Abstract:
A precious metal structure which has an internal gas permeable membrane is described herein for a glass manufacturing vessel configured to have molten glass flow therein. The internal gas permeable membrane can be supplied with an atmosphere of gas (or gases) to control the flux of hydrogen into our out of the molten glass or otherwise improve the production of the molten glass. In this manner, the undesirable detrimental reactions that can occur at the interface of the molten glass and precious metal interface which can cause defects in the molten glass such as bubbles or solid inclusions can be stopped or at least substantially reduced.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of U.S. patent application Ser. No. 13/524,558 filed on Jun. 15, 2012, now U.S. Pat. No. 9,073,771, the content of which is relied upon and incorporated herein by reference in its entirety, and the benefit of priority under 35 U.S.C. §120 is hereby claimed. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a glass manufacturing vessel, glass manufacturing systems, methods for producing a glass sheet or glass article, and a method for fabricating the glass manufacturing vessel. The glass manufacturing vessel is configured to have molten glass flow therein. Plus, the glass manufacturing vessel includes an external layer, an intermediate layer, and an internal layer, where the intermediate layer is positioned between the external layer and the internal layer, and where the intermediate layer has a gas permeable structure that permits an atmosphere of gas to pass therein between the external layer and the internal layer. For example, the atmosphere of gas can be such to maintain a positive pressure within open spaces of the intermediate layer and to suppress blister formation within the molten glass. In addition, the present invention relates to a device (e.g., bell device, stirrer, thermocouple, level probe) configured to be partially inserted into molten glass. Furthermore, the present invention relates to a system which incorporates a bell device for manufacturing glass tubing. 
       BACKGROUND 
       [0003]    A wide variety of devices such as Liquid Crystal Displays (LCDs), smart phones, tablet computers utilize flat glass sheets. A preferred technique for manufacturing these flat glass sheets is the fusion process. In the fusion process, the glass sheets are made by using glass manufacturing vessels that contain precious metals, e.g. platinum or platinum alloys. The precious metals are generally considered to be inert in relation to most glasses, and thus should not cause any inclusions in the glass sheets. However, this is not necessarily valid. 
         [0004]    There are oxidation reactions that occur at the metal/glass interface inside the glass manufacturing vessel which leads to the generation of gaseous inclusions in the molten glass and thus the glass sheet. One of the more common oxidation reactions that occur at the metal/glass interface is the conversion of negatively charged oxygen ions to molecular oxygen which is caused by the thermal breakdown of water and hydroxyl species in the molten glass. This phenomenon occurs because at the elevated temperatures of glass melting and delivery, a low partial pressure of hydrogen exists in the molten glass. Thus, when hydrogen comes in contact with the precious metal vessel containing the molten glass, the hydrogen rapidly permeates out of the glass manufacturing vessel, depleting the metal/glass interface of hydrogen. Based on the chemical balance, for every mole of hydrogen that leaves the glass manufacturing vessel, ½ mole of oxygen is left behind at the glass/metal interface. Thus, as hydrogen leaves the glass manufacturing vessel, the oxygen level or partial pressure of oxygen at the metal/glass interface increases, which leads to the generation of blisters or gaseous inclusions in the molten glass. In addition, there are other reactions which involve the catalyzing or oxidation of other species within the molten glass such as halogens (Cl, F, Br) which can lead to the generation of gaseous inclusions within the molten glass and the resulting glass sheet. Further, there are oxidation reactions which can occur due to electrochemical reactions at the metal/glass interface. These electrochemical reactions can be associated with thermal cells, galvanic cells, high AC or DC current applications and grounding situations. 
         [0005]    Today, there are several known methods that can be used to address these problematical oxidation reactions which cause the formation of gaseous inclusions in the molten glass and the resulting glass sheet. These known methods range from the use of glass coatings, atmospheric control around the external surfaces of the glass manufacturing vessels to DC protection. All of these methods have their uses, but come with significant costs and can be difficult to implement and maintain. For instance, there is a method which involves the use of a humidity controlled enclosure that surrounds one or more of the precious metal-containing glass manufacturing vessels and is used to control the partial pressure of hydrogen outside the vessel(s) so as to reduce the formation of gaseous inclusions in the glass sheets. Several different types of these humidity controlled enclosures are discussed in U.S. Pat. No. 5,785,726 and U.S. Pat. No. 7,628,039 (the contents of which are incorporated by reference herein). Although the use of a humidity controlled enclosure is effective, it is also expensive both in the capital cost to construct as well as the cost of operation. The principle expenses of operation are nitrogen, energy for air conditioning and steam production as well as the energy required for the fans that drive gas circulation. Thus, it would be desirable to provide an alternative method to prevent the formation of gaseous inclusions in glass sheets. This need and other needs are satisfied by the present invention. 
       SUMMARY 
       [0006]    A glass manufacturing vessel, glass manufacturing systems, methods for producing a glass sheet or glass article, a method for fabricating the glass manufacturing vessel, a device configured to be partially inserted into molten glass, and to a system for manufacturing glass tubing are described in the independent claims of the present application. Advantageous embodiments of the glass manufacturing vessel, glass manufacturing systems, methods for producing a glass sheet or glass article, the method for fabricating the glass manufacturing vessel, the device configured to be partially inserted into molten glass, and to the system for manufacturing glass tubing are described in the dependent claims. 
         [0007]    In one aspect, the present invention provides a glass manufacturing vessel configured to have molten glass flow therein. The glass manufacturing vessel comprises: (1) an external layer with a first side and a second side; (2) an intermediate layer; and (3) an internal layer with a first side and a second side. The intermediate layer is positioned between the second side of the external layer and the first side of the internal layer. In addition, the intermediate layer has a gas permeable structure that permits an atmosphere of gas to pass therein between the second side of the external layer and the first side of the internal layer. 
         [0008]    In another aspect, the present invention provides a glass manufacturing system comprising: (a) a glass manufacturing vessel configured to have molten glass flow therein; and (2) a control system. The glass manufacturing vessel comprises: (1) an external layer with a first side and a second side; (2) an intermediate layer; and (3) an internal layer with a first side and a second side. The intermediate layer is positioned between the second side of the external layer and the first side of the internal layer. In addition, the intermediate layer has a gas permeable structure that permits an atmosphere of gas to pass therein between the second side of the external layer and the first side of the internal layer. The control system supplies the atmosphere of gas to the intermediate layer of the glass manufacturing vessel. 
         [0009]    In yet another aspect, the present invention provides a method for producing a glass article. The method comprising the steps of: (a) flowing molten glass through a glass manufacturing vessel that comprises: (1) an external layer with a first side and a second side; (2) an intermediate layer; and (3) an internal layer with a first side and a second side, where the intermediate layer is positioned between the second side of the external layer and the first side of the internal layer, and where the intermediate layer has a gas permeable structure that permits an atmosphere of gas to pass therein between the second side of the external layer and the first side of the internal layer; and (b) supplying the atmosphere of gas to the intermediate layer of the glass manufacturing vessel. 
         [0010]    In still yet another aspect, the present invention provides a glass manufacturing system comprising: (a) a melting vessel within which glass batch materials are melted to form molten glass; (b) a melting to fining tube which receives the molten glass from the melting vessel; (c) a fining vessel which receives the molten glass from the melting to fining tube and removes bubbles from the molten glass; (d) a finer to stir chamber tube which receives the molten glass from the fining vessel; (e) a stir chamber which receives the molten glass from the finer to stir chamber tube and mixes the molten glass; (f) a stir chamber to bowl connecting tube which receives the molten glass from the stir chamber; (g) a bowl which receives the molten glass from the stir chamber to bowl connecting tube; (h) a downcomer which receives the molten glass from the bowl; (i) a fusion draw machine which includes at least an inlet, and a forming vessel where: the inlet receives the molten glass from the downcomer; the forming apparatus receives the molten glass from the inlet and forms a glass sheet; and (j) at least one of the melting to fining tube, the fining vessel, the finer to stir chamber tube, the stir chamber, the stir chamber to bowl connecting tube, the bowl, the downcomer, and the inlet further comprises: (1) an external layer with a first side and a second side; (2) an intermediate layer; (3) and an internal layer with a first side and a second side, where the intermediate layer is positioned between the second side of the external layer and the first side of the internal layer, where the intermediate layer has a gas permeable structure that permits an atmosphere of gas to pass therein between the second side of the external layer and the first side of the internal layer; and (k) a control system that supplies the atmosphere of gas to the intermediate layer of the at least one of the melting to fining tube, the fining vessel, the finer to stir chamber tube, the stir chamber, the stir chamber to bowl connecting tube, the bowl, the downcomer, and the inlet. 
         [0011]    In yet another aspect, the present invention provides a method for producing a glass sheet. The method comprising the steps of: (a) melting, within a melting vessel, glass batch materials to form molten glass; (b) removing, within a fining vessel, bubbles from the molten glass, where the melting vessel is connected to the fining vessel by a melting to fining tube; (c) mixing, within a stir chamber, the molten glass, where the stir chamber is connected to the fining vessel by a finer to stir chamber tube; (d) receiving, at a bowl, the molten glass, where the bowl is connected to the stir chamber by a stir chamber to bowl connecting tube; (e) receiving, at a downcomer, the molten glass, where the downcomer is connected to the bowl; (f) delivering, to an inlet, the molten glass, where the inlet is associated with the downcomer; (g) delivering, to a forming apparatus, the molten glass, where the forming apparatus is connected to the inlet; (h) forming, at the forming apparatus, a glass sheet from the molten glass; (i) at least one of the melting to fining tube, the fining vessel, the finer to stir chamber tube, the stir chamber, the stir chamber to bowl connecting tube, the bowl, the downcomer, and the inlet further comprises: (1) an external layer with a first side and a second side; (2) an intermediate layer; and (3) an internal layer with a first side and a second side, where the intermediate layer is positioned between the second side of the external layer and the first side of the internal layer, where the intermediate layer has a gas permeable structure that permits an atmosphere of gas to pass therein between the second side of the external layer and the first side of the internal layer; and (j) supplying, from a control system, the atmosphere of gas to the intermediate layer of the at least one of the melting to fining tube, the fining vessel, the finer to stir chamber tube, the stir chamber, the stir chamber to bowl connecting tube, the bowl, the downcomer, and the inlet. 
         [0012]    In still yet another aspect, the present invention provides a method for fabricating a glass manufacturing vessel. The method comprising the step of laminating an external layer, an intermediate layer, and an internal layer, where the external layer has a first side and a second side and the internal layer has a first side and a second side, where the intermediate layer is positioned between the second side of the external layer and the first side of the internal layer, and where the intermediate layer has a gas permeable structure that permits an atmosphere to pass therein between the second side of the external layer and the first side of the internal layer. 
         [0013]    In one aspect, the present invention provides a device configured to be partially inserted into molten glass. The device comprising: (a) a section having a first end and a second end, where the first end is not inserted into the molten glass and the second end is inserted into the molten glass; (b) a mesh wrapped around at least a portion of the section; and (c) a cladding wrapped around at least a portion of the mesh, wherein the mesh has a gas permeable structure that permits gas to pass therein between the section and the cladding, and the gas is permitted to exit from the mesh at the first end which is not inserted into the molten glass. 
         [0014]    In another aspect, the present invention provides a system for manufacturing glass tubing. The system comprising: (a) a glass forehearth through which molten glass flows; (b) a device configured to be partially inserted into the molten glass within the glass forehearth, the device comprising: (i) a section having a first end and a second end, where the first end is not inserted into the molten glass and the second end is inserted into the molten glass; (ii) a bell attached to the second end and inserted into the molten glass; (iii) a mesh wrapped around at least a portion of the section; and (iv) a cladding wrapped around at least a portion of the mesh, wherein the mesh has a gas permeable structure that permits gas to pass therein between the section and the cladding, and the gas is permitted to exit from the mesh at the first end which is not inserted into the molten glass; and (c) the device further configured to have the molten glass flow there around the section which has the mesh and cladding wrapped thereon and the bell before the molten glass exits the glass forehearth to form the glass tubing. 
         [0015]    Additional aspects of the invention will be set forth, in part, in the detailed description, figures and any claims which follow, and in part will be derived from the detailed description, or can be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A more complete understanding of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
           [0017]      FIG. 1  is a schematic view of an exemplary glass manufacturing system which uses a fusion draw process to manufacture a glass sheet in accordance with an embodiment of the present invention; 
           [0018]      FIG. 2  is a cross-sectional side view of a finer to stir chamber tube (with a level probe stand pipe extending therefrom) of the glass manufacturing system shown in  FIG. 1  configured in accordance with an embodiment of the present invention; 
           [0019]      FIGS. 3A-3B  respectively show a cross-sectional side view and a cross-sectional end view of an exemplary glass manufacturing vessel configured in accordance with an embodiment of the present invention; 
           [0020]      FIGS. 4A-4B  respectively show a cross-sectional side view and a cross-sectional end view of an exemplary glass manufacturing vessel configured in accordance with another embodiment of the present invention; 
           [0021]      FIGS. 5A-5B  respectively show a cross-sectional side view and a cross-sectional end view of an exemplary glass manufacturing vessel configured in accordance with yet another embodiment of the present invention; 
           [0022]      FIGS. 6 ,  7 ,  8 A,  8 B,  8 C,  8 D,  8 E and  8 F are photographs used to help describe a process that was used in a lab to form and use an exemplary composite metal structure in accordance with an embodiment of the present invention; 
           [0023]      FIGS. 9A-9B  are two diagrams used to explain one example of how the aforementioned composite metal structure can be applied to a device which is used in a glass forehearth to form glass tubing in accordance with yet another embodiment of the present invention; and 
           [0024]      FIG. 10  is a diagram used to describe a device (e.g., stirrer, thermocouple, level probe) which is configured to be partially inserted into molten glass in accordance with yet another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Referring to  FIG. 1 , there is shown a schematic view of an exemplary glass manufacturing system  100  which uses a fusion draw process to manufacture a glass sheet  102  in accordance with an embodiment of the present invention. The glass manufacturing system  100  includes a melting vessel  110 , a melting to fining tube  115 , a fining vessel  120 , a finer to stir chamber tube  125  (with a level probe stand pipe  127  extending therefrom), a stir chamber  130  (e.g., mixing vessel  130 ), a stir chamber to bowl connecting tube  135 , a bowl  140  (e.g., delivery vessel  140 ), a downcomer  145 , a fusion draw machine (FDM)  150  (which includes an inlet  155 , a forming apparatus  160 , and a pull roll assembly  165 ), and a traveling anvil machine (TAM)  170 . Typically, the glass manufacturing vessels  115 ,  120 ,  125 ,  127 ,  130 ,  135 ,  140 ,  145  and  155  are made from platinum or platinum-containing metals such as platinum-rhodium, platinum-iridium and combinations thereof, but they may also comprise other refractory metals such as palladium, rhenium, ruthenium, and osmium, or alloys thereof. The forming apparatus  160  (e.g., isopipe  160 ) is typically made from a ceramic material or glass-ceramic refractory material. 
         [0026]    The melting vessel  110  is where glass batch materials are introduced as shown by arrow  112  and melted to form molten glass  114 . The fining vessel  120  (e.g., finer tube  120 ) is connected to the melting vessel  110  by the melting to fining tube  115 . The fining vessel  120  has a high temperature processing area that receives the molten glass  114  (not shown at this point) from the melting vessel  110  and in which bubbles are removed from the molten glass  114 . The fining vessel  120  is connected to the stir chamber  130  by the finer to stir chamber connecting tube  125 . The stir chamber  130  is connected to the bowl  140  by the stir chamber to bowl connecting tube  135 . The bowl  140  delivers the molten glass  114  (not shown) through the downcomer  145  into the FDM  150 . 
         [0027]    The FDM  150  includes the inlet  155 , the forming vessel  160  (e.g., isopipe  160 ), and the pull roll assembly  165 . The inlet  155  receives the molten glass  114  (not shown) from the downcomer  145  and from the inlet  155  the molten glass  114  (not shown) then flows to the forming vessel  160 . The forming vessel  160  includes an opening  162  that receives the molten glass  114  (not shown) which flows into a trough  164  and then overflows and runs down two opposing sides  166   a  and  166   b  before fusing together at a root  168  to form a glass sheet  109 . The pull roll assembly  165  receives the glass sheet  109  and outputs a drawn glass sheet  111 . The TAM  170  receives the drawn glass sheet  111  and separates the drawn glass sheet  111  into separate glass sheets  102 . 
         [0028]    In accordance with an embodiment of the present invention, one or more of the glass manufacturing vessels  115 ,  120 ,  125 ,  127 ,  130 ,  135 ,  140 ,  145  and  155  have a configuration which enables an atmosphere of gas to pass therein which helps suppress hydrogen permeation blistering within the molten glass  114  or otherwise benefit the glass production. Furthermore, the glass manufacturing system  100  includes one or more control systems  175  which supply the atmosphere to the one or more specially configured glass manufacturing vessels  115 ,  120 ,  125 ,  127 ,  130 ,  135 ,  140 ,  145  and  155 . For instance, one control system  175  can be used to supply the atmosphere of gas to all of the specially configured glass manufacturing vessels  115 ,  120 ,  125 ,  127 ,  130 ,  135 ,  140 ,  145  and  155 . Or, one control system  175  can be used to supply the atmosphere to one or any combination of the specially configured glass manufacturing vessels  115 ,  120 ,  125 ,  127 ,  130 ,  135 ,  140 ,  145  and  155 . A detailed description about one of the specially configured glass manufacturing vessels  115 ,  120 ,  125 ,  127 ,  130 ,  135 ,  140 ,  145  and  155  namely the finer to stir chamber tube  125  (with the level probe stand pipe  127  extending therefrom) is discussed next with respect to  FIG. 2 . 
         [0029]    Referring to  FIG. 2 , there is shown a cross-sectional view of an exemplary finer to stir chamber tube  125  (with the level probe stand pipe  127  extending therefrom) configured in accordance with an embodiment of the present invention. As shown, the finer to stir chamber tube  125  has an input  202  from which molten glass  114  is received from the fining vessel  120  (not shown) and an output  204  from which the molten glass  144  is provided to the stir chamber  130  (not shown). The finer to stir chamber tube  125  and the level probe stand pipe  127  include an external layer  206  (e.g., precious metal sheet  206 ), an intermediate layer  208  (e.g., mesh screen  208 , beads  208 , corrugated or dimpled metal sheet  208 ) and an internal layer  210  (e.g., precious metal sheet  210 ). The intermediate layer  208  is positioned or otherwise located between the external layer  206  and the internal layer  210 . The intermediate layer  208  has a gas permeable structure that permits an atmosphere of gas to pass therein between the external layer  206  and the internal layer  210 . The control system  175  creates and provides the atmosphere of gas through an input port  212  within the external layer  206  to the intermediate layer  208 . The atmosphere of gas maintains a positive pressure within open spaces of the intermediate layer  208  and suppresses blister formation within the molten glass  114  or otherwise benefits the glass production. The gas may exit the intermediate layer  208  from one or more outlet ports  214  (two shown) formed within the external layer  206 . For example, the gas output from the intermediate layer  208  may be recycled by the control system  175 , or some other recovery system, or released into the manufacturing facility. Alternatively, if the finer to stir chamber tube  125  and the level probe stand pipe  127  are not totally gas tight then only the input port  212  may be used and the gas can leak out at some other place or places in the finer to stir chamber tube  125  and the level probe stand pipe  127 . It should be appreciated that the finer to stir chamber tube  125  and the level probe stand pipe  127  or any glass manufacturing vessel can have any type of shape and this particular precious metal structure  206 ,  208  and  210  or a wide variety of different precious metal structures  206 ,  208  and  210  in accordance with different embodiments of the present invention as will be discussed next with respect to  FIGS. 3-5 . 
         [0030]    Referring to  FIGS. 3A-3B , there are respectively shown a cross-sectional side view and a cross-sectional end view of an exemplary glass manufacturing vessel  300  configured in accordance with an embodiment of the present invention. The glass manufacturing vessel  300  is designed to have molten glass  114  flow therein. The glass manufacturing vessel  300  is configured to have an external layer  206  (e.g., precious metal sheet  206 ), an intermediate layer  208  (e.g., mesh screen  208 , beads  208 , corrugated or dimpled metal sheet  208 ) and an internal layer  210  (e.g., precious metal sheet  210 ). The external layer  206  includes a first side  302  and a second side  304  and the internal layer  210  includes a first side  306  and a second side  308 . The intermediate layer  208  is positioned or otherwise formed between the second side  304  of external layer  206  and the first side  306  of the internal layer  210 . The intermediate layer  208  has a gas permeable structure that permits an atmosphere of gas to pass therein between the external layer  206  and the internal layer  210 . In this example, the internal layer&#39;s second side  308  contacts the molten glass  114 . The control system  175  (not shown) creates and provides the atmosphere of gas through an input port  212  within the external layer  206  to the intermediate layer  208 . The atmosphere of gas maintains a positive pressure within open spaces of the intermediate layer  208  and suppresses blister formation within the molten glass  114  or otherwise benefits the glass production. The gas may exit the intermediate layer  208  from an outlet port  214  (if used) formed within the external layer  206 . The gas output from the intermediate layer  208  may be recycled by the control system  175  (not shown), some other recovery system, or released into the manufacturing facility. A discussion is provided next with respect to  FIGS. 4 and 5  to explain how an existing glass manufacturing vessel can be retrofitted to be configured in accordance with an embodiment of the present invention. 
         [0031]    Referring to  FIGS. 4A-4B , there are respectively shown a cross-sectional side view and a cross-sectional end view of an exemplary glass manufacturing vessel  400  configured in accordance with an embodiment of the present invention. The glass manufacturing vessel  400  is formed by taking an existing glass manufacturing vessel  402  (existing structure  402 ) and applying the intermediate layer  208  (e.g., mesh screen  208 , corrugated or dimpled metal sheet  208 ) over the existing glass manufacturing vessel  402  (existing structure  402 ) and then applying the external layer  206  (e.g., precious metal sheet  206 ) over the intermediate layer  208 . In this case, the aforementioned internal layer  210  is the existing glass manufacturing vessel  402  (existing structure  402 ). The intermediate layer  208  has a gas permeable structure that permits an atmosphere of gas to pass therein between the external layer  206  and the existing glass manufacturing vessel  402  (existing structure  402 ). The control system  175  (not shown) creates and provides the atmosphere of gas through the input port  212  within the external layer  206  to the intermediate layer  208 . The atmosphere of gas maintains a positive pressure within open spaces of the intermediate layer  208  and suppresses blister formation within the molten glass  114  or otherwise benefits the glass production. The gas may exit the intermediate layer  208  from the outlet port  214  (if used) formed within the external layer  206 . The gas output from the intermediate layer  208  may be recycled by the control system  175  (not shown), some other recovery system, or released into the manufacturing facility if the system if not fully gas tight. 
         [0032]    Referring to  FIGS. 5A-5B , there are respectively shown a cross-sectional side view and a cross-sectional end view of an exemplary glass manufacturing vessel  500  configured in accordance with an embodiment of the present invention. The glass manufacturing vessel  500  is formed by taking an existing glass manufacturing vessel  502  (existing structure  502 ) and applying the external layer  206  over the existing glass manufacturing vessel  502  (existing structure  502 ). In this case, the external layer  206  has a corrugated or dimpled structure such that the intermediate layer  208  is formed by the open spaces that are created when the external layer  206  is positioned next to the existing glass manufacturing vessel  502  (existing structure  502 ). In the illustrated example, the corrugated external layer  206  is positioned to be just off the existing structure  502  so the gas atmosphere can pass through all of openings created by the corrugated external layer  206 . Alternatively, the corrugated external layer  206  can contact the existing structure  502  but in this case the input port  212  would be around the entire perimeter of the corrugated external layer  206  so the gas atmosphere can pass the openings created by the corrugated external layer  206 . In another example, the dimpled external layer  206  can have dimples that contact the internal layer  210  at selected points and thus create the gas permeable layer  208  so the gas atmosphere can pass in between the dimpled external layer  206  and the internal layer  210 . If desired, the glass manufacturing vessel  502  does not need to be made from existing glass manufacturing vessel  502  but could be made by taking a new structure (e.g., downcomer, bowl) and then applying the external layer  206  which has the corrugated or dimpled structure over the new structure. In any case, the aforementioned internal layer  210  is the existing glass manufacturing vessel  502  (existing structure  502 ) or the new structure. Plus, the formed intermediate layer  208  permits an atmosphere of gas to pass therein between the external layer  206  and the existing glass manufacturing vessel  502  (existing structure  502 ) or the new structure. The control system  175  (not shown) creates and provides the atmosphere of gas through the input port  212  within the external layer  206  to the intermediate layer  208  (e.g., open spaces). The atmosphere of gas maintains a positive pressure within open spaces of the intermediate layer  208  and suppresses blister formation within the molten glass  114  or otherwise benefits the glass production. The gas may exit the intermediate layer  208  from the outlet port  214  (if used) formed within the external layer  206 . The gas output from the intermediate layer  208  may be recycled by the control system  175  (not shown), some other recovery system, or released into the manufacturing facility. 
         [0033]    In view of the foregoing, one will appreciate that in one of its simplest forms the present invention relates to the fabrication and use of a glass manufacturing vessel  300 ,  400  and  500  (which can have any physical shape) that has an intermediate layer  208  (e.g., integral gas permeable membrane  208 ) located or formed between two layers of precious metal  206  and  210 . The intermediate layer  208  (e.g., integral gas permeable membrane  208 ) would have an atmosphere of gas passed through it to suppress hydrogen permeation blistering in the molten glass  114  or to provide an atmosphere of benefit to the glass production. In addition, one will appreciate that the glass manufacturing vessel  300 ,  400  and  500  with this composite metal  206 ,  208  and  210  could be used for the melting, delivery or forming of glass. The glass manufacturing vessel  300 ,  400  and  500  with the intermediate layer  208  (e.g., integral gas permeable membrane  208 ) could be fabricated in many ways several of which are discussed below. 
         [0034]    One exemplary method of fabricating the glass manufacturing vessel  300  (for example) is the lamination of the intermediate layer  208  (e.g., woven precious metal mesh  208 ) between the external and internal layers  206  and  210  (e.g., two layers of platinum cladding  206  and  208 ). This can be done by roll bonding, welding or by the fabrication of concentric cylinders that are nested together.  FIGS. 6 and 7  are photographs of an exemplary composite metal structure  206 ,  208  and  210  that was fabricated in the lab by roll bonding.  FIG. 6  is a cross section of the precious metal mesh  208  laminated between two sheets of 0.010″ thick precious metal  206  and  210  (see also  FIGS. 8A-8F ).  FIG. 7  is a close-up of the cross section of the precious metal mesh  208  laminated between the two precious metal sheets  206  and  210  where the atmosphere can pass in open spaces  702  between the two precious metal sheets  206  and  210 . 
         [0035]    The control system  175  can provide the protective atmosphere which could be introduced into the intermediate layer  208  (e.g., woven precious metal mesh  208 ) through the ends or by one or more inlet ports  212  drilled into the external (non-glass contact) skin of the structure. Typically, the control system  175  would only need to supply a volume of gas which is enough to maintain a positive pressure of gas inside the intermediate layer  208 . In one example, the control system  175  should be able to humidify whatever gas mixture is introduced into the intermediate layer  208 . In addition, the control system  175  should be able to mix various gases such as nitrogen and water or combustible gases and supply the atmosphere using mass flow controllers. Furthermore, the control system  175  should be able to accurately control the partial pressures of the various gases to help suppress hydrogen permeation blistering in the molten glass  114  or otherwise benefit glass production. 
         [0036]    Referring to  FIGS. 8A-8F , there are photographs used to help describe a process that was used in a lab to form and use the exemplary composite metal structure  206 ,  208  and  210  shown in  FIGS. 6-7 . The first step in the fabrication of the gas permeable precious metal structure  206 ,  208  and  210  is to assembly the starting materials which in this case include a 40 mesh Pt-10Rh screen  208  and two 0.010″ thick Pt sheets  206  and  210  (see  FIGS. 8A-8C ). The 40 mesh Pt-10Rh screen  208  used in this demonstration was woven in structure and constructed of 0.008″ diameter wires. However, it should be appreciated that a broad range of wire diameters, mesh sizes, cladding thicknesses and metal compositions could be used for the gas permeable precious metal structure  206 ,  208  and  210 . In any case, the sandwich of Pt metal sheets  206  and  210  with the 40 mesh Pt-10Rh screen  208  positioned in between the two Pt metal sheets  206  and  210  was spot welded together in the center for ease of handling and to keep the structure together during the assembly process. Then, the sandwich of Pt metal sheets  206  and  210  with the 40 mesh Pt-10Rh screen  208  was heated to 1200° C. and transferred hot to the rolling mill  802 . Thereafter, the sandwich of Pt metal sheets  206  and  210  with the 40 mesh Pt-10Rh screen  208  was rolled together with a roll gap setting to give a 10% reduction in thickness (see  FIG. 8D ). This roll cladding procedure was repeated one more time with an additional 10% reduction in thickness, after reheating the sandwich of Pt metal sheets  206  and  210  with the 40 mesh Pt-10Rh screen  208  to 1200° C. (see  FIG. 8E ). The cross sections of the structure produced in this experiment are shown in  FIGS. 6-7  where it can readily be seen that the woven structure of the 40 mesh Pt-10Rh screen  208  provides areas of continuous porosity  702  where the protective atmosphere would flow between the two Pt metal sheets  206  and  210 . 
         [0037]    To verify that the assembled sandwich of Pt metal sheets  206  and  210  with the 40 mesh Pt-10Rh screen  208  did indeed include a gas permeable membrane  208  that was an integral part of the cladding a flow test was run. For this test, the two longer sides of the laminated structure  206 ,  208  and  210  were welded together to provide a gas tight seal. This left the laminated structure  206 ,  208  and  208  with openings at both shorter ends. As shown in  FIG. 8F , a plastic tube  802  was taped to one short end (located behind thumb) of the laminated structure  206 ,  208  and  210  as an inlet for gas. Then, liquid soap  806  was applied to the opposing short end  808  of the laminated structure  206 ,  208  and  210  as a method to detect gas flow through the laminated structure  206 ,  208  and  210 . A slight flow of gas was applied through the plastic tub  802 . As can be seen in  FIG. 8F , the gas flow resulted in the liquid soap  806  generating bubbles at the other end  808  of the laminated structure  206 ,  208  and  210 . 
         [0038]    The process described above is exemplary and by no means the only method for fabricating and utilizing the composite metal structure  206 ,  208  and  210 . As an alternative, the metal external layer  206 , intermediate layer  208  (e.g., mesh) and the metal internal layer  210  could be fabricated together by standard sheet metal technology of forming and welding. Additionally, the intermediate layer  208  could be beads of precious metal or an inert refractory material that provide some structural support and separation for gas flow between the external layer  206  (e.g., precious metal sheet  206 ) and the internal layer  210  (e.g., precious metal sheet  210 ). In addition, the intermediate layer  208  with the porous structure could be formed by joining a corrugated or dimpled external layer  206  to a corrugated or dimpled internal layer  206  to make a laminate structure. Alternatively, the intermediate layer  208  with the porous structure could be formed by joining a corrugated or dimpled external layer  206  to flat internal layer  210  or vice versa joining a flat external layer  206  to a corrugated or dimpled internal layer  210  to make a laminate structure. Furthermore, it is possible to use dissimilar materials for the external layer  206  and the internal layer  210  cladding of the laminate structure. For instance, a material such as Iridium that has favorable properties for glass contact yet is prone to oxidation could be used as the internal layer  210 . The iridium would provide erosion and contamination resistance, yet be protected from oxidation on its external surface by flowing a reducing environment within the intermediate layer  208  between the external layer  206  and the internal layer  210 . The external layer  206  could be made of standard precious metal for resistance to oxidation. Moreover, the mesh that is used as the intermediate layer  208  could be made of some material with superior strength to the standard Pt-20Rh alloy. The mesh would not necessarily have to be compatible with the molten glass  114 , since it would not come in contact with the molten glass  114 . 
         [0039]    Finally, the composite metal structure  206 ,  208  and  210  and in particular the intermediate layer  208  (e.g., gas permeable precious metal structure  208 ) should be designed from an atmosphere flow standpoint such that the intermediate layer  208  has open spaces (e.g., pore sizes) that are large as possible to minimize the pressure drop and flow restriction for the atmosphere inside the gas permeable precious metal structure  206 ,  208  and  210 . From a strength standpoint, the composite metal structure  206 ,  208  and  210  should be designed such that the intermediate layer  208  has open spaces (e.g., pore sizes) which are minimized to support the external layer  206  and the internal layer  208  on either side of the intermediate layer  208  and prevent the external layer  206  and the internal layer  210  from sagging or creeping into the open spaces (e.g., pores) in the intermediate layer  208 . For instance, the bigger the open spaces (e.g., pore sizes), the more likely the internal layer  210  will sag into the void area from the hydrostatic pressure of the glass head inside the glass manufacturing vessel. Basically, all of these factors should at least be taken into account when designing the composite metal structure  206 ,  208  and  210  for use in the glass manufacturing system. 
         [0040]    From the foregoing, one skilled in the art will appreciate that present invention relates to a method and procedure to fabricate and use an intermediate layer  208  (e.g., integral gas permeable structure  208 ) between the external layer  206  and internal layer  210  which can be the platinum cladding of a glass manufacturing vessel for manufacturing high quality glass. The integral gas permeable structure  208  is internal to the precious metal cladding  206  and  210  and serves as a distribution system for the protective atmosphere for hydrogen permeation blistering suppression or otherwise benefiting the glass production. In other words, the “capsule” intermediate layer  208  is actually part of the structure of the platinum wall of the melt, delivery and forming glass manufacturing vessels. As discussed above, there are many ways to make the composite metal structure  206 ,  208  and  210  with the integral gas permeable structure  208 . One exemplary process is to laminate a precious metal sheet  206  (e.g., platinum sheet  206 ), a woven precious metal mesh screen  208  and another precious metal sheet  210  (e.g., platinum sheet  210 ). One layer of the precious metal sheet  210  would be the glass contact or inside surface of the glass manufacturing vessel  300 ,  400  and  500 . The mesh screen  208  would serve to create a gas permeable gap between the two precious metal sheets  206  and  210 . The open spaces of the mesh screen  208  is where the atmosphere would flow to surround the precious metal sheet  210  that is in contact with the production molten glass  114 . The external layer  206  of platinum would serve as the external vessel to contain the protective atmosphere and prevent its leakage or dilution. The present invention would eliminate the need for an external capsule and the large Environmental Control Unit (ECU) used for the generation and control of the protective atmosphere. There are many advantages that the present invention has over the current technology. For instance, some of the advantages that the present invention has over the existing capsule and enclosure technology are as follows: 
         [0041]    Capability Advantage
       The laminated or internal porous structure of the present invention is an integral part of the platinum cladding of the melt, delivery or forming system and as a result there is flexibility in where and how it can be installed.   The laminated or internal porous structure of the present invention can be used as a replacement for any area of current cladding in a glass manufacturing system. For instance, there may be an area of the melt, delivery or forming system where the current protective atmosphere adversely affects the life of performance of the parts of the system and the laminated or internal platinum structure of the present invention can be used in this area of the melt, delivery or forming system.   The laminated or internal porous structure of the present invention can be used to improve sealing in general and to improve the ability to have better atmosphere control because leakage into and out of the protective atmosphere can be controlled.       
 
         [0045]    Cost Advantage
       From a cost standpoint, the present invention would greatly reduce the capital cost for hydrogen permeation protection by eliminating the need for a humidity controlled enclosure on the aforementioned glass manufacturing system  100 . It would also substantially reduce the cost of the ECU for supplying the protective atmosphere, since the present invention would require only a low amount of protective atmosphere flow.   There are also operational savings in both nitrogen consumption and energy usage. The present invention could be a gas tight structure and thus require much less make-up nitrogen in order to maintain a positive pressure of protective gas. Additionally, the amount of protective atmosphere needed to circulate in the integral system would be a small percentage when compared to the existing humidity controlled enclosure thus requiring less energy for steam generation and the circulation of the protective atmosphere.   The present invention could also allow a cost reduction in the amount of precious metal (e.g., platinum) required for cladding on the glass manufacturing vessels. For example, the one concept of a laminated structure with precious metal mesh  208  between two layers of precious metal skin  206  and  210  could give equivalent structural stiffness and strength with less precious metal due to the low amount of precious metal per unit volume for a mesh/screen structure versus solid precious metal.       
 
         [0049]    Furthermore, it should be appreciated that the glass manufacturing vessels  300 ,  400  or  500  can be used in any type of glass manufacturing system that uses precious metal or any glass melted or flowing in precious metal. Plus, the glass manufacturing vessels  300 ,  400  or  500  can be used to manufacture, for example, optical glasses, borosilicate glasses, alumino-borosilicate glasses, and soda-lime-silicate glass. Furthermore, the glass manufacturing vessels  300 ,  400  or  500  can be used to produce any type of glass article such as, for example, lenses, plate glass, table ware, containers, glass tubing, glass parts for optical applications and not just a glass sheet. 
         [0050]    Moreover, it should be appreciated that the inventive concept of the aforementioned integral capsule can be used to address problems in other glass manufacturing applications such as, for example, a glass tubing manufacturing application. Referring to  FIG. 9A  (PRIOR ART), there is illustrated a portion of a traditional glass tubing manufacturing system  900  where a device  902  is located in a glass forehearth  904  and molten glass  906  which is received from a tank (not shown) and flows in the direction of arrows  908  around the device  902  and out of an opening  910  formed by a ring  912  at the bottom of the glass forehearth  904  to manufacture glass tubing  914 . The device  902  includes a section  916  and a bell  918  which are attached to one another. The section  916  has one end  920  a portion of which is extending above the molten glass  906  and a second end  922  which is located in the molten glass  906  and attached to the bell  918 . The bell  918  is positioned within the opening  910  formed by the ring  912  however the bell  918  does not contact the ring  912 . The bell  918  has a circular-shaped top portion  924  which is attached to the section&#39;s second end  922  and a circular-shaped bottom portion  926  from which the glass tubing  914  is drawn from. The bell&#39;s circular-shaped top portion  924  has a larger diameter than the section&#39;s second end  922 . In addition, the bell&#39;s diameter is continually reduced as one moves from the circular-shaped top portion  924  to the circular-shaped bottom portion  926 . Alternatively, the bell  918  can be shaped where the lower portion  926  has a larger diameter than the top portion  924  and in this case the top portion  924  would be located below the ring  912 . In any case, the section  916  and bell  918  both have an opening  928  formed therein through which a gas  930  (e.g., air  930 ) travels in a direction indicated by arrows  932 . The flowing gas  930  functions to keep the glass tubing  914  that is formed from collapsing. The device  902  is held somewhere external to the glass forehearth  904  by a bell positioner (not shown) which can raise, lower and move the device  902  in any direction to properly position the device  902 . 
         [0051]    The traditional glass tubing manufacturing system  900  suffers from a problem where the metal (e.g., platinum, stainless steel, high temperature alloys (e.g., inconnel), precious metal) used to make the bell&#39;s section  916  can be contaminated with carbon (C) (and possibly other elements) which forms CO 2  bubbles  934  when in contact with the molten glass  906  (see expanded view  936 ). The CO 2  bubbles  934  end-up as blister defects in the glass tubing  914 . The mechanism by which this blister formation happens is the oxidation of the carbon (C) from the contaminated section  916 . As the carbon (C) is oxidized at the metal-glass interface  938 , more carbon (C) from the bulk metal diffuses to the surface metal. Thus, the CO 2  bubbles  934  form at the metal-glass interface  938  and eventually the CO 2  bubbles  934  are incorporated in the molten glass  906  as defects. This reaction would continue on until the carbon (C) in the contaminated section  916  is exhausted which can take a long time because of the kinetics of the metal-glass interface  938  reactions. During this time defective glass tubing  914  is being made. A detailed discussion about how this problem can be solved is provided next with respect to  FIG. 9B . 
         [0052]    Referring to  FIG. 9B , there is illustrated a portion of a glass tubing manufacturing system  900 ′ which is the same as the aforementioned glass tubing manufacturing system  900  except that it incorporates an improved device  902 ′ in accordance with an embodiment of the present invention. The improved device  902 ′ is located in the glass forehearth  904 ′ and molten glass  906 ′ which is received from a tank (not shown) flows in the direction of arrows  908 ′ around the improved bell device  902 ′ and out of the opening  910 ′ formed by the ring  912 ′ at the bottom of the glass forehearth  904 ′ to manufacture glass tubing  914 ′. The improved device  902 ′ is the same as the aforementioned bell device  902  in that it includes the section  916 ′ (with the first end  920 ′, the second end  922 ′, and hole  928 ′) and the bell  918 ′ (with the circular-shaped top portion  924 ′, the circular-shaped bottom portion  926 ′, and hole  928 ′) through both of which a gas  930 ′ (e.g., air) flows in direction of arrows  932 ′ to help prevent the glass tubing  914 ′ which is being formed from collapsing. However, the improved device  902 ′ has at least a portion of the contaminated section  916 ′ wrapped with a mesh  917 ′ (e.g., platinum mesh  917 ′, gas permeable structure  917 ′) and then a non-contaminated cladding  919 ′ (e.g., platinum-rhodium cladding  919 ′, stainless steel cladding  919 ′, high temperature alloy cladding  919 ′ (e.g., inconnel cladding  919 ′)) is wrapped around the mesh  917 ′. The section&#39;s mesh  917 ′ and cladding  919 ′ would extend above the molten glass  906 ′ and be open to an ambient atmosphere  938 ′ or a combustion atmosphere  940 ′ in the forehearth  904 ′. This atmosphere  938 ′ or  940 ′ would contain some level of oxygen. By diffusion and convection, this atmosphere  938 ′ or  940 ′ would fill the void area that the mesh  917 ′ makes between the contaminated section  916 ′ and the non-contaminated cladding  919 ′. The contact of the ambient or combustion atmosphere  938 ′ or  940 ′ with the exposed surface of the section  916 ′ would cause the oxidation of the carbon (C) in the section  916 ′ (see expanded view  942 ′). This oxidation reaction would form CO 2  gas  944 ′. The difference between the problematic CO 2  bubbles  934  and this CO 2  gas  944 ′ is that the CO 2  gas  944 ′ would form in the void area of the mesh  917 ′ and harmlessly diffuse out of this area into the ambient or combustion atmosphere  938 ′ or  940 ′ rather than into the molten glass  906 ′. The CO 2  gas  944 ′ formed would not cause blisters in the molten glass  906 ′. Plus, the formed CO 2  gas  944 ′ would not contaminate the cladding  919 ′ because for carbon (C) to adversely affect the metal cladding  919 ′ (precious metal cladding  919 ′) it must be in the reduced or elemental form. If desired, the improved device  902 ′ may contain an optional input port  950 ′ and an optional output port  952 ′ both of which would extend through the cladding  919 ′. The optional input port  950 ′ would be connected to non-contaminated tubing  954 ′ through which a gas (e.g., air) would flow to assist in the removal of the CO 2  gas  1044  from the mesh  917 ′. The optional output port  952 ′ would be connected to non-contaminated tubing  956 ′ through which the gas (e.g., air) and CO 2  gas  944 ′ would flow from the mesh  917 ′. It should be appreciated that any device which contains a contaminate such as carbon and contacts molten glass  906  can be wrapped in the mesh  917 ′ and cladding  919 ′ like the improved device  902 ′ to help prevent or at least reduce the formation of CO 2  bubbles  934  or other problematical gas bubbles in the molten glass  906 ′. An example of such a device is discussed below with respect to  FIG. 10 . 
         [0053]    Referring to  FIG. 10 , there is illustrated a device  1000  which is configured to be partially inserted into molten glass  1006  in accordance with yet another embodiment of the present invention. The device  1000  is located in a vessel  1004  which contains molten glass  1006 . The device  1000  includes a section  1016  (which is contaminated with for instance carbon) and a component  1018  (e.g., stirrer blades  1018 , thermocouple  1018 , level probe  1018 ) which are attached to one another. The contaminated section  1016  has one end  1020  a portion of which is extending above the molten glass  1006  and a second end  1022  which is located in the molten glass  1006  and attached to the component  1018 . In this example, the contaminated section  1016  is shown having a hole  1028  formed therein which could for instance be used as a wire way. Alternatively, the contaminated section  1016  could be solid. The device  1000  has at least a portion of the contaminated section  1000  wrapped with a mesh  1017  (e.g., platinum mesh  1017 , gas permeable structure  1017 ) and then a non-contaminated cladding  1019  (e.g., platinum-rhodium cladding  1019 , stainless steel cladding  1019 , high temperature alloy cladding  1019  (e.g., inconnel cladding  1019 )) is wrapped around the mesh  1017 . The section&#39;s mesh  1017  and non-contaminated cladding  1019  would extend above the molten glass  1006  and be open to an ambient atmosphere  1038  or a combustion atmosphere  1040  in the vessel  1004 . This atmosphere  1038  or  1040  would contain some level of oxygen. By diffusion and convection, this atmosphere  1038  or  1040  would fill the void area that the mesh  1017  makes between the contaminated section  1016  and the non-contaminated cladding  1019 . The contact of the ambient or combustion atmosphere  1038  or  1040  with the exposed surface of the contaminated section  1016  would cause the oxidation of the carbon (C) in the contaminated section  1016  (see expanded view  1042 ). This oxidation reaction would form CO 2  gas  1044  which would harmlessly diffuse out of this area into the ambient or combustion atmosphere  1038  or  1040  rather than into the molten glass  1006 . The CO 2  gas  1044  formed would not cause blisters in the molten glass  1006 . Plus, the formed CO 2  gas  1044  would not contaminate the cladding  1019  because for carbon (C) to adversely affect the metal cladding  1019  (precious metal cladding  1019 ) it must be in the reduced or elemental form. If desired, the device  1000  may contain an optional input port  1050  and an optional output port  1052  both of which would extend through the cladding  1019 . The optional input port  1050  would be connected to non-contaminated tubing  1054  through which a gas (e.g., air) would flow to assist in the removal of the CO 2  gas  1044  from the mesh  1017 . The optional output port  1052  would be connected to non-contaminated tubing  1056  through which the gas (e.g., air) and CO 2  gas  1044  would flow from the mesh  1017 . 
         [0054]    Although several embodiments of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that the invention is not limited to the disclosed embodiments, but is capable of numerous rearrangements, modifications and substitutions without departing from the invention as set forth and defined by the following claims.