_STEAM-HAMMERS._
The direct application of steam to forging-hammers is without
doubt the greatest improvement that has ever been made in forging
machinery; not only has it simplified operations that were carried
on before this invention, but has added many branches, and extended
the art of forging to purposes which could never have been attained
except for the steam-hammer.
The general principles of hammer-action, so far as already
explained, apply as well to hammers operated by direct steam; and
a learner, in forming a conception of steam-hammers, must not fall
into the common error of regarding them as machines distinct from
other hammers, or as operating upon new principles. A steam-hammer
is nothing more than the common hammer driven by a new medium,
a hammer receiving power through the agency of steam instead of
belts, shafts, and cranks. The steam-hammer in its most improved
form is so perfectly adapted to fill the different conditions
required in power-hammering, that there seems nothing left to be
desired.
Keeping in view what has been said about an elastic connection
for transmitting motion and power to hammers, and cushioning the
vibratory or reciprocating parts, it will be seen that steam as a
driving medium for hammers fills the following conditions:--
_First._--The power is connected to the hammer by means of the
least possible mechanism, consisting only of a cylinder, a piston,
and slide valve, induction pipe and throttle valve; these few
details taking the place of a steam-engine, shafts, belts, cranks,
springs, pulleys, gearing, in short, all such details as are
required between the hammer-head and the steam-boiler in the case
of trip-hammers or crank-hammers.
_Second._--The steam establishes the greatest possible elasticity
in the connection between a hammer and the driving power, and at
the same time serves to cushion the blows at both the top and
bottom of the stroke, or on the top only, as occasion may require.
_Third._--Each blow given is an independent operation, and can
be repeated at will, while in other hammers such changes can only
be made throughout a series of blows by gradually increasing or
diminishing their force.
_Fourth._--There is no direct connection between the moving parts
of the hammer and the framing, except lateral guides for the
hammer-head; the steam being interposed as a cushion in the line
of motion, this reduces the required strength and weight of the
framing to a minimum, and avoids positive strains and concussion.
_Fifth._--The range and power of the blows, as well as the time in
which they are delivered, is controlled at will; this constitutes
the greatest distinction between steam and other hammers, and the
particular advantage which has led to their extended use.
_Sixth._--Power can be transmitted to steam-hammers through a small
pipe, which may be carried in any direction, and for almost any
distance, at a moderate expense, so that hammers may be placed
in such positions as will best accommodate the work, and without
reference to shafts or other machinery.
_Seventh._--There is no waste of power by slipping belts or other
frictional contrivances to graduate motion; and finally, there is
no machinery to be kept in motion when the hammer is not at work.
Keeping these various points in mind, an apprentice will derive
both pleasure and advantage from tracing their application
in steam-hammers, which may come under notice, and various
modifications of the mechanism will only render investigation more
interesting.
One thing more must be noticed, a matter of some intricacy, but
without which, all that has been explained would fail to give a
proper idea of steam-hammer-action. The valve motions are alluded
to.
Steam-hammers are divided into two classes--one having the valves
moved by hand, and the other class with automatic valve movement.
The action of steam-hammers may also be divided into what is termed
elastic blows, and dead blows.
In operating by elastic blows, the steam piston is cushioned at
both the up and down stroke, and the action of a steam-hammer
corresponds to that of a helve trip-hammer, the steam filling the
office of a vibrating spring; in this case a hammer gives a quick
rebounding blow, the momentum being only in part spent upon the
work, and partly arrested by cushioning on the steam in the bottom
of the cylinder under the piston.
Aside from the greater rapidity with which a hammer may operate
when working on this principle, there is nothing gained, and much
lost; and as this kind of action is imperative in any hammer that
has a 'maintained or positive connection' between its reciprocating
parts and the valve, it is perhaps fair to infer that one reason
why most automatic hammers act with elastic blows is either because
of a want of knowledge as to a proper valve arrangement, or the
mechanical difficulties in arranging valve gear to produce dead
blows.
In working with dead blows, no steam is admitted under the piston
until the hammer has finished its down stroke, and expended its
momentum upon the work. So different is the effect produced by
these two plans of operating, that on most kinds of work a hammer
of fifty pounds, working with dead blows, will perform the same
duty that one of a hundred pounds will, when acting by elastic or
cushioned blows.
This difference between dead and elastic strokes is so important
that it has served to keep hand-moved valves in use in many cases
where much could be gained by employing automatic acting hammers.
Some makers of steam-hammers have so perfected the automatic class,
that they may be instantly changed so as to work with either dead
blows or elastic blows at pleasure, thereby combining all the
advantages of both principles. This brings the steam-hammer where
it is hard to imagine a want of farther improvement.
The valve gearing of automatic steam-hammers to fill the two
conditions of allowing a dead or an elastic blow, furnishes one of
the most interesting examples of mechanical combination.
It was stated that to give a dead or stamp stroke, the valve must
move and admit steam beneath the piston after the hammer has made
a blow and stopped on the work, and that such a movement of the
valve could not be imparted by any maintained connection between
the hammer-head and valve. This problem is met by connecting the
drop or hammer-head with some mechanism which will, by reason of
its momentum, continue to 'move after the hammer-head stops.' This
mechanism may consist of various devices. Messrs Massey in England,
and Messrs Ferris & Miles in America, employ a swinging wiper bar,
which is by reason of its weight or inertia retarded, and does not
follow the hammer-head closely on the down stroke, but swings into
contact and opens the valve after the hammer has come to a full
stop.
By holding this wiper bar continuously in contact with the
hammer-drop, elastic or rebounding blows are given, and by adding
weight in certain positions to the wiper bar its motion is so
retarded that a hammer will act as a stamp or drop. A German firm
employs the concussion of the blow to disengage valve gear, so
that it may fall and effect this after movement of the valves.
Other engineers effect the same end by employing the momentum of
the valve itself, having it connected to the drop by a slotted or
yielding connection, which allows an independent movement of the
valve after the hammer stops.
(1.) In comparing steam-hammers with trip or crank hammers
what mechanism does steam supplant or represent?--(2.) What
can be called the chief distinction between steam and other
hammers?--(3.) Under what circumstances is an automatic valve
motion desirable?--(4.) Why is a dead or uncushioned blow most
effective?--(5.) Will a hammer operate with air the same as with
steam?