GB1564650A

GB1564650A - Rubber pads for railjoints

Info

Publication number: GB1564650A
Application number: GB5385977A
Authority: GB
Original assignee: Kawasaki Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1977-01-14
Filing date: 1977-12-23
Publication date: 1980-04-10
Also published as: BR7708647A; DE2753005B2; FR2377478B1; JPS5550521B2; DE2753005A1; JPS5389104A; FR2377478A1

Description

(54) RUBBER PADS FOR RAIL JOINTS (71) We, KAWASAKI STEEL CORPORATION of, No. 1-28, 1-chome, Kitahonmachi-Dori, Fukiai-Ku, Kobe City, Japan, a company organized according to the laws of Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to rubber pads for rail joints particularly for use in heavy duty railways.

With such railways, it is conventional to arrange rubber pads under the lower flanges of the rails all the way along the length of the rails for elastically supporting loads being moved along the rails. Such railways are commonly found laid along beams, cross-beams or girders or buildings such as factories. They may be used, for example, for guiding overhead cranes.

The rubber pads which have been used have generally been made of moulded rubber or equivalent materials such as elastic synthetic resins. fibre-reinforced composite materials or laminated materials. The term "rubber pad" as used herein is intended to mean all the above mentioned materials.

Recently it has been found that, as a result of increasing plant size. heavy duty railways in such industrial plants as steel works have had to support an increasing load. It has also been found that the passage of a heavy load over a joint between rails may cause a shock which may adversely affect not only the equipment moving over the rails but also the rails themselves.

According to one aspect of the present invention, there is provided an elongate rubber pad for location beneath a joint formed between adjacent railway rails, which pad is formed on at least one surface with a plurality of grooves extending transverse to its length, in which pad the depths of said grooves decrease from either end of the pad along the length of the pad towards the middle thereof such that the spring constant (as hereinafter defined) of the pad reaches a maximum value substantially in the middle of the pad.

According to another aspect of the present invention, there is provided an assembly comprising two railway rails joined together to form a single length of rail and an elongate rubber pad located beneath said rails substantially symmetrically about the joint therebetween, which pad is formed on at least one surface with a plurality of grooves extending transverse to its length, and in which pad the depth of said grooves decreases from either end of the pad along the length of the pad towards the middle thereof such that the spring constant of the pad reaches a maximum value substantially under said join.

Preferably, the configuration of grooves on the pad is such that ends of the pad have a spring constant which is similar to that of pads located under intermediate portions of the rails.

Rubber pads according to the invention are particularly suitable for use with rails which are subjected to relatively high loads such as rails for overhead cranes, rails laid on concrete or steel plate floors in factory yards and rails running across iron bridges.

Preferably the pad is formed with said grooves on both its upper and lower surfaces, grooves on the lower surface of the pad being formed in locations such that they lie between grooves on the upper surface of the pad.

As a modification, the pad may be formed by two pad sections, each of which is formed on at least one surface with a plurality of grooves extending transverse to its length, in which pad sections the depth of the grooves decreases along the length of each pad section from one end thereof to the other, the pad sections being adapted to be joined together at respective ends formed with shallow grooves.

When a heavy load passes across the join between two rails under which is located a pad according to the invention, the depression of the two rails at the joint may be kept at the same level as that of intermediate portions of the rails. It is thus possible to prevent the occurrence of shocks at such a joint.

Figure 2a is a plan view of the tie pad according to the invention; Figure 2b is an elevation of the tie pad shown in Figure 2a; Figure 3 is an enlarged sectional view of the portion A in Figure 2b; Figure 4 is an enlarged sectional view of the portion B in Figure 2b; and Figure 5 is a graph showing the distribution of depths of the grooves of the tie pad according to the invention.

The distribution of spring constants along a rubber pad according to the invention may be calculated in the following manner.

Let us assume that when a beam having a uniform section and an infinite length is laid on an elastic floor, and is deformed by a load P1 the reaction force is proportional to the deformation and has a cabman's distribution. The reaction R per unit length of the beam may be expressed by R = ky, where y is the deformation and k is the modulus of the foundation.

Accordingly, the differential equation of the elastic curve is EI Y4 = -ky dx4 and its general solution is as follows where ss4 represents k 4EI and A, B, C and D are integration constants.

y = essX(Acosssx +Bsinssx) + e-ssX(Ccosssx +Dsinssx) If the origin of the co-ordinates is the loading point, the reaction is symmetrical with respect to the loading point, so that it is sufficient to consider only the reaction on one side of the loading point. It is assumed that deformation and bending moment are zero at an infinite distance from the loading point. As the positive value of x increases, the function ssx also increases, so that A must equal B (A = B) in order to fulfil the above assumption at x = Co. Accordingly, the equation of the elastic curve on the right side of the loading point is given by the following.

y = e-BX(Ccospx + Dsinpx) As the above elastic curve is symmetrical with respect to the y axis, the deformation at the loading point or origin is zero. This is indicated by

Therefore, C = D Hence, y = Ce-PX(cospx + sinpx) This equation may be differentiated three times to obtain tf = 4C'33ecos'3x Moreover, the shearing force at x = 0 on the right side is P 2 so that it is indicated by EIS = - P Therefore,

Hence, C = -P/8ss3EI Thus, the equation of the elastic curve caused by the load P is as follows.

P y = 8ss EI e-ssx(cosssx + sinssx) Accordingly, the deformation y0 at the loading point (x = o) is given by P y0 = 8ss EI ...... ....... (1) Now, let us assume that a long beam laid on the same elastic floor is subjected to a load at one end to produce a resisting moment m about the loading point. The integration constants A and B are equal to zero as above (A = B = 0) and the equation of the elastic curve is the same as the above.

y = e-ssx(Ccosssx + DSINssX( This equation may be differentiated twice giving

and again, giving

= -P EI P-ssm Therefore, C = 2'33EI , D = -2ss3EI e-ssx Hence, y = 2'33EI [Pcosssx + '3m(sin'3x-cos'3x)j Substituting x = 0 in this equation gives the deformation y'0 at the loaded point.

P-ssm ... . (2) y'0 = 2ss EI Moreover, when the resisting moment is zero. the deformation y"0 is as follows.

P y"0 = -2γ EI.... . (3) As may be seen from the above description, the depression of a rail between its two ends is given by equation (1), the depression of one end of a rail to be jointed with the resisting moment of connecting plates is given by equation (2) and the depression of a rail to be jointed without connecting plates is given by equation (3).

Now, let us consider, as an example, a 75 kg rail (E = 2,100 ton/cm2, I = 2,030 cm4) laid elastically at its intermediate portion on a rubber pad having a width 13.8 cm and a spring constant K = 2 ton/cm2/cm subjected to a load 50 ton of a wheel.

k k = bK = 13.8 x 2 = 27.6 ton/cm/cm and ss4 = 4EI , hence k ~ 27.6 = 161 86x10- and 4EI 4x2,100x2,030 therefore, ss # 0.036-cm.

Substituting these values in the equation (1) gives the depression at the intermediate portion.

y - P 50 = 0.031 cm 8'33E1 8x0.036 x2,100x2,030 It is assumed that the allowable resisting moment of the connecting plates is m = 2x33 cm3x2 ton/cm2 = 132 ton-cm. In order to make the depression of the end of the rail with the connecting plates equal to the depression of the rail at its intermediate portions, the deformation from the equation (2) is made equal to that given by the equation (1).

P- 'm#j-'X132= y 8(3EI 2ss' x2,100x2,030 = 0.031 cm Accordingly, ss' +0.000499ss'-0,000189 = 0 and ss' # 0.055-cm.

Moreover, since pi4 = k' = K'x13.8 = 0.0554 4EI 4x2,100x2,030 K' = 11 ton/cm2/cm.

When the connecting plates are not used, from making y(} = y"() and P P 8ss EI = 2γ EI in the same manner, it is found that y3 = 4ss = 4 X 0.0363 = 0.000186 andy = 0.057-cm and hence K" = 13 ton/cm2/cm since 0.057j = K"x13.8 4x2,100x2,030 As may be seen from the above calculation, uniform deformation at the middle and at the ends of a rail may be obtained to allow smooth travelling of wheels by arranging below the joint of the rails rubber pads having a spring constant of 5.5 times (k'/K = 11 . 2 = 5.5) or 6.5 times (K"/K = 13 # 2 = 6.5) the normal value for pads under intermediate portions of the rails, depending on whether or not connecting plates are being used.

The depression h of a wheel at a clearance between the rails is calculated on the assumption that the radius of the wheel r is 40 cm and the clearance t is 0.6 cm.

If the weight of the wheel is w, the variation in potential energy is AE = Wh = 0.001125 Wkgm. The variation of speed #V cm/sec resulting from AE is given by AV2 = 2h = 2 x 0.001125 = 0.00225 from Wh = 1W#V.

2 This variation in speed is, for example, AV = 0.0475 cm/sec = 0.002 kgmhr/ joint which is negligible in effect and considerably less than that resulting from a shock caused by depression.

It is clearly evident from the above description that it is advantageous to provide a rubber pad having at its center immediately below the joint of the rails a spring constant 5.5 to 6.5 times of that of the rubber pad at the intermediate portion of the rail.

The spring constant kp is defined as ALx5 kp = E, h where AL : Pressure exterted area cm2 h : Thickness of rubber cm E : Modulus of elasticity kg/cm2 f : Elasticity correction factor.

The correction factor is given by Eap f = E , where Eap is the virtual modulus of elasticity and f represents 1.33 + 1.1S2, where S is the form factor and is given by AL = AF' AF being the free surface area cm2.

The spring constant of a grooved rubber pad consists of the initial spring constant (before the grooves are collapsed) and the final spring constant (after the grooves are collapsed).

As an example, a calculation will be effected based on rubber pads formed with grooves having a width of 4.5 mm, a depth d .0046 1.0 mm and d = 1.9 mm respectively and a pitch of 40 mm.

First, in order to obtain the initial spring constant Kp, with d = 1.9 mm, the width b of the rubber pad is assumed to be 14 cm for simplicity, although b is actually 13.8 cm.

AL = (a-0.9)b = (4-0.9)14 = 43.4 cm2 AF = 14(2d+ 0.45)2+2{(4 x 0.6)(0.45 x2d)} 14(0.38+0.45)2+2((4x0.6)-(0.45x2x0. 19)) = 23.24+4.45 = 27.69 AL = at S2 = 2.455 f = 1.33+ 1.1S2=4.03 kpi = AL.f E h = 43.4x4.03 . 72 0.6 21,000 kg/cm (480 kg/cm . . per 1 cm2) In order to obtain the final spring constant Kp2 with d = 1.9 mm, the deformation when the groove is about to be collapsed is indicated by 5.

43.45 = 2(0.45x0.19)14 6 = 0.055 cm (at this moment the groove is filled up.) AL = 4x14 = 56 cm2 AF = (0.6-0.055)4x2 = 4.36 AL 56 - = AF = 4.36 = 12.84, 82 = 165 f = 1.33+1.1S2=183 56x183x72 kp2 = 0.545 = 1,354,000 kg/cm (24,200 kg/cm .... per 1 cm2) The initial spring constant kp3 with d = 1.0 mm may be calculated in the same manner.

kp3 = 27,600 kg/cm (640 kg/cm .... per 1 cm2) The final spring contant K4 with d = 1.0 mm is = # 1,179,000 kg/cm (21,000 kg/cm .... per 1 cm2) For a better understanding of the invention, and to show how it may be carried into effect, reference will be made, by way of example, to the accompanying drawings, in which: Figure 1 is a graph showing the relationship between load and deformation of a tie pad according to the invention laid underneath a join between two rails, and of a tie pad under the intermediate portion of a rail.

Figure 2a is a schematic plan view of one form of tie pad according to the invention; Figure 2b is a schematic elevation of the tie pad shown in Figure 2a; Figure 3 shows a vertical cross-section of a tie pad according to the invention at the position marked A on Figure 2b; Figure 4 shows a vertical section through a tie pad according to the invention at the position marked B on Figure 2b; and Figure 5 is a graph showing the distribution of groove depths along a tie pad according to the invention.

Figure 1 is a graph which shows the spring constant Kpl to Kp4 in relation to loads and deformations. As the stress = 100 kg/cm- is generally used at intermediate portions of the rails, deformations are in the order of 0.58mm. With the spring constant K4 the load required to produce the same deformation is in the order of 600kg which is about 6 times that of the intermediate portion. Accordingly, it is desirable for that portion of the pad which is under a join to have a spring constant which is in the range from 5.5 to 6.5 times as big as the spring constant of the same pad at intermediate portions of the rail. This multiplication factor may be calculated from the flexural rigidity.

Figures 2a and 2b show a tie pad 1 having a gap of 6mm, a width of 138mm and a length of 1020mm for arrangement underneath the intermediate portion of a rail on which an overhead crane for a 73kg load is to run. The pad 1 is formed on its upper and lower surfaces with transverse grooves 2 having a depth of 1.9mm and a length of 4.5mm at intervals of 40mm along the pad. At the end of the pad, there are provided shaped joints 3.

As may be seen from Figure 2a, grooves on the lower surface of the pad (which are shown by dotted lines) occur in between grooves on the upper surface of the pad (which are shown by unbroken lines). Figure 2a also shows a tie pad 4 according to the invention provided at its ends with shaped joints 5 for connecting it to pads such as 1. The pad 4 is formed with a plurality of transverse grooves 2' which have varying depth along the length of the pad. In fact, the depth of the groove 2' decreases progressively from one end of the pad towards the centre of the pad and then increases progressively towards the other end of the pad. The grooves at each end of the pad 4 (position J, Figure 2B) have a depth of approximately imam.

Figure 2B shows a side view of an arrangement comprising two railway rails 7 and 7' which abut against each other position J where they are connected by joint plates (not shown). An elongate rubber pad according to the present invention is arranged beneath the two rails with its centre substantially at the position J. It is, of course, possible for the pad to be modified so that it is in effect two pads which are joined to each other at the position J.

Figure 3 shows a cross-section through the pad at the position J. Figure 4 shows a cross-section through the pad at position B, the joint between the pad according to the invention and the conventional pad being shown. Figure 5 shows the distribution of groove depth along a pad according to the present invention.

Elongate rubber pads according to the invention are particularly suitable for use under rail joints in heavy duty railways to be used for movement of overhead cranes - the reduction in the severity of shocks as the crane passes over a join between two rails reduces the possibility of rivets in the crane being loosened. In addition, the rubber pads may be used in conjunction with railays which are directly fastened to a concrete floor and this reduces the frequency with which it is necessary to mend the concrete underneath the rail joints.

WHAT WE CLAIM IS: 1. An elongate rubber pad for location beneath a join formed between adjacent railway rails, which pad is formed on at least one surface with a plurality of grooves extending transverse to its length. in which pads the depth of said grooves decreases from either end of the pad along the length of the pad towards the middle thereof such that the spring constant (as hereinbefore defined) of the pad reaches a maximum value substantially in the middle of the pad.

2. A pad as claimed in claim 1, wherein the pad is formed with said grooves on both its upper and lower surfaces grooves on the lower surface of the pad being formed in locations such that they lie between grooves on the upper surface of the pad.

3. A modification of the pad claimed in claim 1, wherein the pad is formed by two pad sectins, each of which is formed on at least one surface with a plurality of grooves extending transverse to its length, wherein the depth of said grooves decreases along the length of each pad section from one end thereof to the other, said pad sections being adapted to be joined together at respective ends formed with shallow grooves.

4. An elongate rubber pad for location beneath a join formed between adjacent railway rails, substantially as hereinbefore described with reference to the accompanying drawings.

5. An assembly comprising two railway rails joined together to form a single length of rail and an elongate rubber pad located beneath said rails substantially symmetricaly about the join therebetween. which pad is formed on at least one surface with a plurality of grooves extending transverse to its length and in which pad the depth of the grooves decreases from either end of the pad along the length of the pad towards the middle thereof, such that the spring constant of the pad reaches a maximum value substantially under said join.

6. An assembly as claimed in claim 5. wherein the pad is formed with said grooves on both its upper and lower surfaces, grooves on the lower surface of the pad being formed in locations such that they lie between grooves on the upper surface of the pad.

7. A modification of the assembly claimed in claim 5, wherein the elongate rubber pad is formed by two pad sections each of which is formed on at least one surface with a plurality of grooves extending transverse to its length, wherein the depths of said grooves decrease

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. required to produce the same deformation is in the order of 600kg which is about 6 times that of the intermediate portion. Accordingly, it is desirable for that portion of the pad which is under a join to have a spring constant which is in the range from 5.5 to 6.5 times as big as the spring constant of the same pad at intermediate portions of the rail. This multiplication factor may be calculated from the flexural rigidity. Figures 2a and 2b show a tie pad 1 having a gap of 6mm, a width of 138mm and a length of 1020mm for arrangement underneath the intermediate portion of a rail on which an overhead crane for a 73kg load is to run. The pad 1 is formed on its upper and lower surfaces with transverse grooves 2 having a depth of 1.9mm and a length of 4.5mm at intervals of 40mm along the pad. At the end of the pad, there are provided shaped joints 3. As may be seen from Figure 2a, grooves on the lower surface of the pad (which are shown by dotted lines) occur in between grooves on the upper surface of the pad (which are shown by unbroken lines). Figure 2a also shows a tie pad 4 according to the invention provided at its ends with shaped joints 5 for connecting it to pads such as 1. The pad 4 is formed with a plurality of transverse grooves 2' which have varying depth along the length of the pad. In fact, the depth of the groove 2' decreases progressively from one end of the pad towards the centre of the pad and then increases progressively towards the other end of the pad. The grooves at each end of the pad 4 (position J, Figure 2B) have a depth of approximately imam. Figure 2B shows a side view of an arrangement comprising two railway rails 7 and 7' which abut against each other position J where they are connected by joint plates (not shown). An elongate rubber pad according to the present invention is arranged beneath the two rails with its centre substantially at the position J. It is, of course, possible for the pad to be modified so that it is in effect two pads which are joined to each other at the position J. Figure 3 shows a cross-section through the pad at the position J. Figure 4 shows a cross-section through the pad at position B, the joint between the pad according to the invention and the conventional pad being shown. Figure 5 shows the distribution of groove depth along a pad according to the present invention. Elongate rubber pads according to the invention are particularly suitable for use under rail joints in heavy duty railways to be used for movement of overhead cranes - the reduction in the severity of shocks as the crane passes over a join between two rails reduces the possibility of rivets in the crane being loosened. In addition, the rubber pads may be used in conjunction with railays which are directly fastened to a concrete floor and this reduces the frequency with which it is necessary to mend the concrete underneath the rail joints. WHAT WE CLAIM IS:

1. An elongate rubber pad for location beneath a join formed between adjacent railway rails, which pad is formed on at least one surface with a plurality of grooves extending transverse to its length. in which pads the depth of said grooves decreases from either end of the pad along the length of the pad towards the middle thereof such that the spring constant (as hereinbefore defined) of the pad reaches a maximum value substantially in the middle of the pad.

along the length of each pad section from one end thereof to the other, said pad sections being adapted to be joined together at respective ends formed with shallow grooves.

8. An assembly, substantially as hereinbefore described with reference to the accompanying drawings.