US3504177A

US3504177A - Pressure-seal for transfer of continuous material

Info

Publication number: US3504177A
Application number: US721771A
Authority: US
Inventors: Richard A Walker; William E Mckee
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1968-04-16
Filing date: 1968-04-16
Publication date: 1970-03-31
Anticipated expiration: 1987-03-31

Description

March 31, 1970 R. A. WALKER ET 3,504,177

PRESSURE-SEAL FORTRANSFER OF CONTINUOUS MATERIAL Filed April 16, 1968 Richard A.Wolker, William E. M Kee,

INVENTORS.

ALLEN ALDICKE, J r.,

AGENT.

United States Patent Oifice 3,504,177 Patented Mar. 31, 1970 U.S. Cl. 250-495 4 Claims ABSTRACT OF THE DISCLOSURE A I-seal is provided for the continuous transfer of continuous material between zones of difierent pressure. The J-seal contains a high density liquid, preferably a metal, which liquefies at a fairly low temperature. In addition, a coating liquid is provided on top of the high density liquid. This coating liquid coats the continuous material passing through the seal to prevent the high density liquid from adhering to the continuous material. In a special case, the temperature of the liquefied high density material is used to cause a temperature responsive reaction in the continuous material passing through the seal. Wiper means are provided at the outlet of the J-seal whereby to remove excess liquid from the continuous material. V

BACKGROUND This invention is directed to a seal which permits the transfer of continuous material from a zone of one pressure to a zone of another pressure, and in a special case causes thermally induced reaction in the transit.

In those prior situations in which continuous material has been transferred from a chamber of one pressure to a chamber at another pressure, labyrinth seals or liquid seals have been used. However, labyrinth seals permit the transfer of considerable fluid material together with the continuous material. Such labyrinth seals must be extensive if there is to be limited leakage between chambers of substantial pressure dilference, and they must closely fit the shape of the material being transferred. Even when accurately fitted, they are unsatisfactory when absolute minimization of fluid transfer is desired.

Liquid seals and molten-metal J-seal are well known in vacuum technology, for example, see A. Roth, Vacuum Sealing Techniques, Pergamon Press, 1966, Chapters 3 and 6. Mercury is the most eflicient seal liquid, but the use of mercury presents great danger of toxicity to human operators and causes corrosion damage to metal equipment. Oil as a seal liquid requires excessive column height; this is due to the fact that the column height is inversely proportional to the density of the liquid and directly proportional to the pressure diflferential. Thus, low density materials, such as vacuum pump oils, require a column height on the order of 11-13 meters for a pressure differential of l-atmosphere.

Molten metals and fusible alloys as the seal liquid overcome the problem of excessive column height, requiring a column approximately 1% meters high. However, these metals may be incompatible with the material to be transferred through the seal; for example, Woods alloy forms a metal coating on Mylar tape as it emerges from the seal. An additional disadvantage of some metals and alloys is that the surface of the molten metals tends to oxidize, which then causes additional impurities to cling to the transferred material.

SUMMARY In order to aid in the understanding of this invention it can be stated in essentially summary form that it is directed to a seal which permits the continuous transfer of continuous material between zones of diiferent pressure. A high density liquid material is located in the seal, the head of the liquid seal material balancing the pressure idiference between the two chambers. The continuous material passes through this liquid.

It is desirable that the liquid seal material be of high density, and thus liquid metals or easily liquefiable metals are preferred. In addition, to prevent the seal liquid from coating upon the transferred material, a coating is first :applied to the material being transferred to prevent the seal liquid from adhering. In one species, thermal reaction is caused in the continuous material as it is transported through heated liquid seal material.

Accordingly, it is an object of this invention to provide a seal which permits a continuous transfer of continuous material between zones of different pressure. It is a further object to provide such a seal wherein liquid is used to balance the pressure heads between the two zones, and each continuous material is transferred through the seal liquid. It is a further object to provide a high density liquid seal material in order to minimize the height of the seal. It is still another object to provide a liquid metal as the seal material to provide a high density liquid. It is still another object of this invention to provide liquid metal which is liquid at room temperature or slightly above room temperature so that maintaining the seal metal in the liquid state can be readily accomplished. It is still another object to provide a coating upon the continuous material being transferred through the seal to prevent adherence of the seal liquid to the continuous material. It is yet another object to provide thermal reaction in the continuous material as it passes through the heated liquid seal material to cause reaction during the transit through the sea]. It is yet another object to provide an optional second coating material which may dissolve the first coating, or to supply a protective, decorative or other useful coating on the continuous material. Other objects and advantages of this invention will become apparent from a study of the following portion of the specification, the claims and the attached drawing.

BRIEF DESCRIPTION OF THE DRAWING The single figure of the drawing illustrates, partially in section, a chamber at subatmospheric pressure connected by the seal for continuous transfer of material of this invention to the ambient atmospheric pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing illustrates the transfer of continuous ma terial 10 from a chamber 12 at a first pressure through seal 14 to a chamber 16 at a second pressure. In the illustration, chamber 12 is totally enclosed except for the seal outlet and for vacuum pump outlet 18 to which a vacuum pump is connected for maintaining the interior of chamber 12 at a subatmospheric pressure. The continuous material 10 is either moved into chamber 12 through an additional seal similar to seal 14, or is provided in a roll 20 within the chamber and makes its egress through seal 14. In such a case, the movement of the continuous material 10 is downward in the main portion of seal 14. In other situations, it may be desired that the material be moved into'chamber 12, and that case the material 10 moves upward in the main portion of seal 14 and is wound upon roll 20.

Seal 14 is J-shaped with the longer length of the I connected to the region of lower pressure. Liquid 22 is positioned within seal 14, and when the chamber 12 is evacuated, extends farther up in longer leg 24 to top surface 26 than in the shorter leg 28 wherein the liquid terminates at top surface 30. The difference in height between

surfaces

26 and 30, when related to the density of liquid 22 balances the pressure between the chambers '12 and 16. Thus, in order to maintain this height differential to a minimum value, it is preferable to have a maximum density of the liquid 22. To this end, the liquid 22 is preferably a molten metal of substantial density, such as low melting point alloys of bismuth-lead-tin which often contain cadmium and sometimes contain indium or antimony. Examples are Woods Fusible Alloy, Cerrobend and Cerrolon; other suitable materials may be selected from a table published in Mechanical Engineers Handbook, sixth edition, McGraW-Hill Book Company, Inc., 1958 at page 6-103. Unalloyed, lowmelting-point metals such as indium, gallium, mercury, tin, bismuth, and the like are also suitable.

In view of the fact that most of these metals are solid at ordinary room temperatures, heat is supplied to the tubular seal by means of heater 32. Heater 32 is shown as a coil wrapped around the entire portion of the seal tube which can contain liquid 22. Sufficient heat is supplied during operation to maintain fluidity of the liquid.

When the pressures in

chambers

12 and 16 are equal, such as on'start up and shut down, the

top surfaces

26 and 30 will move so that they are at the same level. In order to accommodate the material in the shorter leg 28, bulb 34 is provided at its upper end. The volume of bulb 34 is sufficient to accept the volume of liquid moving into the shorter leg when the levels equalize.

There are some occasions for particular types of continuous material 10 and particular types of liquid 22 that the liquid will attack or will adhere to the continuous material. In order to prevent this, coating material 36 is placed above top surface 26 when the material 10 is moving downward, out of chamber 12 and coating material 38 is placed on top surface 30 when continuous material 10 is moving upward into chamber 12. If desired, the coating material can be positioned on both top surfaces, no matter which way the continuous material 10 is moving. Coating material 36 is of such nature that, for vacuum situations in chamber 12, it has a very low vapor pressure to prevent contamination of the interior of chamber 12. For example, the coating material can be selected from the various well-known vacuum pump oils. As the continuous material 10 leaves the chamber, the coating material 36 coats the continuous material 10 to leave a fine layer thereon, which fine layer prevents the liquid 22 from adhering to the continuous material 10. In such case, the coating material 38 acts as a stripper which removes any of the liquid 22 which may be mechanically carried along with continuous material 10 as it leaves top surface 30. Coating material 38 may be a solvent to affect removal of material 36, or it may be a lacquer or similar material which will provide a protective, decorative or other useful coating on the continuous material; as material 38 is outside of the vacuum chamber, it need not be a low-vapor-pressure material. It should also be noted that coating material 38 provides the additional advantage of preventing aerial oxidation of the molten metal, by providing a barrier-to-oxygen penetration from the atmosphere.

In order to remove the excess coating material 38, air or other gaseous jets are discharged from annulus 40 onto the continuous material 10. This removes the principal amount of coating material on continuous material 10. If desired, and if the character of the continuous material 10 permits it, squeegees or hot gas drying could be used to eliminate the excess coating material, or to bake the protective coating if desired.

As a particular example of usage of the seal of this invention, an electron-beam-sensitive material is provided upon roll and is unwound down through the seal to exit above annulus 40. Electron gun 42 selectively exposes portions of the continuous material, and the continuous material moves downward through the seal and is re moved to chamber 16 for development of the exposed image. By this means, the continuous sensitive material 10 is removed from the exposure area which need be in vacuum to a zone where it can be processed.

As an additional embodiment of this invention, when the material of continuous material 10 is such as to be treatable by heat, the heat treatment can take place while the material traverses seal 14. In this case, when a heat developable continuous material is provided on roll 20, it can be electron beam exposed by means of electron gun 42 and thence it can be developed by passage through seal 14, providing the temperature and time within the seal is correct for proper development. When Minnesota Mining and Manufacturing Dry Silver Film Type 783 is used as the continuous material 10, and is exposed in chamber 12 by a suitable exposure source, it can be developed when it traverses seal 14. For example, electron beam produced latent images on such film can be developed by heating the film to C. for 15-20 seconds. By this means image development is accomplished.

This invention having-been described in its preferred embodiment, it is clear that it is susceptible to numerous modifications and changes within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.

What is claimed is:

1. Apparatus comprising:

a vacuum-treating chamber for treating a continuous strip material therein;

sealing means disposed at the exit of said chamber and through which said material passes;

said means comprising a vertically arranged U-tube having a first body of molten metal therein and a second liquid body supported on said molten metal at the vacuum chamber end thereof;

said second liquid body of a characteristic to coat said strip material passing therethrough whereby to inhibit adherence of the molten metal on the strip material; and

said tube including, at the outlet end thereof, downwardly directed air wiper means which encompass said strip material passing therethrough whereby to remove excess liquid material.

2. Apparatus as in claim 1 including a third body of liquid supported on the outlet end of said molten material and adapted to treat the strip material passing therethrough.

3. Apparatus as in claim 1 wherein the strip material is an electron-beam-sensitive material and an electron gun is disposed in said chamber whereby to selectively expose portions of said strip material to create a latent image.

4. Apparatus as in claim 3 wherein the exposed strip material is thermally responsive for development of said latent image and heating means are combined. with said molten metal seal whereby to develop said latent image when the strip material passes through the body of molten metal.

References Cited UNITED STATES PATENTS 1,595,239 8/1926 Minton 118-50 X 1,595,474 8/1926 Minton 118-50 X 2,125,364 8/193'8 Waldron 118-50 2,630,484 3/ 1953 Groak.

' 2,656,284 10/1953 Toulmin 118-50 X 3,038,731 6/1962 Milleron 277-135 X 3,081,485 3/1963 Steigerwald 118-620 X 3,195,110 7/1965 Nail.

3,334,566 8/1967 Friedel -89 3,379,113 4/1968 Hosoya et al. 95-89 MARS KAPLAN, Primary Examiner US. Cl. X.R.