The New Zealand Railways Magazine, Volume 5, Issue 9 (April 1, 1931)
The Heating of Tyres — Methods Old and New
The reorganisation of the New Zealand Railway Workshops has resulted in many marked improvements, not the least of which is the method of renewing tyres, both for locomotives and other rolling stock.
Under the old method, tyres, after they had been bored to suit the wheel centres, were taken outside, and stacked, ten or more high, in a position adjacent to a hand crane. Usually they were rolled out of the shop by man power. If a suitable line was available they would be loaded on a trolly, and pushed out to the crane. Much time was occupied gathering pieces of wood with which to heat the tyres. The wood was piled in the centre of the stack of tyres, and ignited. Then ensued a wait of several hours, until the tyres were hot enough to slip over the wheel centres, which had been placed in a vertical position, with the aid of the hand-crane.
For the benefit of the uninitiated, it should be explained that the tyres are always bored so many thousands of an inch less than the wheel centres, the allowance, in each case, being determined by the diameter of the centres. When heated, the tyres expand sufficiently to drop over the wheel centres. In cooling, the tyres contract, and grip the wheel centres very firmly. Suitable grabs, connected with short chains were used to lift the hot tyres from the stack.
An improvement was effected when the hand operated crane was altered by the addition of an air cylinder, and operated pneumatically. This system, with slight modifications has been in use for years. After the heated tyres had been applied to all the top wheel centres, it was necessary to wait until the tyres, by cooling, had gripped the centres tightly enough to remain in position while the wheels and axle were reversed. The remaining tyres in the stack were now applied to the wheel centres.
Electric Heating Process.
With the advent of the reorganisation scheme, the procedure of applying new tyres has been improved still further. The tyres are still bored out on the tyre boring mills, but an electric overhead crane in the machine shop picks up the tyre immediately it is bored and whisks it into position on the new electric heaters. These, three in number, take power at 230 volts, single phase. Heating of the tyres is effected by electror-magnetic induction, producing a large flow of current through the tyre, thereby causing a high temperature. By simple changes in the terminals, a temperature to suit different sized tyres is obtained. The tyre rests on suitable supports over the central core of the heater, but without touching any portion of the machine.
Next, the regulator arm is brought forward, and downward, by means of a hand-wheel and screw, until its under side makes contact with the top of the central core. The core, and regulator arm, are composed of a series of flat laminated strips of soft iron. These strips constitute the medium for the transference of the current through the machine. It is this flow of current through the heaters, setting up electro-magnetic induction, which causes the tyre to heat up.
With the tyre in position, all the operator has to do is to switch on the current. Whilst one tyre is heating up, which occupies from ten to twenty minutes, according to the size of the tyre, others are similarly positioned on the rest of the heaters, and wheel centres placed in readiness.
Small pellets of a special fusible metal are laid upon the tyres. “When these melt, it indicates to the operator that the desired temperature has been reached.
When tyres are sufficiently cooled, the wheels are smartly removed to the powerful, up-to-date, high speed, wheel lathes, for turning.
A succession of heated tyres is thus assured. The conditions of the operator are greatly improved, as he is independent of the state of the weather, has the advantage of an efficient electric crane service, and is not inconvenienced by the smoke, sparks, and dust nuisance, as obtained in the past.
Many accidents are caused by the care-lessness or indifference on the part of those who make use of cranes, chains, slings, lifts, etc. Always see that the, apparatus used is suitable for the work you want it to do. Remember that no machine, chain or rope, is stronger than its weakest part.—Sir Gerald Bellhouse, C.B.E. (H.M. Chief Inspector of Factories).