Abstract:
A seal has a non-woven fabric folded along lines transverse to the opposite side of the seal and secured by adhesive to fabric strips. The non-woven fabric forms elongated cells with a plurality of the cells receiving inserts to increase seal stiffness. By securing one of these strips to a stationary component of the sealing surfaces, the opposite strip may expand or collapse relative to a movable sealing surface to accommodate excursions of that surface. Multiple layers of cells may be provided in the seals. The inserts may have various cross-sectional configurations including circular, triangular or rhombic and formed of tubes, solid rods or coiled springs.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to seals and particularly to fabric seals for usage in low leakage static or dynamic sealing applications.  
         [0002]     The increased worldwide demand for electricity leads to the necessity of designing large-scale, high-powered, high-efficiency, and low cost power generation turbomachines with high standards for reliability and performance. One of the primary concerns in a turbomachine design is its sealing performance because it has direct impact on machine operating reliability and efficiency. A number of seals are used in turbomachines such as gas/steam turbines, compressors, and generators for minimizing leakage flows. According to the movement of a seal relative to its sealing surface, seals can be classified as stationary seals affording leakage barriers around and between stationary components or rotating seals affording leakage barriers between stationary and rotating components. Over the years, various techniques have been developed to improve both stationary and rotating seals. Much of this development has occurred in the turbine industry where parasitic flow control is critical.  
         [0003]     As a circumferential contacting seal, brush seals have been widely used in turbomachines due to their distinguishing characteristics, i.e., lower leakage flow rate compared with labyrinth seals and seal flexibility for accommodating excursions at the interface without excessive wear and loss of sealing capability. However, brush seals formed of brush bristles are usually expensive and have exhibited hysterisis and were difficult to manufacture. The crucial seal parameters such as cant angle and bristle height depend on the process capability or manufacturing technique and are very difficult to control. A conventional brush seal is made by either folding bristles over a metal plate or sandwiching bristles between a pair of ring-shaped metal support plates and welding ends of the bristles and plates to one another adjacent common edges thereof. Since the metal bristle holder is usually machined with a tight tolerance, a brush seal can fit only a specific sealing dimension. This can result in very high costs for brush seals in tooling, manufacturing, and installation and leads to a long cycle time in brush seal fabrication.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     According to a preferred embodiment of the present invention, there is provided an insert loaded flexible seal formed of a fabric, preferably a non-woven fabric, disposed between a pair of strips, preferably also formed of a fabric material. Preferably, a continuous non-woven fabric layer is folded onto itself and is secured, for example, by adhesive along the fold lines to itself or to the strips to form a plurality of cells extending longitudinally between opposite sides of the seal. Consequently, the cells lie between the pair of fabric strips and the seal responds substantially freely to forces acting on the seal. That is, generally rectilinear, triangular or rhombic cells which are collapsible and expandable in a direction between the two sealing surfaces are provided, the cells having dimensions varying from hundreds of micrometers to several centimeters.  
         [0005]     In a particular application of the present invention, one of the strips may, for example, be adhered by adhesive to a stationary component, i.e., a stator surface. The other strip is located adjacent the rotating surface. Because the non-woven fabric forming the cells lies between the strips, the seal responds substantially freely to applied forces. Thus, any radial excursion of the rotating surface is accommodated by the collapsing and expansion of the cells of the seal. The strip in contact with the rotating surface may have a wear-resistance material applied to its surface. For example, a coating of Teflon or a near frictionless carbon coating can be applied to that strip.  
         [0006]     As will be appreciated, the seals can be formed of one or more layers of cells with inserts in the cells. The thickness of the seal can thus be varied depending upon the sealing application. For example, for certain applications, the fabric layers may be formed of a mixture of metallic and non-metallic fibers enabling the seal for use in intermediate to high pressure applications. Various other design parameters may be altered depending upon the application such as fabric construction, material, fabric layer thickness, type and form of inserts, cell construction and dimensions. One particular advantage of the present seal is that in contrast to brush seals having bristles which are laid at certain angles to the shaft surface to facilitate seal flexibility and avoid excessive fiber stress during shaft excursion, the present seal is independent of the direction of rotation of the shaft. The risk of seal damage due to reverse rotation is thus eliminated. Secondly, seal flexibility is adjustable. For example, seal flexibility may be increased by increasing the cell size and/or the number of cell layers, as compared with a less flexible seal with decreased cell size and/or cell layers. For applications which require substantial seal stiffness, as in the preferred embodiment hereof, inserts are placed in the seal cells. Such inserts may take numerous types, forms and sizes. For example, thin walled pipes formed of rubber or plastic, such as aerated plastic sticks, solid rods of like material, or wire coils. According to the particular cell shape, these inserts can have different cross-sectional shapes, e.g., round, triangular and rhombic. In addition, the insert material can be either non-metallic or metallic. For sealing hydrogen gas, e.g., in hydrogen-cooled generators, non-metallic materials are used for safety considerations.  
         [0007]     A third immediate advantage of the present seal is that it provides solutions for applications having large sealing dimensions and/or irregular sealing geometry. Conventional seals require machining brush holders precisely with tight tolerances. As a result, each seal can serve only a specific sealing dimension. As a sealing dimension becomes large, it becomes very difficult to make the seal. The present seal can readily and easily fit different sealing dimensions and complex sealing geometry.  
         [0008]     In a preferred embodiment according to the present invention, there is provided a seal between first and second spaced components comprising first and second fabric layers spaced from one another with a first layer thereof for securement to the first component and a second layer thereof disposed adjacent the second component, a third fabric secured to and between the first and second layers, the third fabric defining a plurality of cells between the first and second layers having major length dimensions extending in directions generally coextensive with the layers of the seal, the third fabric biasing the second layer in a direction towards the second component and inserts extending within a plurality of the cells to provide stiffness to the seal.  
         [0009]     In a further preferred embodiment according to the present invention, there is provided a seal between first and second spaced components comprising first and second fabric layers spaced from one another with a first layer thereof for securement to the first component and a second layer thereof disposed adjacent the second component, a third fabric secured to and between the first and second layers, the third fabric defining a plurality of cells between the first and second layers having major length dimensions extending in directions generally coextensive with the layers of the seal, the fabric cells having elongated multiple sides between the layers and inserts extending within a plurality of the cells to provide stiffness to the seal, the inserts being substantially coextensive in length with the length of the cells.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of a fabric seal construction illustrated without the inserts of the insert loaded seal hereof;  
         [0011]      FIG. 2  is an enlarged fragmentary cross-sectional view of the seal of  FIG. 1  illustrating its fabric construction;  
         [0012]      FIG. 3  is a perspective view of the fabric seal located between stationary and rotary components;  
         [0013]      FIG. 4  is a view similar to  FIG. 1  illustrating a different form the fabric seal;  
         [0014]      FIG. 5  is a view similar to  FIG. 2  illustrating a manner of formation of the seal of  FIG. 4 ;  
         [0015]      FIG. 6  is a view similar to  FIG. 1  illustrating a further form of a seal;  
         [0016]      FIG. 7  is a view similar to  FIG. 1  illustrating a preferred embodiment of the present invention affording a fabric seal with inserts having increased stiffness;  
         [0017]      FIGS. 8-16  are perspective views of inserts for use with the seal illustrated in  FIG. 7 ;  
         [0018]      FIG. 17  is a perspective view of triangularly-shaped inserts located in triangularly-shaped cells of the fabric seal for increasing stiffness;  
         [0019]      FIG. 18  is a perspective view illustrating a combination of insert types in the cells of the fabric seal; and  
         [0020]      FIG. 19  is a perspective view similar to the  FIG. 18  illustrating an alternate arrangement of different types of inserts in the cells. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Referring now to the drawings, particularly to FIGS.  1   2 , there is illustrated a seal constructed in accordance with the preferred embodiment of the present invention and generally designated  10 . The seal  10  includes a seal body  12  formed of a non-woven fabric material sandwiched between a pair of strips  14  and  16 . The seal is for disposition between a pair of components, e.g., first and second stationary components  13  and  15 , i.e., a stationary seal, or a stationary component and a rotatable component, i.e., a dynamic seal (see  FIG. 3 ). In  FIG. 1 , the strips  14  and  16  are preferably formed of a non-woven fabric material and form a stationary seal. Thus, strips  14  and  16  may be secured to the stationary components  13  and  15 , respectively, for example, by an adhesive. In the case of a dynamic seal as illustrated in  FIG. 3 , strip  14  may be secured to a stationary part  29  and strip  16  may lie closely adjacent to or in engagement with a rotary component  31 . The seal  10  thus seals between the two components.  
         [0022]     Preferably, the fabric body  12  is formed of a single continuous non-woven fabric folded at spaced locations relative to one another and adhered at the fold lines, e.g., by an adhesive, to form a multiplicity of cells  18 . For example, and referring to  FIG. 2 , the non-woven fabric  12  may be secured along an edge  20  by an adhesive to the fabric  14  and have alternating folds  22  and  24  between strips  14  and  16  until the strip is folded along fold line  26  and adhered to strip  16 . The continuous non-woven fabric layer  12  may then reverse direction and extends to strip  14 . Layer  12  thus has alternating folds forming fold lines  28  and  30  until it is secured, preferably by adhesive, to the first fabric  14  along a fold line  32 . The non-woven fabric  12  continues from one side of the seal, i.e., one pressure region, to the opposite side of the seal, i.e., the other pressure region, with similar alternate folds between the material strips  14  and  16  forming the cells  18 . The fold lines of fabric  12  intermediate strips  14  and  16  are adhered, e.g., by adhesive, to one another. For example, fold lines  22  and  30  are adhered to one another. Thus, the cells and fold lines extend longitudinally about the seal in and on opposite sides of the seal. That is, the cells  18  extend longitudinally about the seal and together with the fabric  12 , lie between high and low pressure regions on opposite sides of the seal. Seal  10  can be formed in a flat configuration or may be irregular in shape or circular, for example, as illustrated in  FIG. 3 .  
         [0023]     In  FIG. 3 , a seal similar to the seal disclosed in  FIGS. 1 and 2  is disposed between a stationary component and a rotating component. The multi-cell seal formed by the non-woven fabric  12  is adhered as in the prior embodiment to strips of preferably non-woven fabric material  14  and  16 . The fabric material  14  is adhered to a stationary component  29 , for example by an adhesive. The fabric material  16  lies directly adjacent and is engagable with the rotating surface of the rotating component  31 . It will be appreciated that the seal  12  in  FIG. 3  may expand or collapse in response to rotary excursions of the rotatable component while maintaining the integrity of the seal.  
         [0024]     In  FIGS. 4 and 5 , additional layers of cells for the seal are provided. That is, instead of the two layers of cells  18  illustrated in the seals of  FIGS. 1-3 , the seal illustrated in  FIGS. 4 and 5  has three cell layers. The manner of fabrication of the seal is similar to that discussed above with respect to the seal of  FIGS. 1 and 2 . That is, a continuous non-woven fabric  12  is adhered to the strip  14  and extends at an angle to a first fold line  30  and then to a second fold line  32  where the material is reversely folded, and then to a third fold line  34  where a further reverse fold is provided. Each reverse fold is 90°. The non-woven fabric material then extends from fold  34  to the fabric  16  where it is folded again at  36 , secured to fabric  16 , e.g., by adhesive, and returned to the fabric  14  alternately being reversely folded. A reverse fold  40  is adhered to the fold  32 , for example by an adhesive. The reverse fold  40 , however, is folded through 135° to form an angle of about 45° with fabric  14 . The material reverse folded at  40  extends along the inside surface of fabric  14  along a diagonal of the otherwise rectilinear cell  18 . The non-woven fabric then, again folds along a fold line  42  through a reverse 135° angle and the folds repeat with the folds being secured to previously folded fold lines, for example, by adhesive. As in the prior embodiment, the fabric  12  is alternately reversely folded between strips  14  and  16  from one side of the seal to the opposite side, sealing the pressure regions on opposite sides of the seal from one another.  
         [0025]     Referring now to  FIG. 6  which illustrates a further embodiment of the seal, the seal has significantly higher seal stiffness and less seal flexibility then the seals disclosed in the prior embodiment. In this form, the non-woven fabric  50  disposed between the fabric strips  52  and  54  is folded and secured to the strips along each fold line  56  and  58  thereby defining generally triangularly shaped elongated cells  60 . The fold lines are preferably secured by an adhesive to the fabric strips. The resultant seal may be employed for similar gaps as in the prior embodiment but has a higher seal stiffness and less flexibility.  
         [0026]     Referring now to  FIGS. 7-10 , for those seal applications requiring a high degree of stiffness, and in accordance with a preferred embodiment hereof, one or more inserts may be disposed in the cells defined by the non-woven fabric in each of the previously described embodiments. In  FIG. 7 , the non-woven fabric  12  extends between non-woven strips  70  and  72  similarly as illustrated in  FIG. 5  but forms only a single row of rectilinear cells  74  between strips  70  and  72 . The intermediate fold lines  76  and  78  are adhered to one another while the fold line  80  is adhered to strip  70  and folds lines  82  and  84  to strip  72 . The generally rectilinear or rhombic-shaped cells  74  formed may receive circular elements, e.g., a rod, a tube or a coiled spring, to add stiffness to the seal. For example, in  FIG. 8 , a plastic pipe  85  having a thin wall thickness may be disposed in one or more of the cells  74 . Alternatively, as illustrated in  FIG. 9 , a flexible rubber or aerated plastic rod  86  may be disposed in one or more of the cells  74 . An additional form of insert is illustrated in  FIG. 10  comprising a helical wire coil  88  which likewise may be disposed in the cells. The inserts significantly increase the stiffness of the seal while reducing seal flexibility and therefore afford a seal of this type useful for sealing between higher pressure differentials.  
         [0027]     Alternatively, the inserts can be made with different materials and have different forms for use with variously shaped cells of the seal illustrated in  FIGS. 1-7  and  17 - 19 . For example, the inserts may have a generally triangular-shaped tubular cross-section as illustrated by insert  89  in  FIG. 11 , a solid triangular-shaped cross-section illustrated by insert  92  in  FIG. 12  or a triangular cross-section formed by a coiled spring insert  93  illustrated in  FIG. 13 . Thus, with respect to  FIG. 17 , the seal may include any one of the triangularly-shaped inserts of  FIGS. 11-13 , respectively, or may comprise a combination of two or more of the three different types of inserts illustrated in  FIGS. 11-13 . It will be appreciated that in the seal of  FIG. 17  (similar to that of  FIG. 6 ), the preferred non-woven fabric is adhered to the strips  14  and  16 , preferably by adhesive, forming triangularly-shaped cells which receive the triangularly-shaped inserts. Further, the inserts of  FIG. 17  may comprise two or more of the different types of inserts illustrated in  FIGS. 11-13 , e.g., alternating inserts  89 ,  92  or  92 ,  93  or  89 ,  93  or in various other combinations in adjacent cells.  
         [0028]     Further, as illustrated in  FIGS. 14-16 , the inserts may have a rhombic configuration which may take a number of different forms of inserts. For example,  FIG. 14  illustrates an insert  94  formed of a tube having a rhombic cross-section.  FIG. 15  illustrates an insert  96  in the form of a solid plastic rod having a rhombic cross-section.  FIG. 16  illustrates an insert  98  in the form of a coiled wire having a rhombic cross-sectional configuration. Thus, the inserts of  FIGS. 14-16  may be used as inserts for the seals illustrated in  FIGS. 1-5 ,  7 ,  18  and  19 .  
         [0029]     It will also be appreciated that the inserts of each type may be used in a single seal. For example, as illustrated in  FIG. 18  (a seal similar to the seal of  FIG. 7 ), inserts  85  and  88  ( FIGS. 8 and 10 , respectively) are alternatively disposed in the adjacent cells. It will be appreciated that the solid inserts  86  of  FIG. 9  could likewise be applied in the seal of  FIG. 18  whereby the inserts may comprise two or more of the different types of the circular inserts illustrated in  FIGS. 8-10 .  
         [0030]     Referring now to  FIG. 19 , the seal (similar to the seal of  FIG. 7 ) includes inserts of the different cross-sectional configurations. In the illustrated form of seal, the rhombic and circular inserts  94  and  88 , respectively, are utilized. While the rhombic tubular and circular coil spring inserts  94  and  88  are illustrated, it will be appreciated that the rhombic solid or coil spring of  FIGS. 15 and 16 , respectively, may be used in conjunction with solid circular or coil spring inserts as illustrated in  FIGS. 9 and 10 , respectively. It will also be appreciated that different forms of the rhombic and circular cross-section inserts may be utilized in conjunction with one another.  
         [0031]     Also, the cellular form of the intermediate fabric provides a bias toward the strips, i.e., the fabric tends to separate the strips one from the other. To enhance that bias, the fabric may be formed of a combination of metallic fibers and non-metallic fibers, the proportions being dependent upon the application of the seal. For example, in a hydrogen atmosphere in a cooling system for an electrical generator, non-metallic fibers are used to avoid sparking.  
         [0032]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.