Note: Descriptions are shown in the official language in which they were submitted.
131q318
AUS 1384~1392/l~cS
:
CONDUIT CONSTRICTION MEANS
This invention relates to a means of
providing a constriction to the movement of a fluid
within a conduit.
~here are situations wherein it is necessary
wholly or partially to prevent the movement of a
fluid in a conduit by means of a constriction
inserted into the conduit as opposed to, say, by
controlling the flow by means of valves. Such a
case arises, for example, where the conduit is not
simplyia fabricated tube but a borehole in rock. It
is frequently desired when blasting rock by means of
fluid explosive compositions (that is, explosive
compositions which are capable of being pumped or
lS poured) that the explosive in the borehole have air
spaces. In relatively soft overburdens, these air
spaces can not only increase explosive power (by
means of the gas pressure built up within the aix
spaces) but also reduce costs (by reducing the
quantity of explosive needed).
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The provision of air spaces, or ~air decking"
as it is known in the trade, was formerly achieved
by the use of simple wooden platforms ~ecured in
place by wedges. More recent developments have
utilised the in situ generation of gas to inflate a
bag which bears against the sides of the borehole
and thus supports an explosives charge~ An example
of this approach may be found in PCT Published
Application W086/00~60.
There has now been discovered a simple, cheap
and efficient means of providing a constriction in a
conduit. There is therefore provided, according to
the present invention, a means for providing a
constriction to the movement of a fluid within a
conduit, the means comprising a wall-gripping member
which is tubular and capable of being expanded into
gripping contact with the walls of the conduit, and
comprising an exterior surface and an interior
surface, at least part of the exterior surface prior
to expansion conforming closely to the cross-section
of the conduit whilst allowing free movement within
the conduit, and the interior surface being so
shaped that movement of the fluid acting thereupon,
when the wall-gripping member is prevented from
moving relative to the conduit, causes the
wall-gripping member to expand into gripping contact
with the conduit wall.
The invention also provides a method of
providin~ a constriction in a fluid-carrying conduit
comprising the~insertion into the conduit of a
constriction means as hereinabove described.
For the purposes of this invention, the word
"fluid" is considered to encompass any substance
which can be caused to flow. Thus, po~ders and
granular solids such as ANFO (ammonium nitrate-fuel
oil) explosives may be considered fluids. Other
substances which may be considered fluids are thick,
viscou~ or sticky substances whose consistencies
131931~
may verge on the solid and whose flow
characteristics may be quite different to thase of,
say, water. However, even these substances can be
caused to flow in a conduit. Typical of such
substances are emulsion explosives which are
generally thick pastes.
The wall-gripping member is tubular, that is,
it has the form of a tube, having both an interior
surface and an exterior surface. This tube has
several important characteristics, namely:-
~a) at least part of the exterior surface must
conform closely to the cross-section of the
conduit whilst still allowing free movement
of the wall-gripping member therein; and
tb) it must be able to be expanded into gripping
contact with the walls of the conduit (the
means of achieving this expansion will be
further discussed hereinunder).
It is preferable that the entire exterior
surface of the cylinder conform closely to the
cross-section of the conduit this gives the
maximum gripping surface. The grip can be enhanced
for applications such as boreholes where the wall is
not completely smooth by making the wall-gripping
member of a material possessing a degree of
resilience and~or equipping the surface with a
series of ribs or undulations better to grip the
walls.
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The wall-gripping member must be able to be
expanded into gripping contact with the wall ac a
result of the movement of the fluid acting upon the
interior surface of the wall-gripping member. There
S are a number of ways of achieving this. The fluid
; may act either directly or indirectly on the
interior surface, that i , it may impinge upon the
interior surface or it may act on that surface by
means of an intermediate member interposed between
fluid and interior surface.
In the case of direct impingement by the
fluid, the interior surface is preferably so shaped
as to define a conical or frus~o-conical or
pyramidal or frusto-pyramidal space which tapers in
the direction of flow. The apex angle of th cone
or pyramid is not critical and a suitable angle can
be readily selected by a person skilled in the art.
It will be obvious to such a skilled person that the
apex angle cannot be too large or too small as this
will result in insufficient translation of the force
of flow into transverse expansion of the
wall-gripping member to grip the wall.
The matter as to whether the space is
conical/pyramidal or fru~to-conical/frusto-
pyramidal, that i8, whether the cone or pyramidpenetrates completely through the wall-gripping
member, is largely determined by the choice of apex
angle in combination with the length of the
wall-gripping member - the smaller the apex anglP,
the more likely is the space to be frusto-conical/
frusto-pyramidal. The choice as to whether the cone
or pyramid should penetrate comple~ely through the
wall-gripping member is dependent on the nature of
the fluid and the technology involv~d. For example,
in the explosives field, many explosives
1319318
compositions such as emulsion explosives are thick
and viscous and will not flow through a relatively
small hole. On the other hand, if the composition
comprises dry ANFO prills, such a hole will allow it
to run through. This can easily be prevented by
providing the wall-gripping member with a suitable
loose or flexible liner (for example, a plastic
bag) .
In the case of the use of an intermediate
member, the fluid exerts a force on the intermediate
member which in turn exerts a force on the
wall-gripping member, causing it to expand. The
intermediate member ~hereinafter referred to as "the
expansion member") exerts its effect by means of its
shape, which is so shaped with respect to the
interior surface of the wall-gripping member that
its movement relative to the wall-gripping member in
the direction of flow causes the wall-gripping
member to expand into gripping contact with the
walls of the conduit. This can be achieved by any
suitable means known to the art.
The simplest (and most preferred) way of
achieving this is to have a conical/pyramidal or
frusto-conical/frusto-pyramidal expansion member,
the member tapering in the direction of flow, and a
matching shape for the interior surface of the
wall-gripping member, the dimensions of the two
bsing selected such that a movement on the part of
the expansion member will cause the wall-gripping
member to expand sufficiently to grip the conduit
wall.
1 31 93 1 8
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The property of expandability of the
wall-gripping member may be achieved by any
convenient means. For example, the wall-gripping
member may be elastomeric, and the movement of the
fluid or expansion member causes the wall-gripping
; member to expand and grip the wall. This is a
valuable embodiment especially where a completely
fluid-t~ght seal i8 required in a smooth-walled
condui~. For other applications, for example, where
the wall-gripping member is relatively rigid, and
where the fluid is suitably viscous or where it is
not desired to effect a completely fluid-tight seal,
the expansion may be achieved by some form of
segmentation of the wall-gripping member. By
"segmentation" is meant the sectioning of the
wall-gripping member in a longitudinal plane so as
to give relatively rigid segments which can then be
caused to move relative to one another in directions
transverse to the direction of the movement of the
fluid or expansion member.
A typical structure is a wall-gripping member
is one which has been segmented symmetrically into
two segments and is held together at one side by
externally-mounted hinges. The movement of a fluid
or an expansion member will cause this wall-gripping
member to expand by the pivoting of the segments
about the hinge line. An alternative to this is to
make the wall-gripping member of a material capable
of deformation and to section the wall-gripping
member only partially, leaving the two segments
united on one side by a relatively thin strip of
material. On application of fluid or an expansion
member, the wall-gripping member will deform at this
piece of material, the segments hingeing apart into
gripping contact with the walls. The choice of
appropriate materials and dimensions is well within
the skill of the art.
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In many of the embodiment~ hereinabove
described, the wall-gripping member will need to be
restrained from premature expansion in place. This
may be achieved by holding the wall-gripping member
closed by xesilient means. These can be any
suitable resilient means, ~he cheapest being
circumferential elastic bands, although springs and
other means may also be used. The resilient mean~
are preferably recessed into the exterior surface of
the wall-gripping member so as not to interfere with
the movement of the un~xpanded wall-gripping member
in the conduit. Where the wall-gripping member
comprises circumferential ribs or undulations as
hereinabove described, recessing can be readily5 achieved.
In a preferred embodiment, the wall-gripping
member is completely sectioned and its integrity is
maintained by the abovementioned resilient means.
The invention provides a means for providing a0 constriction to the movement of a fluid within a
conduit, the means comprising a wall-gripping member
and an expansion member, being characterised in that
~a) the wall-gripping member is tubular and open
at at least that end facing the direction of
fluid movement, has an exterior surface the
circumference of at least part of which
conforms closely with the circumference of
the wall of ~he conduit while permi~ting free
movement of the wall-gripping member within
the conduit, and is sectioned longitudinally
in at least one plane, integrity being
assured by resilient restraining means; and
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~b) the expansion member is so shaped in relation
to the interior surface of the wall-gripping
me~ber that its movement in the direction of
fluid movement relative to the wall-gripping
member which is prevented from ving
relative to the conduit causes the ~ections
of the wall-gripping member to move apart and
grip the walls of the conduit.
In an especially preferred embodiment, the
wall-gripping member is sectioned by two mutually
perpendicular planes so as to give four identical
quarter-cylinders. It is of course possible to have
a larger number of segments, but four gives an
especially good combination of grip, robustness and~ ease and cheapness of manufacture and assembly.
The means by which is achieved the prevention
of movement of the wall-gripping member in order to
effect constriction may be any means known to the
art. For example, the wall-gripping member may be
held against the fluid movement by, for example,
ropes, cables or wires. Thus, in a vertical
borehole for exsmple, the wall-gripping member may
be suspended by any suitable means and expanded into
wall-gripping contact by means of a fluid against
any force seeking to maintain the integrity of the
cylinder. The force compelling the expansion member
to move may be the flow rate or weight of the fluid.
In some situations, for example, where the conduit
is vertical or near-vertical this may be usefully
augmented by using a heavy expansion member, for
example, one made of concrete or another heavy
material.
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In a very simple embodiment w~ich is of great
value in the air decking of fluid explosives in
vertical "down" boreholes, the constriction means
comprises an expansion member which is a
frusto-conical container (such as a bucket) in a
quartered cylinder, the cylinder havin~ an interior
surface which closely matches that of the exterior
of the bucket and an exterior suxface which is a
close fit within the borehole. The integrity of the
cylinder is assured by means of strong elastic bands
which are recessed in the surface of the cylinder in
circumferential grooves. The constriction means is
suspended in the borehole by ropes or cables and the
addition of explosive causes the expansion of the
quartered cylinder.
In some cases where vertical conduits are
concerned, it may be preferable to add a substantial
quantity of fluid such that ~here is an initial
impact which abruptly forces the constriction means
to expand. A heavy ob~ect such as a rock can be
used instead of the substantial guantity of fluid to
produce the same effect. In other cases, gradual
build-up of pressure is sufficient.
The man skilled in the art will be able to
perceive many po~sible variations all of which lie
within the scope of this invention. The choice of
shapes and materials for the various components is
wide and can be chosen to suit any particular
conditions or circumstances. A particularly
advantageous class of materials from which the
wall-gripping member may be made is that cf
polyurethanes - these are cheap and allow accurate
moulding of any desired shape. They can be easily
provided with a ribbed or undulating exterior as
hereinabove described so as better to grip the sides
of a conduit. In addition, where required, the
expansion member may be simply a bucket of plastics
material.
- 1 31 ~3 1 8
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However, the materials and methods hereinabove
described are by way of example only and are not to
be construed as limiting the scope of the invention
in any way.
The constricting means according to this
invention has been found to be particularly good at
providing air decking in vertical boreholes which
are to be filled with explosives. They permit the
accurate placing and correct dimensioning of air
spaces and are very cheap. The invention therefore
also provides a means of blasting comprising a
charge of explosive in a vertical borehole, the
charge comprising at least one air space whose upper
boundary is provided by a constriction means
according to this invention.
Where the constriction means according to
this invention is used with explosives, the
constriction is more or less complete; fluid
explosive compositions of the type used by the art
for the blasting of rock and ore are generally
viscous pastes or granular solids and very little
gets through the small gaps resulting from the
expan~ion o~ the wall-gripping member ~egments. In
other applications where fluids are more
2S free flowing ~for example, water or gases) fluid may
be able to get past the constriction means, but the
amount getting past can be precisely tailored with
respect to a given flow rate, for example, by means
of porting in the expansion member.
The invention will now be further described
with reference to a preferred embodiment for use in
the provision of aix spaces in a column of explosive
in a vertical borehole.
Figure 1 is a perspective view of a
constriction means according to the invention.
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11
Figure 2 is a longitudinal cross-section of
part of vertical borehole ~howing the constriction
means of Figure 1 in place with a charge of
explosives.
A constriction means according to the
invention comprises a frusto-conical plastics bucket
1 which is seated in an essentially cylindrical
wall-gripping means 2 made of a polyurethane. The
wall-gripping means is sectioned diametrically by
two mutually perpendicular cuts 3 which give four
quarter-cylindrical segments 4, the integrity of the
cylinder being maintained by circumferential elastic
bands 5. The surface of ~he wall-gripping means
comprises a series of regular circumferential
alternating peaks and troughs 6 giving an undulating
surface. The elastic bands 5 are seated within two
of the troughs at opposing ends of the wall-gripping
means and exert sufficient tension that the weight
of the bucket 1 alone causes no separation of the
segments. The dimensions and shapes of the bucket
and wall-gripping means are such that the diameter
of the mouth of the bucket is narrower than the
exterior diameter of the wall-gripping means, and
such that the interior shape of the wall-gripping
means is the same frusto-conical shape as the
exterior of the bucket, the latter fitting within
the former such that it stands slightly proud of it
at the top but does not extend down to the bottom
thereof.
The constriction means is lowered into a
borehole 8 by means of the wires 7 and held at the
desired height. A charge of fluid explosive 9 is
then loaded into the borehole. This fills up the
bucket 1, and, as more explosive is loaded, forces
it to move downwards. The wires 7 hold the
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wall-gripping means in place, and as a re~ult the
segment~ 4 of the wall-gripping means are forced
apart against the restraint of the elastic bands 5
until they contact the wall of the borehole 8 and
grip it. The greater the weight of explosive, the
more tightly the wall-gripping means grips the walls
- these borehole walls are not, of course,
completely smooth~ and the undulating surface of the
wall-gripping member will find adequate purchase to
support a substantial charge of explosive. The
dimensions of the wall-gripping means with respect
to the boreholes and the amount of travel of the
bucket needed for to effect grip of the walls can be
readily determined for any given situation and
standard-sized constriction means may be provided
cheaply and simply for standard-sized boreholes.
Moreover, one of the features of the preferred
~mbodiment describned hereinabove is its ability to
be used in several different sizes of boreholes.
The explosive charge is fired by means of a
primer charge 11 and a detonation cord 12, the
former being placed in the bucket prior to lowering
the constriction means into position.
