Patent Publication Number: US-2013251454-A1

Title: Mine seal with electrically non-conductive ties

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 12/367,806, filed Feb. 9, 2009, which is a non-provisional of U.S. Patent Application Ser. No. 61/052,282, filed May 12, 2008, all of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to mine seals, and more particularly to such a seal which is resistant to the passage of electrical current through the seal. 
     BACKGROUND OF THE INVENTION 
     In particular, the present invention is an improvement on the mine seal disclosed in co-assigned U.S. Pat. No. 5,167,474 titled “Form for Making a Permanent Concrete Mine Stopping” and incorporated by reference herein for all purposes not inconsistent with this disclosure. This patent discloses a mine seal comprising two opposing spaced apart walls defined by a number of side-by-side extensible and contractible metal panels connected by horizontal ties spanning the space between the walls and by horizontal angle bars on the outside of the panels. The space between the walls is filled with full weight concrete or other suitable filler material (e.g., yieldable foamed concrete) which hardens or cures to form a permanent mine seal. 
       FIGS. 1-4  show four different prior art versions of a mine seal made in accordance with the invention disclosed in U.S. Pat. No. 5,167,474 which have been used commercially. In  FIGS. 1A and 1B , the mine seal  1  comprises two spaced apart walls  3  made of extensible and contractible panels  5 . The walls are connected by ties  9  and angle bars  15 . Each tie  9  comprises a pair of end tie plates  17  connected by a metal chain  21  passing through keyhole openings  23  in the tie plates, the chain being secured in each opening by passing a link of the chain into the reduced-diameter portion of the keyhole opening  23 . The tie plates  17  have V-shaped openings  27  for receiving the angle bars  15 .  FIGS. 2A-2C  show a second variation of a mine seal  101  in which each tie  109  comprises an elongate metal plate or bar  131  having two V-shaped openings  135  adjacent opposite ends of the bar for receiving the angle bars  141 . Each V-shaped opening  135  is formed by the combination of a notch  145  in a respective end of the metal bar  131  and a mating notch  147  in an end piece  151  secured by suitable fasteners  153  (e.g., rivets) to the bar.  FIGS. 3A-3C  show a third variation of a mine seal  201  in which each tie  209  comprises an adjustable-length elongate metal plate or bar  231  made of multiple overlapping sections  233  secured together by suitable fasteners  235  (e.g., bolts) extending through selected aligned holes  236  in the overlapping sections. The bar  231  has two V-shaped openings  237  adjacent opposite ends of the bar for receiving the angle bars  239 . Each V-shaped opening  237  is formed by the combination of a notch  245  in a respective end of the metal bar  231  and a mating notch  247  in an end piece  251  secured by suitable fasteners  253  (e.g., rivets) to the bar.  FIGS. 4A-4B  show a fourth variation of a mine seal  301  in which each tie  309  comprises a pair of end tie plates  341  connected by a metal rod  343  secured to the end tie plates. The end tie plates  341  have V-shaped openings  353  for receiving the angle bars  355 . 
     In the various embodiments of the above-referenced mine seal, the ties  9 ,  109 ,  209  and  309  are of a conductive material. Recently, MSHA (Mine Safety and Health Administration of the U.S. Department of Labor) has promulgated rules prohibiting conductors through permanent seals. Accordingly, there is a need to for an electrically non-conductive mine seal. 
     SUMMARY OF THE INVENTION 
     In general, In general, this invention is directed to an electrically non-conductive tie for use in a mine seal having opposing walls defining a space for receiving filler material. The tie has opposite ends, a length and a width and is made at least in part from an electrically non-conductive material which extends across substantially the entire width of the tie for preventing conduction of electrical current from one end of the tie to the other. Openings are provided adjacent opposite ends of the tie for receiving wall supports for the mine seal. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  show a first version of a prior art mine seal; 
         FIGS. 2A-2C  show a second version of a prior art mine seal; 
         FIGS. 3A-3C  show a third version of a prior art mine seal; 
         FIGS. 4A and 4B  show a fourth version of a prior art mine seal; 
         FIGS. 5A-5C  show a first embodiment of a mine seal of this invention; 
         FIGS. 6A-6C  show a second embodiment of a mine seal of this invention; 
         FIGS. 7A-7C  show a third embodiment of a mine seal of this invention; 
         FIGS. 8A-8C  show a fourth embodiment of a mine seal of this invention; and 
         FIGS. 9A-9D  show a fifth embodiment of a mine seal of this invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 5A-5C  show a first embodiment of an electrically non-conductive mine seal of the present invention, generally designated  401 . The seal comprises two spaced apart walls  403  made of extensible and contractible panels  405 , at least one but typically a plurality of electrically non-conductive ties  409  extending between the walls  403  to hold them in place against forces tending to separate the walls, and a filler material  411  filling the space between the walls. The walls panels  405  are connected by wall supports  415  comprising, in this embodiment, a plurality of horizontal bars (e.g., angle bars) extending on the outside of the walls. These components are described in more detail below. 
     As noted, the walls  403  are desirably made of extensible and contractible metal panels  405 , such as those described in U.S. Pat. No. 5,167,474 and as further described in U.S. Pat. No. 4,483,642, both of which are incorporated by reference herein for purposes not inconsistent with this disclosure. As therein described, the panels  405  are adapted to yield during a mine convergence so that the seal retains its structural integrity and maintains a good pressure fit against the mine walls to prevent leakage past the seal. It will be understood that the walls  403  can be made of other structural wall elements. 
     The filler material  411  can be full-weight concrete, foamed concrete, or other suitable material, such as described in U.S. Pat. No. 5,167,474. 
     Each electrically non-conductive tie  409  is a metal tie having at least one insulating gap  421  along its length spanned by an electrically non-conductive member  425  to prevent (or at least substantially prevent) the conduction of electrical current through the mine seal along the tie. In this particular embodiment, the tie  409  comprises a pair of end plates  431 ,  433  connected by a metal link chain  437  passing through keyhole openings  441  in the end plates. The chain  437  is secured in each opening  141  by passing a link of the chain into the reduced-diameter portion of the keyhole opening  441 . One end plate  431  is a metal plate of one-piece construction. The other end plate  433  comprises a pair of metal sections  445 ,  447  spaced apart to provide the insulating gap  421 . The gap is spanned by the non-conductive member  425  which is secured to the metal sections by suitable means  451 , e.g., mechanical fasteners such as rivets or bolts, or other attachment mechanisms. 
     Referring to  FIG. 5C , the insulating gap  421  has a dimension  461  along the length of the tie  409  which will vary, e.g., according to the type of filler material  411  used. If full-weight concrete is used as the filler material  411 , the minimum dimension  461  is determined by the likelihood of a single or perhaps few pieces of concrete aggregate that could bridge the gap in an electrical conduction fashion that is atypical of the concrete in general. Foamed cement does not include either fine or coarse aggregate, but there may some risk that a piece of foreign material could find its way across the gap in the completed structure. Taking these factors into consideration, gap  421  has a minimum dimension  461  of at least about 0.5 in., and in this embodiment the dimension  461  is about 2.0 in. Of course, dimension  461  may be substantially larger, all the way to a situation where the tie is made completely of dielectric material, although costs and thickness must also be considered. 
     The electrically non-conductive member  425  spanning the gap  421  has a first dimension  471  along the length of the tie greater than the dimension  461  of the gap, so that the member overlaps the metal end plate sections  445 ,  447  a distance sufficient to provide fastening areas sized for secure attachment of the member  425  to the metal sections. The non-conductive member has a second dimension  475  generally transverse to the dimension  471  (i.e., generally across the width of the tie). Desirably, this dimension  471  is not substantially greater than and, even more desirably about equal to the corresponding dimension (e.g., height) of the metal end plate sections  445 ,  447  so that the size of the non-conductive member  425  is kept relatively small to avoid lines of cleavage in the seal  401 . 
     The non-conductive member  425  has suitable physical properties, including the strength in tension to hold the walls  403  in place during and after placement of the filler material between the walls of the mine seal, and the tensile, shear and/or tear strength necessary to withstand the forces (e.g., localized stress in the areas of the fasteners) required to attach the member to the metal sections of the end tie plate. Desirably, the non-conductive member  425  is of a material which permits fabrication at reasonable cost, which is resistant to failure in bending or other non-tensile modes during handling, installation and pouring of the filler material between the walls of the seal, resistant to water in storage and as the cement is poured and prior to curing, and resistant to the moisture always present in a mine atmosphere which prevents the seal from becoming fully “dry.” The member  425  should also have suitable dielectric properties, including good dielectric strength so that electrical current due to lightning strikes, for example, is not conducted across the seal through the tie. 
     Many types of non-conductive material meet the above criteria. However, many of these materials, including many commonly used plastics, are not strong enough to make the connection to the metal end plate sections  445 ,  447  without using many fasteners over a large area and without requiring large cross sectional areas. One material which has been found to be suitable is Micarta® structural insulating board, a phenolic plastic laminate developed by Westinghouse. This material has sufficient tensile strength and toughness to keep the size of the non-conductive member  425  relatively small. By way of example but not limitation, for a metal end tie plate  433  having a height of about four inches, a thickness of about 1/16 in. and a gap dimension  461  of about two inches, a non-conductive member  425  of Micarta® structural insulating board has a dimension  471  of about four inches in. (allowing about a one inch lap on opposite sides of the two-inch gap  421 ), a dimension  475  of about four inches and a thickness of about ¼ in. The non-conductive member  425  may be made from other non-conductive materials (e.g., fiber-reinforced plastic). 
     The outer ends of the tie end plates  431 ,  433  protrude through the walls  403  of the seal (e.g., between adjacent panels  405 ) and have V-shaped openings  481  for receiving the wall supports  415 . The supports  415  and openings  481  may have other shapes. 
     Each tie  409  has a suitable marking  485  on the tie to indicate that it is an electrically non-conductive tie, thereby differentiating it from the prior art conductive ties. Desirably, this marking  485  is on a portion of the tie which is readily visible when the after the mine seal has been installed, such as the outer end sections (e.g.,  447 ) of the tie protruding outward beyond the walls  403  of the seal  401 . Desirably, the marking is of a permanent nature, and in one embodiment comprises a marking stamped into the metal or piercing the metal, such as the letter “I” indicating that the tie is “insulated.” Other markings may be used. 
       FIGS. 6A-6C  illustrate a second embodiment of a mine seal, generally designated  501 , made in accordance with this invention. The seal comprises two spaced apart walls  503  each made of extensible and contractible panels  505 , electrically non-conductive ties  509  extending between the walls  503  and holding them in place against forces tending to separate the walls, and a filler material  511  filling the space between the walls. The walls panels  505  are connected by wall supports  515  comprising, in this embodiment, a plurality of horizontal bars (e.g., angle bars) extending on the outside of the walls  503 . 
     The filler material  511  can be full-weight concrete, foamed concrete, or other suitable material, such as described in U.S. Pat. No. 5,167,474. 
     In this embodiment, each tie  509  comprises an elongate metal plate or bar  519  having at least one insulating gap  521  along its length spanned by a non-conductive member  525  to prevent the conduction of electrical current through the mine seal along the tie. The physical and electrical characteristics of the gap  521  and non-conductive member  525  are essentially identical to those of the gap  421  and non-conductive member  425  of the previous embodiment. The means for attaching the non-conductive member  525  to the metal tie  509  is also the same as the means  451  of the first embodiment. 
     Each tie  509  has two openings  527  adjacent opposite ends of the bar  519  for receiving the wall supports  515 . As best illustrated in  FIG. 6C , each opening  527  is formed by the combination of a notch  531  in a respective end of the metal bar  519  and a mating notch  535  in an end section or piece  537  secured by suitable fasteners  541  (e.g., rivets) to the bar  519 . The openings  527  can be formed in other ways and have other shapes. 
     As in the previous embodiment, each tie  509  desirably has a suitable marking  585  on the tie to indicate that it is an electrically non-conductive tie, thus differentiating it from the prior art conductive ties. 
       FIGS. 7A-7C  illustrate a third embodiment of a mine seal, generally designated  601 , made in accordance with this invention. The seal comprises two spaced apart walls  603  each made of extensible and contractible panels  605 , non-conductive ties  609  extending between the walls  603  and holding them in place against forces tending to separate the walls, and a filler material  611  filling the space between the walls. The walls panels  605  are connected by wall supports  613  comprising, in this embodiment, a plurality of horizontal bars (e.g., angle bars) extending on the outside of the walls  603 . 
     The filler material  611  can be full-weight concrete, foamed concrete, or other suitable material, such as described in U.S. Pat. No. 5,167,474. 
     In this embodiment, each tie  609  comprises an adjustable-length elongate metal plate or bar  611  comprising a plurality of overlapping sections  615  secured together by suitable fasteners  619  (e.g., bolts) extending through selected aligned holes  620  in the overlapping sections  615 . The tie  609  has at least one insulating gap  621  along its length spanned by a non-conductive member  625  to prevent the conduction of electrical current through the mine seal along the tie. The physical and electrical characteristics of the gap  621  and non-conductive member  625  are essentially identical to those of the gap  421  and non-conductive member  425  of the first embodiment. The means for attaching the non-conductive member  625  to the metal tie  609  is also the same as the means  451  of the first embodiment. 
     Each tie  609  has two openings  627  adjacent opposite ends of the bar  611  for receiving the wall supports  613 . Each opening  625  is formed by the combination of a notch  631  in a respective end of the metal bar  611  and a mating notch  635  in an end piece  637  secured by suitable fasteners  641  (e.g., bolts or rivets) to the bar  611 . The openings  625  can be formed in other ways and have other shapes. 
     As in the previous two embodiments, each tie  609  desirably has a suitable marking  685  on the tie to indicate that it is a non-conducting tie, thereby differentiating it from the prior art conductive ties. 
       FIGS. 8A-8C  illustrate a fourth embodiment of a mine seal, generally designated  701 , made in accordance with this invention. The seal comprises two spaced apart walls  703  each made of extensible and contractible panels  705 , non-conductive ties  707  extending between the walls  703  and holding them in place against forces tending to separate the walls, and a filler material  709  filling the space between the walls. The walls panels  705  are connected by wall supports  711  comprising, in this embodiment, a plurality of horizontal bars (e.g., angle bars) extending on the outside of the walls. 
     The filler material  709  can be full-weight concrete, foamed concrete, or other suitable material, such as described in U.S. Pat. No. 5,167,474. 
     In this embodiment, each tie  707  comprises a pair of end tie plates  713 ,  715  connected by a metal rod  717  secured to the end tie plates. One of the end plates  713  is of one-piece construction. The other end plate  715  comprises a pair of metal sections  719 ,  720  spaced apart to provide an insulating gap  721  ( FIG. 8C ). The gap is spanned by a non-conductive member  725  which is secured to the metal sections by suitable means  731 , e.g., mechanical fasteners such as rivets and bolts, or other attachment mechanisms. The physical and electrical characteristics of the gap  721  and non-conductive member  725  are essentially identical to those of the gap  421  and non-conductive member  425  of the first embodiment. 
     The outer ends of the ties  707  protrude through the walls  703  of the seal and have openings  781  for receiving the wall supports  711 . The wall supports  711  and openings  481  may have other shapes. 
     As in the previous two embodiments, each tie  709  desirably has a suitable marking  785  on the tie to indicate that it is a non-conducting tie, thus differentiating it from the prior art conductive ties. 
       FIGS. 9A-9D  illustrate a fifth embodiment of a mine seal, generally designated  801 , made in accordance with this invention. The seal comprises two spaced apart walls  803  each made of extensible and contractible panels  805 , non-conductive ties  809  extending between the walls  803  and holding them in place against forces tending to separate the walls, and a filler material  811  filling the space between the walls. The walls panels  805  are connected by wall supports  813  comprising, in this embodiment, a plurality of horizontal bars (e.g., angle bars) extending on the outside of the walls  603 . 
     The filler material  811  can be full-weight concrete, foamed concrete, or other suitable material, such as described in U.S. Pat. No. 5,167,474. 
     In this embodiment, each tie  809  comprises an adjustable-length elongate plate or bar  811  comprising a plurality of overlapping sections  815  secured together by suitable fasteners  819  (e.g., bolts) extending through selectively aligned holes  820  in the overlapping sections  815 . In one embodiment, the bolts are of metal. The overlapping sections  815  are made entirely or substantially entirely of an electrically non-conductive material (such as the non-conductive material described in previous embodiments) to prevent the conduction of electrical current through the mine seal along the tie. 
     The tie  809  has two openings  827  adjacent opposite ends of the tie  809  for receiving the wall supports  813 . Each opening  827  is formed by the combination of a notch  831  in a respective end of the bar  811  and a mating notch  835  in an end section  837  of the tie. Two end sections  837  are secured to respective ends of the bar  811  by suitable fasteners  841  (e.g., metal bolts or rivets). The openings  827  can be formed in other ways and have other shapes. In one embodiment, the end sections  837  are of metal. Alternatively, the end sections  837  may be of an electrically non-conductive material. 
     As in the previous two embodiments, each tie  809  desirably has a suitable marking  885  on the tie to indicate that it is a non-conducting tie, thereby differentiating it from the prior art conductive ties. 
     It will be noted that the insulating gap (e.g.,  421 ,  521 ,  621 ,  721 ) described in previous embodiments can be located anywhere along the length of the tie (e.g.,  409 ,  509 ,  609 ,  707 ) so long as the gap is between the side walls of the mine seal. Further, there may be more than one insulating gap (and associated electrically non-conductive member) along the length of the tie. To prevent the conduction of electrical current along the tie, the insulating gap should extend across substantially the entire width of the tie, and desirably across the entire width of the tie. 
     The lengths of the ties described above will depend on the depth of thickness of the seal itself. In general, however, the length of a tie will vary from four feet or less to ten feet or more. 
     Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. By way of example, a non-conductive tie of this invention can be made entirely from a suitable electrically non-conductive material (e.g., of the types discussed previously), thereby eliminating the need for a separate non-conductive member. In some embodiments, the end sections of the tie located outboard of the walls of the seal (e.g., end sections  837  in  FIGS. 9B and 9D ) are made from metal and the remainder of the tie is made entirely or substantially entirely from an electrically non-conductive material. If the portion of the tie between the walls of the seal comprises more than one section of an electrically non-conductive material (e.g.,  FIG. 9B ), the fasteners (e.g., bolts  819  in  FIG. 9B ) holding the sections together may be made of metal or of an electrically non-conductive material. 
     This invention is also directed to a form for making a mine seal of this invention. The form comprises a plurality of wall panels (e.g.,  405 ,  505 ,  605 ,  705 ,  805 ) adapted to be installed as walls in spaced apart relation for defining a space for receiving a filler material, and at least one electrically non-conductive tie (e.g.,  409 ,  509 ,  609 ,  707 ,  809 ) adapted to extend between the walls and to hold them in place against forces tending to separate the walls. Desirably, the form also includes wall supports ( 415 ,  515 ,  613 ,  711 ,  813 ) secured to the ties. Once the form is in place, filler material is deposited between the walls and allowed to cure to form the mine seal. Various embodiments of a form of this invention are shown in the Figures and described above. 
     When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.