Patent Application
20100170956
1. Field of the Invention
The present invention relates to railroad cross ties and, more particularly, composite railroad cross ties and methods of manufacturing composite rail road cross ties.
2. Description of the Related Art
Railway tracks are typically supported on a plurality of individual cross ties. Wooden cross ties are one of the most common types of railroad cross ties. When using a wooden cross tie, the railway tracks are typically secured to the cross tie using tie plates and spikes that are driven into the cross tie. Various other materials, however, are also used to form railroad cross ties. For example, concrete and steel are also used to form cross ties.
Composite railroad cross ties which utilize recycled plastic resins are also known in the art. One example of a composite railroad cross tie is disclosed in U.S. Pat. No. 6,179,215 B1 the disclosure of which is incorporated herein by reference. Composite cross ties often include an inner core that includes a steel reinforcing member encased in concrete and an outer resinous casing surrounding the inner core. The outer casing may be formed out of a material that includes recycled plastic resins. The outer casing provides protection against adverse weather conditions for the inner core. The formation of the outer casing on the inner core, however, may leave the two end surfaces of the inner core exposed. Polymeric end caps can be placed on the two exposed end surfaces of the cross tie in an effort to protect these end surfaces from adverse weather conditions. It has, however, proven difficult to secure polymeric end caps on the exposed end surfaces of composite railroad ties in a reliable manner.
The present invention provides a railroad cross tie construction and method of manufacture that provides well-secured end caps on the opposing ends of the cross tie.
The invention comprises, in one form thereof, a railroad cross tie having a longitudinal length. The cross tie includes an inner core including at least one longitudinally extending reinforcing member and an outer casing substantially enclosing the inner core along the longitudinal length of the cross tie. First and second end caps are engaged with the outer casing with the first end cap being disposed proximate a first end of the inner core and the second end cap being disposed proximate a second opposite end of the inner core. The cross tie also includes at least one expansion gap that is longitudinally disposed between the first and second end caps. A longitudinal dimension of the expansion gap is varied by differential thermal expansion between the inner core and the outer casing.
The invention comprises, in another form thereof, a railroad cross tie having a longitudinal length and which includes an inner core including at least one longitudinally extending reinforcing member, an outer casing substantially enclosing the inner core along the longitudinal length of the cross tie and first and second end caps. The first end cap is disposed proximate a first end of the inner core and the second end cap is disposed proximate a second end of the inner core with each of the first and second end caps being welded to the outer casing.
The invention comprises, in yet another form thereof, a railroad cross tie having a longitudinal length and which includes an inner core including at least one longitudinally extending reinforcing member, an outer casing substantially enclosing the inner core along the longitudinal length of the cross tie, and first and second end caps. The first end cap is disposed proximate a first end of the inner core and the second end cap is disposed proximate a second end of the inner core. At least a portion of each of the first and second end caps is overlain by the outer casing such that dislocation of the outer casing is required to detach the first and second end caps from the cross tie.
The invention comprises, in still another form thereof, a railroad cross tie having a longitudinal length and which includes an inner core including at least one longitudinally extending reinforcing member, an outer casing substantially enclosing the inner core along the longitudinal length of the cross tie and first and second end caps. The first end cap is disposed proximate a first end of the inner core and the second end cap is disposed proximate a second end of the inner core. First and second retention members are respectively disposed at the first and second ends of the inner core with the first end cap being secured to the first retention member and the second end cap being secured to the second retention member.
The invention comprises, in still another form thereof, a method of manufacturing railroad cross ties wherein each of the cross ties has a longitudinal length. The method includes providing a plurality of longitudinally extending inner cores for manufacturing a corresponding number of cross ties, securing two adjacent inner cores together in an end-to-end configuration by attaching a connecting member to each of the adjacent inner cores, and forming an outer casing on the exterior of the adjacent inner cores. The adjacent inner cores are then separated to form first and second cross ties by separating the connecting member into a first part and a second part wherein the first part of the separated connecting member forms a portion of the first cross tie and the second part of the separated connecting member forms a portion of the second cross tie.
The above mentioned and other features of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates several embodiments of the invention, in various forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed.
Two similar cross tie designs in accordance with the present invention are illustrated in
As illustrated in
Inserts 32 are seated within the profile of the reinforcing members 26, 26′ at locations where spikes are commonly used to attach tie plates to cross ties. The illustrated inserts 32 are 10% polyethylene and 90% rubber (by volume), however, various other materials may also be used to form inserts 32. Both the polyethylene and the rubber used to form inserts 32 may be recycled materials. The polyethylene may be a high density polyethylene obtained from recycled household containers while the rubber may be crumb rubber obtained from used automotive tires. The use of such inserts 32 with cross ties 20 allows conventional spikes and tie plates (not shown) to be used to secure railroad rails to the cross ties 20 in the same manner that such spikes and tie plates are used to secure railroad rails to wooden cross ties.
Insulative reinforcing member 30 is shown in greater detail in
Insulator 30 is positioned between the two longitudinally spaced sets of inserts 32 so that, if the spikes used to secure the rails to cross ties 20 contact metallic reinforcing members 26′, insulator 30 will prevent the communication of an electrical current between the two rails secured to the cross tie 20. Railroad rails are often used as electrical conductors for communication signals that facilitate the operation of trains on the rails. The use of insulators 30 to prevent the communication of electrical currents between the two separate rails attached to cross tie 20 helps to preserve this functional aspect of the rails attached to the cross tie 20.
In an alternate embodiment, insulative reinforcing member 30 comprises two (2) separate tubular pultrusions, each being slidingly received and seated within one of the side-by-side elongate troughs 26c of the reinforcing members 26′. Similarly, steel straps 31 would be tightly secured about the outer perimeter of each of the two reinforcing members 26′ being joined together by the two separate tubular pultrusions to securely engage each of the two reinforcing members 26′ with the two tubular pultrusions. It is further noted that the two separate pultrusions can be replaced by solid elongate beam members similar in shape to the inserts 32 and used in place of reinforcing member 30. In both alternate embodiments, however, the two separate tubular pultrusions and the solid elongate beam members would be made of an electrically insulative material such as fiberglass and polyester so that, in addition to joining the reinforcing members 26′ to one another, the reinforcing members 26′ are also maintained apart and are electrically insulated from one another.
Each inner core 22 also includes a pair of retention members 34 disposed at the opposite ends of the inner core 22. The illustrated retention members 34 are formed out of sheet steel. A retention member 34 is welded to each end of reinforcing member 26 with the outward facing planar surfaces 36 of members 34 being positioned perpendicular to the longitudinal axis 21 defined by cross tie 20 and which is also the longitudinal axis of the inner core 22. The use of a metallic plate to form retention member 34 allows interlocking C-shaped flange members 38 to be easily formed on retention member 34 by bending outwardly projecting tabs on the metallic plate to form inwardly opening C-shaped flanges. As discussed below, C-shaped flanges 38 secure connecting members 40 to inner core 22.
After assembling reinforcing members 26′ with insulator 30 and attaching retention members 34 to the opposing ends of the inner core assembly, stiffening plate 27 is welded to reinforce member 26 and inserts 32 are positioned at the proper locations within the troughs 26c formed by the W-shaped profile of reinforcing members 26′. Concrete is then used to fill the remaining volume of the inner core 22. When using a single reinforcing member 26, stiffening plate 27 is welded to reinforcing member 26, retention members 34 are attached to the opposite ends of reinforcing member 26 and inserts 32 are positioned in troughs 26c before filling the remainder of troughs 26c with concrete.
As mentioned above, the W-shaped profile of the illustrated reinforcing members 26, 26′ defines two upwardly opening troughs 26c (
The concrete is allowed to reach its initial set before outer casing 24 is applied to inner core 22 as discussed in greater detail below. Delaying the application of the outer casing 24 by at least about 24 hours provides the concrete with sufficient time to reach its initial set in the absence of unusual conditions or unique concrete mixtures. The 24 hour waiting period also provides time for evaporation of excessive surface water that may have accumulated on the upper surface of the concrete during the initial set. In the illustrated embodiment, concrete material 28 is a conventional mixture that includes portland cement, aggregate and fines.
When applying the outer casing 24 to inner cores 22, the inner cores 22 are passed through an extruder apparatus 60 (
Connecting members 40 are preferably made of 100% polyethylene by injection molding. As can be seen in
Connecting members 40 also include spacing members 48 which project longitudinally outwardly, away from the block portion 42. Spacing members 48 bias the substantially planar portion 44 of connecting member 40 away from planar surfaces 36 on retention members 34 to thereby form expansion gaps 50 between connecting members 40 and retention members 34. By biasing connecting member 40 away from planar surfaces 36 on retention members 34, spacing members 48 also keep flange members 46 tightly engaged within C-shaped flanges 38 on retention members 34.
After outer casing 24 has been applied to the inner cores 22 and the connecting members 40, the connecting members 40 and the outer casing 24 coating the connecting members 40 are severed at the longitudinal midpoint of the connecting members 40 at the block portion 42. The resulting two parts of the connecting member 40 form two separate end caps 40a located on separate cross ties 20. The exploded view of
The manufacture of cross ties 20 will now be discussed. As mentioned above, the inner core 22 of the embodiment of
For both of the illustrated embodiments, the concrete material 28 is advantageously allowed to set for at least about 24 hours before applying the outer casing 24. Prior to applying the outer casing 24, a plurality of the inner cores 22 are connected together in an end-to-end fashion with connecting members 40, with the longitudinal axes of the plurality of inner cores 22 being substantially co-linear as exemplified by
The inner cores 22 may be connected with connecting members 40 either after the filling of troughs 26c with concrete 28, or, as depicted in
The extruder apparatus 60 includes one or more feedstock sources 62 for feeding an extruder screw 64 with the feed stock material 23 that will form outer casing 24. In the illustrated embodiment, outer casing 24 is formed out of a mixture containing 50% polyethylene and 50% rubber (by volume) but other suitable compositions may be used in alternative embodiments.
The extruder screw 64 extrudes molten material 23 into mold cavity 66 where it is applied to inner cores 22 which are being transported through mold cavity 66. Mold cavity 66 has an inlet port 68 and an outlet port 70 through which the inner cores 22 respectively enter and depart mold cavity 66. Conveyor systems 72 on either side of mold cavity 66 support the linked together inner cores 22 and provide the driving force for moving inner cores 22 through mold cavity 66. Connecting members 40 link the inner cores 22 together and impart both pushing and pulling forces between the linked inner cores 22 as the inner cores 22 are transported along conveyor systems 72 and through molding cavity 66. Connecting members 40 are, thus, subjected to both compressive and tension forces.
While the feed material 23 is molten when introduced into mold cavity 66, it is relatively viscous and is not in a free flowing liquid state. As a result, the feed material 23 does not fill expansion gap 50 and, to the extent that it enters expansion gap 50 at all, it enters only a relatively insignificant portion of the outer edges of gap 50. Due to the viscous nature of feed material 23, feed material 23 does not completely fill mold cavity 66 and the area of mold cavity 66 near inlet port 68 will not be filled with material 23 as schematically depicted in
After exiting mold cavity 66, the inner cores 22 which now have outer casing 24 applied thereto may be passed through a curing oven and/or a cooling station (not shown) prior to separating the coated inner cores to form individual cross ties 20. After outer casing 24 has been applied to the inner cores 22 and the connecting members 40 between inner cores 22, a cutting apparatus 74 is used to sever the outer casing 24 and connecting members 40 at the longitudinal midpoint of connecting members 40 as schematically depicted in
As can be seen in
The cross tie 20 formed after the severing operation depicted in
A thermal die apparatus 76 that can be used to heat seal seam 52 by welding is illustrated in
Apparatus 76 includes a thermal die 78 that is heated and pressed against an end of a cross tie 20 to heat seal seam 52 by partially melting one or both of end cap 40a and outer casing 24. Thermal die 78 includes an outer portion 82 that is positioned opposite outer casing 24 and an inner area 84 that is positioned opposite end cap 40a. A projecting rib 83 is preferably provided and engages the area immediately adjacent seam 52 on both sides of seam 52 for transferring thermal energy deep into this area thereby further assuring the polyethylene end cap 40a and the polyethylene and rubber casing 24 are melted and welded at the seam 52. A drive unit 80 such as a pneumatic ram moves die 78, and thus rib 83, into and out engagement with the end surface of cross ties 20 as indicated by arrow 81. In
When die 78 is pressed against the end of cross tie 20, it will transfer thermal energy to the outer casing 24 and end cap 40a and thereby at least partially re-melt one or both of these portions of cross tie 20 at least along the location of seam 52. When the re-melted portions re-solidify after cross tie 20 no longer is engagement with die 78, the re-solidified portions will form a weld 53 (
A significant advantage of the illustrated cross tie 20 is that end caps 40a remain reliably attached to cross tie 20. When manufacturing cross ties 20, the feed material 23 will be at an elevated temperature when it is applied to inner cores 22 while the inner cores 22 will be at or near the ambient environmental temperature. For example, the feed material is at a temperature of approximately 375° F. (191° C.) in the illustrated embodiment. As outer casing 24 cools, the longitudinal length of outer casing 24 will shrink relative to the longitudinal length of inner core 22. This differential shrinkage causes the opposing ends of inner core 22 to push longitudinally outwardly against the end caps.
Moreover, in light of the differences in the coefficient of thermal expansion between the outer casing 24 and inner core 22, the outer casing 24 and inner core 22 will elongate and contract at different rates when the cross tie 20 is placed in use outdoors and is subjected to the elements and temperature variations. These differences in thermal growth and contraction will also cause the opposing ends of inner core 22 to push longitudinally against the end caps.
The illustrated cross ties 20 have several separate features which can be used either separately or in combination to enhance the securement of end caps 40a to cross ties 20 and for preventing the end caps 40a from becoming dislodged as a result of differential thermal expansion between the core 22 and casing 24. These features include expansion gaps 50; the mechanical interlocking of end caps 40a with inner core 22; the welding of end caps 40a to outer casing 24; and, the overlaying of a portion of end caps 40a by outer casing 24.
As discussed above, end caps 40a are disposed proximate opposing ends of inner core 22 with the entire longitudinal length of inner core 22 disposed between the two end caps 40a. Expansion gaps 50 are located between end caps 40a and the opposing ends of inner core 22. In the illustrated embodiment, expansion gaps 50 are defined by the planar surfaces 36 of retention members 34 which face and are spaced apart from the planar central portions 44 of end caps 40a. The longitudinal dimension of expansion gaps 50 will vary in response to the differential thermal expansion of outer casing 24 and inner core 22 to thereby reduce some of the forces applied to end caps 40a that are induced by the differential thermal expansion and contraction of outer casing 24 and inner core 22. In the illustrated embodiment, the longitudinal distance between surface 36 and surface 44, i.e., the longitudinal dimension of expansion gap 50, is preferably approximately 0.125 inches (0.317 cm) when connecting member 40 is secured to retention member 34 of inner cores 22 and prior to the application of outer casing 24. This longitudinal distance can, however, be greater as needed to accommodate the differential thermal expansion. It is also noted that, in the illustrated embodiment, retention member 34 and inner core 22 have a common width (W) and height (H) that is substantially equivalent to the width (W) and height (H) of expansion gap 50 (as depicted against connecting member 40 in
As also discussed above, the illustrated embodiments of cross ties 20 include end caps 40a that are mechanically interlocked with inner core 22 by the engagement of flanges 46 with C-shaped flanges 38 of retention members 34. This mechanical fixation of end caps 40a to inner cores 22 helps to ensure that end caps 40a remain firmly attached to inner core 22 as end caps 40a are subjected to stresses caused by variations in the thermal expansion or contraction of outer casing 24 and inner core 22 or other forces which might have an impact on the attachment of end caps 40a.
The thermal welding of end caps 40a to outer casing 24 along seam 52 also helps to ensure that end caps 40a remain secured to cross ties 20. When the thermal weld joining end caps 40a to outer casing 24 extends along the entire length of seam 52, the weld also acts as a seal inhibiting the inward migration of moisture through seam 52.
The physical configuration of end caps 40a and outer casing 24 also helps to secure and retain end caps 40a on cross ties 20. As discussed above, end caps 40a include outwardly extending flanges 46 that are received by C-shaped flanges 38. Once outer casing 24 has been formed on inner cores 22 and connecting members 40 and the individual cross ties subsequently separated, the outer casing 24 will include a portion 25 that overlays flanges 46 and block 42 and thereby prevents end caps 40a from being detached from cross tie 20. The general extent of overlaying portion 25 is indicated between dashed lines and seam 52 in
While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.
