized in present manufacturing practices, generally'depending on the metalinvolved, to provide metallic tubing. -In themanufacture of tubing from the harder metals, such as, iron and steel, the metal may beprovided in the form of a sheet or ystrip which is rolled and continually welded in order to form a tube. Alternatively, tubes from such metals maybe cast-by welllknown casting processes. 'Of the-softer metals, such as, aluminum, copper, lead, tin, etc., tubesmay-be formed by anextrusion process. Thislatter process may provide -tubes of 25 to SO-'feet in length and greater. "However, -thehardermetals are quite difcult to extrude, the prac- Vticalitiesand-economicsof manufacture are very high,

and thus resort is-made to casting and welding. Those metals which are easily extrudible, the softer metals, are often limited'inlength because Ythe apparatus employed must'generally be aslong as theeifective lengths of the tubing. "There are alsopractical and economic problems in bothprocesses -because of the necessity of starting with a solid preformed body. In either process, it is understood,fzthat in order to'providea separate interior ilining, yfor example, Va noncorrosive one, separate -or additional means is necessary, if feasible. It is thus very desir-able tohave an economical and practical process fto providetubing of short or long lengths from various metals, both the harder and softer metals and without the necessity of Vstartingwith preformed bodies and at the-Sametime providing alining therefor if desirable. `It

hasbeen discovered that the inherentproblems and diiculties as described may be overcome bythe application v,of la dip forming process in tube manufacture.

Accordingly, itzis an object of this invention to provide Yan improved method of producing tubing.

-It isanother object-ofthis invention to provide an improved method of dip forming tubing.

iIt is still..another object ofthis invention to provide an improvedmethodof .dip forming.' tubing of extensive lengths.

It is another object ofv'this yinventionto provide an -improved method of dip forming .tubing with coated interiors.

Briefly described, this invention includes passing .a wire, core or rod of a low-temperature1melting point material ythrough a bath of a 'hightemperature melting -pointfmaterial and regulating therate of traversal of the corethrough the molten bath -so that the high temetc.

Lbaths, etc. :wire 1 in ya solidstatehaving a rst cross sectional con- `guration and area iswcontinuously withdrawnfrom a Vsteel solidies on the-strip-and'the'stripis -therefore increased in size,or,-thatone metal, for example-iron, may be passed through a bath of adissimilarmetal, for eX- ample, Zinc, to have a zinc-coating solidified fthereon. 'Similarvprocesses maybe employed either for joining purposes as in tube manufacture or for increased wall section, However, `these Vprocesses relate -to .what may be described as a single occurrence process which provides ya -given coating to agiven structure with the added coating remaining as an integral structure with the vcoreto produce a final product. `given to ythe-dip 'forniing process in tubingmanufacture .primarily because of appreciably Vdiminishing the ecolnomicfactor. vAs beforestated,it is extremely difficult `to extrude, for example, harder metals as ziron, steel,

SeriousA consideration has L been nickel,retc.in:tube formand it is.a1so diicultltoprovvide extensive lengths of tubings from these and other such metals.

Accordingly,.it hastbeendiscovered that metal tubings,

also of the hardenmetals, and of extensive lengths 'may be-providedby means of an unique application'ofthe dip forming process. .Essentially "thisiprocess includes passing ametal wire, rod orcore, forexample, silver,'through .a bath of, for example, iron, to provide a solidified iron coating'or'tube onthe silver .core'bydip formingprocess. Thereafter, thcscomposite structure is heated yjust above the meltingzpointof the silver 4so thatithe silver isliqueed and removedfrom the Vcomposite structuretozprovide an iron tube. A.dipformingpprocess and apparatus ,is the Asubject of. a copending"applicationfS.N. 530,283, Carreker, `filed...n1gust Z4, `19:55, `now U;S. .Patent.No. 3,008,201,

and `assigned :to 'the Vsame .assignee as ',the present invention. The fsubject of this `copending applicationis :included 4by reference Vherewith and ,'the apparatus r`used .thereinis ,apreferred form of the .apparatus and insofar 'as applicable, the stepwiseprocess to be employed'in-the practice :ofthis invention. Accordingly, :FIG. 1 -of this application, is similar to FIG. lof'the aforementioned 'copending application.

4Referring now to FIG. 1, there is villustrated aschematic representation tof a dip Vforming apparatus ofths invention as one working example. Exemplary materials to becdescribedfin yrelation-.to oneworkingexample are iron J*and silver, although -t is to-be understood that various othercombinations, such as, cOPper-SteeLand othersto 'be hereinafter described maybe suitably employed. Silver thas 'a melting point-otabout 960 C. --and is readily 4available or easily .produced in wireor'rod form, but more particularly, `represents lno difficu'Lt Yproblem in zextrusion'ibecausegofits :good ductile properties. Furthermore, silver may be `readily '.and` easily cleaned. by -well known chemical cleaning compositions, .such as acid As illustrated in FIG. 1,'an elongated silver -storage means 2, such as, a reel or thelike, and isgguided by Vany appropriatefmeans, such as, a sheath,;pulleyror drum 3 through .preliminary treatment appanatusA. Ap- -paratus 41in .this instance includes'i-a-well known roll type of Ystraightening `dev-ice ,for the silver wire 1. After -t-raversingi-the :straightener-4, the wire '21 yproceeds-into a conventional surfacecleaningwapparatus y5, for example, .an '.electrolytic cleaning bath, and arinsing or washing bath 6. The-straightened, clean andwet-wire 1 is then guided by guide means 7, which is sirnilar to -guide means 3, intoiand through an elongated enclosure orwtubular conduitl 8. Conduit S'includes Aa drying means 9, whichLmay be suppliedwitha Ineutral atmosphere'from asource 10,

`ancil conventional power drivenfeed rolls 11 which fricytionally engage and drive wire 1 intoa'vacuum Ventrance chamber 12. `Chamber '12.is provided with a vacuum source 13 which permits the wire to pass into chamber 12, but prevents the passage of atmosphere therewith. Wire 1 then proceeds into an entrance port 14 provided in the bottom of a crucible 15, and then passes through a bath of molten material, for example, iron, which is contained in Crucible 15. The molten iron in crucible 1S accretes or ldeposits and solidiies upon and around the outer surface of si-lver wire 1 as a sheath or coating, increasing its cross sectional area appreciably, and provid- .ing :an elongated and composite body 16 as best shown in FIG. 2.

Referring now to FIG. 2, wire 1 is illustrated as passing through yentrance port 14 and through the molten bath of iron 17. Molten iron 17 commences solidifying on Wire 1 adjacent the entrance port and continues to attach or solidify on wire 1 in increasing quantity until wire 1 has passed through the bath. The r-ate of deposition is of course dependent on the kind of metals employed -together with their related melting points and more impor-tantly on the rate of traversal of the Wire 1 through the bath. Since dip forming, to apply steel on steel, lead on copper, tin on copper and zinc on steel, etc., is Well known, the various design conditions for the practice of this invention are easily calculated or set up. Ordinarily, the requirements are that the metals have sulliciently different melting points commensurate with transit time in the bath, 4or rate of traversal therethrough, such that melting of the core material is substantially prevented. The temperature differential is not, however, the prime requisite. It is further dened by saying that the heat capacity of the core material must be sutiiciently high so that the core material may take up or adsorb suicient heat from the bath material to provide solidica-tion of the bath material Without melting of the core material. In a working example of this invention, a silver wire of about 1 inch yto ll/z inches in diameter, at room temperature, may be fed through a molten bath of iron or steel at about 1570o C. With la rate of travel of about 25 to 300 feet per second or about a l second transit time, a l/l to 1/8 inch coating is attained. A further working embodiment of this invention applies to the formation of copper tubing utilizing lead or tin as the wire or core material. Best results lare obtained when the core material has been precleaned as described and where vacuum entry is employed.

After emerging from cruoible 15, the silver-iron composite body is passed into a sizing apparatus, such as, a pair of sizing rolls 18. Apparatus 18 functions to remove or correct minor surface irregularities and provide the proper or predetermined O.D. In this respect, it is to be understood that shrinkage or contraction of the coating about the core material or wire introduces stresses in the coating which may lead to cracking. Such cracking is dependent on the various metal combinations employed, time-temperature conditions and the Sizes or wall thicknesses of the final tube. These conditions may be prevented or minimized in marginal lapplications by providingA surface variations in the core material so that contraction of the coating may be adsorbed by movement of the oore material. Alternatively, the core material may be porous or hollow, etc. It is to be noted that a splined or corrugated core configuration may be employed to provide a resultant tubular configuration having internal projections or ns. Composite body 16 is guided by means of a temperature controlled duct conveyor 19, to any suitable receiving means, such as a reel 20, where it may be temporarily permitted to accumulate. Thereafter, the composite body 16 is Withdrawn from receiving means 20 and passed through winding and cutting apparatus 21 whereby body 16 is suitably wound, or cut to length, `and manually or automatically placed within a furnace 22 in order that the temperature may be raised suiliciently to melt the silver and the silver removed therefrom. Furnace 22 may be suitably combined lwith the same furnace utilized to melt the iron in crucible 1S.

The resulting :iron tube is removed as the final product as indicated by arrow 23. K

From the foregoing, it may be readily understood that an apparatus is provided in which continuous casting or dip forming by accretion upon a length of core material provides an increased cross sectional material which may thereafter be processed into tubular form. One or more passes through bath 15 may be made depending on the final tube size desired. The composite body 16 also may be arranged in various configurations in furnace 22 to have molten silver ow therefrom by gravity, such as by 'having the composite body wound into a configuration similar to an Archimedes screw, or it may be rotated, or suitably moved to provide the same result. A connection is illustrated between furnace 22 and storage means 2 to indicate that the silver may be solidied and extruded in wire for-m for a repeat of the process, or to indicate closed circuitry where desired.

TWo important advantages are to be gained 4by the practices of this invention. One of these important advantages is the production of tubes in an etiicient and economic manner vof those metals difficult to extrude and also a more economical production of ordinary tubing, such as for example, copper and the softer metals. In addition to the general practices of this invention, nonmetals also may be employed as a core material together with other metals or non-metals. A unique example is the utilization of mercury in the frozen state to provide tubular oonguration from metals or non-metals from which the mercury may be extracted at room temperature. In any instance, best results are obtained when the melting points of the materials are reasonably spaced with consideration of the heat capacity of the core material to avoid melting of the core material. A difference of about 300 C. is preferred for most metals.

The second important advantage in the process is the provision of a coating or lining in tubular configuration. In many industrial processes and in particular in food processing apparatus, there is required, or desired, extensive lengths of relatively low cost tubing having a preferred internal coating which is generally non-corrosive or which does not affect taste of the products ilowing therethrough. The silver-iron combination provides a thin silver coating in an iron tube, and in the tin-copper combination, the process provides a tin coating on a copper tube. The coating or alloyng, referred to as joining, is controlled first by the choice of materials used, i.e., where the materials are or are not capable of alloying with each other, and to what degree. The thickness of the lining or the extent of alloying may :be controlled by controlling the rate of cooling of the composite structure 16 in temperature duct 19 after it leaves bath 15, with longer cooling periods providing increased thickness of coating or increased alloying.

-In extensive operation a furnace 22 may be provided to replenish molten material in crucible 15 in order to maintain a predetermined level and uniform size of the composite body. Starting of the sequence is facilitated, for example, by employing a starting section of the core material of a material having a higher melting point than the bath material, or by suitable apparatus which will commence drawing wire 1 through Crucible 15 at the entrance seal 14, or by a tlying start process. The rod wire or core material of this invention may be an alloy as well as the bath material may be an alloy. Core alloys may be desirable for various purposes, for example, for increased strength such as, a copper lead alloy as a core material where lead alone would be too soft.

While a specic method and apparatus in accordance with this invention has been shown and described, it is not desired that the invention be limited to the particular description nor to the particular configurations illustrated, and it is intended by the appended claim to cover all modifications within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

An improved method of forming tubular congurations of a given metal with an integral metal lining therein which comprises providing a molten metal bath of iron, providing -an elongated core of a solid state metal taken from the class consisting of copper, silver, tin, aluminum, lead and nickel, passing the said core through the said bath in -a dip forming process to provide a coating of iron on said core to form a composite body, thereafter passing said composite body through a temperature controlled duct, controlling the rate of cooling of said composite body in said duct to in turn vary the coating action between said iron and said core providing a lining for said iron, and thereafter heating said composite body for melting and removal of the remainder of said core resulting in an iron tube with a core metal lining.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Great Britain July 22,

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