MODERN TURNOUTS FOR INTRODUCTION OF HIGH SPEED ON THE EXISTING TRACK

A.K.Singhal, Executive Director/Track-II/RDSO A.K.Mishra, Director/Track-III/RDSO

SynopsisTurnouts are considered to be weak link in Railway track. Any effort to upgrade

the existing track for high speed must include improvements in various components of a turnout. Improvement in the turnout designs in past using curved switches, cast manganese steel (CMS) crossings and pre-stressed concrete turnout sleepers has served Indian Railways(IR) well to cater for the needs of increasing traffic. Further improvements have been made in turnout design by development of design of thick web switches and weldable CMS crossings to cater for the needs of increase in axle load and increase in speed in ever increasing traffic on IR. This paper deals with these improvements in the design of switch and crossing facilitating continuation of long welded rail(LWR) through turnouts which will help IR in implementing high speed ( upto 200 Kmph) on the existing track.

1. INTRODUCTION

For past few years, there has been a conscious effort for introduction of high speed in Indian Railways. With the increase in speed on highways and introduction of more and more airlines, there is a need to increase the speed of trains to remain competitive in transport business. In addition, the high speed trains are environment friendly and consume lesser amount of natural resources in comparison to roadways and airways.

The turnouts remain a weak link in track due to transfer of wheel from one rail to the other near switch and negotiation of gap at crossing. These two locations offer a resistance to continuous movement of the train and hence subjected to stresses far in excess of continuous track. At present, over-riding switches and cast manganese steel (CMS) crossings on fan-shaped pre-stressed concrete (PSC) sleeper are used in turnouts. Over-riding tongue rails are made up of standard rail section with machining at the bottom of the rail for overriding on the foot of stock rail. Due to planning at head and foot, the cross section of such tongue rails becomes smaller and they depend on stock rail for withstanding vertical and lateral forces. There are two fish plated joints in such switches which cannot be welded. Another location of concern is CMS crossing where gap near nose of crossing is negotiated by rail wheels. These CMS Crossings are to be laid with gapless joints at toe and heel. But, in actual practice, these joints develop into full fledged fish plated joints due to various factors. Therefore, there are six fish plated joints left on one turnout out of which three lies on the mainline. As the fish plated joints are difficult to maintain properly over PSC sleepers, these locations remain the weakest link requiring regular maintenance. As the train has to move over a series of turnouts in station limit, the running invariably deteriorates which is reflected in the lower TGI values in station limit. The problem gets compounded because of the difficulty in maintenance of station limit tracks by machines for periodic packing, overhauling and deep screening.

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Track is required to be laid and maintained with stricter tolerance in case of high speed and any gap in track is not desirable. The same is very much applicable to the track at turnouts too. In view of above, the turnout should not have any fish plated joints. In addition, it should facilitate continuation of long welded rail (LWR) for eliminating fish plated joints beyond the turnouts in station limit. The turnout using thick web switch and weldable CMS crossing fulfils above requirement for high speed track and the design of such turnouts has recently been developed by IR. 2. TECHNICAL SUPERIORITY OF THICK WEB SWITCHES

Thick web switches (TWS) are being used world over due to their technical superiority over Over-riding switches (ORS), some of which are mentioned hereunder:

a) World over, cross section of the tongue rail in modern design is asymmetrical section that is lower than the standard rail profile. This has the advantage that very little machining of the foot of tongue rail is required. There have been incidences of fracture of tongue rails in ORS in which the crack has initiated from the edge of under-cutting portion of foot of tongue rail. No such failure is possible in TWS making it safer compared to ORS.

b) Tongue rail of TWS is having asymmetrical section, the moment of inertia (Iyy) of which is higher compared to the tongue rail made of standard symmetrical rail for ORS. This results in high lateral rigidity in tongue rail ensuring minimum distortion under lateral loads. Due to above advantage, TWS require lesser maintenance and have more service life.

c) The lower height of asymmetric tongue rail allows the use of elastic fastening system for holding stock rail on both sides which is necessary for modern turnout. In case of ORS, the stock rail is not fastened on tongue rail side causing disturbance of track geometry and track parameters frequently requiring regular maintenance.

d) In case of ORS, holes are required in the web of stock rail for fixing the slide chair. Such holes are not required in stock rail of TWS eliminating the likelihood of bolt hole failure resulting in enhanced safety on such turnouts.

e) The top of tongue rail is level with stock rail in TWS, whereas in ORS twist upto 6mm is inbuilt in design. Therefore, if TWS is used, twist in track will be eliminated which is an important consideration in high speed.

f) The tip of tongue rail is housed in the recess under the head of stock rail which is formed by machining of the stock rail head. This reduces shock at entry and wear at switch tip. This is a pre-requisite for high speed track as there must not be any obstruction in the path of wheel.

g) The TWS is provided with 160 mm throw with spring setting device (SSD) which ensures proper housing of tongue rail and adequate flange way clearance up to junction of rail heads (JOH). SSD acts as an alternative to double pull

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arrangement for achieving full housing/butting of tongue rail with stock rail up to JOH. The provision of SSD obviates any likelihood of tight gauge in switch portion in floating condition and hence provides obstruction free path to high speed rail wheels.

h) TWS are provided with Clamp point lock which provides direct locking of the switch rail with the stock rail for the complete effectiveness of the locking which is absolutely necessary for high speed.

Due to the abovementioned technical superiority of TWS , TWS is a must for high speed routes.

Thick Web Switch

2.1 FIELD PERFORMANCE OF THICK WEB SWITCHES

400 sets of thick web switches(TWS) using asymmetric tongue rail section ZU-1-60 on PSC sleepers were laid in track in CR, ER, SER, NR & WR from the year 2000 onwards as per firms’ design with K-type/ERC fastening with spring setting device(SSD). Recently, RDSO collected details of field performance of TWS and over-riding switches (ORS) from all concerned zonal railways to assess the comparative advantages of TWS. The details of 219 sets of TWS were received along with the detail of ORS. The following inferences are drawn from the details received from above zonal railways:

a) Some of the thick Web Switches have already lived a life of more than 500 GMT and are still in service. As per field report, on an average TWS shall have service life more than double the life of ORS.

b) Requirement of reconditioning of tongue rail is very less in TWS compared to that in ORS.ORS has problem of wear of tongue rail and hence reconditioning is required much more frequently than TWS.

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c) Housing is very good in TWS and there is no compatibility issue with S&T department whereas there is problem of housing in ORS.

d) TWS being sturdier requires lesser maintenance inputs due to lesser disturbance in track geometry.

The above inferences are very much relevant for high speed track for safety, reliability, riding comfort and maintainability and reestablish the technical superiority of thick web switches. These switches, already being used world over, are ideal for high speed track.

2.2 DEVELOPMENT OF DESIGN AND DRAWING

RDSO has already developed design and drawings for 1:16 (Drg. No. RDSO/T-7075 ), 1:12 (Drg. No. RDSO/T-6154) and 1:8.5 turnouts (Drg. No. RDSO/T-6279) with ZU-1-60 thick web switch. These thick web switches have been designed with 160 mm throw along with spring setting device (SSD) with the provision of point clamp lock at the location of leading stretcher bar. The provision of SSD ensures proper housing of tongue rail and adequate flange way clearance up to junction of rail heads (JOH) whereas point clamp lock ensures direct locking of the switch rail with the stock rail for the complete effectiveness of the locking. In above RDSO design, elastic fastening has been provided on the inside foot of stock rail using ERC, leaf spring & wedge arrangement. Leaf spring and wedge arrangement holding the stock rail on tongue rail side can be seen in the photograph below. This system is useful in continuing LWR through turnouts.

RDSO has also developed specification for thick web switches which is an improvement over the specification (IRS: T-10-2000) for over-riding switch. Switches made from asymmetric thick web rails shall be machined by CNC machine to achieve correct profile and prescribed roughness factor on all machined surfaces. In addition, specification for end forging of asymmetric thick web tongue rail has also been

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developed according to which the minimum length of forged section with desired rail profile shall be 500 mm and transition length of forging shall be in the range of 150 mm to 200 mm. The minimum length of 500 mm for desired rail profile has been incorporated to accommodate 1 metre long fish plate. Bhilai Steel Plant of Steel Authority of India Limited has already installed required plant and machinery for the production of end forged ZU-1-60 thick web rail.

These thick web switches of RDSO design are being manufactured by Indian switch manufacturers and have been laid in track by RVNL. Hence, the thick web switches of RDSO design can be manufactured indigenously.

3. TECHNICAL SUPERIORITY OF WELDABLE CMS CROSSING

As mentioned in preceding paragraph , the present design of CMS crossing provides for gapless machined joints at toe and heel but ,in actual practice, gapless joints are not possible due to following reasons :

a) Tolerances in the size of fish plate bolt hole, bolt, rail hole and the position of hole from the end of CMS Crossing.

b) Difference in vertical wear of top surface of CMS crossing and rail leading to impact of wheel tread.

c) Fish plate bolt hole is perpendicular to fish plate whereas bolt hole in CMS crossing is perpendicular to the centre line of crossing.

The joints at toe and heel are subjected to impact force due to hammering action of rail wheel which leads to displacement/crushing of grooved rubber sole plate (GRSP), opening of liners and elastic rail clips (ERCs), formation of grooves at the top of PSC sleeper and rounding of ballast underneath. Due to attrition and crushing, ballast becomes caked and elasticity of medium reduces considerably. All these factors lead to a situation where the impact force is not dissipated properly from rail to the formation below causing excessive stress in the CMS crossing also.

Design length of CMS crossing is less; therefore, joints are very near to nose of crossing. Disturbances created by joints to the moving wheel are not dampened in small length, causing large impact forces at the nose of CMS crossing. Due to this reason, problems like chipping of nose and loosening of fittings are felt in the field.

CMS crossing has different metallurgy in comparison to rail; therefore, it cannot be welded with adjacent rails by conventional welding methods. In foreign countries welding of CMS crossing with normal rail is being done by using intermediate piece. This piece has such metallurgical properties so that it can be welded with normal rail as well as CMS crossing. Intermediate piece is normally made of nickel-chrome steel [17-19% Cr & 9-12% Ni] and is manufactured either cast or rolled to the shape of rail having dimensions slightly more than normal rail. The same is first welded with normal rail by flash butt welding method. This piece is then cut to length of 20-30 mm and welded with CMS crossing by same method. Chiseling, grinding and post heating are required to be done after welding as per requirement which depend upon material properties of intermediate piece.

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Hence, in case of weldable CMS crossing, welded joint is provided between the crossing and the adjoining rails. As a result, fish plated joints are removed at the approach of the crossing. The hammering action of rail wheels is eliminated leading to riding comfort and enhanced life of track components. This further helps in reducing the maintenance efforts. It is also possible to carry out LWR through points and crossings if joints in the vicinity of CMS crossing are welded.

IR imported 20 turnouts in the year 1991 in which Weldable CMS crossings were supplied. These turnouts were laid in Allahabad division of NCR and the performance was reported to be satisfactory in terms of maintenance efforts, riding quality and wear.

3.1 DEVELOPMENT OF DESIGN AND DRAWING

Present geometrical design of CMS crossing of IR cannot be welded with rail as end geometry do not match. In view of above, RDSO has developed design and drawing of Weldable CMS crossings on existing PSC sleepers for 1 in 12 (Drg. No. RDSO/T-6412) and 1 in 8½ (Drg. No. RDSO/T-6441) turnouts by increasing the length at toe and heel ends and matching the profile of normal rail so that this CMS crossing can be welded with intermediate piece. During design, care has been taken to eliminate sharp radius of curves and to ensure proper matching of rail foot, web and head.

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In the design one more feature has been added. Vertical stiffeners have been provided at the bottom side of crossing in between the sleeper location. These stiffeners shall give lateral rigidity to CMS crossing under dynamic load therefore any likelihood of cracking of CMS crossing can be eliminated.

RDSO has also firmed up specifications along with testing procedure for Weldable CMS Crossing to ensure quality control during manufacturing. The specification of Weldable CMS Crossing is an improvement over the specification IRS-T29 for CMS Crossing. In respect of chemistry, the maximum limit of Ni, Mo, Cr, Cu and Al has also been specified. Also, it has been specified that the manganese shall not be less than 10 times the carbon content. The radiographic examination has also been prescribed in entire cross-section for 80 mm length at ends of CMS Crossings to be welded with rail.

The Drawings for Weldable CMS crossings have been issued for trial purpose. Some Indian CMS crossing manufacturers having collaboration with foreign companies have offered to manufacture Weldable CMS crossings of RDSO design for trial purpose.

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Use of Weldable CMS crossing, as mentioned above, results in elimination of joints at toe and heel but one gap near nose of crossing is still to be negotiated. It has been learnt that such crossings are used in European countries for high speed.

4. LWR THROUGH TURNOUTS

Long welded rails (LWR) are very useful in eliminating fish plated joints and providing continuous path for smooth running which is a pre-requisite for high speed track. In ‘Indian Railway system’, station yards are located at an interval of 8-10 Km. Turnouts at stations make continuation of LWRs difficult through them. To have effective CWR of longer length, it is desirable to continue LWR through turnouts. Elimination of joints improves safety, enhances passenger comfort and reduces wear and tear of track components and maintenance effort.

In past, arrangement of strengthening frame was used in switch and crossing portion on wooden sleeper layout for continuing LWR through Points and Crossings which did not perform satisfactorily. Subsequently, LWR through 1:12 60 Kg turnout with 10125 mm over-riding curved switch and 60 Kg Heat treated welded crossing was tried at Bhopal division of WC Railways in 2003. This arrangement performed satisfactorily. There was no maintenance problem, though the turnout was laid with ERC Mk-III and stock rails were having slide chairs fitted with bolts. In this layout, no special fittings such as HTS bolts or anti creep arrangements were provided. The tongue rails joints were also not welded to have free movement.

With the advancement, it has been observed that CMS crossing can also be welded with the normal rail. In fact, most of the world railways are using weldable CMS crossing for continuing LWR through Points and Crossings.

By the use of weldable CMS crossing there is no chance of relative movement of different components of crossing being monolithic and therefore no stress frame is required in this portion. Further, PSC sleeper with ERC provides much higher toe load, therefore, chances of movement of rail are minimum or within limit as this arrangement holds the rail properly and rail sleeper assembly acts as one unit.

4.1 DETAILED CALCULATION FOR LWR THROUGH TURNOUT

Detailed calculation has been done to check whether the proposed arrangement is safe to withstand thermal forces.

4.1.1 Basic parameters:Thermal force P = EAαtE = 2.15 x 106 Kg/cm2

A = 76.86 cm2 {for 60 Kg (UIC) rail}α = 0.00001152for temperature zone – IVt max = 76° Ct mean = 38° Ctd = t mean + 5° C to t mean + 10° C

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(For calculation purposes, take td = t mean + 7.5° Ctd = 38° C + 7.5° C = 45.5° CRange of temperature variation on compression side :t max – td = 76° C - 45.5° C = 30.5° CRange of temperature variation on tension side :t d – t min = 45.5° C – 0 = 45.5° CBallast resistance for sleeper density of 1800 sleepers/KmR = 14.77 Kg/cm/Rail

4.1.2 Thermal Force :P = 2.15 x 106 x 76.86 x 0.00001152 x 45.5 = 86617 Kg

4.1.3 Ballast Resistance : This much strength is required to be generated within the breathing length so as to prevent any longitudinal movement beyond the breathing length. On the other hand, longitudinal movement of tongue rail will depend on breathing length.Breathing length = 86617/(14.77 x 100) = 58.64 m

4.1.4 Sufficient longitudinal strength is required to be generated by the fastenings at rail seat level in 58.64 m length which is generated as shown below :Nos. of sleepers in 58.64 m length with spacing 550 mm = 58.64/0.55 = 106Resistance required per rail seat = 86.617/106 = 817 KgTaking transfer function (H/V) = 0.4Toe load needed per sleeper per ERC = 817/(0.4 x 2) =1021.25 Kg

4.1.5 If ERC mark V or any other fastening with average toe load of 1350 Kg is used, resistance offered by 106 rail seats :Total Resistance Force = 106 x 1350 x 2 x 0.4 = 114.48 T

4.1.6 Movement of Tongue/Stock railCase of rising temperature (Tp > Td)Elongation = AEα2t2/2Rt = Tmax – Td = 30.5° C

= 76.86x2.15x106 x (0.00001152)2 x 30.52/(2 x 14.77) = 0.69 cm = 6.9 mm

Case of falling temperature (Td > Tp)Movement of tongue/stock rail from stage of maximum temperature to minimum temperature for decreasing trend Contraction = AEα2t2/4Rt = Tmax – Tmin = 76° C

= 76.86x2.15x106 x (0.00001152)2 x 762/(4 x 14.77) = 2.144 cm = 21.44 mm

Therefore , total movement is 21.44 mmMovement of tongue/stock rail in Tension side = 21.44 – 6.9 = 14.54 mm

4.1.7 As the resistance force is more than the thermal induced force, the above arrangement of continuing LWR through Points & Crossing is expected to be

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effective. Further 27Ø HTS bolts will be used in heel and distance block which will also resist thermal force by transferring the same to the stock rail.

4.1.8 These counteracting forces shall not permit relative movement between tongue rail and stock rail. Calculated theoretical total movement of tongue rail by 22 mm is not likely to affect the operation of point and signaling gear as there will not be relative movement of tongue rails.

4.1.9 From the calculation, it has been observed that resisting force is more than induced thermal forces. Total theoretical movement of tongue/stock rail due to rise and fall in temperature with respect to the distressing temperature comes to approximately 7 mm and 15 mm respectively. The actual movement is expected to be less as experienced in Bhopal division and also due to provision of creep anchors in lead portion of turnouts. Further, in view of no relative movement of tongue rail, the operation of point and signaling gear will remain unaffected.

4.2 LAYOUT FOR LWR THROUGH TURNOUTS

In view of above, LWRs may be continued through turnouts with following arrangements:a) Use of Zu-1-60 thick web switches with elastic fastenings and using 27Ø HTS

bolts in heel and distance blocks

b) Use of ERC MK-V in complete turnout zone and up to 4 adjacent rail lengths on either side of turnout

c) Use of specially designed anti creep device behind heel of switch

d) Use of Weldable CMS crossing

e) Use of creep anchors in lead portion

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5. OTHER IMPROVEMENTS IN TURNOUTS

5.1 EXPLOSIVE DEPTH HARDENED (EDH) CMS CROSSING

CMS crossings provided with fish plated joints can be removed from the track easily for reconditioning/replacement compared to Weldable CMS Crossing. To reduce the maintenance (reconditioning) requirement, Weldable CMS Crossing may be explosive hardened in wear prone areas. The initial hardness of CMS Crossing is about 220 BHN while that of cast steel wheels is 320-340 BHN. By the time hardness of CMS Crossing is increased through work hardening, wear to the extent of 2 to 3 mm takes place quickly. ‘Explosive hardening’ process has been developed to overcome this problem. With this process, initial hardness of 350 BHN is achieved in wear prone areas and hence service life of CMS Crossing before reconditioning increases. In this connection, ‘Explosive hardening’ of CMS Crossings of RDSO design has been done by one of the manufacturer of CMS Crossing which is under trial at Northern Railway.

5.2 IN-SITU RECONDITIONING OF CMS CROSSING

At present, CMS Crossings are required to be removed from track so that reconditioning is done in controlled temperature condition in welding workshop. This activity requires traffic block for removal and insertion of crossing in addition to transportation of the same to welding workshop. Weldable CMS Crossing, being welded at toe and heel, shall require greater effort for reconditioning at welding workshop and thermit welding of rail joints shall be required at either side. In view of above, in-situ reconditioning is desirable for weldable CMS Crossing. Such reconditioning requires proper temperature control measures to avoid any overheating which may lead to crack. One technology for in-situ reconditioning of CMS crossing using translamatic robotic welder has been adopted for regular use in IR which guarantees minimum 80 GMT service life. Other world proven and indigenous technologies are at various stages of evaluation/development.

5.3 SWING NOSE CROSSING

Use of Weldable CMS crossing results in elimination of joints at toe and heel but one gap near nose of crossing is still to be negotiated. Studies conducted by ORE have indicated that for speeds upto 200 kmph on the straight side and 160 kmph on turnout side, it is not necessary to avoid this gap. However, the gap near nose of crossing can be avoided for better riding comfort and maintainability which is possible by the use of swing nose crossing. Swing nose crossings are being used in advanced railway systems for obtaining gapless track in crossing portion specifically for high speed routes and higher axle load.

5.4 MOVABLE SWITCH DIAMOND

Conventional obtuse crossings in Diamonds have unsupported and unguided flange way gaps that wheels have to negotiate. These gaps generate high dynamic loads that adversely affect ride quality, track speeds and components’ life. Due to the high dynamic loads generated in the conventional design of Diamond, there are significant

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maintenance problem. The service lives of crossings and diamonds are greatly affected by train speeds and wheel loads. To overcome the above problem, design of 1 in 10 and 1 in 8.5 movable switch diamond with double slip, single slip and without slip with PSC sleepers have recently been developed by RDSO. This design is having an innovative concept of movable obtuse crossing to avoid unsupported and unguided length at throat of obtuse crossing.

6. CONCLUSION

There has been continuous improvement in the design of turnouts on IR. At present, over-riding switches and CMS crossings are used over fan shaped PSC sleepers on large scale.

Indian Railways is pioneer in development of designs of turnouts, diamonds, movable switch diamonds and scissor crossovers for all locations over PSC Sleepers along with the design of PSC Sleepers.

Time has come to switch over to modern turnouts on Indian Railways by introducing thick web switches and weldable CMS crossings for high speed track. Such turnouts are widely used in advanced railways.

Design, Drawings and Specifications for above turnout components have been developed such that these can be produced indigenously.

LWR can be continued through turnouts using thick web switches and weldable CMS crossings for elimination of fish plated joints in station limit which is a pre-requisite for introduction of high speed.

No extra/special arrangement is required from signal department for implementation of above modern turnout on Indian Railways.

Technology of explosive hardening and in-situ reconditioning shall lead to enhancement of service life of Weldable CMS Crossing. Thick Web Switches, being sturdier, is having more service life. Hence, the use of modern turnout comprising of thick web switch and weldable CMS crossing along with LWR through turnout shall reduce the maintenance effort significantly.

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