GB2114635A - Resilient seats for railway rails - Google Patents

Abstract

In a rubber chair pad comprising a web 15 having two upstanding parallel walls 14 for embracing the base flange of a railway rail, the walls 14 are reinforced by embedded bars 11, preferably of metal strip or angle, having rubber-embedded projections such as 12 or 12a to provide the pad with reinforced locating ears for embracing conventional railside clip anchorage blocks. In modifications the locating ears of the pad have holes to receive depending projections of an insulator overlying the said flange under a rail clip. Some details are given of synthetic rubber compositions, and of methods of moulding and testing the pad. <IMAGE>

Description

SPECIFICATION Improvements in or relating to seats for railway lines This invention relates to improvements in seats for railway lines.

Railway lines are commonly of I-Section and, when laid, are supported at spaced intervals on sleepers to which they are secured. The sleepers have commonly been made of wood and the rail has been supported in a metal chair bolted to the sleeper and having two integrally formed spaced tubular portions which extend longitudinally on either side of the rail and hold it against lateral displacement to maintain the gauge. The tubular portions each have a passage therethrough and a separate resilient member formed from metal rod is engaged in the passage formed through each tubular portion and is configured to have a portion which bears downwardly against the lower flange of the rail when so engaged.

Because of the difficulties in the supply of wooden sleepers for railway lines and the increasing costs thereof there is a tendency to replace such wooden sleepers by sleepers made of concrete.

Concrete sleepers, however, have the disadvantage that they tend to disintegrate or fragment when exposed to vibration. Also, there exists a requirement that the railway line should be electrically insulated from earth.

In order to overcome these disadvantages it is known to form the chair in two similar halves without the connecting web and to place a pad of electrically insulating and resilient material between the rail and the concrete sleeper to absorb vibrations, at least to some extent, and electrically to insulate the rail from the concrete sleeper. In order to complete the electrical insulation, a packing piece of a hard moulded synthetic plastics material is provided which has a first flange which overlies the base flange of the rail between the latter and that portion of the metal resilient member intended to bear against this base flange and which has a second flange which depends downwardly from the first flange between the adjacent tubular portion of the chair part and serves to insulate the rail electrically from this chair part and to maintain the gauge.This packing piece has two spaced outwardly projecting portions which are disposed one at each end of the adjacent chair part and which serve to hold the packing piece against displacement in the direction of length of the rail.

In practice, however, this known arrangement has the disadvantage that the pad tends to creep and become displaced over a period of time.

It is an object of the present invention to provide an improved seat for a railway line in which the disadvantages referred to above are materially reduced if not entirely obviated.

According to the present invention there is provided a seat for a railway line comprising a pair of spaced longitudinally extending parallel reinforcing members each having a pair of spaced outwardly extending portions, the reinforcing members being moulded into a resilient pad of synthetic rubber to provide upstanding walls arranged to receive the lower flange of an I-section railway line therebetween electrically insulated from the reinforcing members moulded into said walls with an integrally moulded web extending between said walls and below such railway line to seat the line and to further provide outwardly projecting portions arranged to embrace a chair plate in electrically insulated relationship thereto to retain the seat in position.

Preferably, the reinforcing members are metal rods or bars with the spaced outwardly projecting portions integrally formed therewith.

Conveniently, the reinforcing members are formed as angle section members with an upstanding wall part and an outwardly extending flange which is a cut-away intermediate the length thereof to leave a gap therein to receive the chair plate and provide the two spaced outwardly projecting portions.

Desirably, the synthetic rubber is composed of as parts by weight per hundred parts of synthetic rubber, 1 00 parts of styrene butadiene rubber, 45-55 parts of high styrene resin, 5 to 6 parts of activators, 1 to 2 parts of antioxidant phenol condensate, 3-5 parts of processing aids, 4-6 parts of a softener resin, 4 to 6 parts of naphthenic process oil, 100 to 120 parts of a reinforcing filler consisting of silica and carbon black, 2--4 parts of accelerators, and 2-3 parts of vulcanising agent.

With advantage, the styrene butadiene rubber includes oil extended styrene butadiene rubber, the activators comprise a blend of zinc oxide and stearic acid, the accelerators are comprised of Ncyclohexyl-benzothiazole-2 sulphenamide, mercaptobenzthiazole and tetramethylthiuram monosulphide and the vulcanising agent is sulphur.

The invention also provides a method of producing a rail seat according to any one of the five immediately preceding paragraphs which comprises disposing two elongate reinforcing members in a mould to extend in longitudinally spaced parallel relationship with the spaced projections extending outwardly, filling the mould with a synthetic rubber which extends about and between the reinforcing members and vulcanising the rubber.

Embodiments of the present invention will now be described by way of example, reference being made to the accompanying drawings in which: Figure 1 is a fragmentary plan view showing a known arrangement for mounting a railway line of a concrete sleeper, Figure 2 is a section taken on the line Il-Il of Figure 1, Figure 3 is a section taken on the line Ill-Ill of Figure 1, Figure 4 is a plan view of a rail seat according to the present invention, Figure 5 is an end elevational view of the rail seat shown in Figure 4, Figure 6 is a section taken on the line VI--VI of Figure 4, Figure 7 is a side elevational view of the rail seat shown in Figure 4, and Figure 8 is a section taken on the line VIlI-VIlI of Figure 4.

Figure 9 is a plan view of a rail seat and a packing member according to another embodiment of the present invention, Figure 10 is a sectional view of the rail seat and packing member taken on the line X-X of Figure 9, Figure 11 is a plan view of a rail seat and a packing member according to a further embodiment of the present invention, Figure 1 2 is a sectional view of the rail seat and packing member taken on the line XlI-XII of Figure 11.

The Figures illustrating the various embodiments are not drawn to the same scale.

In the known arrangement illustrated in Figures 1 to 3, an I-Section rail, indicated generally at 1, is supported on a concrete sleeper 2 with a pad 3 of electrically insulating resilient material disposed between the lower flange 5 of the rail and the sleeper. A packing piece 6 of hard electrically insulating moulded plastics material is provided on each side of the lower flange 5 and is shaped with a first flange 6a which overlies the lower flange 5 and a second depending flange 6b disposed between the edge of this lower flange 5 and the adjacent chair plate 7 which has a substantially flat portion 7a and an enlarged or tubular portion 7b through which a passage extends. The chair plates 7 are secured to the sleeper 2 in any suitable manner such as a spike embedded in the concrete of the sleeper.

A resilient member 8 of metal rod is provided configured to be engaged in the passage of the tubular portion 7b and to have a portion 8a which bears down against the first flange 6a of the packing piece 6. This flange 6a serves electrically to insulate the resilient member 8 from the rail 1 and the flange 6b serves electrically to insulate the rail 1 from the chair plate 7 and, because it fits closely between the latter and the lower flange 5, to maintain the gauge; or, in other words, to maintain the position of the iine.It will be seen that the known resilient member 8 is configured so that the portion 8a forms part of an end portion which extends in a direction opposite to that of the other end portion 8b of the resilient member 8 and an intermediate portion 8c is provided and arranged to bear against the substantially flat chair portion 7a when the end portion Sb is driven into the passage in the tubular portion 7b of the chair plate.

Each packing piece 6 has two spaced outwardly projecting ears 6c which extend one on each side of the associated chair plate 7 and hold the packing piece against displacement in the direction of length of the rail 1.

In use the pad 3 is subjected to considerable pressure and vibration and tends to wear and fail electrically and also to creep.

In the embodiment of the invention illustrated in Figures 4 to 8 a seat for a railway line comprises a pair of spaced elongate parallel reinforcing members 11, each having a pair of integrally formed spaced outwardly projecting portions 12, the reinforcing members being moulded into a resilient pad 13 of synthetic rubber to provide upstanding longitudinally extending parallel walls 14. The reinforcing members 11 are preferably of metal, e.g., mild steel, and being moulded into the pad 13, are firmly retained and electrically insulated from the lower flange of the rail which is intended to sit between the walls 14 and on the integrally formed web 1 5 extending between the walls.The projection portions 12 are intended to embrace an associated chair plate 7 and operate in an identical manner to the ears 6c of the previously described known example to retain the seat against longitudinal displacement in the direction of the rail. The projecting portions being embedded in the synthetic rubber are electrically insulated from the chair plate which, when it extends between the projecting portions, is also electrically insulated from the rail by the rubber covering on the reinforcing members 1 The lower flange of the rail is resiliently supported on the web 1 5 which also electrically insulates the rail from the sleeper.

As described with reference to the previously known example, a resilient member 8 of metal rod is used, configured as previously described, to engage at one end in the chair plate 7 and to bear down at the other end on the lower flange of the rail. Electrical insulation is provided either by a sleeve of electrically insulating material slipped over this other end of the resilient member or by a coating or pad of electrically insulating material applied and bonded thereto, or inserted between the resilient member and the lower flange of the rail. An enhanced support against lateral forces is provided by extending the web 1 5 outwards as at 1 5a from the projections 12 to the ends of the reinforcing members 11 from which the projections are spaced.

As has been mentioned, the reinforcing members 11 are preferably of metal and the purpose of the spaced projections 1 2 is to retain the seat against displacement in the direction of length of the rail by projecting on either side of a chair plate 7. It will be apparent that this can be achieved by other constructions.One such other construction which is particularly suitable is to form the reinforcing members 11 of angle section with an upstanding wall corresponding to the reinforcing member 11 and an outwardly projecting flange which can be cut away intermediate its length to embrace the chair plate leaving two end flanges such as indicated at 1 2a in dotted lines in the left-hand side of Figure 4 which end flanges replace the projections 1 2 and which, embedded in the synthetic rubber of the web extensions 15a, provide additional support. Such an angle section metal reinforcing member could be produced by extrusion. It will be realised that Figure 4 is a composite drawing and in practice both walls 14 would be provided with projections 12 or with flanges 12a.The synthetic rubber employed has the following general composition: parts per hundred of rubber (p.h.r.J Styrene butadiene rubber 100 High styrene resin 45-55 Activators 5-6 Antioxidant phenol condensate 1-2 Processing aids Softener resin 4-6 Carbon black 50-60 Silica 50-60 Accelerators 2 4 Vulcanising agent 2-3 In the above formulation, the high styrene resin gives the product hardness and resilience whereas the carbon black and the silica act as reinforcing fillers which reinforce but do not contribute to the resilience of the product. The total of reinforcing fillers should therefore be kept between 100 and 120 p.h.r. in order to retain sufficient resilience.

The processing aids are provided in known manner to improve the flow of the mix and the softener resin to soften the mix to the desired consistency.

A preferred formulation for the synthetic rubber is as follows:- p.h.r.

Styrene butadiene rubber 100 High styrene resin 50 Activators 5.5 Antioxidant phenol condensate 1.50 Processing aids 4.00 Softener resin 5.00 Naphthenic process oil 5.00 Carbon black 55.00 Silica (aluminium silicate) 55.00 Accelerators 3.00 Vulcanising agent 2.80 It will be appreciated that for certain conditions of operation the mix may include an antiozonant in addition to or as a replacement of at least part of the antioxidant.

The following formulation has been found to be the most preferred: p.h.r.

Styrene butadiene rubber 40.00 Oil extended styrene butadiene rubber 60.00 High styrene resin 50.00 Activators, zinc oxide/stearic acid blend 5.50 Antioxidant phenol condensate 1.50 Softener, resin 5.00 Processing aid 4.00 Naphthenic process oil 5.00 Carbon black, HAF 55.00 Silica 55.00 Accelerators N-Cyclohexyl-benzothiazole-2 sulphenamide 1.50 Mercaptobenzthiazole 1.00 Tetramethylthiuram monosulphide 0.50 Vulcanisation agent sulphur 2.80 286.80 The seat according to the invention is moulded by compression or injection moulding techniques under pressure at a temperature and for a time suitable to achieve the desired degree of vulcanising and hardness and resilience in the product.The temperature should generally be held between 150"C to 1 850C. A temperature of 1 600C for a period of 25 minutes is suitable as is a temperature of 1 800C for 5 minutes. The synthetic rubber product should have a hardness of between 90 to 950 IRHD (International Rubber Hardness Degrees).

One method of making a rail seat according to the invention is to support the reinforcing members 11 of metal on pins in the mould and to hold them thus supported by magnetic means. The mould is then closed and the mix is injected into the mould under a pressure of the order of 21,335 p.s.i (1500 Kg/cm2). After a period of 5 minutes at 1800 C, the mould is opened and the seat removed.

A test rig was set up to test a rail seat according to the invention. The rig comprised a length of rail seated in a seat according to the invention on a concrete sleeper and secured by chair plates constructed identically to the chair plates 7 described with reference to Figures 1 to 3 and with resilient retaining members of metal rod constructed and configured identically to the resilient retaining member 8 described with reference to Figures 1 to 3. The intermediate portion 8a of the member 8 had a pad of electrically insulating material bonded thereto electrically to insulate the retaining member 8 from the lower flange of the rail. The whole was inclined at 220 to the horizontal with the direction of length of the rail substantially horizontal and the plane of the base of the lower flange of the rail inclined at 220 to the horizontal.The direction of length of the sleeper was therefore inclined at 220 to the horizontal. The rail and sleeper were supported on a spring designed to give an upward thrust of 1 ton (1,016 kg). A vertical load was applied to the rail at a frequency of 5 Herz and because of the inclination of the rail the pressures and vibrations of actual use were simulated. The seat was required to pass a test in which a load of 10 tons (10,160 kg) was applied at the frequency of 5 Herz for 2 million cycles followed by an increase of the load to 15 tons (15,240 kg) at 5 Herz for 1 million cycles.

In a first test, a rail seat constructed according to the invention but using natural rubber and a hardness of 940 IRHD showed signs of chafing after 450,000 cycles at 10 tons (10,1 60 kg) and then progressively failed.

A second test with a seat made of natural rubber as before but with a hardness of 76 IRHD failed after only a few cycles as the seat lacked rigidity and hardness.

In a third test with a seat made from a mix of the most preferred formulation described above and a hardness of between 90 and 950 IRHD, the seat survived the full test without any signs of wear and without any breakdown in the electrical insulation.

In this seat according to the invention, the reinforcing members 11 were of mild steel strip with a height of 3/8 inch (9.5 mm) and a width of 1/8 inch (3.2 mm). The web 1 5 had a thickness of 3/16 inch (4.8 mm) and the reinforcing members 11 and projections 12 were covered with a minimum of 1/1 6 inch (1.6 mm) of the vulcanised synthetic rubber so that the upstanding wall 14 had a height above the top face of the web 15 of 7/16 inch (11.1 mm) and a width of 1/4 inch (6.4 mm) and the projections 12 with their covering of synthetic rubber had a dimension in the direction of length of the walls 14 of 3/8 inch (9.5 mm) and a height from the top face of web extension 1 5a of 5/16 inch (7.9 mm). The overall width of the web 1 5 between the walls 1 4 was 5-5/8 inch (142.9 mm) to suit the width of the lower flange of the rail.

As has been mentioned above, the reinforcing fillers carbon black and silica contribute to the hardness of the seat and it is preferred that the particle size of such fillers should lie in the range of 29-37 NM for the carbon black and 55-80 y for the silica.

The formulations given above relate to styrene/butadiene synthetic rubber compositions. Other types of synthetic rubber, such as polyvinylchloride (PVC)/nitrile polymer blends may also be used and a range of hardness in the range of 90 to 950 IRHD achieved. These rubbers should also contain fillers to achieve the desired hardness and resilience together with activators, accelerators and a vulcanising agent; a stabiliser for the PVC is generally required also. The filler may consist of from 60 to 75 phr of carbon black: one filler composition consists of 5-1 0 phr of carbon black having a particle size of about 21 NM and 55-65 phr of carbon black having a particle size of about 29 NM. A typical formulation is as follows: p. n. r.

60/40 PVC/Nitriie Polymer Blend 100.00 PVC Stabiliser 1.00 Activators Zinc oxide 5.00 Stearic acid 1.00 Fillers Carbon Black N110 (particle size 21 NM) 7.50 Carbon Black N330 (particle size 29 NM) 60.00 Antioxidant 2,2,4-Trimethyl-1 ,2-Dihydro-Quinoline 2.00 Accelerators Mercapto benzthiazole disulphide 3.00 Zinc dimethyldithiocarbamate 1.50 Sulphur 0.40 191.40 This formulation gives a hardness in the range 90 to 950 IRHD and adequate resiliency.

In the embodiment of the invention illustrated in Figures 9 and 10 a seat for a railway line comprises a pair of spaced elongate parallel reinforcing members 21, each having a pair of integrally formed spaced outwardly projecting portions 22, the reinforcing members being moulded into a resilient pad 23 of synthetic rubber to provide upstanding longitudinally extending parallel walls 24.

The reinforcing members 21 are preferably of metal, e.g., mild steel, and, being moulded into the pad 23, are firmly retained and electricaily insulated from the lower flange 5 of the rail which is intended to sit between the walls 24 and on the integrally formed web 25 extending between the walls. The projecting portions 22 are intended to embrace an associated chair plate 7 and operate in an identical manner to the ears 6c of the previously described known example to retain the seat against longitudinal displacement in the direction of the rail.In this embodiment the reinforcing member 21 and projections 22 can be formed from a single strip having.an intermediate portion which extends longitudinally towards two slots 27, then outwardly towards the outer wall surface of wall 24 and then longitudinally towards the ends of the wall 24 and substantially parallel to the intermediate portion.

The projecting portions being embedded in the synthetic rubber are electrically insulated from the chair plate which, when it extends between the projecting portions, is also electrically insulated from the rail by the rubber covering on the reinforcing members 21. The lower flange of the rail is resiliently supported on the web 25 which also electrically insulates the rail from the sleeper.

As described with reference to the previously known example, a resilient member 8 of metal rod is used, configured as previously described, to engage at one end in the chair plate 7 and to bear down at the other end on the lower flange of the rail. Electrical insulation is provided between each rod 8 and lower flange 5 by a packing member 26 of a hard electrically insulating moulded plastics material such as ethylene vinyl acetate (EVA). The packing member 26 is formed as a generally planar longitudinal member 26a which, in use, overlies the lower flange 5 of the rail 1. Depending from the undersurface of each packing member 26 are two spaced projections 26c which are dimensioned to be a friction fit in two corresponding slots 27 which are formed in, and open inwardly of the walls 24. The slots 27 are effectively closed, in use, by adjacent edge of flange 5.As will be seen each packing member 26 is longer than the longitudinal dimension of the chair plate 7 (that is, in the direction of the rail 1) and the projections 26c are so positioned near its ends that they engage the slots 27 on either side of its associated chair plate 7.

In the embodiment of the invention illustrated in Figures 11 and 12 a seat for a railway line comprises a pair of spaced elongate parallel reinforcing members 31, each having a pair of integrally formed spaced outwardly projecting portions 32, the reinforcing members being moulded into a resilient pad 33 of synthetic rubber to provide upstanding longitudinally extending parallel walls 34 generally similar to the embodiment described with reference to Figures 4 to 8. The reinforcing members 31 are preferably of metal, e.g., mild steel, and, being moulded into the pad 33, are firmly retained and electrically insulated from the lower flange of the rail which is intended to sit between the wails 34 and on the integrally formed web 35 extending between the walls.The projecting wall portions 32 are intended to embrace an associated chair plate 7 and operate in an identical manner to the ears 6c of the previously described known example to retain the seat against longitudinal displacement in the direction of the rail. The projecting portions being embedded in the synthetic rubber are electrically insulated from the chair plate which, when it extends between the projecting portions, is also electrically insulated from the rail by the rubber covering on the reinforcing members 31. The lower flange of the rail is resiliently supported on the web 35 which also electrically insulates the rail from the sleeper.

As described with reference to the previously known example, a resilient member 8 of metal rod is used, configured as previously described, to engage at one end in the chair plate 7 and to bear down at the other end on the lower flange of the rail. Electrical insulation is provided between each rod 8 and flange 5 by a packing member 36 of a hard electrically insulating moulded plastics material such as ethylene vinyl acetate (EVA). The packing member 26 is formed as a generally planar longitudinal member 36a which, in use, overlies the lower flange 5 of the rail 1. Depending from the undersurface of each packing member 36 are two spaced projections 36c which are dimensioned to be a friction fit in two corresponding holes 37 formed in the walls 24. In this embodiment the projections 36 and holes 37 are circular in cross section. As will be seen each packing member 36 is longer than the longitudinal dimension of the chair plate 7 (that is in the direction of the rail 1) and the projections 36c are so positioned near its ends that they engage the holes 37 on either side of its associated chair plate 7.

The seats described in relation to Figures 9, 10, and 11, 1 2, can be made in a similar manner and from the materials discussed in relation to the embodiment described in relation to Figures 4 to 8.

Claims (20)

Claims

1. A seat for a railway line comprising a pair of spaced longitudinally extending parallel reinforcing members each having a pair of spaced outwardly extending portions, the reinforcing members being moulded into a resilient pad of synthetic rubber to provide upstanding walls arranged to receive the lower flange of an I-section railway line therebetween electrically insulated from the reinforcing members moulded into said walls with an integrally moulded web extending between said walls and below such railway line to seat the line and to further provide outwardly projection portions arranged to embrace a chair plate in electrically insulated relationship thereto to retain the seat in position.

2. A seat according to Claim 1 in which the reinforcing members are metal rods or bars with the spaced outwardly projecting portions integrally formed therewith.

3. A seat according to Claim 1 or 2 in which the reinforcing members are formed as angle section members with an upstanding wall part and an outwardly extending flange which is a cut-away intermediate the length thereof to leave a gap therein to receive the chair plate and provide the two spaced outwardly projecting portions.

4. A seat according to Claim 1, 2 or 3 in which the synthetic rubber is composed of as parts by weight per hundred parts of synthetic rubber 100 parts of styrene butadiene rubber, 45-55 parts of high styrene resin, 5 to 6 parts of activators, 1 to 2 parts of antioxidant phenol condensate, 3-5 parts of processing aids, 4-6 parts of a softener resin, 4 to 6 parts of naphthenic process oil, 100 to 120 parts of a reinforcing filler consisting of silica and carbon black, 4 parts of accelerators and 2-3 parts of vulcanising agent.

5. A seat according to Claim 4 in which the styrene butadiene rubber includes oil extended styrene butadiene rubber, the activators comprise a blend of zinc oxide and stearic acid, the accelerators are comprised of N-cyclo-hexyl-benzothiazole-2 sulphenamide, mercaptobenzthiazole and tetramethylthiuram monosulphide and the vulcanising agent is sulphur.

6. A seat according to Claim 1,2 or 3 in which the synthetic rubber is composed in parts by weight per 100 parts of rubber, of 100 parts of a 60% PVC/40% nitrile polymer blend and from 60 to 75 parts of a filler consisting of carbon black, together with a PVC stabiliser, activators, accelerators and a vulcanising agent.

7. A seat according to Claim 6, in which the synthetic rubber contains as the filler from 5 to 10 parts of carbon black having a particle size of about 21 NM and from 55 to 65 parts of carbon black having a particle size of about 29 NM.

8. A seat according to Claim 1 or 2 or any one of Claims 4 to 7 as dependent upon Claim 1 or 2, wherein each wall member has two inwardly opening slots formed therein and positioned so that, in use, the slots are spaced from and on either side of an associated chair plate, and further comprising a packing member for insulating a railway line from the associated chair plate, the packing member having a surface arranged partially to overlie a part of a lower flange of the railway line and two spaced projections projecting from said surface and positioned and dimensioned to fit in said slots.

9. A seat according to Claim 1 or 2 or any one of Claims 4 to 7 as dependent upon Claims 1 or 2, wherein each wall member has two downwardly extending holes formed in the upper surface thereof and positioned so that, in use, the holes are spaced from and on either side of an associated chair plate, and further comprising a packing member for insulating a railway line from the associated chair plate, the packing member having a surface arranged partially to overlie a part of a lower flange of the railway line and two spaced projections projecting from said surface and positioned and dimensioned to fit in said holes.

10. A seat according to Claim 8 or 9, wherein the packing member is of a hard plastics material.

11. A seat for a railway line constructed substantially as herein described with reference to Figures 4 to 8 of the accompanying drawings.

1 2. A seat for a railway line constructed substantially as herein described with reference to Figures 9 and 10 or Figures 11 and 12 of the accompanying drawings.

13. A railway line of I-section seated on a sleeper by means of a seat according to any one of the preceding claims with the lower flange seated on the web between the upstanding walls, chair plates disposed one on either side of the line secured to the sleeper and extending between the spaced outwardly projecting portions to retain the seat and a separate resilient retaining member engaged in each chair plate and bearing through an electrically insulating layer or packing member, on the lower flange of the rail.

14. A method of producing a rail seat according to Claim 1,8 or 9, which comprises disposing two elongate reinforcing members in a mould to extend in longitudinally spaced parallel relationship with the spaced projections extending outwardly, filling the mould with a synthetic rubber which extends about and between the reinforcing members and vulcanising the rubber.

1 5. A method according to Claim 14 in which the reinforcing members are metal members supported in the mould on spaced pins and magnetically retained in position during the moulding operation.

1 6. A method according to Claim 14 or 1 5 in which the synthetic rubber is composed of as parts by weight per hundred parts of synthetic rubber, 100 parts of styrene butadiene rubber, 45-55 parts of high styrene resin, 5 to 6 parts of activators, 1 to 2 parts of antioxidant phenol condensate, 3-5 parts of processing aids, 4-6 parts of a softener resin, 4 to 6 parts of naphthenic process oil, 100 to 1 20 parts of a reinforcing filler consisting of silica and carbon black, 2 parts of accelerators and 2-3 parts of vulcanising agent.

1 7. A method according to Claim 1 6 in which the styrene butadiene rubber includes oil extended styrene butadiene rubber, the activators comprise a blend of zinc oxide and stearic acid, the accelerators are comprised of N-cyclohexyl-benzothiazole-2 sulphenamide, mercaptobenzthiazole and tetramethylthiuram monosulphide and the vulcanising agent is sulphur.

1 8. A method according to Claim 14 or 15, in which the synthetic rubber is composed, in parts by weight per 100 parts of rubber, of 100 parts of a 60% PVC/40% nitrile polymer blend and from 60 to 75 parts of a filler consisting of carbon black, together with a PVC stabiliser, activators, accelerators and a vulcanising agent.

1 9. A method according to Claim 1 8, in which the synthetic rubber contains as the filler from 5 to 10 parts of carbon black having a particle size of about 21 NM and from 55 to 65 parts of carbon black having a particle size of about 29 NM.

20. A method according to Claim 14 substantially as herein described.