The Locomotive Of Today

132 The Framing, Wheels, etc. : Tyres, etc. The section of the rim depends upon the tyre fastening employed. In American practice cast iron has until recently been generally used for all wheels, but now Steel is being largely employed for the larger ones. When of cast iron they are often lightened by having the spökes and rim cast hollow, a form of which made with a very deep dish is shown in cross section at B. This setting out of the boss is done in order to secure a very long journal on the axle. The rim is hollowecl out as seen at the bottom of the sketch. This, in many examples,. is cast in segments to prevent the contraction, when cooling,. from straining the periphery. Tyres are of open hearth, crucible or Bessemer Steel, one-third of the length of the ingot from the top being cut off, and the tyre blank made from the remainder under a heavy hammer, the centre is punched out in the direction of the length of the ingot, and the ring thus formed is rolied to the required section. They are then bored out in a lathe to the proper size and shape to suit the style of securing adopted. A small amount of shrinkage is allowed for, this being generally about one hundredth of an inch per foot diameter of tyre. The tyre is now heated to a black heat, placed upon the wheel and allowed to cool but not quenched in water, as this might make it brittle and liable to crack. A variety of methods of securing the tyres on the wheels, in addition to the shrinkage, have been adopted, but we confine our remarks to three types. First, that of studding or bolting them on, in which case holes are drilled through the rim of the wheel into the tyre and tapped; set bolts are then screwed in. Secondly, the method shown at D, which is formed of a ring, turned, cut, and then sprung into a groove provided in the tyre and held by hammering the tyre down to it at intervals. Thirdly, by Mansell rings or a modification in which one ring only is used as shown at C, where the tyre has a lip sufficiently deep to take the side of the wheel rim and a groove upon its inside in which the ring fits, this is carried down exactly like the lip of the tyre upon the other side of the rim; rivets are then put in holes drilled through the ring, wheel rim and tyre lip, securing the whole together, so that when tyres are held by this method they may even be broken into small pieces and yet not fly from the wheel. The outside diameter of the tyre is made up of the flange upon the inner side and the tread which bears upon the rail. The usual British form is shown at C, the flange projects down a little more than one inch, and is of the shape shown.