US3471321A - Vapor coating aluminum on ironcontaining substrate - Google Patents

Description

Oct. 7, 1969 c. M. OUALLINE, JR., ETAL 3,471,321

VAPOR COTING ALUMINUM ON IRON CONTAINING SUBSTRATE Filed Dec. 30, 1964 ATTORNEY United States Patent O U.S. Cl. 117-102 4 Claims ABSTRACT F THE DISCLOSURE Disclosed are methods and apparatus for coating a metallic member with a film of a different metal without the formation of an undesirable alloy or compound layer intermediate the metallic member and the metal film. The method disclosed is a vapor phase process comprising the formation of a metal subhalide vapor by reacting a metal halide compound with elemental metal of the same kind as the metal of the metal halide compound, conducting the subhalide vapor while at a temperature of no less than about 700 C. to 800 C. into Contact with the metallic member to be coated while maintaining the temperature of the member at a value below the melting point of the elemental metal to thereby deposit a substantially pure film of the elemental metal on the member, and removing the member from contact with the subhalide vapor while the temperature of the member is maintained below the melting point of the metal. The member to be coated may be, for example, copper, tantalum, tungsten, niobium, molybdenum, nickel, platinum, paladium, silver, gold, titanium, iron, steel, chromium and mixtures and alloys thereof. The metal film may be for example, aluminum, titanium, chromium, nickel, manganese, germanium and cobalt. Disclosed also is an apparatus for coating the member which comprises a reaction chamber, an outer casing surrounding said reaction chamber and defining cavities at opposite ends of said reaction chamber, means for the introduction of reactant vapor into said reaction chamber, means for evacuating said cavities to maintain subatmospheric pressure in said reaction chamber and said cavities, and means for moving said metallic member through said reaction chamber.

This invention relates to methods and apparatus for the coating of metallic surfaces.

In many instances it is desired to produce a thin coating of metal over a dissimilar metallic surface, for example, to produce a thin coating or film of a metal on a wire or strip made of a dissimilar metal.

The coating of a wire of one metal with a different type of metal is most commonly accomplishedby drawing `the wire through a bath of the molten coating metal. Another method, applicable in certain instances, is the electrophoretic deposition of powdered aluminum around wire with subsequent compaction. Still another method is based on compacting line metallic powder around the wire and heating.

The foregoing methods have varying degrees of applicability, depending on the dissimilar metals involved and depending on the particular degree of metal film purity and other characteristics required for the ultimate coated product.

T o facilitate consideration of certain specific problems 3,471,321 Patented Oct. 7, 1969 lCC presented by the prior art methods, consider the coating of an iron or steel wire with aluminum. If the aluminum coating is applied by passing the iron or steel wire through a molten bath of aluminum, it is found that the high temperature contact between the liquid aluminum and iron causes the formation of an iron-aluminum intermetallic compound or of an alloy, in general, this intermetallic compound is brittle and the coated wire consequently has physical limitation imposed upon it by the brittle regions present in the structure. Moreover, in quite thin films the intermetallic iron-aluminum compound extends into the outermost regions of the coating and militates against a high purity outer metal film. To eliminate or minimize reaction of iron and aluminum, asin the formation of intermetallic compound between the two, alloying agents must generally be added to the molten aluminum bath, for example, silicon is often added. The presence of the alloying agent, even in comparatively small amount, lowers electrical conductivity of the resulting coating or film and also makes it less resistant to corrosion.

Bath or hot dip coating is difficult to conduct in a manner such that uniform coating thicknesses are obtained, and particularly difficulty is encountered when thin coatings are attempted. Moreover, iron dissolves from the wire (or other metal being coated) and contaminates the molten aluminum.

The methods of coating a wire by electrophoretic deposition of powdered aluminum around the wire, followed by subsequent compaction, or by the compaction of aluminum powder around a wire, both require relatively expensive powdered aluminum and are quite difficult processes to control, for example, to control so that a predetermined coating thickness having desired film characteristics is obtained. Preparation of thin films by these methods is particularly difficult.

It is known that certain metals form subhalides when placed in reactive contact with vapor of a halide compound of the metal. For example, it is known that liquefied metallic aluminum maybe reacted with aluminum trichloride to produce aluminum monochloride. This reaction has been used as a method of refining aluminum, however, as far as is known, it has never been used for the deposition of thin films of pure aluminum on metallic members, for example, thin films of pure aluminum on iron or steel. It is believed that one reason the reaction has never been adapted to a process for coating members of iron and steel is the difficulty presented by formation of intermetallic compound between the metal of the body to be coated and the deposited aluminum. It would be expected that the aluminum would enter into reaction, or alloy with, the iron from the underlying body. For example, in the case of coating iron and steel bodies, formation of undesirable intermetallic iron-aluminum compound would ibe expected.

However, it has now been found, in accordance with the present invention, that aluminum, as well as certain other metals which would be expected to cause difficulty by alloying the compounding with the underlying body to be coated, may be deposited under certain conditions on a dissimilar metallic body by disproportionation of a subhalide compound of the coating metal. Moreover, it has been found that this may be accomplished in a manner by which thin films may be produced of controlled thickness and a high degree of purity, with essentially no intermetallic compound being formed between the film metal and the metal surface coated.

Accordingly, it is seen to be an object of the present invention to provide a process for coating metallic surfaces with a film of a dissimilar metal in such a manner that a high purity tilm is obtained which is not alloyed with or otherwise compounded with the coated body. Moreover, it is an object to provide such a process which can be operated to produce films of controlled and uniform thickness, including quite thin films. It is a further object to provide such a process which can form a coa-ting of pure metal from scrap or comparatively impure metal feed material. It is yet an additional object to provide such a process which can coat a continuously moving metallic member or substrate, for example, a wire or strip. It is yet an additional object to provide comparatively simple yet eficient apparatus for practicing the foregoing processes.

In accordance with the present invention, a vapor phase process is provided for coating a metallic surface with a dissimilar metal film. The process comprises forming a subhalide vapor by reacting a metal halide compound with elemental metal of the same kind as contained in the metal halide compound, followed by contacting the subhalide vapor so produced with the metallic surface to be coated while maintaining the temperature of the metallic surface to be coated at a value below the melting point of the metal in the metal subhalide compound. Subhalide vapor decomposes, i.e. reacts by disproportionation, to deposit pure metal on the comparatively cold surface to be coated accompanied by the formation of metal halide vapor. The surface of the member to be coated is maintained at a temperature above the condensation temperature of the metal halide to prevent deposition of the metal halide on the surface.

In a preferred embodiment, the metal to be deposited is aluminum and the surface upon which it is to be deposited comprises a major proportion of iron, e.g. iron, steel, etc.

In a specific preferred embodiment, the surface to be coated is the surface of an iron or steel wire. The wire is continuously moved through a closed system in which the subhalide disproportionation reaction, accompanied by deposition of aluminum on the wire, takes place. The speed of the wire is regulated such that its temperature does not exceed a critical maximum of about 550 C. Before the Wire is moved into contact with halide vapor, it is preferably raised to a temperature no lower than a value corresponding to the condensation temperature of aluminum trichloride under the pressure which it exists in the system.

An important feature of the present invention is the effective total re-cycle of the metal halide involved. The metal halide serves as a transfer or carrier means for elemental metal to be deposited, but there is no net consumption of the metal halide in the processing reactions. Metal halide only need be supplied to make up for system losses.

The apparatus aspects of the present invention provide means for forming vapor of a metal halide compound, means for contacting the metal halide vapor with a source of elemental metal of the same kind as the metal of the metal halide compound in order to form subhalide vapor, and means for moving a metallic member into the presence of the subhalide vapor which was formed on the contact of the metal halide vapor and the elemental metal. The means for moving the metallic member are of such a nature that the temperature of the metallic member is controlled while the member is in the presence of the subhalide vapor so that disproportionation of the subhalide vapor will occur in the vicinity of the member to deposit elemental metal from the subhalide vapor on the member, the elemental metal being deposited as a solid so that alloying and intermetallic compound formation with metal from the member being coated is essentially eliminated.

In one preferred embodiment, a closed system is provided for subatmospheric pressure deposition of the coating metal on the member being coated. The system pressure is preferably maintained at between about 2O and mm. of mercury. Partial pressure of subhalide vapor preferably ranges from about 10%-25% of the system pressure. One aspect of this embodiment provides apparatus adapted to permit diffusion of metal halide vapor being formed on disproportionation so that full re-cycle of aluminum trichloride is effectively provided.

In another embodiment, a full tiow system is provided for the deposition of metal on a dissimilar metallic surface being passed through the system. This embodiment includes a liquid metal-to-vapor contact vessel wherein a metal halide-rich vapor stream contacts a liquid metal of the same type contained in the metal halide to produce metal subhalide vapor. The metal subhalide vapor so produced changes the stream composition to cause it to be metal subhalide-enriched. A heated coating chamber is provided which receives the subhalide enriched vapor. Means are provided for moving a member to be coated through the coating chamber at a predetermined rate such that its temperature does not exceed tthe melting point of tthe metal being deposited. Means are provided for returning metal halide-enriched vapor to the contact vessel after disproportionation of the subhalide-enriched vapor to deposit metal on a metal surface being coated has occurred within the coating chamber. Preferably, the heating means for the system insure that the member being coated is at a minimum temperature no less than the condensation temperature of the metal halide, prior to contact of the member with any vapor containing metal halide.

For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevational sectional view of apparatus for coating a wire in accordance with the present invention; and

FIGURE 2 is a schematic, flow diagram illustrating a full ow process for practice of the present invention, and illustrating certain apparatus utilizable in such process.

Turning now to FIGURE 1, therein is shown a closed reactor system, indicated generally by the numeral 11. Reactor system 11 may be utilized to coat metallic members with a thin layer of metal; specifically to coat a wire, eg. iron or steel, with a thin layer of metal, e.g. aluminum.

The reactor system 11 includes the annular quartz outer reactor casing 13 and the oppositely disposed reactor closure fittings 15 and 17. Closure fittings 15 and 17 may be made, for example, of brass. Fittings 15 and 17 each include an enlarged disk 18 which serves as a respective end wall or head for the opposite ends of the outer reactor casing 13. The disks 18 are held tightly in position against the casing ends, as by C-type clamps 19, which engage edge portions of a disk and a respective shoulder formed on each casing end by enlarged diametrical casing end portions 21 and 23. O-rings (not illustrated), or other conventional seal elements, are provided to insure a tight seal. Closure fittings 15 and 17 each carry outwardly projecting Vacuum staged wire guide assemblies 27. Each assembly 27 is generally of cylindrical configuration and formed with a coaxially disposed array of apertures in its structure in alignment with aperture 29 in the disk portion 18 of the closure fitting. A plurality of axiallyaligned spaced-apart guide rings 31 are carried within successive annular compartments 32 which are formed within the body of each wire guide assembly 27. The aligned central openings in guide rings 31 and the coaxially-disposed apertures in each wire guide assembly permit wire to pass through the assembly and its corresponding aperture 29 in closure disks 18.

Various materials of construction may be used for the formation of the guide rings 31, an example being alumina.

Nipples 33, 35, 37 and 38 extend from the sides of each wire guide assembly 27 and respectively communicate with spaced-apart coaxial cavity regions 39 formed in the body of each fitting 27.

Outer reactor casing 13 is provided with a pair of nipples 40, which permit communication wtih the interior of the casing.

A reactor chamber 41 is contained within the interior of outer reactor casing 13. Reactor chamber 41 may be of any desired shape, for example, cylindrical, and it `may be made of various materials, for example, graphite. Conduit means 43, formed in the outer casing 13, extends from chamber 41 downwardly to supply vessel `45 and permits communication between the interior of reactor chamber 41 and the interior of the supply vessel 45. Conduit means 43 is tted with a valve 47 which Imay be adjusted as desired, but which is normally open during operation. A conduit 51 leads into a lower side portion of vessel 45. A valve means 53 is provided for conduit 51.

Vessel 45 is submerged in the heat transfer fluid 57, which is contained within heat transfer uid tank 59. The heat transfer fluid 57 may be kept at a controlled temperature by means of resistance heater 61, which has its power input controlled by a rheostat 63. The heat transfer uid temperature is sensed by the thermocouple 65, which is disposed to contact the heat transfer liquid 57. The output from thermocouple 65 leads to temperature controller 67, the output of which controls the power to maintain a desired predetermined temperature for heat transfer fluid 57.

Heating means are provided to maintain the conduit 43 at a constant temperature somewhat above the temperature of heat transfer iluid 57. 'Resistance heating tape may be wrapped about the conduit and supplied with power to accomplish this purpose, or various other conventional heating means may be used. In FIGURE 1, the heating means are schematically represented as resistance heater 69. Conventional control means (not illustrated) control the power to resistance heater 69 to maintain the conduit 43 at the desired predetermined temperature.

RF heating is provided for graphite reaction chamber 41 by means of RF coil 75, which is disposed about the outer regions of casing 13, adjacent the proximity of graphite reactor chamber 41. The .RF power source 77 is controlled by power controller means 79, the output of which is dependent upon the output of thermocouple 80, which is xed in the walls of graphite chamber 41. It can thus be seen that power to RF coil 75 is controlled to maintain the temperature of the reactor chamber 41 at a desired predetermined value.

A dish 81 rests on the oor of reaction chamber 41. It may be made of various materials, for example, alumina.

Wire supply spool 82 and wire take-up spool 83 are rotatably mounted at opposite ends of the closed reactor system 11. Wire 85 passes from supply spool 82 via the wire apertures of wire guide assembly 27 of fitting 15 into the interior of casing 13 and enters the reactor charnber 41 through a close tting chamber wall aperture 87 and exits from the chamber 41 through a close fitting aperture 89 in an oppositely disposed wall region to emerge in the interior portion of casing 13 adjacent tting 17. Thereafter, the wire 85 emerges from the assembly 11 by passing through the wire guide 27 of closure fitting 17, and is taken up on spool 83.

An example of the operation of the apparatus of FIGURE 1 will now be given. The vessel 45 is loaded with aluminum trichloride, represented by the numeral 90 in FIGURE 1. The dish 81 in reactor chamber 41 is filled with aluminum 91. The valve 47 i-s Placed in an open position. The valve 53 is in the closed position. The RF heating coil 75 is activated by supplying power from power source 77. Vacuum pumps, schematically illustrated by arrows 92, 93, 95, and 97 are connected to nipples 35, 37, 3S and 40, respectively, and activated to evacuate the chamber 41 and the interior of casing 13. Note that a staged vacuum pump-seal configuration is thus provided to maintain desired low pressures within the system while permitting wire to enter and leave the low pressure interior of the system. Argon, helium, or other inert gas from a suitable supply, schematically illustrated by arrows 99, is continuously passed through the wire guide assemblies 27 via nipples 33. For the most part this inert gas is exhausted by the various vacuum pumps. Its presence provides an inert atmosphere for the low pressure interior of casing 13.

A pressure of from about 20 to 100 mm. of mercury, preferably 2() to 40 mm. of mercury, is established and maintained within the interior of casing 13. The heat transfer uid 57 is raised to and maintained at a temperature of no less than about 100 C., preferably about 135 C. The RF heating coil 75 is activated and the controls set so that the temperature within reactor chamber 41 is in excess of 700-800 C., preferably about 1025 C., and no greater than about 1250 C. The temperature of conduit 51 is maintained by resistance heater 69 at over 100 C., preferably at about 140 C.

Aluminum trichloride is vaporized and enters the reactor chamber 41. A slightly higher pressure exists within reactor chamber 41 than within the regions in casing 13 which surround chamber 41. A small leakage of gas from the chamber outwardly into the cylinder accordingly occurs through the clearances of the apertures S7 and 39.

The aluminum 91 in dish S1 is in the liquid state in view of the high temperature that prevails in reactor chamber 41. Aluminum trichloride gas in chamber 41 contacts the liqueiied aluminum and reacts with it in accordance with the following reaction:

Thus, it is seen that aluminum monochloride is formed. The aluminum monochloride so formed is gaseous. It transfers by diffusion from the region of its formation to the wire 35, which is being pulled through the reactor chamber 41 by means of the take-up reel 83.

When the aluminum monochloride strikes the comparatively cold wire, disproportionation of the aluminum monochloride occurs as follows:

Thus, it is seen that the aluminum monochloride decomposes into aluminum trichloride and aluminum. The aluminum is deposited upon the cold wire. The speed of the wire is maintained such that its temperature lies below the melting point of aluminum. Accordingly, a solid film of high purity aluminum is deposited upon the wire. Essentially no alloying or intermetallic compounding occurs 'between the aluminum and the wire.

The configuration of the reactor system 11, including its heating means (RF coil 75) is such that wire, maintained at the proper speed, enters reactor chamber 41 after the wire has reached a temperature in excess of the condensation temperature of aluminum trichloride under the pressure conditions of the system. This prevents deposition of aluminum trichloride on the wire. Preferably, the initial temperature of the wire entering the reactor chamber 41 is no less than about 200 C.

The wire speed for a graphite reactor chamber temperature of about 1025 C. may vary from on the order of about one foot per minute to on the order of about feet per minute, with from about 10-60 feet per minute being the preferred speed range.

The aluminum trichloride formed at the wire upon disproportionation of the aluminum monochloride diffuses into the atmosphere prevailing in the reactor chamber 41, and in time again contacts the liquefied aluminum 91 in dish 81 to form more aluminum monochloride for disproportionation reaction at the wire. Thus, effectively, a re-cycle of aluminum trichloride is provided. Note that no aluminum trichloride whatsoever is consumed in the reaction. The consumption of aluminum trichloride supply 90 is limited to the make-up of aluminum trichloride losses through the vacuum system described.

The concentration of the aluminum monochloride vapor in the reactor chamber 41 is such that it has a partial pressure which is about 10%-25% of the total pressure prevalent in the chamber, the balance being attributable to a major proportion of aluminum trichloride vapor and a minor proportion of inert gas.

In another method of operation, valve 53 is opened and hydrogen gas or other carrier gas is permitted to flow through conduit 51 into vessel 45. The hydrogen produces a driving or carrier means to assist in carrying aluminum trichloride into the vicinity of liquid aluminum 91 in dish 81. While a considerable amount of loss is experienced by the mode of operation involving hydrogen flow (flow established through wire clearance of apertures 87 and 89), some advantage is gained in speeding up the contact of aluminum trichloride for reaction with aluminum to form the monochloride.

FIGURE 2 illustrates a somewhat modified system for coating wire with metal in accordance with the present invention. Therein, a furnace 101 is disposed intermediate wire feed reel 103 and wire take-up reel 105. Wire 107 pass from the feed reel 103 through a wire inlet passage in one wall of furnace 101 and exits through an outlet passage in an opposite wall to wind on the take-up reel 105. The cylindrical contact vessel 109 preferably has its interior packed with particles of aluminum, or the like. A feed line 111 communicates with the upper side portion of the vessel 109 and a discharge line 113 leads from the bottom. Liquid aluminum input enters from an aluminum make-up source, schematically illustrated by an arrow 115, via valve 117 to join fiuid flowing in line 113. Line 113 leads to the pump 119, which pumps the fluid via heat exchanger 121 to contact feed line 111. Liquid aluminum flows downwardly in the contact vessel 109 to countercurrently contact aluminum trichloriderich gas passing upwardly in the vessel. Aluminum monochloride is formed by the reaction between the hot liquid aluminum and aluminum trichloride-rich gas. Aluminum monochloride so formed in the column provides an aluminum monochloride-enriched gas at the top of the column. This aluminum monochloride-enriched gas flows through conduit 123 to enter the furnace 101, where it contacts the comparatively cold wire 107. Disproportionation of the aluminum monochloride results and aluminum is deposited on the wire simultaneously with formation of aluminum trichloride gas. The aluminum trichloride gas is returned to the bottom of the column 109 by means of line 12S. In establishing operation for the system of FIGURE 2, it should be appreciated that aluminum trichloride vapor must be introduced into the system, for example, via the inlet line 127 from an external supply, schematically illustrated by arrow 128. In operation, the valve 130 in line 127 is adjusted to admit additional aluminum trichloride to compensate for system losses.

In the system of FIGURE 2, it is sometimes found desirable to introduce a quantity of gas which is inert relative to the reactions and constituents involved, e.g. hydrogen, argon, helium, etc. may be used. The gas can be introduced continuously at a comparatively slow rate or it may be injected at intervals, as desired. The inert gas may be introduced at various locations in the system, for example, into the bottom of column 109 along with the aluminum trichloride-rich gas flowing in line 125.

Temperature of the furnace 101 is maintained at over 700-800 C., desirably at about 1025o C., but no greater than about l025 C. Wire speed is maintained so that maximum wire temperature remains well below the melting point of aluminum during its passage through the furnace 101. Moreover, the speed is maintained, such that wire is above the condensation temperature of aluminum trichloride before it enters a furnace region where the aluminum trichloride-aluminum monochloride gas mixture is present. Generally, the heat conductivity of the wire permits sufficient heat transfer along it to insure that the entering wire temperature is sufiicient, but if required for certain system geometry or at high wire speeds, a preheater may be provided for the 107 before it enters the furnace.

Preferably the furnace 101, which provides, in effect, heated coating chamber means, is operated so that an inert environment is provided for contact of wire 107 and subhalide vapor. Thus, an internal chamber, with appropriate wire guide fittings (such as wire guide assemblies 27 of FIGURE l) may be used, with heat applied to the exterior of the chamber by various means, e.g. electrical heating, heat transfer from hot gases, etc.

The thickness of coating deposited on a wire-like member, in accordance with the present invention, may vary over a wide range. For example, a coating or film of about l to 2 microns thickness may be deposited on a steel wire of '0.40 inch diameter by use of the apparatus of FIGURE l, with a wire speed of about 25 feet per minute and a reactor chamber temperature of approximately 1025o C. If the speed is decreased to about 5 feet per minute, the thickness of the coating is about 4 to 6 microns. Thicker and thinner films may be obtained by varying speeds and other conditions. If desired, a wire may be passed through the present process for several runs, to make a film as thick as wanted.

While it is preferred that members coated in accordance with the present invention comprise a major proportion of iron (eg. iron, steel, high carbon steel, stainless steel wire, etc.), various other metals and alloys may serve as the material of construction for a member to be coated. Examples of such materials are copper, tantalum, tungsten, niobium, molybdenum, nickel, platinum, palladium, silver, gold, titanium, chromium and mixtures and alloys thereof.

Films of metals other than aluminum may be deposited in accordance with the present invention. For example, titanium, chromium, nickel, manganese, germanium and cobalt films or coatings may be deposited by disproportionation of the subhalide of such metals.

While the chloride is preferred for practice of the present invention, other halides are applicable. For example, aluminum tribromide, aluminum triiodide, and aluminum trifluoride may be used in place of aluminum trichloride.

The term wire like, as used herein, is intended to refer to an elongated member such as a wire, strip, rod, etc.

What is claimed is:

1. A process for continuously coating a wire-like mernber comprising a major proportion of iron with an aluminum film comprising:

(a) forming aluminum monochloride by reacting aluminum trichloride vapor with elemental liquid aluminum at a temperature no less than about 700 C., and passing said aluminum monochloride into a reactor chamber maintained at a temperature of at least 700 C.,

(b) moving said wire-like member through said reactor chamber containing said aluminum monochloride7 said wire-like member having a temperature greater than 200 C. and being moved through said chamber at a rate such that the temperature of said wire-like member does not exceed a critical maximum temperature of 550 C., said rate ranging between about l and feet per minute,

(c) effecting disproportionation of said aluminum monochloride to deposit aluminum on said wire-like member and liberate aluminum trichloride to effect an aluminum trichloride-rich atomsphere.

(d) recycling said aluminum trichloride-rich atmos- 9 10 phere into contact with said elemental liquid alu- 2,711,973 6/ 1955 Wainer et al. 117-107.2 mnum in accordance with step (a). 2,731,361 1/1956 Nack et al. 117-107 .2 X 2. The method of claim 1 in which the pressure in said 2,856,312 10/1958 Nowak et al. 117-1072 X pressure in said reactor chamber is maintained at no 2,887,407 5/ 1959 Koch 117-107.2 greater than about 100 mm. of mercury. 5 2,930,347 3/1960 Bnllol 117-107.1 X 3. The method of claim 1 in which a carrier lgas lis 3,096,209 7/ 1963 Ingham 117-107.2 X employed in a system to carry said aluminum mono 2,898,230 8/1959 Bulloi 117-107.2 chloride into said reactor chamber.

4. The method of claim 3 in which the partial pressure OTIIER RFFERENES of aluminum monochloride in said system is maintained 10 Powell et al- ValPl Plating, Published by John Wiley at about 5%-25% of the system pressure. & SOUS 1955 TS695B3, PP- 3, 4, 9 t0 11, 25, 26 and 29 References Cited relied upon' UNITED STATES PATENTS ANDREW G. GOLIAN, Primary Examiner 1,770,177 7/ 1930 Martin. 15 US. C1. X.R. 2,344,138 3/ 1944 Drummond ll7-107.1

2,384,500 9/1945 Stoll -..-2 11S-49.1 X 117-107'1 107'2

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