BBBBflt] «BlJIUrIrlr - Clpdigital.org

September, 1925
Forging - Sf amping - Heaf Treating
F o u r R o l l T y p e o f B o a r d D r o p H a m m e r
Board Drop Hammers Provided with Two Sets of Rolls Instead
of One Have Been Designed to Meet the Demand
F O R many years a stock subject for discussion
whenever drop forgers met has been the relative
merits of steam drop hammers and board drop
hammers. The board drop hammer has had some advantages
in the original cost of the installation, since
it could be set up and operated with only a motor and
a lineshaft, whereas, a steam boiler plant was required
for the steam drop hammer. On the other hand, in
handling some types of work, the steam drop hammer
had considerable advantage, due to the fact that
it can strike either a light or heavy blow, whereas,
the board drop hammer in forging any one piece, must
strike a fixed weight of blow, at least as far as practical
operation is concerned. The relative production
and relative operating cost of the two types has been
the favored subject of discussion, the answer depending
to a great extent on the local conditions. The
swing toward the use of central station power in late
years has of course been a factor in favor of board
drop hammers, and another thing which nas brought
about its adoption in many cases recently is the fact
that board drop hammers designed in the last few
years are of much more substantial and rugged construction
than those of earlier design. In fact, the
superintendent of a large forge shop, addressing a recent
meeting of the American Drop Forge Institute.
stated that the important members of 600-lb. board
drop hammers which he was buying today were- as
heavy in cross section as those of hammers rated at
3000-lbs. on which he learned his trade.
Capacity of Board Drop Hammer Limited.
However, it was thought that the steam drop hammer
would always dominate the field in large sizes,
as they could be built almost to any capacity that
might be required, since there was nothing to prevent
the use of larger cylinder bores or high pressure
steam to lift a ram of any size. The feeling has been,
however, that it would not be practicable to build
board drop hammers larger than about 4000-lbs. or
5000-lbs. in rated size. It will be understood that in
the case of board drop hammers the rated size is
the nominal weight of the hammer head or ram, and
in the case of the steam drop hammers the rated size
is the nominal weight of the falling parts which consist
of the ram, the piston rod and the piston head.
In the case of board drop hammers, the hammer ram
is lifted by means of boards which are wedged in
plate in the ram and which are gripped by revolving
rollers. In large hammers the rolls must have a tremendous
pressure on the boards in order that merely
by friction they can accelerate and lift the heavy ram.
There is a limit to the unit pressure per inch of width
of board which can be carried by the hard maple before
the board is crushed, or it is burned by the friction
and wears very rapidly. If the rams in various
sizes of hammers are designed with about the same
proportions, it is evident that if the width of the hammer
board is increased, the weight of the ram will
increase as the cube of the width; that is, :f the board
for Board Hammers of Large Capacity
329
is twice as wide, a ram of the same proportion would
weigh eight times as much. Putting the same statement
in another way, the width of board on a 5000-lb.
hammer is only about 30 or 40 per cent more than
on a 2500-lb. hammer, instead of being twice as much.
Therefore, the unit pressure on the boards of the
larger hammer must be considerable greater and the
life of the boards is correspondingly reduced.
New Type of Board Hammer.
A new type of board drop hammer recently placed
on the market by the Erie Foundry Company of Erie,
Pa., is designed to meet the demand for large board
drop hammers and at the same time to reduce the
wear on boards and belts, and thus minimize two of
the largest items of board drop hammer operating
cost. This has been accomplished by providing the
hammer with two sets of rolls instead of one. so that
the total pressure of the rolls against the board is applied
at two points; thus, with the same effort applied
to lifting the ram, the unit pressure of the board is
only half as great. Actually, however, the lifting effort
has been increased so that the hammer can be
operated more rapidly, and at the same time the unit
pressure on the board is much less than in any other
hammer. The design lends itself to the use of a gear
reduction between the pulley shaft and the roll shaft
so that the pulleys are run at about twice the rpm.
of the rolls and this increases the speed of the belt
and reduces the tension to figures which would be
recommended by belting manufacturers. This cannot
be done on any other type of hammer and it is claimed
that the cost of belting repairs and maintenance will
be much reduced.
The distinguishing feature of the new type of hammer
is of course the design of the lifter or head, although
there is some interesting construction at other
points to which reference will be made later. A closeup
view of the head is shown in the accompanying
cuts Fig. I. The head is symmetrical front and
back, the only difference being that the front eccentric
operates at each stroke of the hammer, being actuated
by the friction bar; while the back eccentric is adjustable
to accomodate varying thicknesses of boards.
Roll Pressure Must be Equalized.
The upright side housings of the head are supported
'w the heavy cast steel tie plate, which also
carries the floating head or clamp which is of the
usual design. Journaled in the uprights of the head
are the cast steel eccentrics. Each eccentric carries
two equalizers or eveners, which are free to turn
about the eccentric. The diameter of the eccentric
which carries the equalizers is turned on a different
center from the diameter which is journaled in the
side frame; so, as the eccentric is rotated, the equalizers
are forced in toward the hammer board. The
tops of each pair of equalizers are fastened together
by means of heavy cast steel bars so that the pair of
equalizers must always work as a unit and the ends