Stretcher bar

Abstract

 The invention relates to a stretcher bar for use on a railway point mechanism. The stretcher bar comprises two sub bars (44) threadably connected to opposite sides of a adjustment barrel (30) wherein the sub bars (44) are oppositely threaded such that rotation of the adjustment barrel (30) adjusts the overall length of the stretcher bar. The barrel (30) is composed of two parts which are electrically insulated form each other by a layer of insulating material (42). A method of installing and adjusting the stretcher bar between two switch rails is also disclosed.

Description

[0001] The present invention relates to stretcher bars for use in railway point mechanisms.

[0002] Stretcher bars are required by legislation and are essential elements of a railway point mechanism acting to ensure that switch rails are maintained at the correct separation in relation to one another as a train passes over points. Moreover, stretcher bars provide a fixing location for the attachment of ancillary equipment for point drive, detection and adjustment.

[0003] Known stretcher bars ensure that when a switch rail is closed to a stock rail, (i) the fit is uniform over the length of the switch rail; and (ii) the opposite switch rail is open from its corresponding stock rail thereby allowing sufficient clearance for train wheels to pass over the points (See Fig. 1). Stretcher bars also ensure that the switch rail is prevented from lifting off its base plates under certain conditions of train movement.

[0004] Opposite switch rails must be electrically insulated from each other in order to conform with Railway Signalling legislation and accordingly insulating material is incorporated into each stretcher bar.

[0005] Conventional stretcher bars comprise of two flat steel bars bolted together through a Tufnol® (insulated) joint, the bars being attached at their opposite ends to switch rails via lugs (See Fig. 2). Installation is very time consuming and expensive.

[0006] Although one end of the of conventional stretcher bars is pre-drilled for attachment to the lug, the other end of the bar is left blank. The reason for this is that each bar must be customised to account for the variation in the switch opening along the length of the switch rail. Typical opening gaps are 108 mm at the thin (toe) end of the switch rail to 50 mm at the thick (heel) end and therefore determine the length of any stretcher bar at a particular point along the length of a switch rail. These dimensions can vary over time due to wear on the switch and stock rails.

[0007] Installation of a stretcher bar involves clamping the blank end and adjusting the stretcher bar to suit the switch rail gap. Once in its correct location the stretcher bar is marked and then disassembled. The stretcher bar is then taken off-site to be drilled according to the markings. Finally, the stretcher bar is returned and attached, via lugs, to the switch rails via the existing and newly drilled holes.

[0008] The whole process typically takes 90 minutes of on-site time per stretcher bar. Given that three or more stretcher bars are installed (depending upon switch rail length), this is a very time consuming activity. Access time for maintenance activities is a finite commodity per event (typically only 3-4 hours at a junction depending upon train movements) and therefore planning such maintenance is a skilled and time consuming logistical exercise.
Furthermore, dealing with such small variations in such a safety critical environment demands the employment of skilled technicians further increasing installation and maintenance costs.

[0009] A further disadvantage of conventional stretcher bars is that once they are installed they are non-adjustable. Accordingly, any wear on the switch or stock rails during their working life cannot be taken up. Consequently, the fit of the switch rail to the stock rail may become flawed over time leading to reliability problems with switch movement (i.e. points failures).

[0010] Periodic renewal of switch and stock rails necessitates removal of the stretcher bars. Typically, switch and stock rails are removed one side at a time (i.e. over two separate maintenance periods) and new stretcher bars are once again customised to suit the new points installation with consequential time and cost implications.

[0011] According to a first aspect of the present invention there is provided a stretcher bar for use on a railway point mechanism characterised in that the stretcher bar comprises a bar having a threaded end and an adjustment mechanism, the threaded end adapted to cooperate with a thread formed in the adjustment mechanism such that the overall length of the stretcher bar can be adjusted to correctly fit between two rails of the point mechanism.

[0012] Preferably, the threaded end is adapted to be received within a threaded aperture in the adjustment mechanism.

[0013] Preferably, the adjustment mechanism comprises a barrel which is rotatable on the threaded end of the bar.

[0014] Preferably, the barrel is formed from two parts, each part having a threaded aperture.

[0015] Preferably, the two parts of the barrel are held together by at least one nut and bolt.

[0016] Preferably, the stretcher bar comprises two sub bars, each sub bar having a threaded end receivable within the threaded apertures on the respective parts of the barrel.

[0017] Preferably, the respective threaded ends of the sub bars are oppositely threaded such that rotation of the barrel thereon adjusts the length of the stretcher bar.

[0018] Preferably, nuts are provided on each threaded end and adapted to be selectively tightened such that they abut opposite ends of the barrel thus preventing further rotation thereof.

[0019] Preferably, the nuts are jam nuts.

[0020] Preferably, opposite ends of the stretcher bar are fitted to the rails by lugs.

[0021] Preferably, the stretcher bar fits between two switch rails.

[0022] Preferably, insulating material separates opposite ends of the stretcher bar thereby ensuring that the ends are electrically insulated from each other.

[0023] Preferably, the insulating material is sandwiched between the parts of the barrel.

[0024] Preferably, the stretcher bar is positioned under the rails.

[0025] According to a second aspect of the present invention there is provided a method of installing the stretcher bar of the first aspect to a railway point mechanism characterised in that the method comprises the steps of (i) fitting a first lug to a first end of a stretcher bar; (ii) fitting a second lug to a first rail; (iii) positioning said first end below a second rail; (iv) securing said first lug to the second rail; (v) adjusting the length of the stretcher bar such that the free end of the stretcher bar is aligned with the second lug; and (v) fitting said free end of the stretcher bar to the second lug.

[0026] Preferably, an additional step of adjusting the stretcher bar to a selected length is performed.

[0027] Preferably, an additional step of tightening the nuts on each threaded end is performed such that they each abut opposite ends of the barrel thus preventing further rotation thereof.

[0028] Preferably, an additional step of further adjusting the length of the stretcher bar is performed in order to allow for wear of the rails.

[0029] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, wherein:

Figs. 1 and 2 show a conventional stretcher bar; and

Fig. 3 shows front and plan exploded views of an adjustable stretcher bar according to the present invention.

[0030] Figs. 1 and 2 show a conventional stretcher bar 10 connected to switch rails 12 via lugs 14. The stretcher bar 10 is composed of two flat steel bars 16 bolted together through a Tufnol® joint 18 which comprises insulating material 20 sandwiched between the bars 16.

[0031] Fig. 3 shows front and plan views of an adjustable stretcher bar comprising a barrel 30 formed in two halves. Each half has a threaded apertures 32 and 34 disposed through their central longitudinal axes. Further apertures 33 are provided on each half having axes parallel to and equidistant from the central longitudinal axis.

[0032] Referring to the drawings, each half of the barrel 30 has a flat surface 36 arranged perpendicular to its central longitudinal axis. When assembled, the flat surfaces 36 are connected by nuts and bolts disposed through apertures 33 and 34. Collets and washers of Tufnol® material surround the nuts and bolts to prevent any metal to metal contact. The flat surfaces 36 abut opposing sides of Tufnol® insulating material 42 sandwiched between the two surfaces 36. The two halves of the barrel 30 are therefore arranged symmetrically about the Tufnol® insulating material 42. Accordingly, each end of the stretcher bar is electrically insulated from the other.

[0033] The threaded apertures 32 each receive a complementary male threaded member 46 which forms the inner end of a flat steel bar 44. Each threaded member has a "Staytite" jam nut 50 thereon which is capable of being tightened against one half of the barrel 30. The distal ends 47 of the threaded members 46 are flattened after the jam nuts 50 are mounted thereon such that the nuts 50 cannot be removed.

[0034] Each flat steel bar 44 is fixed relative to its corresponding half of the barrel 30 by tightening the jam nut 50 against the side of the barrel 30 opposite the flat surface 36. Each flat steel bar 44 has pre-drilled holes 48 having axes perpendicular to those of the apertures 32, 33 and 34.

[0035] In use, the stretcher bar is pre-assembled and fitted to the rails according to the following method: (i) a first lug is fitted to a first end of a stretcher bar; (ii) a second lug is fitted to a first rail; (iii) the first end is positioned below a second rail; (iv) the first lug is fitted to the second rail; (v) the length of the stretcher bar is adjusted such that the free end of the stretcher bar is aligned with the second lug; and (v) the free end of the stretcher bar is fitted to the second lug.

[0036] It will be appreciated that the stretcher bar of the present invention has many advantages over conventional stretcher bars. For example, since both ends of the stretcher bar are pre-drilled and the length of the stretcher bar can be easily adjusted, there is no longer a need to fit the stretcher bar on-site, mark it and subsequently take it off-site for drilling. The consequential savings in time (and therefore costs) are significant, i.e. three bars can be fitted, adjusted and tested in around 60-70 minutes compared to 270 minutes for conventional stretcher bars.

[0037] Moreover, the adjustment mechanism is highly visible lying substantially midway between the switch rails. This means that any defects can be quickly and easily identified. The flattened ends of the threaded members ensure that the jam nuts cannot be removed and therefore limit the range of adjustment of the stretcher bar. Furthermore, the process of adjusting the stretcher bar is made simpler by the ease of accessibility compared to conventional stretcher bars where adjustment is hampered by the rails.

[0038] Various modifications may be made without departing from the scope of the invention. For example, it will be appreciated that the adjustable stretcher bar may comprise only one adjustable threaded member instead of two.

[0039] A scale may be provided on the barrel (in cm and/or mm) to provide a visual verification of the length of the stretcher bar.

[0040] The insulating material 42 may be formed as an integral part of either or both of the flat surfaces 36. Indeed, the entire barrel 30 may be formed from an insulating material.

[0041] The threaded members 46 connected to the flat steel bars 44 may instead be connected to the barrel 30 and received in apertures formed on the flat steel bars 44.

[0042] The jam nuts 50 may be replaced by any other reliable and releasable securing device.

Claims

1. A stretcher bar for use on a railway point mechanism characterised in that the stretcher bar comprises a bar (44) having a threaded end (46) and an adjustment mechanism (30), the threaded end (46) adapted to cooperate with a thread (32) formed in the adjustment mechanism (30) such that the overall length of the stretcher bar can be adjusted to correctly fit between two rails (12) of the point mechanism.

2. A stretcher bar according to claim 1 wherein, the threaded end (46) is adapted to be received within a threaded aperture (32) in the adjustment mechanism (30).

3. A stretcher bar according to claim 1 or 2 wherein, the adjustment mechanism comprises a barrel (30) which is rotatable on the threaded end (46) of the bar (44).

4. A stretcher bar according to claim 3 wherein, the barrel (30) is formed from two parts, each part having a threaded aperture (32).

5. A stretcher bar according to claim 4 wherein, the two parts of the barrel (30) are held together by at least one nut and bolt.

6. A stretcher bar according to claim 3 or 4 wherein, the stretcher bar comprises two sub bars (44), each sub bar (44) having a threaded end (46) receivable within the threaded apertures (32) on the respective parts of the barrel (30).

7. A stretcher bar according to claim 6 wherein, the respective threaded ends (46) of the sub bars (44) are oppositely threaded such that rotation of the barrel (30) thereon adjusts the length of the stretcher bar.

8. A stretcher bar according to claim 6 or 7 wherein, nuts (50) are provided on each threaded end (46) and adapted to be selectively tightened such that they abut opposite ends of the barrel (30) thus preventing further rotation thereof.

9. A stretcher bar according to claim 8 wherein, the nuts are jam nuts (50).

10. A stretcher bar according to any one of claims 1 to 9 wherein, opposite ends of the stretcher bar are fitted to the rails (12) by lugs (14).

11. A stretcher bar according to any one of claims 1 to 10 wherein, the stretcher bar fits between two switch rails (12).

12. A stretcher bar according to any one of claims 1 to 11 wherein, insulating material (42) separates opposite ends of the stretcher bar thereby ensuring that the ends are electrically insulated from each other.

13. A stretcher bar according to claim 12 when dependent upon any of claims 4 to 11 wherein, the insulating material (42) is sandwiched between the parts of the barrel (30).

14. A stretcher bar according to any one of claims 1 to 13 wherein, the stretcher bar is positioned under the rails (12).

15. A method of installing the stretcher bar of claim 1 to a railway point mechanism characterised in that the method comprises the steps of (i) fitting a first lug (14) to a first end of a stretcher bar; (ii) fitting a second lug (14) to a first rail (12); (iii) positioning said first end below a second rail (12); (iv) securing said first lug (14) to the second rail (12); (v) adjusting the length of the stretcher bar such that the free end of the stretcher bar is aligned with the second lug (14); and (v) fitting said free end of the stretcher bar to the second lug (14).

16. A method according to claim 15 wherein, an additional step of adjusting the stretcher bar to a selected length is performed.

17. A method according to claim 16 wherein, an additional step of tightening the nuts (50) on each threaded end (46) is performed such that they each abut opposite ends of the barrel (30) thus preventing further rotation thereof.

18. A method according to claim 16 wherein, an additional step of further adjusting the length of the stretcher bar is performed in order to allow for wear of the rails (12).

Drawing