Patent Publication Number: US-2003221462-A1

Title: Fiber forming bushing assembly having flange support

Description:
BACKGROUND OF THE INVENTION  
       [0001] This invention relates in general to fiber forming bushing assemblies and more particularly to a fiber forming bushing assembly having a flange support.  
       [0002] Fiber forming bushing assemblies are well known in the prior art. An example of a prior art bushing assembly is illustrated in FIG. 1. The bushing assembly shown comprises a bushing  16 , a frame  18  about the bushing  16 , and a refractory material  20  between the bushing  16  and the frame  18 . A throat  30  is provided at the top of the bushing  16 . A flange  34  is provided about the throat  30 . A cooling coil  40  is attached to the flange  34 . The bushing  16  has a body  21  that is defined in a lateral direction by opposing end plates  22  and in a longitudinal direction by elongate side walls  24 . The end plates  22  extend downward in a generally vertical direction. Upper portions  38  of the side walls  24  are slanted or angled outward and beneath the flange  34  while lower portions of the side walls  24  extend downward in a generally vertical direction.  
       [0003] In a fiber forming operation, the bushing assembly is secured beneath a bushing block  12  at a forming position by clamping the frame  18  to a forehearth steel (not shown). The flange  34  is adapted to engage an underside of the bushing block  12 . Molten glass G flows from the bushing block  12  into the throat  30  of the bushing  16 . The molten glass G exits the bushing  16  (e.g., as glass fibers F) through tip plates  26  provided at the bottom of the bushing  16 .  
       [0004] Ideally, the flange  34  extends perpendicularly from the throat  30  and parallel relative to the underside of the bushing block  12 . An upper surface of the flange  34  is adapted to engage the underside of the bushing block  12  so as to provide a seal between the flange  34  and the bushing block  12  to prevent molten glass G from escaping or leaking between the flange  34  and the bushing block  12 . In some instances, a small amount of molten glass G may leak between the flange  34  and the bushing block  12 . However, the temperature of this small amount of glass G drops significantly as it passes between the flange  34  and the bushing block  12  and approaches the cooling coil  40  (i.e., heat for the molten glass G dissipates into the cooling coil  40 ). Molten glass G that reaches the edge of the flange  34  is solidified due to the effect of the cooling coil  40 . The solidified glass forms a seal to prevent the molten glass G from flowing any further.  
       [0005] Various size bushings are required, depending on the production requirements (e.g., the number of fibers F being formed). The bushing  16  shown has two tip plates  26  and, consequently, is a wider bushing. That is to say, the bushing  16  has greater dimension from front to back or a lateral direction of the bushing  16  (from left to right, or vice versa, when viewing FIG. 1). The upper portion  44  of each side wall  24  of this bushing  16  is at a tighter angle relative to the flange  34  than a narrower bushing. Therefore, very little clearance is provided between the flange  34  and the cooling coil  40  and the upper portion  44  of each side wall  24 . Consequently, it is more difficult to ensure continuous backfill of refractory material  20  in the area or cavity defined between the flange  34  and the cooling coil  40  and the upper portion  44  of each side wall  24 . A more continuous backfill can be achieved by raising the moisture content of the refractory material  20 . However, an increased moisture level of the refractory material  20  has an adverse affect on the strength and integrity of the refractory material  20 . Such refractory material tends to crack and separate from the bushing  16  and frame  18 , resulting in premature failure of the bushing  16 .  
       [0006] A discontinuous backfill results in the presence of voids V in the refractory material  20 . The voids V weaken the support provided by the refractory material  20 . Downward forces from the molten glass G against the bushing screen, clamping pressure, and gravitational force cause plastic and/or creep deformation of the flange  34  and the upper portion  44  of each side  24 . This causes the flange  34  to separate or pull away from the bushing block  12 , as illustrated in FIG. 1 of the prior art. When the flange  34  separates from the bushing block  12 , more molten glass G can penetrate between the flange  34  and the bushing block  12 . As the amount of molten glass G penetrating between the flange  34  and the bushing block  12  increases, the molten glass G does not cool sufficiently by the time it reaches the edge of the flange  34 . Consequently, the molten glass G between the flange  34  and the bushing block  12  is at a heightened temperature. The cooling coil  40  is not designed to cool molten glass G at the heightened temperature. Consequently, the molten glass G leaks beyond the edge of the flange  34  and the cooling coil  40  and results in a premature failure of the bushing  16 .  
       [0007] What is needed is a support that provides greater subjacent support for the peripheral flange in a longitudinal direction of the bushing to prevent the flange from sagging and thus prevent molten glass from leaking between the flange and the bushing block, thereby eliminating premature failures and prolonging the life of the bushing.  
       SUMMARY OF THE INVENTION  
       [0008] The present invention is directed toward a fiber forming bushing assembly comprising a bushing and a support. The bushing includes a bushing body and a flange. The bushing body is defined at least in part by a throat and a side wall beneath the throat. The side wall has an upper portion. The flange extends from the throat. The support is positioned between the flange and an upper portion of the side wall. The support is formed of a ceramic material.  
       [0009] The present invention is also directed toward a fiber forming bushing assembly having a bushing body defined at least in part by a throat, opposing end plates extending in a lateral direction, and elongated side walls extending in a longitudinal direction. The end plates and side walls are beneath the throat. Each side wall has an upper portion. The flange extends from the throat. The flange comprises a lateral portion and an elongate portion. A support is positioned between each of the elongate portions of the flange and the upper portion of a corresponding one of the side walls. Each support is formed of a ceramic material.  
       [0010] Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a side elevational view of a prior art bushing.  
     [0012]FIG. 2 is a side elevational view of a bushing according to a preferred embodiment of the invention.  
     [0013]FIG. 3 is a front elevational view of the bushing shown in FIG. 2.  
     [0014]FIG. 4 is an enlarged perspective view of the flange support according to a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0015] Referring now to the drawings, there is illustrated in FIG. 2 a fiber forming position  10  comprising a bushing block  12  and a bushing assembly  14 . The bushing assembly  14  basically comprises a bushing  16 , a frame  18  about the bushing  16 , and a refractory material  20  (e.g., a castable refractory material) between the frame  18  and the bushing  16 . The frame  18  is secured beneath the bushing block  12  by clamping the frame  18  to a forehearth steel (not shown). Molten glass G is supplied to the bushing  16  through the bushing block  12 . The molten glass G passes through the bushing  16  and exits the bushing  16  in the form of fibers F (e.g., glass fibers).  
     [0016] The bushing  16  is basically comprised of an electrically conductive bushing body  21  and an electrically conductive screen located within the bushing body  21 . In a preferred embodiment of the invention, the bushing body  21  is in the form of a metal box having an elongate, substantially rectangular shape. The bushing body  21  is defined in part by opposing end plates  22  and elongate side walls  24  extending between the end plates  22 . The bottom of the bushing body  21  is defined by a tip plate  26  having a plurality of orifices (not shown) formed therein, preferably including tubular members  28 , as described in commonly-assigned U.S. Pat. No. 4,161,646, which is incorporated herein by reference. The tip plate  26  extends in a side to side or longitudinal direction between the end plates  22  and a front to rear or lateral direction between the side walls  24 . An opening is provided at the top of the bushing body  21  for receiving the molten glass G from the bushing block  12 . The opening is defined by a throat  30 .  
     [0017] A pair of opposing electrical terminals or ears  32  is attached to the opposing end plates  22 . The ears  32  are adapted to be connected to a source of current (not shown). Current is adapted to flow through the ears  32  and further into and through the bushing body  21  to resistance heat the bushing body  21  and thereby maintain the glass G under the desired thermal condition.  
     [0018] A flange  34  extends from the throat  30  at the top of the bushing body  21 . The flange  34  includes a lateral portion  36  that extends in the lateral direction adjacent each of the end plates  22  and an elongate portion  38  that extends in the longitudinal direction adjacent each of the elongate side walls  24 . The flange  34  engages an underside of the bushing block  12  to form a seal between the bushing block  12  and the flange  34  to prevent molten glass G from escaping or leaking from between the bushing block  12  and the flange  34 .  
     [0019] To further reduce the risk that molten glass G will escape from between the bushing block  12  and the flange  34 , a cooling coil  40  is attached to the flange  34  (e.g., with metal tabs  41  that are welded to the flange  34 ). In a preferred embodiment of the invention, the cooling coil  40  is a continuous cooling coil that is attached to an outer peripheral edge of the flange  34 .  
     [0020] In accordance with the present invention, a support  42  is positioned beneath the flange  34  in an area or cavity defined between each elongate portion  38  of the flange  34  and an upper portion  44  of each side wall  24 . The support  42  is positioned juxtaposed the throat  30  of the bushing body  21  and beneath the flange  34  to provide lateral support for the throat  30  and subjacent support for the flange  34 .  
     [0021] The upper portion  44  of each side wall  24  is disposed at an acute angle θ relative to the corresponding elongate portion  38  of the flange  34 . The measure of the angle θ depends at least in part upon the width W of the bushing body  21 . That is to say, the measure of the angle θ is inversely proportional to the width W of the bushing body  21 , assuming a constant bushing height and throat width.  
     [0022] The support  42  is shaped and dimensioned to fit between each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24 . Consequently, the support  42  is preferably wedge-shaped. In a preferred embodiment of the invention, the support  42  has a shape complementary to that of the cavity provided between each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24 . Moreover, the support  42  is dimensioned to fit closely relative to each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24 . The support  42  preferably fits flush against each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24  or up to within {fraction (1/16)} inch of each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24 .  
     [0023] The shape of the support  42  depends at least in part upon the shape of the cavity defined between each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24 . The shape of this cavity depends upon shape of the bushing body  21 . For example, the throat  30  is preferably substantially vertical. The flange  34  is preferably at about a right angle relative to the throat  30 . The upper portion  44  of each side wall  24  is vertically spaced from the flange  34  by the vertical dimension of the throat  30 . The upper portion  44  of each side wall  24  is oriented at an acute angle θ relative to the flange  34 . As stated above, the measure of the angle θ is inversely proportional to the width of the bushing  16 . If the cooling coil  40  is mounted to the underside of the flange  34 , then the shape of the support  42  can further depend at least in part upon the space provided between the throat  30  and the cooling coil  40 .  
     [0024] An example of a support  42  according to a preferred embodiment of the invention is illustrated in FIG. 4. The support  42  shown has a cross-section that is polygonal in shape. It has an upper surface  46  and an inner surface  48  which preferably extends downward from the upper surface  46  at about a right angle relative to the upper surface  46 . An outer surface  50  of the support  42  preferably extends downward from the upper surface  46  and at about a right angle relative to the upper surface  46  and substantially parallel to the inner surface  48 . A lower surface  52  of the support  42  extends between the inner and outer surfaces  48 ,  50 . The lower surface  52  extends at an obtuse angle relative to the inner surface  48  and an acute angle relative to the outer surface  50 . The upper surface  46  is adapted to engage the underside of the flange  34 . The inner surface  48  is adapted to engage the throat  30 . The lower surface  52  is adapted to engage the upper portion  44  of the side wall  24 . The length of the support  42  depends at least in part upon the longitudinal dimension of the bushing  16 . The width or lateral dimension of the upper surface  46  depends at least in part upon the width or lateral dimension of the flange  34  and the distance between the throat  30  and the cooling coil  40 . The vertical dimension of the inner surface  48  depends upon the vertical dimension of the throat  30 . The dimensions of the outer surface  50  and the lower surface  52  depend at least in part upon the dimension of the upper portion  44  of the side wall  24 , which is largely dependent upon its angle θ.  
     [0025] It should be clearly understood by one of ordinary skill in the art of the invention that the shape of the support  42  can vary and that the present invention is not intended to be limited to the shape shown and described. For example, the outer surface  50  of the support  42  may extend at an acute or obtuse angle relative to the upper surface  46 . The support  42  can have rounded corners, as shown, or relatively sharp corners (not shown). Moreover, the ends  54 ,  56  of the support  42  can be squared off, as shown, or, although not shown, rounded, similar to the rounded corners. It should also be understood that the outer surface  50  can have a relief (not shown) for receiving the cooling coil  40 .  
     [0026] The support  42  is preferably formed from a non-deteriorating material that has a resistance to high temperature and a high tensile strength. The material is preferably resistant to high temperatures, for example, in a range of about 2,100 to 2,900 degrees Fahrenheit. The modulus of rupture (MOR) of the support  42  preferably exceeds that of the refractory material  20 . The MOR of the refractory material  20  is in the range of about 200 to 1000 pounds per square inch (PSI). A support  42  according to a preferred embodiment of the invention would have a MOR of several thousand PSI.  
     [0027] In the most preferred embodiment of the invention, the support  42  is extruded from a ceramic material, such as mullite, zircon, alumna, or an equivalent thereto. Such materials have tensile strengths capable of withstanding stress endured by the elongate portion  38  of the flange  34  over its entire span and maintaining rigidity during the service life of the bushing  16 .  
     [0028] It should be appreciated by one of ordinary skill in the art of the invention that the support  42  may be formed from a high temperature-high strength material other than a ceramic material. Moreover, the support  42  may be formed from a composite material, such as a ceramic matrix with a high temperature-high strength fiber reinforcement.  
     [0029] In the preferred embodiment of the invention, the cooling coil  40  is mounted to an underside of the flange  32  so that a support  42  is held in place between each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24  by the cooling coil  40 . In this way, the cooling coil  40  holds a support  42  between each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24  while the refractory material  20  is cast and permitted to set up. It should be clearly understood that, after the refractory material  20  sets up, the refractory material  20  holds the support  42  in place.  
     [0030] The support  42  provides a continuous rigid structural support for the upper end of the bushing  16  and, more particularly, the throat  30  and each elongate portion  38  of the flange  34 . The support  2  fits tightly in the clearance provided between each elongate portion  38  of the flange  34  and the upper portion  44  of each side wall  24 . The support  42  maintains the rigidity and shape of the throat  30  and the flange  34  during the operation of the bushing  16  and thus reinforces the throat  30  and prevents each elongate portion  38  of the flange  34  from collapsing during the service life of the bushing  16 . Consequently, a proper seal is maintained between the underside of the bushing block  12  and each elongate portion  38  of the flange  34 , thus minimizing the gap between the underside of the bushing block  12  and each elongate portion  38  of the flange  34 . This, in turn, reduces the risk of glass leaking between the bushing block  12  and each elongate portion  38  of the flange  32 . Any leakage that does occur will be solidified by the cooling coil  40 .  
     [0031] In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.