WO2013043399A1

WO2013043399A1 - Isolator for use in separating glass sheets from a glass ribbon

Info

Publication number: WO2013043399A1
Application number: PCT/US2012/054383
Authority: WO
Inventors: Gautam N KUDVA; Terry Jay OTT
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2011-09-20
Filing date: 2012-09-10
Publication date: 2013-03-28
Anticipated expiration: 2014-03-20
Also published as: JP2014530165A; TWI589536B; TW201315690A; KR101906642B1; KR20140065400A; JP6072043B2; CN104039718A; CN104039718B

Abstract

An isolator assembly (13) is disclosed for use between a pull roll assembly (140) and a scoring/separating assembly (150) of a glass manufacturing system (100) which produces a glass ribbon (11) from which glass sheets (15) are separated. The isolator assembly (13) includes S-shaped edge guides (30) which engage opposing edges of the ribbon (11) and cause the ribbon's centerline (18) to traverse an S-shaped curve as it passes through the isolator assembly (13). The isolator assembly (13) reduces motion of and/or stress in the glass ribbon (11) above the assembly (13) as a result of forces applied to the ribbon (11) below the assembly (13) by the scoring/separating assembly (150). Methods for producing glass sheets (15) using the isolator assembly (13) and a glass manufacturing system (100) employing the assembly (13) are also disclosed.

Description

ISOLATOR FOR USE IN SEPARATING GLASS SHEETS FROM A GLASS RIBBON

[0001] This application claims the benefit of priority of US Provisional Application Serial No. 61/536,607 filed on September 20, 2011 the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

[0002] This disclosure relates to the manufacture of glass sheets and, in particular, to methods and apparatus for separating individual glass sheets from a moving glass ribbon.

DEFINITIONS

[0003] Throughout this disclosure, the following phrases/terms shall have the following meanings/scope:

(1) The word "glass" includes both glass and glass-ceramics.

(2) The phrase "substantially vertical" means within ±10° of perfectly vertical.

(3) The phrase "substantially flat" means that the maximum deviation from

perfectly flat is less than or equal to 20 millimeters.

BACKGROUND

[0004] The fusion process is one of the basic techniques used in the glass making art to produce sheet glass. See, for example, Varshneya, Arun K., "Flat Glass," Fundamentals of Inorganic Glasses, Academic Press, Inc., Boston, 1994, Chapter 20, Section 4.2., 534-540. Compared to other processes known in the art, e.g., the float and slot draw processes, the fusion process produces glass sheets whose surfaces have superior flatness and smoothness. As a result, the fusion process has become of particular importance in the production of the glass substrates used in the manufacture of displays such as liquid crystal displays (LCDs).

[0005] The fusion process, specifically, the overflow downdraw fusion process, is the subject of commonly assigned U.S. Patents Nos. 3,338,696 and 3,682,609, to Stuart M. Dockerty. A schematic drawing of an exemplary glass manufacturing system 100 that uses the fusion process to make glass sheets 15 is shown in FIG. 1. As shown therein, the glass manufacturing system 100 includes a melting vessel 110, a fining vessel 115, a mixing vessel 120 (e.g., stir chamber 120), a delivery vessel 125 (e.g., bowl 125), a fusion draw machine (FDM) 141 and a traveling anvil machine (TAM) 150. [0006] The melting vessel 1 10 is where the glass batch materials are introduced as shown by arrow 112 and melted to form molten glass 126. The fining vessel 115 (e.g., finer tube 115) has a high temperature processing area that receives the molten glass 126 (not shown at this point in FIG. 1 ) from the melting vessel 110 and in which bubbles are removed from the molten glass 126. The fining vessel 115 is connected to the mixing vessel 120 (e.g., stir chamber 120) by a finer to stir chamber connecting tube 122, and the mixing vessel 120 is connected to the delivery vessel 125 by a stir chamber to bowl connecting tube 127.

[0007] The delivery vessel 125 delivers the molten glass 126 through a downcomer 130 into the FDM 141 which includes an inlet 132, a forming vessel 135 (e.g., isopipe 135), and a pull roll assembly 140. As shown, the molten glass 126 from the downcomer 130 flows into inlet pipe 132, through opening 136 in the side of forming vessel 135, and then into the forming vessel's trough 137. The molten glass overflows the top of trough 137 (i.e., it overflows the trough's weirs) and runs down the two sides 138a and 138b of the forming vessel before fusing together at what is known as the root 139. In particular, the root 139 is where the two sides 138a and 138b of the forming vessel come together and where the two overflowing sheets of molten glass 126 join together to form glass ribbon 11 which is drawn downward by the pull roll assembly 140.

[0008] Because the glass ribbon is thicker at its edges (the "beads") than it is in the center, the ribbon exhibits different cooling rates in the across-the-ribbon direction. These different cooling rates, in turn, impart temporary shapes to the ribbon (e.g., bow) in both the across- the-ribbon and the down-the-ribbon directions.

[0009] The pull roll assembly 140 delivers the drawn glass ribbon 11 (which at this point in the process has a curved/bowed shape) to scoring/separating assembly 150 (e.g., a traveling anvil machine or TAM), which in its base form includes a flat nosing device 152 and a scoring device 154 that are used to score and separate the bowed glass ribbon 11 into distinct glass sheets 15 (see the enlarged top view of the TAM 150 illustrated in FIG. 1). The scoring device 154 is not used until after the flat nosing device 152 engages the bowed glass ribbon 11. In a process known as "pressing," the ribbon tends to become flattened as it engages the flat nosing. The scoring device 154 then extends a scoring wheel 156 which scores the glass ribbon 11 and also pushes the ribbon even more against the nosing (a process known as "ironing"). After scoring, the flattened glass ribbon 11 is bent in a direction perpendicular to it's original curved surface and separated to create an individual glass sheet (see sheet 15 below scoring/separating assembly 150 in FIG. 1). [0010] The pressing, ironing, scoring and separating processes cause motion in the glass ribbon 1 1 which travels up the continuous ribbon. These motion sources in turn contribute to the creation of two attribute issues to the final product or glass sheets 15. First, motion may create internal stress variations within the ribbon and thus in glass sheets cut from the ribbon. Second, this lower motion may cause a shape change in the visco-elastic portion of the ribbon and thereby "freeze" a shape into the product. A stressed glass sheet 15 can distort/warp and when a stressed sheet is cut into smaller pieces by, for example, a display manufacturer, those smaller pieces can distort/warp. In view of the tight tolerances associated with display manufacturing, minimizing such distortion/warpage is an important challenge to glass manufacturers.

[0011] A number of technologies have been developed to help reduce the motion of the glass ribbon 11 and thus help reduce the creation of internal stress variations within the ribbon while it is being scored/separated into individual glass sheets. For example, commonly-assigned U.S. Patent No. 7,895,861 describes the use of conformable nosing devices which more closely match the shape of the ribbon during scoring and separation, while commonly-assigned U.S. Patent Application Publication No. US 2006/0042314 describes the use of various non-contact stabilization devices to reduce ribbon motion.

[0012] Although these approaches reduce the problems associated with stress generation caused by ribbon motion and the sheet scoring/separation process, as glass ribbons become thinner and/or wider, the problems become more pressing and more difficult to solve.

Consequently, additional measures for addressing the problems are needed. The present disclosure provides methods and apparatus for substantially isolating the sheet

scoring/separation process from the ribbon creation process and thus reduce both the adverse effects of ribbon motion and ribbon shape on the sheet scoring/separation process and the adverse effects of the sheet scoring/separation process on the ribbon creation process.

SUMMARY

[0013] In accordance with a first aspect, a glass manufacturing system (100) is disclosed which includes:

(a) at least one vessel (110,115,120,125) for melting batch materials and forming molten glass;

(b) a forming vessel (135) for receiving the molten glass and forming a glass ribbon (11) which has a centerline (18) and two opposing edges; (c) a pull roll assembly (140) for drawing the glass ribbon (11 ) in a substantially vertical direction; and

(d) a scoring/separating assembly (150) for scoring and separating the glass ribbon (11) into individual sheets (15);

wherein the system (100) includes an isolator system (13) between the pull roll assembly (140) and the scoring/separating assembly (150) for reducing motion of and/or stress in the ribbon (11) above the isolator system (13) as a result of forces applied to the ribbon (11) below the isolator system (13) by the scoring/separating assembly (150), the isolator system (13) including S-shaped edge guides (30) which engage the two opposing edges of the ribbon (11) and cause the centerline (18) of the ribbon to traverse an S-shaped curve as it passes through the isolator system (13), the centerline (18) of the ribbon (11) being substantially vertical both before it enters and after it leaves the isolator system (13).

[0014] The reference numbers used in the above and below summaries of the various aspects of the invention are only for the convenience of the reader and are not intended to and should not be interpreted as limiting the scope of the invention. More generally, it is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention.

[0015] Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as exemplified by the description herein. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. It is to be understood that the various features of the invention disclosed in this specification and in the drawings can be used in any and all combinations, as exemplified by the following additional aspects.

[0016] In accordance with a second aspect, there is provided the glass manufacturing system of aspect 1 wherein each of the S-shaped edge guides comprises a plurality of rollers, each roller having a diameter sufficiently small so that the glass ribbon does not conform to the surface of the roller.

[0017] In accordance with a third aspect, there is provided the glass manufacturing system of aspect 2 wherein (i) each of the S-shaped edge guides has an upper and a lower section which are concave in opposite directions, (ii) each section has a radius of curvature R, and (iii) each roller has a diameter that is less than or equal to R/n where n is greater than 5. [0018] In accordance with a fourth aspect, there is provided the glass manufacturing system of any one of aspects 1-3 wherein each of the S-shaped edge guides has an upper and a lower section, each of which has a radius of curvature R that satisfies the relationship:

0.3 < R < 5,

where R is in meters.

[0019] In accordance with a fifth aspect, there is provided the glass manufacturing system of any one of aspects 1-4 wherein each of the S-shaped edge guides has an upper and a lower section, the upper section having an entrance for the glass ribbon and the lower section having an exit for the glass ribbon, the exit being horizontally offset from the entrance by a distance J that satisfies the relationship:

1 < J < 25,

where J is in millimeters.

[0020] In accordance with a sixth aspect, there is provided the glass manufacturing system of any one of aspects 1-5 wherein each of the S-shaped edge guides has a vertical height H that satisfies the relationship:

25 < H < 100,

where H is in centimeters.

[0021] In accordance with a seventh aspect, an isolator system (13) is disclosed for use between a pull roll assembly (140) and a scoring/separating assembly (150) of a glass manufacturing system (100) which produces a glass ribbon (11) from which glass sheets (15) are separated, the isolator system (13) including S-shaped edge guides (30) which, during use, engage opposing edges of the ribbon (11) and cause the ribbon's centerline (18) to traverse an S-shaped curve as it passes through the isolator system (13) with the centerline (18) being substantially vertical both before it enters and after it leaves the isolator system (13), wherein, during use, the isolator system (13) reduces motion of and/or stress in the glass ribbon (11) above the isolator system (13) as a result of forces applied to the ribbon (11) below the isolator system (13) by the scoring/separating assembly (150).

[0022] In accordance with an eighth aspect, there is provided the isolator system of aspect 7 wherein each of the S-shaped edge guides comprises a plurality of rollers, each roller having a diameter sufficiently small so that the glass ribbon does not conform to the surface of the roller.

[0023] In accordance with a ninth aspect, there is provided the isolator system of aspect 8 wherein (i) each of the S-shaped edge guides has an upper and a lower section which are concave in opposite directions, (ii) each section has a radius of curvature R, and (iii) each roller has a diameter that is less than or equal to R/n where n is greater than 5.

[0024] In accordance with a tenth aspect, there is provided the isolator system of any one of aspects 7-9 wherein each of the S-shaped edge guides has an upper and a lower section, each of which has a radius of curvature R that satisfies the relationship:

0.3 < R < 5,

where R is in meters.

[0025] In accordance with an eleventh aspect, there is provided the isolator system of any one of aspects 7-10 wherein each of the S-shaped edge guides has an upper and a lower section, the upper section having an entrance for the glass ribbon and the lower section having an exit for the glass ribbon, the exit being horizontally offset from the entrance by a distance J that satisfies the relationship:

1 < J < 25,

where J is in millimeters.

[0026] In accordance with a twelfth aspect, there is provided the isolator system of any one of aspects 7-11 wherein each of the S-shaped edge guides has a vertical height H that satisfies the relationship:

25 < H < 100,

where H is in centimeters.

[0027] In accordance with a thirteenth aspect, a method of producing a glass sheet is disclosed that includes:

(a) melting batch materials to form molten glass;

(b) processing the molten glass to form a glass ribbon (1 1) which has a centerline (18) and two opposing edges;

(c) drawing the glass ribbon (11 ) in a substantially vertical direction using a pull roll assembly (140);

(d) scoring the glass ribbon (11 ) to form a score line; and

(e) separating a glass sheet (15) from the glass ribbon (11) along the score line; wherein prior to step (d), the method comprises imparting an S-shape to the glass ribbon (11) at a location below the pull roll assembly (140) so as to reduce motion of and/or stress in the ribbon (11) above the S-shape as a result of forces applied to the ribbon (11) during steps (d) and/or (e), the centerline (18) of the ribbon (11 ) being substantially vertical both before and after the S-shape is imparted to the ribbon (11). [0028] In accordance with a fourteenth aspect, there is provided the method of aspect 13 wherein the imparting of the S-shape to the ribbon causes the centerline of the ribbon to be displaced horizontally by a distance J that satisfies the relationship:

1 < J < 25,

where J is in millimeters.

[0029] In accordance with a fifteenth aspect, there is provided the method of aspect 13 or aspect 14 wherein S-shape is imparted to the ribbon over a vertical distance H that satisfies the relationship:

25 < H < 100,

where H is in centimeters.

[0030] In accordance with a sixteenth aspect, there is provided the method of any one of aspects 13-15 wherein the thickness of the glass ribbon at its edges is less than or equal to 2.5 millimeters and the imparting of the S-shape produces a maximum calculated stress in the edges of less than 35 MPa.

[0031] In accordance with a seventeenth aspect, there is provided the method of any one of aspects 13-16 wherein the thickness of the glass ribbon along the ribbon's centerline is less than or equal to 0.5 millimeters.

[0032] In accordance with an eighteenth aspect, there is provided the method of any one of aspects 13-17 wherein the imparting of the S-shape causes the ribbon to be substantially flat in the across-the -ribbon direction.

[0033] In accordance with a nineteenth aspect, there is provided the method of any one of aspects 13-18 wherein the scoring and separating is performed with a flat nosing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a schematic view of an exemplary, prior art, glass manufacturing system which employs the fusion process.

[0035] FIGS. 2-4 are graphs illustrating the effects of standard sheet scoring/separation cycles on ribbon motion (ribbon position) as a function of thickness and cycle time. The thicknesses for FIGS. 2, 3, and 4 are 0.7 mm, 0.5 mm, and 0.4 mm, respectively.

[0036] FIG. 5 is a schematic view illustrating the use of an exemplary embodiment of an isolator system of the present disclosure in the exemplary glass manufacturing system of FIG.

1. [0037] FIG. 6 is a schematic view showing a glass ribbon which has an exemplary S-shaped region therein as a result of passing through an isolator system of the present disclosure.

[0038] FIG. 7 is a schematic side view of an S-shaped edge guide of an exemplary embodiment of an isolator system of the present disclosure.

[0039] FIG. 8 is a schematic side view of an S-shaped edge guide of a further exemplary embodiment of an isolator system of the present disclosure.

[0040] FIG. 9 is a schematic side view illustrating representative parameters of an edge guide of an exemplary embodiment of an isolator system of the present disclosure.

[0041] FIG. 10 is a plot showing calculated maximum bending stress in psi (horizontal axis) in the thickest part of a glass ribbon, e.g., the beads of the ribbon, as a function of bend radius in feet (vertical axis) for thicknesses ranging from 0.5 to 3.0 millimeters.

DETAILED DESCRIPTION

[0042] FIGS. 2-4 illustrate one of the key challenges posed by a decrease in the thickness of a glass ribbon, namely, greater ribbon motion. In particular, these figures plot the center position of a glass ribbon (vertical axis) at the nosing versus time (horizontal axis) over the course of a separation cycle (single sheet cycle). Three glass thicknesses are illustrated, i.e., the standard 0.7 mm thickness (FIG. 2) and two thinner thicknesses, i.e., 0.5 mm (FIG. 3) and 0.4 mm (FIG. 4). The horizontal grid lines on these figures have a 10 mm spacing.

[0043] As is evident, as the thickness decreases, the amplitude of the motion substantially increases. As also illustrated in FIGS. 2-4, as the thickness decreases, the separation cycle becomes shorter because each glass sheet contains less glass. The shorter separation cycle further exasperates the motion problem because there is less time for the motion to damp out during any given cycle. Thus, while standard thickness products have a long enough cycle time and ribbon stiffness to allow the perturbations to be substantially damped prior to the next cycle, the faster draw speeds and shorter cycle times associated with thinner products (i.e., products having a thickness less than or equal to 0.5 mm) result in propagation of ribbon motion from one sheet cycle to the next thus leading to the risk of a runaway process.

[0044] To help stabilize a glass ribbon during its creation, it is generally desirable to provide the ribbon with a bowed shape transverse to its direction of motion (see the curvature of ribbon 11 in the enlarged view of FIG. 1). This bowing needs to be sufficiently large to avoid snapping of the ribbon from a concave -towards-the -nosing configuration to a concave- away- from-no sing configuration (referred to as a "bow pop"). [0045] As the glass ribbon becomes thinner and thus less stiff, the curvature needs to increase to avoid bow pops. However, as the curvature increases, the probability that the ribbon will crack while it is being pressed/ironed against the nosing increases. Hence, the ribbon scoring/separation process window on thin/low stiffness/large size substrates is bounded on one side by the need for a larger bow to help minimize bow pops and on the other side by the fact that too large a bow causes crackouts during separation.

[0046] Bow, bow pop, and crackouts are just three of the considerations that come into play in reconciling the need to stabilize the ribbon during its creation with need to

successfully and efficiently separate individual glass sheets from the ribbon. Other factors that affect the process include:

(1) Applied Tension— Although it does not achieve full flattening of the ribbon to the nosing, some transverse tension applied by vacuum (suction) cups is often used before scoring to help flatten the ribbon. As bow size increases for a less stiff ribbon, achieving vacuum and tensioning becomes more difficult.

(2) Scoring— The ironing process can push any bow that remains after the applied tension step to the nosing, but at times, the shape that remains after the tension is applied is sufficiently large so that the ironing pushes the shape along like a wave causing a flip in the shape of the ribbon at the end of the nosing.

(3) Bending— After ironing, there is often still some bow against the nosing, and the bending process used to achieve separation forces this bow flat against the nosing. The vertical shape component produced by this flattening can be detrimental to the stability of the sheet above the TAM.

(4) Snap— As the separated sheet snaps off of the ribbon, the ribbon's bow returns and the ribbon bounces off of the nosing. Although the edges of the ribbon (the beads) can be held in place to mitigate the risk of bow pop during the snap, the edges eventually need to be released so that the nosing can be retracted.

(5) Nosing Retraction— With the individual sheet separated, the ribbon is now short, and as the nosing retracts, the entire ribbon moves to it's starting (short ribbon) position, the full ribbon and short ribbon positions being different due to the length, weight, and 2D temperature field of the ribbon.

(6) Sheet Growth— As the ribbon grows in length and its two dimensional

temperature field changes, the ribbon bow and position along the length of the draw shifts. [0047] In accordance with the present disclosure, it has been recognized that much of the ribbon shape and ribbon motion issues arise because of a disconnect between the need for a bowed ribbon for stability and the need for a flat ribbon for the separation processes (score, bend, snap). With historic approaches, presenting a flat ribbon while maintaining process stability has proven difficult because small changes in the bottom-of-the-draw (BOD) cycle (ribbon growth, nosing retraction, sheet transfer to a conveyor which can generate wind currents) add to the risk of a bow pop.

[0048] In accordance with the disclosure, this fundamental conflict between stability and separation is addressed by isolating the lower ribbon from the upper ribbon. Specifically, as schematically illustrated in FIG. 5, an isolator system 13 is introduced between pull roll assembly 140 and scoring/separating assembly 150 to substantially isolate the upper ribbon from BOD ribbon interactions.

[0049] In an embodiment, isolator system 13 provides a continuous flat ribbon at the scoring/separating assembly 150 (e.g., at the TAM nosing) by putting the substantially vertical ribbon provided by the pull roll assembly through a catenary arc in one horizontal direction followed by a catenary arc in the opposite horizontal direction (i.e., through a jog) so the ribbon continues to travel in a substantially vertical plane after leaving the isolator. In this way, the ribbon is moving as it has in the past (i.e., substantially vertically) when it reaches the scoring/separating assembly (e.g., the TAM equipment), which is an important benefit in terms of retrofitting the isolator to existing equipment. Moreover, the "S-bend" can force the ribbon flat at the scoring/separating assembly which is a desirable configuration for the ribbon in that assembly. In addition, the "S-bend" can limit the effects of the BOD separation motions to the lower portions of the FDM where the ribbon is sufficiently cool so that it behaves substantially elastically. In this way, the generation of undesirable internal stress in the ribbon as a result of BOD motions can be reduced.

[0050] FIG. 6 schematically illustrates a glass ribbon 11 which has been subjected to S-bending in accordance with the present disclosure. As shown, the ribbon has an S-bend section 1 lb surrounded above and below by substantially vertical sections 1 la and 11c. Because of the S-bend, although sections 11a and 1 lc are both substantially vertical, they do not lie in the same plane, i.e., section 11c is jogged forward in FIG. 6 relative to section 11a. If desired, the jog could be in the opposite direction, i.e., section 11c could be jogged backward relative to section 11a. For reference, nosing line 17 is shown in FIG. 6. Although FIG. 6 is not drawn to scale, in practice, as illustrated in FIG. 6, nosing line 17 will be located relatively close to S-bend section 1 lb to take advantage of the stiffness imparted to the ribbon by the S-bend during scoring and separation.

[0051] In terms of the various factors affecting ribbon stability and the separation process discussed above, an isolator that includes an "S-bend" can provide the following benefits in various embodiments:

(a) Ribbon Bow - Bow is no longer needed for ribbon stability at the

scoring/separating assembly (e.g. the TAM). Accordingly, bow can be managed above the S-bend for ribbon stability during the creation process with the "S-bend" providing isolation for the ribbon with regard to the separation activity taking place below in the bottom of the draw region.

(b) Applied Tension - To the extent still desired, e.g., for very wide ribbons, the applied tension can be applied to a flattened ribbon which can improve the effectiveness of the applied tension and reduce variability in applied tension with process changes.

(c) Scoring, Bending, Snap - These steps can now occur on a flattened ribbon which can enhance the effectiveness of the steps and reduce variability.

(d) Sheet Growth and Nosing Retraction - Though sheet weight delta from

beginning to end of process and thermal patterns will still occur, the isolation provided by the "S-bend" can reduce the adverse effects of these changes on the forming zone and/or at least make the effects of the weight delta more consistent from cycle to cycle.

[0052] Because the central portion of the ribbon becomes the quality portion of the separated glass sheets, the S-bend is achieved through the use of edge guides that contact the edges, but not the center (quality) portion, of the ribbon. FIG. 7 shows an edge guide 30 in the form of a channel having an S-shape, while FIG. 8 shows an edge guide equipped with rollers 33 to reduce the amount of drag applied to the ribbon by the edge guide.

[0053] When rollers are used, the number of rollers (n) is selected so that in the across- the-ribbon direction, the glass ribbon makes line contact, as opposed to area contact, with the rollers, i.e., so that there are enough tangent points (tangent lines) to avoid substantial wrapping of the ribbon around individual rollers. Looked at another way, the number of rollers (n) is selected so that each roller has a diameter that is sufficiently small so that a low stiffness ribbon will ride on the surface of the roller as opposed to conforming to the radius of the roller. Such conformation is undesirable because it can cause the bending stress in the glass to exceed safe operating levels (see the discussion of FIG. 10 below). In an embodiment, for an S-bend composed of two arcs, each of radius R (see the discussion of FIG. 9 immediately below), the diameter of the rollers can, for example, be R/n where n is greater than or equal to 5.

[0054] FIG. 9 is a schematic diagram illustrating representative parameters for an edge guide designed to produce a jog whose front-to-back depth is J. Assuming J is relatively small and further assuming that the jog is composed of two arcs (two catenaries) of equal radii R, the overall equipment length of the edge guide (H_Equi_pment) can be estimated from the Pythagorean theorem as follows:

H_Equipment = 2 * J(R² - (R - J I If Eq. (1 )

[0055] In practice, H and J are selected to satisfy the competing demands of, on the one hand, reducing the across-the-ribbon bow at the separating/scoring assembly and isolating that assembly from the FDM machine, and, on the other hand, holding the overall length of the draw substantially constant or, at least, not excessively increasing the draw's length. In addition, R needs to be large enough to avoid creating excessive stress in the edges of the ribbon as those edges pass through the S-bend.

[0056] An estimate of the edge stress can be obtained using Roark's formula for the bending stress (σ) in a sheet as a function of sheet thickness (t) and radius of curvature (R):

^Σ0^«0 ^_ · ^{1 Ο£Ί} 'Μ ' ½ Eq. (2)

[0057] FIG. 10 plots Eq. (2) for maximum thicknesses across the ribbon (i.e., the body of the ribbon and/or the beads as the case may be) of 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm (bottom to top curves in FIG. 10). As can be seen from these curves, for a given maximum stress level, a smaller bend radius can be used with smaller maximum thicknesses. In general terms, maximum safe bending stress for the types of glasses used in display applications is on the order of 3000-5000 psi (20-35 MPa), thus making 15 feet (4.5 meters) a conservative radius of curvature even for the largest maximum thicknesses of FIG. 10. Table 1 evaluates Eq. (1) for R = 15 feet (4.5 meters) and horizontal jogs of 0.25, 0.50 and 1.00 inches (0.6, 1.3, and 2.5 centimeters), while Table 2 gives the corresponding values for R = 10 feet (3.0 meters), which is a conservative radius for ribbons having a maximum thickness of 2.0 mm and below. As these tables show, the incorporation of an S-bend between a pull roll assembly and a scoring/separation assembly can be achieved with edge guides having relatively short equipment lengths. It should be noted that for smaller maximum ribbon thicknesses, R can be substantially reduced below 3.0 meters, e.g., as small as, for example, 0.3 meters. [0058] As shown in Tables 1 and 2, the equipment length increases as the size of the jog increases. In general, the size of the jog needed to achieve substantial flatness at the scoring/separation assembly (e.g., at the nosing of such an assembly) increases with decreasing glass thickness. In practice, an appropriate jog size for any particular application of the present disclosure can be readily determined by persons skilled in the art either empirically and/or by modeling, e.g., finite element modeling of the stresses in the glass ribbon as it passes through the S-bend.

[0059] A variety of modifications that do not depart from the scope and spirit of the invention will be evident to persons of ordinary skill in the art from the foregoing disclosure. For example, although the invention has been discussed and illustrated in terms of a fusion process, it is also applicable to other downdraw processes such as slot draw processes in which the forming vessel includes a slot through which molten glass is drawn, rather than an isopipe over which the molten glass flows. The following claims are intended to cover the specific embodiments set forth herein as well as modifications, variations, and equivalents of those embodiments of the foregoing and other types.

Table 1

15 foot (457 cm) Radius

1.00" (2.5 cm) Jog 0.50" (1.3 cm) 0.25" (.6 cm) Jog

Jog

Equipment Length 26.81 " (68.10 cm) 18.97" (48.18 cm) 13.41 " (34.06 cm)

Table 2

10 foot Radius

1.00" (2.5 cm) Jog 0.50" (1.3 cm) 0.25" (.6 cm) Jog

Jog

Equipment Length 21.89" (55.6 cm) 15.48" (39.3 cm) 10.95" (27.8 cm)

Claims

What is claimed is:

1. A glass manufacturing system comprising:

(a) at least one vessel for melting batch materials and forming molten glass;

(b) a forming vessel for receiving the molten glass and forming a glass ribbon which has a centerline and two opposing edges;

(c) a pull roll assembly for drawing the glass ribbon in a substantially vertical direction; and

(d) a scoring/separating assembly for scoring and separating the glass ribbon into individual sheets;

wherein the system comprises an isolator system between the pull roll assembly and the scoring/separating assembly for reducing motion of and/or stress in the ribbon above the isolator system as a result of forces applied to the ribbon below the isolator system by the scoring/separating assembly, the isolator system comprising S-shaped edge guides which engage the two opposing edges of the ribbon and cause the centerline of the ribbon to traverse an S-shaped curve as it passes through the isolator system, the centerline of the ribbon being substantially vertical both before it enters and after it leaves the isolator system.

2. An isolator system for use between a pull roll assembly and a

scoring/separating assembly of a glass manufacturing system which produces a glass ribbon from which glass sheets are separated, said isolator system comprising S-shaped edge guides which, during use, engage opposing edges of the ribbon and cause the ribbon's centerline to traverse an S-shaped curve as it passes through the isolator system with the centerline being substantially vertical both before it enters and after it leaves the isolator system, wherein, during use, the isolator system reduces motion of and/or stress in the glass ribbon above the isolator system as a result of forces applied to the ribbon below the isolator system by the scoring/separating assembly.

3. The system of Claim 1 or Claim 2 wherein each of the S-shaped edge guides comprises a plurality of rollers, each roller having a diameter sufficiently small so that the glass ribbon does not conform to the surface of the roller.

4. The system of Claim 1 or Claim 2 wherein (i) each of the S-shaped edge guides has an upper and a lower section which are concave in opposite directions, (ii) each section has a radius of curvature R, and (iii) each roller has a diameter that is less than or equal to R/n where n is greater than 5.

5. The system of Claim 1 or Claim 2 wherein each of the S-shaped edge guides has an upper and a lower section, each of which has a radius of curvature R that satisfies the relationship :

0.3 < R < 5,

where R is in meters.

6. The system of Claim 1 or Claim 2 wherein each of the S-shaped edge guides has an upper and a lower section, the upper section having an entrance for the glass ribbon and the lower section having an exit for the glass ribbon, the exit being horizontally offset from the entrance by a distance J that satisfies the relationship:

1 < J < 25,

where J is in millimeters.

7. The system of Claim 1 or Claim 2 wherein each of the S-shaped edge guides has a vertical height H that satisfies the relationship:

25 < H < 100,

where H is in centimeters.

8. A method of producing a glass sheet comprising:

(a) melting batch materials to form molten glass;

(b) processing the molten glass to form a glass ribbon which has a centerline and two opposing edges;

(c) drawing the glass ribbon in a substantially vertical direction using a pull roll assembly;

(d) scoring the glass ribbon to form a score line; and

(e) separating a glass sheet from the glass ribbon along the score line;

wherein prior to step (d), the method comprises imparting an S-shape to the glass ribbon at a location below the pull roll assembly so as to reduce motion of and/or stress in the ribbon above the S-shape as a result of forces applied to the ribbon during steps (d) and/or (e), the centerline of the ribbon being substantially vertical both before and after the S-shape is imparted to the ribbon.

9. The method of Claim 8 wherein the imparting of the S-shape to the ribbon causes the centerline of the ribbon to be displaced horizontally by a distance J that satisfies the relationship:

1 < J < 25,

where J is in millimeters.

10. The method of Claim 8 wherein S-shape is imparted to the ribbon over a vertical distance H that satisfies the relationship:

25 < H < 100,

where H is in centimeters.

11. The method of Claim 8 wherein the thickness of the glass ribbon at its edges is less than or equal to 2.5 millimeters and the imparting of the S-shape produces a maximum calculated stress in the edges of less than 35 MPa.

12. The method of Claim 8 wherein the thickness of the glass ribbon along the ribbon's centerline is less than or equal to 0.5 millimeters.

13. The method of Claim 8 wherein the imparting of the S-shape causes the ribbon to be substantially flat in the across-the-ribbon direction.

14. The method of Claim 13 wherein the scoring and separating is performed with a flat nosing.