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CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of earlier filed United States Provisional patent application Serial No. 60/194,525, filed Apr. 14, 2000, and entitled “Improved Three-Prong Shell”. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an improved expansion assembly for mine roof bolts used in relatively-small diameter holes and, more particularly, to expansion assemblies that can be used with or without resin-bonding materials.  
           [0004]    2. Brief Description of the Prior Art  
           [0005]    Examples of four-prong mine roof bolt expansion shell assemblies used in one-inch diameter mine roof bore holes are disclosed in U.S. Pat. Nos. 4,904,123; 4,969,778; and 5,078,547, all herein incorporated by reference in their entirety and all assigned to the assignee of the present invention.  
           [0006]    In general, four-prong mine roof bolt expansion shell assemblies include a plug, which is attached to a mine roof bolt in mine roof support applications, and a four-prong expansion shell that slidingly engages the plug.  
           [0007]    In one commercial embodiment, the plug has a height of approximately 1 {fraction (3/16)}inches, an outside diameter of approximately 0.9 inches, and is made from ASTM A220 Grade 50005 pearlitic malleable iron. The plug has approximately 6.5 degrees of side taper, with the length of taper being approximately one inch. Internally-defined threads are provided for attaching the plug to a mine roof bolt, wherein the threads are generally {fraction (5/8 )}inch,  11  per ASTM F432-95.  
           [0008]    The plug defines four resin grooves spaced ninety degrees apart with respect to each other, with each resin groove being approximately 0.074 inch deep and approximately 0.268 inch wide. The plug further defines a number twelve through hole that receives a wooden shear pin which acts as a delay mechanism. The total area of resin grooves is approximately 0.040 square inch, and the total area for resin flow in a substantially one-inch diameter bore hole is approximately 0.117 square inch.  
           [0009]    The four-prong expansion shell generally has four prongs and an inside square taper leave. The four-prong expansion shell is preferably made from ASTM A47 Grade 32510 ferritic malleable iron, has a height of approximately 2{fraction (11/32)} inches, and an outside diameter of approximately {fraction (15/16)} inch. The degree of inside taper leave is approximately 6.5 degrees, and the length of taper is approximately {fraction (39/64)} inch. The four prongs define four grooves spaced ninety degrees apart, with each groove width being approximately {fraction (1/4)} inch and each groove length being approximately 2{fraction (1/16)} inches. The inside diameter of the four-prong expansion shell is approximately {fraction (21/32)} inch. Each of the four prongs define approximately eight total serrations spaced approximately 3/16 inch apart with respect to one another, with three serrations at ten degrees and five serrations at twenty degrees. The total serrated surface area of all of the four prongs is 3.483 square inches.  
           [0010]    Given the fact that the bore hole diameter is fixed in small bore applications to approximately one inch, there is little flexibility with respect to the diameter of the expansion shell. However, there is an ever present need to secure small diameter bore hole mine roof bolts in mine roofs such that the bolts will resist higher stress loads.  
         SUMMARY OF THE INVENTION  
         [0011]    One embodiment of the present invention generally includes an expansion assembly configured to be attached to a mine roof bolt. The expansion assembly may include a plug defining an interior cavity and an outer surface and an expansion shell having a plurality of spaced-apart prongs and defining a plurality of shell grooves, wherein each of the spaced-apart prongs is oriented diametrically opposed to a corresponding shell groove. In one configuration, the expansion shell is positioned adjacent to the outer surface of the plug and is slideably movable with respect to the plug.  
           [0012]    The plug may generally define an internal cavity, define threads in the internal cavity, define three resin grooves spaced about 120 degrees apart, and may also define a side extension that extends along a length of the plug. The expansion shell may define only three prongs also spaced approximately 120 degrees apart and three shell grooves, and may further comprises a ring, with the three prongs integrally-formed with the ring. The expansion shell may also define eight spaced-apart serrations, with three of the serrations angled in one orientation and five of the serrations angled at a second orientation.  
           [0013]    The present invention helps to increase the stress load resistance of small diameter mine roof bolts by providing an expansion shell assembly for small diameter bore holes, particularly one-inch diameter mine roof bore holes, wherein the plug has three resin grooves, and the expansion shell has three prongs.  
           [0014]    The three-prong design increases the amount of surface area for resin flow, increases the total external area of the three-prong expansion shell which permits the three-prong expansion shell to set or grab the walls of the bore hole quicker (allowing a smaller support nut to be used), and is less expensive to manufacture.  
           [0015]    These and other advantages of the present invention will be clarified in the description of the preferred embodiment taken together with the attached drawings in which like reference numerals represent like elements throughout. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a perspective view of an expansion assembly installed on a mine roof bolt according to one embodiment of the present invention;  
         [0017]    [0017]FIG. 2 is a side view of a plug;  
         [0018]    [0018]FIG. 3 is an end view of the plug shown in FIG. 2;  
         [0019]    [0019]FIG. 4 is a side view of an expansion shell having only three prongs;  
         [0020]    [0020]FIG. 5 is an end view of the expansion shell shown in FIG. 4;  
         [0021]    [0021]FIG. 6 is side view of the expansion assembly and mine roof bolt shown in FIG. 1 partially installed in a bore hole defined in a mine roof, along with resin/catalyst;  
         [0022]    [0022]FIG. 7 is a side view of the expansion assembly and mine roof bolt shown in FIG. 6 installed in the mine roof;  
         [0023]    [0023]FIG. 8 is an end view of the mine roof bolt and expansion assembly shown in FIGS. 6 and 7, along with a resin/catalyst flow pattern; and  
         [0024]    [0024]FIG. 9 is an isolated view of the resin/catalyst flow pattern shown in FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    An expansion assembly  10  according to the present invention is shown generally in FIGS.  1 - 9 , and further described in United States provisional Patent application Serial No. 60/194,525, filed Apr. 4, 2000, herein incorporated by reference in its entirety.  
         [0026]    As shown in FIG. 1, the expansion assembly  10  is usually positioned on a mine roof bolt  12 , such as a cable bolt, solid bolt, or combination bolt. The expansion assembly  10  generally includes a plug  14  and a three-prong expansion shell  16 .  
         [0027]    The plug  14 , shown in greater detail in FIGS.  2 - 3 , is preferably made from ASTM A220 Grade 50005 pearlitic malleable iron. As shown in FIG. 2, the plug  14  defines an internal cavity  17  which defines internal threads  18 , with the threads  18  preferably being {fraction (+5/8)} inch,  11  per ASTM F432-95. The plug 14 further defines three resin grooves  20  spaced about 120 degrees apart, with the depth DP of each resin groove  20  being about 0.075 inch and the width W of each resin groove  20  being about 0.192 inch. The total cross-sectional area of each of the resin grooves  20  is approximately 0.04 square inch.  
         [0028]    As shown in FIG. 3, the plug  14  generally has a height H of about {fraction (15/16)} inches and an outside diameter D of about 0.9 inch. The degree of side taper ST is approximately 6.5 degrees and the length L of the taper is approximately one inch. A through hole  22  (preferably number twelve in size) is defined by the plug  14  for receiving a wooden shear pin (not shown), which acts as a delay mechanism during rotation of the mine roof bolt  12  shown in FIG. 1. With continuing reference to FIG. 3, a side extension  24  extends along the height H of the plug  14  for resisting relative rotation between the three-prong expansion shell  16  and the plug  14 .  
         [0029]    As shown in FIG. 4, the three-prong expansion shell  16  is preferably made from ASTM A47 Grade 32510 ferritic malleable iron, has three prongs or leaves  26 , and may further define one or more substantially flat surfaces  25  approximately 0.4 inch in width FW. The prongs  26  define three shell grooves 28 spaced about 120 degrees apart and substantially diametrically opposed to a corresponding one of the three prongs  26 , with the shell groove width GW being about {fraction (1/4)} inch. The internal diameter ID of the three-prong expansion shell  16  is about {fraction (21/32)} inch.  
         [0030]    As shown in FIG. 5, the three prongs  26  are preferably integrally formed with a ring  30  having a shell height SH of about 2{fraction (15/32)} inches and an outside diameter OD of about {fraction (15/16)} inch. The degree of inside taper IT is about 6.5 degrees, and the length of taper SL is about {fraction (39/64)} inch and the groove length GL being about 2{fraction (1/16)} inches. There are preferably eight total serrations SR spaced about {fraction (3/16)} inch apart, with three serrations  32  angled at ten degrees from vertical and five serrations  32 ′ angled at twenty degrees from vertical. The total external surface area of the three-prong expansion shell  16  is approximately 3.978 square inches in this configuration.  
         [0031]    The expansion assembly  10  of the present invention may be used as follows. As shown in FIG. 6, the plug  14  is threadedly connected by the internal threads  18  to the mine roof bolt  12 , with the mine roof bolt  12  preferably being {fraction (5/8)} inch in diameter. The three-prong expansion shell  16  is loosely attached to the mine roof bolt  12  and held in position by a support  34 . The support  34  is preferably a cylindrically-shaped nut having an outside diameter of approximately {fraction (15/16)} inch and a thickness of approximately {fraction (1/8)}-{fraction (3/8)} inch, depending on the rigidity of the mine roof strata. For example, if the mine roof strata is weak, a thicker support is generally required. If the mine roof strata is more substantial, a thinner thickness may be used. Curable resin/catalyst  36  is inserted into a bore hole  38 . The mine roof bolt  12  is then rotated to mix the resin/catalyst  36  and cause the plug  14  to thread downwardly on the mine roof bolt  12 , shown by arrow A 1 , until the plug  14  contacts the shear pin (not shown) received by the through hole  22 . The three-prong expansion shell  16  rotates with the mine roof bolt  12 . As the resin/catalyst  36  cures and hardens, the plug  14  and the shell  16  are prevented from rotating. Further rotation of the mine roof bolt  12  causes the plug  14  to snap through the shear pin, and the plug  14  is further urged downwardly on the mine roof bolt  12 . The tapered plug  14  expands the prongs  26  of the three-prong expansion shell  16  as the shell  16  slides over the plug  14 , forcing the prongs  26  to firmly grasp a surface of the bore hole  38 .  
         [0032]    As shown in FIG. 7, once the three-prong expansion shell  16  sets firmly against or into the bore hole  38 , the mine roof bolt  12  is tensioned. When resin/catalyst  36  is not used, the shear pin is not required.  
         [0033]    [0033]FIG. 8 shows the plug  14  and the three-prong expansion assembly  16  described in connection with FIGS.  1 - 7  and the mine roof bolt  12  described in connection with FIGS.  6 - 7  installed in a bore hole  38 , along with resin/catalyst  36 .  
         [0034]    [0034]FIG. 9 is a isolated view of the resin/catalyst  36  pattern shown in FIG. 8. As illustrated in either FIG. 8  and FIG. 9, the total cross-sectional area of the resin/catalyst pattern is approximatelly 0.142 square inches.  
         [0035]    The results of pull test bolt head deflections conducted at the Ohio Valley Company Powhatan No. 6 Mine are summarized in Table 1, entitled Pull Test Results. Prior to the pull tests, a series of approximately one-inch bore holes were driled into mine roof of the No. 6 mine. Next, a series of INSTAL B brand of mine roof bolts, commercially available from Jennmar Corporation of Pittsburgh, Pennsylvania, were each configured with an expansion assembly  10  according to the present invention . FOSROC brand of resin/catalyst was then inserted into each bore hole, followed by corresponding mine roof bolt. Each bolt was then installed and tensioned in the manner described above.  
                                                   TABLE 1                           PULL TEST RESULTS                Bolt Head Deflection (in inches)                LOAD (in tons)   Bolt #1   Bolt #2   Bolt #3   Bolt #4               0   0.000   0.000   0.000   0.000       1   0.000   0.000   0.000   0.000       2   0.000   0.000   0.000   0.000       3   0.016   0.014   0.012   0.015       4   0.029   0.025   0.024   0.031       5   0.052   0.054   0.049   0.054       6   0.083   0.077   0.074   0.084       7   0.106   0.104   0.099   0.110       8   0.140   0.140   0.125   0.150       9   0.175   0.189   0.164   0.186       9   0.239   0.235   0.221   0.254                  
 
         [0036]    As illustrated above, the present invention increases the amount of surface area for resin flow on the exterior of the expansion shell, increases the total external surface are of the three-prong expansion shell which permits the three-prong expansion shell to set or grab the walls of the bore hole more efficiently, and is less expensive to manufacture.  
         [0037]    The invention has been described with reference to the preferred embodiment.Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Summary:
An expansion assembly configured to be attached to a mine roof bolt, wherein the expansion assembly may include a plug defining an interior cavity and an outer surface and an expansion shell having a plurality of spaced-apart prongs, preferably three prongs, and defining a plurality of shell grooves, wherein each of the spaced-apart prongs is oriented diametrically opposed to a corresponding shell groove.