3 Railway Track. (Permanent Way) 31. The Permanent Way. The combination of rails, fitted papa yeebets and tes i x i the railway track or permanent way. Sometimes temporary tracks are also laid. for conveyance of earth and materials on construction works. The name_permanent_wav_ is gi istingui yout from Fig. 3-1, Typical Cross-section of a Permanent Way ‘on Embankment. In nent way, the rails are joined in series by fish plates. and bolts and then” they are fixe 'o-sleepers By ai tastenings. The sleepers properly spaced, restingon ballast, are suitably packed and boxed with ballast. "The layer of ballast rests on the prepared subgrade called the formation. The rails act as gitders to transmit the wheel load to the sleepers. The sleepers hold the rails in the proper position with Tespect to the proper tilt, gauge and level, and transmit the load from rails to the ballast. The ballast distributes the load over the formation and holds the sleepers in position. On curved tracks. super-elevation is maintained by ballast and the formation is levelled. Minimum ballast cushion is maintained at the inner rail, while the outer rail gets more ballast cushion. Add:tional quantity of ballast is provided on the outer cess of each track for which the base width of the ballast is more than it is for @ straight track. 4l42 RAILWAY ENGINEERING 3'2. Requirements of an Ideal Permanent Way. Permanent ‘rack is regarded to be semi-elastic in nature. There is possibility of track getting disturbed by the moving wheel loads. The track should, therefore, be constructed and maintained keeping the Tequirements of a permanent way, in view, so as to achieve higher speed and better riding qualities with less future maintenance, ‘Following are some of the basic requirements of a permanent way : (i) The gauge should be correct and uniform. (ii) The rails should be in proper level. in a straight track, ‘two rails must be at the same level. On curves, the outer rail should have proper superclevation and there should be proper transition at the junction of a straight and a curve. (iii) The alignment should be correct, i.e., it should be free from kinks or irregularities. (iv) The gradient should be uniform and any change of grad- ent should be followed by a smooth vertical curve. (v) The track should be resilient, ie., there must be a certain amount of elasticity in the track. (vi) The track should have enough lateral strength, so that alignment is maintained even due to (a) side thrust on tangent lengths and centrifugal force on curves (6) lateral forces duc to ‘expansion of rails, particularly welded raiis. (vii) The radii and superelevation on curves should be properly designed and maintained. (viii) Drainage system must be perfect. (ix) Joints, including points and crossings which are regarded “0 be weakest points of the railway track, should be properly designed and maintained. (x) If there is trouble from the creep, the precaution should be taken to prevent it. (xi) The various components of the track, i.e., the rails, ‘iittings, sleepers, ballast and formation must fully satisfy the requirements for which they have been provided. If any component is lacking in fulfilling its requirements then cither it should be im- proved or replaced. (xii) There should be adequate provision for easy renewals and replacements. 3:3. Capacity of a Railway Track. Capacity of a railway track or track capacity is the hourly capacity of the track to handle the irains safely or in other words it is the number of trains that can be tun safely on a track per hour. Thus the track capacity can be tncreased by the following two factors — (i) By achieving faster movement of trains on a track, ana (ii) By decreasing the distance between successive trains.RAILWAY TRACK 43 The following are some of the general measures which can be ‘taken to increase the track-capacity. _ (1) All the trains should be made to run at the same speea tor which uniformity of gauges and traction should first be achieved in ithe country. (2) All sections should be made of equal length. _ (3) Multi-aspect signalling should be adopted to alert the driver for positions of sections. For example, a multi-colour light signal with red, yellow, double yellow and green light will respec- tively give indications of danger (red), caution (yellow), attention (double yellow) and clear (green). (4) The speed of trains can be increased by use of ciesel or electric traction. (5) The speed can also be increased by making suitable im- ocean in the existing tracks and removing the speed restrictions, rif any. (6) A reduction in the time of stoppages of trains. (7) The length of scctions should be decreased by providing, additional crossing sections. (8) The length of crossing sections (or loops) should be increased in order to enable the longer goods trains to pass. (9} New lines should be constructed for operational and in- dustrial purposes, (10) A quick arrangement for shunting to attach or detach the ‘coaches, ie., additional operating facilities in the station yards should be provided. (11) Provision of proper control and signalling arrangement «.g., electronic system which maintains high speed continuously. (12) The sections with increased traffic and all important yards should be interlocked. (13) The traffic control on. B.G. and M.G. should be centra- lized. (14) Interlocking standard should be revised to permit higher speeds on main trunk routes. (15) Various safety measures should be taken such as Telecom- munication facilities for short and long distances, operation of new wire lines, provision of higher frequency instruments for marshalling yards, etc. ‘The above-mentioned measures will help in improving the track capacity to a great extent. _ \3AP Gauges in Railway Track, Definition, The Gauge of a railway track is defined as the clear distance between inner or _Tunning faces of two track rails (Fig- 31) rs The distance between the inner faces of a pair of wheels is called the “wheel gauge”.44 RAILWAY ENGINEERING: 3°41. Different Gauges in India and Abroad. In 18th century, the British Railways were using the flanges on the outside of rails and the gauge was defined as the distance between the outer faces: of the rails. The gauge then maintained was 5’ (1°524 m). Subse- quently, the adoption of flanges inside the wheel rails changed the definition of gauge. The position of rails on track was not changed in view of economy and clear distance between inner faces was- defined by gauge. So present gauge=Past gauge—2 x rail width at top. ax, 2 2x =4'-8 + ‘or’ 1°435 m. 1435 m. is the standard gauge in most of the countries even today. In India, the East India Company adopted 1°676 m. (5'—6") gauge as the standard gauge. In 1871, in order to build cheap railways for the development of the country, the government adopt- ted metre gauge i.e, 1m wide. In addition to broad gauge (standard gauge) and metre gauge for hilly areas and for developing poor areas, India has 0°762 m. (2’—6") and 0°610m. (2’-0") narrow gauge tracks and feeder tracks respectively. Thus, at present in India the existing gauges are : Type of gauge (i) Standard gauge (B.G.) (if) Metre gauge (M.G.) (iii) Narrow gauge (N.G.) (iv) Feeder track-gauge (L.G.) (or Light gauge) Gauge width =1°676 m. =10m. "762 mA =0°610 m. The prevailing gauges in other countries are given below : Table 3°1. Gauges in Different Countries s.No. | Type of Gauge | (ii) Metre gauge (ili) Narrow gauge | Gauge Width | | @ ls dard H 435 m ‘andard gauge “435 m. s ! “451 m. Countries U.LK., U.S.A., Canada, etc. (Whole of Europe except Russia, Spain and Portugal.) France. Switzerland, A gentina. Japan, Australia, South. Africa, etc , India, U.K, India'and South’ Africa. “Selection of Gauge. The following factors govern the among the different gauges.RAILWAY TRACK 45 (1) Cost of Construction. There is little increase in the initial cost if we select a wider gauge (say B.G.), This is due to following Teasons : (q)-The cost of bridges, tunnel, station buildings, staff quarters, signals, cabins and level crossings is the same for all the gauges. (by The cost of earth work, (in making embankments and cuttings) ballast, sleepers, rails, etc. would proporti i with increase in gauge width. (Q There is little proportional increase i land for permanent track with increase in gauge. (d) The cost of rolling stock is independent of the gauge used for the same volume cf traffic. We can, therefore, conciude that there is not an appreciable increase in cost due to increase in width of gauge. (2) Volume and Nature of Traffic. It is evident that with greater trafic volume and load carrsing capacity, the trains should be fun by'a better traction technique or by better locomotives. For heavigr Joads and high speed, the wider gauges are required because subsequently the operating cost per tonne-km. is less for more carrying capacity. (2}-Development of the Areas. Narrow gauges can be used to. -develop the thinly populated areas by joining the poor developed areas with ceveloped or urban arcas. (4) Physical Features of the Country. Use of Narrow gauge 1s warranted in hilly regions where broad and metre gauges are not possible duc to steep gradients and sharp curves. In_ plains also, where high speed is not required and the traffic is light, N.G. 1s a correct choices (5ySpeed of Movement. The speed of a train is almost 1 tothe gauge. Speed is the function of diameter-oF in i€MMited by the_gauge.” ‘The “Wheel diameter sis generally 0°75 times that of the gauge. Lower speeds discourage the customers, and so for maintaining high speeds, the Broad gauges are prefesred. £43. Uniformity of Gauges. Gauge to be used in a particular country should be uniform throughout as far as possible, because it will avoid many difficuhies experienced in a non-uniform system and will result in the following advantages : H)The delay, cost and hardship in transhipping passengers and goods from the vehicles of one gauge to another is avoided. (2)Ass the transhipping is not required there is no breakage of goods. {eybimicultics in toading and unloading are avoided and labour expenses are saved. (4) Possibility of thefts and misplacement, whule changing from one vehicle to another, is eliminated.46 RAILWAY ENGINEERING 45) Large sheds to store goods are not required. (6) Labour strikes, etc. do not affect the service and operation . of trains. (‘TSurplus wagons of one gauge cannot be used on another gauge. This problem will not arise if guage is uniform. $)“Locomotives can be used on all the tracks if a unifor a type of gauge is adopted. plication of equipment such as platforms, sanitary arrangements, clocks, etc. is avoided. This saves a lot of extra expenditure. (10)Buring military movement, no time is wasted in changing personnel and equipment from one vehicle to another if gayge is uniform. (1}) It is quite expensive to convert one gauge into another at a later stage as it may require new rolling stock, fresh construction and widening of bridges and tunnels. (12) Due to late arrival of trains at the junction, where chai of gauge is involved, the missing links result in number of difficulties Passengers have to pass time on platforms. In uniform gauge this prablem does not happen. (13) Poiter charges are increased \ change compartment due to a different. gav gauge is uniform. In India. efforts are being made to convert MG_ lines to B.G. lines on important s as aud when funds are available, 3°5. Railway Track Cross-sections. The ty pical cross-sections ofa single line and double line, in cutting and embankment on straight and curved tracks for steam traction and electric traction have been shown in Figs. 3'2 to 3°6. . Fig. 3.RAILWAY TRACK 47 _ PERMANENT L. 16 Me3x DEPTH OF curiae een, GANK 293 pret oF Tees a ‘The Cross-section of a B.G. Track in Cutting for Double Line fon Straig'.t ‘Hacky Fig. 3:3. SUPER CATCH WATER, ELEVATION Bac ‘ORAIN (s Eh pe z it BERM SE INDICATOR — GRADIENT TROLLY WNGICATOR REEUSE INDICATOR a4, FORMATION The Cross-section of a B.G, Track for a Single Line Fig. (on Curved Track) Ss Kl, ? rac, STRUCTURE | (PORTABLE) BALLAST ‘SUSHION The Cross-section of a B. G. Track for Double Line Fig. 35. with Electric-traction48 RAILWAY ENGINEERING Bagge —_, / A { war "Pe ris, corey waren ret Som Fig. 36. The Cross-section of a B.G. Track for Double Line in Cutting (on Curved Track) 36. Coning of Wheels. The distance between the inside edges of wheel flanges is generally kept less than the gauge. So there is a gap between the flanges and running edges to tiie rail nearly equal to 1 cm. (3/8") on either side. Normally the tyre is absoluicly_ dead centre on the head of the rail, as the wheel is coned to keep it in this central position automatically. These whecls are voned ata slope of 1 in 20 (as shown in Fig. 3°7). SLOPE.Lin 20, Fig. 3-7. Coning of Wheels on Level-track The advantages of coning the wheels are : (i) To reduce the wear and tear of the wheel flanges and rails, which is due to rubbing action of flanges with inside faces of the rail head. (ii) To provide a possibility of lateral movement of the axle with its wheels. (iii) To prevent the wheels from slipping to some extent. Theory of Coning. On a level track, as soon as the axle moves towards one rail, the diameter of the wheel tread over the rail increases, while it decreases over the other rail. This prevents the further movement and axle retreats back to its original position (i.e., with equal diameters on both rails and equal pressure on both rails).RAILWAY TRACK 49 On a curved path, (the behaviour of wheels on rails is explain- ed under the article on resistance due to curves), it is seen that due totigidity of the wheel base either of the wheel must slip by an ‘amount equal to the difference of length or the axle must slightly ‘move outwards to provide a tread of longer diameter over the outer ail aad smaller diameter over the inner rail as shown in Fig. 3°8. OUTER RAIL REAR AXLE ® Fig. 3°8. Behaviour of Coning on Curves (PLAN) If the tread diameter on both the rails is same, the amount ‘of slip will be given by Slip=6(Re— Ri) where Ro=R+ £50 PAILWAY ENGINEERING R=Rr-< 6=Angle at centre in radians “ Slip=0xG For B.G. track G: wer metres and Slip= Ee Xx 1676 where 0°=angle at centre degrees Slip=0'029 (approx. for I° of central angle) Therefore, the slip is about 0°029 m per degree of centrat angle. Coning of wheels on curves is not of much use as the leading axle if due to centrifugal force moves towards the outer rail the rear axle (or trailing axle) will move towards the inner rail and the full advantage of coning wheels cannot be availed. In other words, there is no free lateral movement of wheels and this leads to follow- ing disadvantages : (i) Pressure on outer rail is more and less on inner rail and this results in wear. (if) Due to the centrifugal force, the horizontal components. tend to turn the rail out and gauge is widened. 1:20 TO VERTICAL TO VERTICAL Fig. 3-9. Behaviour of Coning on Cutves (Elevation) (iii) If no base plate is used, sleepers under the edee of the raik are damaged. In order to eliminate or minimise the above demerits “tilting of rails” is dome. In tilting of rails, the base plate or sleeper is not laid horizontal but at a slope of | in 20 inwards. This is known as “adzing of sleepers” as shown in Fig. 3°9. To minimise the wear and tear of the rails and wheels on curves, the American practice is to reduce coning to | in 40 and in. some cases even 1 in 100.RMILWAY TRACK St Summary The structure provided by Rails, Sleepers and Ballast over the formation for the movement of trains is called a railway track. For achieving high speeds with comfortable riding qualities,- the basic 10. ments of an ideal permanent way should be satisfied. Typical Questions ‘What do you understand by a railway track and a permanent way ? Mention the requirements of an ideal permanent way. Draw a typical cross-section of a permanent way. Discuss in brief the basic functions of various components of the railway track. Enplain what is meant by track-capacity and discuss important measures for increasing the line capacity, Define gauge of a railway track. Enumerate different gauges used in India aud discuss their suitability at different locations with reasons. Why the uniformity of gauges is desirable in any country? Mention: the demerits of non-uniformity of gauges. It is often said that uniformity of gauge on a network of railways is a boon to any country. Comment. Draw the typical cross-sections of a ri conditions. (D) A BG. straight track in cutting for a double line. (él) A B.G. track on curves for a straight line. il) A double line B.G. track for use of electric traction. (iv) A double line B.G. track on curves in cutting. Discuss thenecessity and effects of coning of wheels and tiling of rails, Write short notes on: () Battle of gauges, (i) Gauges—Board, Metre and Narrow, (lif) Common gauges of the world, (iv) Factors in gauge selection for a new track, (v) Requirements of an ideal permanent way (vf) Track Capacity, (vii) A dimensional cross-section of a B.G. track ‘ona single line, (viii) Components of a railway track and their functions. What are the factors affecting the choice of paritcular gauge. For connecting two industrial cities in India, which gauge you will recommend and why ? Iway track under the following,4 Rails 41. Intreduction. The rails on the track can be considered as steel girders carrying axle loads. They are made of high carbon steel to withstand wear and tear. Flat-footed rails are mostly used in railway track. 42. Functions of R: following purposes : () Rails provide a hard, smooth and unchanging surface for passage of heavy moving loads with a minimum friction between the steel rails and steel wheels. (ii) Rails bear the stresses developed due to heavy vertical loads, lateral and braking forces and thermal stresses. (iii) The rail material is such that it 's minimum wear to avoid replacement charges and failures of rails due to wear. (iv) Rails transmit load to sleepers and consequently reduce Pressure on bailast and formation. 43. Composition of Rail Steel. To meet the above functions, rails should be of good stec! meeting all its requirements. Generally rails are made by open hearth process : Rails in the railway track serve the (a) For Ordinary Rails. High carbon steel with following composition is used : Carbon (C)—0°55 to 0°68 per cent Manganese (Mn)—0°65 to 0°90 per cent Silicon (Si)—0°05 to 0°3 per cent Sulphur ($)—0-05 per cent or below Phoshorus (P) —0°05 per cent or below (b) Fer Rails on Points and crossiags. Medium carbon steel with following composition is used : Carbon (C)—0°5 to 9°6 per cent Manganese (Mn)—0°95 to 1°25 per cent Silicon (Si)—0°05 to 0°20 per cent Sulphur (S)—0°06 per cent or below Phosphorus (P)—0°06 per cent or below For carbon steel with a rail section of 248 kg/m, a reduction of 0-05 per cent in carbon and increase of 0°01 per cent in phospao- rus content is permissible. 52RAILS 33 44, Requirements of Rails. Rails work as continuous girders. carrying axle loads. They should meet the following requirements to serve intended purpose : (i) They should be of proper composition of steel as. given above and should be manufactured by open hearth or duplex process. (ii) The vertical stiffness should be high enough to transmit the load to several sleepers underneath. The height of rail should, therefore, be adequate. (iii) Rails should be capable of withstanding lateral forces. Large width of head and foot endows the rails with high lateral stiffness. (iv) The head must be sufficiently deep to allow for an eee tate margin of vertical wear. The wearing surface should be ard. (¥) Web should be sufficiently thick to bear the load coming on it and should provide adequate flexural rigidity in horizontal plane. (vi) Foot should be wide enough so that rails are stable against overturning. (vif) Bottom of the head and top of the rails foot should be so shaped as to enable the fish plates to transmit efficiently the verti- cal load from the head to the foot at rail joints. (viii) Relative distribution of material in head, web and foot of rail must be balanced. (ix) The centre of gravity of the rail section must lie approxi: mately at mid-height so that maximum tensile and compressive stresses are equal. (x) The fillet radii must be large to reduce the concentration ol stresses. ‘) (xii) The rail specimen should withstand the blow of falling weight in test (as specified by Indian Railway Standards without fracture). 45. Types of Rail Sections. The three types of rail sections which have been tried so far for the construction of railway track, are - (1) Double headed rails (D.H. Rails) (2) Bull headed rails (B.H. Rails) (3) Flat footed rails (F.F. Rails) Fig. 4-1. Types of Rail Sections34 RAILWAY ENGINEERING In the beginning, the rails used were double-headed (D.H.) of ‘a dumb-bell section. The idea behind using of these rails was that when the head has worn out in course of time, the rail can be invert- sed and reused. But experience showed that the lower table formed such indentations that smooth running with that surface at the top was impossible. The next development was that of a bull-headed (B.H.) rail, in which the head was made a little thicker and stronger than the lower part, by adding more metal to it. Side by side with the B.H. rails, flat-footed rails also called Vignole’s rails after the name of the inventor, were developed. It ‘was originally thought that the flat-footed rails could be fixed to sleepers directly and would eliminate chairs and keys required for the B.H. rails. It was observed that heavy train loads caused the foot of the rail to sink into the wooden sleeper, making the spikes work loose. To remedy this, steel bearing plates came to be used, between the sleeper and the rail, at rail joints and other important ‘places. In India, flat-footed rails are most commonly tscu. The standard sections used on Indian Railways are given in table 4°]. Table 4°1. Standard Rail Sections Types of Rails F.P S. Units 1 MKS, Units* Gauges ! — Type Weight lbsivd | Type Weight kelm (elm) | 1 Broad Gauge | 115R | 115 (57 kg/m) | S5R | 55 (BG.) 9OR| 906447 kam) =| 45R | 45 75R. 75 (37-2 kg/m) 35R 35 -2, Metre Gauge 72R] 75 (37-2 kg/m) 35R 35 (M.G.) 60 R| 6u (29-8kg/m) 30R 30 50 R| 50124-8kg/m) 25R 25 3. eee Gauge | 50R| 50 (24-8kg/m) 25R 25 (NG) The rail section should be such as to utilize every bit of the material in the section to its maximum so that the section is ‘economically designed. The section should be able to bear all the stresses au should be such that even after the wear caused by the roiling wheels be able to carry the wheel load as designed. Table 4.2 shows the comparison of Flat-footed Rails with Bull-headed Rails and Double headed Rails. Sures rounded up to the multiples of five.RAILS 35 Table 4-2. Comparison of Rail Types S. Point of Flat-footed Rails Bull-headed Rails and No. Comparison | Double-headed Rails 1, | Strength and| These have more| — These have less strength stiffness strength and stiffness | and stiffness. for the same weight, both| laterally and vertically. . itting of these rails ) __ The fitting of these rails 2. | Laying and Re- is difficult and time-consu- laying impler and so can be | i easily laid and relaid. | ming as they are supported No chairs are required. | on chairs. 3. | Arrangements The arrangements are! The arrangements are at points, cross-| simpler. | complicated. ings and at 1 sharp curves | ' . | Alignment and' In this impact_ of | These rails when fitted stability of | Rolling wheels affects | on chairs, provide a more track | the fittings, and the | solid, smooth track and j loosening of fittings dis-| better alignment. Due turbs the alignment and | to broad base of chairs gives less stability. and wooden keys, the pres sure is distributed over the larger area and hence rails | can be used on soft wood- 1 en sleepers. 5. | Initial cost These rails require less | _ These require more and | and cheaper fastenings, | costly fastenings and hence \ | \ so the cost is less. cost is more | 6. igidity These rails can be | These rails without chairs | used, without bearing | cannot de used on inferior plates, on sleepers as | typc of sicepers being less these rails are strong as | strong as far as vertical far as vertical loads arc | loads are concerned, [1 is concerned. Hence they | less rigid. are more rigid. ‘7. Inspection | __Daily inspection is| _ Incase of B.H. or D.H. | not necessary as no spe- | rails, daily inspection of | cial risk is there. wooden keys is necessary. 8. | Replacement of; In F.F. rails, the dog | These rails can he chan- rails spikes have to be taken | ged easily by driving out outin addition to fish | tne keys and taking out bolts and fish. plates 10 | fish bolts and fish plates, change the rail. So repla-| without disturbing siccpers. cement is difficult. 9. | Maintenance | The maintenance cost] It requires heavy nrain= est is less. ; tenance cost. 10. | Suitability They are more suit- | These are more suitable able due to better stabi- | when lateral loads are lity, economy, strength | more important rather and stiffness than vertical loads. In general the merits and demerits of F.F. Ras and B.H. rails are enumerated below : FF. Rails : Merits. (i) They have more strength and stiffness, both vesti- cally and laterally, than B.H. Rails.56 RAILWAY ENGINEERING (ii) Fitting of rails with sleepers is simpler, so they can be easily laid and relaid. (iii) No chairs or keys are required as in case of B.H. Rails. (iv) In points and crossings, the arrangements are simpler than: B.H. Rails. Demerits. (i) The fittings get loosened more frequently than in case of B.H. Rails. The impact of rolling wheels directly affects the fittings. (i) The straightening of bent rails, replacing of rails and dehogging of battered rails are difficult. B.H. Rail: Merits. (i) They keep better alienment and give more solid. and smoother track. (ii) The ratls are easily disconnected from sleepers as they have no direct connection with the latter. (iit) The heavy chairs with larger bearing on sleepers give longer life to wooden sleepers and greater stability to the track. Demerits, (i) They require additional cost of iron chairs. (ii) They have less strength and stiffness. They require heavy maintenance cost, \ABe Selection of Rails. A rail is _designated by its-weight eth. The various important factors to be considered in. ing the aera of rail to be used are the following : JAP Speed of the train. £2) The gauge of the track. 3) The axle load and nature of traffic. <4) Type of raiis, i.c., whethet D.H. or B.H. or ELF, rails. 45) Spacing of sleepers or siceper density. 46) Maximum permissible wear on top of rails. (5 per cent of the weight of rail is allowed). It is evident that heavier the rail, bigger would be the section and higher would be its carrying capacity. A general ruie adopted is to specify a cettuin ccnstant value of the ratio between the weight of the rail and the locomotive axle load. In India this ratio is 510. Weight of the railin tonnes 1 Locomotive axle load in tennes 310 Thus, fer a locomotive of axle load of 22°86 tonnes, the weight. 2 of rail required will be=-*"- This 448, kg section includes 5 p.c. wear. The necessity of today. is to incidase the weight of the rail, /.e., to decrease the rtioRAILS 57 ( ie, 30) because heavy rails are preferred to light rails due to- the following reasons . (i) More powerful locomotives with electric and diesel traction are getting into use. (ii) From maintenance point of view also, it is desirable to provide heavier rail section with bigger span between sleepers. (iii) The cost of a rail varies with its depth but modulus of section, which is a measure of strength, varies as the square of depth and stiffness varies as 1°5 power of the depth. (iv) A loaded wheel depresses a rail between the two sleepers. For a given load, the deflection is less for a heavier rail than for a lighter rail. Lower the deflection. lesser is the pulling power required, The weight of rail used in India is 447 kg for B.G. and 24°8 to 29°8 kg. for M.G. The research experiments have proved that a 52 kg/m rail’ section is more economical, durable and suitable than a 45 kg/m rail section for a B.G. track. 4°7. Length of Rails. The rails of larger length are preferred to smalier length of rails, because_they give mere streneth and economy for a railway track. The weakest point of a track isthe: joint Between two Tails. Lesser the number of joints, lesser would be the number of fish plates and this would lead to less maintenance cost, smooth running of trains and comfort to the passengers. Moreover, the mere number of joints would increase wear and tear of the vehicle. Though the long length of the rails is desired, however, the length is governed by the following factors : (1) The length of the r: is so chosen that the manufacturing cost is most reasonable. (2) It depends upon the transportation facilities, so only. those Ienatits of rails are possible which can be transported by longest wagons available on the railways. ~ ap (2) To, some extent, the length is also limited by the facilities. of lifting and handling, during the loading and unloading of wagons. (4) More the length of the rail, more will be the gap required “pansion ull due to temper: pverthe expansion is not proportional to gap because. 3 ckthomoxemen raii». so.expansion gap is not limiting factor for length of it affects to some extei an On Indian Ratlways the standard lengths are the following : length==12'80 m. (42 ft) for B.G. (say 13 m) and length=[1'89 m. (39 ft) for M.G. (say 12 m) It is proposed tc increase the longths economically th the: 256 or 192m for B.G. in furture. In countries like U.S.A. and58 RAILWAY ENGINEERING U.K., etc. a Jength of 30 m is commoly used. The other alternative to increase the length of rails, is to weld the rails at the site as it eliminates the difficulty of transportation, handling and lifting. 48. Corrugated or Roaring Rails. In certain places the heads of rails are found to be corrugated rather than straight ones, when the vehicles pass over such rails, a roaring sound is created which 1s intense enough to be unpleasant. The corrugations consist of minute depressions on the surface of rails. They are usually created at places where brakes are applied or trains start. Their shape and size is not definite and occur at irregular intervals. Corrugated rails are peculiar in nature, peculiar in occurrence and peculiar in its real cause. Some of the peculiarities of corrugated rails in nature are : __ (i) Corrugations develop in any fart of the rail and the whole rail gets corrugated in a short time. (ii) These occur at any gradient and on any track, whether a straight track or track at curves. (iii) When corrugated rails are relaid in other sections, the corrugations sometimes get smoothened. (iv) When new rails are laid in places where corrugation is prevalent, the new rails get corrugated. (*) Rails carrying empty trains are easily corrugated than rails carrying loaded trains, etc. ‘The corrugations are peculiar in their occurrence also, because these arc found under the following conditions but presence of any of these conditions is not the token to develop the corrugations in rails : wo Where the ballast consists of broken bricks. (ii) Where brakes are applied to trains for stopping them. (iii) Where trains start. (ir) In electrified sections of a railway track. (v) Corrugations along the track. in case of long tunnels. The corrugations are peculiar in their real cause in the sense that serveral theories have been propounded, but none of them so far could explain the real cause of corrugations in rails. Some of the theories are as follows : () Some explain, the corrugations are due to excess of phos- phorus in the composition of rail steel. (ii) Some give the reason that the resiliency of a track has an important bearing on the corrugation. (iit) Some attribute to the reason that as the metal of the wheel and the raii is very hard and the surfaces of the wheel tread and the rail are smooth, so the wheel and rail would be in contact at a point ora line only. As the intensity of weight over this small area is not uniform but is very great at its centre (nearly twice of the average intensity) which produces corrugations. (iv) Some put forward this theory that the wheel skids in time with the periodicity of the springing of the vehicle, due to bad jointssRAILS 59 or due to the application of brakes. Such skidding will occur under .a peculiar combination of weight of track and nature of formation. Remedial Measure. The corrugations in Germany are removed by grinding a few thousandths of a millimetre off the rail heads. For this, rail grinding trains are used which move at 3 km.p.h, when the grinders are in action. 49 Hogged Rails. Due to battering action of wheels over the end of the rails, the rails get bent down and are deflected at ends. These rails are called “Hogged Rails”. Tiis hogging of the rails at the ends is due to loose packing under the joints and loose fish plates. This defect causes rough riding and the following measures are taken to rectify the hogged rails. (i) Cropping. ‘In this the hogged ends of the rails are cut off and fresh holes for fixing the fish plates are provided. This cutting of rails either is done in workshop or at site. This former method of cutting the rails at workshop is both tedious and unecono- mical. So the hogged portion is desired to be cut at the site by use of portable drilling machine and power saws. After cutting the defective ends, the rails are pulled back equal to the length of the cut off. This method is very common in advanced countries. (ii) Replacing. In this, the hogged rails are completely removed and teplaced by new rails. However, this method is very uneconomical. (iii) Welding. Hogged rails are brought to the level by welding the worn out or deflected ends. (iv) Dehogging. This is the method of straightening the end ‘by means of jim crow or a dehogging machine. But it is seen that jim crow cannot straighten it satisfactorily. So cropping becomes the only satisfactory measure to remove this defect. 410. Kinks in Rails. When the ends of adjoining rails move slightly out of position, “shoulders” or kinks” are formed. The causes of formation of kinks may be the following : (1) Loose packing at joints. (ii) Defect in gauge and alignment iii) Defect in cross level at joints. (iv) Uneven wear of rail head, svhere kinks are formed at joints. The kinks produce the following undesirable effects : (i) These kinks cause unpleasant jerks in vehicles passing over ‘them. (i) Due to uneven wear of rail heads, these kinks appear at places other than the joints and obstruct the smooth running of strain: ‘) A series of kinks arc seen at curves due to which defect in gauge alignment and camber may occur. This involves sometimes a serious risk in turning operations of trains. The following measures are generally taken to remove this defect : (i) Correct alignment of joints and curves. (ii) Proper packing at joints.60 RAILWAY ENGINEESING (iii) Proper maintenance of the track periodically in respect of Cross levels, gauge, welding of worn out portions, etc. 411. Buckling of Rails. Buckling means the track has gone out of its original position or alignment due to prevention of expan- sion of rails in hot weather. This buckling may take place on tangent lengths or at curves. The causes of buckling are summarised below : . (# When expansion gap is not sufficient, the force of expan- sion throws the track out of position, namely buckling occurs, or (ii) The fish plates being bolted so tight that the rails are not allowed to slip or expand, or Due to welded rails on weak tracks. Buckling im tracks has caused serious derailments. Various precautions or measures to be taken to prevent buckling are : (i) The ballast section. sleeper density and the rail sections must be redesigned. (ii) Number of welded rails should not be very large. if) Provision of steel sleepers or anchoring of welded rails, should be done. _ Gv) Proper Jubrication of contact surfaces of fish plates and rails at regular intervals (once in a year or two years) is necessary. _ (1) Expansion gap should take into account the crpansion of rails due to rise in temperature in uiat region. (vi) The tish bolts should not be tightencd so much as to prevent the expansion o¢ contraction of rails. 412. Damaged Rails. These are the rails which should be removed on account of their becoming unsafe for a railway track due to any of following causes : . (i) The wear of rails. (ii) The defect, due to manufacture ot rails. (iii) Defect of hogging in excess. (ir) Due to damage caused to the rails. The defect of wear will be dealt in subsequent articles. The defects due to manufacture in India are comparatively few. The hogging of rails is discussed in preceding articles. Damage to the rails may also be caused by one or more of the following reasons : (i) Careless unloading or bandling of rails. ii) Bending rails to sharp curves. (iii) Improper striking of rails while fixing to the sleepers. (iv) Poor maintenance of track, such as loose sleepers at joints, loose fish boits, incorrect superelevation at curves, etc. (¥) Slipping or skidding of whee!s due to overload or bad application of brakes. Slipping of wheels burns the top of rail, whic the skidding produces flat spot on the wheel tread. Such flat spots affect the raii head adversely.RAILS 61 () Slippiag occurs when : Circumferential movement of wheel or tyre > forward move- ment of axle. 3 nd For example, aaa ud > zr (Circumferential movement > forward movement) (Forward movement) Fig. 4-2. Slipping of Wheels. a d-> (i) ‘Skidding occurs when : Forward movement of axle > circumferential movement of ewheel or tyre. F 3 nd For example, —>ad> . 3 ud So, skid= z nd— zz =0°25 xd. (Forward Movement) Fig. 4-3. Skidding of Wheels62 RAILWAY ENGINEERING: (vi) Due to damaged tyres of wheels. (vii) Excessive speed due to which the existing defects in rait are increased. (viii) Bending or braking due to an accident. 4°13. Rail Failures. The sudden failure of a rail is generally due to defects in its manufacture, although the other causes may also exist. Two such other causes, which are common, are (i) an abrupt change of section of rail, (ii) notches with corners in the foot of the rails. Such failures, though rare on Indian Railways, may occur in one or more of the following forms (Fig. 4°4) : (i) Crushed Heads. Crushed heads are those which have sagged or flattened. Besides the defect of manufacture, crushed heads are due to (a) slipping of whecls, (6) flat spots on wheels ‘which are developed due to skidding of wheels, (c) weak support at the railend. This weak end support may be duc to loose fish bolts. (Fig. 4°4 a]. (ii) Square or Angular streak. The rail may be completely broken either in a vertical plane or in an inclined plane. [Fig. 4°4()] (ii?) Split Heads. In this, cracks occur in the widdle of the head or pieces are split from the side to the end of the head. If the surfaces of the crack, when opened, appear smooth and dark, the defective rail is known as “piped rail” and this is duc to cavity formed during manufacture or shrinkage of metal due to the metal not having been closely welded together. (Fig. 44 (c)] SS se (a) Crushed Head. (6) Angular or Square Crack. £ £ Fe HOLES. (c) Split-head. (a) Split Web. (©) Horizontal Fissure. (f) Transverse Crack. Fig. 4-4. Different types of rail failures.RAILS 63 (iv) Split Web. This is the through crack in the web, though not necessarily, run through bolt holes. [Fig. 4°4 (d)]. (v) Horizontal Fissures. These are developed in the rail head. They are more in the form of a fracture and develop gradually [Fig. 4°4 (e) ]. (vi) Transverse Fissures. This is the most common cause of rail failures in America. It is a cross wire crack which starts from a point inside the head and spreads like contours shape gradually. The broken surface has a smooth oval or round bright spot. This defect is a manufacturing defect or may be due to overstraining of metal in service [Fig. 4°4 ( f )]. (vii) Flowing Metal in Heads. The metal in the head is forced to the sides, the rail head being widened and depressed. .(viii) Horizontal Cracks These occur at rail ends between head and web. Such cracks are believed to be duc to worn fish plates or insufficient ballast packing under joint sleepers, resulting in pumping of joints and consequent fatigue failure of steel. This defect is very common in rails ia America and is increasing day by day. This defect is either due to fatigue caused by shearing stresses or due to reversal of stresses (from high compressive to low tensile stresses) in the rail between supports. : In India, Sonirail Detector, an electronic device for testing of rails and web defects detection, is used. \ (14. Wear on Rails. Wear is one of the prominent defects of rails. When the axle loads are abnormally heavy and the train moves with very fast speed then the concentrated stresses exceed the elastic limit resulting in metal flow ; on the gap or joint the ends are battered and at the curves skidding, slipping and the striking of wheel flang es with rails results in wear and tear of rails, Classification of Wear. Wear can be classified in accordance with the location and position of wear. (a) On the basis of location : The wear is prominent on the following locations : (i) On sharp curves. (ii) On gradients. (iii) On approaches to stations, where brakes are frequently applied. (iv) In tunnels (a) where sand is used on rails to produce more friction on damp rails but on the contrary it gives more wear. (>) In tunnels, the gases coming out of the engine being confined attack the metal and result in wear. (v) In coastal area, due to action of sea breeze. (vi) On weak foundations—sinking of rails due to heavy loads gives uneven surface which results in wear. On_the basis of position of wear : The following are the positions of wear on rails : on top or head of rail, A Wear. 427 Wear _at the ends of rails. :“64 RAILWAY ENGINEERING ear on the sides of the head. (1) Wear on Top or Head of Rail. This type of wear occurs on straight i.e. tangent tracks and at-curves, cam On Tangent Tracks. The following are the factors which cause or encourage the wear on top of rails on tangent lengths : +7 Due to flow of metal—This is because the heavy loads concentrated on small area produce the stresses which exceed the elastic limit and hence plastic flow of the metal takes place and burrs are formed, which later get chipped off by wheel flanges, as shown in Fig. 4 al Heavy axle load and its recurring impact causes the wear at the top of rails. jue to abrasion of rolling wheels, the rails are generally worn out at the top of rails. (Due to constant brake application, which results in skid- ding and burning of the rail head. This finally results in excessive wear and abrasion. (») Due to use of sand which is done to produce friction in case of dampness in tunnels. The grinding action of sand particles with rails gives rise to wear. (vi) Due to fluctuations in gradients. wit} Due to corrosion of rails by the action of sea breeze, which also gives rise to wear on top of rails. (viii) Due to bad track, viz.. loose packing of ballast or loose- ness between rails and sleepers, wear increases. On Curves. The wear on top of rails at curves is due to the following causes : ue to slipping or skidding of wheels. i}Due to centrifugal force_and improper superelevation, load on one rail is greater than the other. If superelevation is more or less for a given speed, the load will be more on inner or outer rail respectively. More wheel Joad will cause more wear. (iii) Due to adzing of sleepers. On curves, the sleepers have to be laid at a slope for the purpose of superelevation, but when the WEAR AT INSIDE BURR Hfow SLOPE OF THE OUTER RAIL =m 1 1 IN L BURR f y GAUGE _ {| GAUGE Face TOP RAL WEAR INNER RAIL{TOP WEAR) OUTER RAIL (TOP & SIDE WEAR) Fig. 45. Wea: on Rails."RAILS 65 tail is laid at a slope of 1 in 20 on the sloping sleeper, the resulting slope or tilt is different from the slope of wheel cone, giving lesser area of contact between the wheel and the rail, resulting in more wear. It is observed that the maximum wear at tangent lengths is due to the floy of metal and at curves is due to slipping and skidding, ‘ea the Ends of the Rails. Wear at the ends of the rails is due to high static pressure combined with impact blows. This is prominent on straight tracks only and is much more than the wear on top of rails. This type of wear occurs, when a wheel jumps over the gap, i.e., expansion gap between the rail ends, giving blow to the end of the rail, as shown in Fig. 4°6. The ends of the rail get WHEEL 46. Wear at the Ends of the Rails. battered. This battered end causes rough riding in the track, loosens the ballast under the jaints.2 This further increases the intensity of blows and results in battering of ends and flow of metal towards the gap and subsequently gets chipped off, ‘This type of wear is encouraged due to following factors : (i) Due to loose fish plates and fish bolts. (ii) Due to heavy Toads a js and large joint openings. (iii) Difference in rail height at joints. (iv) Small wheels. {v) Bad conditions of the vehicle springs. (vi) Poor maintenance of the track. (3) Wear on Sides of the Rail Head. This type of wear is ‘only prominent when the rails are laid at curves. This wear is more than first two types of wear and is most destructive too. This wear is due to following causes (Figs. 4°5, 3° and 39): , @AAt curves, there is greater thrust on inner rail, when trains run at lesser speed than equilibrium speed. Gy Due to the rigidity of the wheel base, (ii)Alipping aad skidding of wheels at curves. Actually, the thrust cf wheel flanges (which is developed due to wheel base and tangential force) against the inside of the outer tail grinds the rails, causing side wear (Refer Fig. 4°5).66 RAILWAY ENGINEERING: Allowable Limits of Wear. The allowable limit of wear depends upon the weight of rails and consequently the weight of rail is proportional to the axle load. In India, the prescribed limit for wear is 5% of rail weight because all the wear takes place in the head which contains 33% to 40% of the metal in rail. Allowable wear of 25% of the section of head is also adopted. I nen Methods to Reduce Wear. In addition to coning of wheels on tangent tracks and proper superelevation on curves, the following meted are employed to réduce the wear and prolong the life of rails : - (i), When the wear exceeds the prescribed limit (i.e., 5% of tke total weight of section, for 44°7 kg/m rail when the rail reduces its wt. 2°5 kg or at the most 8% i.e., say 4 kg) the rail must be replaced. (ii) Use of special alloy steel. The use of special alloy steel is justified though costly at places where wear is considerable, such as at points and crossings, approaches to station yards where applica- tion of brakes is a common feature, in station yards, on gradients etc. (iii) Regular tightening of fish bolis and packing of ballast is necessary to reduce the wear at ends. (iv) Reduction in number of joints by welding and reduction in width of gap, will reduce the wear. (») Welding or dehogging of battered ends at proper time will also reduce the wear. (vi) Maintenance of track, with special reference to the joints, is necessary to reduce the wear. (vii) Maintenance of correct gauge will reduce the side wear. (viii) Correct adzing or use of bearing plates will reduce the side wear in particular. (ix) Lubricating of the gauge face of outer rail on curve, will reduce the wear. (x) Interchanging inner and outer rails and changing faces at curves will reduce the wear because in doing so, the top wear is exchanged with side wear and life of the rail is increased. (xi) At curves, the check rails parallel to the inner rails can be troduced to check wear. Because/the gap between inner rail and check rail is equal to flange thickness of wheel, so the outer wheel is prevented from damaging the outer rail Thus the side wear on FLANGEWAY CLEARANCE CHECK RAIL OUTER RAIL INNER RAIL Fig. 4°7. Check Rail to Reduce WearRAILS 67 inner side of the outer rail is reduced by introducing the check rail (Fig. 4°7). In India the use of check rails with 8° and over for B.G.,. with 14° and over for M.G., is made. (xii) Application of heavy mineral oil, in case of corrosion of rail metal under adverse atmospheric conditions, reduces the wear of rails. The use of the worn up rails should be discarded under the following conditions : (i) When the wear on the rails exceeds 5% (prescribed limit of wear) or at the most 8% of the total weight of rail. Fish plates are struck or cut by the flanges. (iit) Gauge side is worn (side wear) as much as 3 mm. (iv) Gauge side of the head is worn to the.shape of wheel flange, so that wheels are liable to mount the top. (9) The top of head is worn by 9°5 mm. (vi) Either head or web is split. Reconditioning of worn up rails can also be done by following ways (from economic point of view) : (ij) A.rail worn out at the top or side may be re-rolled to a Jighter section. (ii) If battered or chipped off at ends, it may be built by welding. (iii) Tf hogged or bent on surface at ends, then cropping the ends, redrilling the holes and using stiffer fish plates will make the rails ready for reuse. Summary Rails work like steel girders in carrying load. They provide hard, smooth and unchanging surface for passage of loads, and are made of high carbon steel. A good rail should have tensile strength of not less than 72 kg/mm?. Flat-footed rails are commonly used on Indian Railways, The weight of rail and length of rail for the two gauges are : Weight of Rails kglm Length of Rails in metres BG. 447 128 M.G. 24°83 —29°8 11°89 Roared rails, Hogged rails, Rails having kinks, Buckled rails, Damaged and Failed rails should not be used, till they are suitably remedied. Flowing of rail metal which ultimately gets chopped off is called wear of rails. Indian standards specify that amount of wear should not be more than 5 per cent of the weight of the rail.s 10. RAILWAY ENGINEERING Typical Questions Describe the functions and requirements of rails in a railway track. Discuss different types of rail sections with sketches. Mention the relative merits and demerits of Flat-Footed rails (F.P. Rail) and Bull-Headed rails (B.H. Rails). ‘Explain the characteristics of various rail types in tabular form with regard to their performance in the railway track. Discuss the criteria for deciding the cross-section and length of rails. Illustrate the various types of rail failures with sketches. What is meant by weer of rails 7 How do you classify the wear? Discuss the various causes of wear and suggest suitable measures to reduce the wear of rails. Write short notes on (2) Composition of steel, (6) Heavy rails v/s Light r {c) Weight of rails, (d) Length’ of rails, (2) Corrugated or Roaring (f) Hogged’ rails, (g) Kinks in ‘rails, (4) Buckling of rails, (i) Damaged rails. Explain what do you mean by bucking of rails? Why and how buckling occurs ? Draw sketches to illustrate and explain the following : (0), FF. Rails, ’5) Slipping and skidding of wheels, (c) Split web and split head, (¢) Wear at the ends of rails.5 Rail Joints and Welding of Rails RAIL JOINTS Rail Joints are necessary to hold together the adjoining ends of the rails in the correct position, both in the horizontal and vertical planes. Rail joints form the weakest part of the track. It is observ- ed that strength of a rail joint is only 50 percent of the strength of a rail. * S'1. Requirements of an Ideal Joint. An ideal or perfect rail joint is one which provides the same strength and stiffness as the other section of the track. The following requirements should be met by an ideal joint : (i) The two rail ends should remain true in line both laterally and vertically when trains move cn the track. This is necessary to avold whee! jumping or changing its correct path of movement. (ii) The rail joint should be as strong and stiff as the rail itself and should be elastic both laterally and horizontally. (iii) The Rail Joint should provide enovgh space for free expansion and contraction to account the effect of temperature variations. (iv) A good joint should be easily disconnectable so that it can. be easily taken out without disturbing the whole track for the Purposes of changing a rail or a fish plate, and lubricating the con- tact faces. (v) It should not allow the rau ends to get battered in any. case. joint should fulfil the above requirements with the minimum initial and maintenance cost i.e., it should be economical. 5°2. Types of Rail Joints. The following types of joints are commonly used on Indian and foreign railways : (1) Supported Rail Joints. When the rail ends rest on a single sleeper called a “joint sleeper” it is termed as “supported joint”. The duplex joint sleeper with other sleepers is an example of the supported joint. Three sleeper support (as JOINT shown in Fig. 51) with long fish plate, i.¢., combined sup- Ported and suspended joint, is Most objectionable. Because in this case when the packing under the outer sleeper gets loose, undue load comes on central’sleeper and joose central Fig. 5°1. Supported Rail Joints 6970 RAILWAY ENGINEERING sleeper converts this joint into a weak suspended joint. ONT (2) Suspended Rail Joint. When rail ends are projected beyond sleepers called “shoulder sleeper”, it is termed as sus- pended joint (as shown in Fig. 5:2). This type of joint is generally used with timber and steel trough sleepers on Indian and foreign railways. {———— SLEEPERS (SHOULDER SLEEPERS) Fig. 5:2. Suspended Rail Joint. . (3) Bridge Joint. When: the rail ends are projected beyond ssleepers as in case of ‘suspended joint and they are carried by a flat or corrugated plate called a “bridge plate”, it is termed as 2 bridge joint. This type of joint is not used on Tadian Railways (Fig. 5°3). Fig. 5:3. Bridge Joint. (4) Base Jo'nt. This is similar to the bridge joint, with the difference that the inner fish plates are of bar type and outer fish plates are of the special angle type, in which the horizontal leg is further extended over the sleepers to be bolted to both bridge plate and sleeper. Due to complicated design, this is not generally used. (S) Welded Rail Joints. These are the best joints as they fulfil nearly all the requirements of an ideal or perfect joint and will be discussed in next article. (6) Staggered or Broken Joint. In this, position of joints is the basis of its nomenclature, the joints of one rail are not directly opposite to the joint of the other rail (Fig. 5°4). These joints are Ras PLAN OF TRACK Fig. 54, Staggered Rail Joint. Fig. 5:5, Square or Even Rail Joint,@AIL JOINTS AND WELDING OF RAILS 1 generally provided on curves, where the length of outer curve is greater than the length of inner curve. (7) Square or Even Joint. In this also, the position of rail joint is the basis of its nomenclature, the joints of one rail of track ‘are directly opposite to the joints of other rail. This is generally used on straight length of track (Fig. 5°5). (8) Compromise Joint. Where two different rail sections are required to be joined B,H.RAIL ‘together, it is done by means FF RAR of fishplates which ‘fit both the rails and this is ter- med as compromise joint (Fig. 5°6). (9) Insmiated _ Joint. FISH PLATE When insulating medium is ve Joi inserted in a rail joint to stop Fig. 5°6. Compromise Joint. ‘the flow of current beyond the track-circuited part, it is called insu- lated joint. (10) Expansion Joint. In bridges, provision for expansion and contraction is left both in girders and rails. This gap is 2°2cm in case of “‘mitred” joint and 7°2 cm, in case of “Halved Joint.” Experiments carried out in India have revealed that compara- tively, in view of stresses produced in rails and fish plates, the wooden sleepers are best for joints. They produce less stresses in rails and fish plates, and their performance, from the point of view of deflection, maintenance of gauge and cross levels, is best. Duplex sleepers, however, produce minimum deflection. Joints should be avoided at the following places : (i) At level crossings (where railway track crosses the road). (ii) On short bridge spans of any type. (iii) On approaches of bridges. (iv) On ends or centre of span of long bridges, if at al’, “he use of a joint is warranted, it should be at a point $rd of the ‘span length. The number of joints can be reducéd by the process of welding of rails. Welded joints are perfect and strongest type of joints. WELDING OF RAILS . 53. Purpose of Welding. Welding of rails serves the follow- ‘ing purposes : (i) To increase the Jength of the rail by joining two or more rails and thus to reduce the number of joints, and requirements of fish plates, which lead to economy and strength. (ii) To repair the worn out or damaged rails and thus increase stheir life. (iii) To buildup worn out points and rails on tne sharp ‘curves. (iv) To build up the burnt portion of rail head caused due tu ‘slinpage of whedls over the rail or other defects or spots in rail steel.nR ‘RAILWAY ENGINEERING: 5°4. Advantanges of Welding Rails. (1) It satisfies the con— dition of a perfect joint and hence increases. the life of the rail and. reduces the maintenance cost by about 20 to 40 ver cent. (2) It reduces the creep as the length of rail increases and. fricticn as a result will also increase. . (3) Expansion effect due to temperature is also reduced which also reduces the creep. (4) The discontinuity of joint as a source of weakness in track is reduced. The defects such as hammering at rail joints, displace- ment o1 joints, disturbance in alignment and running surface, which result in bad riding. are eliminated. (5) Long rail lengths dampen the intensity of high frequency vibrations due to moving loads. (6) Welding increases the life of rails due to decrease in the wear of rails. (7) Welding facilitates track ciscuiting on electrified tracks. (8) Welded rails on large bridges for the length of span are helpful as they give betrer performance. (9) Welded rails on curves is under investigation. Maximum curve radius may be welded depending upon resistance and lateral displacement of track. (10) The cost of track construction by welding of rails decreases due to less number of rail joints. 5'5. Success of Welded Rails. Due to modern improved methods of fixing of rails with sleepers, the length of the rails can be- increased as it is observed that a sufficient amount of resistance is available at several slecper fastenings to resist the expansicn of rails. due to rise in temperature but there are no sufficient restraining forces available near the ends. If the restraining forces near the ends are insufficient, the forces due to expansion will supersede and buckling. will take place. The buckling will depend upon the degree of anchorage and the rise in temperature. More the number of rails. welded together, more will be the tendency of the track to buckle. The success of welded rails depends upon : (i) Better degree of fixity of rails to the sleepers (i.e., better degree of anchorage). (ii) Better precautions against buckling of the rails, and (iii) Regular maintenance. In India, the present practice is to weld five rails with an expansion gap of 6 mm in both B.G. and M.G. tracks. 5°6. Methods of Welding of Rails. The following four methods. are employed for welding of rail (1) Electric Arc welding. (2) Oxy-acetylene welding. (3) Flash butt welding. (4) Cheinical or thermit welding. (1) Electric Arc Welding. In this, as shown in Fig. 5°7, the current is passed through the rail and at the same time through a‘RAIL JOINTS AND WELDING OF RAILS 3 thin rod known as electrode. As the electrade approaches the rail, an electric arc is formed and with the heat the electrode gets melted. and the molten metal of the electrode deposits on the rail, providing. a firm bond. Mobile electric arc welding plants are easy to handle. This plant consists of an engine, generator.and some accessories. WELDED JOINT Fig. 5-7. Electric Arc Welding. This method of welding is used for building up worn out points and crossings, damaged rails and other small welding operations. Gas eld Prevents entering of impurities and air into the molten metal, (2) Oxyacetylene Welding. In this method, intense heat is. Produced by combining the oxygen and acetylene gas, which melts. the electrode and deposits the molten metal on the rail. This plant consists of two cylinders (one for oxygen and the other for ace- tylene). This is best from mobility point cf view. This method like arc welding is used for repairing worn out or damaged parts of points and crossings. This is specially useful for cutting of steel. (3) Flash-butt Welding. In this, powerful current is passed through two rails, the ends of which are to be jointed together. The width of the gap between two rails is varied till both the ends get heated upto a required temperature. Then, they are brought in contact resulting in flash. Then the current is stopped and rails are- pressed together under a pressure of 20 tonnes. This method of welding, being most satisfactory, is used for welding the rails in workshop. This method of welding involves heavy welding plant and that too immobile and hence uneconomical for small jobs at site. For large’ jobs at site, this may be eco- nouical. (4) Chemical or Thermit Welding. This involves the use of chemicals, aluminium and iron oxide. in this method, aluminium and iron oxide are mixed in powder form and ignited. On ignition, the chemical reaction takes place and produces intense heat because this reaction is exothermic in nature. (Fe2Os+2Al=Al2Os+2Fe- +Heat). After the reaction, the Fe gets separated and is deposited:W4 RAILWAY ENGINEERING ‘in the gap of the rail ends which are preheated. Actually these two ends with chemical mixture in between the gap are entrapped in a mould to prevent the flow of mixture as shown in Fig. 5°8. FLOW OF MIXTURE “7, CONTAINER Fig. 5°8. Chemical or Thermit Welding, The heating of the two ends is done by use of a furnace at the ‘bottom of the rail joint. After the mixture solidifies, the mould is removed and surface grinding ix done. The chemical welding is generally adopted in the process of renewal of rails. This plant is mobile in nature and can be used at site for welding of rails. 5:7. Length of Welded Rails. It is a well-known fact that rail joint is the weakest part of the track. Lesser number of rail joints results in low cost of maintenance, less number of fish-plates, decrease in wear and tear of the vehicle, and subsequently leads to smooth running of trains and comfort to passengers. Therefore, the length of rail should be as long as possible, however, its length is Jimited by the following factors : (i) The length of rail is adopted by the facilities provided for the manufacture of rails at reasonable cost. (i) The length of the rails should be such that they may be carried in the longest wagon available on the railways. (iii) The length of the rails is also limited bv the availabie facilities for lifting and handling the rails. Due to above limiting factors for rail-length, it is proposed that tails can be welded together for increasing the rail length. However, the length of welded rails depends upon the expansion gap to be provided under increased temperature. It has been observed that the variation in Jength due to temperature is not proportional to the length of the rail. In India, the practice of welding 5 rails at a time iis followed as it is observed that longitudinal expansion due to 5 welded rails length, (i.e. 64 m) is the same as for 12°80 m rail- length. Let I= length of the rail in cm. o-efficient of expansion in per °C. t=the rise in temperature above the tempera- ture at which the track is laid.RAIL JOINTS AND WELDING OF RAILS 15 then increase in length due to expansion is B=] xaxt wi) But this increase in length (8/) is not proportional to the length of rail, i.e. J, as seen in equation (i), because the rail fittings hold down the rails to the sleeper, prevent the larger movement and transfer the longitudinal stresses in the transverse and vertical direc- tion. These transverse or lateral stresses may put the track out of alignment due to buckling and may result in derailment of trains. Let A=Cross-sectional area of a rail in cm* E=Modulus of elasticity of steel in kg/cm? '=Force in kg. required to prevent expansion due to temperature. then or u w= (di) Example 1. What is the increase in the length of rail of 128m when the rise of the temperature of the track is 30°C and given that a=1°15 x 1075 per °C. Solution. The increase in length due to expansion is given by Bi=Ixax¢ [from eq. (i)] * 81=12°8 X 1°15 x 1075 x 100 x 30 =0°442 cm. or 4°42 mm, Ans. Example 2, What should be the length of track (i) to over~ ome temperature stress (ii) to prevent creep for equilibrium ? When it is given A=60 cm®, a=1°15X 1075 per °C, E=21°5 x 105. kg/cm? and rise in temperature, ie. 1=30°C. Assume 700 kg/km as resistance to track movement. Solution. The force required to prevent the expansion due to temperature is given by F: A.E. . .A.E.t. [from Eq. (i)] or =(f)x At. where ‘f” is the stress in rail per® rise in temperature=«.E. So F=1°15x 10-5 x 21°5 x 108 x 60x 30 4,460 kg. (i) Length of track required to overcome temperature stress a= 4460 im, 63°5 km Ans. 1 To prevent creep for equilibrium, the length of welded ck. =2xLt. =2x 635 =127 km Ans.76 RAILWAY ENGINEERING - Summary Rail joints are provided to join two adjacent rails. They are weakest parts of the track and should therefore be rigidly constructed as per requirements of an ideal joint. The number of joints can be reduced by welding of rails. Welding of rails provides very strong rail joint with many advantages. The Indian practice is to weld maximum of 5 rail lengths. Methods of welding have their own utility as given below : Method of Welding Suitability (1) Electric Arc welding. Building worn out points and crossing, damaged rails and small welding operations. (2) Oxyacetylene welding. Used in repairing works cutting of stecl on site works. (3) Flash butt welding. Used largely for welding of rails in workshops. (4) Chemical or Thermit Used in renewal of rails. Due weiding. to mobile plant can be used at site for welding. ‘Typical Questions 1, What are the requirements or characteristics of an ideal rail joint ? Tilustrate by neat sketches. Discuss different types of rail-joints with the help of neat sketches id give their merits and limitations. Explain in nutshell the means adopted for strengthening rail joints in» India. Give merits and demerits of welded rail joints. 4. What is the necessity of welding the rails ? How the welding of rails is carried out? 5. Write short notes on: Qo Bridge joint, (ti) Supported joint, (47) Compromise jo‘nt, ‘) Merits of welding rails. (v) Che oor ther ‘ i) Flash-butt welding, (vii) Length of welded rails. 6. Write short specification for welding of rails and laying welded rails for trunk and main tracks in India, 7. Describe, in short, the methods of welding the rails giving suitability of each, 8. What are thz factors limiting the length ot the welded rails. Obtain an expression for force required to prevent expansion of rails due to- temperature.