US3562002A

US3562002A - Method and apparatus for vapor deposition

Info

Publication number: US3562002A
Application number: US725264A
Authority: US
Inventors: Hugh R Smith Jr
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1968-04-24
Filing date: 1968-04-24
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09

Abstract

A METHOD AND APPARATUS ARE DESCRIBED FOR FEEDING WIRE INTO A VAPOR SOURCE CRUCIBLE IN A VACUUM DEPOSITION SYSTEM TO EITHER REPLENISH MATERIAL VAPORIZED IN THE CRUICBLE OR TO PRODUCE A UNIFORM COATING ON THE WIRE. THE WIRE IS URGED INTO THE CRUCIBLE THROUGH A HEATED GUIDE MEMBER UPON WHICH VAPOR WILL NOT CONDENSE AND SOLIDIFY.

Description

H. R. SMITH, JR

METHOD AND APPARATUS FOR VAPOR DEPOSITION Feb. 9, 1971 4 Sheets-Sheet 1 Filed April 24 1968 Feb, 9, 1971 H. R. SMITH, JR

7 METHOD AND APPARATUS FOR VAPOR DEPQSITION 4 SheetsSheet 2 Filed April 24.

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METHOD AND APPARATUS FOR VAPOR DEPOSITION Filed April 24, 1968 4 Sheets-Sheet s JD v M z Q 4 5 w w W) T 13 v \I\ g 6/ I R X /5 Ii 45 22 7 1 \\\\W\ Y/VF Feb. 9, 1971 HI R. SMITH, JR 3,562,002

METHOD AND APPARATUS FOR VAPOR DEPOSITION Filed April 24, 1968 4 Sheets-Sheet 4 NON I III ,IIIIIIIIIIIE QOE HUGH SJI'T H JR.

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United States Patent US. Cl. 11793.3 14 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus are described for feeding wire into a vapor source crucible in a vacuum deposition system to either replenish material vaporized in the crucible or to produce a uniform coating on the wire. The wire is urged into the crucible through a heated guide member upon which vapor will not condense and solidify.

This invention relates to the feeding of wire into vapor source crucibles in vacuum deposition systems. More particularly, the invention relates to an improved method and apparatus for feeding wire into a vapor source crucible in such a system either to replenish material vaporized in the crucible or to produce a uniform coating on the wire. This application is a continuation-in-part of application Ser. No. 637,386, filed May 10, 1967, now abandoned.

Vacuum deposition systems generally involve the condensation of a vapor of one material on a substrate of another material, performed in a relatively high vacuum environment. The materials may be of various types, such as metals and ceramics, and the substrate may be of any of a variety of thicknesses. The process may operate on a substrate comprising a continuously moving film, or the substrate may be of a more discrete form.

In a vacuum deposition system, the vapor is often produced by utilizing a crucible containing charge material which is melted and vaporized by high energy electron beams directed through the open end of the crucible and against the charge material. The production of vapor by such means provides good control over the thickness, density, and uniformity of the deposited vapor and also facilitates efiicient utilization of materials.

For extended periods of operation, it is necessary to replenish the charge material which is vaporized in the crucible. One method of material replenishment or feeding is by placing batches of the charge material in solid form into the crucible through the open end thereof. Such a feeding method is not sufliciently sophisticated for many operations in that it usually necessitates interruption of the vapor deposition process.

Another method of feeding is by inserting a continuously moving rod or wire of the charge material through the open mouth of the crucible. (In this specification and claims, the term wire is intended to include a piece of elongated slender metal or non-metal of circular cross section and, in addition, any elongated form of metallic or non-metallic material of circular or non-circular cross section, such as an elongated rod or tube.) In wire feeding apparatus, the wire moves into the crucible at a rate just suiiicient to supply losses of the charge material due to vaporization. Although this type of feeding avoids any necessity for interrupting the process, certain difficulties may arise in that, due to the high heat of the crucible, the wire may melt too soon. When this happens, the molten drops may not enter the crucible in the proper place to replenish the molten charge, but instead may fall out of the crucible or may solidify on cool parts of the crucible ice away from the area of the molten charge. Early melting might also cause the wire to jam in the feeding apparatus. Another difficulty is that the feeding apparatus, being near the open end of the crucible, may interfere with the vapor beam emanating from the mouth of the crucible and become heavily coated or clogged with condensate.

In a particular type of vacuum deposition system, the crucibles are cylindrical and rotate about their axes, which are horizontally disposed. The reason for rotating the crucible is twofold. First, an even distribution of the melted charge material is effected about the wall of the crucible to provide a symmetrical vapor beam of even density moving out of the crucible mouth. Second, although the electron beam or beams may impinge upon only a small area of the molten charge, by rotating the crucible, all of the charge is bombarded by each electron beam with a substantially uniform transfer of energy from the beam throughout the charge. Such a rotating crucible has particular advantage in coating vertically disposed substrates such as glass because, due to the horizontal attitude of the crucible axis, the vapor beam emitted from the crucible is substantially horizontal. Two or more of such crucibles may be arranged in banks in a deposition system for coating particularly large substrates.

Bulk feeding of such crucibles has proved unsatisfactory, as has continuous front feeding by wire, for the difficulties mentioned in the above discussion of these two feeding methods. Development of feeding methods other than the two types described is further complicated due to the fact that the crucible is rotating and, at some point in the feed process, a transistion must occur in the feed material from a non-rotating condition to a rotating condition.

Rotary vapor source crucibles may be used to produce a uniform coating on wire or other elongated substrates without having to turn the substrate in order to expose all surfaces to the fiow of vapor from the source. Large amounts of vapor are typically present in vapor source crucibles. Accordingly, wire being fed into the crucible may undergo non-uniform and excessive coating, or excessive heating, as vapor condenses on the wire too soon and in an irregular manner.

It is an object of this invention to provide an improved method and apparatus for feeding wire into a vapor source crucible.

Another object of the invention is to provide a method and apparatus for continuously feeding a charge material into a vapor source crucible other than through the open end of the crucible.

Still another object of the invention is to provide an improved method and apparatus for continuously feeding charge material into a rotating crucible.

A further object of the invention is to provide a method and apparatus for feeding charge material in wire form into a rotating crucible through an opening in a wall of the crucible.

It is another object of the invention to provide wire coating apparatus in which close regulation of wire temperature may be achieved, and in which non-uniform coating is avoided.

Other objects and the various features of the invention will become apparent to those skilled in the art from the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is an elevational view of a vapor source assembly including feeding apparatus according to the invention;

FIG. 2 is an enlarged partially sectioned view of a portion of the assembly of FIG. 1;

FIG. 3 is a further enlarged sectional view of the crucible and a portion of the drive shaft therefor of the assembly of FIGS. 1 and 2;

FIG. 4 is a still further enlarged full section view of a portion of the vapor source assembly of FIGS. 1 and 2 at the end thereof opposite the crucible;

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 3; and

FIG. 6 is an elevational view of apparatus of the invention as utilized for coating wire.

In accordance with the invention, wire is fed into a vapor source crucible 11 having a guide member 12 disposed in an opening 13 in a wall 14 of the crucible. The guide member has a wire conducting passage 15 therethrough communicating with the interior of the crucible. The Wire is urged through the wire conducting passage into the crucible and the guide member is heated to provide a temperature at the end of the guide member adjacent the interior of the crucible which exceeds the melting temperature of the material in the wire.

A flow of gas may be established through the wire conducting passage 15 toward the interior of the crucible 11 to prevent vapor from entering the passage and condensing on portions of the guide member 12 having temperatures which do not exceed the condensation temperature of the material in the wire. Such gas flow is also advantageous during start up and shut down operations wherein the end of the guide member adjacent the interior of the crucible may not be of a temperature exceeding the melting temperature of the material in the wire. The gas issuing from the passage forms a protective cloud over such end of the guide member and inhibits condensation of vapor thereon.

In connection with apparatus utilizing a rotating vapor source crucible, the wire is fed through a hollow drive shaft 16 for'the crucible 11. The guide member 12 is positioned such that the passage 15 therethrough coincides with the axis of rotation of the crucible. The wire is guided in the hollow drive shaft by an elongated nonrotating snout 17 cantilevered from a supporting plate 55 of the apparatus. The snout may be provided with coolant conduits for keeping the wire cool during its passage through the hollow drive shaft.

Referring in more detail to the drawings, apparatus is illustrated which is constructed in accordance with the invention, and the method of the invention may be practiced in connection with such apparatus. Although the illustrated embodiment is designed specifically for use in connection with apparatus for vaporizing aluminum, it is to be understood that wire of other feed materials might also be utilized with little or no modification required. Moreover, although certain materials are specified for various portions of the apparatus described subsequently, it is to be understood that other materials may be suitable in some circumstances.

The vapor source assembly illustrated includes a cooled crucible 11 having an annular coolant flow chamber 18 in the walls thereof. Suitable baffies, not shown, may be provided in the coolant flow chamber for directing coolant in a desired flow. The crucible may be constructed of copper and the coolant circulated may be water. The crucible is of generally cylindrical shape, having an open end through which the vapor produced in the crucible escapes in the form of a vapor beam. The rim of the open end of the crucible is surrounded by a lip 19 and the flow chamber 18 extends partially into the lip. The opposite end of the cylindrical crucible is closed by an end wall 14. The closed end wall includes an inlet passage 21 and an outlet passage 22 through which coolant may be passed into and from, respectively, the flow chamber 18 in the cylindrical crucible walls.

The closed end wall 14 of the crucible 11 has an opening 13 therein, the axis of which is aligned with the axis of the cylindrical crucible. The opening has two sections of different diameters, with the smaller of the two communicating with the interior of the crucible. The crucible is secured to a drive shaft 16 which mates in the larger section of the opening in the end wall of the crucible.

A fitting 23, which is welded to the end of the drive shaft, is suitably secured to the end wall 14 of the crucible in the larger part of the opening 13 therein. The drive shaft extends from the crucible axially thereof and is journalled by a plurality of bearings 24 enclosed in a housing 25 for the source assembly. The housing for the source assembly is supported in an opening 26 in a wall of a vacuum chamber housing 27 by means of a bolted flange and O-ring vacuum seal 20.

The vapor source assembly housing 25 is provided with an appendage 28 through which a power shaft 29 extends perpendicularly of the drive shaft 16. A bevel gear 31 on the power shaft engages an annular bevel gear 32 on the drive shaft for driving same. Ball bearings 33 are provided in the appendage 28 for journalling the power shaft 29. The housing 25 includes a pair of annular shoulders 34 and 35 which extend inwardly toward the drive shaft and which contain seals 36 and 37 to enclose a lubricant chamber 38 for the bevel gears 31 and 32 and the bearings 24 in 'which the drive shaft is journalled. Lubricant may also enter the appendage 28 to lubricate bearings 33, and an annular seal 40 is provided to contain lubricant in the appendage 28. Suitable means, not shown, for conducting lubricant to and from the chamber may be provided.

The drive shaft 16 is constructed with two

coolant flow passages

39 and 41 therein which extend along the drive shaft between the outer surface and the axis thereof. Each of the passages is slightly less than semi-annular in cross section and one of the passages 39 carries coolant to the crucible while the other 41 carries coolant from the crucible. The passages in the drive shaft communicate with the inlet and

outlet passages

21 and 22 in the crucible 11 through

suitable openings

42 and 43 near the crucible end of the drive shaft.

Coolant is supplied to the coolant flow passages in the drive shaft through a coolant inlet conduit 44 in the vapor source assembly housing 25. The coolant inlet conduit communicates with an annular coolant inlet chamber 45 formed between the inwardly projecting annular shoulder 35 in the housing and a further inwardly projecting annular shoulder 46. Shoulder 46 is sealed against the outer periphery of the drive shaft by a seal 47. Coolant under pressure in chamber 45 enters passage 39 in the rotating drive shaft 16 through an opening 53. v

A further annular shoulder 48 projects inwardly from the housing 25 near the rearward end of the drive shaft and is sealed by seals 49 against the outer periphery of the drive shaft. This shoulder 48, together with the previously mentioned shoulder 46, forms an outlet chamber 51 for the coolant. Coolant returning from crucible 11 through passage 41 enters chamber 51 through an opening 54 in the drive shaft. A coolant outlet conduit 52 in the vapor source assembly housing communicates with the outlet chamber to remove coolant therefrom for disposal or recirculation.

Thus, coolant enters the inlet chamber 45 through the inlet conduit 44 flows through the opening 53 in the outer wall of the drive shaft 16, through the coolant conducting passage 39 therein, through the opening 42 and coolant conducting passage 21, into flow chamber 18 in the crucible 11. Coolant flowing back from flow chamber 18 enters the coolant conducting passage 41 in the drive shaft through passage 22 and opening 43. The returning coolant then flows rearwardly along the drive shaft through the outlet opening 54 in the drive shaft into the outlet chamber 51, and from there through the outlet conduit 52. This coolant flow is maintained while the drive shaft and crucible are rotating at a relatively high speed. The drive shaft, being hollowed and thereby providing direct communication with the interior of vacuum housing 27, must therefore be vacuum sealed at its rearward end. This is accomplished by seals 49 and by a sealing plate 55 secured over the open rear portion of the vapor source assembly housing 25.

In vapor depositing aluminum, insulation between the cooled walls of the crucible 11, which may be copper, and the molten aluminum contained in the crucible may be provided by a layer of tungsten sheet 56. The inner surface 57 of the tungsten sheet is sprayed with zirconium oxide to provide good thermal insulation and to prevent chemical reaction between the highly reactive molten aluminum and the tungsten. To further insure this, zirconium may be melted into the crucible prior to placing aluminum therein such that, when the vapor source is in full operation a layer of molten zirconium-aluminum alloy is disposed in the melt 60 between the molten aluminum in the melt near its surface and the tungsten sheet. This also provides superior thermal insulation between the relatively cool walls of the crucible and the high temperature molten aluminum.

The charge material in the crucible 11 is melted by one or more high energy electron beams directed into the crucible through the open end thereof to impinge on the surface of the charge material. The beams are produced by one or more electron beam guns 59 which are mounted in vacuum chamber housing 27. Guns 59 may be of a type known in the art and preferably have provision for varying the intensity and direction of the electron beams (indicated by the dotted lines) which they produce. The charge, when molten, is held by centrifugal force against the inner side of the cylindrical walls of the crucible.

In order to replenish the aluminum charge material which is vaporized in the crucible 11, aluminum wire is fed into the crucible to be melted therein. The wire enters the crucible through a refractory material guide 12 inserted in the smaller section of the opening 13 of the closed end wall 14 of the crucible and held therein by shoulders 61 which mate in bayonet type recesses in the opening. The material of which the guide 12 is constructed, in the case of molten aluminum charge, should be a material which is not highly reactive with aluminum vapor. A satisfactory material for this purpose is a blend of the ceramics titanium diboride and boron nitride. The guide may be formed by mixing powders of these ceramics and then hot pressing the mixture into the desired shape. Naturally, for vaporizing other materials, a different material of suitable characteristics may be utilized for the guide. A graphite block 62 is disposed just adjacent the refractory material guide. The graphite block is held in place between the fitting 23 and the refractory material guide to thermally isolate the fitting from the guide. The fitting, graphite block, and refractory material guide are each provided with

wire conducting passages

63, 64 and 15, respectively, each of the passages being in alignment, for passing the feed wire into the crucible.

The feed wire is carried up the center of the hollow drive shaft 16 in an elongated guide or snout 17. The snout comprises a pair of concentric

cylindrical sleeves

65 and 66 mounted at-one end to the backing plate 55 of the source assembly housing 25 and cantilevered within the hollow drive shaft 16. The end of the snout 17 adjacent the crucible is provided with a solid block or head 67 of a material, such as copper, and the

sleeves

65 and 66 of which the snout is comprised form coolant conducting passages. The head 67 is provided with an annular recess 68. Openings 69 are provided in the end of sleeve 66 to link the passages formed by the concentric sleeves. A coolant, such as water, may be passed through the passage formed between

sleeves

65 and 66 to the recess 68 in the head, passed through openings '69, and returned through the sleeve 66. This maintains a cool temperature in the head and the snout for cooling the aluminum wire. A coolant inlet conduit 71 and a coolant outlet conduit 72 are provided in sealing plate 55. Inlet conduit 71 communicates with the passage between

sleeves

65 and 66 whereas outlet conduit 72 communicates with the interior of sleeve 66. The conduits operate, respectively, to pass coolant into and from the snout.

The wire is carried through the snout 17 in a guide tube 76 which communicates with a wire conducting passage 77 in the head 67 of the snout. At the end opposite head 67, the guide tube 76 extends through the sealing plate 55 and a backing plate 75 bolted to plate 55 into a seal block 78. The guide tube may, for example, be made of stainless steel. The seal block 78 is contained in a seal housing 79 bolted to the backing plate 75. The seal housing also contains a plurality of axially spaced rubber disc seals 81 having suitable spacing blocks 82 therebetween. The spacing blocks, disc seals and seal block are all held in place in seal housing 79 by a plug 84 threaded into the seal housing to abut the furthest left spacing block 82. Aligned passages 83 extend through the spacing blocks, the plug, and the seal block, and openings are provided centrally of the seals. The openings in the seals are of smaller diameter than the wire. Thus, the passages in the spacing blocks and the openings in the seals permit passage of the wire through the seal housing, while the seals prevent atmosphere from passing into the guide tube and thus contaminating the vacuum in the vacuum chamber housing 27. To further insure proper vacuum sealing, a vacuum pump-out passage 85 is provided in the central one of spacing blocks v82.. A vacuum pumpout tube 86 is attached to the seal housing 79 and communicates with passage 85 so that evacuation of the passage may be attained through use of a suitable vacuum pump, not shown. A gas inlet conduit 87, the purpose of which will be subsequently explained, is provided in the seal housing 79.

Wire enters the seal housing 79 through a guide tube 88 which extends rearwardly of the housing 79 and extends into plug 84, being axially aligned with the passage 83 therein. The tube 88 is supported in a snout 8-9 which is an appendage of a cap 90 bolted to the seal housing The wire is driven through the seal housing and through the guide tube 76 in the snout into the crucible 11 by means of a capstan 91 and pinch roller 92 disposed at the rearward end of the guide tube 88. A suitable straightening device 93 may also be provided for straightening the wire prior to the wire passing between the capstan and pinch roller. The wire is drawn through the straightening device 93 and over an idler wheel 94, from a supply reel 95, The supply reel, idler wheel, straightening device, capstan and pinch roller are all mounted to a suitable supporting frame 96. A motor 97 for driving the capstan 91 through a suitable drive mechanism (not shown) is also mounted on frame 96.

In the rotating type of crucible, such as is shown in the drawings, continuous feeding of the wire through the open end of the crucible presents several disadvantages. The feeding apparatus may partially obstruct the vapor beam and may become heavily coated with condensate as a result of its proximity to the vapor beam. These problems, of course, are present in the case of non-rotating crucibles as well. A particular problem with respect to open end feeding of rotating crucibles where the axis of rotation is horizontal lies in the necessity for getting the wire far enough into the crucible before it melts. The high temperatures in the crucibles, coupled with the fact that the high energy electron beams are entering the crucible through the open end thereof, make this extremely diflicult since the wire is inclined to melt very quickly. If the wire melts too soon, the molten material may spatter out or around the open end of the crucible or clog the condensing on the exposed surface of the guide therefore merely runs off and falls back into the melt. If the crucible and, hence, the guide are rotated, centrifugal force spins the condensed vapor radially outward of the opening in the guide. Heating of the guide occurs as a result of radiation from the molten aluminum and vapor in the crucible and from impingement thereon of some of the fringe electrons in the electron beams entering the crucible. Control over the temperature of the guide is effected by controlling the direction and power of the electron beams, particularly the direction. The beams are directed so that fringe electrons impinge upon the guide to maintain the guide at the desired temperature, consistent with the further consideration that the beams must effect the desired heating and vaporization of the charge. If desired, the guide may be heated to a temperature exceeding the condensation temperature of the aluminum vapor, thus preventing any condensation on the guide. The guide, however, must not be heated to such a temperature as to cause a relatively high rate of reaction between the refractory material and the aluminum vapor that would erode the guide.

The guide, therefore, provides a hot surface or hot spot in a relatively cool end wall of the cooled crucible to insure that the passage through which the wire is passing remains free of condensate. Only the surface of the guide, which is in the crucible and therefore exposed to the vapor, need exceed the vapor melting temperature. As a practical matter, however, such temperatures will exist for a given depth in the guide. Aluminum vapor is generally prevented from entering into the space between the feed wire and the refractory insert and hence from condensing on the walls of the passage beyond the given depth by a slight flow of air through the passage due to the necessarily imperfect nature of the sealing arrangement. In addition, the moving wire will help to abrade any condensate from the walls of the passage. The wire is passed through the guide at a sufficiently high rate as to preclude the possibility of the wire melting prior to entering the crucible due to radiated and/or conducted heat from the guide. In the illustrated apparatus, the graphite block 62 adjacent the refractory guide 12 prevents the fitting 23 from becoming so hot that the aluminum wire passing through the passage therein will be melted or fused to the walls of the passage and also helps to thermally insulate the guide from its cooler surroundings.

As the wire enters the crucible, it will proceed a certain distance and then melt. The drops of molten material will fall down, due to the effect of gravity, into the molten pool of the spinning crucible. Once entering the pool, the

drops form part of the melt and are distributed evenly around the walls of the crucible. The exact distance the wire protrudes into the crucible before it melts will depend upon the temperature of the wire as it enters the crucible (due to radiation and conduction of heat through the refractory guide and the graphic block) which will depend, among other things, upon the feed rate of the wire. The temperature of the wire will also depend upon the heat radiation from the molten material in the crucible and upon the impact of the electron beams directly on the wire. The latter factor is generally the primary factor in determining the position at which the wire will melt.

The combination of the cooled snout and the thermally isolated refractory guide helps to keep the Wire cool and in its solid condition until it is in the proper position for melting and, in addition, prevents vapor condensation from clogging the wire conducting pasage. There will be a temperature gradient in the refractory guide which decreases axially from the crucible end to the graphite block end and which also decreases radially outward toward the water cooled crucible. As pointed out above, the surface of the refractory insert which is in the crucible should exceed the melting temperature of aluminum in order that aluminum will not clog the hole.

Under certain circumstances, such as slow wire feed rates (of the order of 25 inches per minute or less), or in the case of relatively high vapor pressures, the abrading action of the wire and the air flow through the passage may be of little effect. Accordingly, vapor may enter the wire conducting passage in the guide and tend to condense on the walls thereof, clogging the passage. To prevent this, the invention contemplates the establishment of a flow or bleed of a relatively inert gas, for example argon, through the passage toward the interior of the crucible. The gas fiow into the vacuum system is selected so that the vapor pressure of the vacuum system is only raised an amount of the order of 2/ ths of a micron of mercury. It has been found such an increase has a negligible affect on system operation. Under some conditions, it may be possible to use higher flow rates of gas without detrimental effect. The presence of the gas in and around the passage makes it probable that the aluminum vapor particles will collide with an atom of gas and be reflected back out into the crucible before they impinge upon the passage wall or the wire. This prevents the vapor from condensing in the passage and clogging the passage.

In the apparatus illustrated in the drawnigs, the gas enters the sealing cap '55 through the inlet conduit 87 into the space between the snout 17 and the drive shaft 16. The gas, since it cannot flow back out through the stainless steel guide tube 76 due to the rubber disc seals and the wire, finds its way through the

passages

63, 64 and 15 in the fitting 23, graphite block 62 and refractory guide 12, respectively, into the crucible 11.

The gas bleed has particular application during start up and shut down operations of the apparatus. During starting, the temperature of the refractory guide will naturally be below that of the melting temperature of aluminum. To prevent condensation and solidification of aluminum on the guide, such that the hole would become clogged, the gas flow is increased to an extent such that a protective cloud of gas exists over the surface of the guide facing into the crucible. In order to heat the refractory guide to the desired temperature, the electron beams may be deflected slightly from their normal position such that enough electrons will bombard the guide to heat it up quickly. The beams are then restored to their operating position and the aluminum wire is urged through the snout into the crucible and melted by the beams to build up the molten charge. During shut down operations, the gas bleed has a similar effect, while the refractory guide is cooling and while aluminum vapor is .still present in the crucible.

Referring now to FIG. 6, an alternative embodiment of the invention is illustrated. The apparatus of FIG. 6 is for coating wire and utilizes a crucible 111, one end thereof being open and surrounded by a lip 119. Parts similar in function to parts of the previously described apparatus ,are given identical reference numbers preceded by a 1, and 'will not all be described in detail. The crucible 111 is enclosed within a cylindrical vacuum enclosure 201 evacuated through a duct 202 by a suitable vacuum pump 203. Molten material is contained within an annular coaxial recess 156 on the inner side of the crucible 111. As will be explained, the crucible 111 is cooled in order to form a skull 157 of the evaporant material between the molten material 160 and the crucible 111. An electron beam gun 159, of a type similar to the electron beam gun previously described, is utilized for heating the surface of the molten material in the annular recess. The electron beam produced by the gun 159 moves through an arcuate path into the crucible through the open end thereof.

The crucible 111 is supported in the enclosure 201 by a hollow drive shaft 116, the drive shaft also operating to rotate the crucible. The drive shaft 116 extends axially of the crucible through a wall 127 of the enclosure 201 into a sealed housing and bearing arrangement (not shown) identical with that previously described. The

closed end wall 121 of the crucible has an opening 113 therein, the axis of which is aligned with the axis of the crucible. The opening 113 has two sections of different diameters, the smaller of the two communicating with the interior of the crucible. The crucible is secured to the drive shaft 116 which mates in the larger section of the opening 113 in the closed end wall of the crucible. A fitting 123, which is welded to the end of the drive shaft, is suitably secured to the end wall of the receptacle in the larger part of the opening 113 therein. A driving motor and suitable gear arrangement (also not illustrated) for driving the shaft 116 are provided exteriorly of the enclosure 201.

The drive shaft 116 is constructed as in the previously described apparatus, with two

coolant passages

139 and 141 therein which extend along the drive shaft between the outer surface and the axis thereof. Each of the passages is slightly less than semi-annular in cross section. The passage 139 carries coolant to the crucible, while the passage 141 carries coolant from the crucible. The passages in the drive shaft communicate with a coolant fiow chamber 118 in the crucible through an inlet passage 121 and an outlet passage 122. Suitable means as previously described, not illustrated, are provided exteriorly of the enclosure 201 for supplying coolant to the inlet passage 139 and for removing coolant from the outlet passage 141 as the drive shaft 116 rotates.

The wire 204 to be coated is fed into the crucible 111 as in the previously described embodiment. Replenishment feed stock for the molten material 160 may be fed in through the open end of the crucible as needed. Under some circumstances, it may be desirable to maintain the wire 204 at a sufliciently low temperature prior to entry into the crucible as to prevent excessive heating thereof. Such excessive heating may occur when the wire exceeds the melting temperature of the coating material, causing the coating material to run after it condenses on the wire and produce an uneven coating. Moreover, such excessive temperature may be reached at a reaction temperature between the wire and the coating material, or at a temperature beyond which the wire becomes too ductile for proper handling.

In order to cool the wire 204 until just prior to its entry into the crucible 111, the wire is passed up the hollow drive shaft 116 in a wire conducting snout 117. The snout is identical with that previously described and comprises a pair of concentric

cylindrical sleeves

165 and 166 suitably mounted to a support structure, not illustrated, which is fixed with respect to the rotary drive shaft. Accordingly, the snout is cantilevered within the hollow drive shaft and does not rotate therewith. The drive shaft is vacuum sealed (not shown) to the snout as before described to maintain the integrity of the vacuum enclosure 201. This is necessary because the hollow interior of the drive shaft communicates with the interior of the crucible. The end of the snout toward the crucible is provided with a solid block or head 167 of a material, such as copper, and the

sleeves

165 and 166 of which the snout is comprised form coolant conducting passages. The head 167 is provided with an annular recess 168. Openings 169 are provided in the end of the sleeve 165 to link the passages formed by the concentric sleeves. A coolant, such as water, may be passed through the passage formed between the sleeves to the recess 168, passed through the openings 169, and returned through the sleeve 165. This maintains a cool temperature in the head and the snout for cooling the wire 204. Suitable inlet and outlet ducts may be provided in the support structure, not illustrated, for the snout in order to supply the coolant to the snout.

The wire 204 is carried through the snout 117, as in the previously described apparatus, in a guide tube 176 which communicates with a wire conducting passage 177 in the head 167 of the snout. The guide tube 176 and the passage 177 are aligned on the axis of the rotating crucible 111. The wire is fed into the tube 176 as in the previously described apparatus.

The wire 204 is passed through the rotary crucible 111 from the supply reel (not shown) to a takeup reel 206. The takeup reel 206 is mounted on a bracket 207, such bracket being secured to the exterior of the enclosure 201. The wire is guided from the supply reel through the guide tube 176 in the snout 117. After passing through the crucible 111, the Wire emerges from the enclosure through a suitable vacuum valve 208, passes between a pair of drive rollers 209 and around a guide roller 211 to the takeup reel 206. The drive rollers 209 govern the speed of the wire and the takeup reel 206 is driven by suitable means including a slip clutch in order to take up slack in the wire. By regulating the speed of the wire and the cooling rate in the snout, the wire temperature may be controlled.

In order to prevent vapor from condensing on the cooled snout 117 and thereby plugging the passage 177 in the head 167, the smaller section of the opening 113 in the closed end wall of the crucible 111 is closed by a guide 112. The wire 204 enters the rotary crucible axially thereof through a small passage 115 in the center of the guide. The guide is comprised of a suitable refractory material and is held in the wall of the receptacle by shoulders 161 which mate in bayonet type recesses in the small section of the opening 113. The refractory material of which the guide is constructed is selected to be not highly reactive with the material of the wire. The guide is heated to exceed the melting temperature of the deposit material as in the previous embodiment, thereby preventing clogging of the passage 115.

The refractory material guide 112 is heated by the fringe electrons of the electron beam produced by the gun 159. If this is insufiicient, further heating may be accomplished by varying the strength of the deflecting field of the beam to sweep the beam periodically over the guide. By maintaining the refractory material guide at a temperature above the melting temperature of the vapor in the crucible 111, the coating material which condenses on the guide merely runs off. This keeps the passage clear and prevents interference with the movement of the wire 204.

It will therefore be seen that the invention aids in effecting a continuous feed of solid wire, such as aluminum, from a relatively cool environment exteriorly of the vapor source assembly crucible to the extremely hot and high vapor pressure environment of the crucible. The invention effects a continuous feed by providing a temperature transition which is smooth in order that the wire will melt at the proper time. Vapor in the crucible is prevented from condensing around and in the wire passage such that the passage remains free of blockage. By doing so the invention provides an improved method and apparatus for feeding a solid evaporant material, in wire form, into a vapor source crucible. The invention has particular application to those crucibles which are designed to rotate about horizontal axes for coating vertical substrates. The method and apparatus are applicable to various materials and are not limited to use with aluminum, as described in connection with the specific embodiment shown. The invention is superior in many respects to feeding through the open end of the crucible in either a continuous manner or by a batch feeding procedure. The invention may also be applied to the continuous coating of a wire substrate to regulate temperature and produce an even deposit.

Various modifications and embodiments of the invention other than those shown and described herein will be apparent, from the foregoing description, to those skilled in the art and such other modifications and embodiments are intended to fall within the scope of the appendant claims.

What is claimed is:

1. An apparatus for feeding wire into a rotating vapor source crucible through an axial opening in a wall thereof,

such crucible being driven by a hollow drive shaft having one end secured to the crucible around such opening, said apparatus including in combination, a support structure disposed at the end of the drive shaft opposite the cruci ble, elongated guide means secured to said support structure and projecting into the hollow drive shaft, said guide means having a first passage therein for guiding the wire through the rotating drive shaft toward the crucible, a refractory guide disposed in the opening in a wall of the crucible proximate the end of said guide means opposite said support structure, said refractory guide having a second passage therein aligned with said first passage and communicating with the interior of the vapor source crucible for guiding the wire into the crucible, and means for urging the Wire through said first and second passages, said refractory guide being constructed to develop a temperature at the end thereof adjacent the interior of the crucible, due to heat applied to said refractory guide from the crucible, which exceeds the melting temperature of the material in the vapor, whereby accumulation of condensed vapor around the wire conducting passage is prevented to keep said wire conducting passage clear.

2. Apparatus in accordance with claim 1 wherein means are provided for establishing a flow of gas through said second passage toward the interior of the crucible.

3. Apparatus in accordance with claim 1 wherein said elongated guide means comprise a cylindrical member defining a plurality of fluid conducting passages, a solid metal tip at one end of said cylindrical member to which said fluid conducting passages conduct coolant for cooling said tip, and an elongated sleeve defining part of said first passage and extending axially along said cylindrical member to said tip, said tip having a hole therein defining the remainder of said first passage.

4. Apparatus in accordance with claim 1 including means for withdrawing the wire from the crucible after condensation of vapor on the wire.

5. An apparatus for feeding wire into a cooled vapor source crucible through an opening in a wall thereof, including in combination, a guide member disposed in the opening in a wall of the crucible, said guide member having a wire guiding and conducting passage therethrough, means for urging wire through said wire conducting passage into the crucible, said guide member being thermally insulated from said urging means, and means for heating said guide member so that accumulation of condensed vapor on said guide member adjacent the wire conducting passage is prevented to keep said passage clear.

6. Apparatus in accordance with claim 1 wherein means are provided for rotating the crucible about an axis passing through the opening, whereby condensed material in liquid form flows radially outward of the opening.

7. Apparatus in accordance with claim 1 including means for withdrawing the wire from the crucible after condensation of vapor on the wire.

8. Apparatus in accordance with claim 1 wherein means are provided for establishing a How of gas through said wire conducting passage toward the interior of the crucible to prevent vapor from condensing on portions of said guide member within the wire conducting passage.

9. Apparatus in accordance with claim 8 wherein said guide member is comprised of a refractory material.

10. A method for feeding Wire into a cooled rotary vapor source crucible heated by at least one electron beam and having a guide member disposed in an opening in a Wall of the crucible, said guide member having a wire guiding and conducting passage therethrough lying on the axis of rotation of the crucible, said method comprising: rotating the crucible, heating the guide member at least partially by the electron beam, controlling the electron beam to provide a temperature at the end of the guide member adjacent the interior of the crucible which exceeds the melting temperature of the material in the vapor, whereby material which condenses around the wire conducting passage flows radially outward by centrifugal force to keep said wire conducting passage clear, and urging the wire through the wire conducting passage into the crucible at a rate sufficient to prevent melting of the wire prior to entry into the crucible.

11. A method in accordance with claim 10 wherein the wire is the same material as the vapor material and is melted in the crucible to replenish the molten material therein.

12. A method in accordance with claim 10 wherein the wire is maintained at temperatures below the condensation temperature of the vapor material and is drawn through the crucible at a rate which allows a desired amount of vapor to condense on the wire.

13. A method in accordance with claim 11 wherein a flow of gas is established through the wire conducting passage toward the interior of the crucible to prevent vapor from condensing on portions of the guide member within the wire conducting passage.

14. A method in accordance with claim 13 wherein said flow of gas is established prior to the steps of heating the guide member and urging the wire through the wire conducting passage into the crucible, and is maintained after such heating and urging steps have been discontinued, whereby condensation of vapor which would clog the wire conducting passage is prevented during start up and shut down operations, respectively.

References Cited UNITED STATES PATENTS 2,879,739 3/1959 Bugbee et a1. 117-107X 3,019,129 3/1962 Walsh 117-101 3,360,600 12/1967 Du Bois 13-31 ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH, Assistant Examiner US. Cl. X.R.