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Page 2
[Illustration: IMPROVED OVERHEAD TRAVELING CRANE]
[Illustration: FIG. 2 SIDE ELEVATION]
[Illustration: FIG. 3 PLAN]
* * * * *
BEST DIAMETER CAR WHEELS.[1]
[Footnote 1: By Samuel Porcher, assistant engineer motive power
department, Pennsylvania Railroad. Read at a regular meeting of the
New York Railroad Club, Feb. 19, 1891.]
It goes almost without saying that for any given service we want the
best car wheel, and in general it is evident that this is the one best
adapted to the efficient, safe and prompt movement of trains, to the
necessary limitations improved by details of construction, and also
the one most economical in maintenance and manufacture.
It is our aim this afternoon to look into this question in so far as
the diameter of the wheel affects it, and in doing it we must consider
what liability there is to breakage or derangement of the parts of the
wheel, hot journals, bent axles, the effect of the weight of the wheel
itself, and the effect upon the track and riding of the car, handling
at wrecks and in the shop, the first cost of repairs, the mileage,
methods of manufacture, the service for which the wheel is intended
and the material of which it is made.
Confining ourselves to freight and passenger service, and to cast iron
and steel wheels in the general acceptation of the term as being the
most interesting, we know that cast iron is not as strong as wrought
iron or steel, that the tendency of a rotating wheel to burst is
directly proportional to its diameter, and that the difficulty of
making a suitable and perfect casting increases with the diameter.
Cast iron, therefore, would receive no attention if it were not for
its far greater cheapness as compared to wrought iron or steel. This
fact makes its use either wholly or in part very desirable for freight
service, and even causes some roads in this country, notably the one
with which I am connected, to find it profitable to develop and
perfect the cast iron wheel for use in all but special cases.
Steel, on the other hand, notwithstanding its great cost, is coming
more and more into favor, and has the great recommendations of
strength and safety. It is also of such a nature that wheels tired
with it run much further before being unfit for further service than
those made of cast iron, and consequently renewals are less frequent.
The inference would seem to be that a combination of steel and cast
iron would effect the desirable safeness with the greatest cheapness;
but up to the present this state of affairs has not yet been realized
to the proper extent, because of the labor and cost necessary to
accomplish this combination and the weakness involved in the manner of
joining the two kinds of material together.
Taking up the consideration of the diameter of the wheel now, and
allowing that on the score of economy cast iron must be used for
wheels in freight service, we are led to reflect that here heavy loads
are carried, and there is a growing tendency to increase them by
letting the floor of the car down to a level with the draft timbers.
All this makes it desirable to have the wheels strong and small to
avoid bent axles and broken flanges, to enable us to build a strong
truck, to reduce the dead weight of cars to a minimum, and have wrecks
quickly cleared away. The time has not yet come when we have to
consider seriously hot journals arising from high speed on freight
trains, and a reasonable degree only of easy riding is required. The
effect on the track is, however, a matter of moment. Judging from the
above, I should say that no wheel larger than one 33 in. in diameter
should be used under freight cars. Since experience in passenger
service shows that larger cast iron wheels do not make greater mileage
and cost more per 1,000 miles run, and that cast iron wheels smaller
than 33 in., while sometimes costing less per 1,000 miles run, are
more troublesome in the end, it is apparent that 33 in. is the best
diameter for the wheels we have to use in freight service.
When we take up passenger service we come to a much more difficult and
interesting part of the subject, for here we must consider it in all
its bearings, and meet the complications that varying conditions of
place and service impose. In consequence, I do not believe we can
recommend one diameter for all passenger car wheels although such a
state of simplicity would be most desirable. For instance, in a sandy
country where competition is active, and consequently speed is high
and maintained for a length of time without interruption, I would
scarcely hesitate to recommend the use of cast iron for car wheels,
because steel will wear out so rapidly in such a place that its use
will be unsatisfactory. If then cast iron is used, we will find that
we cannot make with it as large a wheel as we may determine is
desirable when steel is used. And just to follow this line out to its
close I will state here that we find that 36 in. seems to be the
maximum satisfactory diameter for cast iron wheels, because this size
does not give greater mileage than 33 in., costs more per 1,000 miles
run, and seems to be nearer the limit for good foundry results. On the
other hand, a 36 in. wheel rides well and gives immunity from hot
boxes--a most fruitful source of annoyance in sandy districts. It is
also easily applicable where all modern appliances under the car are
found, including good brake rigging. In all passenger service, then, I
would recommend 36 in. as the best diameter for cast iron wheels.
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