Watertown republican. [volume] (Watertown, Wis.) 1860-1906, 1875-04-14

MACHINE
ychanics.

!
| Read before the New York Society of Practical
! Engineering, by John w. Sutton.
| Although the use of belts for the
transmission of power is not, strictly
speaking, an American invention, the
great improvements made in this coun-
try have caused it to be known in Europe
as the American system. In Europe
the greater part of the power is trans
mltted by cog-wheels, but in this coun
try 80 per cent. is transmitted by belt
ing. The latter is used everywhere,
from the sewing to the 500
horsepower engine of the largest fac
tory: Belts can be run in any way, at
any angle. of any length and Of any
speed, and can be put up by any one of or
dlnaryskill. The, belts can be made of any
flexible material rubber, gutta-
percha, cloth, paper, raw-hide, cord or
wlre-and they may either be round or
flat; and the last novelty is sheet
iron belt, and it is said to work
well. Every one uses them. While SO
handy and so popular, they have one
fault. They are not positive. If you
start from the motor with certain num-
Der of revolutions, you lose a portion
of them with every belt used. This is
the only fault of the system It is
noiseless, yielding and regular, but,
unlike cog wheels, it is not positive.
The number of revolutions that are lost
may, and does, vary continually by
changes of the load and of the atmo-
sphere. It is upon these peculiar
changes of our favorite system that [
propose to speak tonight. Belts derive
their power to transmit motion from
the friction between the surface of the
belt and the pulley, and from nothing
else, and are governed by the same laws
as friction between flat surfaces The
friction increases regularly with the
pressure.
The lecturer then gave there suits of
some experiments with belts and pull
legs to prove this. He found that
there was great difference in tie friction
of belts, and it was due to their elastici-
ty of surface; that is, the more elastic the
surface. the greater the friction. He
made experiments With pully and belt,
moved by lever and spring balance, to
show the difference III the actual fric-
ton between the grain and flesh sides of
aleather belt in contact with a smooth
cast iron pulley. He said that the old
rule "that the number of inches in con-
tact, multiplied by one-half the velocity
of the belt IN feet per minute, and divi-
ded by 10000, would give the horse
power" might give it once in 100 times,
but not oftener The rule is that a
belt holds upon a pulley as
the tension pressure), and as
the square of the degrees of
of wrap. A belt wrapped one quarter
around pulley has only onefourth the
power of belt wrapped one-half around
the same pulley with the same tension.
A line around a post will give a good
illustration of this. One-half turn
and mans weight is doubled, while a
full turn and his weight is nearly enough
to stop heavy boat, and two turns and
his weight will stop the boat or the line
will part.
Belts always run to the high part of
the pulley when the shafts are parallel ;
but, when they are not, the belt will
always run towards the ends of the
shafts that are nearest together, and
this tendency is much stronger than to
run to the highest parts of the pulley.
If you have belt that gives trouble in
this way, you can see If it is the fault
of your shafting by drawing a line
across the edges of the two pulleys.
Sometimes the bearings may be in line,
but the tension of your belt is 50 great
as to spring the shaft, so as to throw the
pulleys out of line. A sitter shaft OF
another bearing is the remedy. Leather
and rubber belts each have their advo-
Gates, and each party say theirs is very
much better; but each kind is better in
its place. Where the belt is lear, q
rubber belt will transmit twenty pei
cent. more power with the same tension,
and will last as long and run perfectly
straight. It can be made of any length
or width, or exactly the same thickness
in every part, perfectly smooth on its
surface, and when in use, every part
will come in contact with the face of the
pulley. The greater tractile power of a
rubber belt is due to it's surface elastici-
ty. Leather belts have to be made from
pieces, and, as the leather is not per
fectly fiat, perfectly fat belt cannot be
made from it. Ii belt is cut from the
back of hide, the edges are not SO
firm as the center, and upon crowned
pulley they will not hug SO we'll as If
they were of the same frmness as the
center. If the belt is cut from one side
of the back, then one edge will be less
firm than the other, and the belt will be
crooked, and one side will have more
tension than the other. Leather belts
are usually riveted at the joints. Now,
if rivet-head touches the pulley the
friction is less than if the leather touch
ed it. If the head is above the surface
of the belt, then portion of the belt is
not in contact with the pulley; and if
the head is below the surface of the belt
then of course there is no contact. Now,
every rivet in belt is in one or the
other of those positions, and leather
belts would be improved by using some
thing else in their place. Double leath-
er belts are more used than single ones,
but it is clearly mistake, as a single
! leather one will transmit more of the
power than a double one. If you look
at the face of leather belt, you will
see, when it has been used for time,
the face has a notified appearance, light