Minster IOI, Service Manual

Page: 73 / 92

The illustration shows how press tonnage is affected by
a change in length of the crank lever arm, or effective
moment arm, as the slide nears bottom of its stroke.
From this it also follows that a press with a short stroke
will not have the same tonnage characteristics as a
press with a long stroke, even though both may be
rated for full tonnage the same distance off bottom.
This relationship is further illustrated by the curves
shown on the Tonnage Charts, pages H-5 thru H-7. Six
different tonnage charts are included in the manual —
for the #4 thru #7 Minster O.B.I. flywheel type press
and the #6 & #7 Minster O.B.I single geared presses.
PRESS DRIVES
The electric motor supplies energy to the press fly-
wheel at an almost constant rate. Here the kinetic ener-
gy is stored until a portion of it is expended to help
perform work by the press. Position of the flywheel
within the press drive is very important because its
location will have an effect upon the operating charac-
teristics of the press. It may be located directly on the
crankshaft, or on a driveshaft connected to the crank-
shaft through a gear train.
A press which has the flywheel located directly on the
crankshaft is called a flywheel type or non-geared
press. In presses of this type, flywheel energy which
has been spent during each stroke should be recov-
ered during the unloaded portion of the stroke. To meet
these operating conditions, flywheel type presses
should be used primarily for work where flywheel ener-
gy is expended only very near bottom of the stroke.
Operations such as blanking, cutting or piercing thin
stock are usually best suited for this application.
Speed of flywheel type presses will be higher than
geared presses because the flywheel is mounted on
the press crankshaft and all flywheels are subject to
certain minimum speeds. Slow flywheel speed will pro-
vide only very little energy for work. Speed of flywheel
type (non-geared) presses is usually in excess of 80
strokes per minute.
On single geared presses, flywheel energy is transmit-
ted to the slide through a single gear reduction, The
gear ratio permits greater flywheel speeds with resul-
tant higher energy to perform heavier work than the
non-geared press. Single geared press usually fall in
an intermediate range of from 30 to 80 strokes per
minute. Presses of this type are best suited for shallow
draw work, forming and blanking of heavier materials.
H - 4
Flywheel Type Press
(non-geared)
Single Geared Press