US3029777A

US3029777A - Vapor deposition coating apparatus

Info

Publication number: US3029777A
Application number: US790274A
Authority: US
Inventors: John Z Cerych; Philip J Clough; Robert W Steeves
Original assignee: Nat Res Corp
Current assignee: National Research Corp
Priority date: 1959-01-30
Filing date: 1959-01-30
Publication date: 1962-04-17
Anticipated expiration: 1979-04-17

Description

April 17, 1962 J. z. CERYCH ETAL 3,029,777

VAPOR DEPOSITION'COATINGAPPARATUS Filed Jan. 30, 1959 2 Sheets-Sheet 1 TO \ACUUM PUMP COPPER FIGURE l.

April 17, 1962 J. z. CERYCH ETAL VAPOR DEPOSITION COATING APPARATUS 2 Sheets-Sheet 2 N mmnmI uomnow had:

Filed Jan. 30, 1959 muamou ZPDOZ Mom ,I

a? Q A w m =oo 3000 Jill/[ll @fiiied rates Patent VAPOR DEPGSITION COATING APPARATUS John Z. Cerych, Methuen, Philip J. Clough, Reading,

and Robert W. Steeves, Nahant, Mass, assignors to National Research Corporation, Cambridge, Mass., a

corporation of Massachusetts Filed Jan. 31 1959, Ser. No. 790,274 3 Claims. (Cl. 118-49) This invention relates to coating and more particularly to coating by vapor deposition of a metal or other material under high vacuum conditions. The invention particularly directed to the design of an improved source of vapors.

It is a principal object of the present invention to provide an improved source of coating vapors for coating a substrate in an evacuated chamber.

Another object of the invention is to provide a source of metal vapors, which source has a long operative life.

Still another object of the invention is to provide sources of the above type which are relatively inexpen-' sive to manufacture and which are simple to maintain.

Another object of the invention is to provide sources of the above type which are very efiicient and can be designed for numerous types of heat transfer.

Reference should be had to the following drawings wherein FIG. 1 is a sectional, diagrammatic, schematic View of one preferred embodiment of the invent-ion, and FIG. 2 is a sectional, diagrammatic, schematic view of a portion of FIG. 1 taken along the line 22.

In the present invention there is provided a vaporization chamber (preferably a coating chamber) in which the coating material is evaporated. The substrate to be coated is preferably passed through the coating chamber and it is coated by condensation of the vapors on the surface of the substrate. For convenience of illustration, the invention will be initially described in connection with the vapor deposition of aluminum on a continuous substrate such as sheet steel without any intent to limit the invention to this specific preferred embodiment. When so utilized, the coating chamber includes a support for holding molten aluminum, the support preferably comprising a carbonaceous crucible having a surface of boron nitride, Zirconium carbide or other material which is relatively inert to molten aluminum at elevated temperatures. There is also provided a molten bath which is maintained in contact with the support for the molten aluminum, this molten bath being for the purpose of transferring heat to the support and the molten aluminum to vaporize the aluminum. There is also a heater for maintaining the molten bath at a suiiiciently high temperature that the molten aluminum is heated to a temperature where its vapor pressure is above the residual pressure in the coating chamber. In a preferred embodiment of the invention the molten bath is molten copper which is heated by heat from a hollow tube running through the bath. This tube is preferably heated, in turn, by a gas flame inside thereof.

Referring now to FIGS. 1 and 2 there is illustrated one specific preferred embodiment of the invention wherein the vacuum chamber is defined by a wall 10, the vacuum chamber including a coating chamber .12 and a sealing chamber 14 through which a substrate 16 is arranged to pass. The substrate 16 passes in contact with a drum above a bath 18 of molten, aluminum confined in asupport 20 which is illustrated as a carbonaceous crucible. The carbonaceous crucible 2b is preferably supported by a second container 22 having an outer steel jacket 24 and an inner graphite liner 26. The container 22 confines a mass of molten copper 28. The heat source, generally indicated at 30, preferably comprises an outer tube of graphite 32 and an inner tube of a refractory metal such as alloy steel 34, this inner tube is preferably arranged to be heated by a gas flame (not shown). In this specific preferred embodiment of the invention, the carbona'ceous crucible '20 is preferably supported by "a lip 40 which engages a matching lip *42 :on the popper-holding container 22. A cooled plate 44 is preferably provided for clamping the crucible in position to prevent its being lifted up by the pressure of the moltencopper. This cool plate also prevents heat radiation upwardly from the container for the molten copper. This is particularly useful when the substrate to be coated is sensitive to heat.

As best seen in FIG. 2, the inner alloy steel tube (34 of the heat source extends through the vacuum-tight wall 10 so that it can be at atmospheric pressure. The ends of the alloy steel tube 34 are preferably cooled by suitable cooling coils illustrated at 5010 simplify the forming of a vacuum-tight joint between the tube 34 and the wall 10.

Means are preferably provided to adjust the level of the molten copper and to thereby control the area of contact between the molten copper and the aluminum-holding crucible. In the preferred :form illustrated, this means comprises a graphite piston 52 'whichis -:c'a'rried on Ia .rod 54 to permit raising and lowering of the .piston "the molten copper bath. When the piston 52 .is pushed down into the bath it raises the level of the bath. Conversely, when the piston is raised the bath level falls. Tllii'sprovides an excellent means for controlling the rate :of evaporation of the aluminum since .this evaporation rate is a direct function of the rate of input of .heat to the aluminum, which rate is, in turn, ailirect function of the area of contact between the copper and the crucible.

In the use of the specific apparatus shown,

chambers

12 and 14 are evacuated by suitable-vacuum pumps .(not shown) so as to provide a low free air pressure on the order of 1 micron Hg abs. in the coating-chamber :12. The molten copper is then heated, preferably by means of a luminous gas flame inside of tube 34, to a temperature on the .order'of 1400" C. to 1500 C. This 'heatstl're aluminum '18 to a temperature on the order-of 1350" C., at which temperature copious quantities of aluminum vapors are generated for deposition on a substrate 16 which is moved over the source of aluminum vapors. When it is desired to slow down the generation of aluminum vapors (for example due to the slowing down of the substrate for splicing or otherwise), the graphite piston 52 is raised, thus lowering the level of the molten copper and cutting down the rate of heat transfer .to the molten aluminum. When the 'substrate speed is to be resumed the graphite piston is again pushed down into the bath of molten copper, thus increasing the generation of aluminum vapors.

During the operation of the source, it is preferred that the cooling plate 44 at the top of the source remainsufliciently cool so as to be below the melting point of aluminum. Thus any molten aluminum tending to creep out of the source and over the lip will be'frozen in place adjacent the lip.

In a preferred embodiment of the invention, a-suitable means is provided for feeding molten aluminum 'to the source, but for simplicity of illustration this feeding means has not been shown-in the drawings.

The invention is of utility in connection with the coating of numerous substrates such as metals, pawn-plastics, textiles and the like. Equally, it can be applied forproducing metal powders where aluminum is vaporized into an evacuated chamber and is condensed .infree space as described in the copending application of Cerychet al., Serial No. 787,055, filed January 15, 1959. Similarly,

the invention can be employed in the production of finely divided metal compounds by vaporizing metals such as aluminum into a partially evacuated space containing a partial pressure of a reactive gas. Similarly, metal vapors can be used to apply thick coatings on such discrete objects as nuts and bolts wherein the objects are to be given corrosion resisting coats on the order of 1 mil thick. Th metal vapors can be also used to coat metal powders. For example, magnesium hydride may be coated with aluminum by passing magnesium hydride in powder form through a stream of vapors generated in a source of the type described above.

The invention may be utilized for the vaporizing of material other than aluminum or for vaporizing various organic and inorganic compounds. While copper is a preferred heat transfer medium with the preferred aluminum evaporation, other materials and compounds can be employed in less preferred embodiments of the invention. The principal requirement is that the vapor pressure of the heat transfer medium be lower than the vapor pressure of the material being vaporized at the vaporization temperature.

Other physical arrangements of the invention can be employed. The graphite crucible 20 can be a long boat, for example, rather than the plurality of individual crucibles illustrated. The crucible 20 may b built up as a compound structure and may be formed of numerous materials which are inert either to molten copper or molten aluminum or capable of supporting coatings which are inert to these materials. Similarly, the container 22, for holding the molten copper, can assume many different shapes. It can be subdivided into a number of sections and can have numerous means for controllably adjusting the level of the molten copper therein. While one preferred embodiment employing the graphite piston 52 has been illustrated, numerous other systems, such as gas pressure and the like, can be employed if desired. A separate chamber in conjunction with chamber 22 can be provided into which the molten copper can be drained during replacement of the crucibles thus avoiding the necessity of freezing and reheating the copper. The copper can, if desired, be frozen adjacent the outer walls of the container 22 to form a solid skull of the copper. This embodiment of the invention is particularly feasible when the aluminum, for example, can be vaporized at temperatures not too greatly in excess of the melting point (1083 C.) of the copper. This relatively lower vaporizing temperature for the aluminum is particularly feasible when materials such as strip steel are to be coated. Other sources of heat can be employed in place of the luminous gas flame mentioned previously. This can be a high temperature source of heat such as a carbon rod or a refractory metal rod or strip heated to an elevated temperature on the order of 2000 C. Equally, continuous heat can be employed from a graphite or metal heating element and the heating element can be heated by direct resistance or by induced currents.

The seal chamber 14 mentioned briefly in the foregoing description has not been shown in detail in the drawing for simplicity of illustration. It can take many forms, however, such as the slot type seal described in Stoll Patent 2,3 84,500. Equally. the substrate 16 can be placed in the chamber 14 in the form of a roll and unwound and rewound in chamber 14 without passing through any seal to atmosphere.

Sinc many variations on this basic apparatus can be accomplished within the spirit of the invention, it is intended that the description and drawings herein be taken in a descriptive and non-limiting sense.

What is claimed is:

1. Apparatus for evaporating a material under a high vacuum into a vaporization chamber, means for evacuating said vaporization chamber, a support for holding the material to be evaporated in the vaporization chamber, a molten bath in contact with the support, a heater for maintaining the molten bath at a temperature sufficiently elevated that the material to be evaporated is heated to a temperature Where its vapor pressure is above the residual pressure in the vaporization chamber.

2. Apparatus for coating a substrate by evaporating a material under high vacuum in a coating chamber and depositing the material on the substrat in the coating chamber, a support for holding the material to be evaporated in th coating chamber, a molten bath in contact with the support, a heater for maintaining the moiten bath at a temperature sutficiently elevated that the material to be evaporated is heated to a temperature where its vapor pressure is above the residual pressure in the coating chamber.

3. The apparatus of claim 2 wherein the heater comprises tube means extending through the molten bath, and means for generating heat inside of said tube means.

4. The apparatus of claim 2 wherein the heater comprises means for generating a gas fiow within a tube means passing through the molten bath.

5. The apparatus of claim 2 wherein the heater comprises an electrical resistant element within a tube means passing through the molten bath.

6. Apparatus for coating a substrate by evaporating aluminum under high vacuum in a coating chamber and depositing the aluminum on the substrate in the coating chamber, means for holding a molten bath of copper, a heater for maintaining the molten bath at a temperature sufficiently elevated that the aluminum to be evaporated is heated to a temperature where its vapor pressure is above th residual pressure in the coating chamber, a sealed top for said bath-holding means, crucible means for supporting molten aluminum carried by, and forming a part of, the sealed top, cooling means adjacent the upper edges of the crucible means.

7. Apparatus for coating a substrate by evaporating aluminum under high vacuum in a coating chamber and depositing the aluminum on the susbtrate in the coating chamber, means for holding a molten bath of copper, a heater for maintaining the molten bath at a temperature sufl'iciently elevated that the aluminum to be evaporated is heated to a temperaure where its vapor pressure is above the residual pressure in the coating chamber, a sealed top for said bath-holding means, crucible means for supporting molten aluminum carried by, and forming a part of, the sealed top, cooling means adjacent the upper edges of the crucible means, the upper surface of the crucible means being substantially inert to molten aluminum and the lower surface of the crucible means being substantially inert to the molten bath.

8. Apparatus for coating a substrate by evaporating a material under high vacuum in a coating chamber and depositing the material on the substrate in the coating chamber, a support for holding the material to be evaporated in the coating chamber, a molten bath in contact with the support, a heater for maintaining the molten bath at a temperature sufficiently elevated that the material to be evaporated is heated to a temperature where its vapor pressure is above the residual pressure in the coating chamber, means for raising and lowering the level of the molten bath to change the amount of heat transferred from the molten bath to the support.

References Cited in the file of this patent UNITED STATES PATENTS 1,824,865 Bowden Sept. 29, 1931 2,664,853 Schuler Ian. 5, 1954 2,683,294 Bauer et a1. July 13, 1954 2,772,318 Holland Nov. 27, 1956

Claims

1. APPARATUS FOR EVAPORATING A MATERIAL UNDER A HIGH VACUUM INTO A VAPORIZATION CHAMBER, MEANS FOR EVACUATING SAID VAPORIZATION CHAMBER, MEANS FOR EVACUATMATEIAL TO BE EVAPORATED IN THE VAPORIZATION CHAMBER, A MOLTEN BATH IN CONTACT WITH THE SUPORT, A HEATER FOR MAINTAINING THE MOLTEN BATH AT A TEMPERATURE SUFFICIENTLY ELEVATED THAT THE MATERIAL TO BE EVAPORATED IS HEATED TO A TEMPERATURE WHERE ITS VAPOR PRESSURE IS ABOVE THE RESIDUAL PRESSURE IN THE VAPORIZATION CHAMBER.