Note: Descriptions are shown in the official language in which they were submitted.
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PICK HOLDER EXTR~CTION
BACKGRO~nND OF TXE 'NV~NllON
T~IS I~V~N'1'10N relates to extracting a pick holder from a piCk
box in a continuous miner drum; to extraction means for carrying out
the method of the invention, to a pick holder~ and to an extraction
tool.
In one kind of continuous miner, for example a continuous miner
manufactured by the firm Voest Alpine, there is provided a plurality
o~ pick boxes arranged in predete~ ;ne~ fashion on a drum o~ the
continuous miner. Each pick box has a substantially blind socket
within which a pick holder is replaceably received. A shank of a
pick is in turn replaceably received within the pick holder such as
to allow rotation of the pick relative to the pick holder in use.
Receipt of the pick holder in the pick box is by means of a tight,
~rictional, press fit. The pick holder is to be removable to allow
replacement~ reconditioning, and the like.
In known pick holders there is provided an internal
circumferential groove to retain a pick in use via a ret~; n i ng ring
on a shank of the pick. One way to remove the pick holder from the
0 20 pick box (when the pick has been removed), is by dilating a collar
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on a shank of an extracting tool to locate in said internal
circumferential groove and to apply an extraction force on the
shank. The force is then transmitted via a shoulder of the internal
circumferential groove to extract the pick holder from the pick box.
Although this method is generally used, it has at least two
problems. First, the integrity of locating the collar of the
extracting tool in the internal circumferential groove is not good.
It does happen that the internal collar slips, which may result in
a very unsatisfactory and possibly dangerous situation and possible
damage to equipment. Second, the collar of the extracting tool is
to be dilatable to enable it to engage the internal circumferential
groove, thus reguiring a composite (more than one part) design which
is expensive to manufacture. Such extracting tool h~ worn
fairly quickly and has to be reconditioned or replaced after a
relatively small number of extracting operations.
An alternative, known, method is to provide an external
circumferential groove in a portion of the outer surface of the pick
holder which protrudes from the pick box. This method has generally
the same disadvantages as the first mentioned known method. In
addition, the external circumferential groove is exposed to the
working conditions and bec_ -s worn and unusable for locating
purposes fairly quickly. Furthermore, the protruding portion or
head may shear off, which renders extraction by means of the
external groove impossible.
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It is an object of this invention to provide a method, an
extracting ~e~n-c~ a pick holder and an extraction tool which ; l~ov~
on the prior art and which do not suffer, or at least suffer to a
smaller degree, from the problems of the prior art.
S SUY~RY OF ~H~ INVENTION
In accordance with a first aspect of this invention, there is
provided a method of extracting a pick holder from a pick box of a
continuous miner drum, the method including providing an internal
rotary fastening formation in a bore of the pick holder, providing
a complemental external rotary fastening formation on a shank of an
extraction tool, interengaging the complemental rotary fast~n;n~
~ formations by relative rotation between the pick holder and the
extraction tool and applying an extraction force to the pick holder
via the shank and via the engaged rotary fastening formations.
15In a preferred method, the rotary fast~n;ng formations may be
screw threads and interengaging the complemental rotary fastening
~ormations may be by screwing them together. In other methods, mere
twisting or pivoting may be required.
The method may include centring the shank of the extraction
tool relative to the pick holder when applying the extraction force.
Centring may be effected by supporting the shank in the mouth or
bore of the pick holder with little clearance. Supporting the shank
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in the mouth or bore may be via a sleeve received over the shank and
fitting into the mouth or bore with little clearance, or by
appropriate selection of the diameter of the shank.
The invention extends in accordance with a second aspect to
extraction means suitable for use in extracting a pick holder from
a pick box of a continuous miner drum, the extraction means
including, in combination
an internal rotary fastening formation in a bore of the pick
holder; and
a complemental, external rotary fastening formation on a shank
of an extraction tool, the shank being receivable in the bore of the
pick holder and the complemental rotary fast~n; n~ formations being
interengagable by relative rotation to allow an extraction force to
be applied to the pick holder via the extraction tool and the
interengaged rotary fastening formations in use.
In a preferred embo~; -nt, the rotary fastening formations may
be in the form of screw threads which are screw thr~ingly
interengagable. In other embodiments, other kinds of rotary
fastening formations requiring mere twisting or pivoting (e.g. a
bayonet-type connector) may be provided.
The internal screw thread may conveniently be positioned
axially remote from a mouth of the pick holder spaced behind an
internal circumferential groove provided for anchoring a pick in the
pick holder.
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~he internal screw thread may be of a diameter such that an
outer or major diameter of the complemental screw thread on the
Ç shank is smaller than the bore of the pick holder.
By way of development, the external screw thread on the shank
may have a leading thread in the form of a cleaning or op~n; n~
thread, tap fashion, to clean up the internal screw thread. Thus,
the leading thread may be sharp or knife edged. Then, the external
screw thread may have at least one longitudinal groove or passage to
pass matter which has been cleared from the internal screw thread.
Advantageously, the extraction means may further comprise a
collar or sleeve which is replaceably received around the shank and
which is of an outer diameter allowing it to enter the bore of the
pick holder with little clearance so as to support the shank in the
bore with little clearance.
The invention extends in accordance with a third aspect to a
pick holder suitable for receipt in a pick box of a continuous
miner, the pick holder including an internal rotary fastening
formation in a bore thereof.
The invention extends yet further in accordance with a fourth
aspect to an extraction tool suitable for use in extracting a pick
holder having an internal rotary fastening formation in a bore
thereof from a pick box of a continuous miner, the extraction tool
having a shank and, toward one end of the shank, an external rotary
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fastening formation, and, toward an opposed end of the shank,
engagement means for applying an extraction force to the shank.
BRIEF DESCRIP~ION OF THE DRAWINGS
The invention is now described by way of example, with
reference to the acc~ p~nying diay, ~tic drawings. In the
drawings
Figure 1 shows, in side view, a prior art embodiment of a pick
holder of the general kind to which this invention relates;
Figure 2 shows, in a view corresponding to that of Figure 1, a
lo pick holder in accordance with this invention; and
Figure 3 shows, schematically, in part sectional side view,
extraction of a pick holder from a pick box in accordance with this
invention.
DETAILED DESCRIPTION
With reference to Figure 1, a prior art or known pick holder of
the general kind to which this invention relates is generally
indicated by reference numeral 10. It comprises a round cylindrical
outer surface 12 which is machined to a close tolerance to allow the
pick holder 10 to be frictionally received, by means of a press fit,
within a complemental bore of a pick box.
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The pick holder 10 has a concentric inner bore 14 of a size
slidingly to pass a shank of a pick. The inner bore 14 is open at
a mouth 16 at a front of the pick holder 10.
The bore 14 opens up in a rearward portion of the pick holder
10 in the form of a diverging passage 26 rllnn; ng out in a rear end
24 of the pick holder 10.
Toward a rear of the bore 14, but slightly spaced from the
start.of the diverging passage 26, there is provided an internal
peripheral groove 18 within which an ~p~n~hle locating ring of the
pick is received to locate the pick axially within the pick holder
10 and to allow free rotation of the pick relative to the pick
holder 10.
When the pick has been removed from the pick holder 10, the
pick holder 10 can be extracted from the pick box by passing a shank
of an extraction tool into the inner bore 14, dilating a dilatable
collar to seat in the internal peripheral groove 18 and by applying
an extraction force on the shank. This method has at least two
disadvantages which are severe and which have been described above.
A fore portion of the pick holder 10 projects in use from the
pick box. An outer circumferential groove 22 is provided in such
protruding portion 20.
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An alternative method of extracting the pick holder 10 from the
pick box, is to provide a contractible jaw which is contracted to
seat in the outer circumferential groove 22. An extraction force can
then be applied via the jaw to the pick holder 10 to extract it from
the pick box. As described above, this method has the same
disadvantages as the method used with the internal peripheral groove
18. In addition, the external extraction method further has the
disadvantage that the outer circumferential groove 22 is exposed to
working co~ditions of the pick and thus quickly becomes worn to an
extent in which it is unusable for extraction purposes.
With reference to Figure 2, a pick holder in accordance with
this invention is generally indicated by reference numeral 110. In
many respects it is similar to the pick holder 10 of Figure 1 and
similar features and components are not again described. Those
features and components are numbered using like reference numerals.
is will herein be placed on the differences of the pick holder
110 over he pick holder 10.
First, the pick holder llo does not require an outer
circumferential groove in its protruding portion 120. It can,
however, be provided with such a groove to allow an operator the
option of extracting it from a pick box by the known method.
The major difference is that an internal screw thread 30 is
provided in the internal bore 114 at a position spaced behind the
internal circumferential groove 118. The screw thread 30 is
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provided such that a major root thereof is not larger than the
nominal diameter of the inner bore 114. The screw thread 30 is
- conveniently of saw-tooth shape.
Reference is also made to Figure 3 where an extraction device
S is generally indicated by reference numeral 50 in operative
condition to extract the pick holder 110 from a pick box 40. It is
emphasised that, especially Figure 3, is schematic to illustrate the
principle of the invention.
The extraction device 50 has a centre shank 52 having, at one
10 end, a screw thread 54 complemental to the screw thread 30 of the
pick holder 110. Furthermore, the diameter of the shank 52 is
selected such that it is snugly, slidingly received in the inner
bore 114 o~ the pick holder 110. As described above, the screw
thread 30 projects inwardly thus allowing the screw thread 54 to
15 interengage the screw thread 30 and yet be able to enter the inner
bore 114. If desired, one thread of the screw thread 54,
advantageously the screw thread which will be a leading screw thread
in use, may be a cleaning screw thread, tap-fashion.
At an end of the shank remote from the screw thread 54, it has
20 a screw thread 56 for a locating or anchoring nut 58.
The extraction device 50 further comprises an annular hydraulic
jack means 60 and a bush 62 arranged in series around the shank 52.
An outer end of the hydraulic jacking means 60 abuts the nut 58 and
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an opposed end of the bush 62 abuts a nose 44 of the pick box 40.
The bush 62 fits snugly around the protruding portion 120 of the
pick holder 110.
Extension of the hydraulic means 60 imparts an extraction force
on the shank 52 which is transmitted via the interengaging screw
threads 54, 30 to the pick holder 110 to extract it from the pick
box 40.
The screw threads 30, 54 are conveniently of a relative course
kind and may be of rounded or saw-tooth cross-section.
It will be appreciated by a person skilled in the art that the
method and extraction means in accordance with the invention are of
high integrity which would not slip or otherwise fail unless under
most extreme circumstances. Furthermore, the extraction means is of
simple construction thus allowing it to be manufactured at
relatively low expense and with a high degree of integrity.
The Applicant is aware that persons skilled in the art of the
invention have been aware for a long time that extraction of pick
holders or the kind described from pick boxes is problematic,
dangerous, time consuming and requires relatively expensive
extraction equipment. The Applicant believes that this invention,
which appears to be surprisingly simple, nevertheless provides a
very elegant and effective solution to a problem which has been
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widely known for a long time and which, until this invention has
been made, has escaped a good solution.
