Note: Descriptions are shown in the official language in which they were submitted.
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T~IS INVENTIO~ relates to an elongate
mine support used for supporting mine hanging walls
relative to their footwalls.
A great variety of such mine supports are
known, and more particularly this invention relates
to a mine support which is constituted primarily of
timber and has a yieldable characteristic when placed
under axial load.
It is known to locate a length of timber
within a metal sleeve or other circumferential
reinforcing element, with wood removed from the
timber in a variety of patterns, to encourage a
controlled collapse of the mine support in use under
axial load.
The pattern of removal of wood is subject
to great variations, with equal variety in
effectivity.
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One mine support which is widely used
comprises a length of timber with a relatively heavy
gauge metal leeve therearound with timber protruding
from both ends of the sleeve. This support, commonly
known as a "pipe stick", has no wood removed for
collapsibility, and relies on the axial deformation
of the sleeve to provide control of the collapsing
wood fibres whilst maintaining axial rigidity.
Generally, the removal of the wood to
cause a collapsible characteristic only provides a
predictable collapsibility at the initial stages of
compression, and it is difficult to obtain a
predictable collapse characteristic for the desired
percentage reduction in the length of a mine support.
It is the object of this invention to
provide a suitable elongate mine support which is
constituted of timber and has circumferential
reinforcing elements, and which exhibits a controlled
collapsibility under axial load.
In accordance with this invention there
is provided a mine support comprising a timber load
supporting element having approximately planar
longitudinalLy extending surfaces spaced
circumferentially therearound, there being
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circumferential reinforcing means around the eiement
adapted for restraining, when the element is under
axial load, timber expansion transverse to the
element length, the reinforcing means being received
against the timber between the adjacent planar
surfaces substantially without being in contact with
the surfaces themselves.
Further features of the invention provide
for the element surface located between planar
surfaces lies approximately on the circumference of a
cylindrical shape.
A feature of the invention provides for
the planar surfaces to taper from a shallowest
portion where they meet the circumferential surface
of the element, to a deepest portion at one element
end. Preferably the location of the shallowest
portion is removed from one element end and at the
deepest portion the adjacent edges of the planar
surfaces meet on the said cylindrical circumference.
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Alternatively the cross-sectional shape
and area of the element is uniform along its length,
and the planar surfaces are uniformly shaped and
spaced equally around the circumference. There is
also provided for there to be either five or six
planar surfaces.
The reinforcing means is preferably a
metal sleeve having a wall thickness of between 1,2
and 3mm. Further preferably the metal is a steel
having at least one of the following characteristics
is cold rolled sheeting having a yield stress of
roughly 230 MPa; has a tensile strength of
approximately 320 MPa; and, has an elongation of
between 37% and 43~.
There is still further provided for the
metal sleeve to have at least one indentation
extending at least part way around the circumference
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of the sleev~, the indentation being adapted to cause
a weakness in the metal to allow collapse of the
metal substantially at this position when the mine
support is collapsing under axial load.
The indentations can be circumferential
and spaced apart along the sleeve, or can be in the
form of a spiral formation having a slight pitch.
The indentations optionally can also be
formed by circumferential rings which have an
outwardly extending semi-circular cross-sectional
shape, the rings being spaced apart at least part way
along the length of the suppport.
Preferred embodiments of the invention
are described below by way of example only, and with
reference to the accompanying drawings, in which:
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Figure 1 is a partly sestioned side view
of one embodiment of the invention;
Figure 2 is an isometric view from above
of the embodiment of Figure l;
Figure 3 is an underneath end view of the
embodiment of Figure 1:
Figure 4 is a side view of an alternative
embodiment of the invention;
Figure 5 is an isometric view of a still
further embodiment of the invention; and,
Figures 6 & 7 are end views of further
configurations of planar surfaces.
Referring to Figures 1 to 3, a timber
load supporting element 1 is produced by rounding a
rough timber pole, and then removing wood to form
longitudinally extending planar surfaces 2. The are
six such planar surfaces spaced around the pole
circumference. The surfaces extend from a shallowest
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position 3 removed from the one end 4 of the timber,
from whence they taper downwardly towards the other
end 5 of the timber.
The adjacent edges of the planar
surfaces, at the deepest portion at the end 5, are in
contact with each other and this intersection
position lies on the circumference of the rounded
poles. Thus from the underside, the end 5 of the
pole (Figure 3) is hexagonal, whereas ~he opposite
end is a simply the rounded pole end.
The pole is inserted in a metal sleeve
which extends to cover the length of the planar
surfaces. The planar surfaces do not extend
laterally sufficiently to reduce the radius of the
timber between adjacent surfaces, so that the sleeve
is in contact with the circumference of the timber
pole at all positions other then those lying on a
planar surface. Thus there is a longitudinal line 7
along the outer surface of the timber (Figure 1)
along which the circumference of the timber pole
retains its integrity.
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The metal sleeve is made from cold rolled
stèèl sheeting having a wall thickness of 2,4mm, a
yield strength of approximately 230 MPa, a tensile
strength of approximately 320MPa and an elongation of
37 to 43%. Preferably the carbon content of the
steel is less than between 0.04and 0.08%. A wall
thickness range of between 1,2 and 3 mm can be used
with appropriate variations in performance Such
sleeving is commercially available in the Republic of
1~ South Africa, where it is used as piping for
conveyance of agricultural water supply.
The sleeve is formed further however to
have circumferential rings 8 therearound, spaced
apart from the end 5 to extend partway along the
length. Four such rings are provided, having
outwardly projecting semi-circular cross sectional
shapes, which are formed by any suitable method, but
can be conveniently formed by deforming the supported
sleeve radially outwardly with a turning tool.
In use, the support is located between a
mine hanging and footwall and, under axial
compression, the void between the planar surfaces and
the surrounding metal sleeve allows for timber fibre
expansion into these voids thus causing a controlled
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collapse of the timber under axial load. The timber
commences its disintergration in this manner at the
end where the planar surfaces are deepest, since this
is the weakest portion of the element.
Furthermore, the relatively thin gauge of
the steel sleeve permits axial deformation thereof
and also assists in controlling the collapse of the
support, whilst still giving effective transverse
support to the wood fibres. Particularly the axial
rigidity of the prop, it is speculated, is maintained
since the longitudinal portions of the timber between
the planar surfaces are maintained along the length
of the support and the periphery thereof, which is
not the case in prior art patterns of removal of wood
fibre, where a conical or other sharpened end taper
is created.
The rings on the sleeve assist in
allowing the metal sleeve to collapse axially in a
concertina-like manner and thus also permit the
sleeve to deform axially in controlled manner,
without inviting excessive deformation of the sleeve
by outward or inward buckling or bulging.
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It has been found under laboratory
testing that the embodiment exhibits a satisfactory
collapsable characteristic.
Referring to Figure 4, a mine support 9
comprises a length of timber pole 10 which is of a
uniform hexagonal cross-sectional shape, havi~g a
metal sleeve 11 therearound which extends from one
end and stops short of the other end of the timber
pole.
The sleeve fits against the longitudinal
corners of the intersections of the planes of the
planar surfaces forming the polygonal shape. The
metal sleeve has an indentation 12 therein extending
from the one end a short distance up towards the
middle thereof. The indentation is formed by a
turning process in which a tool is held against the
supported sleeve to cause a groove to be marked in a
spiral manner around the tube, to define a spiral
wound set of bulges between the grooves.
Referring to Figure 5, a still further
embodiment is shown, which comprises a timber pole 13
of uniform
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hexagonal cross-sectional shape being surrounded by a
metal sleeve 14 for the full length of the timber~
The sleeve is in contact with the corners of the
hexagonal shape. The sleeve has rings lS at both
ends thereof which are formed by circumferential
indentations or grooves spaced apart from each sleeve
end. The indentations are formed also by a turning
process.
Figures 6 and 7 show, by way of
illustration of the scope of the invention,
alternative configurations of planar surfaces for
timber elements. Figure 6 shows a tapering
triangular cross-sectional shape with the element
surface at the position of deepest taper between the
planar surfaces being fairly wide, to compensate for
the greater amount of timber removed for the planar
surfaces than is the case with say the hexagonal
shape. The rounded sections of original
circumference are u~ed to support a metal sleeve or
other circumferential reinforcing member.
Figure 7 shows the original circumference
of a timber pole with four irregularly placed planar
surfaces.
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The indentat ions in the sleeve of the
embodiments of Figures 4 and 5 assist with the
controlled axial collapse of the sleeve by provoking
a concertinaring and wrinkling deformation rather
than bulges or tearing.
Preferably the indentations of the
embodiments of Figures 4 and 5, for timber of 154mm
diameter from corner to opposing corner, should have
a spacing of greater than 20mm. ~arrower spacing is
inclinded to cause too rapid and uncontrolled
deformation of the sleeve.
These two embodiments have been tested
with timber poles of Saligna, Wattle, Piniculata and
Cloesiana and the wattle was found to be the best
with Saligna second. It is not claimed that this
will invariably be the case.
The hexagonal shape has been found to
provide sufficient longitudinal rigidity along the
corners of the hexagonal yet also sufficient void
between the planar surfaces and the surrounding sleeve
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sleeve to provide for wood fibre deformation under
axial compression.
Variations may be made to the above
described embodiment without departing from the scope
S of the invention. The configuration of planar
surfaces on the timber element can vary widely and
can be varied to obtain a desired yield
characteristic. The more timber that is removed the
less resistance to compression the support will have,
but the yieldability is likely to be better. A
balance has to be obtained, for a desired yield
characteristic, between providing void space for
timber fibre expansion without unduly weakening the
support, and maintaining a suitable longitudinal
rigidity by providing a number of longitudinal timber
areas between planar surfaces which retain the full
radial measurement of the timber along their
lengths. The planar surfaces can be of other regular
geometric ~igures or can be irregular, and the extent
of the timber left between planar surfaces can vary.
The reinforcing means can be wound over
the pole, can be a strip or band, and need not be
metal.
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