GB2211587A

GB2211587A - Conduit constriction means

Info

Publication number: GB2211587A
Application number: GB8824146A
Authority: GB
Inventors: Ross Peter Sanders
Original assignee: ICI Australia Operations Pty Ltd
Current assignee: Orica Australia Pty Ltd
Priority date: 1987-10-23
Filing date: 1988-10-14
Publication date: 1989-07-05
Also published as: GB8824146D0; CA1319318C; ZW12688A1

Abstract

A means for the constriction of fluid movement in a conduit comprises a tubular wall-gripping member which is freely movable within the conduit but which is capable of lateral expansion to grip the conduit wall. The wall-gripping member has an exterior (wall-gripping) surface and an interior surface which is so shaped that, when the wall-gripping member is prevented from moving in the conduit, the action of the fluid, either directly or indirectly, on the interior surface causes expansion. In a preferred embodiment, a tube 2 is segmented into four segments 4 which are secured by circumferential elastic bands 5. The interior surface is frusto-conical and the action of fluid on a similarly-shaped frusto-conical vessel 1 placed therein causes expansion. This means is particularly useful in the explosives industry for providing "air-decking" in vertical blastholes. <IMAGE>

Description

CONDUIT CONSTRICTION WEANS This invention relates to a means of providing a constriction to the movement of a fluid within a conduit.

There 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 simply a 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 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 air spaces) but also reduce costs (by reducing the quantity of explosive needed).

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 secured 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 W086/00660.

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 providing 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, powders and granular solids such as ANFO (ammonium nitrate-fuel oil) explosives may be considered fluids. Other substances which may be considered fluids are thick, viscous or sticky substances whose consistencies may verge on the solid and whose flow characteristics may be quite different to those 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 (b) 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.

The wall-gripping member must be able to be expanded into gripping contact with the wall as a result of the movement of the fluid acting upon the interior surface of the wall-gripping member. There are a number of ways of achieving this. The fluid may act either directly or indirectly on the interior surface, that is, 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 frusto-conical or pyramidal or frusto-pyramidal space which tapers in the direction of flow. The apex angle of the 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 frusto-conical/frustopyramidal, that is, whether the cone or pyramid penetrates 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 angle, the more likely is the space to be frusto-conical/ frusto-pyramidal. The choice as to whether the cone or pyramid should penetrate completely through the wall-gripping member is dependent on the nature of the fluid and the technology involved. For example, in the explosives field, many explosives 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 being 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.

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-tight seal is required in a smooth-walled conduit. 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.

In many of the embodiments 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 resilient means. These can be any suitable resilient means, the cheapest being circumferential elastic bands, although springs and other means may also be used. The resilient means are preferably recessed into the exterior surface of the wall-gripping member so as not to interfere with the movement of the unexpanded wall-gripping member in the conduit. Where the wall-gripping member comprises circumferential ribs or undulations as hereinabove described, recessing can be readily 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 a 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 the conduit while permitting 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 (b) the expansion member is so shaped in relation to the interior surface of the wall-gripping member that its movement in the direction of fluid movement relative to the wall-gripping member which is prevented from moving relative to the conduit causes the sections 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 example, 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.

In a very simple embodiment which 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 having an interior surface which closely matches that of the exterior of the bucket and an exterior surface 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 there is an initial impact which abruptly forces the constriction means to expand. A heavy object such as a rock can be used instead of the substantial quantity 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 possible 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 of 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.

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 expansion of the wall-gripping member segments. In other applications where fluids are more 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 air spaces in a column of explosive in a vertical borehole.

Figure 1 is a perspective view of a constriction means according to the invention.

Figure 2 is a longitudinal cross-section of part of vertical borehole showing 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 the 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 wall-gripping means in place, and as a result the segments 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 embodiment deserib ad 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.

Claims

The claims defining the invention are as follows:

1. A means for providing a constriction to the flow 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 which comprises 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 of the wall-gripping member within the conduit, and the interior surface being so shaped that flow 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.

2. A means according to claim 1, the means comprising a wall-gripping member and an expansion member, the wall-gripping member being 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 of the wall-gripping member within the conduit, and the interior surface being so shaped with respect to the shape of the expansion member that movement of the expansion member in the direction of flow of the fluid, 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.

3. A means according to claim 1 or claim 2, wherein the wall-gripping member has an exterior surface which comprises ribs or undulations.

4. A means according to any one of claims 1 to 3, wherein the wall-gripping member is made of a resilient material.

5. A means according to any one of claims 1 to 4 wherein the interior surface is so shaped as to define a conical or frusto-conical or pyramidal or frusto-pyramidal space which tapers in the direction of fluid flow.

6. A means according to any one of claims 1 to 5, wherein the wall-gripping member is elastomeric.

7. A means according to any one of claims 1 to 5, wherein the wall-gripping member is segmented along at least one longitudinal plane to give at least two segments.

8. A means according to claim 7, wherein the segments are hinged together such that the movement of an expansion member causes the segments to pivot apart about the hinge line.

9. A means according to claim 7, wherein the hinge comprises a relatively thin strip of the material of the wall-gripping member left after the member has been partially segmented.

10. A means according to claim 7, wherein the segments are held together by resilient means.

11. A means according to claim 10, wherein the resilient means are circumferential.

12. A means according to claim 7, wherein the wall-gripping member is segmented into four equal segments.

13. A means according to any one of claims 7 and 10 fo 12 wherein the interior surface of the wall-gripping member is conical or frusto-conical in shape and the expansion member has an exterior with a similar conical or frusto-conical shape.

14. A method of regulating the flow of a fluid in a conduit comprising inserting therein a means according to any one of claims 1 to 13.

15. A means substantially as hereinabove described with reference to the drawings.