EP0880621B1

EP0880621B1 - Manufacturing elastic rail clamps

Info

Publication number: EP0880621B1
Application number: EP97904527A
Authority: EP
Inventors: Hartley Frank Young; Barry Marshall; Brian George Conroy
Original assignee: Pandrol Ltd
Current assignee: Pandrol Ltd
Priority date: 1996-02-13
Filing date: 1997-02-11
Publication date: 2000-09-06
Anticipated expiration: 2017-02-11
Also published as: EP0880621A1; PL183779B1; TR199801560T2; AU1730297A; WO1997030225A1; EA199800716A1; DE69703029D1; EA000383B1; PL328327A1; BG102681A

Description

This invention relates to manufacturing elastic rail clamps used in rail fastening systems, and particularly, although not exclusively, to a method of manufacturing rail clamps of the kind which are applied at right angles to the rails.

An elastic rail clamp is described in US Patent 4,313,563 (Young). This clamp is designed for use with a custom made shoulder into which the base of the elastic clamp fits.

Previously-considered manufacturing methods for producing such a rail clamp also suffer the problem of the presence of inclusions in the finished clamp at points of highest stress, which can lead to fatigue failure.

It is therefore desirable to produce such clamps by a method which can avoid the presence of inclusions at high stress points of the clamp.

According to the present invention there is provided a method of manufacturing a rail clamp for fastening a rail to an underlying rail plate or rail tie, the clamp comprising a base portion, adapted to seat in a slot in the rail plate or rail tie or in an anchoring device secured to the rail plate or rail tie, and a pair of substantially parallel members which extend from the base portion to a rail engaging portion, the parallel members being curved so that the rail engaging portion lies adjacent to the base portion, the method comprising: i) forming a workpiece by bending a length of bar stock to provide a pair of limbs; ii) pressing the workpiece thereby to flatten and/or reduce the thickness of the bar stock to form a blank; and iii) deforming the blank to form the clamp.

Previously considered manufacturing methods for producing a rail clamp of the type described in US 4,313,563 also suffer from the disadvantage that the clamp must undergo a "coining" operation to prevent undue stress concentrations being built up in the vicinity of sharp corners which result from a stamping process. In addition, previously considered manufacturing methods required the formed clamp to undergo a "scragging" operation in which the clamp is overdeflected in order to induce a permanent deformation of its shape and an advantageous initial stress distribution in the clamp. However, use of a method embodying the present invention can avoid the need for such coining and/or scragging operations if the bar stock is round and the workpiece is pressed such that the blank has rounded edges.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example, to the accompanying drawings in which:

Figs. 1 to 5 illustrate steps of a previously considered method for manufacturing an elastic rail clamp;

Figs. 6 to 10 illustrate steps of methods embodying the present invention;

Figs. 11 shows a blank used in the previously-considered method of Figs. 1 to 5;

Fig. 12 is a side view of a clamp manufactured in accordance with the method of Figures 1 to 5;

Fig. 13 is a perspective view of a workpiece used in a method embodying the present invention; and

Fig. 14 is a perspective view of a blank manufactured in accordance with a method embodying the present invention.

Steps of a previously-considered method of manufacturing an elastic rail clamp are shown in Figs. 1 to 5. The method starts with the production of a rectangular blank 1 (Fig. 1). The blank would normally be formed from steel.

The rectangular blank is then split into two substantially U-shaped blanks 2 (Fig. 2). Each U-shaped blank 2 forms the basis of a rail clamp.

The U-shaped blank is cropped to length and the sharp edges are coined to produce smooth edges (Fig. 3). The cropping and coining operations are usually done with a hot blank. The rounding of the edges by the coining operation is necessary to avoid undue stress concentrations in the finished clamp.

Coining is a well-established process which attempts to improve a sheared edge to that of an edge normally associated with hot rolled steel. The process is usually carried out in a power press employing a pair of dies. The raw blank is placed in the dies and squeezed to form the round edges on the blank. This operation is critical to the fatigue life of a spring clamp manufactured from sheared flat material and requires a high degree of quality control during processing.

In the previously-considered method the cropped and coined blank is then hot formed into the clamp shape shown in Fig. 4, by bending the free ends over to form toe portions 7 which bear on the rail when the clamp is in use. A base portion is produced by bending the central portion of the U-shaped blank. The base portion is for engagement with the baseplate in which the clamp will be used.

The clamp is then subjected to a scragging operation in which the base portion 5 of the clamp is held rigidly between two jaws 6. A force is applied to the toe portions 7 so as to overdeflect the clamp. The force is then released. The force may be applied and released more than once, for example three times, and then the clamp is removed from the jaws 6. Such an operation produces a clamp 8 having the required initial stress distribution and shape.

Figs. 6, 7, 8 and 9 illustrate various steps of manufacturing methods embodying the present invention.

As shown in Figs. 6a and 5b, a round bar of material, usually steel, is bent, at a position between its ends, to form a starting workpiece 10 of generally U-shaped form, having two limbs 14 interconnected by an arcuate portion 16. In the workpiece of Fig. 6a the limbs 14 are parallel, and in the Fig. 6b workpiece the limbs 14 converge towards their free ends.

The workpiece 10 is then flattened to form a blank 11. Figs. 7a and 7b show blanks 11 produced from the workpiece of Fig. 6a and 6b respectively. The blanks are produced by heating the workpiece 10 and pressing it in an open die pressing operation. The configuration of the plates of the press depends upon the final clamp shape which is required. An example of such a press is shown in side elevation in Fig. 8. The workpiece is placed in a lower die 22. An upper die 21 is brought into contact with the workpiece 10 in the direction of arrow f in Fig. 8. The blank 11 is pressed until the upper die 21 reaches stops 24 on the lower die 22. The shaping of the pressure surface 23 of the upper die imparts the required shape to the blank 11. The shaping of the pressure surface 23 has been exaggerated in Fig. 8 for the sake of clarity. Other forms of shaped pressure surface would be used to form the shapes of blank 11 shown in Figs. 7a and 7b.

Since an open die pressing operation is used, the inner and outer side faces 18, 20 of the limbs 14 and the inner surface of the arcuate portion 16 are not constrained by the plates of the press, and so the material of the workpiece 10 can flow unimpeded in the direction away from the centreline of the limbs 14 and inwardly of the arcuate portion 16 as the workpiece is pressed. Consequently, while the upper and lower faces of the workpiece 10 are flattened, the inner and outer side faces assume a rounded shape with no sharp edges.

Alternatively, the workpiece 10 may be flattened by means of a closed die pressing operation to produce a blank 11 as shown in Fig. 9a. Figs. 9b and 9c show cross-sections through the lines IX_b - IX_b and IX_c - IX_c respectively.

The shape of the die used in the closed die pressing operation is such that the excess material overflows about the centre line of the blank and all the external edges of the blank have appropriate radii, since the die itself may be made so as to have no sharp edges, all being rounded appropriately. A final "clipping" operation to remove excess material is required before the blank is hot formed into the final clip shape.

The thickness of the blank 11 may be varied according to the geometric shape requirements of the clamp and the stress levels which will be present in the various parts of the finished and installed clamp. In the example shown in Fig. 7a an end region 12 of the blank 11, corresponding to the arcuate portion 16 of the workpiece 10 of Fig. 6a, has been tapered. Such tapering may be required so that the clamp can be engaged with a baseplate. The shape of the remaining parts of the blank 11 are chosen to optimise the stiffness of and the stress distribution in the finished clamp. For example, high stress regions may be thicker than low stress regions. Thinner low stress regions would allow greater deflection of the clamp when in use.

As shown in Fig. 10, the flattened blank 11 is formed into a clamp 13 of the required shape. The clamp shown in Fig. 10 is of the type described in US Patent No. 4,313,563, although the method would be applicable to other shapes of clamp, for example those described in International Patent Application No. PCT/GB96/00319 or U.S. Patent No. 3,067,947. The clamp 13 is formed by bending the free ends of the blank 11 to form toe portions 14 which will bear on the rail when the clamp is in use. A base portion is formed by bending the tapered end portion 12 of the blank 11 over the central portion of the blank.

The advantage of the methods described with reference to Figs. 6 to 10 is that the blank produced has smooth rounded edges which have not been sheared. The rounded edges serve to prevent stress concentrations, but do not require coining to achieve this effect. Moreover, blanks produced by an open die pressing operation (Figs. 7a, 7b & 8), rather than a closed die pressing operation (Figs. 9a, 9b and 9c), do not require trimming.

The ability to vary the thickness of the blank, and hence the clamp, can result in a clamp with more advantageous stress distribution than could be achieved with previously considered manufacturing methods. Varying the thickness of the clamp in this way may allow the scragging operation to be reduced or eliminated, and thus clamps may be produced by a method in accordance with the present invention more economically than those produced by the previously considered methods.

The methods described with reference to Figs. 6 to 10 have another advantage which will be described with reference to Figs. 11 to 14.

The blank 2 (Fig. 2) used in the previously-considered manufacturing method is cut from a rolled steel sheet produced by rolling steel ingots. Such ingots contain impurities or inclusions particularly in central regions of the ingots. As shown in Fig. 11, these inclusions 31 are concentrated in a central region of the rolled sheet 30.

Blanks

32 and 33 are cut from the sheet 30, and so the finished clamp will contain inclusions at its edges as shown in Fig. 12. Lines AA and BB in Fig. 11 show the positions of highest stress in the finished clamp. As will be appreciated from Fig. 11 there are three sheared edges having inclusions 31 in the regions of highest stress in the finished clamp. Fatigue failures can initiate and grow from these inclusions.

However, in a manufacturing method in accordance with the present invention, the inclusions are kept within the clamp and are not present at the edges of the finished clamp. As shown in Fig. 13, inclusions 31 in the bar stock are concentrated within the bar 34. When the bar is pressed as described above, the inclusions 31 are kept within the pressed blank 35 and hence away from the edges of the finished clamp, as shown in Fig. 14. Such a distribution of inclusions in the clamp reduces the likelihood of fatigue failure of the clamp.

Claims

A method of manufacturing a rail clamp (13) for fastening a rail to an underlying rail plate or rail tie, the clamp (13) comprising a base portion (12), adapted to seat in a slot in the rail plate or rail tie or in an anchoring device secured to the rail plate or rail tie, and a pair of substantially parallel members (14) which extend from the base portion (12) to a rail engaging portion, the parallel members (14) being curved so that the rail engaging portion lies adjacent to the base portion (12), the method comprising:

i) forming a workpiece (10) by bending a length of bar stock to provide a pair of limbs;

ii) pressing the workpiece (10) thereby to flatten and/or reduce the thickness of the bar stock to form a blank (11); and

iii) deforming the blank (11) to form the clamp (13).
A method as claimed in claim 1, wherein the bar stock is round and the workpiece (10) is pressed such that the blank (11) has rounded edges.
A method as claimed in claim 1 or 2, in which, during the pressing step, the material of the workpiece (10) is free to deform in a direction parallel to a plane containing the centrelines of the limbs.
A method as claimed in any one of the preceding claims, in which the pressing step comprises an open die pressing operation.
A method as claimed in any one of claims 1 to 3, in which the pressing step comprises a closed die pressing operation.
A method as claimed in claim 5, in which, after the pressing step, excess material is clipped from the blank (11).