Abstract:
Push roll spools for engaging and driving softened glass tubes over a shaping mandrel. A push roll spool for use in processing a glass tube may comprise a base having first and second axially spaced ends, and multiple sheets of heat resistant material disposed on the base between the axially spaced ends, forming an axially extending stack. The stack may have a circumferential, generally U-section groove having a profile defined by the peripheral edges of multiple said sheets having different diameters. The U-section groove may be sized to engage and drive a glass tube. The U-section groove may have two contact areas at which to engage and drive a glass tube. The heat resistant material may comprise mica or a mica composition, for example mica paper or ceramic fiber millboard.

Description:
[0001]    This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 62/112292 filed on Feb. 5, 2015 the content of which is relied upon and incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to various types of rolls, such as push rolls and pull rolls, for use in the manufacture of circular tubing and other shaped non-circular sleeves or tubes, used for example in a glass manufacturing process. 
       BACKGROUND 
       [0003]    Rolls are used in glass manufacturing to apply a force, for example a vertical force, to convey a feed stock of glass from which an intermediate or final product is formed. For example, pull rolls are used in the manufacture of sheet glass to pull a ribbon or web of glass from which individual sheets are formed. The amount of frictional force applied by pull rolls to glass is utilized to control the nominal thickness of the glass as the glass is drawn from softened glass, such as in an overflow downdraw fusion process, as described in U.S. Pat. Nos. 3,338,696 and 3,682,609, or a similar process. 
         [0004]    Pull rolls are typically designed to contact the glass web at its outer edges, usually in an area just inboard of the thickened beads that form at the very edges of the glass ribbon. An important aspect of pull roll function is to avoid cracking of the ribbon which can cause process outages and restarts. Because pull rolls are in direct contact with the surface of the glass ribbon, damage to the surface of the glass may occur from contact with the pull rolls. In addition, tramp glass particles can become embedded in the surface of the pull roll resulting in additional damage to the glass as the pull rolls contact the glass. 
         [0005]    In addition to a main pull roll, additional rolls are sometimes used in glass drawing processes to stabilize glass motion, or to create tension across the glass. When drawing a tube or rod, such as a hollow or solid cylinder, of softened glass over a shaping mandrel, it may be advantageous to have—in addition to, or in place of, pull rolls—one or more push rolls that are designed to push the tube of softened glass over the shaping mandrel. Accordingly, there is a need for new push roll designs. 
       SUMMARY 
       [0006]    The present disclosure relates generally to push or pull roll spools for engaging and driving softened glass tubes over a shaping mandrel. 
         [0007]    Optionally, a push roll spool for use in processing a glass tube may comprise a base having first and second axially spaced ends. The push roll spool may comprise multiple sheets of heat resistant material disposed on the base between the axially spaced ends, forming an axially extending stack. The stack may have a circumferential, generally U-section groove having a profile defined by the peripheral edges of multiple said sheets having different diameters. The U-section groove may be sized to engage and drive a glass tube. The U-section groove may have two contact areas at which to engage and drive a glass tube. The heat resistant material may comprise mica or a mica composition, for example mica paper or ceramic fiber millboard. 
         [0008]    Optionally, a method for producing a push roll spool for use in glass manufacturing may comprise: providing a plurality of sheets of a heat resistant material; stacking the plurality of sheets; compressing the plurality of sheets axially; and optionally grinding the plurality of sheets to form a concave groove around the spool. The heat resistant material may comprise mica or a mica composition, for example mica paper or ceramic fiber millboard. 
         [0009]    Optionally, a method for producing a glass sleeve with a flattened portion may comprise the steps of: providing one or more rotatable push rolls, each rotatable push roll comprising a concave contact surface made of a first heat resistant material; providing a substantially cylindrical tube made of glass, the substantially cylindrical tube having a longitudinal axis, an outer curved surface, and an inner curved surface at least partially enclosing a space; introducing the concave contact surface into contact with the outer curved surface to push the substantially cylindrical tube; heating at least a portion of the substantially cylindrical tube to a temperature within the softening range of the glass; introducing one or more shaping mandrels into the partially-enclosed space; and moving the substantially cylindrical tube over the one or more shaping mandrels to deform the tube, forming the flattened portion. The concave contact surface may contact the substantially cylindrical tube at (for example) two contact areas. The substantially cylindrical tube may be moved over the one or more shaping mandrels to deform the tube, forming two opposing flattened portions, two opposing curved portions, or both. The two opposing curved portions may be substantially semi-circular. The first heat resistant material may comprise mica or a mica composition, for example mica paper or ceramic fiber millboard. One or more rotatable pull rolls having a flat contact surface made of a second heat resistant material may be introduced such that the flat contact surface contacts the outer surface to pull the substantially cylindrical tube over the one or more shaping mandrels. The second heat resistant material may comprise mica or a mica composition, for example mica paper or ceramic fiber millboard. 
         [0010]    Additional features and advantages of the present disclosure will be 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 embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0012]    The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity or conciseness. 
           [0013]      FIG. 1  is a perspective view of a push roll spool. 
           [0014]      FIG. 2  shows a plan view of a sheet of heat resistant material. 
           [0015]      FIG. 3  is a perspective view of a pull roll spool. 
           [0016]      FIG. 4  is a perspective view of a push roll spool mounted on a roll shaft. 
           [0017]      FIG. 5A  shows a schematic of a non-complementary contact between a push roll spool and a glass tube. 
           [0018]      FIG. 5B  shows an enlargement of a portion of  FIG. 5A . 
           [0019]      FIG. 5C  shows a close-up view of a contact area. 
           [0020]      FIG. 5D  shows a close-up view of a contact area. 
           [0021]      FIG. 6  is a schematic illustration of the glass tube to glass sleeve manufacturing process. 
           [0022]      FIG. 7  is a perspective view of a glass sleeve. 
       
    
    
       [0023]    The following reference characters are used in this specification:
     10  Push roll spool     11  Roll shaft     12  Glass tube     13  Midsection (of  10 )     15  Surface (of  10 )     20  Compacted stack     22  Glass sleeve     24  Sheet or disc     25  Hole     26  Sheet or disc     27  Keyway     28  Sheet or disc     29  Key     40  U-section groove (of  10 )     42  Contact area     44  Contact area     50  Heating zone     52  Clamp     70  Shaping mandrel     90  Pull roll spool     95  Surface (of  90 )     100  Hub shaft     110  Particle   
 
         [0047]    The foregoing summary, as well as the following detailed description of certain inventive techniques, will be better understood when read in conjunction with the figures. It should be understood that the claims are not limited to the arrangements and instrumentality shown in the figures. Furthermore, the appearance shown in the figures is one of many ornamental appearances that can be employed to achieve the stated functions of the apparatus. 
       DETAILED DESCRIPTION 
       [0048]    In the following detailed description, numerous specific details may be set forth in order to provide a thorough understanding of embodiments of the present invention. However, it will be clear to one skilled in the art when embodiments of the present invention may be practiced without some or all of these specific details. In other instances, well-known features or processes may not be described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals may be used to identify common or similar elements. 
         [0049]      FIGS. 1, 4, 5A, and 5B  illustrate a push roll spool  10  of the present disclosure for contacting and driving a glass material over one or more shaping mandrels  70 . The push roll can also be used, for example, to push an end of one heated glass tube axially against the end of another heated glass tube to join them. This end-to-end joining can optionally be carried out repeatedly with a series of tubes to form a longer or even substantially continuous glass tube in a manufacturing operation. The glass material will typically be glass and in the form of a substantially cylindrical glass tube  12 . A push roll spool  10  comprises a compacted stack  20  of multiple sheets or discs such as  24 ,  26 ,  28  of a heat resistant material that are compressed together. The heat resistant material will typically be mica or a material containing mica, for example mica paper or a ceramic fiber millboard. 
         [0050]    The compacted stack  20  may be manufactured from a roll of heat resistant material from which multiple sheets such as  24 ,  26 ,  28  are punched out or otherwise formed. Each of the multiple sheets such as  24 ,  26 ,  28  will typically have a hole in the center of the sheet  24 ,  26 ,  28 , to allow the sheets  24 ,  26 ,  28  to be stacked onto a hub shaft  100 . An example of a sheet is shown in  FIG. 2 . Once multiple sheets such as  24 ,  26 ,  28  are stacked on a hub shaft  100 , the sheets  24 ,  26 ,  28  may be clamped together to form the compacted stack  20  of the push roll spool  10 . “Mushrooming” optionally can be managed by beginning and ending the stack with a silicone-impregnated mica paper board (in which the silicone has been oxidized to be a silica binder). Once the stack  20  is formed, the push roll spool surface  15  optionally may be ground to achieve a desired roll shape and surface finish. Optionally, carbide grinding can be used to grind the surface  15  of the push roll spool  10  to the desired roll shape and surface finish. For example, a push roll spool  10  may have a U-section groove  40  ground into its midsection  13 . The “midsection”  13  does not need to be in or near the middle of the stack  20 ; it can be anywhere in the stack  20 . Grinding the push roll spool  10  into the desired shape after assembly may help to prevent “mushrooming” of the push roll spool  10  shape that can occur when attempting to form a compacted stack  20  by compressing multiple sheets such as  24 ,  26 ,  28  having different diameters. Optionally, a push roll spool  10  may be formed by cutting multiple sheets such as  24 ,  26 ,  28  to different diameters such that the push roll spool  10  has its desired final shape upon assembly of the compacted stack  20 . 
         [0051]    Optionally, a pull roll spool  90  may be formed, as shown in  FIG. 3 . Examples of pull rolls are disclosed in U.S. Pat. No. 8,820,120 (issued Sep. 2, 2014 to Cook et al.) and U.S. Ser. No. 14/454,278 (filed Aug. 7, 2014), which are both incorporated by reference in their entirety. A pull roll spool  90  may have a flat surface finish. A pull roll spool may also be formed by stacking multiple sheets such as  24 ,  26 ,  28  on a hub shaft  100 . Once multiple sheets such as  24 ,  26 ,  28  are stacked on a hub shaft  100 , the sheets  24 ,  26 ,  28  may be clamped together to form the compacted stack  20  of the pull roll spool  90 . Optionally, carbide grinding can be used to grind the surface  95  of the pull roll spool  90  to the desired roll shape and surface finish. For example, a pull roll spool  90  may optionally be ground to ensure that the surface  95  is flat. 
         [0052]    As illustrated in  FIG. 4 , a push roll spool  10  may be mounted on a roll shaft  11 . Similarly, a pull roll spool  90  may be mounted on a roll shaft  11 . Optionally, as illustrated in  FIG. 4 , a pair of push roll spools  10 ,  10  may be used to drive a glass tube  12 . 
         [0053]    As illustrated in  FIGS. 5A and 5B , the U-section groove  40  of a push roll spool  10  may optionally be designed to be non-complementary to the glass tube  12  that the push roll spool  10  is designed to engage and drive, where non-complementary means that the push roll spool  10  contacts the glass tube  12  at limited contact areas  42 ,  44  along the surface of the U-section groove  40 . Reducing the contact area to two contact areas  42 ,  44  rather than an extensive contact surface is designed to decrease the occurrence of defects in a glass tube  12  driven by a push roll spool  10 .  FIGS. 5C and 5D  each show a close-up view of a contact area  44  in which a particle  110  is penetrating into the surface  15  of a push roll  10  either between a pair of sheets  24 ,  26  ( FIG. 5C ) or within a single sheet  26  ( FIG. 5D ). 
         [0054]      FIG. 6  schematically depicts an exemplary glass manufacturing apparatus for forming a glass sleeve  22  from a glass tube  12 . Optionally, the entering glass tube  12  is substantially cylindrical. One or more push roll spools  10 —typically, a pair of opposing push rolls  10 ,  10 —may drive the glass tube  12  through one or more heating zones  50  and over one or more shaping mandrels  70  to form a glass sleeve  22 . One or more clamps  52  may optionally be used to maintain alignment. Optionally, one or more pull roll spools  90  may be employed to pull the glass sleeve  22 .  FIG. 7  illustrates a possible a glass sleeve  22  that may be formed pursuant to one of the presently disclosed manufacturing processes. 
         [0055]    While the push roll spools  10  have been described in the present disclosure as being used in conjunction with an apparatus which utilizes a down-draw process, it should be understood that the push roll spools  10  may be used with similar processes in which glass tubes  12  are shaped into different shapes, such as glass sleeves  22 . By way of example and not limitation, the push roll spools  10  of the present disclosure may also be used in conjunction with up-draw processes, slot-draw processes, float-draw processes, tube end-to-end joining processes and other, similar processes. 
         [0056]    Optionally, the compacted stack  20  may be formed from multiple sheets such as  24 ,  26 ,  28  of mica paper. The multiple sheets such as  24 ,  26 ,  28  of mica paper generally comprise layers of overlapping mica platelets oriented substantially in parallel with one another and joined together by van der Waals forces, electrostatic forces, sintering, and/or the like. This configuration of the mica platelets provides for maximum stability of the resultant mica paper. Optionally, the mica paper is formed without the addition of a binder or any other matrix of material in which the mica platelets are embedded. The mica platelets in the mica paper generally have a high aspect-ratio (i.e., the ratio of the average diameter to average thickness) and are highly delaminated. For example, the aspect-ratio of the mica platelets contained in the mica paper may optionally be in a range from about 50 to about 500. While not wishing to be bound by theory, it is generally believed that high aspect-ratio mica platelets oriented in parallel with one another improve the mechanical strength, geometrical stability, and wear resistance of the compacted stack. Specifically, it is believed that the interfacial friction between the mica platelets improves the resistance of the platelets to pull-out during use, thereby improving the wear resistance of the compacted stack and decreasing the occurrence of defects in glass tubes  12  driven by the push roll spools  10 . 
         [0057]    Optionally, the mica paper may be formed from phlogopite mica platelets so as to increase the temperature range in which the mica paper is stable. For example, the mica paper may be phlogopite or muscovite mica-paper commercially available from Cogebi Group, Belgium; Corona Films, USA; or Von Roll, USA. Optionally, this mica paper may not include a binder material. However, it should be understood that other types of mica paper may be used, including mica paper formed from other types of mica platelets and/or mica paper which includes a binder. For example, other suitable types of mica paper may include, without limitation, mica paper formed from fluorophlogopite mica (which is more thermally stable than phlogopite mica) or mica paper formed from muscovite mica. 
         [0058]    Mica paper of various thicknesses can be used to form each of the multiple sheets such as  24 ,  26 ,  28  of heat resistant material, an example of which is depicted in  FIG. 2 . For example, each sheet  24 ,  26 ,  28  may optionally have an uncompressed thickness greater than about 100 μm. Following compression, each sheet  24 ,  26 ,  28  may have a compressed thickness of less than or equal to about 100 μm. However, it should be understood that mica paper with larger and smaller compressed thicknesses may also be used. The compacted stack  20  may be compressed to a target density or porosity that determines the Shore D hardness of the compacted stack  20 . Generally, the greater the compression, the harder the compacted stack  20 . 
         [0059]    Sheets of heat resistant material  24 ,  26 ,  28  with compressed thicknesses as specified above facilitate forming a compacted stack  20  with the desired mechanical properties as well as the ability to withstand and/or mitigate damage to the contact surface caused by debris (i.e., glass particulates or the like) encountered during the glass drawing process. In particular, forming the compacted stack  20  from relatively thin sheets  24 ,  26 ,  28  of heat resistant material (i.e., sheets with a compressed thickness of less than or equal to about 200 μm) permits particles  110 , such as debris or other particulate matter positioned on the contact surface, to be enveloped between adjacent sheets (as illustrated in  FIG. 5C ) and/or between platelets within a single sheet (as illustrated in  FIG. 5D ) such that it minimizes the flaws created on the surface of the glass tube  12  when the push roll spool surface  15  contacts the glass tube  12 . 
         [0060]    Although the mica paper used for the multiple sheets such as  24 ,  26 ,  28  of heat resistant material has been described as being formed without a binder material, it should be understood that, optionally, the mica paper may contain a binder material to improve the mechanical stability of each sheet. For example, the mica paper may be impregnated with a filler material which may further bind the mica platelets together. The filler material may be organic, semi-organic, or inorganic. When the filler material is organic, the filler material may be removed from the mica paper by pyrolysis or a chemical process (i.e., dissolved). The filler material may be, for example, silicone or another polymeric resin which improves the mechanical stability of the mica paper without significantly decreasing the flexibility of the mica paper. In general, the filler material increases both the density of the mica paper and the hardness of the mica paper. 
         [0061]    Although the multiple sheets such as  24 ,  26 ,  28  of heat resistant material are described as being formed from mica paper, it should be understood that the sheets  24 ,  26 ,  28  may optionally be formed from other inorganic materials including, without limitation, ceramic fiber millboard, ceramic materials, elemental metals, metal alloys or the like. For example, the multiple sheets such as  24 ,  26 ,  28  may be formed from refractory paper (such as asbestos fiber paper, mica flake paper, ceramic fiber paper, or graphite paper), metal foils (such as aluminum foil or platinum foil), or a single crystal sheet (such as mica). 
         [0062]    Optionally, each sheet of heat resistant material is formed with a central hole  25  to facilitate positioning each sheet on a hub shaft  100 . Although the hole  25  is depicted in  FIG. 2  as generally circular, it should be understood that the hole  25  may have other geometric shapes. For example, where each sheet is installed on a hub shaft  100  with a hexagonal cross section, the hole  25  may also be hexagonal so as to prevent the sheets from rotating on the hub shaft  100 . The hole  25  may also be optionally formed to include a keyway  27 , as depicted in  FIG. 2 . Where the hole  25  includes a keyway  27 , the keyway  27  may engage with a corresponding key  29  formed on the hub shaft  100  to prevent the sheets  24 ,  26 ,  28  from rotating on the hub shaft  100 . Optionally, the hole  25  and keyway  27  may be formed via a punching operation. 
         [0063]    Prior to assembling each of the multiple sheets such as  24 ,  26 ,  28  on the hub shaft  100 , the sheets  24 ,  26 ,  28  may be pre-fired to calcine the sheets to preempt hardening of the sheets  24 ,  26 ,  28  during subsequent usage at elevated temperatures. Optionally, the sheets  24 ,  26 ,  28  are pre-fired by stacking the sheets  24 ,  26 ,  28  and heating them according to a heating schedule suitable for calcination. For example, the sheets  24 ,  26 ,  28  may be heated to a maximum temperature of about 700° C. at a ramp rate of 2° C./min and held at this maximum temperature for about 6 hours. Optionally, the sheets  24 ,  26 ,  28  may be calcined following assembly and compression of the ring sheets. 
         [0064]    Optionally, the multiple sheets such as  24 ,  26 ,  28  are stacked and axially compressed on the hub shaft  100  such that the push roll spool  10  permits particles  110 , such as tramp glass particles or other debris, to penetrate into the contact surface of the push rolls  10  such that the flaws caused by the particles  110  are minimized and/or the particles  110  do not contact as hard against the surface of the glass tube  12  driven by the push rolls  10 , thereby reducing the occurrence of repetitive defects and/or cracking. The resistance (or compliance) of the contact surface of the push roll spools can be qualitatively assessed using conventional hardness metrics, such as the Shore durometer metrics. The hardness of push roll spools is typically measured with the Shore D scale and, in particular, according to ASTM D2240. The indenter used in the Shore D hardness measurement is conical, and, as such, the Shore D hardness measurement of the push roll surface  15  is generally indicative of the ability of the roll assembly to envelop particles  110  between multiple sheets such as  24 ,  26 ,  28  (as illustrated in  FIG. 5C ) or within a single sheet  26  (as illustrated in  FIG. 5D ). The smaller the Shore D number, the easier it is for particles  110  to penetrate into the contact surface of the push roll spool  10 . A smaller Shore D number also indicates that the push roll spool  10  is able to envelop larger particles  110   
         [0065]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.