so that it causes the hammer to stop at the top of its stroke after
working; thus enabling the material to be placed on the anvil before
starting the hammer. The movable fulcrum, B, consists of a stud, free to
slide in a slot, C, in the framing, and held in position by a nut and
toothed washer. On the fulcrum is mounted the socket, D, through which
passes freely a round bar or rocking lever, E, attached at one end to
the main piston, F, of the hammer, G, and having at the other extremity
a long slide, H, mounted upon it. This slide is carried on the
crank-pin, I, fastened to the disk, J, attached to the driving shaft, A.
The crank-pin, in revolving, reciprocates the rocking lever, E, and
main piston, F, and through the medium of the pneumatic connection, the
hammer, G. The slide, H, in revolving with the crank-pin, also moves
backward and forward along the rocking lever, approaching the fulcrum,
B, during the down-stroke of the hammer, and receding from it during
the up-stroke. By this means the velocity of the hammer is considerably
accelerated in its downward stroke, causing a sharp blow to be given
while it is gently raised during its upward stroke.
To alter the force of the blow, the hammer, G, is made to rise and fall
through a greater or less distance, as may be required, from the fixed
anvil block, K, after the manner of the smith giving heavy or light
blows on his anvil. It is evident that this special alteration of the
stroke could not be obtained by altering the throw of a simple crank and
connecting rod; but by placing the slot, C, parallel with the direction
of the rocking lever, E, when the latter is in its lowest position, with
the hammer resting on the anvil, and with the crank at the top of its
stroke, this lowest position of the rocking lever and hammer is made
constant, no matter what position the fulcrum, B, may have in the slot,
C. To obtain a short stroke, and consequently a light blow, the fulcrum
is moved in the slot toward the hammer, G; and to produce a long stroke
and heavy blow the fulcrum is moved in the opposite direction.
Fig. 3 gives the details of the pneumatic connection between the main
piston and the hammer, in which packing and packing glands are dispensed
with. The hammer, G, is of cast steel, bored out to fit the main piston,
F, the latter being also bored out to receive an internal piston, L. A
pin, M, passing freely through slots in the main piston, F, connects
rigidly the internal piston, L, with the hammer, G. When the main piston
is raised by the rocking lever, the air in the space, X, between the
main and internal pistons, is compressed, and forms an elastic medium
for lifting the hammer; when the main piston is moved down, the air in
the space, Y, is compressed in its turn, and the hammer forced down to
give the blow. Two holes drilled in the side of the hammer renew the air
automatically in the spaces, X and Y, at each blow of the hammer.
Figs. 4 to 6, on the next page, represent the medium size forging
hammer, for making forgings in dies, swaging and tilting bars, and
plating edged tools, etc.
The hammer weighs 1 cwt., has a stroke variable from 4 in. to 141/2 in.,
and gives 200 blows per minute; the compressed air space between the
main piston and the hammer is sufficiently long to admit forgings up to
3 in. thick under the hammer.
To make forgings economically, it is necessary to bring them into the
desired form by a few heavy blows, while the material is still in a
highly plastic condition, and then to finish them by a succession of
lighter blows. The heavy blows should be given at a slower rate than the
lighter ones, to allow time for turning the work in the dies or on the