CA 02178814 2004-12-15
A1G I N-HOLE ROCK DR I Lh I BtG- MACHINE
This invention relates to an in-hole_rock drilling machine
caiaprislng a tubular pausing with a guide hushing in its
(rant end arranged to guide the front cad of a piston hammer
and a valve hauling in the rear end of the machiae~housing-
arranged to guide the rear-end of the piston hammer.
Machines of this type are known in the prior art; the machine in EP 0 394
255 is exemplary in this regard. However, machines of this type in the
prior art are expensive because of the demand they place on tolerances.
It is an object of the invention to make such a- machine more simple and
in particular it is an object to reduce the demands on axial tolerances and
to simplify the assembling and dissassembling of such a machine.
The invention will be described with reference to the
drawings which show an embodiment of the invention.
Figures 1 and 2 are together a side view of an in-hale rack
drilling machine in accordance with the invention; Figure 1
shows the rear part of the machine and Figur-s 2 shows the
front part. An intermediate part of the machine is act
shown.
The in-hole rock drilling machine shown in the Figures has a
pausing, the stain Bart of which is a cyli.adrical tube 12
that has an interior shoulder 13 and interior threads in
each end. _
A drill bit I4 is maintained in the housi3g by means of a
sleeve 15 screwed into the tube I2. The sleevQ 15 is in
splined connectiaa with the drill bit. The drill bit is
guided in the housing by the sleeve 15 and a guiding bushing -
26 and a stop riag 17 prevents the drill bit from falling
out. The drill bit 14 is thus axially movable a~iimited
distance in the housing 12 and it cannot turn relative to
the housing. In a conventional way, the drill bit 14 has am
axial flushing fluid. passage that ends in flushing fluid
electing ho7.es in its front surface.
CA 02178814 2004-12-15
2
r ,
' A guide bushing 18 takes support against the shoulder 13 and
a distance sleeve 19..takes.suppart against the guide bushing
18. A valve housing 20 with a back head 38 takes support
against the distance sleeve 19.__ and and a tube farmed filter
support 21 with a filter 21a takes support against the back
s head 38 flf thewaive.housing 20. A backhead 22 of the
machine housing is screwed into the rear end of the tube 12
and it is arranged to axially clamp the parts 18,29,20,38,21
against the shoulder l3.These parts 18,19,20,38,21 act
' together as a spring and their cumulative 3enght is such
that they are compressed when the backhead 22 is screwed
into place. .prefera'fiiy, the overall axial compression is
0.4 --2 mm. The distance sleeve 19 contributes most to this
compression because of its dominating length and its
comparatively small steel area in its crass section. It is
adapted to be compressed at least 0.3 and preferably 0.8 - 3
pro mills of, its, l,e~gth. The filter support 21 may have
about the same cross section area of steel as the distance
sleeve 19, and is also adapted to be axially compressed at
least 0.3 pro mills of its length, but it is shorter and its
contribution to the spring action is therefore smaller.
The back 'read 38 of the
valve housing 20 is.thus clamped agaiast the main part of
the valve housing 20. The back head 22 of the machine
housing is arranged to be screwed to a conventional drill
tubing that transmits rotation to the drilling machine and
also transmits hydraulic drive fluid is the form of pressure
water to the drilling machine. In operation, the annular
space 58 at the bac3s of the valve housiag_20 is thus
continuously filled-with filtered water under pressure. When
assembling the machine, one puts all the Farts
18,19,20,38,21 loosely an tap of one another which makes the
assembling simple and reduces the demand an axial -
talernnces. The added tolerance is taken up by the axial
elastic compression. All the parts slide easily in the
machine housing and are therefore easy to remove when the
machiae is._te be dissassembled.
A tube 23 forms part of the valve housing 20. A piston
hammer 24 with a through channel 25 has its front end guided
~
VO 95116848 3 217 8 814 p~~gE94101201
in the guide bushing 18. The rear end 27 of the piston
hammer 24 extends into an annular cylinder chamber 26 (drive
chamber) that is farmed in the valve housing 20 between the
sleeve-like front portion 35 of the valve housing and the
tube 23 of the valve housing. The rear end of the piston
hammer 24 is thus guided by the walls of the cylinder
chamber 26, that is, by the valve housing 20. The rear end
27 of the piston hammer 24 has a groove 28 with a rear end
wall 29 so that the piston hammer 20 has a defined outer
guiding surface 30 behind the end wall 29. The piston hammer
24 has also an interior guiding surface 31 of defined
length. Suitably, the outer and inner guiding surfaces 30,31
could have about the same length. The actual length of the
guiding surfaces is defined by the guiding surfaces 18 Cat
the front end of the piston hammer) and 30,31 <at the rear
end of the piston hammer) and it takes up only a minor part
of the length of the piston hammer 24. The actual length of
guiding is less than 20%. of the length of the piston hammer.
The ma,~or part 32 of the piston hammer 24 is between these
guiding surfaces and it has a wide clearance to the distance
sleeve 19 of the machine housing 12. Suitably, in order to
get as heavy a piston hammer as possible, the ma,lor part 32
of the piston hammer 24 can be radially enlarged as compared
with its guided end portions.
The guiding surface 33 of the piston hammer sliding against
the guide bushing 18 has a smaller,diameter than the guiding
surface 30 against the valve housing 20 so that the piston
hammer will have a differential piston area in the front
drfve chamber 34 that is formed axially between the guide
bushing 18 and the valve housing 20. If the groove 28 and
the front guiding surface 33 have the same diameter, then
this differential area is represented by the area 36, that
is, by the area of the rear wall 29 of the groove 28. This
differential area is smaller than the annular piston area 37
in the rear cylinder chamber 26.
SUBSTITUTE SI~~~T
WO 95116848 PCTJSE94101201
2178814 4
The valve housing 20 contains a spool valve 40 with three
control surfaces A1,A2,A3 that are in three annular control
chambers 45,46,47. The effective area of surface A3-is a
differential area since the diameter of the sliding surface
of the valve 40 close to the surface.-A1 is greater than the
diameter of the sliding surface close to the surface A2. The
relation between these areas are A3 C A1 < A2+A3 . The area
A2 is greater than the area A3-and suitably, A1 and A2 can
be equal or about equal and about twice as large as A3.
There is another annular chamber 48 and it is open to the -
annular chamber-47 when the valve 40 is in its illustrated
position. When the valve 40 is in its other position, a
shoulder 49 in the valve housing separates the chambers 47
and 48. The valve 40 has a row of large holes 50 and two
small holes 51.
A control conduit 52-leads between the annular chamber 46
and the rear cylinder chamber 26 and it has a control port
53 into the rear cylinder chamber 26. Another control condit
54 leads between the annular-chamber 45 and the rear
drivechamber 26 and it has control ports 55 and 56 to the
drive chambers 26 and 34 respectively. A number of parallel
channels 57 lead axially through the valve housing 20 and
connect the front drive chamber 34 with the continuously
pressurized space 58 at the rear of the valve housing 20. A
number of channels 59 connect a row of ports 60 into the
rear drive chamber 26 with a row of ports 61 into the
annular chamber 48. A number ofchannels connect a row of
ports 62 into the annular chamber 4T with the continuously
pressurized space 5$ at the back of the valve housing 20.
A cycle of the operation of the machine will now be
described.
Presume that the valve 40 is in its illustrated position and
that the piston hammer 24 has gust begun its work stroke
forwardly in order to strike the drill bit 14. C The piston
hammer 24 is shown in its impacting position.) Through the
SUBSTITUTE SHEET
~
VO 95!16848 217 8 814 p~lSE94101201
parts 62,61 and 60, the valve 40 connects the rear cylinder
chamber 26 with the chamber 58 that is continuously under
pressure. The control surface A1 of the valve is under
pressure during the entire work stroke of the piston hammer
24 since the control port 56 of the control passage 54 is at
first open to the continuously pressurized front drive
chamber 34 and then, shortly after the closing of the port
56, the control port 55 of the control passage 54 is instead
opened to the rear drive chamber 26 which is under pressure.
As shown, the length of the guide surface 30 of the piston
hammer can be such that both ports 56 and 55 are closed
during a short period, which, however, will be so short that
it will not influence the pressure in the control passage
54. As long as the control port 53 of the control passage 52 -
is closed, the valve-40 will therefore remain stable in its
illustrated forward position because the area A1 overcomes
the area A3. The leakage from the annular chamber 46
prevents a pressure build up in the annular chamber 46.
When the piston hammer in its work stroke opens the control
port 53 of the control passage 52 ,lust after it has opened
the control port 55 of the control passage 54, the passage
52 and the annular chamber 46 are pressurized , and since
the area A2 that is then put under pressure equals the area
Al that is already under pressure, these areas balance each
other and the area A3 will force the valve into its rearward
position which is not illustrated. The holes 51 in the valve
40 will he open into the annular chamber 46, but they are so
small that they do not prevent the pressurization of the
annular chamber 46. The leakage through the holes 51 is so
small that it does not significantly influence the overall '
power efficiency. The valve 40 is dampened by its nose 65
cutting off a damping chamber so that the valve is retarded
' before it lands in its rear non-illustrated position and it
will therefore not tend to rebaunce. The annular chamber 48
is cut off from the annular chamber 47 and is instead
coupled to the interior of the valve through the holes 50 in
the valve. Through the tube 23, the interior of the valve is
SUBSTITUTE SHEET
R'O 95116848 PC1'/SE94/01201
2178814 s
continuously open to-the channel 25 in the piston hammer and
the channel 25 is always open to the flushing fluid passage
in the drill bit 14. The rear drive chamber 26 will
therefore be depressurized simultaneously with the piston
hammer reaching its impacting position, and the continuously
pressurized front drive chamber 34 starts to drive the
piston hammer rearwardly in fts return stroke.
The relative axial positions of the control ports 53 and 55
can be varied and the control port 53 need not be axially
forwardly of the part 55. -
The water that flows out of the rear drive chamber 26 during
the return stroke of the piston hammer 24 is thus utilized
as a flushing fluid for flushing the debris out of the
barehole.
When the rear drive chamber 26 is depressurlzed, the control
surfaces A1 and A2 are both depressurized since both the
port 55 of the control passage 52.and the port 53 of the
control passage 52 will be open. to the rear drive chamber
26.
During its return stroke, the piston hammer 24 will close
the ports 55 and 53. The annular chamber 46 will however
remain drained; now through the small holes 51 through the
valve_ Then the piston hammer 24 opens the part 56 of the
control passage 54 so that the control passage 54 and the
annular chamber 45 will be pressurized from the front drive
chamber 34 and the surface A1 will be pressurized. Since the
surface A2 is not pressurized, the surface A1 will force the
valve 40 to switch to its forward position in which it is
shown. During the last portion of the forward movement of
the valve 40, the two small holes 51 in the valve are cut
off from the annular chamber 46 and the water closed in the
chamber 46 and the control passage 53 retards the valve
before the valve lands since a pressurewill build up
against the control surface A2. This pressure cannot be so
SUBSTITUTE SI-61=~°
~O 95116848 217 8 8 l 4 p~1gE94J01201
7 _
high that it ,jeopardizes the valve staying stably in its
forward position since the row of large holes 50 in the
valve is close to the annular chamber 46. The leakage out
through the holes 50 together with the lekage past the end
of the valve 40 will be comparatively big and bfgger than
the leakage into the closed part 53. The valve will now
pressurize the rear drive chamber 26 via the ports 62,61,60
and the passages 59 between the ports 61 and 60 so that the
piston hammer decelerates, turns and accelerates in its work
stroke as previously described and the cycle is repeated.
SUBSTITUTE SHEET
