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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
       [0001]    This invention relates to manhole structures. In particular, it relates to a method and device for sealing a manhole structure. 
       BACKGROUND OF THE INVENTION 
       [0002]    Manholes are used to provide street-level access to sewer lines and other underground structures. Most often, the top portion of the manhole has the form of a cylindrical frame (or casting) with a lid. The lower portion of the casting, which is not generally seen after installation, often resembles a hat with a brim. This hat-shaped casting rests on a concrete cone leading to a sewer line. The upper portion of the casting defines an opening that may be closed with a lid. The elevation of the manhole casting and lid may be raised to the level of the surrounding surface grade by placing one or more concrete adjusting rings between the bottom of the casting and the cone. A manhole structure is thus created by stacking a number of components on top of each other. After the manhole structure is installed, the space around it is typically filled in with earth so that the lid at the top portion of the manhole casting is conveniently accessible at street-level. 
         [0003]    Manholes created by such stacking of components are vulnerable to leaks. Water and other contaminants may enter through gaps between the stacked components after installation. Once the manhole structure has been installed and earth has been filled in around it, gaps below the ground level become difficult to reach. It is thus desirable to seal the manhole structure during installation to prevent future leaks at the interfaces between the stacked components. 
         [0004]    Various methods and devices are known for sealing the external surfaces of manhole structures. One method employs an elastomeric band positioned around the top portion of the cone and extending over the adjusting rings to the base of the manhole casting. Because the cone and the adjusting rings have generally the same outer perimeter, one or more sealing bands may be used to provide an external seal for the gaps between these components. A band extends over the cone (and any adjusting rings) to the casting base as in U.S. Pat. No. 5,876,533 or may extend in tapered form to the upper portion of the casting as in U.S. Pat. No. 7,150,580. 
         [0005]    To reduce the risk of accumulating water or contaminants between the inner layer of the seal and the outer layer of the manhole, methods have been devised for keeping the external seal snugly fitted to the manhole structure. A heat-sealing method, for example, is known whereby the sealing band is heated before fitting so that it may be secured tightly to the manhole structure, thereby reducing bulges and air pockets. But methods that use heat require a heat source, often torches and other special tools that involve hazards to the user. 
         [0006]    What is needed in the industry is a device and method for sealing a manhole structure so that the seal is retained in close proximity to the external surfaces of manhole structure without the use of heat-sealing methods. 
       SUMMARY OF THE INVENTION 
       [0007]    The problems described above are solved in substantial part by a band for sealing a manhole structure that has an L-shaped corner with that is more rigid than the rest of the band. The band includes first and second portions extending from the L-shaped corner at a generally 90-degree angle to each other. The L-shaped corner may extend equal or unequal distances in the direction of the first and second portions. The band may be integrally molded or formed by from separate pieces of material. 
         [0008]    The rigidity of the L-shaped corner may be enhanced by making it from a thicker material than the first or second portions. The thickness of the L-shaped corner may be at least twice the thickness of the first and second portions. 
         [0009]    A method for using a band with an L-shaped corner includes rolling the band over the exterior of the casting and the upper margin of a manhole structure and fitting the L-shaped corner to the upper margin defining a corner such that the first portion extends toward the casting and the second portion covers at least part of the upper margin. The L-shaped corner may be fitted to either a corner defined by the upper margin of a cone (when no adjusting rings are used) or to a corner defined by the uppermost adjusting ring. An adhesive may be applied to the band&#39;s inner surface to enhance the seal formed against the manhole structure. A butyl mastic adhesive may be used, either alone or in conjunction with a primer applied to the surfaces of the manhole structure that will contact the adhesive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is cut-away plan view of an embodiment of the invention in place around a manhole structure. 
           [0011]      FIG. 2  is a cross-section view of an embodiment of the invention in place around a manhole structure. 
           [0012]      FIG. 3  is a detailed cross-sectional view showing an embodiment of the invention in place around the upper margin of a manhole structure. 
           [0013]      FIG. 4A  is a cross-sectional view of the embodiment of the band of the invention. 
           [0014]      FIG. 4B  is a detailed cross-sectional view of an embodiment of the corner of the band of the invention. 
           [0015]      FIG. 5  is an exploded cross-sectional view of a manhole structure and an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    As shown in  FIGS. 1-5 , sealing band  10  is generally L-shaped, with a first portion  12  that extends horizontally in relation to a manhole structure, a second portion  14  that extends vertically, and a corner  34  linking the first and second portions. 
         [0017]    In  FIG. 1 , band  10  is shown in position around a cross section of manhole structure  16 . Manhole structure  16  includes a cone  18  and a casting  20 . Cone  18  has a lower portion  22  that extends downward to a sewer (not shown) and an upper margin  24  on which casting  20  is disposed. The casting  20  is generally hat shaped and includes a brim portion  26 , an upper portion  28 , and a lid-receiving portion  30 . 
         [0018]    Band  10  is positioned around the exterior periphery of the upper margin  24  of cone  18  and overlaps with part of brim portion  26  of casting  20 . In the embodiment shown in  FIG. 1 , cone  18  is shown without adjusting rings. 
         [0019]    The positioning of band  10  around manhole structure  16  is shown in greater detail in  FIG. 2 , which shows a cut-away view of manhole structure  16 . In  FIG. 2 , manhole structure  16  includes cone  18  and casting  20  as in  FIG. 1 , but also includes adjusting rings  32 . As shown in  FIG. 2 , band  10  extends around the periphery of cone  18  and adjusting rings  32 . When adjusting rings  32  are stacked on cone  18 , one or more adjusting ring,  32  may be used. In such embodiments, corner  34  of band  10  corresponds to a corner  35  defined by the uppermost adjusting ring  32 . 
         [0020]    In an embodiment, the material used to form corner  34  of band  10  is thicker than the material that forms first and second portions  12 ,  14 . As shown in  FIG. 3 , which provides a detail of the cross-sectional view of band  10 , the inner side  36  of corner  34  is reinforced with more material than the other portions of band  10 . 
         [0021]    As shown in  FIG. 4A , first and second portions  12 ,  14  of band  10  may be unequal in length. Referring back to  FIGS. 1 and 2 , it can be seen that first portion  12  extends from corner  34  to cover the interface between the uppermost adjusting ring  32  (or upper margin  24  of cone  18 ) and the brim portion  26  of casting  20 . Second portion  14  extends beyond the height of the stacked adjusting rings  32 . First and second portions  12 ,  14  may also extend the same distance from corner  34 . 
         [0022]    For example, where cone  18  in  FIG. 1  is 39¼″ in diameter and casting  20  is 29″ in diameter, there are 5⅛″ of material from corner  32  to the end of first portion  12  and 16″ of material from corner  34  to the end of second portion  14 . In this embodiment, band  10  has an outer circumference of 123¼″ and an inner circumference of 91″. 
         [0023]    In the embodiment shown in  FIG. 4B , corner  34  is thicker than the rest of band  10 , which is shown in  FIG. 4B  by the curvature of the inner side  36  of corner  34 . In this embodiment, corner  34  is made from the same material as first and second portions  12 ,  14 . Corner  34  may extend equally in both directions. In the embodiment shown in  FIG. 1 , corner  34  extends 1″ toward each of the first and second portions  12 ,  14 . In other embodiments, corner  34  may extend unequally. 
         [0024]    Corner  34  may be formed integrally, for example, by molding. Or first and second portions  12 ,  14  may be attached to corner  34 . In a preferred embodiment, first and second portions  12 ,  14  are made of a resilient material that can be rolled over a manhole structure and has sufficient thickness to withstand the environmental conditions generally found at manhole-construction sites. For example, band  10  may be constructed from ethylene propylene diene monomer (EPDM) rubber. The thickness of the first and second portions is approximately 65 mili-inches (mils). The thickness of the preformed corner portion is approximately twice that, or 130 mils. 
         [0025]    Alternatively, a more rigid material may be used to form corner  34  than is used for the rest of band  10 . In this alternative embodiment, the thickness of corner  34  may not be different than the thickness of the rest of band  10 , and may even be less, depending on the material used. 
         [0026]    In use, band  10  is preformed in generally the shape shown in  FIG. 5  and brought to a site where a manhole structure is being installed. As shown in  FIG. 1 , manhole structure  16  may be created by placing casting  20  directly on cone  18 . Frequently, however, the elevation of cone  18  alone is insufficient to reach the desired surface grade. Thus, one or more adjusting rings  32  are added to the top of cone  18 , as best shown in  FIG. 5 . Band  10  is positioned so that corner  34  is fitted to the topmost adjusting ring  32 , if adjusting rings  32  are used, or to the upper margin  24  of cone  18 , if no adjusting rings  32  are used. In this position, first portion  12  extends to cover brim portion  26  of casting  20  while second portion  14  extends to cover either the upper margin of cone  24  (if no adjusting rings  32  are used, or adjusting rings  32 . 
         [0027]    In an alternative embodiment, as shown in  FIG. 6 , an adhesive  37  is applied around either the inner side  38  of first portion  12  or the inner side  40  of second portion  14 , or both. For example, as shown in  FIG. 4A , butyl mastic  37   a  may be applied all the way around the underside of first portion  12 . The adhesive may be applied in different proportions, for example, where the first portion  12  is 5⅛″, the adhesive  37 a may be applied as a strip 5″ wide. This arrangement will enhance the seal created by first portion  12  against uppermost adjusting ring  32  and brim portion  26  of casting  20 . Near the bottom edge  42  of second portion  14 , a 2″ wide strip of adhesive  37   b  may be used to provide an enhanced seal around lower portion  22  of cone  18 . Strips of other sizes may also be used to seal first portion  12  or second portion  14  to manhole structure  16 . A primer  43  may also be applied to the external surfaces of manhole structure  16  to enhance the seal formed by the adhesive. For example, when a butyl mastic adhesive is placed on first or second portions  12 ,  14 , a primer-delivery device  44  may be used to apply primer  43  in aerosol form to the corresponding portions of the manhole structure.

Summary:
The invention relates to a device and method for sealing a manhole structure. A band with a relatively rigid angled corner engages the upper margin of a manhole structure. Adhesives may also be used with the band to enhance the seal with the manhole structure.