IMPROVEMENTS IN ROCK DRILLS
Year: 1877

page_text: LETTERS PATENT to Theodor Frölich, of No. 28, Fenchurch Street, in the
City of London, for the Invention of "IMPROVEMENTS IN ROCK DRILLS." A
communication from abroad by Julius Frölich, of Düsseldorf, in the Empire of
-Germany.
PROVISIONAL SPECIFICATION left by the said Theodor Frölich at the Office
of the Commissioners of Patents on the 30th October 1877.
THEODOR FRÖLICH, of No. 28, Fenchurch Street, in the City of London.
"IMPROVEMENTS IN ROCK DRILLS." [A communication from abroad by Julius
Frölich, of Düsseldorf, in the Empire of Germany.]
This Invention has for its object improvements in rock drills, and relates especially
to that class of drills in which the cutting tool is mounted at the end of a rod, which
also carries a piston working in a cylinder to which air or other fluid under
is supplied, and in which the cylinder is moved progressively forward along a bed
or guide on which it is mounted as the tool penetrates the rock.
pressure
In order to control the admission of air to and its escape from the main cylinder
a slide valve is employed; it is fixed between two small pistons, which are received
into corresponding cylinders. Each of these cylinders is connected by a passage
with the main cylinder, and the ports in which these passages terminate are alter-
nately uncovered by the main cylinder as it moves to and fro. As each port is
uncovered the compressed air passes from the main cylinder to the small cylinder
corresponding to the port uncovered, and moves the piston therein, and with it the
valve. Each of these small valve cylinders is provided with a vent admitting of
the escape of the air when the connection with the main cylinder is closed, and the
size of these vents controls the speed at which the reciprocating motion of the main
cylinder is maintained.
The advance of the main cylinder with the parts connected therewith as the work
progresses is effected automatically by means of a screw and nut. The nut is
connected with the cylinder in such manner as to leave it free to turn, and it has

page_text: ratchet teeth upon it with which a driving pawl engages. The pawl is mounted
upon a lever receiving motion from a piston contained in another small cylinder,
which at the time when forward movement is required receives air from the main
cylinder. To effect this the main piston rod is grooved, and when its piston
approaches the front end or cover of the main cylinder the groove permits an escape
of air into a channel, which conducts it into the small cylinder for working the
driving pawl, where, acting upon the full area of the piston, it imparts a forward
motion to it. There is another similar groove in the main piston rod, which allows
the escape of the air from this small cylinder when the main piston approaches the
end of its return stroke, and then the small piston returns, for its smaller area
around the piston rod is always exposed to pressure.
In order to produce the necessary rotation of the cutting tool, there is a twisted
or rifled bar which extends down the centre of the main cylinder, and the main
piston is fitted to work upon it; as a nut upon a screw. This bar is provided with
à head, upon the surface of which ratchet-like teeth are cut, and facing it is a disc
with corresponding teeth. When the teeth interlock, the rifled bar is held and
prevented turning by stops, which at all times prevent the rotation of the disc.
The disc forms the head of a plunger or ram entering another small cylinder, to
which the compressed air is constantly admitted, whilst the disc itself and the head
of the rifled bar are contained in a chamber having free communication with the
rear end of the main cylinder; thus, during the return stroke of the main piston,
the pressure on the plunger or ram is effective to press the disc and head together;
and as the main piston moves along the rifled. bar, it is compelled to turn partly
round, but during the forward stroke the main piston, in place of turning within
the cylinder, causes the partial rotation of the rifled bar, the locking teeth then
separating, for at this time both sides of the plunger or ram are exposed to an equal
pressure, and the plunger or ram having no effective support retires and offers no
resistance to the rotation of the rifled bar.
th

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Theodor Frölich in the Great Seal. Patent Office on the 30th April
1878.
THEODOR FRÖLICH, of No. 28, Fenchurch Street, in the City of London.
IMPROVEMENTS IN ROCK DRILLS." (A communication from abroad by Julius
Frölich, of Dusseldorf, in the Empire of Germany.)
This Invention has for its object improvements in rock drills, and relates especially
to that class of drills in which the cutting tool is mounted at the end of a rod, which
also carries a piston working in a cylinder to which air or other fluid under pressure
is supplied, and in which the cylinder is moved progressively forward along a bed
or guide on which it is inounted as the tool penetrates the rock.
In order to control the admission of air to and its escape from the main cylinder,
a slide valve is employed; it is fixed between two small pistons, which are received
into corresponding cylinders. Each of these cylinders is connected by a passage
with the main cylinder, and the ports in which these passages terminate are alter-
As each port is
nately uncovered by the main piston as it moves to and fro.
uncovered the compressed air passes from the main cylinder to the small cylinder
corresponding to the port uncovered, and moves the piston therein, and with it the
valve. Each of these small valve cylinders is provided with a vent admitting of
the escape of the air when the connection with the main cylinder is closed, and the
size of these vents controls the speed at which the reciprocating motion of the main'
cylinder is maintained.
The advance of the main cylinder with the parts connected therewith as the work
The nut is
progresses is effected automatically by means of a screw and nut.
connected with the cylinder in such manner as to leave it free to turn, and it has
ratchet teeth upon it with which a driving pawl engages. The pawl is mounted
upon a lever receiving motion from a piston contained in another small cylinder,
which at the time when forward movement is required receives air from the main
cylinder. To effect this the main piston rod is grooved, and when its piston
approaches the front end or cover of the main cylinder the groove permits an escape
of air into a channel, which conducts it into the small cylinder for working the
driving pawl, where, acting upon the full area of the piston, it imparts a forward
inotion to it. There is another similar groove in the main piston rod, which allows
the escape of the air from this small cylinder when the main piston approaches the
end of its return stroke, and then the small piston returns, for its smaller area around
the piston rod is always exposed to pressure.
In order to produce the necessary rotation of the cutting tool, there is a twisted
or rifled bar which extends down the centre of the main cylinder, and the main
piston is fitted to work upon it, as a nut upon a screw. This bar is provided with
a head, upon the surface of which ratchet-like teeth are cut, and facing it is a disc
with corresponding teeth. When the teeth interlock, the rifled bar is held and
prevented turning by stops, which at all times prevent the rotation of the disc. The
dise forms the head of a plunger or ram entering another small cylinder, to which
the compressed air is constantly admitted; whilst the disc itself and the head of the
rifled bar are contained in a chamber having free communication with the rear end
of the main cylinder; thus, during the return stroke of the main piston, the pressure
on the plunger or ram is effective to press the disc and lead together, and as the
main piston moves along the rifled bar, it is compelled to turn partly round; but
during the forward stroke the main piston, in place of turning within the cylinder,
causes the partial rotation of the rifled bar, the locking teeth then separating, for at
this time both sides of the plunger or ram are exposed to an equal pressure, and the
plunger or ram having no effective support retires and offers no resistance. to the
rotation of the rifled bar.

page_text: DESCRIPTION OF THE DRAWINGS.
Figure 1 is a longitudinal section of the rock drill; Figure 2 is a plan of the
same, with some of the parts removed; Figures 3 and 4 are transverse sections taken
respectively on the lines 1, 1, and 2, 2, in Figures 1 and 2.
a; a, is trough line, frame, or guide, capable of being fixed by a bolt a¹ in any
required position upon a suitable standard or upright; b is a cylinder; it is cast
with lugs b1, b', upon it, which are received into grooves in the sides of the trough a,
along which the cylinder has an automatic movement; this it derives from the nut c
carried upon the cylinder cover d and the screw e which is fixed to the trough a.
When the nut is turned, by means herein-after more fully described, it progresses
along the screw and carries the cylinder with it; f is the piston working in the
cylinder b; it is formed of a piece with its piston rod g, which passes out of the
cylinder through a packed gland in the cylinder cover a, and which also forms the
tool holder, g¹ being the socket for receiving the tool.
The reciprocating motion of the piston is maintained by compressed air. The
admission and the escape of the air is determined by the slide valve working over
the ports 1, 2, 3, of which the centre port ² is the outlet. The valve is held
between the two subsidiary pistons 1, l, which are connected by the pieces 1, 1, and
they work in cylinders m, m; n, n, are passages connecting the cylinders m with
the main cylinder b; and as the piston f approaches the end of its stroke in either
direction, it uncovers the mouth of one or other of the passages n, and the compressed
air, passing into the corresponding cylinder m, reverses the position of the slide valve,
which entails the return of the main piston f. When air is thus admitted to one of
the cylinders m, the movement of the valve is retarded by the air contained in the
opposite cylinder m, which can only escape by the orifice m³, and the larger this
orifice the more rapid will be the reciprocation of the main piston f
The orifices m' are formed in screw plugs, which can be readily changed; o, o, are
valve-like plugs in the ends of the cylinders m, m. They serve to move the valve i
from the outside in starting the drill in work.
It is necessary when the drill is at work to turn the tool partly round between
the blows, which it strikes upon the face of the rock; to ensure this the piston f is
fitted with a bushing f' adapted to work as a nut upon the rifled or twisted bar p.
This bar is held in the collar q, secured between the end of the cylinder 6 and its
cover d, and upon the head of the bar p brequet ratchet teeth are formed. There
are also similar teeth formed upon the head of a plunger working in another sub-
sidiary cylinder d¹ formed in the cover d. The interior of the cylinder d' is at all
times in communication with the supply of compressed air by the passage d². The
head of the plunger r has wings upon it entering corresponding grooves in the
cover d, so that the plunger, whilst free to move endwise, is prevented turning.
Consequently, as already explained, when the compressed air is operating in the
cylinder b to drive the tool up to the work, the plunger r is exposed to equal pressure
on both sides, and it will then yield back freely to permit the bar p to turn; but,
during the return stroke, the plunger is exposed to pressure only within the cylinder 4
d, and consequently its head is pressed firmly against the head of the bar p, which,
being thus locked fast, compels the piston f to turn within the cylinder b; 8, 8, are
elastic packings at the end of the cylinder 6 to receive the piston f and prevent it
striking directly against the cylinder covers.
The nut c receives its rotary motion from a lever t, which is able to turn upon it, 5
and which carries a pawl (or by preference two pawls t¹, t,) engaging with ratchet
teeth cut upon the periphery of the nut c. The lever t is jointed, as the Drawing
indicates, with the rod of a piston u working in a cylinder v. The space in the
cylinder v, around the rod of the piston u, is at all times supplied with air under

page_text: pressure, and the other end of the cylinder v is, by a passage w, connected with a
cavity in the cylinder cover h. The cavity x from time to time receives com-
pressed air from the interior of the main cylinder; this it does whenever the piston f
approaches the front cover d, for then the grooves g², g², in the piston rod (it is
preferred to have several grooves) reach such a position as to give free admission
for the air to the cavity as soon as the slide valve i is moved over to cause the
return of the main piston f. The air so passing reaches the cylinder v, where it
causes the movement of the piston u, and consequently the partial rotation of the
nut c. On the return motion of the piston f, the grooves g³, g³, in the piston rod
again place the cavity in communication with the interior of the cylinders bon
the front side of the piston, and this at a time when this end of the cylinder is
discharging its contents. The air which previously passed into the cylinder v now
flows back, and the piston v returns in consequence of the constant pressure on its
under side, which thus becomes unbalanced.
The stroke of the piston u can be adjusted by means of the regulating screw 2, so
that the forward movement of the cylinder may be made by shorter or longer steps,
as the nature of the work renders most suitable.
Having thus described the nature of the said Invention, and the manner of per-
forming the same, I would have it understood that I claim,-
First. The method of obtaining the reciprocating action of the piston of a rock
drill by arranging passages in connection with the piston, which, when their mouths
are uncovered by the piston, allow compressed air (or fluid) to pass from the cylinder
to other subsidiary cylinders provided with narrow outlet passages, and in which
are pistons carrying the slide valve which controls the supply to the main
cylinder.
Second. The method of obtaining the feed or forward motion, as the work
progresses, by means of a subsidiary piston and cylinder supplied with compressed
air (or fluid) from the main cylinder by passages in the rod of the main piston, which
serve as a valve.
Third. The method of obtaining the rotary motion of the tool by a rifled bar
working through a corresponding collar in connection with the piston, the rifled bar
being held stationary and released alternately by a locking instrument, actuated
by a piston working in a subsidiary cylinder, supplied with compressed air or
fluid.
Fourth. The construction of rock drills, substantially as described, and represented
in the annexed Drawings.
In witness whereof, I, the said Theodor Frölich, have hereunto set my
hand and seal, this Twenty-ninth day of April, in the year of our Lord
One thousand eight hundred and seventy-eight.