US3649237A

US3649237A - Float glass apparatus with adjustable cooling means

Info

Publication number: US3649237A
Application number: US781044A
Authority: US
Inventors: Franz Classen; Karl Kaes; Gunter Labrot; Heinz Pape
Original assignee: FLOATGLAS GmbH
Current assignee: Erste Deutsche Floatglas & Co oHG GmbH; FLOATGLAS GmbH
Priority date: 1967-12-04
Filing date: 1968-12-04
Publication date: 1972-03-14
Anticipated expiration: 1989-03-14
Also published as: DE1596430B1; GB1283022A; NL6814777A; NL153159B; FR1604875A; BE721211A

Abstract

Float glassmaking apparatus comprises a chamber containing a bath of molten tin. The chamber has glass inlet and outlet openings, and heating and cooling elements having each a coolant flow circuit therein are disposed lengthwise of the glass flow path through the chamber. These elements are arranged in pairs staggered lengthwise of the chamber with the elements of each pair passing into the chamber through gastight joints in opposite sidewalls of the chamber. The elements are adjustable transversely of the chamber and are pivoted for rotation about horizontal and/or vertical axes outside the chamber. The elements are insulated on the upper surface thereof facing the roof of the chamber and have axially extending fins on the lower sides thereof. Temperature measuring means are provided to control drive means for adjustment of the transverse position of the elements.

Description

Unite States atent Classen et al.

[ 1 Mar. 14, 1972 FLOAT GLASS APPARATUS WITH ADJUSTABLE COOLING MEANS inventors: Franz Classen, P012, Grengel; Karl Kaes, Portz-Wahn; Gunter Labrot, Porz; Heinz Pape, Porz-Grenge1, all of Germany Erste Deutsche Floatglas Gmbl-l & Co. 0116, Porz b/Cologne, Germany Filed: Dec. 4, 1968 Appl. No.: 781,044

Assignee:

Barradell-Smith et al. ..65l99 Warren ..65 /99 Primary Examiner-S. Leon Bashore Assistant Examiner-] B. liardaway Attorney-Pennie, Edmonds, Morton, Taylor and Adams ABSTRACT Float glassmaking apparatus comprises a chamber containing a bath of molten tin. The chamber has glass inlet and outlet openings, and heating and cooling elements having each a coolant flow circuit therein are disposed lengthwise of the glass flow path through the chamber. These elements are ar- Foreign Application Priority Data Dec. 4, 1967 Germany ..F 35311 us. 01 ..65/162, 65/99 A, 65/182 R, 65/204, 65/356 Int. Cl.

Field of Search justment of the transverse position of the elements.

References Cited UNITED STATES PATENTS /1927 Hitchcock 5 /13 7 10 Claims, 13 Drawing Figures PATENTEDMAR 14 I972 3.649.237

PATENTED MR 1 4 I972 SHEET 3 [IF 8 V mw mm nna 1 HNM W S. w lliH 9 L NB N H R mm Q? flin 8 x mm mm INVENTORS. FRANZ CLASSEN KARL KAES BY GUNTER LABROT HEINZ PAPE MW ATTORNEYS PAFENTEDMAR 14 m2 SHEET '4 BF 8 ATTORNEYS LABROT PAPE W INVENTORS. FRANZ CLASSEN BY KARL KAES GUNTER 6 HEINZ f I w} PATENTEUMAR 14 I972 SHEET 5 OF 8 KARL KAES GUNTER LABROT HENZ PAPE 'f ria i ATTORNEYS PATENTEUHAR 14 I972 SHEET 6 OF 8 E i E fi.

Fm mm NW INVENTORS. FRANZ CLASSEN KARL KAES BY GUNTER LABROT HEINZ PAPE ATTORNEYS PATENTEBMAR 14 I972 3,649,237

SHEET 7 OF 8 Dbe #7? sTm I A: g z 2 2: In 3 m5 H Q fim a2 :2 :2 a! at g C H H m. E 2 wk I NZ PAPE FLOAT GLASS APPARATUS WITH ADJUSTABLE COOLING MEANS The invention relates to the continuous production of an endless ribbon or strip of flat glass on a bath of molten metal such as tin, above which a protective gas atmosphere is maintained. Known installations for this purpose comprise a tank or vessel defining a chamber in which the molten metal is contained, the chamber being closed except for an inlet opening at which the molten glass enters and an outlet opening through which the solidified glass ribbon emerges. Supply lines for a protective gas also pass into the vessel, which is moreover provided with heating and cooling elements disposed along the path traversed by the glass ribbon in its passage through the chamber, which may be referred to as a float tank or chamber.

The term cooling element is used herein to denote a temperature control device comprising a channel or conduit through which a heat exchange medium is caused to flow, either to deliver heat to the environment in which the element is located, in which case the element acts as a heating element, or to withdraw heat therefrom, in which case the element acts as a cooling element.

In known apparatus of this kind the cooling elements take the form of tubes through which coolant flows and which extend across the metal bath from one sidewall of the float tank to the other, passing through the sidewalls at gastight joints. It has also been proposed to use cooling tanks of fixed size, through which coolant likewise flows, that are mounted centrally above the metal bath inside the float tank. The supply and discharge lines to these cooling tanks also pass through the sidewalls of the float tank at gastight joints with the latter. These lines may simultaneously serve for supporting the cooling tanks from the sidewalls of the float tank, as disclosed for example in German Pat. No. 1,212,257.

In these known systems the cooling elements are concentrated at the entering end of the float tank, where the molten glass spreads out over the bath of tin, and at the downstream end of the float tank adjacent the glass discharge opening thereof. The cooling elements at these two ends of the float tank perform different functions. At the entering end it is necessary to insure that the glass spreads out over the bath of tin in a layer of uniform thickness, and this in turn requires that closely controlled constant temperatures be maintained across the width of the bath and above the layer of glass. Due to the high heat losses through the sidewalls of the tank, there tends to be developed a relatively steep temperature gradient between the centerline of the tank and the sides thereof. Consequently, in order to compensate for this temperature gradient, the cooling must be more effective in the central part of the tank, i.e., along the longitudinal centerline thereof, than at the sides thereof. The width of the central strip thus defined, where more intense cooling is required, may vary according to the width and the thickness of the glass ribbon being produced and also on other operating conditions.

The cooling devices heretofore proposed do not permit free and arbitrary variation in the dimensions of the cooling elements effective inside the float chamber. It is however desirable to be able to vary those dimensions, and it may be necessary to do so. Thus for example, the cooling surfaces must be matched or adjusted to changes in the thickness and/or width of the glass ribbon being produced. Even without change in the dimensions of the glass ribbon, it may be necessary to change the distribution of temperatures crosswise of the tank since those temperatures may, unless suitably adjusted, produce nonuniform viscosity of the glass and hence variation in the thickness of the ribbon crosswise thereof. Such undesirable temperature distributions may occur, e.g., if the action of the cooling elements is impaired by fouling or obstruction thereof, limiting the flow of coolant therethrough. Such an undesirable distribution of temperatures may also arise if the melt of glass entering the float tank does not have a completely uniform temperature.

In apparatus of the kind to which the invention relates it has heretofore been necessary, in order to counteract these effects, to remove the cooling elements from the chamber and to replace them with others having cooling surfaces of different shapes or dimensions.

In general, the cooling elements near the outlet end of the chamber have the function of holding the temperature of the glass ribbon constant within narrow limits. It is desirable that the temperature of the glass ribbon be as low as possible upon emergence from the float tank in order to minimize its sensitivity to mechanical damage during takeoff. On the other hand however, as the temperature falls, the risk of breakage increases substantially. In view of these conflicting requirements it is necessary, at least at selected stations lengthwise of the chamber, that the temperature be kept within a very narrow range of only a few degrees centigrade, the temperature being of course not necessarily the same at different such stations.

It is also desirable that the cooling elements at the outlet end of the float tank be designed to be rapidly and, if necessary, automatically removed if, e.g., for some reason the temperature of the glass ribbon at the outlet end of the chamber falls below the permissible limit so that the risk of breakage suddenly increases, or if the ribbon has broken, because then the glass beneath the cooling elements would immediately become frozen in, resulting in a lengthy shutdown.

It is therefore an object of the invention to provide an improved cooling system that makes it possible to withdraw the cooling elements rapidly from the float chamber and to insert them rapidly into it. It is another object of the invention to provide cooling apparatus for glass float tanks which is readily capable of modifying the cooling action on the glass ribbon in its transverse direction so as to adapt the cooling action to changed circumstances, such as those resulting from changes in glass manufacture or from malfunctions at any point in the process, e.g.

In accordance with the invention there is provided, in a glass float tank of the type hereinbefore described, cooling apparatus comprising at least one pair of cooling elements extending transversely of the float tank from the opposite sidewalls thereof and having each a separate coolant flow circuit, these cooling elements being independently adjustable in position crosswise of the float tank and/or in inclination to the horizontal. The cooling apparatus of the invention can be employed at any location within the float tank. It can be used, e.g., to effect stronger cooling of the edge portion of the glass ribbon than of the center portion thereof. This is necessary for example in the manufacture of a glass ribbon of a particular, small thickness which must be stretched laterally by means of edge clamps to prevent the ribbon from contracting in width as it would otherwise do to achieve its natural thickness, namely that which the ribbon would take on if allowed to respond fully to the surface tension properties of the glass and of the metal bath. In such a case the edge portions of the glass ribbon must be strongly cooled in order to make it possible to grasp the ribbon at the edges thereof.

Another advantage of the invention is that plants employing it can be constructed with smaller clearances between sides of the float tank and the walls of the shop, since it is no longer necessary as heretofore to be able to withdraw the cooling elements on each side of the float tank.

According to a further feature of the invention, the two cooling elements of one or more pairs are staggered in position lengthwise of the float tank so as to make possible a partial overlapping of the two in their position crosswise of the float tank. This makes possible a more intense cooling of that portion of the width of the ribbon in which the two elements overlap. The location of the overlap can be adjusted by adjusting the position of the cooling elements crosswise of the tank and the extent of the overlap can be adjusted by adjusting one element with respect to the other.

By providing plural pairs of cooling elements disposed adjacent each other longitudinally of the float and by adjusting the extent of crosswise overlap of the cooling elements of each pair, it is possible in accordance with the invention to obtain a plurality of zones of graduated cooling transversely of the bath.

The cooling elements may be provided on the upper surface thereof with thermal insulation so as to confine their cooling action to the lower side thereof which is presented to the glass ribbon. An advantage of such a layer of thermal insulation is that the temperature imposed by the glass on the lower side of the cooling elements is higher than it would otherwise be. This results in a reduction in the amount of condensation products which form on the cooling elements and which have a tendency to produce defects in the surface of the glass ribbon when they fall from the cooling elements onto the glass ribbon.

To intensify their cooling action or to compensate for any reduction in the cooling action of the cooling elements resulting from the application of thermal insulation thereto, cooling fins can be provided on those cooling elements, preferably on the lower surface thereof and preferably extending longitudinally of the float tank.

Desirably, in accordance with the invention, each cooling element is supported on a mount disposed outside the float tank and constructed to permit insertion and withdrawal of the cooling element to any desired position.

In accordance with another feature of the invention, the coolers can be made to pivot or swing in vertical andlor horizontal planes about locations adjacent the openings in the sidewalls of the float tank at which they enter it. By pivoting the cooling elements in vertical planes it is possible to achieve a variation in cooling effect crosswise of the glass ribbon, whereas pivoting them for motion in horizontal planes produces a time shift in relation to the cooling of the edges and center of the ribbon, which in some cases may be advantageous.

The cooling system of the invention is well suited for the automatic control of glass ribbon temperature. According to a further feature of the invention a series of temperaturerecording devices are installed inside the float tank and above the float, at suitable locations crosswise thereof. The measured temperatures can then be used to control the cooling elements, their positions, and the flow of coolant therethrough, so that temperature equalization is achieved by intensified cooling at points of elevated temperature.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described in terms of a number of presently preferred nonlimitative exemplary embodiments thereof and with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal vertical sectional view through a float tank for the production of float glass in accordance with the invention;

FIGS. 2 and 3 are fragmentary plan sectional views through a float tank in accordance with the invention, illustrating a pair of cooling elements of the invention in two different relative positions;

FIG. 4 is a plan sectional view similar to that of FIGS. 2 and 3 but illustrating a second form of cooling element according to the invention;

FIG. 5 is a plan sectional view similar to that of FIG. 2 but illustrating two pairs of cooling elements in accordance with the invention having different amounts of overlap transversely of the float tank;

FIGS. 6 and 7 are transverse vertical sectional views of a float tank in accordance with the invention, showing cooling elements thereof in two different angular orientations with respect to the bath;

FIG. 8 is an enlarged view, illustrating the gastight means provided for passage of the cooling elements of the invention through the sidewalls of the float tank;

FIG. 9 is a diagrammatic view of a temperature measuring circuit in accordance with the invention for controlling the position of the cooling elements of the invention transversely of the float tank;

FIG. 10 is a circuit diagram of apparatus usable in conjunction with that of FIG. 9; and

FIGS. 11A, 11B and 11C are fragmentary plan sectional views similar to that of FIG. 2, illustrating the positions assumed by the cooling elements of two pairs of cooling elements as a function of temperature measurements made with the apparatus of FIG. 9.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. I illustrates a plant in accordance with the invention for the manufacture of flat glass by the so-called float method. In FIG. I molten glass indicated at I flows from a furnace (not shown) over a fixed dam 2 and beneath an adjustable gate 3 into a float tank 6 at an inlet opening 1' thereof. Inside the tank the glass spreads out over a bath 5 of molten tin, forming a layer 5 of uniform thickness. The layer extends lengthwise of the tank in the shape of a strip or ribbon, and takeoff rolls 7 disposed outside the tank beyond an outlet opening I0 withdraw the glass in the form of an endless ribbon. To prevent oxidation of the tin a protective gas is introduced into the space inside the chamber 6 above the tin bath at a pressure slightly above atmospheric through inlet lines indicated at 11, 12 and 13.

Cooling elements for heating or cooling the glass are shown schematically in FIG. I at 14, I5 and I6 and are disposed inside the chamber above the molten tin along the length of the chamber. Whether heat must be supplied to the bath or removed therefrom depends essentially on the design of the plant and on the operating conditions therein. Thus, e.g., for the manufacture of glass of small thickness, heat must be supplied at various points lengthwise of the chamber in order to maintain the necessary temperature gradient lengthwise of the chamber. When instead the ribbon of glass is desired to be thick, the temperature profile is adjusted primarily with the help of elements through which a coolant is circulated so as to remove heat.

The primary function of the cooling elements M near the upstream end of the chamber is to effect temperature equalization across the width of the chamber and hence across the width of the glass ribbon. The downstream elements 16 serve primarily to adjust the temperature level of the glass at their location to a desired absolute value and to hold it there.

Referring now to FIG. 2, there is shown a first embodiment of the cooling system of the invention. The cooling system of FIG. 2 comprises two rectangular

tubular cooling elements

20 and 21 which project through the side walls of the chamber 6 into the interior thereof. The

openings

22 and 23 through the sidewalls are closed off by means of

bellows

24 and 25 coupled between the chamber side walls and the cooling elements. Exteriorly of the chamber the cooling elements rest on rollers 26 beneath them and are held in contact with those rollers by an upper roller 27 for each of the cooling elements. See FIGS. 6 and 7. These rollers permit the cooling elements to be displaced lengthwise of their own axes, i.e., transversely of the chamber 6. A heat exchange medium which may serve either for heating or cooling flows through each of the cooling elements, entering at 28 and leaving at 29 as illustrated in FIG. 2.

The two

cooling elements

21 and 22 of the pair shown in FIG. I are slightly staggered or displaced with respect to each other lengthwise of the chamber, i.e., of the flow path of the glass therethrough. This makes it possible to bring the two cooling elements into overlapping relation with each other as illustrated in FIG. 3. With the position of the cooling elements shown in FIG. 2, in which the two do not overlap, there is obtained substantially the effect of a single cooling element extending entirely across the chamber whereas when the two are in overlapping relation as illustrated in FIG. 3, there is obtained an increased cooling effect over a portion A of the width of the chamber measured by the extent of overlap of the two cooling elements. In the edge portions B a smaller cooling effect obtains, where the two cooling elements do not overlap.

A second embodiment of the invention is illustrated in FIG. 4. In this embodiment the two

cooling elements

30 and 31 are provided with beveled or tapered ends as indicated at 32 and 33 so as to provide a graduated cooling effect over that portion of the width of the bath occupied by these tapered end portions. Thus in FIG. 4 a doubled cooling effect (that of two cooling elements) is obtained over the width range A in which the two cooling elements overlap each other in their full width, which width is measured lengthwise of the tank 6. Over the ranges A of the width of the bath there is obtained a graduated cooling effect varying between that of two cooling elements and that of one, whereas over the width ranges B the cooling effect is that of one element only. The width ranges B are those at or near which the edges of the glass ribbon 5 are located.

By providing two or more pairs of cooling elements side by side as indicated in FIG. 5, there can be obtained even more intense cooling effect in the middle of the chamber, with a graduation as desired from the middle out toward the edges. Thus in FIG. 5 there are provided two pairs of

cooling elements

36, 39 and 37, 38 of the type shown in FIG. 4. Over a width zone C the four cooling elements overlap in their full width to provide maximum cooling effect from all four cooling elements. In the adjacent width zones D, the cooling effect is that of three cooling elements plus a fraction of a fourth cooling element diminishing from unity at the edges of the zone C to zero at the outer edges of the zones D. In the next outer zones E the cooling effect is that of two cooling elements plus a similarly diminishing fraction of a third cooling element, and in the outermost zones F the cooling efiect is constant, namely that provided by two cooling elements.

In the embodiments of the invention thus far described more cooling has been provided at the middle of the glass ribbon than at the edges thereof. It is however possible to adjust the position of the cooling elements crosswise of the chamber so as to put the zone of maximum cooling at any desired location crosswise of the float chamber.

FIGS. 6 and 7 illustrate an embodiment of the invention in which the cooling elements can be rotated in vertical planes so as to vary the separation inside the chamber between the glass ribbon and the cooling elements. To this end in FIGS. 6 and 7 the

rollers

26 and 27 are disposed on the ends of screws 42 threaded into fixed support members 42. Handwheels 43 are provided to turn the screws. Suitable means not shown are provided to maintain the axes of the

rollers

26 and 27 parallel to the lengthwise axis of the chamber 6, i.e., perpendicular to the plane of FIGS. 6 and 7.

The cooling elements 40 and 41 of FIG. 6 are provided with layers of

thermal insulation

44 and 45 on the upper surface thereof inside the chamber so as to limit the cooling action thereof substantially to the underside thereof. They are moreover provided with fins 41' on their lower surfaces, preferably extending parallel to the long dimension of the chamber, i.e., perpendicular to the plane of FIG. 6, for increased heat transfer effect on their undersides.

By means of pivotal mounting of the cooling elements as illustrated in FIGS. 6 and 7, the separation of the cooling elernents from the glass ribbon may be varied. This provides a further means of controlling temperature crosswise of the ribbon 5. Thus with the cooling elements pivoted upwardly as in FIG. 6, the cooling effect thereof will be reduced at the middle of the ribbon compared to the cooling effect thereof at the edges of the ribbon. Conversely with the cooling elements pivoted downwardly as illustrated in FIG. 7 their cooling effect will be greater at the middle of the ribbon than at the edges thereof. Of course the cooling elements illustrated in FIGS. 6 and 7 may overlap each other crosswise of the float chamber in the manner illustrated in FIGS. 3 and 4. The support of the cooling elements may also or alternatively be arranged to allow the cooling elements to pivot in substantially horizontal planes, again substantially about their points of passage through the sidewalls of the chamber.

FIG. 8 illustrates one form of sealing mechanism which can be used in the invention to provide a substantially gastight joint between the cooling elements and the sidewalls of the float chamber, while retaining freedom of motion for the cooling elements and facilitating rapid withdrawal or change thereof.

The opening 22 through the wall of the chamber 6 traversed by the cooling element is surrounded by a frame 50 of U- shaped profile. Eyes 51 are welded to the lower side of the frame 50 on the exterior thereof. The lower ends 54 of a frame comprising two bars 53 is inserted into the openings 52 of these eyes. The upper ends 55 of the bars 53 hook over the frame 56. A frame 57 is fastened to the frame of the bars 53 by means of bolts 58 in such fashion that the frame 57 can be adjusted horizontally. The frame 57 is pressed at a gasket 51 against the sealing surface of the frame 50 by operation of eccentric levers 60 on the frame of bars 53. A bellows 62 of gastight flexible material, such as metal or coated asbestos cloth, is mounted on frame 57, and provides for relative motion between the cooling element 20 and the chamber wall 6. A gland-type seal is provided between the outer end of the bellows and the cooling element. This seal comprises a hollow ring 63 engaged about the cooling element with an annular gasket 64 inside the ring 63. An annular wedge 65 and screws 66 squeeze the gasket between the cooling element and the ring 63.

The bellows 62 provide the flexibility necessary for motions of the cooling elements required in normal operating adjustments. For greater motions of the cooling elements, the screws 66 may be loosened to permit motion of the cooling element with respect to the gland. Labyrinth-type seals may be employed in place of gland 63.

FIG. 9 is a schematic representation of a control system for adjustment of the position of the cooling elements A1 and A2 shown in that figure, in accordance with variations in temperature across the width of the ribbon 5 inside the chamber 6. In the control system of FIG. 9 reference characters TI through T5 identify temperature measuring devices mounted inside the chamber at intervals crosswise thereof and above the bath. The devices TI to T5 are moreover located downstream of the cooling elements Al and A2 in the sense of glass travel. The temperature representative signal generated by the device T3 at the middle of the chamber constitutes a reference temperature signal, and the differences between the temperatures measured there and at the other devices Tl, T2, T4 and TS serve to control adjustment in the positions of the cooling elements A1 and AZ. By application of a countervoltage of constant value, the voltage generated by each temperature measuring device is reduced to a value just below that correspond ing to the set value temperature at each position. In this way there is obtained good resolution of the temperature intervals to be measured.

The residual voltage differences thus obtained are fed to transformers MU (FIG. 10) where they are amplified and converted to direct currents. These direct currents produce voltage drops at resistors Rl through R5 which are proportional to the measured temperatures.

The voltage drops thus obtained are compared with voltage drops developed at resistors R3 associated with the central temperature measuring device T3. These comparisons yield difference voltages which, in turn, correspond to the temperature difierences between the respective measuring points and the temperature at the center of the glass ribbon. These difference voltages are connected to limit the value annunciators G1 through G5 which may, as illustrated in FIG. 10, take the form of measuring devices with separately adjustable maximum value contacts XWl through XWS and minimum value contacts XWI' through XWS respectively.

These contacts are interrogated periodically by an interrogating timer AZ, the interval between two interrogations being at least equal to the time required for a point on the glass ribbon to travel from the cooling elements Al and A2 to the temperature measuring devices T1 through T5 of FIG. 9. If one or more of the contacts XWl to 5 and XWl' to 5' are in closed condition at the time of interrogation (closure of the contacts coupled to interrogator AZ), i.e., if an unwanted temperature difference is present, one or more of relays CI to C4 will be energized, thereby energizing one or both of the motors MI and M2 of FIG. 9. This will drive the cooling elements A1 and/or A2 to appropriate positions, via mechanical couplings N1 and N2. when relay C1 operates, the motor M2 is caused to turn in a direction such that cooling element A2 is withdrawn from the float chamber, whereas when relay C2 operates the direction of the current supplied to the motor M2 is reversed, so that it inserts element A2 into the chamber. The relays C3 and C4 function similarly, C3 controlling the insertion of element A1 and C4 its withdrawal. The positions to which the cooling elements are driven in response to these relay actuations can be accurately fixed by means of the limit switches E1 through E4, actuated by the cooling elements in their motions.

In FIG. an emergency switch NA operates, when actuated, to withdraw all cooling elements from the chamber and to render the automatic control circuit inoperative. Immediate withdrawal of the coolers is necessary, for example, if the glass ribbon should break, in order to prevent the glass from freezing in beneath the coolers.

FIG. 11 shows three examples of different cooling element positions controlled by the apparatus of FIGS. 9 and 10.

The cooling element position shown in FIG. 11A corresponds to the condition in which the temperature measured at T4 is too high as compared with the temperature measured at T3 by a value preset in limit value indicator G4 (FIG. 10). Accordingly, the cooling element A], which under normal conditions is inserted like the element A2 to the middle of the glass ribbon and thus serves to cool the glass ribbon uniformly over its full width, has advanced to the position of the temperature measuring device T4. Because the temperature measured at T4 exceeds the maximum value preset at the limit indicator G4, contacts XW2 close. Relay C3 is thereby energized, the limit switch E3 being still closed. Closing of relay C3 causes the motor M1 to drive the cooling element A1 into the chamber until the cooling element opens the limit switch E3, the limit switch being so positioned that when it is thus opened the inner end of the cooling element Al extends to and beyond the transverse position of the temperature-measuring device T4 as indicated in FIG. 11A. The cooling element A2 is in its normal position extending to and just past the center line of the chamber or float tank. Hence a doubled cooling effect is achieved across that portion of the tank width separating the temperature measuring devices T3 and T4. If instead the temperature at T4 should fall below that at T3, the cooling element Al will be withdrawn to its starting position, namely that indicated for it in FIG. 11C.

In FIG. 11B two pairs of cooling elements are operative. FIG. 11B corresponds to a case frequently encountered in which the temperature falls off from the centerline of the chamber toward the edges, so that TI T2 T3 T4 T5. With'this temperature distribution the cooling elements BI and B2 are additionally inserted into the chamber, overlapping each other between the positions identified by the temperature measuring devices T2 and T4. At the centerline all four cooling elements are operative. At the positions of the temperature-measuring devices T2 and T4, three coolers are operative, whereas at the edges of the ribbon, i.e., at the locations of the devices T1 and T5, only two cooling devices are operative.

FIG. 11C in turn illustrates a disposition of the two pairs of cooling elements providing intensified cooling at the centerline and also at the edges of the glass ribbon.

While the invention has been described hereinabove in terms of a number of presently preferred embodiments thereof, the invention itself is not limited thereto, but rather includes all modifications of and departures from those embodiments properly falling within the spirit and scope of the appended claims.

We claim:

1. Apparatus for the manufacture of flat glass by the float method comprising a substantially closed vessel containing a bath of molten metal and having opposite sidewalls between glass inlet and outlet openings and having at least one aperture in each of said sidewalls, at least one pair of cooling elements having separate closed coolant flow circuits therethrough, each of said elements having a length more than half the width of said vessel between the sidewalls thereof, the two elements of each pair being displaced with respect to each other lengthwise of the glass flow from said inlet to said outlet opening, whereby said elements may be positioned in at least partly overlapping relation, and means outside said vessel adjustably supporting each of said elements in cantilever fashion to extend through one of said apertures at least part way across the vessel above said bath.

2. Apparatus according to claim 1 wherein said supporting means comprise releasable locking means permitting motion of said elements lengthwise thereof.

3. Apparatus according to claim wherein each cooling element is provided with thermally insulating material over at least part of the upper surface thereof.

4. Apparatus according to claim 1 wherein each cooling element includes cooling ribs on the underside thereof.

5. Apparatus according to claim 1 in which each of said elements is tapered in width over at least a part of the length thereof.

6. Apparatus according to claim 1 including a plurality of pairs of cooling elements disposed along the glass flow path between said inlet and outlet openings.

7. Apparatus according to claim 1 wherein said supporn'ng means define for each cooling element a pivot point adjacent a sidewall of the vessel about which the cooling element is rotatable in a substantially vertical plane.

8. Apparatus according to claim 1 wherein said supporting means define for each cooling element a pivot point adjacent a sidewall of the vessel about which the cooling element is rotatable in a substantially horizontal plane.

Q. Apparatus according to claim I further including for each of said cooling elements motor means to reversibly advance and withdraw said cooling element through a sidewall of the vessel, and temperature-measuring means within the vessel for control of said motor means.

10. Apparatus according to claim 1 further including for each of said cooling elements a substantially gastight seal about said cooling element at its passage through the sidewall of the vessel, said seal including a flexible bellows.

Claims

3. Apparatus according to claim 1 wherein each cooling element is provided with thermally insulating material over at least part of the upper surface thereof.

7. Apparatus according to claim 1 wherein said supporting means define for each cooling element a pivot point adjacent a sidewall of the vessel about which the cooling element is rotatable in a substantially vertical plane.

9. Apparatus according to claim 1 further including for each of said cooling elements motor means to reversibly advance and withdraw said cooling element through a sidewall of the vessel, and temperature-measuring means within the vessel for control of said motor means.