Scientific American Supplement, No. 664, September 22,1888Various
History
Scientific American Supplement, No. 664, September 22,1888
Various
Science -- Periodicals
The next application, nickel and silver platers and buffers, are good
contract customers as a rule; one case in our experience showing but
an average use of 20 per cent. of the contract horse power hours.
This, however, is probably an exceptional case, and, as near as we can
estimate on this class of work, the actual motor service will not
exceed in any case 60 per cent. of the contract hours; a fair average
being probably 45 or 50 per cent.
The next two applications, printing presses on news and job work, are
probably met with more frequently than any other. On exclusively news
work, the instances where the motor is in service more than 3 or 4
hours is rare. It is, however, usual in news offices to find two or
more job presses. If the newspaper printed happens to be a morning
paper, the hours of news work are usually between 12 midnight and 4
o'clock in the morning, the job work being done through the day. I
have in mind a case of this description. In the shop is one cylinder
press and three job presses connected to a 2 H. P. motor. This motor
is on an incandescent circuit of 110 volts. To develop its rated power
at 110 volts would require about 16 amperes in the motor. An ampere
motor in series with the motor while running off the morning paper
with only the cylinder press in operation stood at 12 amperes. For 3
hours this load was practically constant, when it was thrown off
entirely. This gave on the night service but 30 per cent. of the
contract hours. This motor required 5 amperes to drive the shafting,
and but 8 amperes or one H. P. to drive the three job presses with the
cylinder press off. Here then is but a 50 per cent. use if the presses
be used constantly; there are, however, many days when they are
comparatively idle, 30 to 40 per cent., therefore, is a very safe
estimate of the maximum use of this motor on the day circuit, or, had
the motor been a 1 H. P., which would have been sufficient to drive
the job presses, the use would be 60 to 80 per cent. of the contract
hours, probably not above 60 per cent. All printing offices will
probably come within this range, unless the motor be larger than is
necessary to do the work.
Machine shops doing principally lathe work as a matter of course use a
larger percentage of their contracted power than shops doing lathe and
bench work with the same hands. In no case will the service of the
motor exceed 65 or 70 per cent. of its contract use, for machine
shops, like sewing machine shops, will never average over 75 per cent.
of the shop capacity for operators the year round. The average,
especially in the case of a shop doing much bench work, will fall as
low as 40 per cent.
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