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Page 3
Next taking up steel wheels, a great deal might be said about the
different makes and patterns, but as the diameter of wheels of this
kind is not limited practically to any extent by the methods of
manufacture, except as to the fastening of the wheel and tire
together, we will note this point only. Tires might be so deeply cut
into for the introduction of a retaining ring that a small wheel would
be unduly weakened after a few turnings.
On the other hand, when centers and tires are held together by
springing the former into the latter under pressure, it is possible
that a tire of larger diameter might be overstrained. But allowing
that the method of manufacture does not limit the diameter of a steel
wheel as it does a cast iron one, the claim that the larger diameter
is the best is open to debate at least, and, I believe, is proved to
the contrary on several accounts. It is argued that increasing the
diameter of a wheel increases its total mileage in proportion, or even
more. Whether this be so or not, there are two other very
objectionable features that come with an increase in diameter--the
wheel becomes more costly and weighs more, without giving in all cases
a proportionate return. We have to do more work in starting and
stopping, and in lifting the large wheel over the hills, and when the
diameter exceeds a certain figure we have to pay more per 1,000 miles
run. I am very firmly convinced that the matter of dead weight should
receive more attention than it does, with a view to reducing it. The
weight of six pairs of 42 in. wheels and axles alone is 15,000 to
16,000 lb.
The matter of brakes is coming up for more attention in these days of
high speed, heavy cars and crowded roads, and the total available
braking power, which has hitherto been but partially taken advantage
of, must be fully utilized. I refer to the fact that many of our
wheels in six-wheel trucks have gone unbraked where they should not.
As the height of cars and length of trucks cannot well be increased
for obvious reasons, it is necessary to keep the size of the wheels
within the limits that will enable us to get efficient brakes on all
of them that carry any weight. This is not easy with a 42 in. wheel in
a six-wheel truck, which is usually the kind that requires most
adjustment and repairs after long runs. The Pullman Co. has recognized
this fact, and is now replacing its 42 in. wheel with one 38 in. in
diameter.
A 42 in. wheel with 4 in. journal has a greater leverage wherewith to
overcome the resistance of journal friction than the 38 in. wheel with
the same journal, and even more than the 36 in. and 33 in. wheels with
33/4 in. and 31/2 in. journals respectively, but the fact remains that the
same amount of work has to be done in overcoming the friction in each
case, and what may be gained in ease of starting with the large wheel
is lost in time necessary to do it, and in the extra weight put into
motion.
A large wheel increases the liability to bent axles in curving on
account of greater leverage unless the size and weight of the axle are
increased to correspond, and the wheel itself must be made stronger. A
four or six wheel truck will not retain its squareness and dependent
good riding qualities so well with 42 in. wheels as with 33 in. ones.
Besides the brakes, the pipes for air and steam under the cars
interfere with large wheels, and as a consequence of all this 42 in.
wheels have been replaced by 36 in. ones to some extent in some places
with satisfactory results. On one road in particular so strong is the
inclination away from large wheels that 30 in. is advocated as the
proper size for passenger cars.
On the other hand, there is no doubt a car wheel may be too small, for
the tires of small wheels probably do not get as much working up under
the rolls, and therefore are not as tough or homogeneous. Small wheels
are more destructive to frogs and rail joints. They revolve faster at
a given speed, and when below a certain size increase the liability to
hot journals if carrying the weight they can bear without detriment to
the rest of the wheel. Speed alone I am not willing to admit is the
most prolific source of hot boxes. The weight per square inch upon the
bearing is a very important factor. I have found by careful
examination of a great many cars that the number of hot boxes bears a
close relation to the weight per square inch on the journal and the
character of lubrication, and is not so much affected by the size of
wheel or speed. These observations were made upon 42 in., 36 in. and
33 in. wheels in the same trains. We find, furthermore, that while a
3-3/8 in. journal on a 33 in. wheel is apt to heat under our passenger
coaches, a 33/4 in., even when worn 3-5/8 in., journal on a 36 in. wheel
runs uniformly cool. In 1890 on one division there were about 180 hot
boxes with the small wheel, against 29 with the larger one, with a
preponderance of the latter size in service and cars of the same
weight over them.
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