US2983249A

US2983249A - Vacuum seal for vapor deposition apparatus

Info

Publication number: US2983249A
Application number: US750975A
Authority: US
Inventors: Charles A Baer; Philip J Clough; James H Gardner
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1958-07-25
Filing date: 1958-07-25
Publication date: 1961-05-09
Anticipated expiration: 1978-05-09

Description

y 9, 1 c. A. BAER ETAL 2,983,249

VACUUM SEAL FOR VAPOR DEPOSITION APPARATUS Filed July 25, 1958 Vacuum Pumps 2 Sheets-Sheet 1 e as INVENTORS FIGURE Char/e; U -eh BY {AI/ I Clem/ L James C are ha)- May 9, 1961 C. A. BAER ETAL VACUUM SEAL FOR VAPOR DEPOSITION APPARATUS Filed July 25, 1958 FIGURE 2 2 Sheets-Sheet 2 vbcuuna Storage Chamber INVENTORS' Cl'wu- (4: 50: r

' BY PAH/ j, elm/ L United States VACUUM SEAL FOR VAPOR DEPOSITION APPARATUS Filed July 25, 1958, Ser. No. 750,975

14 Claims. (Cl. 11849) This invention relates to coating and more particularly to continuous coating equipment of the type wherein a substrate such as paper, plastic or steel is coated with metal or the like by vaporization and deposition of the metal on the substrate under high vacuum. For convenience, the invention will be initially described in connection with the high vacuum vapor deposition of alumi" num on a substrate such as steel.

In the high speed, continuous coating of aluminum on steel under high vacuum conditions, it is necessary to move the steel sheet into a vacuum chamber where the pressure is on the order of one millionth of atmospheric pressure and then to move the substrate out of the high vacuum chamber to the atmosphere. Since it is extremely difiicult to provide a single seal for accomplishing the 'lion to one pressure drop required, it has been proposed to utilize a number of seals through which the substrate passes between chambers of decreasing pressure.

It is a principal object of the present invention to provide coating equipment of the above general type where in the seals between stages of decreasing pressure are capable of passing considerable irregularities in the sheet such as tears, welds, splices, dimples, wrinkles and the,

like without harming the sheet or the seal.

Another object of the present invention is to provide a seal of the above type which has a high impedance to the flow of gas between two adjacent chambers at relatively low pressure while permitting free passage of the substrate between the chambers. I

Another object of the invention is to provide a seal of the above type which can have the additional function of transferring heat to or from the substrate.

Still another object of the invention is to provide a seal of the above type which has a long life and which can be readily renewed without affecting the operation of the seal and without interfering with the coating operation.

These and other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

Fig. 1 is a schematic, diagrammatic, fragmentary, sectional view of one embodiment of the invention.

Fig. 2 is an enlarged, fragmentary, sectional view of another embodiment of the invention.

In the present invention, the substrate to be coated is passed from the atmosphere through a plurality of atent O chambers to a high vacuum chamber having a source of coating vapors, such as a source of aluminum vapors. The initial pressure drop from atmosphere may conveniently constitute a barometric leg or the like or a steam seal of the type described in the copending application of Hnilicka, Serial No. 698,626, filed November 25, 1957. This provides for the principal pressure drop from atmospheric pressure. This also provides only condensible vapors within the system which can be readily and simply pumped by condensation. However to impede the passage of even these residual vapors between the chambers of decreasing pressure, it is desirable to provide passages which will freely pass the substrate but will serve as high impedances for vapors and gases under the relatively low driving force of pressure differentials of less than a few millimeters of mercury abs.

This is achieved in the present invention by filling the passages between such chambers with a particulate solid material which is capable of impeding the flow of gases between the chambers at pressures of less than 50 mm. Hg abs. In one preferred embodiment of the invention the particulate solid material comprises small spheres. When the sheet to be coated is a steel sheet, the small spheres are preferably small steel balls. When the sheet to be coated is paper, the small spheres are preferably lightweight, plastic balls or hollow aluminum balls. In a preferred embodiment of the invention the sheet is arranged to pass upwardly through the mass of spheres, the spheres being supported for free movement upwardly with the substrate to permit relatively free passage of tears or other irregularities in the substrate.

Referring now to Fig. 1, there is shown a section of a vacuum coating apparatus wherein a vacuum coating chamber 10 including a source 12 of aluminum vapors, the source being schematically indicated as an induction heated crucible over which a substrate 14 is guided by means of rolls 16. The high vacuum chamber 10 is isolated from an intermediate vacuum chamber 18 by means of a wall containing a passage 22 therethrough. As shown, this passage is of considerable vertical height and is filled with individual small spheres 24. A pair of guide rolls 26 guide this sheet in a straight line through an opening 28 at the bottom of the passage 22. As shown, the opening 28 is slightly less than the diameter of any individual sphere 24 so that none of the spheres 24 can escape downwardly through the opening 28. An opening 31 is also provided for permitting the escape of fine dust or broken spheres to prevent their accumulation in the passage 22. A higher pressure chamber 32 is similarly isolated from intermediate pressure chamber 18 by means of a wall 34 containing an identical passage 22 containing a plurality of spheres 24'.

Suitable vacuum pumps

35, 36 and 38 are provided for evacuating

chamber

10, 13 and 32, respectively. In one preferred embodiment of the invention, these pumps maintain the pressure in chamber 10 at one micron Hg abs., the pressure in chamber 18 at microns Hg abs, and the pressure in chamber 32 at 10 mm. Hg abs. Additional pumps such as vapor condensers can be provided where desired.

In one preferred embodiment of the invention illustrated in Fig. l, the spheres 24 are preferably small steel balls /2 inch in diameter. This is particularly desirable when the substrate 14 is a sheet of steel to be aluminized. These steel balls have a high impedance to the flow of vapors therethrough when the total pressure drop across the mass of balls is on the order of less than 50 mm. Hg abs.

Fig. 1 has been primarily described and illustrated in connection with its use in the coating of a steel sheet. When a less rugged material, such as paper, plastic, textile or the like, is to be coated, it is preferred that the steel balls be replaced by lighter weight particles such as hollow, plastic spheres or, solid, plastic spheres, foamed particles, or natural, lightweight particles such as cork, polyvinyl chloride, sawdust, vermiculite and the like. Such materials, due to their lighter weight, are more easily displacedby tears, splices or imperfections in the more fragile substrates but have equally good impedance to the flow of vapors therethrough. Such materials can also be utilized with sheet steel but are not as resistant to abrasion as the steel balls previously described. However, where provisions are made for periodic renewal of the mass of particles even those particles which are fairly rapidly abraded can be satisfactorily employed. In fact, in some cases the particulate solids can serve as a polishing medium for polishing the metal substrate immediately prior to or immediately following the coating operation.

Referring to Fig. 2, there is shown a modification of one of the seals of Fig. 1 wherein the particulate solid material constitutes spheres or small pieces'of a material such as cork, Styrofoam or the like which may have high absorptive capacity for water vapor and gases. In this v case, the particulate material indicated at 50 is supported in a passage 52 in a wall 54 between a high vacuum chamber 56 and a lower vacuum chamber 58. The substrate 60 is shown as passing upwardly through the mass of particulate solids between a pair of rolls 62 at the bottom of the passage 52. The bottom of the passage is provided with a cone-shaped opening 64 which deflects particulate solids into a pipe 66 through which the solids can be periodically drained by gravity to a vacuum storage tank 68. This is desirable when the apparatus is to be exposed to the atmosphere for servicing, such as rethreading the substrate, after a break, or the like. When the porous particulate material is stored in the vacuum chamber, it will not absorb water vapors or gases and will not increase the. pump-down time when the high vacuum system is to be put back into operation. The particulate solids can be fed back to the system by means of an elevator, schematically indicated at 70 and a feed pipe 72. If desired, the flow of particulate solids 50 can be intermittently or continuously accomplished through passage 52 so as to provide for continuous or intermittent treatment of the particulate solids to remove fines, particles of dirt, pieces of paper and the like which may be entrained in the mass of particulate solids. This recycle of the particulate solids also provides for the maintenance of any desired level of solids in the system despite entrainment of the solids by the substrate or other removal of the solids from the passage due to irregularities in the substrate causing splashing".of the particulate solids.

While several preferred modifications of the invention have been described in connection with the discussion of Figs. 1 and 2, numerous modifications thereof can be made without departing from the spirit of the invention. In one such modification portions of the vertical walls defining the sphere-containing

passage

22 and 22 are made flexible so as to permit lateral movement of the spheres when necessary to permit passage of an obstruction carried by the sheet. This can be in addition to the 7 vertical movement permitted by the loose mounting of the spheres in these passages 22 and 22'. It is also feasible to move the substrate downwar l-y through the particulate solids, although this embodiment of the invention is less preferred since it is apt to cause packing and jamming of the solids.

A tremendous variety of materials can be employed as particulate solids; They can be dense, porous, hollow,

' not to interfere with the deposition of an adherent vacuum deposited film. After the substrate has beencoated,

however, it can advantageously begiven a subsequent overcoating and this can take place by transferring a coating from the surface of the solid particles to the substrate. For example, steel after aluminizing can be given a light coating of oil by passing through a mass of steel balls continuously wetted with oil. Equally, a wax, lacquer or other film can be applied to a substrate by passing the substrate through solid particles of Wax and the like or through a mass of solid particles carrying wax on the surface thereof. 1

While one preferred embodiment of the invention described above contemplates the use of spheres for the par'tic'ulate'solids, such spherical form is not essential. This is particularly true when the particles are lightweight and are agitated from time to time to prevent jamming or channeling of the materials. Examples of non-spherical materials are sawdust, asbestos and the like.

Since certain changes may be made in the above appar-atus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompartying. drawings be interpreted as illustrative and not in'a limiting sense.

What is claimed is:

1; In apparatus for coating a substrate under vacuum which includes a vacuum chamber containing a source of coating vapors and a plurality of vacuum chambers through which the substrate is passed from atmosphere to the coating chamber, the improvement which comprises a passage of adequate length between two of said chambers, a portion of the passage being filled with a sufficient mass of particulate solid material to effectively impede flow of gases between said chambers at pressures of less than 50 mm. Hg abs.

2. The apparatus of claim 1 wherein said particulate solid material comprises 'a non porous solid.

3. The apparatus of claim 1 wherein said particulate solid material comprises small spheres.

4. The apparatus of claim 1 wherein said particulate solid material comprises small metal balls.

5. The apparatus of claim 1 wherein the particulate material comprises a mass of powdered material.

6. The apparatus of claim 1 wherein the substrate metallic.

7. The apparatus of claim 1 which includes an evacuated storage chamber for holding a supply of said particulate material and means for feeding particulate material to and from the storage chamber.

8. The apparatus of claim 1 wherein the particulate solid material comprises hollow spheres.

9. The apparatus of claim 1 wherein means are provided for degassing the particulate solid material prior to inserting Lhe'particulate material in the passage.

10. The apparatus of claim 1 which includes means for passing the substrate upwardly through the mass of particulate solids, the particulate solids being supported for free movement upwardly with the substrate to permit passage of a tear or other irregularity in the substrate.

11. The apparatus of claim 1 which includes means for agitating the particulate solids to prevent jamming thereof.

12. The apparatus of claim 1 which includes means for treating the particulate solids to remove fines, dirt and the like therefrom.

13. The apparatus of claim 1 wherein the mass of particulate solids are supported to permit limited lateral movement thereof as well as vertical movement thereof.

14. In apparatus for coating a substrate under vacuum which includes a vacuum chamber containing a source for vaporizing material to be coated, and separate vacuum chambers through which said substrate is passed fi'om atmosphere to the coating chamber, the improvement which comprises a passage of suflicient length to contain a considerable mass of particulate solid material, said passage connecting two of said chambers having confining walls for containing a substantial mass of said particulate solid material, said solid material being of sufficient depth to impede the flow of gases between said chambers at pressures less than 50 mm. Hg abs., and said particulate solid material comprising small spheres.

References Cited in the file of this patent UNITED STATES PATENTS Wickham et a1. Aug. 7, 1906 'Brammer Nov. 19, 1929 =Fruth Oct. 20, 1942 Connell Jan. 13,1953

FOREIGN PATENTS Italy Mar. 26, 1954 Great Britain Jan. 23, 1957