US 3763571 A
This is a method of, and apparatus for, contactless guiding a web of material to be treated by a fluid medium, the flow energy of which is produced in a nozzle. One and the same nozzle can be optionally used to produce cushions of the treating medium which maintain the web of material in a floating condition or to produce a jet shaped by the back of an airplane wing profile whereby the web of material is kept in a floating condition by subjecting it to pressure and suction forces.
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Description (OCR text may contain errors)
United States Patent [191 Vits [ APPARATUS FOR CONTACTLESS GUIDING OF WEBS  Inventor: Hilmar Vits, Leichlingen, Germany  Assignee: Vits Maschinenbau GmbH,
Langenfeld (Rhineland), Germany  Filed: Apr. 26, 1971  Appl. No.: 137,298
 Foreign Application Priority Data Apr. 27, 1970 Germany P 20 20 4302  U.S. Cl 34/57 A, 314/156, 226/97  Int. Cl. F26!) 17/10  Field of Search 34/10, 57 R, 23,
 References Cited UNITED STATES PATENTS Hutzenlaub 34/23 X Oct. 9, 1973 3,384,282 5/1968 Vits 34/156 X 3,181,250 5/1965 Vits 34/23 FOREIGN PATENTS OR APPLICATIONS 1,145,572 3/1963 Germany 34/156 Primary Examiner-William F. ODea Assistant Examiner-William C. Anderson Attorney-Michael S. Striker [5 7] ABSTRACT This is a method of, and apparatus for, contactless guiding a web of material to be treated by a fluid medium, the flow energy of which is produced in a nozzle. One and the same nozzle can be optionally used to produce cushions of the treating medium which maintain the web of material in a floating condition or to produce a jet shaped by the back of an airplane wing profile whereby the web of material is kept in a floating condition by subjecting it to pressure and suction forces.
8 Claims, 6 Drawing Figures PATENTEDUU 9W 3 763 571 SHEET ll]? 2 APPARATUS FOR CONTACTLESS GUIDING F WEBS The present invention relates to methods and apparatus having the object to provide various different possibilities of contactless guiding webs of material through spaces in which said webs are to be treated while the volume of treating medium used, mainly air, is maintained substantially constant.
Various methods of, and apparatus for, contactless guiding of webs of material employing air jets produced by nozzles to maintain the web in a floating condition have been suggested heretofore. However, only a few of these prior art methods and apparatus have found any widespread acceptance for practical application while the majority of said methods and apparatus have proved inadequate even for simple applications in a limited field. Furthermore, in an age of automation, there is a growing need for processes by which flat materials can be treated in the form of webs rather than sheets. Thus, an increasing number of products and ever greater quantities of materials must be treated in a floating condition. In the majority of cases, thermal processes are involved, i.e., with the material kept in a floating condition it is the task of the air to effect the heat transfer and thus accomplish the object of the treatment such as drying the surface. While such drying processes must nowadays be counted among the conventional methods of treatment, the annealing of metal strips in a floating condition is still an object of the most recent state of the art.
In the latter case, the apparatus employed for the treatment, especially the annealing furnace, must meet extremely exacting requirements, because at temperatures of up to 700 C or more it is still difficult, even with the means provided by modern technology, to produce the necessary high air velocities economically. It is, therefore, another object of the methods suggested by the present invention to provide contactless guiding of both heavy and light metal strips at comparatively low air pressures which at the temperature applied for the treatment do not amount to more than a quarter of those occurring at room temperature.
The annealing furnaces must be capable of heating strips of 1 mm thickness as well as strips with a thickness of 50 microns in the manner required. A reduction of the air pressure in the guide nozzles below the web in accordance with the weight to be handled would adversely affect the heat transfer and substantially reduce the capacity of the annealing furnace. For an economic operation of annealing furnaces with floating conveyance it is, therefore, essential that strips of greatly differing weights can be passed through the furnace without contact while maintaining the full volume flow of the treating medium.
Another object of the present invention concerns the production of high-quality mica papers used by the electrical industries for insulating purposes. Since mica paper does not contain any bonding agent, its strength is poor. It must, therefore, be soaked in insulating varnish and then dried. If dried on a traveling screen belt, part of the varnish will adhere to said screen beltwhich will thus be soiled very soon and tends to become incrusted as a result of its continuous movement through the drier. Furthermore, the treated mica paper tends to stick to the screen belt so that upon removal the web will be broken or torn with the result that the percentage of waste will be correspondingly high. Although it is possible to treat such mica paper in a drier with floating conveyance, the webs tend to break on their way through the drier because the paper is extremely fragile, especially between wet and dry portions early in the process, at joints in the web or at faults already existing in the raw material or caused during application of the varnish. When this occurs, the entire quantity of the high-quality material then in the drier is lost.
To solve this problem, attempts have been made heretofore to find a method which would enable a web of material to be alternately guided on a screen belt conveyor or in a floating condition, as desired. If this were possible, production could be commenced by placing the start of the web onto the screen belt conveyor. After securing the start of the web on a roll, the web could be caused to float by a suitable switching operation to prevent the conveyor belt, which would be traveling empty until or unless switched off, from being soiled; the belt conveyor would be restarted only when the floating condition is canceled in order to once more support the web on the screen, e.g., when joints or rents enter the drier.,To ensure that the web will be dried in the same manner as before, there must be no change in the volume of air passing through the drier. This would also ensure the application of a uniform coat by the varnishing machine at uniform speed. Thus, the belt conveyor would be used only temporarily and, depending on the fault rate, could be kept running much longer than was hitherto possible before operation would actually have to be interrupted. Floating conveyance of the by far greater part of the mica paper would enable the paper to be treated without any marks, whereas a large proportion of the material treated in the known driers with traveling belt screens shows marks caused by contact with the screen.
According to the present state of the art, only two re ally effective systems are available for floating conveyance of webs of material. Air-cushion-producing nozzles in accordance with U.S. Pat. No. 3,181,250 develop high pushing power and could be used to force a web of material against a belt screen conveyor and to convey even comparatively thick metal strips in a floatingcondition. Furthermore, nozzles cooperating with convex surfaces similar to the back profile of an airplane wing and capable of absolutely reliably conveying even very thin webs of material (foils) in floating condition at high air velocities have been provided by the inventor of the present invention. These nozzles cooperating with said airplane wing profiles have been suggested in U.S. Pat. No. 3,384,282. However, in terms of air pressure, all these types of nozzles including those not described above have the one and only purpose to provide a single stable zone above or below the nozzle systems or on both sides of the web.
It is, therefore, the completely novel object of the present invention to define methods of, and apparatus for, providing at least two stable zones of the fluid medium which can be alternately selected by a quick and simple switchover. More particularly, it is the object of the present invention to enable the characteristics of both the known air-cushion-producing nozzles and the previously suggested nozzles cooperating with airplane wing profiles to be accomplished within fractions of a second by means ofa simple switching operation. Comparing a typical air-cushion-producing nozzle as illustrated, for example, in FIG. 10 of U.S. Pat. No. 3,181,250 with a typical nozzle cooperating with an airplane wing profile as shown, for example, in FIG. 7 of U.S. Pat. No. 3,384,383, it will be found that apparently the two types of nozzles are absolutely incompatible. Surprisingly, however, what appears to be impossible at first glance, i.e. to reconcile these two basically different designs, can actually be achieved with the knowledge provided by the present invention.
In accordance with the present invention, this problem is solved by converting the flow of the fluid medium, such as air, in opposite directions, which is a characteristic feature of the air cushion arrangements, to the unidirectional flow produced by nozzles cooperating with an airplane wing profile and vice versa. A secondary flow resulting from the natural negative pressure at the back of the airplane wing profile can be replaced by actively blowing a jet of the fluid medium through a perforation in the profile with a correspondingly smaller aperture. The physical means by which this conversion can be effected is a tiltable piece whose position determines the effect produced, i.e. whether the action is that of an air-cushion-producing nozzle or that of a nozzle cooperating with an airplane wing profile, not to mention the effects of possible intermediate positions.
Various embodiments of the invention are shown, by way of example, in the accompanying drawing, in which:
FIG. 1 is a vertical section through a nozzle in accordance with the invention which can be switched from air cushion operation to that of a nozzle cooperating with an airplane wing profile; the section passes through the longitudinal center line of the web and shows the moving parts of the nozzle in a position in which the nozzle produces an air cushion.
FIG. 2 is the same section as that in FIG. 1, but showing the nozzle in a position in which it has the effect of a nozzle cooperating with an airplane wing profile. FIG. 3 shows a plurality of nozzles in accordance with the invention. These nozzles may be employed, for example, to guide metal strips in annealing furnaces, acting on one side of the strip only.
FIG. 4 shows an arrangement of nozzles in accordance with the invention disposed on both sides of the web with a predetermined spacing and location with respect to the floating web.
FIG. 5 corresponds to the representation in FIG. 4 except that the web is supported on a belt conveyor.
FIG. 6 is a graph illustrating the twofold characteristic obtainable in accordance with the invention by a change-over nozzle in the two positions which a tiltable piece forming part of said nozzle can assume.
In FIG. I, the numeral 1 indicates the web of material moving from left to right in a floating condition above a nozzle in accordance with the invention. This nozzle is the terminal point of a supply duct 2 whose lower part has been broken away in the drawing and into which air or some other medium in the form of a gas and/or vapor enters in the direction indicated by the arrow 3. The nozzle has two lateral walls identified by the numerals 4 and 5 on the left and right respectively. A tiltable piece 6 with a convex surface curved toward the web 1 and resembling the back of an airplane wing profile is disposed between said lateral walls and tiltably supported by joints 7 on the end faces of the nozzle body. To retain the tiltable piece 6 of the nozzle in its tilted end positions, links 8 are provided at the end faces of the nozzle body, said links being engaged by pins 9 which can be eccentrically rotated about the axle 10. The tiltable piece or member 6 is recessed with respect to the end portions of the lateral walls 4, 5 of the nozzle body so that the fluid medium, such as air, entering the nozzle in the direction of the arrow 3 is forced to leave the nozzle through two nozzle slots in two separate streams. As these two streams, with the tiltable piece 6 positioned as shown in FIG. 1, are flowing in opposite directions, a dynamic pressure will build up in the space between the tiltable piece 6 and the web 1, causing the two partial streams to be deflected from their original directions, as indicated by the arrows 11 and 12. The forces required to effect this deflection are provided by the dynamic pressure in the space between the tiltable piece 6 and the web 1. Additionally, this space is supplied with air entering through the perforation 13.
FIG. 2 depicts the position of the change-over nozzle shown in FIG. 1 after it has been converted from an air-cushion-producing nozzle in accordance with FIG. 1 to a nozzle cooperating with an airplane wing profile in accordance with FIG. 2 by rotating the eccentric pin 9 clockwise about the eccentric axle l0. Owing to the substantially greater nozzle slot as compared with the position shown in FIG. 1, the stream 14 between the end portion of the left-hand nozzle wall 4 and the tiltable piece 6 has now been changed so that the fluid medium will flow over the convex back of the tiltable piece 6 curved in the form of an airplane wing profile, the more so as the second stream 15 is now flowing in the same direction since the right-hand end of the tiltable piece 6 is now located above the end of the righthand nozzle wall 5. The air jets 16 from the perforations in the back of the tiltable piece 6 are deflected by the strong air flow with the basic direction indicated by the arrow 14, which has a favorable effect on the boundary layer formed at the web with the result that the web 1 will not touch the right-hand end of the tiltable piece 6. This effect has been produced heretofore by the known nozzles cooperating with airplane wing profiles where the inflow of ambient air produced by the perforation is already sufficient to reduce or even eliminate, where necessary, the negative pressure which occurs when the gap between the web and the airplane wing profile is too narrow. However, what is novel is the fact that according to the present invention this airplane wing profile is provided by the tiltable piece 6.
The combined open area of the perforations I3 is smaller than half of the combined open cross section of the slots of the nozzle through which the air streams ll and 12, respectively 14 and 15 emanate, in either position of the tiltable member 6.
FIG. 3 shows three nozzles 17 in accordance with the invention disposed in series. Each of these nozzles corresponds to the illustrations of FIGS. 1 and 2, except that the position of the tiltable pieces is that of FIG. 2. Above the nozzles is the web 1. This arrangement is preferred for annealing furnaces in which the heat transfer by convection must be strictly limited to the underside, the clearance height in the upper part of such annealing furnaces being comparatively great to permit the web to be introduced by hand from outside. At the temperatures existing in such furnaces any mechanical equipment would be bound to fail.
In FIG. 4, the floating web 1 moves below the change-over nozzles 18, in accordance with the invention, which operate on the principle of nozzles cooperating with an airplane wing profile, while the changeover nozzles 20, in accordance with the invention, operate on the principle of air-cushion-producing nozzles as shown in FIG. 1 to improve the heat transfer and to assist in lifting the web 1 from the screen belt 19.
The possibility of eccentric adjustment at 9, 110 enables all of the upper nozzles 18 and all of the lower nozzles to be set so that in accordance with FIg. 5 the nozzles 18 will act as air-cushion-producing nozzles as shown in FIG. 1 and the nozzles 20 as nozzles cooperating with airplane wing profiles as shown in FIG. 2. Thus, no pressure is applied from below and the top of the web 1 is not exposed to suction but, on the contrary, to pressure forces so that the web 1 is kept in firm contact with the conveyor belt 19.
FIG. 6 shows the characteristic curves illustrating the action of nozzles in accordance with the present invention in their alternate positions. The abscissa 211 represents the distance of the web 1 from the nozzle arrangement. The ordinate 22 indicates the pushing power of the air flow or dynamic air pressure above the nozzle and, thus, the forces acting on the web. The curve 23 is that of a change-over nozzle operating on the principle of an air-cushion-producing nozzle in accordance with FIG. 1, while the curve 24 is obtained when the tilting piece 6 in the change-over nozzle assumes a position as shown in Flg. 2. The operating point 25 is applicable when a strong, heavy metal strip must be treated, calling for a relatively high pushing power with a small distance between the strip and the nozzles.
At an operating point 26, with the same distance between the web and the nozzles as in the case of the operating point 25, only a slight pushing power is required such as that required to support the weight of a very thin metal foil. The operating point 27 is realized by the nozzles 18 of FIG. 4 in the position in which they act on the principle of nozzles cooperating with an airplane wing profile. As these nozzles 18 are disposed above the web 1, they develop a negative pushing power, in other words, they attract the web by suction.
The operating point 28 is associated with the nozzles 20 of FIG. 4 which, at this distance, still develop forces to assist in lifting the web from the traveling screen 119.
The operating point 25 is also characteristic of the operating point of the nozzles 18 in FIG. 5 which force the web ll against the traveling screen 19 with a high pushing power, i.e. highly reliably, whereas the operating point 27 corresponds to the lower nozzles 20 in FIG. 5, i.e., the nozzles 20 do not apply any pushing forces to the web 1 so that the latter cannot be lifted from the traveling screen.
II. A nozzle comprising a pair of nozzle slots for the ejection of streams of compressed gas therethrough, said nozzle slots extending transverse to a predetermined direction and being formed by outer stationary guide faces arranged spaced from each other in said predetermined direction and oppositely inclined with respect thereto and inner guide faces on an adjustable member having an airplane wing profile; means connected to said adjustable member for moving the same between a first position in which the guide faces on said adjustable member cooperate with said stationary guide faces so that the gas stream emanating from one of said slots extends substantially in said predetermined direction and the gas stream emanating from the other of said slots is inclined to and directed towards the gas stream emanating from said one slot, and a second position in which a guide face on said movable member in the region of said other slot cooperates with the adjacent stationary guide face so that the gas stream emanating from said other slot extends substantially in the same direction as the gas stream emanating from said one slot; and means for supplying a gas under pressure to said movable slots.
2. A nozzle as defined in claim 11, wherein said adjustable member is arranged tiltable between said first and said second position thereof.
3. A nozzle as defined in claim 2, wherein said stationary guide faces have each an end edge extending transverse to said direction and being spaced from the edge of the other stationary guide face, and wherein said adjustable member has in the region of said other slot a concavely curved guide face which is located in said first position of said adjustable member inwardly spaced from the adjacent stationary guide face and in said second position spaced from and opposite the end edge of said adjacent stationary guide face.
4. A nozzle as defined in claim 3, wherein said adjustable member has in the region of said one slot a convexly curved guide face located in said first and said second position inwardly spaced from the stationary guide face adjacent thereto.
5. A nozzle as defined in claim 1, wherein said adjustable member is hollow and has a wall, the interior of said hollow member communicating with the means for supplying compressed gas to said nozzle slots, said wall being provided with peforations so that compressed gas will flow through said perforation outwardly.
6. A nozzle as defined in claim 5, wherein the combined open cross section of said perforations is less than half of the combined open cross sections of said slots in either position of said adjustable member.
7. A nozzle as defined in claim 1, wherein said stationary guide faces form part of a nozzle box, wherein said adjustable member is mounted in said nozzle box, tiltable about a tilting axis, and wherein said means for moving said adjustable member between said positions thereof comprise eccentric means turnably mounted in said nozzle box and connected to a portion of said adjustable member spaced from the tilting axis thereof, said means for supplying gas under pressure to said slots communicating with the interior of said nozzle box.
8. A nozzle as defined in claim ll, wherein said stationary guide faces form part of a pair of lateral walls of a nozzle box and form inner faces of portions of said lateral walls extending toward each other and ending in end edges extending transverse to said direction spaced from each other, said adjustable member being hollow and being mounted in said nozzle box tiltable about a tilting axis extending transverse to said direction and shiftable in this direction relative to said tilting axis, said hollow member having a wall portion between said end edges, said wall portion being convexly curved, said wall portion being formed with perforations therethrough, said means for moving said adjustable member between said positions thereof comprising eccentric means turnably mounted in said nozzle box and connected to said adjustable member, and said means for supplying gas under pressure to said nozzle slots communicating with the interior of said nozzle box.
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