CA1076080A - Non-metallic-reinforced molded crosstie - Google Patents
Non-metallic-reinforced molded crosstieInfo
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- CA1076080A CA1076080A CA300,080A CA300080A CA1076080A CA 1076080 A CA1076080 A CA 1076080A CA 300080 A CA300080 A CA 300080A CA 1076080 A CA1076080 A CA 1076080A
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- crosstie
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- wood
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Abstract
NON-METALLIC-REINFORCED MOLDED CROSSTIE
Abstract of the Disclosure A reinforced railroad crosstie formed by molding and bonding comminuted lignocellulosic material into a monolithic beam around a plurality of wooden reinforcing members which have relatively clear and straight grain, a high modulus of rupture and a high modulus of elasticity and are able to withstand a high amount of compression without crushing. The reinforcing members are positioned within the crosstie proximate lines of maximum tensile stresses expected to be induced in the tie by different bending influences caused by passing trains and varying conditions of the underlying ballast. The members are also positioned within the crosstie so as to avoid interference with the spikes employed to fasten the rail to the tie.
Abstract of the Disclosure A reinforced railroad crosstie formed by molding and bonding comminuted lignocellulosic material into a monolithic beam around a plurality of wooden reinforcing members which have relatively clear and straight grain, a high modulus of rupture and a high modulus of elasticity and are able to withstand a high amount of compression without crushing. The reinforcing members are positioned within the crosstie proximate lines of maximum tensile stresses expected to be induced in the tie by different bending influences caused by passing trains and varying conditions of the underlying ballast. The members are also positioned within the crosstie so as to avoid interference with the spikes employed to fasten the rail to the tie.
Description
' Back'ground of,'th'e'Invention '`I The present invention relates to a railway cross-~: tie of molded and bonded lignocellulosic material internally .,~, reinforced against positive and negative bending stresses expected from train movements over a railway tTack. Most conventional railway crossties used in this country today are lumber beams, approximately 7 inches thick by 9 inches . ~ . . . . .. . . . . . . .. . . ... .. .
'~
~., .
1076~)~0 - wide by 8 1/2 or 9 feet lon~, that have been cut from sections of live tree trunks selected to be free from soft or decayed spots, shakes, worm holes, and other imperfections. ~efore being placed into service as crossties, these heams are treated with creosote, an oily liquid preservative, to protect them against the effects of exposure to the elements.
~he major disadvantages of using lumber beams for railway crossties are the ever-increasing costs of raw lum-ber, the difficulty of applying creosote with sufficient - 10 penetration to prevent rapid deterioration of the beams, and the need continually to replace and dispose of those beams that are split, rotted and worn. As an example of this latter problem it has been reported that the Santa Fe Railroad alone uses approximately 1.6 million lumber crossties an-nually. A few of these ties are subsequently sold to farmers and ranchers along the railway right-of-way, but most must be buried underground as current ecological considerations pro-hibit their being burned in the open or left along the right-o~-way for extended periods of time.
Previous attempts have been made to develop a sub-stitute for the conventional wooden crosstie, such as by manufacturing crossties from synthetic resins as shown in Groff U.S. patent 3,289,940, or from concrete, steel or thin particle board sheets made from recycled ties or other ligno-cellulosic materials and laminated together. These attempts have not been successful, however, due to the higher costs of the substitute crossties, lack of sufficient strength and durability in some cases to withstand the cyclic bending and vibratory loads peculiar to crossties, lack of hardness and undue susceptibility to tie plate wear, non-adaptability 10~6080 of such substitute materials to the use of conventional : rail-fastening spikes, inability to hold such spikes in .
place under normal service, and, in the case of the metal substitutes, electrical conductivity o~ the material employed. (Since the metal rails fastened to the ties to form the railway are also often utilized as electrical conductors for the railway signal system, it is imperative that the crossties be electrically nonconductive so not to create an electrical circuit between the rails and thereby lQ disrupt the signalling system.) One approach to overcoming the aforementioned problems of conventional railway ties produced from raw lumber, and the aforementioned types of substitute crossties, has achieved success by the use of a mix-ture of comminutea lignocellulosic material bondedtogether and molded in the form of a highly densified, thick monolithic beam, having the dimensions of a conventional lumber railway crosstie, around a plurality of elongate metal reinforcing rods. Such highly densi-fied synthetic crossties provide an economical, elec-trically non-conductive substitute for the conventional wooden railway crosstie and have good resistance to decay, stress and wear and excellent spike-holding qualities. The bond between the metal rein-forcing rods and thc lignocellulosic material is considerably enhanced by lateral protrusions attached along the rods to prevent slippage. However {
:1076080 the metal used to produce the elongate reinforcing members and the lateral protrusions add a certain amount to the .
eost of production which would be desirable to eliminate if possible. Also, the positioning of the spikes used .
5 to fasten the rails to the ties is somewhat critical if interference with the signalling system is to be avoided sinee they eannot touch the conductive metal reinforcing members.
Another approach to overcoming the problems of .
10 eonventional railway erossties is suggested in Collins et al .
U.S. patent 3,908,902 wherein railway ties are molded from a ~, . mixture of eomminuted material and a binder, and slabs of wood are ineluded in the mix for reinforcement. Although - the use of such wood slabs may tend to increase the strength of sueh erossties and reduce the reinforcing cost and the problem of interference with the signalling system, the Collins et al ties are produced at the relatively low pres-sure of only 300-800 psi which would indicate low resistance to stress, vihration and wear and low-spike holding qualities.
Higher pressure would crush most common wood reinforcing -- material during the tie manufacturing process, rendering - it ineffective. Also, the arbitrary placement of wooden slabs in such a tie as reinforcing material may fail to maximize the tie's resistance to the particular types of bending stresses to which railway crossties are typically subjected.
Aecordingly, a need exists for an economical rein-forced molded railway tie utilizing lignocellulosic particles which has excellent resistance to decay, stress and wear and excellent spike-holding qualities, and utilizes a reinforcing {' material which can withstand high compressive force without crushing, is less expensive than metal and produc~s a molded crosstie which is stronger than that produced by metal reinforcing. Also, it is desirable to reduce the criticality of the placement of reinforcing members in such a tie with respect to the spikes while utilizing the place-ment of the reinforcing members to maximize the tie's resistance to special tie bending stresses.
10- Summary of the Invention The present invention is directed to a reinforced, molded substitute for the conventional wooden railway crosstie which satisfies the foregoing requirements. More particularly, the crosstie of the present invention utilizes a plurality lS of particularly strong, elongate wooden reinforcing members selectively placed in a mixture of comminuted lignocellu-losic material bonded together and molded under high pres-sure and with substantial densification in the form of a thick monolithic beam having the dimensions required for railway crossties.
- Preferably the lignocellulosic material used to mold the beam is comminuted wood from old worn wooden ties which may contain rotted portions rendering the ties no longer resistant to normal railway stress, and may include the rotted as well as the sound wood portions. However, other suitable lignocellulosic materials including but not limited to hardwood or softwood chips, shavings, sawdust and barks, bagasse, straw, rice hulls, corn stalks, reeds, vegetable stems, cork and the like, or mixtures thereof, are also contemplated for use in various propor~ions depending upon their fibrous characteristics and the required resistance of the finished crosstie to bending-induced tensile stresses.
If a substantial proportion of the lignocellulosic material is composed of comminuted reclaimed ties, it may be neces-sary to add little or no additional creosote when the newties are formed as the creosote already in the wood of the old ties may be sufficient to protect the new tie from the effects of exposure. Regardless of the source of the creo-sote, a monolithic tie of the present invention made from comminuted creosoted lignocellulosic particles will be substantially more resistant to rotting from exposure to the elements since the creosote will be homogeneously mixed throughout the new tie rather than concentrated adjacent the surface only, as is the case with conventional lumber ties.
A particularly efficient mechanical process for converting comminuted lignocellulosic material into the thick, highly densified rigid form of the present invention is described in Edward Potter et al U.S. patent 3,804,935, issued April 16, 1974. Thermoplastic or thermosetting resin binders of any known suitable type, or preferably a mixture of both, may be utilized as the bonding agent with the lignocellulosic - particles constituting 75% or more by weight of the particle and binder mixture, and preferably more than 80% by weight.
A densifying pressure of at least 1,200 psi, and pre-ferably more than 2,000 psi, should be utilized to densify the material to at least about four times and pre-ferably at least five times its uncompressed density, thereby resulting in a final density in the range of about 35-80 lbs/ft3 depending upon the type of lignocellulosic material utilized, and to form the material to thickness, width and length dimensions at least as great as those of a conven-tional wooden railway cros-stie to produce a monolithic (rather than laminated) tie. It is preferred that the den-sifying pressure used be more than 2,000 p5i in order toobtain a greater density, which makes the tie harder and therefore more wear-resistant than lumber ties and provides it with better spike-holding characteristics and resistance to vibration due to the high internal pressure of the bonded lignocellulosic material, the latter being particularly advantageous in the use of conventional spikes to fasten the rails to the tie.
The reinforcing is achieved by the use of elongate wooden members (or other non-metallic elongate reinforcing members made from such substances as high-strength organic polymers) having a tensile strength and modulus of elas-ticity greater than that of the bonded particle matrix in which they are embedded, and placed in the molded tie to extend lengthwise proximate the upper and lower surfaces of the tie on either side of the neutral bending axis.
- Thus positioned, the reinforcing members are proximate and parallel to the different lines of maximum tensile stress that will be induced within the tie when it is subjected to - the downward forces-of a passing train, as will be-explained in detail hereafter. The reinforcing members are also located generally in a vertical plane passing through the longitudinal center of the tie, thereby enabling the spikes which fasten the rail to the tie to be driven into the tie on either side of its longitudinal center, as is the convention, without damaging or being obstructed by the wooden reinforcing mem-bers within the tie. Although this positioning is desirable, it is-not as critical as with the use of metal reinforcing rods since the wood is non-conductive and thus the metal spikes may-come in contact with the wooden reinforcing members without producing an electrical path between the two rails which would interfere with a railway signalling system utili~ing the two rails as electrical signal conductors.
The wood or other non-metallic material utilized for the elongate reinorcing members should be-characterized by a high enough density to resist without fracture thb crushing forces of at least 1,200 psi and preferably more than 2,000 psi in a direction transverse to the length of the member (transverse to the grain in the case of wood) to which the tie is subjected during production, a high modulus of rupture, of at least about 13,000 psi, to prevent breakage during bending of the tie, and a high ~odulus of elasticity, on the order of at least about 1,800,000 psi, to provide substantial stiffness necessary to resist such bending during the cyclical loading to which the tie is subjected. Moreover the wooden members should have relatively clear, that is, knot-free, straight grain to avoid concentrations of stress which might lead to breakage.
Most wood is unsatisfactory as reinforcing material in such a tie because it lacks the aforementioned characteris-tics, particularly the necessary crush-resistance transverse to the grain. However, it has been found that timber species of the genus Dipterocarpus are particularly suitable for use as a reinforcing material in such railway ties and particularly ties produced at the preferable molding pressure of more than 2000 psi. Such wood is generally ~ound in Asia and is usually marketed as "yang" in Thailand, "apitong" in the Philippine Islands, "gurjun" in India and surma and "keruing"
in Malaysia and Indonesia, to list a few of its common names. Hardwood species having similar properties can also be found in Central and South America and Africa. It is also recognized that limited other types of wood such as some types of oak or birch might also be used if they have the aforementioned characteristics and are sorted to find adequately clean pieces.
Surrounding the sides, ends and bottom of each tie when installed in a conventional railway is a ballast of crushed rock or gravel that serves as a supportive surface to spread the load of a passing train over the earthen sub-grade below the railway, hold the tracks and ties in position, and act as a drainage system. Over a period of time, this ballast will tend to loosen and deteriorate in supportive capability under the repeated pounding of passing trains, leaving the tie relatively unsupported at some points along its length. If the ballast deteriorates near the ends of the-tie, downward pressure exerted against the rails by the wheels of passing trains will cause the ends of the tie to flex downwardly about a fulcrum formed by the ballast at the middle of the railway, thereby bowing the center of the tie upwardly and creating a point of maximum tensile stress in the upper surface of the tie approximately midway between the two rails. Since the bond created between wooden reinforcing members of the type described and the ligno-cellulosic material is relatively strong and continuousthroughout the length of the reinforcing member, the wooden reinforcing member may be placed near the top surface of the tie to resist such stress without the use of radially ex-tending protrusions or localized stress concentr~tions to prevent sliding of the lignocellulosic material relative to ~076080 the reinforcing member as is necessary with metal reinfor-cing.
Conversely, if the ballast material is loosened along the underside of the tie directly below either of the rails, 5 the downward force exerted by passing`trains will cause the -tie to bow downwardly under that rail, creating a point of maximum tensile stress in the lower surace of the tie directly below the rail. Accordingly the placement of such a wooden reinforcing member near the lower surface of the tie will likewise prevent a stress build-up within the tie sufficient to cause cracking across the bottom of the tie. Thus, by placing elongate wooden reinforcing members of the type described longitudinally within the tie approximate the lines of maximum expected stress, i.e., above and below the neutral bending axis of the tie, the lignocellulosic material of the tie is reinforced against the positive and ~ negative bending forces expected to be encountered by rail-- way ties under the varying ballast conditions. l1oreover, due primarily to the good bonding that can be achieved between the wooden reinforcing members and the lignocellulosic ~ material throughout the entire length of the reinforcing members, greater strength can be achieved in such a molded tie using wooden reinforcing members than with the use of metal reinforcing members, and it has been found that the use of wood is less expensive than the use of metal rein-forcing.
It is, therefore, a principal objective of the present invention to provide a reinforced substitute for a conventional lumber railway tie, molded from lignocellulosic waste products and a binder, which is exceptionally strong `- 10760B0 and economical and not likely to interfere with the electrical signalling system of a conventional railway; and which has excellent resistance to decay, stress and wear, and good spike-holding qualities and preferably exceeds conventional lumber ties with respect to these characteristics.
It is a principal feature of the present invention to utilize selectively-placed elongate non-metallic reinforcing members in such a substitute tie wherein such non-metallic members are characterized by an exceptionally high resistance to crushing in a direction transverse to their length combined with a substantial tensile strength and modulus of elasticity.
In accordance with one broad aspect, the invention relates to a reinforced railway crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under pressure of at least 1,200 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam having horizontally-extending length and width dimensions and a vertically-extending thickness dimension, and elongate ~ reinforcing means for strengthening and stiffening said crosstie ~ 20 against bending stress positioned longitudinally within said beam, said reinforcing means being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least 1,200 psi applied in a direction transverse to said grain without fracture.
In accordance with another aspect, the invention relates to a reinforced railway crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of more than 2,000 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam having horizon~ally-extending length and width dimensions and a vertically-extending thickness dimension, and elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam, said reinforcing means being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, such wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of more ;than 2,000 psi applied in a direction transverse to said grain without fracture.
In accordance with a further aspect, the invention relates to a railway assembly comprising: (a) a crosstie lying horizontally on a supportive surface, said crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of at least 1,200 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam; (b) a plurality of spaced, parallel, train supporting rails lying transversely on the upper surface of said beam operatively supported thereby; (c) fastening means attaching said rails to said beam: and (d~ elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam and being made of wood having substantially straight, clear grain running parallel to the length dimension .of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least 1,200 psi applied in a direction transverse to said grain without fracture.
In accordance with yet another aspect, the invention j -lla-, ~
~076080 relates to a railway assembly comprising: (a) a crosstie lying horizontally on a supportive surface, said crosstie comprising ~-a mixture of comminuted lignocellulosic material and binder densified under a pressure of more than 2,000 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam; (b) a plurality of spaced, parallel, train supporting rails lying transversely on the upper surface of said beam operatively supported thereby; (c) fastening means attaching said rails to said beam; and (d) elongate reinforcing 10 means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam and being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater - than that of said bonded mixture and being able to withstand compression of at least more than 2,000 psi applied in a direction transverse to said grain without fracture.
The foregoing objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanYing drawings.
Brief Description of the Drawings FIG. 1 is a sectional side elevation of the reinforced railway tie of the present invention shown in place as a - component of a conventional railway.
FIG. 2 is an end view of two reinforced railway ties of the present invention, installed as components of a conventional railway, with one tie sectioned along line 2-2 of FIG. 1.
FIG. 3 is a simplified side view of an exemplary tie depicting, in exaggerated form, the underlying ballast in a deteriorated condition adjacent the ends of the tie and the resultant force vectors directed against the tie.
FIG. 4 is a diagram indicating the negative bending moments exerted by the weight of a train on the exemplary ~' : 30 :---llc--'',...... h~
-'-,,, ~
:1076080 tie of FIG. 3.
FIG. 5 is a simplified side view of an exemplary tie depicting, in exaggerated form, the underlying ballast in a deteriorated condition beneath each rail and the resultant force vectors directed against the tie.
FIG. 6 is a diagram indicating the predominantly positive bending moments exerted by the weight of a train on the exemplary tie of FIG. 5.
Detailed Description of the Invention Referring to the figures, the reinforced railway crosstie of the present invention, indicated generally at .20, is seen to comprise a mixture of comminuted lignocellu-losic material 22 bonded by an adhesive binder into the form of a beam 24 around a pair of elongate wooden reinforcing members 26 and 28 having a higher tensile strength and modulus of elasticity (Young's modulus) than the bonded mixture 22.
The lignocellulosic mixture 22 is composed preferably of comminuted wood from old rotted, worn or split railway ties;
however, other fibrous vegetable waste materials may be used alone or in mixtures. Suitable thermosetting and/or thermo-plastic binders in sufficient quantities to ensure the forma-tion of a relatively hard, rigid product, for example as taught by the aforementioned Potter et al U.S. patent ` 25 No. 3,804,935, are mixed with the lignocellulosic materials ...
before they are molded around the wooden reinforcing - members 26 and 28. To provide a sufficiently economical product the lignocellulosic materials should comprise at least 75% by weight of the mixture of lignocellulosic particles 30 and binder, and preferably in the range of about 85% to 92~.
The mold in which the beam is to be formed should define an interior enclosure, after compression of the lignocellulosic material and locking of the mold, having thickness, width and length dimensions at least as great as those of a con-ventional lumber crosstie. If desired, molds with lengths longer than a conventional crosstie may be used and the beams produced therein sawed into shorter lengths. The sides of the mold should be tall enough to hold a sufficient volume of uncompressed material to achieve the previously described degree of densification upon compression. Har-dening of the binders used, by curing of a thermosettingbinder with or without heat, or heating and subsequent cooling of a theromplastic binder, are carried out in the mold.
The elongate reinforcing members 26 and 28 are made of wood with the grain of the wood preferably running along the longitudinal dimension thereof. The cross section of the reinforcing members may be any convenient shape, for example a square 1 1/2 inches on each side, but where a square - shape is used it should be oriented with diagonally opposed edges in substantially horizontal and vertical planes re-spectively as shown in FIG. 2 to provide maximum resistance to bending, and the topmost and bottommost edges 27 should be slightly rounded or beveled to prevent stress concentra-tions and resultant cutting of the reinforcing member through the bonded lignocellulosic material 22. A satisfactory crosstie can be made with the application of 1,200 psi or more during the molding process, and the wood or other material used to make the reinforcing members 26, 28 must be able to withstand such pressure applied in a direction transverse to the length and grain~as the case may be,wi~hout failing by ~`
aso fracture; however, a much better crosstie surprisingly having more resistance to wear and stress and better spike-holding qualities than lumber ties can be made by the appli-cation of pressure greater than 2,000 psi, and it is therefore 5 preferred that the reinforcing wood or other material be able to withstand more than 2,000 psi transverse to the length and grain without failing by fracture. Such material will have a relatively clear, straight grain in the case - of wood, a high modulus of rupture (at least about 13,000 10 psi) and a high modulus of elasticity (on the order of at least 1,800,000 psi).
Wood species of the genus Dipterocarpus, found generally in Asia, are particularly suitable for use as reinforcing members in the foregoing application, including 15 those woods marketed by the names "apitong", "keruing", "yang", "gurjun", and others, and comparable woods found in Central and South America and in Africa, all of which are collectively referred to herein in the specification and claims as "apitong". Other woods satisfying the foregoing 20 mechanical requirements are also likely-to be suitable.
During the filling of the mold with the mixture of lignocellulosic material and binders, the elongate reinforcing members 26 and 28 are placed in position and the mixture poured around them by anV convenient method such that, after final ; 25 compression and locking of the mold, the members are positioned 1: .
within the mixture 22 in the locations shown in FIGS. 1 and 2.
In order to maximize the strength of the finished tie by increasing the bond between the reinforcing members and the molded material, the members should be precoated with the 30 binder resin utilized to bond the lignocellulosic particles ~ together prior to placement of the reinforcing members in 4 the mold.
~`` 6 ~076080 The crosstie should be molded in the same orienta-tion as shown in FIGS. l and 2, with the width dimension "w"
parallel to the base of the mold, in which case a relatively thin first course of mixture is spread evenly on the base 5 of the mold, the lower member 28 is laid atop the first course, and covered by a relatively thick second course;
thereafter the upper member 26 is laid atop the second course, and covered by a relatively thin final course.
This orientation of the tie in the mold is important~to 10 produce high surface hardness of the upper and lo~er tie surfaces so as to resist tie plate wear, since the direction of pressure application will thereby be perpendicular to these surfaces and cause flattening of the lignocellulosic fibers along planes parallel to these surfaces.
~' With respect to FIGS. 1 and 2 which show a finished crosstie 24, the reinforcing members 26 and 28 are positioned with one member vertically above the other generally in a vertical plane passing through the midpoint of the tie width ' dimension "w", so as not to interfere with the spikes 30 i 20 employed to fasten the rails 32 and 34 to the crosstie as described below. In addition, upper reinforcing member 26 and lower reinforcing member 28 are positioned above and below ~ the neutral beam bending axis 29 at locations proximate the ,~ crosstie's top surface 36 and bottom surface 38, respectively, ~" 25 so as to lie as close as possible to the lines of maximum ~, tensile stress that will be induced into the bea~ when it ~ is subjected to positive and negative vertical bending forces.
s To`form a railway, the reinforced crossties of the present invention are laid side by side as indicated in 30 FIG. 2, with their width dimensions "w" oriented horizontally , over a supportive surface, for example, a layer of ballast 42 composed of cinders or crushed stone. This ballast completely surrounds each tie up to the level of its top surface 36 to spread the load of the railway over the earthen subgrade, hold the railway in position, and act as a drainage system.
The rails 32 and 34 are attached to the ties by spikes 30 inserted through holes in a metal tie plate 44 and driven into the tie as with conventional wooden ties. The ties are normally pre-bored by means of bore-holes such as 31 to receive the spikes, thereby minimizing the risk of splitting the tie. Normally, two spikes 30 are employed to attach a rail to a tie, the spikes being driven into the tie on either side of the rail at points on either side of the midpoint of the width dimension "w" as shown in the figures. As the wooden reinforcing members 26 and 28 are 15 positioned within beam 24 one above the other at such mid- 1, point, the spikes 30, when driven in their conventional locations, will pass on either side of the reinforcing rods - without substantial interference therewith. This enables the use of conventional rail spikes in the bonded material, which has been sufficiently densified to receive and hold them, by ensuring that they will not be obstructed by or - damage the reinforcing members.
After repeated pounding by the wheels of passing trains against the rails and ties of the railway, the ballast 42 packed around the ties may begin to loosen in certain locations, thereby removing a portion of the tie's support and subjecting it to beam loading. When the ballast loosens near the ends 46 of the tie, as depicted in FIG. 3, the downward forces exerted by passing trains will thereafter cause the ends of the tie to bow downwardly about its middle creating a bending moment diagram roughly as shown in FIG.
4 with a maximum negative bending moment at approximately ~0~6080 the midpoint of the tie inducing a resultant maximum tensile stress in the upper surface 36 of the tie at the same point.
The location of the upper reinforcing member above the neutral bending axis 29 and near the upper surface 36 of the crosstie 24, ensures that a substantial proportion of the tensile stress induced within the lignocellulosic material from the negative bending will be transferred to the reinforcing member, which is prevented from slipping longitudinally relative to the lignocellulosic material by the strong adhesive bond created by the binder between the wooden reinforcing material and the lignocellulosic material throughout the length of the reinforcing member.
If the repeated pounding of passing trains causes the ballast 42 to loosen around the lower surface of the tie directly below one or both of the rails, as depicted in FIG. 5, without also loosening at the adjacent end of the tie, the downward force exerted by the train against the rail will thereafter cause the tie to bow downwardly beneath the rail, creating a bending moment diagram roughly "
as shown in ~IG. 6 and inducing a point of maximum tensile ~- stress in the lower surface 38 of the beam directly below the rail. As before, the location of the reinforcing member ~-~ 28 below the neutral bending axis 29, and the strong bond ~:~ between the reinforcing member and the lignocellulosic material, - 25 ensure that a substantial amount of the tensile stress induced ~: within the lower surface 38 of the tie will be transferred i '~ .
: to the reinforcing member, thereby preventing a stress buildup sufficient to cause cracking of the tie.
The terms and expressions which have been employed in the foregoing abstract and specification are used therein ~076080 as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of exclud-ing equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.
:.
,- :
. .
,, ' ~ .
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~., .
1076~)~0 - wide by 8 1/2 or 9 feet lon~, that have been cut from sections of live tree trunks selected to be free from soft or decayed spots, shakes, worm holes, and other imperfections. ~efore being placed into service as crossties, these heams are treated with creosote, an oily liquid preservative, to protect them against the effects of exposure to the elements.
~he major disadvantages of using lumber beams for railway crossties are the ever-increasing costs of raw lum-ber, the difficulty of applying creosote with sufficient - 10 penetration to prevent rapid deterioration of the beams, and the need continually to replace and dispose of those beams that are split, rotted and worn. As an example of this latter problem it has been reported that the Santa Fe Railroad alone uses approximately 1.6 million lumber crossties an-nually. A few of these ties are subsequently sold to farmers and ranchers along the railway right-of-way, but most must be buried underground as current ecological considerations pro-hibit their being burned in the open or left along the right-o~-way for extended periods of time.
Previous attempts have been made to develop a sub-stitute for the conventional wooden crosstie, such as by manufacturing crossties from synthetic resins as shown in Groff U.S. patent 3,289,940, or from concrete, steel or thin particle board sheets made from recycled ties or other ligno-cellulosic materials and laminated together. These attempts have not been successful, however, due to the higher costs of the substitute crossties, lack of sufficient strength and durability in some cases to withstand the cyclic bending and vibratory loads peculiar to crossties, lack of hardness and undue susceptibility to tie plate wear, non-adaptability 10~6080 of such substitute materials to the use of conventional : rail-fastening spikes, inability to hold such spikes in .
place under normal service, and, in the case of the metal substitutes, electrical conductivity o~ the material employed. (Since the metal rails fastened to the ties to form the railway are also often utilized as electrical conductors for the railway signal system, it is imperative that the crossties be electrically nonconductive so not to create an electrical circuit between the rails and thereby lQ disrupt the signalling system.) One approach to overcoming the aforementioned problems of conventional railway ties produced from raw lumber, and the aforementioned types of substitute crossties, has achieved success by the use of a mix-ture of comminutea lignocellulosic material bondedtogether and molded in the form of a highly densified, thick monolithic beam, having the dimensions of a conventional lumber railway crosstie, around a plurality of elongate metal reinforcing rods. Such highly densi-fied synthetic crossties provide an economical, elec-trically non-conductive substitute for the conventional wooden railway crosstie and have good resistance to decay, stress and wear and excellent spike-holding qualities. The bond between the metal rein-forcing rods and thc lignocellulosic material is considerably enhanced by lateral protrusions attached along the rods to prevent slippage. However {
:1076080 the metal used to produce the elongate reinforcing members and the lateral protrusions add a certain amount to the .
eost of production which would be desirable to eliminate if possible. Also, the positioning of the spikes used .
5 to fasten the rails to the ties is somewhat critical if interference with the signalling system is to be avoided sinee they eannot touch the conductive metal reinforcing members.
Another approach to overcoming the problems of .
10 eonventional railway erossties is suggested in Collins et al .
U.S. patent 3,908,902 wherein railway ties are molded from a ~, . mixture of eomminuted material and a binder, and slabs of wood are ineluded in the mix for reinforcement. Although - the use of such wood slabs may tend to increase the strength of sueh erossties and reduce the reinforcing cost and the problem of interference with the signalling system, the Collins et al ties are produced at the relatively low pres-sure of only 300-800 psi which would indicate low resistance to stress, vihration and wear and low-spike holding qualities.
Higher pressure would crush most common wood reinforcing -- material during the tie manufacturing process, rendering - it ineffective. Also, the arbitrary placement of wooden slabs in such a tie as reinforcing material may fail to maximize the tie's resistance to the particular types of bending stresses to which railway crossties are typically subjected.
Aecordingly, a need exists for an economical rein-forced molded railway tie utilizing lignocellulosic particles which has excellent resistance to decay, stress and wear and excellent spike-holding qualities, and utilizes a reinforcing {' material which can withstand high compressive force without crushing, is less expensive than metal and produc~s a molded crosstie which is stronger than that produced by metal reinforcing. Also, it is desirable to reduce the criticality of the placement of reinforcing members in such a tie with respect to the spikes while utilizing the place-ment of the reinforcing members to maximize the tie's resistance to special tie bending stresses.
10- Summary of the Invention The present invention is directed to a reinforced, molded substitute for the conventional wooden railway crosstie which satisfies the foregoing requirements. More particularly, the crosstie of the present invention utilizes a plurality lS of particularly strong, elongate wooden reinforcing members selectively placed in a mixture of comminuted lignocellu-losic material bonded together and molded under high pres-sure and with substantial densification in the form of a thick monolithic beam having the dimensions required for railway crossties.
- Preferably the lignocellulosic material used to mold the beam is comminuted wood from old worn wooden ties which may contain rotted portions rendering the ties no longer resistant to normal railway stress, and may include the rotted as well as the sound wood portions. However, other suitable lignocellulosic materials including but not limited to hardwood or softwood chips, shavings, sawdust and barks, bagasse, straw, rice hulls, corn stalks, reeds, vegetable stems, cork and the like, or mixtures thereof, are also contemplated for use in various propor~ions depending upon their fibrous characteristics and the required resistance of the finished crosstie to bending-induced tensile stresses.
If a substantial proportion of the lignocellulosic material is composed of comminuted reclaimed ties, it may be neces-sary to add little or no additional creosote when the newties are formed as the creosote already in the wood of the old ties may be sufficient to protect the new tie from the effects of exposure. Regardless of the source of the creo-sote, a monolithic tie of the present invention made from comminuted creosoted lignocellulosic particles will be substantially more resistant to rotting from exposure to the elements since the creosote will be homogeneously mixed throughout the new tie rather than concentrated adjacent the surface only, as is the case with conventional lumber ties.
A particularly efficient mechanical process for converting comminuted lignocellulosic material into the thick, highly densified rigid form of the present invention is described in Edward Potter et al U.S. patent 3,804,935, issued April 16, 1974. Thermoplastic or thermosetting resin binders of any known suitable type, or preferably a mixture of both, may be utilized as the bonding agent with the lignocellulosic - particles constituting 75% or more by weight of the particle and binder mixture, and preferably more than 80% by weight.
A densifying pressure of at least 1,200 psi, and pre-ferably more than 2,000 psi, should be utilized to densify the material to at least about four times and pre-ferably at least five times its uncompressed density, thereby resulting in a final density in the range of about 35-80 lbs/ft3 depending upon the type of lignocellulosic material utilized, and to form the material to thickness, width and length dimensions at least as great as those of a conven-tional wooden railway cros-stie to produce a monolithic (rather than laminated) tie. It is preferred that the den-sifying pressure used be more than 2,000 p5i in order toobtain a greater density, which makes the tie harder and therefore more wear-resistant than lumber ties and provides it with better spike-holding characteristics and resistance to vibration due to the high internal pressure of the bonded lignocellulosic material, the latter being particularly advantageous in the use of conventional spikes to fasten the rails to the tie.
The reinforcing is achieved by the use of elongate wooden members (or other non-metallic elongate reinforcing members made from such substances as high-strength organic polymers) having a tensile strength and modulus of elas-ticity greater than that of the bonded particle matrix in which they are embedded, and placed in the molded tie to extend lengthwise proximate the upper and lower surfaces of the tie on either side of the neutral bending axis.
- Thus positioned, the reinforcing members are proximate and parallel to the different lines of maximum tensile stress that will be induced within the tie when it is subjected to - the downward forces-of a passing train, as will be-explained in detail hereafter. The reinforcing members are also located generally in a vertical plane passing through the longitudinal center of the tie, thereby enabling the spikes which fasten the rail to the tie to be driven into the tie on either side of its longitudinal center, as is the convention, without damaging or being obstructed by the wooden reinforcing mem-bers within the tie. Although this positioning is desirable, it is-not as critical as with the use of metal reinforcing rods since the wood is non-conductive and thus the metal spikes may-come in contact with the wooden reinforcing members without producing an electrical path between the two rails which would interfere with a railway signalling system utili~ing the two rails as electrical signal conductors.
The wood or other non-metallic material utilized for the elongate reinorcing members should be-characterized by a high enough density to resist without fracture thb crushing forces of at least 1,200 psi and preferably more than 2,000 psi in a direction transverse to the length of the member (transverse to the grain in the case of wood) to which the tie is subjected during production, a high modulus of rupture, of at least about 13,000 psi, to prevent breakage during bending of the tie, and a high ~odulus of elasticity, on the order of at least about 1,800,000 psi, to provide substantial stiffness necessary to resist such bending during the cyclical loading to which the tie is subjected. Moreover the wooden members should have relatively clear, that is, knot-free, straight grain to avoid concentrations of stress which might lead to breakage.
Most wood is unsatisfactory as reinforcing material in such a tie because it lacks the aforementioned characteris-tics, particularly the necessary crush-resistance transverse to the grain. However, it has been found that timber species of the genus Dipterocarpus are particularly suitable for use as a reinforcing material in such railway ties and particularly ties produced at the preferable molding pressure of more than 2000 psi. Such wood is generally ~ound in Asia and is usually marketed as "yang" in Thailand, "apitong" in the Philippine Islands, "gurjun" in India and surma and "keruing"
in Malaysia and Indonesia, to list a few of its common names. Hardwood species having similar properties can also be found in Central and South America and Africa. It is also recognized that limited other types of wood such as some types of oak or birch might also be used if they have the aforementioned characteristics and are sorted to find adequately clean pieces.
Surrounding the sides, ends and bottom of each tie when installed in a conventional railway is a ballast of crushed rock or gravel that serves as a supportive surface to spread the load of a passing train over the earthen sub-grade below the railway, hold the tracks and ties in position, and act as a drainage system. Over a period of time, this ballast will tend to loosen and deteriorate in supportive capability under the repeated pounding of passing trains, leaving the tie relatively unsupported at some points along its length. If the ballast deteriorates near the ends of the-tie, downward pressure exerted against the rails by the wheels of passing trains will cause the ends of the tie to flex downwardly about a fulcrum formed by the ballast at the middle of the railway, thereby bowing the center of the tie upwardly and creating a point of maximum tensile stress in the upper surface of the tie approximately midway between the two rails. Since the bond created between wooden reinforcing members of the type described and the ligno-cellulosic material is relatively strong and continuousthroughout the length of the reinforcing member, the wooden reinforcing member may be placed near the top surface of the tie to resist such stress without the use of radially ex-tending protrusions or localized stress concentr~tions to prevent sliding of the lignocellulosic material relative to ~076080 the reinforcing member as is necessary with metal reinfor-cing.
Conversely, if the ballast material is loosened along the underside of the tie directly below either of the rails, 5 the downward force exerted by passing`trains will cause the -tie to bow downwardly under that rail, creating a point of maximum tensile stress in the lower surace of the tie directly below the rail. Accordingly the placement of such a wooden reinforcing member near the lower surface of the tie will likewise prevent a stress build-up within the tie sufficient to cause cracking across the bottom of the tie. Thus, by placing elongate wooden reinforcing members of the type described longitudinally within the tie approximate the lines of maximum expected stress, i.e., above and below the neutral bending axis of the tie, the lignocellulosic material of the tie is reinforced against the positive and ~ negative bending forces expected to be encountered by rail-- way ties under the varying ballast conditions. l1oreover, due primarily to the good bonding that can be achieved between the wooden reinforcing members and the lignocellulosic ~ material throughout the entire length of the reinforcing members, greater strength can be achieved in such a molded tie using wooden reinforcing members than with the use of metal reinforcing members, and it has been found that the use of wood is less expensive than the use of metal rein-forcing.
It is, therefore, a principal objective of the present invention to provide a reinforced substitute for a conventional lumber railway tie, molded from lignocellulosic waste products and a binder, which is exceptionally strong `- 10760B0 and economical and not likely to interfere with the electrical signalling system of a conventional railway; and which has excellent resistance to decay, stress and wear, and good spike-holding qualities and preferably exceeds conventional lumber ties with respect to these characteristics.
It is a principal feature of the present invention to utilize selectively-placed elongate non-metallic reinforcing members in such a substitute tie wherein such non-metallic members are characterized by an exceptionally high resistance to crushing in a direction transverse to their length combined with a substantial tensile strength and modulus of elasticity.
In accordance with one broad aspect, the invention relates to a reinforced railway crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under pressure of at least 1,200 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam having horizontally-extending length and width dimensions and a vertically-extending thickness dimension, and elongate ~ reinforcing means for strengthening and stiffening said crosstie ~ 20 against bending stress positioned longitudinally within said beam, said reinforcing means being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least 1,200 psi applied in a direction transverse to said grain without fracture.
In accordance with another aspect, the invention relates to a reinforced railway crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of more than 2,000 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam having horizon~ally-extending length and width dimensions and a vertically-extending thickness dimension, and elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam, said reinforcing means being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, such wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of more ;than 2,000 psi applied in a direction transverse to said grain without fracture.
In accordance with a further aspect, the invention relates to a railway assembly comprising: (a) a crosstie lying horizontally on a supportive surface, said crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of at least 1,200 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam; (b) a plurality of spaced, parallel, train supporting rails lying transversely on the upper surface of said beam operatively supported thereby; (c) fastening means attaching said rails to said beam: and (d~ elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam and being made of wood having substantially straight, clear grain running parallel to the length dimension .of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least 1,200 psi applied in a direction transverse to said grain without fracture.
In accordance with yet another aspect, the invention j -lla-, ~
~076080 relates to a railway assembly comprising: (a) a crosstie lying horizontally on a supportive surface, said crosstie comprising ~-a mixture of comminuted lignocellulosic material and binder densified under a pressure of more than 2,000 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam; (b) a plurality of spaced, parallel, train supporting rails lying transversely on the upper surface of said beam operatively supported thereby; (c) fastening means attaching said rails to said beam; and (d) elongate reinforcing 10 means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam and being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater - than that of said bonded mixture and being able to withstand compression of at least more than 2,000 psi applied in a direction transverse to said grain without fracture.
The foregoing objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanYing drawings.
Brief Description of the Drawings FIG. 1 is a sectional side elevation of the reinforced railway tie of the present invention shown in place as a - component of a conventional railway.
FIG. 2 is an end view of two reinforced railway ties of the present invention, installed as components of a conventional railway, with one tie sectioned along line 2-2 of FIG. 1.
FIG. 3 is a simplified side view of an exemplary tie depicting, in exaggerated form, the underlying ballast in a deteriorated condition adjacent the ends of the tie and the resultant force vectors directed against the tie.
FIG. 4 is a diagram indicating the negative bending moments exerted by the weight of a train on the exemplary ~' : 30 :---llc--'',...... h~
-'-,,, ~
:1076080 tie of FIG. 3.
FIG. 5 is a simplified side view of an exemplary tie depicting, in exaggerated form, the underlying ballast in a deteriorated condition beneath each rail and the resultant force vectors directed against the tie.
FIG. 6 is a diagram indicating the predominantly positive bending moments exerted by the weight of a train on the exemplary tie of FIG. 5.
Detailed Description of the Invention Referring to the figures, the reinforced railway crosstie of the present invention, indicated generally at .20, is seen to comprise a mixture of comminuted lignocellu-losic material 22 bonded by an adhesive binder into the form of a beam 24 around a pair of elongate wooden reinforcing members 26 and 28 having a higher tensile strength and modulus of elasticity (Young's modulus) than the bonded mixture 22.
The lignocellulosic mixture 22 is composed preferably of comminuted wood from old rotted, worn or split railway ties;
however, other fibrous vegetable waste materials may be used alone or in mixtures. Suitable thermosetting and/or thermo-plastic binders in sufficient quantities to ensure the forma-tion of a relatively hard, rigid product, for example as taught by the aforementioned Potter et al U.S. patent ` 25 No. 3,804,935, are mixed with the lignocellulosic materials ...
before they are molded around the wooden reinforcing - members 26 and 28. To provide a sufficiently economical product the lignocellulosic materials should comprise at least 75% by weight of the mixture of lignocellulosic particles 30 and binder, and preferably in the range of about 85% to 92~.
The mold in which the beam is to be formed should define an interior enclosure, after compression of the lignocellulosic material and locking of the mold, having thickness, width and length dimensions at least as great as those of a con-ventional lumber crosstie. If desired, molds with lengths longer than a conventional crosstie may be used and the beams produced therein sawed into shorter lengths. The sides of the mold should be tall enough to hold a sufficient volume of uncompressed material to achieve the previously described degree of densification upon compression. Har-dening of the binders used, by curing of a thermosettingbinder with or without heat, or heating and subsequent cooling of a theromplastic binder, are carried out in the mold.
The elongate reinforcing members 26 and 28 are made of wood with the grain of the wood preferably running along the longitudinal dimension thereof. The cross section of the reinforcing members may be any convenient shape, for example a square 1 1/2 inches on each side, but where a square - shape is used it should be oriented with diagonally opposed edges in substantially horizontal and vertical planes re-spectively as shown in FIG. 2 to provide maximum resistance to bending, and the topmost and bottommost edges 27 should be slightly rounded or beveled to prevent stress concentra-tions and resultant cutting of the reinforcing member through the bonded lignocellulosic material 22. A satisfactory crosstie can be made with the application of 1,200 psi or more during the molding process, and the wood or other material used to make the reinforcing members 26, 28 must be able to withstand such pressure applied in a direction transverse to the length and grain~as the case may be,wi~hout failing by ~`
aso fracture; however, a much better crosstie surprisingly having more resistance to wear and stress and better spike-holding qualities than lumber ties can be made by the appli-cation of pressure greater than 2,000 psi, and it is therefore 5 preferred that the reinforcing wood or other material be able to withstand more than 2,000 psi transverse to the length and grain without failing by fracture. Such material will have a relatively clear, straight grain in the case - of wood, a high modulus of rupture (at least about 13,000 10 psi) and a high modulus of elasticity (on the order of at least 1,800,000 psi).
Wood species of the genus Dipterocarpus, found generally in Asia, are particularly suitable for use as reinforcing members in the foregoing application, including 15 those woods marketed by the names "apitong", "keruing", "yang", "gurjun", and others, and comparable woods found in Central and South America and in Africa, all of which are collectively referred to herein in the specification and claims as "apitong". Other woods satisfying the foregoing 20 mechanical requirements are also likely-to be suitable.
During the filling of the mold with the mixture of lignocellulosic material and binders, the elongate reinforcing members 26 and 28 are placed in position and the mixture poured around them by anV convenient method such that, after final ; 25 compression and locking of the mold, the members are positioned 1: .
within the mixture 22 in the locations shown in FIGS. 1 and 2.
In order to maximize the strength of the finished tie by increasing the bond between the reinforcing members and the molded material, the members should be precoated with the 30 binder resin utilized to bond the lignocellulosic particles ~ together prior to placement of the reinforcing members in 4 the mold.
~`` 6 ~076080 The crosstie should be molded in the same orienta-tion as shown in FIGS. l and 2, with the width dimension "w"
parallel to the base of the mold, in which case a relatively thin first course of mixture is spread evenly on the base 5 of the mold, the lower member 28 is laid atop the first course, and covered by a relatively thick second course;
thereafter the upper member 26 is laid atop the second course, and covered by a relatively thin final course.
This orientation of the tie in the mold is important~to 10 produce high surface hardness of the upper and lo~er tie surfaces so as to resist tie plate wear, since the direction of pressure application will thereby be perpendicular to these surfaces and cause flattening of the lignocellulosic fibers along planes parallel to these surfaces.
~' With respect to FIGS. 1 and 2 which show a finished crosstie 24, the reinforcing members 26 and 28 are positioned with one member vertically above the other generally in a vertical plane passing through the midpoint of the tie width ' dimension "w", so as not to interfere with the spikes 30 i 20 employed to fasten the rails 32 and 34 to the crosstie as described below. In addition, upper reinforcing member 26 and lower reinforcing member 28 are positioned above and below ~ the neutral beam bending axis 29 at locations proximate the ,~ crosstie's top surface 36 and bottom surface 38, respectively, ~" 25 so as to lie as close as possible to the lines of maximum ~, tensile stress that will be induced into the bea~ when it ~ is subjected to positive and negative vertical bending forces.
s To`form a railway, the reinforced crossties of the present invention are laid side by side as indicated in 30 FIG. 2, with their width dimensions "w" oriented horizontally , over a supportive surface, for example, a layer of ballast 42 composed of cinders or crushed stone. This ballast completely surrounds each tie up to the level of its top surface 36 to spread the load of the railway over the earthen subgrade, hold the railway in position, and act as a drainage system.
The rails 32 and 34 are attached to the ties by spikes 30 inserted through holes in a metal tie plate 44 and driven into the tie as with conventional wooden ties. The ties are normally pre-bored by means of bore-holes such as 31 to receive the spikes, thereby minimizing the risk of splitting the tie. Normally, two spikes 30 are employed to attach a rail to a tie, the spikes being driven into the tie on either side of the rail at points on either side of the midpoint of the width dimension "w" as shown in the figures. As the wooden reinforcing members 26 and 28 are 15 positioned within beam 24 one above the other at such mid- 1, point, the spikes 30, when driven in their conventional locations, will pass on either side of the reinforcing rods - without substantial interference therewith. This enables the use of conventional rail spikes in the bonded material, which has been sufficiently densified to receive and hold them, by ensuring that they will not be obstructed by or - damage the reinforcing members.
After repeated pounding by the wheels of passing trains against the rails and ties of the railway, the ballast 42 packed around the ties may begin to loosen in certain locations, thereby removing a portion of the tie's support and subjecting it to beam loading. When the ballast loosens near the ends 46 of the tie, as depicted in FIG. 3, the downward forces exerted by passing trains will thereafter cause the ends of the tie to bow downwardly about its middle creating a bending moment diagram roughly as shown in FIG.
4 with a maximum negative bending moment at approximately ~0~6080 the midpoint of the tie inducing a resultant maximum tensile stress in the upper surface 36 of the tie at the same point.
The location of the upper reinforcing member above the neutral bending axis 29 and near the upper surface 36 of the crosstie 24, ensures that a substantial proportion of the tensile stress induced within the lignocellulosic material from the negative bending will be transferred to the reinforcing member, which is prevented from slipping longitudinally relative to the lignocellulosic material by the strong adhesive bond created by the binder between the wooden reinforcing material and the lignocellulosic material throughout the length of the reinforcing member.
If the repeated pounding of passing trains causes the ballast 42 to loosen around the lower surface of the tie directly below one or both of the rails, as depicted in FIG. 5, without also loosening at the adjacent end of the tie, the downward force exerted by the train against the rail will thereafter cause the tie to bow downwardly beneath the rail, creating a bending moment diagram roughly "
as shown in ~IG. 6 and inducing a point of maximum tensile ~- stress in the lower surface 38 of the beam directly below the rail. As before, the location of the reinforcing member ~-~ 28 below the neutral bending axis 29, and the strong bond ~:~ between the reinforcing member and the lignocellulosic material, - 25 ensure that a substantial amount of the tensile stress induced ~: within the lower surface 38 of the tie will be transferred i '~ .
: to the reinforcing member, thereby preventing a stress buildup sufficient to cause cracking of the tie.
The terms and expressions which have been employed in the foregoing abstract and specification are used therein ~076080 as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of exclud-ing equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.
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Claims (20)
1. A reinforced railway crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under pressure of at least 1,200 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam having horizontally-extending length and width dimensions and a vertically-extending thickness dimension, and elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam, said reinforcing means being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to with-stand compression of at least 1,200 psi applied in a direction transverse to said grain without. fracture.
2. The railway crosstie of claim 1 wherein said reinforcing means includes a plurality of elongate reinforcing members longitudinally positioned within said beam, at least one of said reinforcing members being located above the neutral bending axis of said beam and at least one of said reinforcing members being located below said neutral bending axis.
3. The railway crosstie of claim 1 wherein said reinforcing means has a modulus of rupture of at least about 13,000 psi, and a modulus of elasticity of at least about 1,800,000 psi.
4. The railway crosstie of claim 1 wherein said lignocellulosic material constitutes at least 75 by weight of said bonded mixture.
5. The railway crosstie of claim 1 wherein said lignocellulosic material comprises in the range of about 85% to 92% by weight of said bonded mixture.
6. The railway crosstie of claim 1 wherein said crosstie has means defining a plurality of empty bore holes proximate each end extending from a surface thereof into said crosstie generally in the direction of said thickness dimension for receiving and tightly holding spikes employed to attache a rail to said crosstie.
7. The railway crosstie of claim 1 wherein said reinforcing means includes a plurality of elongate reinforcing members longitudinally positioned within said beam one above the other at about the midpoint of said width dimension, said holes being spaced laterally on either side of said reinforcing members.
8. The railway crosstie of claim 1 wherein said lignocellulosic material includes comminuted par-ticles of wood impregnated with creosote.
9. A reinforced railway crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of more than 2,000 psi and bonded together as densified in the form of an elongate monolithic railway crosstie beam having horizontally-extending length and width dimensions and a vertically-extending thickness dimension, and elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam, said reinforcing means being made of wood having substantially straight, clear grain running par-allel to the length dimension of said beam, such wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of more than 2,000 psi applied in a direction transverse to said grain without fracture.
10. The railway crosstie of claim 9 wherein said reinforcing means includes a plurality of elongate reinforcing members longitudinally positioned within said beam, at least one of said reinforcing members being lo-cated above the neutral bending axis of said beam and at least one of said reinforcing members being located below said neutral bending axis.
11. The railway crosstie of claim 9 wherein said reinforcing means has a modulus of rupture of at least about 13,000 psi, and a modulus of elasticity of at least about 1,800,000 psi.
12. The railway crosstie of claim 9 wherein said lignocellulosic material constitutes at least 75%
by weight of said bonded mixture.
by weight of said bonded mixture.
13. The railway crosstie of claim 12 wherein said lignocellulosic material comprises in the range of about 85% to 92% by weight of said bonded mixture.
14. The railway crosstie of claim 9 wherein said crosstie has means defining a plurality of empty bore holes proximate each end extending from a surface thereof into said crosstie generally in the direction of said thickness dimension for receiving and tightly holding spikes employed to attach a rail to said crosstie.
15. The railway crosstie of claim 14 wherein said reinforcing means includes a plurality of elongate reinforcing members longitudinally positioned within said beam one above the other at about the midpoint of said width dimension, said holes being spaced laterally on either side of said reinforcing members.
16. The railway crosstie of claim 9 wherein said lignocellulosic material includes comminuted par-ticles of wood impregnated with creosote.
17. A railway assembly comprising:
(a) a crosstie lying horizontally on a supportive surface, said crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of at least 1,200 psi and bonded together as densi-fied in the form of an elongate monolithic railway crosstie beam;
(b) a plurlaity of spaced, parallel, train supporting rails lying transversely on the upper surface of said beam operatively supported thereby;
(c) fastening means attaching said rails to said beam; and (d) elongate reinforcing means for strengthening and stiffening said crosstie against bending stress-positioned longitudinally within said beam and being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least 1,200 psi applied in a direction transverse to said grain without fracture.
(a) a crosstie lying horizontally on a supportive surface, said crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of at least 1,200 psi and bonded together as densi-fied in the form of an elongate monolithic railway crosstie beam;
(b) a plurlaity of spaced, parallel, train supporting rails lying transversely on the upper surface of said beam operatively supported thereby;
(c) fastening means attaching said rails to said beam; and (d) elongate reinforcing means for strengthening and stiffening said crosstie against bending stress-positioned longitudinally within said beam and being made of wood having substantially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least 1,200 psi applied in a direction transverse to said grain without fracture.
18. The railway assembly of claim 17 wherein said reinforcing means includes a plurality of elongate reinforcing members longitudinally positioned within said beam, at least one of said reinforcing members being lo-cated above the neutral bending axis of said beam and at least one of said reinforcing members being located below said neutral bending axis.
19. A railway assembly comprising:
(a) a crosstie lying horizontally on a supportive surface, said crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of more than 2,000 psi and bonded together as den-sified in the form of an elongate monolithic railway crosstie beam;
(b) a plurality of spaced, parallel, train support-ing rails lying transversely on the upper surface of said beam operatively supported thereby;
(c) fastening means attaching said rails to said beam; and (d) elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam and being made of wood having substan-tially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least more than 2,000 psi applied in a direction transverse to said grain without fracture.
(a) a crosstie lying horizontally on a supportive surface, said crosstie comprising a mixture of comminuted lignocellulosic material and binder densified under a pressure of more than 2,000 psi and bonded together as den-sified in the form of an elongate monolithic railway crosstie beam;
(b) a plurality of spaced, parallel, train support-ing rails lying transversely on the upper surface of said beam operatively supported thereby;
(c) fastening means attaching said rails to said beam; and (d) elongate reinforcing means for strengthening and stiffening said crosstie against bending stress positioned longitudinally within said beam and being made of wood having substan-tially straight, clear grain running parallel to the length dimension of said beam, said wood having a tensile strength and modulus of elasticity greater than that of said bonded mixture and being able to withstand compression of at least more than 2,000 psi applied in a direction transverse to said grain without fracture.
20. The railway assembly of claim 19 wherein said reinforcing means has a modulus of rupture of at least about 13,000 psi, and a modulus of elasticity of at least about 1,800,000 psi.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA300,080A CA1076080A (en) | 1978-03-30 | 1978-03-30 | Non-metallic-reinforced molded crosstie |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA300,080A CA1076080A (en) | 1978-03-30 | 1978-03-30 | Non-metallic-reinforced molded crosstie |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1076080A true CA1076080A (en) | 1980-04-22 |
Family
ID=4111115
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA300,080A Expired CA1076080A (en) | 1978-03-30 | 1978-03-30 | Non-metallic-reinforced molded crosstie |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1076080A (en) |
-
1978
- 1978-03-30 CA CA300,080A patent/CA1076080A/en not_active Expired
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