Abstract:
A system for securing a rail to a concrete railroad tie employing an improved insulator spacer that improves the resistance of the insulator spacer to the crushing deterioration induced by laterally-directed compressive forces during service. The improved insulator spacer has at least one composite insert located in an area that is subjected to high compressive loads in service. The composite insert or inserts are sufficiently electrically insulating to operably electrically insulate the rail the improved insulator spacer is in contact with from the shoulder insert the improved insulator spacer is also in contact with.

Description:
FIELD OF THE INVENTION 
     The invention relates to fastening systems for securing rails to concrete railroad ties. In particular, the invention relates to fastening systems having improved insulator spacers. The invention also relates to the improved insulator spacers. The invention further relates to methods of securing a rail to a concrete railroad tie using such an improved insulator spacer and to methods of retrofitting a railroad system having a rail insulated from a shoulder insert mounted in a concrete railroad tie using such an improved insulator spacer. 
     BACKGROUND OF THE INVENTION 
     DESCRIPTION OF THE PRIOR ART 
     Concrete railroad ties have been used in modern railroads for many years. One of the various fastening systems that have been developed for securing rails to concrete railroad ties is shown in FIG.  1 . At each rail seat area  2  where a rail  4  is to be fastened to concrete railroad tie  6 , cast iron shoulder inserts  8 ,  10  are provided opposing each other on the field and gauge sides of the rail seat area  2 , respectively. Each of the shoulder inserts  8 ,  10  is permanently mounted within the concrete railroad tie  6  at a position directly adjacent to the rail seat area  2 . The rail  4  is mounted between the two shoulder inserts  8 ,  10  and upon an elastomeric tie pad  12  that spans the rail seat area  2  between the two shoulder inserts  8 ,  10 . An insulator spacer  14  is placed adjacent to and abutting the base or toe  16  of rail  4  between rail  4  and each shoulder insert  8 ,  10 . Each insulator spacer  14  has an inner surface that is adapted to conform to the shape of the vertical and sloping lateral faces of rail base  16 . A retaining clip  18 , that is attached to a shoulder insert  8 ,  10  by way of being inserted through a longitudinal receiving hole  20  in a shoulder insert  8 ,  10 , presses upon the outer surface  22  of the corresponding insulator spacer  14  to rigidly secure rail  4  to concrete railroad tie  6 . 
     In this system, the tie pad  12  and the insulator spacers  14  act to electrically insulate the rail  4  from its companion rail  4  and from the ground. Such electrical insulation is necessary to permit the rails  4  to be used to conduct electrical signals for monitoring and controlling the progress of the trains that run upon them. 
     However, electrical insulation is not the only important property that an insulator spacer  14  must possess. The passage of a train upon the rails  4  subjects the rails  4  to complex patterns of horizontal and vertical forces and vibrations. These forces are transmitted from the rails  4  to the fastening systems which retain the rails  4  to the railroad ties. These forces are particularly high on curved portions of the track where the laterally-directed compressive force on a shoulder insert  8 ,  10  may exceed 28,000 pounds. Because the insulator spacers  14  are sandwiched between the rails  4  and the shoulder inserts  8 ,  10 , these forces subject the insulator spacers  14  to high compressive loads. To combat these loads, insulator spacers  14  have been made of a monolithic, durable insulating material having high compressive strength, such as 6-6 nylon. However, in service, the repeated exposure of the insulator spacers  14  to high compressive loads causes the insulator spacers  14  to deteriorate over time by way of crushing and abrasion. This deterioration occurs mainly in the portion of the insulator spacer  14  that is compressed between the shoulder insert  8 ,  10  and the vertical face of the rail base  16 , a portion that is referred to as the post. As the deterioration progresses, the rail  4  becomes able to move, thus causing wear and fatigue on the fastening system components and the concrete railroad tie  6  and compromising the safety of train travel upon the rail  4 . Thus, the deterioration makes it necessary to spend time and money to inspect the insulator spacers  14  for wear and to remove and replace worn insulator spacers  14 . 
     It is to be understood that what is being referred to herein by the term insulator spacer is also referred to by those skilled in the art by the simple generic term insulator. However, the term insulator spacer is more descriptive as it brings to mind both the mechanical and electrical functions of the component. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems associated with the insulator spacer deterioration described above by providing an improved fastening system for securing a rail to a concrete railroad tie that employs an improved insulator spacer. The improved insulator spacer has at least one composite insert located in an area of the improved insulator spacer that is subjected to high compressive loads in service. The composite insert or inserts are located and sized so that together the composite inserts carry most of the laterally-directed compressive load that is exerted in service upon the improved insulator spacer by the rail and the shoulder insert. The composite insert or inserts have a compression fatigue lifetime that is substantially longer than that of the material of the improved insulator spacer body that contains the composite insert. The composite insert or inserts are sufficiently electrically insulating so as to operably electrically isolate the rail the improved insulator spacer is in contact with from the shoulder insert the improved insulator spacer is also in contact with. 
     Thus, described is a fastening system for securing a rail to a concrete railroad tie wherein the concrete railroad tie has a rail seat area on which the rail rests. The fastening system comprises a shoulder insert mounted in the concrete railroad tie adjacent to the rail seat area, an improved insulator spacer inserted between the shoulder insert and the rail, and a retaining clip attached to the shoulder insert. The improved insulator spacer has a post and also has a composite insert positioned in the post so that the shoulder insert and the rail each contact the composite insert. 
     The composite insert is designed to place wear resistant, durably tough material in contact with the adjacent surfaces of the rail and the shoulder insert thereby enhancing the mechanical lifetime of the improved insulator spacer of which it is a part. The composite insert also has high compressive strength, electrically insulating material sandwiched between its tough outer layers to provide electrical insulation between the rail and the shoulder insert. 
     An improved insulator spacer having at least one such composite insert is also described. 
     Also described is a method of securing a rail to a concrete railroad tie. This method comprises the step of inserting an improved insulator spacer between a rail and a shoulder insert which is mounted in a concrete railroad tie. The improved insulator spacer used in this method has a post having a composite insert positioned in the post so that the shoulder insert and the rail each contact the composite insert. 
     Also described is a method of retrofitting a railroad system that has a rail insulated by means of an existing insulator spacer from a shoulder insert which is mounted in a concrete railroad tie. This method comprises the steps of first removing the existing insulator spacer and then inserting between the rail and the shoulder insert an improved insulator spacer which has a post having a composite insert positioned therein so that the shoulder insert and the rail each contact the composite insert. 
     Other features and advantages inherent in the subject matter claimed and described will become apparent to those skilled in the art from the following detailed description of presently preferred embodiments thereof and to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The criticality of the features and merits of the present invention will be better understood by reference to the attached drawings wherein similar reference characters denote similar elements throughout the several figures. It is to be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the present invention. 
     FIG. 1 is a schematic showing an isometric view, partially exploded, of a prior art fastening system for securing rails to concrete railroad ties. 
     FIG. 2A is a top view, partially in cross-section, of a fastening system according to an embodiment of the present invention. 
     FIG. 2B is a side view of the fastening system illustrated in FIG.  2 A. 
     FIG. 3 is an isometric view of an insulator spacer according to one embodiment of the present invention. 
     FIG. 4A is a top view of an insulator spacer according to an alternate embodiment of the present invention having first and second separable sections. 
     FIG. 4B is a front elevation view of the insulator spacer shown in FIG. 4A showing the side that faces the shoulder insert. 
     FIG. 5 is an isometric view of an embodiment of a composite insert according to the present invention. 
     FIG. 6 is an isometric view of an insulator spacer according to a further alternative embodiment of the present invention. 
     FIG. 7 is a schematic showing an isometric view, partially exploded, of a fastening system for securing rails to concrete railroad ties according to a further alternative embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2A and 2B illustrate an improved fastening system  26  according to the present invention for securing a rail  4  to a concrete railroad tie  6 . The improved fastening system  26  shown in FIGS. 2A and 2B includes all of the same components as the prior art fastening system shown in FIG. 1 except that the prior art monolithic insulator spacer  14  has been replaced by improved insulator spacer  24  according to the present invention. 
     Referring to FIGS. 2A and 2B, in improved fastening system  26 , rail  4  is seated upon tie pad  12  and a corresponding retaining clip  18  is attached to each of shoulder inserts  8 ,  10  and firmly presses a corresponding improved insulator spacer  24  against the base  16  of rail  4 . These components cooperate to firmly secure rail  4  to concrete railroad tie  6 . 
     A first embodiment of improved insulator spacer  24  is shown in FIG.  3 . Referring to FIG. 3, improved insulator spacer  24  has a vertical member  26 . Vertical member  26  includes post  27  which is the portion of improved insulator spacer  24  that, in service, stands between the shoulder insert  8 ,  10  and the vertical face of the rail base  16 . Improved insulator spacer  24  also has an upwardly sloping member, toe  28 , which has an inner surface  29  that is adapted to conform to the sloping lateral face of the rail base  16 . Toe  28  also has an outer surface  30  which is pressed upon by a retaining clip  18  to clamp toe  28  against an underlying rail base  16 . 
     Vertical member  26  and toe  28  may take on a various geometric configurations so long as improved insulator spacer  24  is able to perform its spacing and electrical insulating functions. For example, vertical member  26  and toe  28  may include pockets, such as shoulder insert receiving pocket  32  in vertical member  26  and retaining clip receiving pocket  34  in toe  28 . These members may also have angular or tapered outlines or surfaces, for example as illustrated in FIGS. 4A and 4B. 
     As shown in FIGS. 4A and 4B, vertical member  26  and toe  28  may be provided as separable sections which are mated together during service. Improved insulator spacer  24  may also be comprised of multiple separable sections in which one or more of the separable sections contain portions of one or both of the vertical member  26  and the toe  28  of the improved insulator spacer  24 . For example, FIGS. 4A and 4B illustrate an alternative embodiment in which improved insulator spacer  24  comprises first separable section  36 , which includes toe  28  and part of vertical member  26 , and second separable section  38 , which chiefly consists of the post  27  of vertical member  26 . 
     Furthermore, embodiments of improved insulator spacer  24  may also be configured without toe  28 . One such embodiment is shown in FIG.  7 . 
     The body of improved insulator spacer  24  may be made of any durable insulating material known to one skilled in the art having a suitably high compression strength for the application. Such materials include materials which are commonly used for insulator spacers, although materials having lower compression strength may also be used because most of the laterally-directed compressive forces on the improved insulator spacer  24  are carried by the composite insert or inserts  40 . Preferably, the body of improved insulator spacer  24  comprises 6-6 nylon. 
     Referring to FIGS. 3,  4 B, and  7 , improved insulator spacer  24  also comprises composite insert  40 . Composite insert  40  is located in post  27 , an area that is subjected to high laterally-directed compressive loads in service. Composite insert  40  has a compression fatigue lifetime that is substantially longer than that of the body material of improved insulator spacer  24  that contains composite insert  40 . 
     Composite insert  40  is designed to place a wear resistant, durably tough material in contact with the adjacent surfaces of the rail  4  and the shoulder insert  8 ,  10  thereby enhancing the mechanical lifetime of the improved insulator spacer  24  of which it is a part. A high compressive strength, electrically insulating material is sandwiched between the outer layers of composite insert  40  to provide electrical insulation between the rail  4  and the shoulder insert  8 ,  10 . 
     FIG. 5 shows an embodiment of a composite insert  40  having three layers. In this embodiment, composite insert  40  comprises first outer layer  42 , insulating layer  44 , and second outer layer  46 . In service, first outer face  48  of first outer layer  42  and second outer face  50  of second outer layer  46  are in contact with, respectively, the vertical face of the rail base  16  and the rail-facing surface of the shoulder insert  8 ,  10  so that composite insert  40  carries most of the laterally-directed compressive load that is exerted in service upon improved insulator spacer  24  by the rail  4  and the shoulder insert  8 ,  10 . 
     First and second outer layers  42 ,  46  are made of a wear resistant, durably tough material. First and second outer layers  42 ,  46  are preferably made of steel having a tensile strength of greater than about 55,000 pounds per square inch, more preferably made of a steel having a yield strength of between about 20,000 and about 30,000 pounds per square inch, and most preferably made of a steel having a yield strength of between about 24,000 and about 30,000 pounds per square inch. Examples of suitable steels are ASTM A283-58 Grade A steel and ASTM A285-57T Grade A steel. Other steels or other materials may be used for the first and second outer layers  42 ,  46  so long as the material used is not brittle, has wear comparability with the surface of the shoulder insert  8 ,  10  or the rail  4  it contacts in service, and provides a compression fatigue lifetime to the composite insert  40  that is substantially longer under service conditions than that of 6-6 nylon. First and second layers  42 ,  46  may be made of the same material or of different materials. 
     Insulating layer  44  is comprised of an electrically insulating material, for example without limitation, a high compression strength plastic or ceramic. Preferably, the electrically insulating material is a mica-filled phenolic plastic such as a Formica® material, which is available from the Formica Corporation, 10155 Reading Road, Cincinnati, Ohio 45241. Other examples of suitable plastics are filled nylons such as a Nylatron® material, which is available from DSM Engineering Plastic Products, 2120 Fairmont Avenue, Reading, Pa., U.S., 19612-4235, and fiberglass-reinforced polyphenylene sulfide compounds such as a Ryton® material, which is available from Chevron Phillips Chemical Co., Specialty Chemicals and Specialty Plastics, P.O. Box 7777, Bartlesville, Okla., U.S. 74005-7777. Suitable ceramics include without limitation aluminum oxide and silicon nitride. 
     The thickness of composite insert  40  is substantially the same as that of the adjacent body material of improved insulator spacer  24  that contains composite insert  40 . Although the composite insert  40  is shown in FIG. 5 as having three layers, it may have any number of layers so long as the layers in contact with the surfaces of the rail and the shoulder insert are made of wear resistant, durably tough material and so long as there is one or more insulating layers that cause the composite insert  40  to be an electrical insulator capable of electrically isolating the rail  4  from the shoulder insert  8 ,  10 . The thickness of each layer will depend on the number of layers used, the particular materials used for each layer, and the overall thickness of the composite insert  40 . A layer may have a thickness that is the same or different from that of another layer or layers. Preferably, to optimize the mechanical properties of the composite insert  40 , the thickness of the insulating layer or layers are minimized and the thicknesses of the durably tough material layers are maximized. For example, for a three-layer composite insert  40  such as that shown in FIG. 5 having steel as the outer layers  42 ,  46  and a mica-filled phenolic plastic as the insulating layer  44 , it is preferred that the insulating layer  44  have a thickness of about one-half of that of each of the outer layers  42 ,  46 . Thus, for a composite insert  40  having an overall thickness of about {fraction (5/16)} inches, the thickness of each of the outer layers  42 ,  46  is preferably about ⅛ inch and the thickness of the insulator layer  44  is about {fraction (1/16)} inch. 
     Although interlayer bonding is not necessary for the use of the present invention, the layers of composite insert  40  are preferably bonded together to facilitate the construction and use of improved insulator spacer  24 . The layers may be bonded together by an epoxy or urethane or by other suitable bonding materials known to those skilled in the art. The bonding material used preferably has a compression strength that is at least as great as that of the lowest compression strength layer of the composite insert. Examples of suitable bonding materials include epoxies such as Concresive® epoxy, which available from ChemRex, Inc., 889 Valley Park Drive, Shakopee, Minn., U.S., 55379, and Polybac1605 epoxy, which is available from Polygem, Inc., 1105 Carolina Drive, West Chicago, Ill., U.S., 60185. Although there is no restriction on the thickness of the interlayer bonding material, preferably, the bonding material thicknesses are on the order of 0.005 inches. 
     The improved insulator spacer  24  may have one or more composite inserts of any size or shape. It is preferred, however, that the corners or ends of the composite insert or inserts  40  be rounded because sharp corners may act as stress raisers in the adjacent body material of the improved insulator spacer  24  and cause cracking in that body material. For example, FIG. 3 shows one embodiment of an improved insulator spacer  24  having a single composite insert  40  which has an oblong cross-section and FIG. 6 shows an alternate embodiment of improved insulator spacer  24  having three cylindrical composite inserts  40 , that is, first, second and third composite inserts  40 A,  40 B,  40 C. 
     Although composite insert or inserts  40  of the improved insulator spacer  24  may be located anywhere in the post  27  of the improved insulator spacer  24 , it is preferred that they be located so as to avoid loading the corners of the shoulder inserts  8 ,  10 . Therefore, where a single composite insert  40  is used, it is preferred that it be centered along the length of the post  27  and its length be no more than about two-thirds the length of the post  27 . For example, referring to FIG. 4B, if post length  52  is about 3 inches, it is preferred that composite insert length  54  be no greater than about 2 inches. 
     One or more composite inserts  40  may be directly incorporated into the body of the improved insulator spacer  24  during the molding of the improved insulator spacer  24  or a separable portion thereof. Alternatively, the body of the improved insulator spacer  24  or a separable portion thereof may be formed with a hole or holes for receiving one or more composite inserts  40 . Preferably, the composite insert  40  is shaped so that the adjacent body material of the improved insulator spacer  24  locks into the composite insert  40  in a tongue and groove fashion to enhance the attachment of the composite insert  40  to the improved insulator spacer  24 . 
     The improved insulator spacer  24  may be used in a method of securing a rail to a concrete railroad tie. This method comprises the step of inserting an improved insulator spacer  24  between a rail  4  and a shoulder insert  8 ,  10  which is mounted in a concrete railroad tie  6 . The insertion is done in a manner that places the composite insert  40  that is located in the post  27  of improved insulator spacer  24  in contact with rail  4  and shoulder insert  8 ,  10 . After the improved insulator spacer  24  is so inserted, a retaining clip  18  may be attached to the shoulder insert  8 ,  10  to secure the rail  4  to the concrete railroad tie  6 . 
     Similarly, the improved insulator spacer  24  may also be used in a method of retrofitting a railroad system utilizing concrete railroad ties  6  that has a rail  4  insulated by means of an existing insulator spacer from a shoulder insert  8 ,  10 . The existing insulator spacer may be any type of insulator spacer including an improved insulator spacer  24 . This method comprises the steps of first removing the existing insulator spacer and then inserting between the rail  4  and the shoulder insert  8 ,  10  an improved insulator spacer  24 . The insertion is done in a manner that places the composite insert  40  that is located in the post  27  of improved insulator spacer  24  in contact with rail  4  and shoulder insert  8 ,  10 . After the improved insulator spacer  24  is so inserted, a retaining clip  18  may be attached to the shoulder insert  8 ,  10  to secure the rail  4  to the concrete railroad tie  6 . 
     It is to be understood that the improved insulator spacers, fastening systems, methods of securing a rail to a concrete railroad tie, and methods of retrofitting encompassed by the present invention are not limited to the particular configurations of the components described in the embodiments discussed above. Rather, the improved insulator spacers, fastening systems, methods of securing a rail to a concrete railroad tie, and methods of the retrofitting encompassed by the present invention are adaptable for use with all component configurations known to those skilled in the art. For example, FIG. 7 shows a fastening system according to another embodiment of the present invention which employs component configurations which differ in some respects from those previously described herein. In particular, in the shown embodiment, the shoulder insert, the clip, and the improved insulator spacer are configured so that the clip is inserted perpendicular to the rail rather than parallel to the rail as was the case in the previously described embodiments. 
     Referring to FIG. 7, rail  4  seats upon tie pad  12  which is situated in rail seat area  2  adjacent to shoulder insert  60 . Improved insulator spacer  24  inserts between rail  4  and shoulder insert  60  and extends downwardly into gap  62  between tie pad  12  and shoulder insert  60  to rest upon concrete railroad tie  6 . When so positioned, composite insert  40 , which is located in post  27  of improved insulator spacer  24 , contacts both rail  4  and shoulder insert  60 . Insulated clip  64 , which comprises insulator portion  66  and first and second hooks  68 ,  70 , is inserted into shoulder insert  60  so that insulator portion  66  passes through shoulder insert throat  72  to contact sloping lateral face  74  of rail  4  and so that first and second hooks  68 ,  70 , respectively, become locked between first and second arms  76 ,  78  and first and second ears  80 ,  82 . With insulated clip  64  so attached to shoulder insert  60 , rail  4  becomes secured to concrete railroad tie  6 . A similar arrangement of components may be used on the side of rail  4  which is opposite shoulder insert  60 . 
     While only a few presently preferred embodiments of the invention are described, it is to be distinctly understood that the invention is not limited thereto but may be otherwise embodied and practiced within the scope of the following claims.