Improvements in Rock Drills and their Mountings.
Year: 1891

page_text: e of Application, 28th July, 1891-Accepted, 29th Aug., 1891
COMPLETE SPECIFICATION.
Improvements in Rock Drills and their Mountings.
I, FREDERICK ALEXANDER PARNELL, of 10 New Broad Street, in the City
and County of London, Mechanical Engineer, do hereby declare the nature of
this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
This invention relates to improvements in rock drills of the percussive class, (and
more especially to those of the type described in a previous Specification of Letters
Patent communicated by Arvid Henry Elliott and granted to Ernest de Pass,
dated February 14th 1878, and numbered 629) and has for its object the provision
of means for ensuring the better packing of the piston, and distributing valve;
together with improvements in the construction of the valve chest; in the means for
securing the drill bits; for ensuring certainty of the feed (when fed automatically
and running at high speeds), and to provide a simple method whereby the wear of
the carriage, or saddle, carrying the drill may be compensated for.
In constructing drills of the class to which this invention refers to it has hitherto
been usual to provide the piston with one, or more, metallic packing rings. These,
having regard to the conditions under which such drills work, have seldom proved
satisfactory, and therefore in drills constructed in accordance with this invention
the metallic rings are done away with and the piston is provided with, preferably
not less than, four leather packing rings, these latter being secured to the piston in
the manner hereinafter described and shown.
In the drill described in De Pass's Specification above referred to, and in other
drills whose valves are actuated by the air, or other fluid, pressure direct, the valve
chests have usually been provided at each end with thick india-rubber cushions,
having on their inner faces steel protecting plates, and which served as buffers to
prevent the valve damaging itself by striking against the end covers of the valve
chest. This arrangement necessitated an abnormally long valve chest, and in
addition to setting up a considerable jarring, and consequent wearing, of the
working parts, it has been found that, after running for a short period, the rubbers
and plates became so jammed in the valve chest as to render it a work of con-
siderable difficulty to remove the valve therefrom..
One object of the present invention is to replace the india-rubber cushions and
plates by so constructing the valve chest as to allow of a small portion of the air,
or other fluid pressure used, passing alternately to the outer faces of the valve and
thereby forming an elastic cushion between it and the end cover.
The arrangements for securing the cushioning of the valve and the methods of
packing the valve and piston are, together with the several further improvements
constituting this invention, shown in the accompanying drawings of which
Figure No. 1 is an elevation, half in section, of the piston, No. 2 a sectional
elevation of the valve chest and valve, and Nos. 3 and 4 sections on the lines 1, 2,
and 3, 4 respectively of the valve as shown in No. 2. Figures No. 5 and No. 6
show respectively the top end of the drill as originally constructed, and the
method and object of prolonging the feed pawl guard, and Nos. 7 and 8 the
slotted end of the piston rod and the improved drill clip and feather piece; Nos. 9
and 10 being a plan and end view of the improved carriage, or saddle.
Referring to No. 1 it will be seen that the piston A is provided with four leather
packing rings a, a, a, a, retained in situ by undercutting the groves in which they
are placed in the manner shown. Figure No. 2 shows that the passage of the air,
or other fluid, to the ports b, c, leading respectively to each face of the piston is
controlled by means of the openings d, e, of the valve, while the passage of the
exhaust from either face of the piston to the exhaust port is controlled by the

page_text: recess B of the valve. (In the drawing the port, is shown open to the exhaust
and the port open to pressure.) Assuming the valve to be moving in the
direction of the arrow a small portion of the air passing by the openings e and h
would form a cushion between the valve and the cover ' while similarly when the
valve moved in the opposite direction the openings d and i would pass the necessary
quantity of fluid to form a cushion between the valve and the cover .
The openings and i are of such a length as will ensure the piston ends P. P. of
the valve cutting off the supply of air, or other fluid, before the valve reaches the
end of its travel.
From Figures No. 2 and 4 it will be seen that the side pressure in the cavity C
of the valve acting on the recess B tends to wear the lower half of the valve away,
and thus in time, though the working faces of the valve and chest keep tight, there
would be a tendency to leak around the top halves of the piston ends P. P. To
prevent any such leakage each piston end is fitted with a semicircular metallic
packing ring R, which, expanding as the wear takes place, compensates for any wear
of the face half of the valve.
In the original construction of the drill described in De Pass's Specification
herein before referred to, the feed wheel guard G as shown in Figure No. 5 did not
prevent the lower end of the feed pawl (held normally in the position shown by
the free end of an adjustable leaf spring bearing in the recess t) being lifted clear
of the guard when the cam M, owing to any abnormal condition of working, such
as excessively high speed, gave it more than the usual upward impulse. To prevent
the pawl being so thrown from gear with the feed wheel and to ensure certainty of
the feed working under all conditions the guard is, in drills constructed in accordance
with this invention, prolonged in the manner shown by the shaded portion G of
Figure No. 6.
66
The improved method of fixing the drill bits consists in slotting out the feather-
way g, shown in Figures Nos. 7 and 8. The feather piece F is placed in this
way," and the drill having been adjusted in place is secured by means of the
stud S acting on the opposite face of the feather piece. The stud S is carried by
the clamp H, which in turn is secured to the suitably drilled out end of the piston
rod A¹ by the taper pin E.
In constructing the improved carriage, or saddle, J, shown by Figures No. 9
and 10 of the accompanying drawings, one of the channels, or grooves, j, j, usually
formed solid on each side is replaced by an adjustable, hardened, slip of metal, k,
extending the whole length of the saddle and secured in position (after proper
adjustment by the set screws s) by means of the studs o, o, the latter preferably
equalling in number the set screws s.
It is obvious that an adjustable slip of metal may be applied to both sides of the
carriage and in the case of very large drills it may be found desirable to do so.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
First Packing the pistons of rock drills of the percussive class substantially as
in the manner described and shown with reference to Figure No. 1 of the accom-
panying drawings.
Second Constructing the valve chests of drills of this class so that an elastic, or
pressure, cushion may be formed alternately at either end thereof, substantially as
in the manner described and shown with reference to Figure No. 2 of the accom-
panying drawings.
Third: Packing the upper halves of the piston ends of valves of the type shown
as and for the purpose described and substantially in the manner described and
shown with reference to Figures No. 2 and 3 of the accompanying drawings.
Fourth Securing the drill bits by the means and substantially as in the manner
described and shown with reference to Figures No. 7 and 8 of the accompanying
drawings.

page_text: Fifth The improved form of feed wheel guard and feed pawl guide constructed
substantially as described and shown with reference to Figures No. 5 and 6 of the
accompanying drawings.
Sixth The method of constructing a drill carriage, or saddle, so as to allow of
the same being adjusted for wear, substantially as described and shown with
reference to Figures No. 9 and 10 of the accompanying drawings.
Dated this 24th day of July 1891.
FREDERICK ALEXANDER PARNELL.