353 TRAIN ItE3ISTANCE ON RAILWAYS. Jwnnary 24, 1871. CHAIZLES B. VIGKOLES, F.B.S., President, in the Chair. No. 1,284.-“ Train Resistance on Railways.”By W. BRIDGESADAMS.’ To analyze this question, it is necessary to determine the theo- retical conditions under which the resistance might be reduced to a minimum on alevel line. Thefirst conditionis, that the rails should be perfectly straightand level, i. e., free from all irregularities, and of such section that they would not materially deflect, oither vertically or horizontally, under the heaviest load borne on them by the pressure of the wheels. Secondly, that they be fixed in supports at sufficiently close intervals to prevent deflec- tion, the supportsbeing as firmand immovable as the piers of a bridge. Thirdly, that the rails be supported elastically on the rigid supports in such mode that no blow can take place, or any greater pressure at one point than another, the elasticaction being equally distributed throughout. Fourthly, that the joints of the rails be so connected that they be equally strong, level, and even with the solid portions of the rails. Fifthly, that the two rails be perfectly parallel throughout to the required gauge when straight, and concentric whencurved. Sixthly, that supposing therails to be sufficiently hard to resistcrushing, the bearingsurface should be as narrow as possible, inasmuch as on curved lines the friction increases in proportion to the breadthof contact. The structureof the vehicles requires that each vehicle must be supported on four wheels as a minimum. If the wheels be fixed on their axles, so that each axle becomes practically one wheel, analogous to a gardenroller, thelines of railbeing perfectly straight and level, with the axle arranged at right angles, and the wheels parallelwith the rails, it follows thatthe only resistance will be the axle friction, and that tire friction will be absolutely nil, supposing the tires to be formed with coned peri- pheries, permitting exact movement in a straight course without forcing the flanges into contact with therails. The amount of this axle friction, under themost favourable circumstances, of abundant oil,lubrication, and bearing surface, equivalent to 90 Ibs. per square inch, is generally assumed to be 41bs. per ton of insistent loadon the level. If, therefore, the practicalresistance per ton 1 The dmussion upon this Paper extended over portions of three evenings, but an abstraot of the whole is given consecutively. Downloaded by [ University of Sussex] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. TRAIN RESISTANCE ON RAILWAYS. 359 is found to amonnt to 10 lbs., 20 lbs., or upwards, per ton of load, it follows that this surplus friction mustbe generated between the tires and the rails, and it is important to inquire whether this is a matter of necessity, or an evil that can be avoided. It may arise either on a straight line or on a curve. On the straight line, by the malformation of the vehicle, owing to the axles being out of parallel with each other; or by the axles, though parallel with each other, not being rectangular to the line of traction, and the wheels at intersectingangles, with constant grinding between flange and rail. On curves, the friction, both of the flanges and of the wheel treads, may be caused by the flanges being constantly at an intersecting angle with the rails, and bydiffering the lengths of the rails, producing a sledge or slidingmovement ; the wheels on the outer rail requiringto work on larger diameters than the inner, and for want of compensation involving great torsion of the axles, eventually leading to their breakage. In such vehicles the amount of the tire friction willbe increased in proportion to the increase in the width of the gauge and in the curvature of the rails. The evil may be exaggerated by faulty structure, either original in the workshop, or, as a consequence of collision, making the frame of the vehicle-which should be a true oblong-a rhomboid, the wheels andaxles taking the same relative position. And, prac- tically, the rails, assumed to be straight and even, are, by faulty worlrmanship and wear, a succession of small curves on which the wheels, by the action of their coned peripheries, are seeking the path of least friction, and by reason of the rigid lateral fixtures of the wheels to the upper structure, that, with its whole load, is carried with them; as any one may verify by watching the sinuous course of a loose coupled goods train. Passenger carriages, close coupled, are prevented from making the same movement, but they become sledges or sliders, and grind away the flanges and treads of their wheel tires, and thecollars of their bearing brasses, at a large cost of engine power, and with an extra development of noise andvibration not compensated for bythe mereperfect vertical action of their springs. Goods and coal trains are loose coupled, for the reason that other- wise their resistancewould overpower the engine. Butthis involves another difficulty in snatches and concussions, breaking the chains andcouplings, and inducing accidents more or less fatal and costly. Nor does this loose coupling contrivance get rid of the difficulty. Torsion of the axles goes on withtire rubbing and flange concussion, ' wringing the necks ' of the revolving axles, andgradually, but assuredly, destroying them,unless so cnol- Downloaded by [ University of Sussex] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. 360 RESISTANCETRAIN ON RAILWAYS. mously heavy that thedestructive action is confined to the wheels and rails instead. In coal trains, on a given line, the breakage of an axle per week is the average result. As the loads on railways increased, the wheel-tireswere crushed out, and rails were made heavier to resistthem. Thentires were made of steel, and rails were crushed beneath them ; and 80 rails in turnwere made of steel, and it is assumed that, by its hardness, the steel will have great durability. But hardness has little to do with the question, which is one of homogeneity. Steel rails rolled from solid ingots do not split like iron rails rolled fromimperfectly welded blocks and drawnout into a skein of fibres. But what are called steel rails are, in their most perfect condition, not steel but iron rails; the carbon which has served the purpose of enabling it to be melted intoan ingot having disappeared in the subsequent processes. Steelproper is a very treacheroas metal, andmust either be equallyhardened and tempered throughout,or perfectlyannealed throughout, In the former case or in the latter it will notbe subject to breakage. But if unequallyhardened, or ifhardened throughout and not tempered, it will break under concussion. But even when so hard as to break like glass,it is not secure against the wearof attrition. The engineer of a London line laid down some exceedingly hard and brittle steel rails, carefully guarding against risk of break- age;and twelve months' wear produced the removal of one- sixteenth of au inch of metal from the surface, as perfectly smooth as though planed off in a machine. The reason was, the amount of sledging or sliding movement, in which the sand embedded in the softer wheel tires cut the hardermetal. The cause of wear between tires and rails resolves itself into the fact, that the wheels do not roll, or only partially roll, and 80 become, more or less, sledges. It is a process of rubbing friction analogous to that of the axles without a lubricant, the noise and vibration experienced by the passenger indicatingthe amount, which is greatest in dry weather. In heavy rain the water acts as a lubricant between wheel and rail, and much of the noise and vibration disappearif the rails be clean. There iu one common case demonstrating the amount of the sledging action. When a rail is turned, after being hammered and notched in the chairs, the square notches gradually become small curves, then larger curves, then the prominences begin to disappear, and after a given time, propxtioned to the weight of the engine and the mileage, the rail becomes a nearly true and level surface, unless crushed out in the process. It. is quite clear that mere rolling could not produce Downloaded by [ University of Sussex] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. TRAIN RESISTANCE ON RAILWAYS. 361 this result, and that it is practically a coarse planing process at the expense of engine power. It is obvious, thatif, by a process of betterstructure, tire friction can be got rid of, trains may run with only the normal amount of resistance belonging to the axle friction. The source of the tire friction is in the rigidity of the structure, and the only mode of avoiding it is by flexibility andcompensation yielding. The first condition is, that instead of keying the wheels fast on to the axles, and so involvingaxle torsion and breakage, every wheel should revolve freely, so as to compensate for the varying lengths of the rails on curves or irregularities. Secondly, that the wheels should bo enabledto slip, or slightly rock, within the tires on elasticcushions, enablingthe tire to treadequably on uneven surfaces, intercepting noise and vibration and pressing always on the rails with equal pressure without jumping. In this .mode all risk of bursting the tire will be avoided. Thirdly, that instead of fixing the wheelsbetween horn plates, always involving mis- chievousflange contact on curves, the axlesshould be ‘caster centred,’ so that the wheelsmay move freelyfrom side to side radially, constant.ly maintaining their parallelism with the rails, and their axles in true radii to the curves, under all conditions. Under such circumstances imperfect structureof the frame, whether original or distorted by collision, will not affect the true running of the wheels.