Some engineers are advocates for a hard steel rail, and claim for it greater durability and longer wear; but even supposing such hard rail should possess a slight superiority over the soft rail, it is well to consider whether such assumed advantage is not obtained at the risk of incurring greater liability to fracture. It must be borne in mind that a rail, once placed in the road, is exposed to all the changes of temperature from heat to frost, and has frequently to sustain increased strains arising from loose sleepers, where the gravel or ballast has been disturbed during heavy rains.
When writing a specification for steel rails, it is usual to state the number of tons per square inch in tensile strain which the steel must be able to sustain without fracture, and also to stipulate that some of the rails will be tested by the falling-weight test. In the latter test a rail is placed, say at 3 feet bearings, and in a similar position to what it would occupy in the road, and a weight of eighteen hundredweight, or one ton or more, according to section of rail, is allowed to fall from a height of 9 or 10 feet, on to the rail, at the centre between the bearings. With three blows from the given height, the rail must not bend or deflect more than a specified amount. The falling-weight test is, perhaps, rather a rough and ready one; but it is always reassuring to prove that the rails will withstand such a severe ordeal, as it must be a very exceptional circumstance in the routine of railway working which will produce a blow or shock
equal in effect to the falling-weight test. The rails form such an important part of the trackway, almost the very basis on which the traffic has to depend for its safety, that, apart from the question of wear, no effort should be spared to ensure their thorough soundness and efficiency.
In modern practice rails are generally used in lengths varying from 25 feet to 30 feet. There is no difficulty in making them longer; but any excess over the above lengths is found to be inconvenient for transport, for handling in the line, and for making the necessary allowance for contraction and expansion at the joints. Steel rails are generally marked on the vertical web with the initials of the railway company, the name of the manufacturer, and the year in which they are rolled. This is done by cutting out the letters in the last pair of rolls through which the rails have to pass before they are completed, so that on the rails themselves the letters stand out in raised characters, thus: G.N.R.I.......C. CAMMELL & Co 1896. In this manner the rails always carry for reference the name of maker and date.
When comparing the relative merits of the flange-rail and bull-head-rail permanent way, the question of strength and durability must be considered, as well as that of economy. The flange-rail road has undoubtedly fewer parts and fastenings, and when the flange is wide, the sleepers sound, and the rail securely held down to the sleepers, the result is a smooth running road. So long as the rail can be maintained in a constant close contact with the wooden sleeper, the running is almost noiseless, the jarring on the rails being absorbed or taken off by the timber; but so soon as a little space or play takes place between the spikes or other fastenings and the upper surface of the flange, the rail obtains a certain amount of rise, or lift, which comes into action upon the passing of every rolling load, producing unsteadiness in the rail and a clattering noise in the running. A flange of 5 inches, on a sleeper 10 inches wide, has a bearing surface of 50 square inches (assuming the sleeper to be square cut, without any wane on the edges), and this area of 50 inches is only about half of the bearing surface on the sleeper of an ordinary modern cast-iron chair.
Main-line locomotives have weights on the driving-wheels varying from 16 to 18 and 20 tons. Taking 18 tons as representing a common practice for a large express engine, would
give 9 tons as the weight imposed on each rail by each driving-wheel Assuming this weight to be distributed over three sleepers would give a dead weight of 3 tons per sleeper, or 134 lbs. on every square inch of the 50 square inches of surface, or rail-bearing area, on each sleeper, without taking into account the effect of the blow or percussion from the rolling load. The presence of a loose sleeper throws additional weight on the adjoining sleepers, and increases the destructive influence on the timber. The constant application of heavy rolling loads on a small bearing area of timber crushes and wears away the timber very rapidly. The small bearing surface of the flange rail expedites the cutting down into the sleeper, and as the rail beds itself further and further into the wood, the fastenings must be driven or screwed down to follow the flange. Spikes may be driven down, but the further they go they have a less thickness of timber for a bed, and therefore a diminished hold. Crab bolts are apt to become rusted or ironbound, so that they cannot be screwed further, and must then be taken out and replaced with new ones. The narrower the flange, the more rapidly does the rail-seat cut down to a thickness inconsistent with safety. The sharp edge of the flange-rail has a tendency to cut a channel in the spike, and it is not at all an unusual occurrence to find strong square shanked dog-spikes, which have been thus cut into to the extent of a third or even half their thickness. The comparative narrow flange places the spikes at great disadvantage in point of leverage for holding down, and this weakness is soon made manifest, particularly on curves, where additional crab bolts or other devices are rendered necessary to counteract the tendency of the rail to rock and tilt over sideways. When the head of the rail cannot be kept in its proper position, the gauge becomes widened, and an irregular sinuous motion takes place in the running of the train. This drawback has been found to be a serious matter where light narrow flange rails have been adopted to carry comparatively heavy, short wheel-base engines. In some cases wrought-iron sole-plates, or even cast-iron bracket-chairs, have been introduced to give more bearing surface on the sleeper and increased support to the rail, but neither of the two methods give the same simple complete hold to the rail that is obtained by the cast-iron chair for the bull-head rail.
On the other hand, the modern cast-iron chair for the bull-head
rail has at least double the bearing surface on the sleeper to that of the flange-rail seat, so that under the same circumstances of rolling load as above described, the weight of 134 lbs. per square inch would be reduced to half, or 67 lbs. The greater length given to the chair effectually prevents any rocking action on the part of the rail, and reduces to a minimum any lifting action on the spike. A good fitting chair—especially when keyed on the inside—provides a most effectual support to the rail both vertically and laterally, and maintains the rail to accurate gauge. By giving proper clearance space at the tops of the chair-jaws, a bull-head rail can be taken out by simply driving out the wooden keys, and a new rail inserted without in any way disturbing the chairs or spikes. To change a flange rail necessitates the slackening and removal of a large number of the spikes and crab bolts.
As the sleepers under the chair road suffer less from the crushing of the timber, they have a much longer life in the line, and remain serviceable until they are incapacitated from decay. This is a very important item in places where timber sleepers are expensive. The steadiness of the chair prolongs the efficiency of the spikes.