AU1364400A - Improved elastic rail fastener - Google Patents

Description

r-luuju I I WWWV1 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT 0 0 ~0.

Application Number: Lodged: Invention Title: IMPROVED ELASTIC RAIL FASTENER 00 0 0* 00 The following statement is a full description of this invention, including the best method of performing it known to us IMPROVED ELASTIC RAIL FASTENER Technical Field This invention relates to rail fasteners for securing rail tracks to a solid base.

In particular, the invention relates to an improved elastic rail fastener.

Background of the Invention Railway tracks on which trains travel are commonly made up of a pair of rails held together by sleepers which are bedded into ballast on the ground. The rails usually sit on plates which are attached to the sleepers by spikes or screws. The rails themselves are secured to the plates by spikes, screwed fasteners, or elastic 10 rail fasteners.

00One of the problems caused by spikes and screws is that due to vibrations induced in the rail by the passing of a train, the fasteners bed down and lose their clamping force, over time, and allow the rail to move, slide or creep from its intended position. Furthermore, over time, the rail may also experience "rolling", whereby it *15 begins to move from side to side about a horizontal axis. These movements have severe consequences on the stability of the track causing misalignment between adjacent sections of track, and can cause increases in separation between a rail and its paired rail which causes the wheels of a train to fall off the rail, resulting in derailment of the train.

20 Traditionally, these problems were addressed by driving rail anchors onto the *"*base of the rail, and engaging the anchors with the sides of the corresponding sleeper. However, this was not an adequate solution, since high cost was associated in obtaining the required number of anchors, as well as the cost of installation. Furthermore, over time the anchors themselves tended to cut into the side of the sleeper and become loose. As a number of anchors became loose, those that remained fast tended to bear the additional load previously taken by the now loose anchors. This non-uniform distribution of loads then caused the overloaded sleepers to move through the ballast, also upsetting track alignment.

Discussion of the Prior Art Many of these problems were overcome by the introduction of elastic fasteners, i.e. fasteners with enough flexibility to absorb much of the vibrational forces without breaking, while maintaining sufficient clamping force on the rail.

However, to be effective the elastic fasteners need to have a large amount of deflection in the installed position so that the initial variation in the geometry of the mating parts is small relative to the total deflection thereby minimising the variation in the clamping toe load and maintaining it within safe limits. If the toe load falls below a safe minimum, the rail will not be restrained adequately conversely, if the load is too high the clip will either break during fitting or fail later due to fatigue.

In practice the vertical rail movement is up to about 1 mm, and so an oscillation of this size must not take the stress in the clip beyond the endurance limit of the steel. This can be achieved if the 1 mm movement is only a small percentage 10 of the initial deflection. In most cases this means that the initial deflection is preferably about 10mm or more.

Therefore the essence of cost effective elastic fastener design to a large extent comes down to obtaining the maximum deflection and toe load from the minimum amount of steel.

15 An elastic fastener is disclosed in US patent no. 4313563 (Young), which foe. provides for a cost effective elastic fastener using the minimum amount of steel but is still capable of effectively absorbing forces.

A typical elastic fastener has a central body portion having two legs extending therefrom, with a "toe" of each leg engaging the rail and clamping it down.

20 The vertical bending moment on a typical fastener leg increases from zero at the toe to a maximum at the junction to the body of the clip. Thus, to accommodate the changing moment profile, the fastener was ideally designed so that the leg cross-section was a minimum at the toes and a maximum at the body junction.

A problem arises, however, when such elastic fasteners are designed to be retro-fitted into pre-existing sleeper plates which were originally intended for rigid dovetail and bolt fastenings and there is insufficient room to provide adequate reasonable clip proportions. In this situation, the ideal fastener is not suitable for pre-existing plates for several reasons.

Firstly, the act of driving the fastener onto the rail causes the fastener toes to strike the edge of the rail base first, then to rise up on top of the rail base to its final position. If the toes are too flexible, they will bend backwards and take on apermanent set soon after striking the edge of the rail base.

3 During track building or resurfacing operations, it is common to flood the track with graded rock ballast and then to level it out, removing the excess ballast with a plough. The blade of the plough is cut out to clear the fasteners, but there is still a substantial side force applied to the fastener legs as rocks are jammed between the blade and fastener legs. The fastener legs must be strong enough to withstand this without taking a permanent set.

Finally, fasteners are sometimes removed by applying a horizontal force to the fasteners' toes. The toes and legs must therefore be strong enough to withstand these secondary forces without becoming damaged.

S 10 It would therefore be desirable to provide a rail fastener which is strong enough to withstand secondary forces brought about by installation, maintenance and removal, while still able to provide sufficient deflection to accomplish its primary function of clamping down a rail.

Summary of the Invention 15 According to a first aspect of the invention, there is provided an elastic rail fastener of a generally U-shaped configuration, including a clamping portion including two legs extending from one side of the fastener, each leg terminating in a toe which operatively engages a rail to provide a clamping force for said rail, and a body portion which is operatively secured to a solid base at one end, characterised 20 in that at least a part of the region of said body portion having the highest bending *moment is reduced in cross-sectional area relative to the rest of said body portion, so as to maximise the deflection contributed by said fastener.

Preferably, the deflection operatively contributed by the body portion is greater than that of the clamping portion.

Preferably, the body portion is secured to a solid base by way of a securing portion, extending from the body portion. The securing portion preferably forms two arms, which are received by the solid base. The base may conveniently be a fixture on a sleeper.

The increased flexibility of the body portion is ideally achieved by a reduction in thickness of the body portion, between, but away from the junction of the body portion and the clamping portion and the junction of the body portion and the securing portion.

According to a second aspect of the invention, there is provided a rail section including a rail segment, a sleeper and a rail plate, wherein the rail segment is secured to the rail section by way of the elastic fastener of the present invention.

Brief Description of the Figures Figure 1 shows a general view of a rail seat assembly, including the elastic fastening means of the present invention.

Figure 2 shows a side elevation of the elastic rail fastener of the present invention.

Figure 3 shows a plan view of the elastic rail fastener of figure 2.

10 Figure 4 shows a plan view of the blank for the elastic fastener of figures 2 and 3 before wrapping to the final shape.

Figure 5 shows a side elevation of the blank of figure 4.

Detailed Description of the Preferred Embodiment One embodiment of the elastic fastener 50 of the present invention is shown in use on a section of rail track generally denoted as Rail 1 is connected to rail plate 3 by fastener 50. Rail plate 3 is connected to sleeper 2 by way of spikes or screws 4. A pad 6 typically fits between rail 1 and rail S.plate 3.

Elastic fastener 50 is U-shaped and typically made from an appropriate material such as steel. Leg 51 of fastener 50 curves around to engage the base 8 of rail 1, providing a downward clamping force to secure rail 1 to sleeper 2. The other end 54 of fastener 50 is received in plate holder 7, to firmly secure fastener to the plate. It will be noted that a portion of fastener 50 is reduced in thickness, as will be discussed below. This reduction in thickness results in an increased flexibility in that region of fastener 50. The amount of thickness reduction is determined by the type of material used to make the fastener, and is reduced to the point where the working stress from the primary load forces generated by a passing train) is as high as the particular material can take without breaking or becoming deformed. This means that the deflection contribution from this part of the fastener will be maximised. Legs 51 do not have a reduced thickness, and can thus withstand the secondary forces described above without breaking or being deformed.

Figure 2, shows fastener 50 in isolation. The end 52 of leg 51 is referred to as he toe, and it is the toe which actually engages rail base 8.

The main body section 53 has a reduced thickness to increase the flexibility of that region. It will be noted that the reduction in thickness begins at a point away from the junctions 55 and 56 of the main section 53 and legs 51 and arms 54 respectively. This is because there is a high stress concentration at these points 10 due to the large change in cross-section.

Although the reduced cross-section of section 53 is preferably achieved by reducing the thickness at a region in that section, it will be understood that reduced section may be achieved by other means, for example by waisting in the clip at section 53. It is strongly preferred that the reduction be achieved by removing 15 material from the outer curve removing material from the inner surface is likely to result in structural failure.

From figure 3, it can be seen that there is a pair of legs 51, and a pair of arms a 54.

Figures 4 and 5 show fastener 50 in the pre-rolled state. Main section 53 20 extends on one side into two legs 51 and on the other into two arms 54. The legs 0 51 and arms 54 meet section 53 at junctions 55 and 56 respectively. The secondary side forces do not cause any significant stresses on section 53 since it is more than twice the width of a single leg 51.

It will be understood of course that the shape of fastener 50 is only preferred, and need not take on the specific form shown here. Conceivably, fastener 50 could be a rectangular piece as seen from a view of figure 4, and simply have a region of reduced thickness as shown in figure The design of the present invention ensures that the main body section 53, which has no significant stress concentrations, is able to contribute a large amount of verified deflection, thus allowing legs 51 to provide sufficient clamping force on the rail 1 (in spite of any variation in installed deflections), and still being able to withstand secondary forces.

It is preferred that the fastener be formed from flat steel bar or plate.

However, the present invention is equally applicable to a clip formed from round or square bar.

It will be understood by the person skilled in the art that the above describes only a preferred embodiment. Many variations are possible within the scope of the present invention.

*eeo* *oo

Claims (9)

1. An elastic rail fastener of a generally U-shaped configuration, including a clamping portion including two legs extending from one side of the fastener each leg terminating in a toe which operatively engages a rail to provide a clamping force for said rail, and a body portion which is operatively secured to a solid base at one end, characterised in that at least a part of a region of said body portion having the highest bending moment is reduced in cross-sectional area relative to the rest of said body portion, so as to maximise the deflection contributed by said fastener. .e

2. An elastic rail fastener according to claim 1, wherein the contribution to S- deflection of said body portion is greater than that of the clamping portion.

3. An elastic rail fastener according to claim 2, wherein the reduced cross- section is provided by reducing the thickness of the fastener in said region. An elastic rail fastener according to claim 3, wherein the thickness is reduced by changing the outer surface of the curve, while the inner surface is unchanged. An elastic rail fastener according to claim 1 or claim 2, wherein the reduced cross-section is provided by reducing the width of the fastener in said region to form a wasted portion.

6. An elastic rail fastener according to claim 1, wherein said body portion is operatively secured by a securing portion which engages a retaining portion attached to a sleeper.

7. An elastic rail fastener according to claim 1, wherein said area of reduced cross-section is confined to a region away from a junction of said clamping portion and said body portion.

8. An elastic rail fastener according to claim 1, wherein said fastener is formed from plate or flat bar steel material.

9. An elastic rail fastener according to claim 1, wherein said fastener is formed from round or square bar steel material. A rail section including rails, a sleeper and a rail plate, wherein said rails are secured to said section by elastic fasteners according to any one of claims 1 to 9.

11. A rail fastener substantially as described herein with reference to the figures. DATED this 27 th day of January 2000. PANDROL AUSTRALIA PTY LIMITED WATERMARK PATENT TRADEMARK ATTORNEYS UNIT 1, THE VILLAGE, RIVERSIDE CORPORATE PARK

39-117 DELHI ROAD NORTH RYDE NSW 2113 PNF:MP:MM P15576AU00