LOCOMOTIVE ENGINE.
457
Fig. 37.
of the two tires are given in figs. 36 and Fig - 36 -
37, half of the real size ; they are both
made slightly conical, being tapered
from If inch to 1J inch thick ; and the
flancli projects one inch and a quarter,
and is three quarters of an 'inch thick
at the edge and an inch thick at the base.
The rims and tires are both turned, and
the tires are heated when put on, and
contract on cooling so as to hold firmly on
the wheel; great care is required in
fitting them, that they may not be
loose upon the wheels nor shrunk too
tight, so as to injure their texture.
They are held in their places by three bolts with countersunk heads in the tires
and nuts screwed on against the inner side of the rims. The tires are turned when
fixed on the wheels to make them truty circular, and to make the two in each pair
exactly alike.
The flancli wheels, like the wheels of all railway carriages, require to be made a
little conical, in order to prevent the flanches being continually in contact with the
rails and rubbing against them, which would cause a great deal of friction; as a
wheel, when running towards one side and bringing the flanch in contact with the
rail, will bear upon a larger circumference than the other wheel, and will tend to run
towards the opposite side and make the wheels central again; the flanches are
thus hardly required on a straight line, and only necessary upon sharp curves to
keep the wheels from running off the line. The rails are laid inclined a little, so as
to fit the conical wheels, and for this reason the driving wheels have to be made
also conical, although they have no flanch. The driving wheels are made without
flanches that they may always have firm hold on the rails, as a flanch on the inner
one, when the engine is turning round a curve, would be forced against the inner
rail, and would interfere with the bearing of the wheel and cause friction; and
flanches upon the front and hind wheels are sufficient to keep the engine upon the
rails. For the improvement of making the middle driving wheels without flanches,
Mr. Stephenson has a patent.
The wheels of the first engines were made entirely of cast iron, but it was found
difficult to make them sound in consequence of the unequal contraction in cooling,
and they were too brittle to bear the shocks produced in running fast; the cast iron
was also found to be too soft and to wear in a groove on the edge with running on the
3 m