US3449102A

US3449102A - Method and apparatus for supporting sheets on a gaseous bed

Info

Publication number: US3449102A
Application number: US702756A
Authority: US
Inventors: Maurice Nedelec; Henri Chaumont
Original assignee: Compagnie de Saint Gobain SA
Current assignee: Compagnie de Saint Gobain SA
Priority date: 1964-03-25
Filing date: 1968-02-02
Publication date: 1969-06-10
Anticipated expiration: 1986-06-10
Also published as: LU48255A1; GB1076872A; BE661523A; ES311009A1; NL137693C; FR1398055A; DE1431606B2; DE1431606A1; NL6503720A

Description

June 10, 1969 NEDELEC ET AL 3,449,102

METHOD AND APPARATUS FOR SUPPORTING SHEETS ON A GASEOUS BED Original Filed March 19, 1965 Sheet 3 of 4 IN VENTORS MAURICE NEDELEC HENRI CHAUMONT ATTO NEYS June 10, 1969 l M. NEDELEC ET-AL 3,449,102 v METHOD AND APPARATUS FOR SUPPORTING SHEETS ON A GASEOUS BED Original Filed March 19, 1965 Sheet June 10, 1969 NEDELEC ET AL METHOD AND APPARATUS FOR SUPPORTING SHEETS ON A GASEOUS BED Sheet Original Filed March 19, 1965 INVENTORS MAURICE NEDELEC HENRI CHAUMONT {5m MW ATTQ. N515;

United States Patent 3,449,102 METHOD AND APPARATUS FOR SUPPORTING SHEETS ON A GASEOUS BED Maurice Nedelec, Paris, France, and Henri Chaumont,

Brussels, Belgium, assignors to Compagnie de Saint- Gobain, Nenilly-sur-Seine, France Continuation of application Ser. No. 441,246, Mar. 19, 1965. This application Feb. 2, 1968, Ser. No. 702,756 Claims priority, application France, Mar. 25, 1964, 968,609 Int. Cl. C03b 17/04, 9/12 U.S. CI. 65-25 10 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for supporting sheets of glass on a cushion of gas formed by gas forced under pressure from a regular pattern of narrow slits opening vertically through a generally horizontal surface. Each plurality of discrete slits, has a passage or passages associated therewith and extending downwardly from the surface, for the escape of gas after emerging from the related slit or group of slits.

This application is a continuation of application Ser. No. 441,246, filed Mar. 19, 1965 now abandoned.

The present invention relates to a method and apparatus for supporting a sheet or moving ribbon of material, such as glass, on a cushion of fluid and particularly a gaseous fluid such as air.

The method and apparatus of this invention are especially suited for supporting a sheet or moving ribbon of glass which is hot and for cooling, heat treating and even shaping the sheet or ribbon being supported, This method and apparatus are also useful to effectively support the sheet or ribbon as it is drawn or otherwise moved over the cushion of fluid when the sheet or ribbon is to be conveyed through an oven, for example.

The method and apparatus of the present invention are particularly adapted for providing an effective fluid supporting cushion with a gaseous fluid such as air or combustion products of a hydrocarbon combined with an excess of air. The invention, however, lies in the manner of causing the fluid to flow under the sheet supported thereon without turbulence and is not limited to the use of any particular fluid.

It is known to support and convey sheet material on a cushion of fluid formed by jets of the fluid forced up out of a multitude of blow-holes in a bed surface. But, for the cushion of fluid to support a sheet satisfactorily, the lifting pressure of the combined flow of fluid from the jets must be quite uniform. This is diflicult to obtain with conventional apparatus, however, because the jets of fluid from the blow-holes impinging on the sheet being supported cause turbulence in the cushion of fluid circulating under the sheet.

It has also been found that when the circulation of the fluid is turbulent more pressure must be applied to the fluid emerging from the blow-holes to achieve a cushion with a given lifting power than in the case of a laminar or streamline flow of fluid under the sheet being supported. Also when the fluid is heated as a means of heat treating the supported material, the number of calories necessary to heat the gas will always be less in the case of a laminar flow of fluid than if the fluid flow is turbulent. A further fact which has been discovered is that when the flow is turbulent and it is desired to increase the temperature of the fluidto heat treat the material, for examplethe output of gaseous fluid emerging from the blow-holes must be increased in order for the sheet to be supported 3,449,102 Patented June 10, 1969 at the same level. On the other hand, if the flow is laminar, an increase in temperature of the fluid permits the output of gaseous fluid to be reduced, with consequent saving of power, while the sheet is maintained at a constant level.

An object of the present invention is to provide apparatus for supporting a sheet of material on a cushion of fluid in which the cushion is formed by streams of the fluid forced up under pressure through openings in a surface adjacent the sheet and in which the fluid flow is principally laminar in order to obtain pressures substantially constant in all directions.

Another object is to provide such apparatus which is adapted to work a sheet supported and transported on the cushion of fluid into a curved trough shape or into a cylindrical shape as the sheet moves over the cushion.

Another object is to provide such apparatus in which the fluid may be utilized for heat treating or cooling the sheet of material supported on the cushion of fluid, and which, when the fluid is heat treated, requires less rather than more pressure on the fluid to maintain the supported sheet at a constant height as compared with previously known apparatus.

Another object is to provide such apparatus in which the fluid forming the supporting cushion may be recirculated.

Another object is to provide such apparatus in which, when the fluid is heated, as for example to heat treat the supported material, the necessary energy and the heat loss is less than with previously known apparatus for supporting material on a fluid cushion.

Another object is to provide such apparatus in which the openings in the surface through which the fluid is forced are formed by slits in the tops of a plurality of separate plug elements supported on a base member wherein each plug element is separately replaceable so that a worn plug element may 'be replaced simply and economically and so that the plug elements are readily interchangeable with other plug elements whose opening slits may be arranged in a different configuration for supporting sheets of different materials which may have different physical properties such as fragility, plasticity and rn-alleability.

Another object is to provide such apparatus in which a sheet is supported evenly at an accurately adjustable height above the surface through which the streams of fluid forming the cushion emerge and in which the surface is provided by separate plug elements supported on an accurately machined surface of a base member which is made of a substantially thermally inert material, such as silica, whereby the shape in which the sheet of material is supported and formed by the cushion of fluid may be varied and adjusted with precision.

The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

FIGURE 1 is a vertical section through one of the nozzle-like plug elements which direct the flow of fluid in one form of apparatus in accordance with the present invention;

FIGURE 2 is a vertical section through a portion of apparatus in accordance with the invention showing two of the nozzle-like elements of FIGURE 1 in position supported on a hollow base member;

FIGURE 3 is a top plan view of the apparatus of FIGURE 2;

FIGURE 4 is a vertical section through an alternate form of nozzle-like plug element showing it in position on an alternative form of base member;

FIGURE 5 is a top plan view of the apparatus shown in FIGURE 4;

FIGURE 6 is a top plan view of several nozzle-like plug elements of a third 'form of apparatus embodying the invention;

FIGURE 7 is a vertical section through a portion of the third form of apparatus of FIGURE 6 and particularly showing the structure and operative arrangement of the plug elements shown in FIGURE 6; and

FIGURE 8 is a view, partly schematic and partly in vertical section, illustrating operation of apparatus in accordance with the invention.

Referring to FIGURES 2 and 4 of the drawings, apparatus of the invention comprises generally a bed 10 having an upper surface indicated by the dash line A-B with a plurality of slits 11 therethrough. A fluid is forced under pressure out through the slits 11 and supports a sheet 12, such as a sheet of glass, above and out of contact with the surface A-B on a cushion of the fluid which circulates between the surface A-B and the sheet 12. Escape passages 13 are provided through the surface A-B adjacent each slit 11 for the escape of fluid back through the surface. As indicated by arrows, the fluid emerges from the slits 1 1 in narrow sheet-like streams, impinges on the lower surface of the sheet 12 supported thereby and then flows back down through passages 13- and out to the sides of the bed 10 as illustrated in FIGURE 8. With this arrangement the streams of fluid flow under the sheet 12 without turbulence and provide uniform sheet-supporting pressure over the area of the surface AB. Among other advantages this renders the method and apparatus of the invention suitable for shaping a sheet 12 which is sufliciently plastic by giving the surface A-B the configuration it is desired to transmit to the sheet 12convex or concave, for exampleand by forcing fluid out of the slits at a uniform pressure across the surface so that a sheet 12 when in a hot plastic state, conforms to the configuration of the surface. In addition, the sheet 12 may be cooled or heat treated by cooling or heating the fluid.

The apparatus of this invention may also be used in combination with other types of heating or cooling apparatus. For example, apparatus of the present invention may be used to heat or cool the lower surface of a sheet 12 passing over the surface A-B of the bed 10 while other heating or cooling apparatus may be arranged to heat or cool the upper surface of the sheet. In this way the upper and lower surfaces of the sheet 12 may at one time be heated or cooled to different temperatures respectively.

In the drawings a first form of apparatus in accordance with the invention is shown in FIGURES 1, 2 and 3; a second form is shown in FIGURES 4 and 5; a third form is shown in FIGURES 6 and 7; and FIGURE 8 illustrates operation of the apparatus.

Referring first to the form of apparatus shown in FIG- URES 1 and 2, the surface A-B is provided by the tops of a plurality of flat-topped cylindrical plug elements 15 which are vertically arranged in side-by-side alignment and mounted on a base member 16 which is hollow to provide a chamber 17 therein for fluid which will hereafter be referred to as a gas or the gas.

Each of the plug elements 15-has a vertical slit 11 therein opening through the top of the plug and the slits 11 are in gas flow communication with the chamber 17. The gas is fed into the chamber 17 under pressure by conventional means (not shown) and flows into the base of the slits 11 and out through the openings of the slits at the tops of the plug elements 15. Since the plug elements 15 are cylindrical there will be spaces between them in addition to which they are spaced apart slightly so that the plug elements have escape passages 13 around and between them for the passage of the gas back down through the surface A-B. The gas then flows out from between the plug elements to the sides of the bed 10, as illustrated in FIGURE 8, to be collected and recirculated by means, an illustration of which is described below with reference to FIGURE 8.

As best seen in FIGURE 1, each of the plug elements 15 is formed by a hollow cylindrical body 20 with a cylindrical core element 21 secured concentrically therein. The upper portion 21a of the core element has an outside diameter which is smaller than the inside diameter of the cylindrical body 20 to provide an annular slit 11 between the core element 21 and the wall of the cylindrical body 20. The bottom end 21b of the core element is enlarged to form a plug press fitted into the lower end of the cylindrical body 20 to secure the core element concentrically within the body 20. The central portion 21c of the core element 21 is tapered inwardly as shown to provide an enlarged annular cavity 22 within the plug element 15. A series of holes 23 through the wall of the body 20 and spaced radially around the body in line with the cavity 22 provides passages for conducting gas into the cavity 22 from outside the plug element. Additional passages into the cavity 22 are provided by holes 24 vertically through the lower portion 21b of the core element 21.

Looking at FIGURE 2, a plurality of the plug elements 15 are mounted on the base member -16. The lower outside portion of cylindrical body 20 of each plug element 15 is a smaller diameter than the upper portion to provide a reduced cylindrical portion 25 with a shoulder 26 between the lower and upper portions. The reduced portions 25 of the several plug elements fit with a sliding fit into holes 27 through the upper Wall 28 of the base member 16 and shoulders 26 rest on the edges of the holes 24 to support the plug element in position. The lower end of each plug element 15 extends down into the chamber 17 with the

holes

23 and 24 opening into the chamber, so that gas from the chamber flows through

holes

23 and 24 to the cavities 22 and into the slits 11. The cavities 22 provide means to reduce and equalize the pressure of the gas flowing from the chamber 17 into the several slits 11.

In practice, using a gas as the fluid, it has been found that for the most satisfactory operation the slits 11 should not exceed about 3 mm. in width. In addition, it is desirable to have the slits 11 extend down into the body 20 a sufficient depth to reduce the pressure of gas between the cavities 22 and the tops of the plug elements 15 to some extent so as to prevent excessive loss of pressure from the chamber 17 when no sheet 12 is in position to be supported above the plug elements 15. In practice, it has been found suitable to have the depth of the slits 11 such that the pressure of gas in the cavities 22 does not exceed about four times the pressure necessary to support a sheet 12 above and out of contact with the top of the plug elements 15 and this is accomplished by having the height of the slits between one-half and three times the outside diameter of the slits 11. In addition, it has been found that by having the radius of the outside circumference of the slits 11 (defined by the inside diameter of the hollow body 20) and the radius of the outer circumference of the plug element 15 respectively in a ratio of between 0.48 and 0.64, that smooth sheet-supporting flow of gas may be provided between the slits 11 and escape passages 13 with a minimum output of gas from the slits 11.

Apparatus in accordance with the invention is particularly intended for supporting hot glass, and for cooling and heat treating glass. It is therefore subjected to high temperatures and extremes of temperature change. In order to avoid the distorting effects of thermal expansion and contraction 011 the configuration and position of the surface A-B the base member 16 is preferably made of a thermally inert material such as a refractory material. In practice, it is made of silica and the upper surface of its wall 28 is machined or otherwise formed with sufficient precision to provide a flat reference surface from which to establish a desired configuration of the surface A-B by preselecting the height of the respective plug elements 15 mounted on the base member 16.

Referring now to FIGURE 4 which illustrates a second form of apparatus in accordance with the invention, as in the first form described above, the surface A-B of the bed is formed by the tops of a plurality of flat-topped cylindrical plug elements 30 which are vertically arranged in spaced-apart, side-by-side alignment on a base member. In this instance, however, the plug elements 30 are fixed on an intermediate base member 31 which is in turn mounted on a base member 32 having a chamber 33 therein. In this embodiment as shown plug elements 30 are mounted in groups of seven on the intermediate base member 31 and the base member 31 with its plug elements secured thereon form a unit which may be removed as a unit from the base member 32 and replaced by another unit having plug elements 30 of a different height, surface configuration or size of slits 11. A plurality of such units may be mounted on a single base member 32 to form a surface A-B of a desired area with each unit tapped into the supply of gas under pressure in the chamber 33.

The plug elements 30' each comprise a hollow cylinidrical body 34 with a cylindrical core element 35 secured concentrically therein by threading the base of the core 35 into the bottom portion of the hollow body 34. A boss 36 extends down from the center of the bottom of the core element 35 and is threaded into the upper end of a passage 37 in the intermediate base member 31 as means to secure the plug element 30 on the intermediate base member.

A central bore 38 in the lower portion of the core element 35 opens through the bottom of the boss 36. The upper end of the bore 38 is in gas flow communication with an annular cavity 39 in the plug element 30 through a plurality of radial holes 40 in the core element 35. The upper portion 35a of the core element 35 is cylindrical and has an outside diameter which is smaller than the inside diameter of the cylindrical body 34 so as to provide an annular slit 11 opening through the top of the plug element 30. As in the embodiment of FIGURES l and 2, escape passages 13 are provided between the plug elements 30, being formed by the cylindrical shape of the plug elements and by spacing them apart. The cavity 39 is formed by tapering the lower central portion of the core element 35 inward from the upper cylindrical portion 35a. The relative dimensions of the slit width and height which are particularly useful when the fluid is a gas and which are discussed above with reference to the embodiment of FIGURES 1 and 2 are equally applicable to this embodiment.

The bottom of the intermediate base member 31 has a hemispherical chamber or cavity 43 formed therein and the passages 37, into which the plug elements 30 are threaded, open into the hemispherical cavity 43. The intermediate base member 31 rests on the upper surface 44 of the base member 32 and is located in position thereon by a plurality of studs 45 which are extending down from the bottom of the intermediate base member 31 into a hole 47 in the upper surface 44 of the base member 32. The hole 47 from the chamber 33 opens through the top of the base member 32 into the hemispherical cavity 43 so that the fluid under pressure in chamber 33 flows to the slits 11 respectively through hole 47, hemispherical cavity 43, passage 37, to the bore 38 of each plug element 30 and then radially out through holes 40 to the annular cavity 39 at the base of the annular slit 11.

Gas under pressure is fed into the chamber 33 through a passage 48 in the bottom of the base member 32 by conventional means (not shown).

As shown in FIGURE 4, the annular cavity 39 in each plug element 30 is smaller in volume than the hemispherical cavity 43 in the intermediate base member 31 and cavity 43 is smaller in volume than the chamber 33 in the base member 32. By this arrangement the pressure of the fluid is not reduced from chamber 33 to cavity 39 in spite of variations of the gas output through slit 11.

In FIGURES 3 and 5 the arrows 50 show the manner in which the gas flows from the slits 11 to the escape passages 13 across the tops of the

plug elements

15 and 30 in the two forms of apparatus shown in FIGURES 2 and 4, respectively. In looking at these figures it will be appreciated that the gas emerging in vertical streams from the slits 11 is first deflected into generally horizontal paths by impinging against the underside of the sheet 12 being supported and that the provision of a smooth sheet supporting flow of gas in accordance with the invention is determined by the configuration and arrangement of the slits 11 and escape passages 13. The gas under pressure emerges from the slits 11 in streams in the form of narrow elongated sheets (cylindrical sheets with the forms of apparatus illustrated in FIGURES 3 and 5) and when the upward flow of the narrow streams of gas is deflected by impinging against the underside of the sheet 12 being supported, the gas streams flow to the nearest escape passages 13. The

plug elements

15 and 30 are of a geometric design, in horizontal cross section, namely circular in the forms shown in FIGURES 2-3 and 4-5, and the peripheral edges of the plug elements define the edges of the escape passages 13 nearest the slits 11. The slits 11 are concentrically inside the edge of the nearest escape passage 13, so that the narrow sheet-like streams of gas from the slits 11, in following a natural course to the nearest escape passage, flow smoothly in uniform paths which traverse the surface A-B, defined by the tops of the

plug elements

15 and 30, in a plurality of directions as shown by the arrows 50 FIGURE 5. Moreover, with the opening of the annular slits 11 concentrically inside the escape passages 13 the gas flows outwardly to the peripheral edge of the plug elements as shown, and no gas flows in a central zone 51 in the central portion of each plug element. Thus, the pressure in the central zones 51 is fairly constant which contributes to the equal distribution of the pressure of the gas flow in all directions radially outwardly from the slits 11.

As illustrated in FIGURES 3 and 5, the

plug elements

15 and 30 respectively are arranged side by side over an area which defines the surface A-B of the bed 10 over which a sheet 12 is supported on the gas streams from the plug elements. The area of the bed surface A-B is, of course, determined by the dimensions of the sheets 12 to be supported. The number of plug elements which are suitably provided for a given area of bed surface vary in accordance with the physical state (i.e. fragility, plasticity and malleability) of the sheet 12. It is desirable to have the dimensions of the tops of the plug elements as large as possible and thus be able to use as few separate plug elements as possible to support the sheet 12. The dimensions of the top of each plug element determine the amount of support each provides and the effective support area at the top of each plug element is the area over which gas flows from the opening of the slit 11 to the escape passage 13. The critical dimensions in determining the appropriate size of the tops of the plug elements are therefore the radius of the outside diameter of the slit 11, the radius of the inside diameter of the escape passage 13 and the relationship between them. As previously mentioned, ratio of the smaller radius which is the radius of the slit 11 in the forms of apparatus shown in FIGURES 2-3 and 4-5, to the larger radius, the escape passage in FIGURES 2-3 and 4.5, is preferably between 0.48 and 0.64. When the sheets 12 being supported are hot the radii of the slits 11 of the plug elements may be smaller than when the sheet 12 is cooler. In other words, as the temperature of the sheet 12 increases the radii of the slits 11 (and also the radii of the escape passages 13 which are defined by the outside diameters of the plug elements 15 and 30) may be decreased and vice versa. When a sheet 12 is drawn or otherwise moved over the supporting cushion of gas to be cooled or heated thereby in accordance with the invention, the dimensions of successive plug elements or groups of plug elements will therefore be varied in accordance with the temperature. In addition, the several plug elements must be spaced relative to each other so as to provide substantially uniform support over the surface A-B of the bed 10 and in general when the sheet 12 being supported is a sheet of glass at a temperature of 650 C. adjacent plug elements are suitably spaced with their axes about mm. apart.

While the plug elements 15 and are described above as being cylindrical and the slits 11 as annular, it will be appreciated that they could equally well be of other geometric designs in horizontal cross sectionsquare, triangular or hexagonal, for example. Moreover, it is not necessary that slits 11 be concentrically inside the escape passages 13. If the slits 11 are concentrically outside the escape passages 13 the suitable relative relationship of the radius of the one with the smaller radius of the two to the one with larger, by which the width of the elfective support area is determined, as discussed above, is similarly pertinent. In this connection, FIGURES 6 and 7 show another embodiment of the invention illustrating an alternative structure and arrangement of plug elements.

In the embodiment of FIGURES 6 and 7 a plurality of plug elements 55, the tops of which form the surface A-B of a bed 10, are supported on a base member 60 having a chamber 56a therein. The plug elements 55 are hexagonal in horizontal cross section and the slits 11a for the emergence of gas through the tops of the plug elements are provided by arranging the plug elements 55 in an interfitting mosaic with the hexagonal configurations of the plug elements 55 matching but spaced apart to provide the hexagonal slits 11a circumferentially around the plug elements. In this embodiment, escape passages 13a for the gas are provided by a bore 57 centrally through the top of each of the plug elements 55. Gas emerging from the slits 11a flows inwardly of the plug elements 55 to the central escape passage 13a after the emerging gas impinges on a sheet 12 being supported. As in the embodiments described with reference to FIGURES 23 and 4-5, the width of the slit 11a is not more than 3 mm. and the ratio of the radius of the bore 57 to the mean radius of the outside circumference of each plug element is preferably be tween 0.48 and 0.64.

Looking at FIGURE 7 the plug elements 55 each have an undercut portion 58 below the top so that the matching undercut portions 58 of adjacent plug elements form a pressure reducing and equalizing chamber 59 at the base of each slit 11a. The top surface 60 of the base member 56 has holes 61 through to the chamber 56a and the chambers 59 in the several plug elements are over the holes 61 so that the chamber 56a in the base member 56 is thus in gas flow communication with the slits 110.

A tubular extension 62 extends down from each plug element 55 and extends down through a pair of aligned holes 63 and 64 through the base member 56. A shoulder portion 65 at the junction of the tubular extension 64 and the main body of each plug element 55 rests on and supports the plug element on the base member 56.

The bore 57 in each plug element 55 opens through the bottom of the tubular extension 62 which extends all the way through the base member 56 (and through the chamber 56a therein) so that the bore 57 opens outside and below the base member.

FIGURE 7 illustrates the mounting and arrangement of the bed 10 (and plug elements 55 by which it is formed) and the base member 56 in an oven 6'7 of which only a part is shown for purposes of illustration. As shown, the base 66 of the oven 67 has a chamber 68 therein into which gas under pressure is conducted through a tubular conduit 69 into which gas is supplied under pressure and by means which are not shown, but which may be of any suitable conventional type. Holes 70 open through the bottom of the base member 56 into the chamber 56a. Conduits 71 fixed through the top of the oven base 66 open into the chamber 68, and the conduits 71 are connected with the holes 70 through flexible connecting tubes '72. As shown by arrows in FIGURE 7, gas from the chamber 68 thus flows into the chamber 56a and then up through chambers 59, to and out through slits 11a. After being deflected by the sheet 12 supported by the cushion of gas above the plug elements 55, the gas flows into the escape passages 13a, through the bores 57, out the bottom ends of the bores below the base member 56, and then out an exhaust passage 75 through the side wall 76 of the oven 67. From the exhaust passage 75 the gas may be recirculated back into the chamber 68 in the base 66 by a conventional fan (not shown).

FIGURE 8 illustrates an operative arrangement of apparatus in accordance with the invention in which a plurality of plug elements, such as described with reference to FIGURES l3, 4-5, and 6-7, forming a bed 10 are supported on a base member 78, having a chamber 79 therein, in an oven 84 In the arrangement illustrated, the base member 78 and bed 10 are supported independently of the structure of the oven 80 by resting on supports 81 which are made of a thermally inert material such as silica. The supports 81 extend out through suitable openings 82 in the sides of the oven 80 and rest on jacks 83 disposed under the outward ends of the supports. Thus the base member 78 and bed 10 are not subject to displacement =by thermal expansion and contraction of the structure of the oven and the jacks 83 provide means to adjust the height of the bed 10, and hence the surface A-B.

As in the embodiments described above narrow sheets of gas under pressure emerging from slits in the surface AB of the bed 10 impinge on the underside of a sheet 12 being supported and flow across portions of the surface and back through escape passages in the surface to provide the gaseous fluid supporting cushion under the sheet 12 in which the gas flow is laminar.

The gas under pressure for the gaseous supporting cushion at the surface A-B is provided by a fan (not shown) in a cabinet 84. If the gas is to be heated, as when the apparatus is used for tempering or annealing a sheet 12 of glass, the cabinet may include a combustion chamber in which a fuel gas is burned and the combustion products mixed with an amount of air at ambient temperatutres sufficient to provide a gas at the temperature desired.

From the cabinet 84 the gas under pressure is conducted by a conduit 85 to a chamber 86 in the base portion of the oven 80 and then up through conduits 87 to chamber 79 in the base member 78. From the chamber 79 the gas flows up through holes 88 in the top of the base member into the respective plug elements forming the bed 10 in which conduit means, as described with reference to FIG-

URES

23, 4 and 7, conduct the gas to the slits opening through the surface A-B. Then, when the gas flows back down the escape passages through the surface AB it flows out to the sides of the bed 10, up around the edges of the bed, up through holes 89 into a collection chamber 99 at the top of the oven. From the collection chamber 90 the gas flows out one of a number of exhaust conduits 91 through the side of the oven 80 into a conduit or header 92, which runs the length of the oven to conduct the gas to a conduit 93, through which the gas flows back into the cabinet 84 to be recirculated by the fan therein.

The gas emerging from the slits in the surface A-B may be cool for cooling a sheet 12 of glass or other material, being supported, or may be heated for tempering or annealing the sheet 12. The gas at the surface A-B is effective primarily for cooling or heating the underside of the sheet 12, therefore supplementary cooling or heating means may be provided above the sheet 12 to cool or heat the upper surface to the same or different degrees depending on the treatment being applied to the sheet 12. In FIG- URE 8 an electric resistance wire heater 95, illustrated schematically, is shown supported in the top portion of the oven 80 above the sheet 12 for applying heat to the upper surface of the sheet 12.

The apparatus and method of this invention is particularly adapted for use with glass and a sheet 12 of glass may be delivered to and removed from the supporting cushion of gaseous fluid provided by the invention by means of conventional delivery and take-off rolls known and used in the glass making art. The sheet 12 of glass may also be delivered to the gaseous supporting cushion directly from a melting furnace and may 'be moved over the cushion as a continuous ribbon. For example, it may be deposited on the cushion at one end of the apparatus in a semi-molten state, be cooled by the gas to a solidified or semi-solidified state, and removed by conventional take-01f rolls.

When the method and apparatus in accordance with the invention are applied for heating glass to be tempered, the temperature of the gas is suitably about 650 C. When they are applied for annealing glass the temperature would be decreased over a period of time from about 650 C. down to ambient room temperatures. The pressure of the gas to support a sheet of glass on a cushion of gas in accordance with the invention varies according to the thickness of the glass. As an example, for sheets of glass from 3 to 8 mm. thick the pressure of the gas to support the sheet would be from about 1.5 to about 5 grams .per square centimeter.

As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

What is claimed is:

1. A method of supporting a sheet of vitreous material for processing on a multiplicity of flowing, annular cushions of gaseous fluid resting on a flat surface comprising directing a thin, annular stream of gaseous fluid in a closed geometric figure vertically under pressure through such surface and causing the fluid to flow horizontally over the said flat surface, which is of width materially greater than the thickness of the said annular stream of gaseous fluid, towards a concentric escape area bounding said surface, as the stream of fluid is redirected horizontally and radially towards said escape area by impingement against the underside of the sheet of material, which is thus supported above said surface upon a horizontally, radially flowing annulus of gas.

2. The method of claim 1 in which the thin annular stream of gaseous fluid has a thickness on the order of a few millimeters.

3. The method according to claim 2 in which the said flat surface is circular and the ratio of the radius of its near circumference to the radius of its outer circumference is between 0.48 to 0.64.

4. A method according to claim 1 in which the narrow stream of fluid is directed through the flat surface along a closed line and flows back through an opening in said surface within the closed line.

5. A method according to claim 1 in which the narrow stream of fluid is directed through the surface along a closed line and flows outward over the said flat surface to a concentrically arranged escape area.

6. Apparatus for supporting a vitreous material in sheet form by means comprising a cushion of horizontally flowing gas, comprising a pattern of coplanar supporting zones alternating with gas escape zones, each supporting zone comprising a thin, annular blowing slot and a gas esca'pe zone, the blowing slot and gas escape zone being separated by a broad flat surface of width materially greater than the width of the thin blowing slot, providing a multidirectional gas flow area extending between the blowing slot and the escape zone, the blowing slot and the escape zone being arranged so that one surrounds the other.

'7. Apparatus according to claim 6 wherein the ratio of the smaller to the larger radius of the broad flat surface is between 0.48 to 0.64.

8. Apparatus according to claim 6 in which the escape zone surrounds the thin blowing slot.

9. Apparatus according to claim 6 in which the escape zone is within the thin blowing slot.

10. Apparatus according to claim 6 in which the annular slot has a width of a few millimeters.

References Cited UNITED STATES PATENTS 2,080,083 5/1937 Magniern -25 3,223,501 12/1965 Fredley et al 65-25 3,338,697 8/1967 McMaster et a1 65348 DONALL H. SYLVESTER, Primary Examiner. ARTHUR D. KELLOGG, Assistant Examiner.

U.S. Cl. X.R. 65-114, 182, 348; 2l41