BBBBflt] «BlJIUrIrlr - Clpdigital.org

330 Forging-Sfamping- Heaf Treating
will always be in line with each other. The rolls are
mounted on shafts which are carried in bores at the
ends of the equalizers, one roll at the top and one at
the bottom of each pair of equalizer-. It will be
readily apparent that the pressure put on the board by
the toIU will always be equally divided between the
top pair and the bottom pair of rolls, regardless of
whether or not the front and back ol the board are
parallel. This point is of particular importance, since
frequently a low spot is worn at one point of the
board, or the board wears tapered, and without the
equalizing feature, one pair of rolls will take all of
the load, not only damaging the board, but also putting
high pressure on the roll bearings and straining
other part.- of the mechani>m which are designed to
take only half the load.
The eccentric is bored out and bushed with bronze
and the main drive shaft runs in these bushings. It
carries at one end the driving pulleys and at the other
end the pinion. The pinion meshes with two gears.
one f>n each of the roll shaft- which extend through
September, 1925
the ends of the equalizers. It should be noticed particularly
that these gears are always in constant mesh
regardless of the position of the eccentric. This design
is not to be confused with the old-style of gear
lifter in which a gear at the front of the board meshed
with one at the back of the board. This old style of
gear lifter is practically obsolete now, because of the
fact that with a thick board the gear- mesh out at
the point of the tooth, while with a thin board they
mesh down near the root of the tooth, and consequentlv
special tooth forms must be used and the
gears wear rapidly and become noisy. The pinion is
only half the size of the gears, so that the main shaft
and the pulleys revolve at twice the speed of the rolls.
Therefore, with the same size pulleys, the belt speed
is twice what it would ordinarily be and consequently
the belt tension only half what it would be. This has
overcome another difficulty which has stood in the
path of the development of large board drop hammers.
Ordinarily the pulley and the roll run at the same
speed, both being keyed to one shaft. Previously, in
FIG 1—A close-up view of the head of the four-roll board drop hammer.