Railways: surface track – Fastenings
Reexamination Certificate
2002-04-09
2003-06-03
Morano, S. Joseph (Department: 3617)
Railways: surface track
Fastenings
Reexamination Certificate
active
06572027
ABSTRACT:
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 two-piece insulator spacers. The invention also relates to the two-piece insulator spacers. The invention further relates to methods of securing a rail to a concrete railroad tie using such two-piece 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 a two-piece 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 (124,550 N). 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 or post face
17
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.
These deterioration problems in their invention which is described in Pilesi et al, U.S. Pat. No. 6,343,748, which is incorporated herein by reference as if set forth herein in its entirety. That invention relates to improved insulator spacers and fastening systems and methods utilizing those insulator spacers. Each of those insulator spacers has one or more composite inserts positioned in its post so that the shoulder insert and the rail each contact the composite insert. Each such composite insert comprises a high compressive strength, electrically insulating material sandwiched between tough outer layers to provide electrical insulation between the rail and the shoulder insert. By locating one or more such composite inserts in the conventional durable, high compressive strength insulating material, e.g., 6-6 nylon, of the insulator spacer's post, the design of the inventors' prior invention placed 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.
In addition to possessing good electrical insulation and resistance against deterioration due to crushing and abrasion, an insulator spacer also needs to have the ability to flex appropriately with the applied loads it encounters in service. Two main flexural components may be identified: (1) a linearly-directed horizontal component; and (2) a rotationally-directed vertical component. These are depicted in
FIG. 2B
respectively by vector arrows X and Y. The linearly-directed horizontal component X compresses the post area of the insulator spacer
24
between the post areas of the rail
4
and shoulder insert
8
,
10
causing the post area of the insulator spacer
14
to flex compressively along the direction of the horizontal component X. The rotationally-directed vertical component Y, which is produced by the vertical distortion of the base or toe
16
of rail
4
, causes the toe
23
of the insulator spacer to flex upward and the body of the insulator spacer
24
to attempt to rotate around its axis Z. In a conventional, monolithic insulator spacer, the response of the insulator spacer to the vertical component Y conflicts with the compressive flex of the post area of insulator spacer caused by the horizontal component X and results in detrimental stresses in the conventional insulator spacer.
An insulator spacer's ability to flex is to a significant degree governed by the elastic modulus of its material of construction. The elastic modulus equals the quotient of the applied stress divided by the resulting elastic strain. The elastic modulus is a measure of a material's stiffness such that the higher the elastic modulus of the material, the stiffer the material is. The optimum elastic modulus value for an insulator spacer depends on the application in which it is used. In some applications, the elastic modulus value that best accommodates the horizontal component X may be different from that which best accommodates the vertical component Y. However, the monolithic structure of conventional insulator spacers militates against, if not completely precludes, optimizing the elastic modulus for both the horizontal component X and the vertical component Y.
SUMMARY OF THE INVENTION
The present invention overcomes the problems associated with prior art systems and improves upon the inventors' own prior invention. The present invention provides an improved fastening system for securing a rail to a concrete railroad tie that employs an insulator spacer comprising a two-piece design consisting of an upper member and a post member. The upper member is pressed upon and there
Burke Richard A.
Pilesi William D.
KSA Limited Partnership
McCarry, Jr. Robert J.
Reed Smith LLP
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