US3607198A

US3607198A - Apparatus for pneumatically supporting flexible ribbons and sheets out of contact with solids

Info

Publication number: US3607198A
Application number: US710016A
Authority: US
Inventors: George Meunier; Hubert Michaud; Roland Souchet
Original assignee: Compagnie de Saint Gobain SA
Current assignee: Compagnie de Saint Gobain SA
Priority date: 1967-03-31
Filing date: 1968-03-04
Publication date: 1971-09-21
Anticipated expiration: 1988-09-21
Also published as: FR1527937A; DE1756070B2; GB1216123A; NL152832B; NO119108B; LU55802A1; DE1756070A1; ES352164A1; BE712995A; NL6803700A

Abstract

Moving hot glass sheet and similar ribbons of material are supported pneumatically out of contact with solid surfaces by establishing alternate zones of static and kinetic gas pressure along the passage of sheet. Each zone extends substantially across the full width of the sheet. Apparatus for controlling the temperature and pressure of the zones so as to perfect the sheet are described.

Description

United States Patent 1111 3,607,198

[72] Inventors George Meunier [56] References Cit d I UNITED STATES PATENTS mud 1,622,817 3/1927 Waldron 65/182 A [211 pp No 710 3,223,498 12/1965 Davidson, Jr.. 65/119 X 3,223,500 12/1965 Misson 65/114 X [22} Med 1968 3 300 290 1/1967 Misson 65/107 x [45 1 paemed Sept 1971 3 365 286 1/1968 Nedelec lllllllllllllllllll 65/114 [73] Assignee Com g k d s |m G 1 Neullly-sur-Selne, France EPrimary ExaminerArthur D. Kellogg [32] Priority Mar. 31, 1967 Attorneys- Dale A. Bauer, John L. Seymour and Bauer and [33] France Seymour 311 W 101,018

[54] APPARATUS FOR PNEUMATIC/ALLY SUPPORTING FLEXIBLE RIBBONS AND SHEETS 3; g SOLIDS EABSTRACT: Moving hot glass sheet and similar ribbons of g 3 material are supported pneumatically out of contact with solid [52] U.S. Cl 65/182 A, isurfaces by establishing alternate zones of static and kinetic 65/25 A, 65/l14,65/119,214/1 BE gas pressure along the passage of sheet. Each zone extends [51] Int. Cl C03b 25/04 1substantially across the full width of the sheet. Apparatus for [50] Field of Search 65/25 A, 1cor1trolling the temperature and pressure of the zones so as to 107, 114, 119, 182 A; 214/1 BE perfect the sheet are described.

PATENTED 8EP21 IHYI saw 1 or 3 0 I. I I I 9, 00

9/ I h 0 I.

Ill/III/l/II/I/A INVENTORS GEORGE MEUNIER HUBERT MICHAUD ROLAND soucu 5m Md ATT RNEYS PATENIED Sam IHYI sum 2 ur 3 INVENTORS GEORGE MEUNIER HUBERT MCHAUD ROLAND SQUCHET ATT NEYS I: v V

PATENTED SEP21 187i SHEET 3 OF 3 e m mln INVENTORS GEORGE HEUNIER HUBERT MICHAUD ROLAND SOUCHET APPARATUS FOR PNEUMATICALLY SUPPORTING FLEXIBLE RIBBONS AND SHEETS OUT OF CONTACT WITH SOLIDS This invention relates to the problem of supporting moving sheets out of contact with solid objects while they are cooling or undergoing treatment. The invention is particularly important in the manufacture of flat glass. It will be described in that application without detracting from the generality of its uses. The word flat in this context includes all forms of glass sheet and ribbon whether curved or truly plane.

Glass sheet is formed from a mass of molten glass, for instance by rolling, and is transported horizontally while cooling it from its plastic state to a state in which it can be mechanically handled without damaging its surface. To move it under the best conditions it has been proposed to support it on gas jets as uniformly arranged as possible to prevent the-deformation of the sheet by jets of different temperature or pressure. The problem has been difficult. It has been attempted to mount nozzles on a pressure chamber, or to provide the chamber with orifices through which, the gas can flow, providing orifices to evacuate the gas from between the blowing nozzles or apertures.

It is an object of this invention to improve the uniformity of support offered by pneumatic means, to provide for. temperature control associated with the pneumatic support and variable along the length of the supporting surface, and to provide for the treatment or surfacing of glass as it undergoes Cooling, for instance for tempering or otherwise applying gaseous treatment to its surface.

The invention provides apparatus fortransporting a sheet or ribbon of glass on -a gaseous cushion to the exclusion of all contact with a solid support in the region where the glass surface can be readily damaged.

The objects of the invention are accomplished generally speaking, by apparatus for the support of moving sheets, ribbons, and the like on a cushion of air which comprises a flat surface, pneumatic pressure means connected thereto, a series of slots of emission extending through the flat surface from the pressure means transversely of the course of the sheet and substantially across its full width, a series of slots of exhaustion in the flat surface parallel to the slots of emission, the slots of emission and exhaustion being generally arranged so that each pair of slots of exhaustion has between them two slots of emission and, between the two slots of emission, part of the flat surface.

A novel process involves the supporting of hot glass sheet moving in a selected direction out of contact with a flat surface which comprises establishing. a series of blades of upwardly moving gas transversely to its line of motion and substantially throughout the width of the sheet, establishing linear apertures of evacuation between some of the said blades and establishing linear zones of static pressure substantially fully across the sheet between alternate pairs of the said blades.

The apparatus contains orifices of emission for the gas associated with orifices of evacuation, all theorifices being slots which extend across the line of motion of the sheet and substantially the full width of the sheet. Each slot of evacuation is separated from the next by two slots of emission which are choked to establish a substantial loss of head, the slots of evacuation being substantially larger in order to permit outflow with only negligible loss of head. The upper surface of the walls of the slots constitute a flat surface, in the sense of the term defined above, which is substantially free of deviations from the flat except for the slots themselves.

It is to be noted that the distribution of the slots of emission and exhaustion establish between two adjacent slots of emission a flat area extending across the line of motion of the sheet, free of apertures, above which the gases form a cushion at constant, static pressure. There are thus established along the path of the moving sheet a series of transverselyextending kinetic, pneumatic zones alternating with static pneumatic zones of support. The gas emitted by each of the two slots of emission, after establishing the zone of static pressure flows toward the nearest slot of evacuation.

The supporting surface thus formed is regular and progressively corrects the defects of the sheet, the different zones playing different corrective roles. It is advantageous that the part of the surface occupied by the slots should not substantially exceed 10 percent of the whole.

The slots of emission should offer a substantial obstruction and loss of head to the passage of the gas in order that thegas, despite the weight of the sheet, adopt a laminar flow as it issues from the slots. Admitting that his difiicult to form linear slots of identical width and to preserve that regularity despite thermal expansion, an advantage of the invention arises from establishing the loss of head by introducing a grill or wire mesh tightly between the two walls. The introduction of this choke makes it unnecessary to machine the surfaces of the slots of emission accurately, Furthermore, this structure guarantees the maintenance of proper spacing of the lips of the slots throughout their length. In practice, the width of the slots of emission are preferably between 0.4 and 0.7 mm. and ordinarily need not be greater than 1 mm.

The slots of evacuation offer only a negligible obstruction to free flow so that the whole of the gaseous cushion which sustains the gas is under a mean pressure which is highly uniform and which is only slightly inferior to the pressure of the gas at the discharge lip of the slot of emission. This is easily accomplished by giving the discharge slots a width of possibly 2 mm.

It follows from thisconstruction that the gaseous cushion thus formed is very thin, on the order of 0. l 5 mm. or even less, but of great rigidity so that the sheet of glass is compelled to shape itself with great exactitude to the surface of reference constituted by the horizontal walls between the slots. When the sheet being transported is soft and deformable the slots should extend fully across the sheet, but the zone of the surface between two slots of emission may be reduced to improve the flow toward the outlet slots, which has shown to be advantageous for the, correction of small irregularities'in the glass sheet. on the contrary, when the sheet has hardened it is of advantage to enlarge the distance between adjacent slots of emission inorder that the zones of static pressure represent an increased proportion of the total area, which may exceed 60 percent of the total surface of the gaseous cushion, the optimum spacing being a function of the conditions existing at a particular location. This spacing is the greater as the material is stiffer, as the speed of the sheet is greater, and as its moment of inertia is the greater; and vice versa.

The slots may be rectilinear, sinuous or broken but it is preferable, especially when the sheet is soft, to use straight line, parallel slots perpendicular to the line of motion of the sheet. In this way all the points of the lower surface of the glass along one transverse line are treated simultaneously and uniformly by gas flowing out of a single slot. This prevents the creation of longitudinal zones in the glass which would otherwise tend to be differently treated and introduce correlative deformations of the sheet, and it contributes largely to reduce and remove defects of planeity. Furthermore, rectilinear, parallel slots are more easily made than others. The slots are readily made by spacing vertical walls a selected distance across the line of motion of the sheet. These walls extend into pressure chambers containing gas under constant pressure.

The chambers are supplied with gas at superatmospheric presthe blades of gas issuing from the slots of emission. The relatively large loss of head suffered by the gas passing through the choked slots assures a constant flow even when the sheet does not fully cover the blades of gas, the excess gas used thus becoming trivial. The lateral flow of gas away from the edges of the sheet above the surface of the pressure chamber is very small and does not disturb the supporting cushion.

Inasmuch as the gas leaving the sheet flows into the interior of the chambered pressure box which presents the slots of emission and exhaustion, it is advantageous to establish thermal equilibrium for the whole process, thereby limiting risks of deformation which might otherwise exist. The spent gases may be entrapped, controlled, and recycled.

When the exhaust gases are finally expended into the atmosphere, it is advantageous to make the size of the section of the slots, or of the discharge conduits, so that the loss of head undergone by the gas in passing through the slots and the conduits is very small. Under these conditions, the pressure of evacuation is substantially the same as atmospheric pressure throughout the full extent of the apparatus.

In a first form of the invention the slots of emission and the slots of evacuation are formed between juxtaposed walls transverse to the lines of motion of the material transported and in a plane perpendicular to it. In another and very valuable form,

the slots of emission of one pair, seated between two consecutive slots of evacuation are separated by a hollow body through the interior of which fluids can be circulated which affect a heat exchange, heating or cooling, with the gases flowing through the slots and also with the supporting cushion and the material transported, in the latter case a substantial heat exchange occurring by radiation to or from the hollow body. To complete these thermal exchanges and make them uniform, the elements separating the slots of emission from the slots of exhaustion may have hollow passages through which hot or cold fluids may pass.

These thermal exchanges can be mild or intense, notably sufficiently intense to accomplish tempering, or of a minor sort which accomplishes merely a progressive cooling. The cooling or heating fluids circulating through the hollow box between the slots may be used to establish a temperature gradient along the length of the moving material.

The cooling of the surface of the pressure box may be advantageously used to prevent adherence of the glass to the box should the two accidentally come in contact.

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.

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

FIG. 1 is a vertical longitudinal section through the upstream end of a preferred form of apparatus;

FIG. 2 is a section on the line lI-II of FIG. 1.

FIG. 3 is a perspective view, sectioned and cut away, illustrating the construction of the apparatus;

FIG. 4 is a schematic vertical, sectional view including a dia gram of the pressures existing under the sheet, as established by the apparatus; and

FIG. 5 is a vertical longitudinal section through a section of a unit of the invention.

In FIG. 1 the gas which is to support the sheet is introduced by a conduit 1 into a pressure box 2. The upper wall of the pressure box is provided with ranks of orifices 3 which are disposed throughout its area and deliver the gases to chambers 4 which are sufficiently larger than the apertures 3 to reduce the speed of the gases. Each pressure chamber 4 distributes gas to two

slots

5, 5a which are parallel to each other and transverse to the direction of motion of the sheet of glass 7 as shown by the arrow. These slots interpose the gaseous cushion between the moving sheet and the top of the apparatus. A substantial reduction in pressure is provided by grilles or

screens

6, 6a, which may be of woven refractory metal, extending the length of each slot between the walls and assuring a good discharge of the gas toward the sheet. This loss of head is-substantial compared to the whole of the gaseous circuit and is calculated to establish a uniform pressure and uniform flow in all parts of the system. The zone of static pressure is found at 8 in even intervals between two slots of

emission

5, 5a. The gas, having established stable pressure in these areas flows toward the slots of evacuation 10 which are parallel to the slots of emission and are composed by the

parallel walls

10a and 10b. The slots 10 open through apertures 12 into canals 11 which are connected by orifices 13 to chamber 14 which is common to all the exhaustion slots. The chamber 14 may be connected to an outlet canal 15 for the recycling of gas.

In the form represented in the drawings, the

slots

5, 5a are separated by a hollow body or profile 16 having interior canals which are connected by conduits 18 to a source of fluid such as water, air, steam, which permits one to control the temperature of the gases flowing upward and of those in static state thereabove.

In FIG. 4 is a pressure diagram in which the zone 8 of static pressure is represented as having a pressure p which is substantially constant and which is substantially equal to the pressure of the gases flowing from

slots

5, 5a. At the right of the exhaustion slots 10 the pressure falls to a valve p The pressure p,,,, for which the cross hatch surface s is equal to two times the cross hatch surface s is the mean pressure of the gaseous cushion which corresponds to the weight of the supported glass.

FIG. 5 shows an apparatus similar in its general principles to that described hereinabove but which has several advantages, especially in that it can be cast, that the number of parts to be fabricated is reduced, time and cost of assemblage are minimized, and the problem of maintaining gas tightness between the compartments of supply and return of the gas is eliminated. The body 19 is cast in the foundry, includes

slots

5, 6 of emission, and slots 10 of exhaustion which discharge into canals 11 connected to the air. These bodies have inclined upper sides 20, prismatic in shape, which receive hollow bodies 21 of trapezoidal section corresponding to the prismatic profile 20. Posts 22 support the trapezoidal profile 21 in proper position, which is established by the grilles or wire mesh 6 which line the inclined walls of elements 11. The tops of

elements

11, 21 conform to the same plane whether it be flat or curved.

The following example illustrates a set of conditions which have been found to be satisfactory, it being understood that the figures would of necessity vary for a sheet of different weight. In making these determinations, a sheet of glass 1.380 m. wide and 6.6 mm. thick was passed over an apparatus constructed as in FIGS. 1 to 4. The apparatus was 1.380 m. wide and 0.325 m. long. The zones 8 in which the gas was static were 21 mm. wide. The zone 9 in which the gas was flowing were 7.6 mm. wide. The width of the slots of emission was 0.7 mm. The height of the slots of emission was 40 mm. These slots contained a grill 30/32 the wires of which were 0.3 mm. in diameter with square apertures of 0.85 mm. The slots of exhaustion were 1.5 mm. wide and their height was 50 mm. The

sheet moved at 2.35 m./m. its temperature as it passed onto the support was 990 C. and its temperature as it left the support (of gas) was 850 C. Air was used to form the cushions, its temperature at entrance was 30 C. and at discharge C. Its flow rate was 10 cm./sec. per cm. of length of the slots or 40 m. /hr. The pressure in the canals was 30 mb. and the thickness of the cushion of air beneath the glass sheet was 0.15 mm. Water was circulated beneath the areas of static pressure in the canal 17 at 500 l./h. entering at 30 C. and leaving at 42 C.

In what has been stated hereinabove, it has been supposed that the gaseous cushion is plane and horizontal, but it can be inclined to the horizontal either longitudinally or transversely. The upper surface of the box which generates the gaseous cushion may be arched either in the direction of motion of the sheet or transversely, for instance in the case where it is desired to support a bent sheet. One may also form the box flat at its extremity, for instance upstream, and go at a progressively increasing arch toward the downstream end, thereby forming a bent sheet progressively from an initially planar sheet.

it is also possible to use two or more apparatus of the type described, one above the other, to generate gaseous cushions on opposite sides of the sheet so as to accomplish at once the treatment of the lower and upper faces of the sheet, the force of the upper blades being compensated by increased pressure below, thus making possible either identical treatment of the upper and lower surfaces or different treatments of preselected sides.

The advantages of the invention are in the accomplishment of the objects hereinbefore stated, and also in supporting the sheet more uniformly, with fewer disturbances, in correcting imperfections in the surface of the sheet, in giving it a superior finish, and in improving the uniformity of treatment of the sheet from side to side.

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. In apparatus for pneumatically supporting a ribbon of sheet material moving in the direction of its length, a pressure box having a flat upper surface over which the sheet material moves in said direction, there being a first multiplicity of slots for the emission of air, in and through said surface, and a second multiplicity of slots in and through said surface, for the exhaustion of air emerging from said first multiplicity of slots, all said slots being parallel and extending continuously substantially the full width of said ribbon, there being a pair of slots of emission between each consecutive two slots of exhaustion, the area occupied by the slots being not substantially more than percent of the whole upper surface, and conduit means connected with said box for supplying air under pressure to all said slots of emission, and for exhausting air from said slots of exhaustion.

2. The apparatus of claim 1, each said slot of emission being about 1 mm. in width measured in said direction, the distance between the slots of emission of each said pair being on the order of times the width, as aforesaid, of each slot of emission.

3. The apparatus of claim 2, each said slot of exhaustion having a width measured in said direction, of about 1.5 to 2 mm.

4. The apparatus of claim 2, the distance between each slot of emission and the slot of exhaustion nearest thereto, being a fraction only of the distance between each said pair of slots of emission, all distances being measured in said direction.

5. The apparatus of claim 4, each said slot of exhaustion being defined by a respective pair of two plates spaced in said direction and having a vertical dimension normal to said direction, of about 40 mm., the upper edges of said plates defining a portion of said first surface.

6. The apparatus of claim 5, and a multiplicity of hollow conduits each interposed between and having its opposed side walls spaced from a respective contiguous one of said plates, to thereby form a slot of emission.

7. The apparatus of claim 6, and means connected with each said hollow conduit to supply heat exchange fluid thereto.

8. The apparatus of claim 6, said hollow conduits being rectangular in vertical planes parallel with said direction.

9. The apparatus of claim 6, said hollow conduits being most and lying in said flat upper surface.

10. Apparatus for the pneumatic support of moving sheet comprising a bed having a flat, horizontal surface and a supporting unit comprising a series of parallel slots of gas emission and discharge extending into the bed from the surface thereof transversely to the motion of the sheet and parallel to one another, means to supply the slots of emission with gas under pressure, means to ispose of the gas from the discharge slot, the slots of emission and discharge being arranged so that a slot of discharge is separated from each of two slots of emission by a narrow area of flat surface, and two slots of emission are separated from each other by a broad area of flat surface, whereby there is provided above the broad area a zone of substantially constant pressure, and above the narrow areas zones of pressure decreasing toward the discharge slot.

11. Apparatus according to claim 10 in which each slot of emission has substantially parallel walls choked by a filling of gas-pervious, flow-impending means.

12. Apparatus according to claim 10 which includes heatexchanging means operatively connected to the broad area of flat surface.

13. Apparatus according to claim 10 in which the bed comprises a repeating sequence of such units, heat-exchanging means is operatively connected to a plurality of broad surfaces, and means are provided to operate different heatexchanging means individually at different rates of heat exchange.

14. Apparatus according to claim 10 in which the broad area is the top of a prism-shaped hollow body fitting into a prism-shaped recess in the bed, the inclined sides of which constitute the walls of slots of emission.

15. Apparatus according to claim 10 in which the slots are uninterrupted throughout the width of the sheet and the distance between two slots of emission is the major part of the distance between two discharge slots.

16. The apparatus of claim 11 said pervious gas flow-impeding means comprising gas-pervious fabric.

17. The apparatus of claim 10, each said portion of said flat surface between two consecutive slots of emission comprising an exterior upper surface of a respective one of a plurality of ducts extending transversely of said direction, and conduit means supplying heat exchange fluid to each said duct.

18. The apparatus of claim 10 each said portion of said flat surface between each consecutive pair of slots of emission defining an area of relatively static constant pressure beneath and supporting the sheet.

19. The apparatus of claim 10 the width of the slots of emission and of exhaustion, being about 1 mm. and 2 mm., respectively.

20. The apparatus of claim 13 the dimensions of the surface between each pair of consecutive slots of emission, measured in said direction, increasing downstream.

21. Apparatus according to claim 13 in which the area between said slots of emission is at least 60 percent of the total surface area of said flat surface.

22. The apparatus of claim 10, and means to maintain the air emerging from at least some of said slots of emission at a temperature different from that emerging from the remaining slots of emission.

23. The apparatus of claim 16, said pervious air flow impeding means comprising refractory wire mesh.

Claims

2. The apparatus of claim 1, each said slot of emission being about 1 mm. in width measured in said direction, the distance between the slots of emission of each said pair being on the order of 20 times the width, as aforesaid, of each slot of emission.
3. The apparatus of claim 2, each said slot of exhaustion having a width measured in said direction, of about 1.5 to 2 mm.
4. The apparatus of claim 2, the distance between each slot of emission and the slot of exhaustion nearest thereto, being a fraction only of the distance between each said pair of slots of emission, all distances being measured in said direction.
5. The apparatus of claim 4, each said slot of exhaustion being defined by a respective pair of two plates spaced in said direction and having a vertical dimension normal to said direction, of about 40 mm., the upper edges of said plates defining a portion of said first surface.
6. The apparatus of claim 5, and a multiplicity of hollow conduits each interposed between and having its opposed side walls spaced from a respective contiguous one of said plates, to thereby form a slot of emission.
7. The apparatus of claim 6, and means connected with each said hollow conduit to supply heat exchange fluid thereto.
8. The apparatus of claim 6, said hollow conduits being rectangular in vertical planes parallel with said direction.
9. The apparatus of claim 6, said hollow conduits being trapezoidal in vertical planes parallel with said direction, the longer of the two parallel sides of the trapezoid being uppermost and lying in said flat upper surface.
10. Apparatus for the pneumatic support of moving sheet comprising a bed having a flat, horizontal surface and a supporting unit comprising a series of parallel slots of gas emission and discharge extending into the bed from the surface thereof transversely to the motion of the sheet and parallel to one another, means to supply the slots of emission with gas under pressure, means to dispose of the gas from the discharge slot, the slots of emission and discharge being arranged so that a slot of discharge is separated from each of two slots of emission by a narrow area of flat surface, and two slots of emission are separated from each other by a broad area of flat surface, whereby there is provided above the broad area a zone of substantially constant pressure, and above the narrow areas zones of pressure decreasing toward the discharge slot.
11. Apparatus according to claim 10 in which each slot of emission has substantially parallel walls choked by a filling of gas-pervious, flow-impending means.
12. Apparatus according to claim 10 which includes heat-exchanging means operatively connected to the broad area of flat surface.
13. Apparatus according to claim 10 in which the bed comprises a repeating sequence of such units, heat-exchanging means is operatively connected to a plurality of broad surfaces, and means are provided to operate different heat-exchanging means individually at different rates of heat exchange.
14. Apparatus according to claim 10 in which the broad area is the top of a prism-shaped hollow body fitting into a prism-shaped recess in the bed, the inclined sides of which constitute the walls of slots of emission.
15. Apparatus according to claim 10 in which the slots are uninterrupted throUghout the width of the sheet and the distance between two slots of emission is the major part of the distance between two discharge slots.
16. The apparatus of claim 11 said pervious gas flow-impeding means comprising gas-pervious fabric.
17. The apparatus of claim 10, each said portion of said flat surface between two consecutive slots of emission comprising an exterior upper surface of a respective one of a plurality of ducts extending transversely of said direction, and conduit means supplying heat exchange fluid to each said duct.
18. The apparatus of claim 10 each said portion of said flat surface between each consecutive pair of slots of emission defining an area of relatively static constant pressure beneath and supporting the sheet.
19. The apparatus of claim 10 the width of the slots of emission and of exhaustion, being about 1 mm. and 2 mm., respectively.
20. The apparatus of claim 13 the dimensions of the surface between each pair of consecutive slots of emission, measured in said direction, increasing downstream.
21. Apparatus according to claim 13 in which the area between said slots of emission is at least 60 percent of the total surface area of said flat surface.
22. The apparatus of claim 10, and means to maintain the air emerging from at least some of said slots of emission at a temperature different from that emerging from the remaining slots of emission.
23. The apparatus of claim 16, said pervious air flow impeding means comprising refractory wire mesh.