BACKGROUND OF THE INVENTION
This invention relates to a drilling arrangement and to a drilling
A number of different drilling feed devices are used in underground
mining and in long hole production drilling. Some of these prior art devices are
shown in Figures 1 to 5 of the attached drawings.
Figure 1 shows a common drilling feed construction which includes
a feed beam 8 with a chain feed 10 wherein a hydraulic or pneumatic motor rotates
a chain sprocket wheel 12 either directly or via a reduction gearbox. The chain
is connected to a rock drill 14 and linear movement is thereby imparted to a drill
rod 16 which passes through a centralizer 18.
It is also known, see Figure 2, to make use of a screw feed mechanism
wherein a suitable motor 20 rotates a threaded bar 22. A threaded bushing 24 which
is engaged with the bar is connected to a rock drill 14 so that rotational movement
of the bar is translated into linear movement of the rock drill and its drill rod
It is also known to make use of telescopic cylinders to advance a
rock drill. Three types of arrangement are known to the applicants.
The first arrangement, shown in Figure 3, includes a cylinder 26 and
first and second pistons 28 and 30 arranged so that the first piston 28 acts a
cylinder tube for the second piston 30. The first piston i.e. the cylinder tube
is movable from a protruding position on one side of the cylinder to a protruding
position on the other side of the cylinder. The cylinder 26 is directly connected
to a rock drill 14 by a mechanical connection 32.
In the second type of arrangement (Figure 4) an elongate first piston
34 extends substantially for the full length of travel of the rock drill and passes
through a cylinder tube 36 which also acts as a second piston located inside a
cylinder 38 which is fixed to a rock drill 14.
in a third arrangement, which is shown in Figure 5, first and second
pistons 40 and 42 are again used with the first piston 40 being located inside
a cylinder 44 and extending from one end of the cylinder. The first piston acts
as a cylinder tube for the second piston 42 which extends from the cylinder tube
in the same direction as a drill rod 16 which is attached to a rock drill 14.
A common feature of the aforementioned telescopic cylinder feed is
that one or both of the piston rods are exposed to the front of the rock drill.
Rocks and material which are loosened during drilling can fall on to the exposed
pistons and damage the pistons or lead to rapid wear of cylinder seals. This results
in additional expense and drilling down time. A similar disadvantage exists in
respect of the chain and screw feed type device in that the chain and the threaded
bar are exposed to material which is loosened during drilling.
It is desirable to have a constant feed force which is exerted by
the drilling feed construction on the rock drill. A constant force is achieved
fairly readily with a chain feed or a screw feed. However with multistage telescopic
cylinder feeds it is necessary to construct the pistons with areas, which are pressurized,
of equal magnitude. This in tum imposes limitations on the dimensions of the feed
cylinder which can hinder or prevent optimal designs from being produced.
U.S. patent No. 4553612 discloses a drilling arrangement in accordance
with the preamble of claim 1, which includes a feed beam, a drill which is mounted
for movement relatively to the feed beam and which is engageable with a drill rod
which extends in a first direction from the drill, and a hydraulic feed mechanism
which includes a cylinder which acts on the drill and a piston which is telescopically
movable into or out of the cylinder and which, when extending from the cylinder,
moves in a second direction which is opposite to the first direction, a protruding
end of the piston being engageable with means on the feed beam. As indicated hereinbefore
it is desirable to have a multistage feed mechanism for controlling the feed of
the rock drill.
SUMMARY OF THE INVENTION
The invention provides a drilling arrangement which includes a feed
beam, a drill which is mounted for movement relatively to the feed beam and which
is engageable with a drill rod which extends in a first direction from the drill,
and a hydraulic feed mechanism which includes a first cylinder which acts on the
drill, and which is characterized in that the feed mechanism is multistage and
includes a second cylinder which is telescopically movable into or out of the first
cylinder and which extends only to one side of the first cylinder, a piston which
is telescopically movable into or out of the second cylinder and which, when extending
from the second cylinder, moves in a second direction which is opposite to the
first direction, a protruding end of the piston being engaged with means on the
feed beam, and differential control means for controlling the force which is exerted
by the hydraulic multistage feed mechanism.
The differential control means may comprise any appropriate device
which controls the said force at a substantially constant value and can for example
consist of an adjustable sequence valve or a spring loaded and restricted one-way
valve, or a shuttle valve.
The differential control means may be located externally of the cylinder,
or inside the cylinder and, in the latter case, may be mounted to one of the pistons.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further described by way of example with reference
to the accompanying drawings in which:
DESCRIPTION OF PREFERRED EMBODIMENT
- Figures 1 to 5 depict prior art devices which have been explained in the preamble
to this specification;
- Figure 6 is a simplified side view of a drilling arrangement according to the
- Figure 7 is a simplified cross sectional side view, on an enlarged scale, of
a drilling feed mechanism used in the drilling arrangement of Figure 6; and
- Figure 8 and its inset drawing Figure 9 illustrate a variation of the arrangement
shown in Figure 7.
Figure 6 of the accompanying drawings illustrates a drilling arrangement
according to the invention which includes a feed beam 110, a drill 112, a drill
rod 114 which extends from the drill and which passes through a drill rod centralizer
116, and a drilling feed mechanism 118.
The mechanism includes a cylinder 120 which is secured to the drill
112 by means of a mechanical connection 121.
Figure 7 illustrates, on an enlarged scale, the construction of the
drilling feed mechanism 118. The mechanism includes the cylinder 120 and, mounted
inside the cylinder, a first piston 122 which acts as a cylinder tube for a second
The cylinder 120 includes seals 126 which act on an outer surface
of the first piston 122. The first piston in tum includes seals 128 and 130 which
respectively act on an outer surface of the second piston and on an inner surface
of the cylinder. The second piston includes seals 132 which act on an inner surface
of the first piston.
The first piston has a first end 134 on one side of the seal 130 and
a reaction surface 135 on an opposite side of the seal. The second piston 124 has
a first end 136 and a protruding second end 138.
A first variable volume 140 is formed inside the cylinder 120 and
is partly bounded by the first ends 134 and 136 of the first and second pistons
respectively. A second variable volume 142 is also formed inside the cylinder,
on an opposed side of the seal 130 and is partly bounded by the reaction surface
A port 144 is used to connect a hydraulic line 146 to the first variable
The supply line 146 also extends via a differential control device
148 to a second port 150 which is in communication with the second variable volume
A second hydraulic line 152 leads to an opposed side of the differential
control device 148 and to a port 154 near the second end 138 of the second piston.
This port extends via an intemal passage 156 in the second piston to an exit port
158 which opens into a volume 160 formed between the first piston and the second
The differential control device 148 includes a restricted spring loaded
one-way valve 162 and a shuttle valve 164.
Referring to Figure 6 it is to be noted that the second end 138 of
the second piston 124 acts against one end of the feed beam 110 and is fixed thereto.
When the volume 140 is pressurized by hydraulic oil introduced via
the supply line 146, a relatively increased pressure is produced in the volume
142 by the action of the spring loaded and restricted check valve 162. By taking
into account the relative areas of the first end 134 and the reaction surface 135
and by appropriately varying the pressure difference between the two volumes 140
and 142 the forces on the end 134 and the surface 135 can be controlled to achieve
a situation in which:
- (a) both pistons are extended in unison relatively to the cylinder until the
first piston 122 reaches a limiting position, whereupon the second piston 124
extends further, from the first piston, or
- (b) the second piston 124 extends from the first piston 122 until a limiting
position is reached, relatively to the first piston, whereupon the two pistons
extend in unison from the cylinder.
For example, in situation (b), the forces on the end 134 and on the
reaction surface 135 can be equalized so that the extension force is that which
arises on the end 136 of the second piston. The extension force remains constant
during the piston extension process.
On the other hand it may be preferable to operate with situation (a),
for the first piston, which has a larger diameter than the second piston, is relatively
stiffer. To achieve this situation the force on the end 134 is slightly greater
than the force on the surface 136. However, with this arrangement, there is a slight
decrease in the extension force when the first piston reaches the end of its stroke
and the second piston then extends from the first piston.
As the second end 138 of the second piston is fixed to the feed beam
the aforementioned movement of the drilling feed mechanism is translated into linear
movement of the drill 112 in a direction which is opposite to the direction in
which the pistons extend relatively to the cylinder 120.
When it is necessary to retract the feed mechanism the line 152 is
pressurized. The volume 142 is thereby pressurized and the first piston is moved
to the right. Similarly the volume 160 is pressurized and the second piston is
moved to the right.
It is to be noted from an examination of Figure 6 that the pistons
122 and 124 extend only from one side of the cylinder 120. They do not extend from
the cylinder in the direction of the drill rod and are, in fact, maintained at
positions behind the advancing drill 112. Consequently substantial protection is
provided for the pistons by the drill 112 itself. The drill protects the pistons
from falling rocks and drill cuttings while drilling is in progress. No inner parts
of the feed mechanism are therefore exposed in front of the drill.
In the Figure 7 arrangement the differential control device 148 is
mounted externally of the cylinder. Figures 8 and 9 show that it is possible to
mount an equivalent device 148A to the first piston 122 inside the cylinder.
The device 148A includes a pilot to open one-way valve 180, a pilot
line 184, and a restricting one-way valve 182. The valve 182 could be replaced
by a sequence valve. Other components shown in Figures 8 and 9 have similar reference
numerals to those employed in Figures 6 and 7. The device 148A operates in substantially
the same way as the device 148 in that the pilot line 184 opens the valve 180 when
the volume 140 is pressurized and allows the hydraulic oil to flow through the
restricting one-way valve 182 to cause a pressure difference, of a desired magnitude,
between the two volumes 140 and 142.
The device 148A, being inside the cylinder, is protected and the extemal
construction of the feed mechanism is simplified.