Vacuum Chamber Seal

Abstract

A gate for an evacuated chamber used for the treatment of metal strip of band having a thickness ranging from tenths of a millimeter to several millimeters comprising a plurality of guide rolls over which the strip is passed alternately overshooting and undershooting the rolls. The chamber is compartmentalized by shoes which closely confront the rolls in diametrically opposite locations, the inter-roll spacing being of the order of the thickness of the strip so that the latter is substantially in constant contact with the rolls over all of its length within the compartments and the strip extends over arcs of substantially 180.degree. while the shoes confront arcs of substantially 90.degree. to 120.degree. of the rolls. At either end of the roll assembly a further inlet or discharge roll is provided for deflecting the strip.

Description

FIELD OF THE INVENTION

The present invention relates to a gate or lock adapted to be provided at the inlet or outlet of an evacuated chamber for processing of metal strip or band to enable the vacuum within the treatment chamber to be sustained. The invention also relates to an associated method.

BACKGROUND OF THE INVENTION

It is known to treat metal strip or band having a thickness ranging from tenths of a millimeter to several millimeters, e.g., steel strip in evacuated chambers, in order for example to apply to a moving metal strip a coating by vacuum deposition of a coating material, e.g., a metal or its alloy. Other metal treatments are, of course known in which a metal band is passed through a chamber in which well defined conditions of pressure and atmosphere are maintained.

In such systems and in systems in which metal treatment is carried out in a pressurized chamber, it is important to provide a gate or lock arrangement at the inlet and outlet sides to permit the suction pressure to be built up in the treatment chamber with a minimum of gas displacement. In conventional locks of this type, the metal strip which must be fed through the gate or lock, is passed over several spaced rolls defining with shoelike transversal compartment walls narrow gaps through which the metal strip passes, but through which also flows a stream of gas. The opposite sides of each gap are maintained to a pressure differential by suitable pumps so that, as the strip approaches the chamber, it encounters compartments in which the pressure progressively reaches that of the chamber.

The principal difficulty with these systems is that, because of the narrow gap across the metal strip at each shoe, the gas flows at relatively high velocity and, since the strip is not supported at opposite sides in the region between successive rolls, vibration is induced in the metal strip.

Such vibration may cause the strip to come into contact with the shoes, thereby damaging the strip or the shoes or causing material to build up upon the shoes and thereby vary the operational conditions of the apparatus or requiring cleaning thereof with disadvantageous downtime.

Another disadvantage of these prior-art systems is that the vibrations may build up to such a level as to cause undulation in the final product or even breakage of the strip with obvious disadvantages.

OBJECT OF THE INVENTION

It is, therefore, the principal object of the present invention to provide an improved apparatus for feeding metal strip to or discharging metal strip from a treatment installation or chamber under a pressure different from ambient without the disadvantages of the systems mentioned earlier.

Another object of the invention is to provide a gate or lock for a metal-treatment chamber under suction or vacuum, especially a chamber for the vapor disposition of a metal bath onto a mettallic strip, whereby damage to the strip is precluded and there is little danger of injury to the apparatus.

Another object of the invention is to provide an improved gate for the purposes described which will allow a sub-atmospheric pressure of a high degree to be maintained in a vapor-disposition chamber with increased efficiency over prior-art systems, with a minimum of downtime, at low capital expense, and without danger of deformation or rupture of metal strip.

SUMMARY OF THE INVENTION

These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, by providing a gate or lock for a strip-metal treatment chamber, preferably a treatment chamber maintained under vacuum and used for the vapor disposition of metal from a metal bath onto the strip, which comprises an ante-chamber or gate chamber communicating with the treatment chamber at the inlet and/or outlet side thereof and provided with a plurality (at least two but preferably more than three) of gate rolls having parallel axes and close spacing such that the strip passes alternately over and under the rolls (i.e., alternately overshoots and undershoots the rolls), the spacing between the rolls being of the same order of magnitude as and preferably equal to the thickness of the strip.

The metal strip, according to the invention, may have a thickness ranging from tenths of a millimeter to several millimeters, e.g. a thickness t = 0.1 to 5 mm and may be composed of steel, copper, aluminum, etc.

According to an important feature of the invention, therefore, the guiding rolls are closely spaced such that the gap between two adjacent rolls is of the order of magnitude of the thickness of the metallic band or strip. Each of the rolls is juxtaposed with a pair of diametrically opposite sealing shoes which overly a relatively large arc or subtend a relatively large angle of the rolls to form small clearances, also of the order or magnitude of the thickness of the band, with the rolls. Preferably, the clearance .DELTA. of the shoes juxtaposed with the exposed surface of a band lying on the confronting surface of the roll is not more than 0.4 mm.

It is important to the present invention to increase the angle of contact between the metallic strip or band and the guide rolls to the maximum possible angle, thereby supporting the entire length of the band within the space occupied by the roll by a surface of one of them in contact with a face of the band or strip; this eliminates the danger of destruction of the band by vibration or damage to the gate or lock. The sealing shoes, according to the present invention, form compartments, i.e. compartmentalize the gate chamber, the compartments being evacuated so that, as the band passes from one compartment to the next, it may encounter spaces successively approaching the pressure within the treatment chamber.

It has been found advantageous to provide at least five such gate rolls and hence at least four such compartments between them, the rolls being driven in synchronism and in the alternately opposite senses so that there is no elongation of the band or strip. Alternatively, the rolls may be freely rotatable in appropriate low-friction bearings so that they are simply entrained by the strip. Since, at the location of closest approach, the band or strip may completely fill the gap between neighboring rolls, all of the rolls will tend to move at the same peripheral speed.

Preferably, all of the rolls have axis of rotation lying along a common horizontal plane and the band extends over angle or arc of 180.degree. about each roll. The sealing shoes advantageously subtend angles of substantially 90.degree. to 180.degree..

It has also been found advantageous, and it is thus a feature of the present invention, to provide respective guide rolls at each end of the aforementioned array of sealing guide rolls and serving as inlet and outlet deflectors for the metal strip. These terminal rolls, which are not provided with sealing shoes, are spaced from the first and last rolls of the array by a distance of the order of magnitude of the thickness of the metal strip or band and deflect the latter through approximately 90.degree. as the metal strip enters or leaves the gate. Throughout, the spacing of the rolls should be such that the metal strip is not under compression or at least not under any significant compression as may cause permanent deformation or damage to any coating which may have been applied to the original band.

While the invention will be described below in greater detail with reference to a vapor-disposition system for the coating of metal strip, especially steel strip, and this is the preferred combination with the novel gate, it should be understood that the gate may be used with chambers under elevated pressure for the treatment of other types of band or strip materials. Furthermore, the individual compartments need not be individually evacuated, but can remain under whatever pressure may develop therein by evacuation of the compartment closest to the evacuated treatment chamber.

DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the sole FIGURE of the drawing which shows in diagramatically vertical section, a gate for a vacuum-disposition apparatus.

SPECIFIC DESCRIPTION

In the drawing, the gate or lock comprises a housing, casing or other sealed enclosure 10 forming a gate chamber generally represented at 20 which is disposed at the inlet and the outlet side of a vacuum-treatment chamber 22. The vacuum-treatment chamber 22, which may be conventional and can comprise a metal bath 24, shown schematically, for the vapor deposition of metal upon a strip 12, can be evacuated by a suction pump 26 to the desired level, generally about 10.sup..sup.-4 Torr.

For the purposes of illustration the window 28 at the left hand end of the gate housing 10 is shown to communicate with the vapor-deposition installation 22 at its inlet side. But the gate of the present invention can also be effective for the discharge of the metal strip, the discharge end being located at the same side or at the opposite side of the vapor-deposition installation 22.

Within the gate housing 10, there is provided an array of five gate rolls 2, 3, 4, 5, 6 which are freely journaled in bearing (not shown) and rotatably entrained by the strip 12 in opposite rotational sense. The rolls are advantageously of chromium steel. They are preferably hollow and cooled by water circulation in order to avoid thermal expansion and to allow for cooling of the heated hot metal strip. Juxtaposed with each roll 2 to 6, is a pair of inwardly extending shoes 11 of aluminum disposed at diametrically opposite sides of the rolls and supported by webs 29 from the wall of the housing 10. The shoes 11 are arcuate and extend over substantial arcs of the rolls or of the metal strip which alternately overshoots and undershoots these rolls 2 through 6. For the above exposed reason the shoes 11 may also be cooled by circulation of a cooling fluid.

At the inlet side of the array, there is an entry roll 1 while a discharge roll 7 is provided at the opposite end of the array, these rolls having the same diameters as rolls 2 through 6 or being of different diameters.

Unlike conventional guides in which the spacing between neighboring rolls is of the order of 300 mm, the spacing s between adjoining rolls is of the same order of magnitude as the thickness t of the band and may even be equal to this thickness. Where some slight clearance is desirable, s = t+.DELTA. where .DELTA. = 0.4 mm. Thus both s and t have dimensions ranging from tenths of a millimeter to several millimeters, e.g. 0.1 to 5 mm.

Because of their close spacing, the band 12 is in contact with each of the rolls 2 through 6 over an angle of about 180.degree.. The contact angle r at the rolls 1 and 7 is about 90.degree.. Of course, the infeed and the discharge direction must not necessarily coincide with the horizontal line.

Since the entire length of strip 12 between rolls 1 and 7 is supported, the flow of gas parallel to the band or strip does not produce vibration.

The rolls 2 through 6 and the juxtaposed shoes 11, with their webs 29 subdivide the chamber 20 into a plurality of compartments 13 which may be evacuated by pumps 30 and 31 via valves 32 such that the pressure drops successively in the chambers to 200, 50, 5 and 2.10.sup..sup.-2 Torr respectively, whereas the pressure valve within the vacuum-treatment chamber 22 is maintained at about 10.sup..sup.-4 Torr. The shoes 11 subtend angles or arcs .beta. of substantially 90 to 120.degree. and may have a spacing of 0.4 mm from the juxtaposed face of the roll or of the metal strip. Under these conditions, the amount of air which flows from one compartment 13 to another is minimalized. The spacing D between the rolls = 2R+t+.DELTA. where .DELTA. = 0 to 0.4 mm and R is the radius of the roll as measured from its center of curvature C. The shoes 11 may have the same center of curvature C and a radius S-R+.DELTA.' where .DELTA.' = 0.4 mm or t+.DELTA..

Claims

We claim:

1. A gate for a metal-strip treatment chamber maintained at a particular non-ambient pressure, comprising

a housing defining a gate chamber communicating with said treatment chamber;

at least three guide rolls all having their axes in a common plane mounted in said gate chamber for rotation and spaced apart by a distance of the order of the thickness of a metal strip to be processed in said treatment chamber, said metal strip passing along alternate sides of said rolls and extending therefrom into said treatment chamber, said strip alternatingly overshooting and undershooting said guide rolls of said array and contacting each guide roll of said array over an arc of substantially 180.degree.; and

respective shoes juxtaposed with each of said guide rolls at diametrically opposite sides thereof and having arcuate faces closely spaced from said guide rolls and subdividing said chamber into a plurality of compartments, each of said shoes subtending an arc of substantially 90.degree. to 120.degree. of the respective guide roll.

2. The gate defined in claim 1, further comprising a further guide roll between the array of first mentioned guide rolls and said treatment chamber, said strip being deflected around said further guide roll between said array and said treatment chamber.

3. The gate defined in claim 2, further comprising another guide roll on the opposite side of said array, said strip being deflected about said other guide roll.

4. The gate defined in claim 3 wherein all of said guide rolls have axes lying in a common horizontal plane and are all of equal diameter, said treatment chamber being a chamber for the vapor disposition of metal onto said strip.

5. The gate defined in claim 4 wherein said treatment chamber is evacuated, further comprising suction pump means connected to said gate chamber.

6. The gate defined in claim 5 wherein said strip contacts said further and other guide rolls over arcs of substantially 90.degree..