Patent Application
20120111054
This disclosure relates to the guiding of flexible glass ribbons without damaging the central portion (quality portion) of the ribbon. Among other things, such guiding can be used in the winding of a thin glass ribbon on a cylindrical core.
As used herein, a guide roller is “mechanically adjacent” to a curved section of a glass ribbon if the guide roller is close enough to the curved section so that the glass ribbon continues to exhibit a level of across-the-ribbon stiffness due to having been curved that is sufficient to allow the roller to move the ribbon laterally without buckling.
As used herein, the term “glass” includes glass and glass-ceramic materials.
Although formed continuously, glass is typically segmented into sheets as soon as it has cooled and solidified. Recent product trends have resulted in requirements for thinner glass. As glass thickness decreases, the sheets and the ribbons from which they are cut become more flexible. This flexibility creates a challenge from a handling perspective, particularly for glass thinner than 0.3 mm.
Glass has a number of unique features that make guiding a glass ribbon particularly challenging. First, the glass is extremely sensitive to surface defects. These defects create stress points that generate cracks and lead to breakage. Thus, direct contact with the glass surface, as is typically done to edge-guide a plastic, paper, or metal web, must be done in a way that minimizes the forces on the glass. Second, when subject to lateral forces, a thin glass ribbon can buckle and eventually break. In contrast, polymer films and paper webs are more compliant and thus respond better to lateral forces.
Third, the ribbon-forming process can produce variations in the thickness of the ribbon across its width, as well as “camber” in the motion of the ribbon.
These unique features of glass ribbons make conveying and winding of ribbons of thin glass more challenging than conveying and winding of flexible webs in the plastic, paper, and metal foil industries. In these other industries, guiding of a web is typically accomplished by using fixed edge guides that rub against the web's edges. Experiments have shown that these techniques are a complete failure when applied to thin glass ribbons because they cause the ribbon to break.
A solution to the guiding problem for thin glass ribbons would allow the ribbon to be wound in a continuous format and provided to users in that form. The users, in turn, could process the glass in the continuous format to make such products as ePaper front plane substrates, photovoltaics protective cover sheets, touch sensors, solid state lighting, solid state electronics, and the like. In general terms, continuous processing is advantageous both to the glass manufacturer and to the user. A need thus exists for effective methods of guiding thin glass ribbons. The present disclosure addresses this need.
In accordance with a first aspect, apparatus is disclosed for guiding a moving glass ribbon (13) having a central portion (4) and first and second edges (3a,3b) which includes:
wherein the curvatures of each of the first and second sections stiffens the ribbon (13) to an extent sufficient to permit the guide rollers (7a,7b,9a,9b) to laterally move the ribbon without causing it to buckle.
In accordance with a second aspect, a method is disclosed for guiding a moving glass ribbon (13) having a central portion (4) and first and second edges (3a,3b) which includes:
wherein the curvatures of each of the first and second sections stiffens the ribbon (13) to an extent sufficient to permit the lateral forces to guide the ribbon without causing it to buckle.
In accordance with a third aspect, a curved air-bar assembly is disclosed which includes a first curved air-bar subsection (41), a second curved air-bar subsection (43), a frame (49), a first coupling mechanism (45,51) connecting the first curved air-bar subsection (41) to the frame (49), and a second coupling mechanism (47,51) connecting the second curved air-bar subsection (43) to the frame (49), the first and second coupling mechanisms being individually adjustable to allow the lateral positions of the first (41) and second (43) curved air-bar subsections relative to the frame (49) to be independently adjusted.
The reference numbers used in the above summaries of the various aspects of the disclosure 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.
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. For example, the various features of the invention may be combined according to the following additional aspects of the invention.
According to a fourth aspect, there is provided the apparatus of aspect 1 wherein:
According to a fifth aspect, there is provided the apparatus of aspect 1 or aspect 4 wherein each of the guide rollers is carried by a pivot arm and each of the pivot arms is spring-loaded to bias its guide roller against the edge of the ribbon.
According to a sixth aspect, there is provided the apparatus of any one of aspects 1 or 4-5 wherein each of the guide rollers has a glass-engaging surface which comprises silicone rubber.
According to a seventh aspect, there is provided the apparatus of any one of aspects 1 or 4-6 wherein the apparatus comprises a ribbon-biasing assembly between the first and second ribbon-guiding assemblies for biasing the ribbon towards the first and second ribbon-curving subassemblies without mechanically contacting the central portion of the ribbon.
According to an eighth aspect, there is provided the apparatus of aspect 7 wherein the ribbon-biasing assembly comprises at least one of:
According to a ninth aspect, there is provided the apparatus of any one of aspects 1 or 4-8 wherein at least one of the first and second ribbon-curving subassemblies comprises a curved air-bar having first and second curved air-bar subsections whose across-the-ribbon positions are independently adjustable.
According to a tenth aspect, there is provided the apparatus of any one of aspects 1 or 4-9 wherein the ribbon's central portion is at least 90% of the ribbon's width.
According to an eleventh aspect, there is provided an apparatus for winding a moving glass ribbon onto a cylindrical core comprising the apparatus of any one of aspects 1 or 4-10.
According to a twelfth aspect, there is provided the method of aspect 2 wherein the curvatures of the first and second sections of the ribbon are concave towards the same side of the ribbon.
According to a thirteenth aspect, there is provided the method of aspect 2 or aspect 12 wherein the ribbon is guided while its motion includes primarily a vertical component and the method further comprises creating a third curved section of the ribbon between the first and second curved sections without mechanically contacting the central portion of the ribbon, the curvature of the third section being: (i) along the direction of motion of the ribbon and (ii) concave in a direction opposite to that of the first and second curved sections.
According to a fourteenth aspect, there is provided the method of any one of aspects 2 or 12-13 wherein the ribbon is guided while its motion includes primarily a horizontal component and the curvatures are concave downward.
According to a fifteenth aspect, there is provided the method of any one of aspects 2 or 12-14 comprising creating a free loop of the ribbon prior to the first and second curved sections, the free loop being concave upward.
According to a sixteenth aspect, there is provided the method of any one of aspects 2 or 13 or 15 wherein the curvatures of the first and second sections of the ribbon are concave towards opposite sides of the ribbon.
According to a seventeenth aspect, there is provided the method of any one of aspects 2 or 12-16 wherein the first and second curved sections are each produced by at least one of:
According to an eighteenth aspect, there is provided the method of any one of aspects 2 or 12-17 further comprising using a pair of curved air-bars to produce at least one of the first and second curved sections of the ribbon and adjusting an across-the-ribbon position of at least one of the pair of curved air-bars at least once.
According to a nineteenth aspect, there is provided the method of any one of aspects 2 or 12-18 wherein the ribbon has a thickness which is less than or equal to 0.3 millimeters.
According to a twentieth aspect, there is provided the method of any one of aspects 2 or 12-19 wherein the ribbon exhibits at least one of camber and an across-the-ribbon thickness variation.
For ease of presentation, the following discussion is primarily in terms of guiding a thin, flexible glass ribbon 13 for winding onto a cylindrical core 11, it being understood that the guiding apparatus disclosed herein can be used in a variety of other applications, e.g., as part of a process which produces individual glass sheets.
The glass ribbon can be produced by various glass forming processes known in the art, including the overflow downdraw fusion process, the slot draw process, other downdraw processes, the float process, and the like. The ribbon can have various compositions and thicknesses, but in general, the guiding apparatus disclosed herein will be of particular value with thin ribbons having a thickness less than or equal to 0.3 millimeters, e.g., thicknesses on the order of 0.22 millimeters and below. Depending on the processes used, the ribbon can have beaded or non-beaded edges, e.g., the beads can be removed from the ribbon prior to guiding and winding.
In the embodiment of
Whatever ribbon-curving subassemblies are used, their purpose is to create two curved sections in the ribbon without mechanically contacting the central portion 4 of the ribbon. Thus, when a pair of cylindrical rollers is used, the rollers contact the surface of the ribbon outside of, and on opposite sides of, central portion 4. In this way, the rollers do not damage the central portion which includes the ribbon's quality portion, i.e., the portion of the ribbon which customers use in their products. The rollers also rotate with the ribbon as illustrated by arrows 21 and 25 to further minimize the chances of mechanical damage to the ribbon.
It should be noted that in
However formed, the two curved sections produced by the ribbon-curving subassemblies serve the role of increasing the stiffness of the ribbon so that the guide rollers can move the ribbon laterally without the ribbon buckling. The curvature, however, cannot be too sharp or the ribbon may break. In general terms, the bending stress 6 produced in a bent ribbon is given by: σ≈0.5*E*t/R, where E is the glass' Young's modulus, t is its thickness, and R is the radius of curvature of the bend. Thus, the curvature needs to be chosen so that the calculated bending stress does not exceed and, preferably, is substantially below the glass' flexural strength. In practice, for a representative display type glass, it has been found that a 4.5 inch (11.43 cm) radius of curvature will produce an acceptable bending stress (on the order of 50 megapascals) for a 150 micron glass thickness, while at the same time producing a level of stiffness in the ribbon sufficient to allow efficient guiding of the ribbon by the guide rollers. Larger radii of curvature have also been found to work successfully. For example, successful guiding has been achieved for the embodiment of
Surprisingly, it has been found that effective guiding of a thin, flexible, glass ribbon cannot be accomplished with a single curved section produced by a single ribbon-curving subassembly. With only a single curved section, the ribbon can pivot about the guiding rollers, rather than being pointed in a desired direction. With two ribbon-curving subassemblies, on the other hand, the two curved sections of the ribbon produced by the subassemblies can together define a direction for the ribbon, e.g., the direction of the centerline of a tangent plane to the two curved sections. The two pairs of guiding rollers of the two ribbon-guiding assemblies will then keep the ribbon moving in this defined direction.
To define a direction, the two ribbon-guiding assemblies need to be close enough together so that they do not become mechanically isolated from one another. Otherwise, the pivoting problem can arise again at each ribbon-guiding assembly. Similarly, the two ribbon-guiding assemblies cannot be too close together without becoming overly sensitive to small changes in the system. Generally, the onset of mechanical isolation becomes evident when the ribbon is capable of twisting between the ribbon-guiding assemblies or exhibits substantial amounts of gravitational sag between the assemblies. Supporting the ribbon between the assemblies with a flat air-bar can increase the amount of spacing between the assemblies that can be tolerated without loss of effective guiding. In general terms, for a glass ribbon composed of a display type glass, distances between the curved sections of the ribbon on the order of 0.5 to 2 meters have been found to work successfully in practice, it being expected that longer distances will also work successfully. As with the radii of curvature used for the curved sections of the ribbon, an appropriate spacing between the ribbon-guiding assemblies can be readily determined by persons skilled in the art for any particular application of the present disclosure.
As can be seen in
Because the guide rollers are mounted on spring loaded pivots, the amount of force that is exerted on the edges of the glass ribbon can be easily controlled through the selection of springs 19. In practice, a lateral force of approximately 0.4-0.5 pounds (0.181 kg to 0.227 kg) has been found to work successfully with a glass ribbons having thicknesses in the range of 0.075 to 0.22 mm and a width of 40 centimeters. Suitable lateral forces for other ribbon dimensions can be readily determined by persons skilled in the art for any particular application of the present disclosure.
As shown in
Although illustrated for first and second guide rollers 7a,7b, the guide roller system and guide roller construction of
As discussed above, one application for the ribbon guiding systems disclosed herein is in connection with the winding of a glass ribbon. In accordance with an embodiment of such winding, ribbon 13 is manufactured continuously and once the manufacturing process is stable, the ribbon is formed into a free loop 17 and then for the embodiment of
In practice, the foregoing winding procedure has been successfully used to wind glass lengths of greater than 200 m on a cylindrical core. The camber of the glass ribbon being wound was measured to be approximately 3 mm over a 5.5 m length and the cross-web thickness variation was measured to be 0.013 mm for 0.15 mm thick material.
From the foregoing, it can be seen that apparatus and methods for guiding a thin, flexible, glass ribbon have been provided which create sufficient forces to effectively guide the glass web laterally, despite the potential existence of camber or thickness variation in the glass. In some embodiments (see, for example,
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. The following claims are intended to cover the specific embodiments set forth herein as well as modifications, variations, and equivalents of those embodiments.
This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/410,075 filed on Nov. 4, 2010, the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61410075 | Nov 2010 | US |
