GB2031561A - Cartridges for plugging blasting holes - Google Patents

Abstract

The invention relates to a cartridge composed of an elastically deformable material, for plugging blasting holes. The cartridge (1) is of generally cylindrical shape in typical cases. It possesses at least one zone (6 or 7) capable of undergoing radial deformation and at least one zone (8) capable of undergoing axial deformation as a result of a radial or axial pressure being exerted on the cartridge or as a result of a variation in the internal pressure. The cartridge is of particular utility in coal mines. <IMAGE>

Description

SPECIFICATION Cartridges for plugging blasting holes This invention relates to a cartridge which, after a filler material has been introduced into it, can be used to ensure the plugging of an explosive charge placed in a blasting hole. It relates more particularly to a cartridge composed of an elastically deformable material, which, after having been filled with water or another filler material, can be used for plugging an explosive charge in a coal mine.

The essential functions of plugs used for blasting in mines and quarries are to increase the effectiveness of the blasting, to reduce the escape of dust, to cool the gases evolved in the explosion, and to prevent inflammable gases which may be present in the environment, such as firedamp, from igniting.

In order to be fully effective, these plugs must be placed as close as possible to the explosive charge, they must seal the blasting hole as effectively as possible, and they must be held firmly in position.

For these reasons, plugs have been used which are in the nature of plugging cartridges consisting of a fine, flexible plastics sheath, one end of which is welded to seal it, and the other end of which has a filling means and a shut-off valve which operates under internal pressure but only after filling. These cartridges have had to be filled in situ using special equipment which introduces water under pressure, after the cartridge has been positioned in the blasting hole.

In order to overcome this disadvantage of these known cartridges, attempts have been made to develop cartridges which are similar but can be filled before they are positioned. Thus, cartridges consisting of a bent tube made of semi-rigid plastics material are known. After filling, these cartridges can be introduced by force into the blasting hole by means of a tamper. The plugs formed by means of these cartridges can therefore be placed close to the explosive charge, and, by virtue of the bending of the cartridges, they are held firmly in place. However, because they are bent, these cartridges must have a diameter substantially less than that of the blasting hole. As a result, these cartridges suffer from the serious disadvantage that they permit only a very imperfect sealing of the blasting hole.

It is an object of the present invention to make possible the plugging of blasting holes by means of cartridges which can be filled before positioning, which can be placed against the explosive charge, which will hold firmly in position, and which will effectively seal the blasting hole. It is also an object of the invention to provide cartridges which will permit easy positioning despite the inevitable variations in diameter of blasting holes.

According to the present invention, we provide a cartridge of generally cylindrical shape, composed of an elastically deformable material, for plugging blasting holes, characterised in that it possesses at least one zone capable of undergoing radial deformation and at least one zone capable of undergoing axial deformation as a result of a radial or axial pressure being exerted on the cartridge or as a result of a variation in the internal pressure.

The general shape of the cartridge according to the invention may be regarded as that of a right cylinder possessing certain slightly enlarged zones.

The envelope of the cartridge preferably possesses a symmetry of revolution. Furthermore, it is desirable that, when no pressure is exerted on the cartridge, the largest diameter ofthe zone(s) capable of undergoing radial deformation should-be greater than the largest diameter of the zone(s) capable of undergoing axial deformation. Usually the largest diameter of the zone (s) capable of undergoing radial deformation is between 110 and 200%, preferably between 120 and 150%, of the largest diameter of the zone(s) capable of undergoing axial deformation.

Any configuration of the zone(s) capable of undergoing radial deformation is possible, provided that the said zone(s) can contract when the plug passes through a cross-section of a blasting hole which is slightly smaller than its own largest cross-section, and provided that the said zone(s) can expand in the event of an increase in the internal pressure inside the cartridge. Thus, the said zone(s) can advan- tageously be provided with longitudinal channels or grooves, paralel to the axis of the cartridge. These longitudinal channels or grooves can be arranged overall or part of the length of the zone concerned, and they can be identical or different. Usually these channels or grooves are preferably identical and uniformly distributed around the circumference of the zone concerned, in order to ensure uniform radial deformation.

Preferably the (or each) zone capable of undergoing radial deformation has longitudinal grooves of triangular cross-section. The greatest depth of these grooves is preferably 25 to 75% of the largest radius of the zone concerned. Preferably, their approximate angle of opening is 1 to 2 radians. The number of these grooves is preferably 3 to 6. Also, they are preferably identical and uniformly distributed around the circumference of the zone concerned.

Preferably the envelope of the zone(s) capable of undergoing radial deformation comprises, at one end, a portion in the shape of a truncated cone, which diverges from that end; the smaliest crosssection of this portion can advanrtageously be joined directly to a zone capable of undergoing axial deformation. Preferably the envelope of the zone(s) capable of undergoing radial deformation also comprises, at the other end, a portion in the shape of a truncated cone, which converges towards that end.

The two portions in the shape of truncated cones can be joined directly at their largest cross-sections, or they can be bridged by a part-spherical or cylindrical portion, the length of which is preferably less than 20%, more particularly less than 10%, of the total length of the zone concerned.

Any configuration ofthe zone(s) capable of undergoing axial deformation is possible, provided that the said zone(s) can shorten when the plug is subjected to an axial pressure, for example during the explosion of the explosive charge, and provided that the said zone(s) can lengthen in the event of an increase in the internal pressure inside the cartridge.

Thus, the said zone(s) can advantageously be cylin drical and be provided with hollow annular channels disposed so as to form a bellows. The numbers and the cross-section of the channels are preferably chosen so as to permit as large an axial deformation as possible. The grooves are preferably identical to one another and of uniform rounded profile.

Moreover, in addition to the zones capable of undergoing radial or axial deformation, a cartridge according to the invention can comprise one or more substantially non-deformable zones, the greatest transverse dimension of which is preferably at least 10%, and more particularly at least 20%, less than the greatest transverse dimension of the zone(s) capable of radial deformation. These substantially non-deformable zones can advantageously be cyiindrical.

Preferably a cartridge according to the invention has, at one end, a closed base, which can be plane or of rounded shape, and, at the other end, a filling neck which can be sealed, for the purpose of filling the cartridge on site before introducing the plug into the blasting hole which is to be sealed.

However, the cartridge can also be filled at the factory, and, in this case, it can be finally closed, for example by welding.

The filling neck can be sealed by any means which ensure good leaktightness, e.g. a valve, a capsule or a screw-threaded cap, the latter being preferred.

Any number of zones capable of undergoing radial or axial deformation is possible; preferably the number is 1,2 or 3. If a cartridge according to the invention has at least two zones of one type, the zones of one and the same type are preferably contiguous. Furthermore, where the cartridge has a filling neck, the latter is preferably adjacent to a zone, ortwo or more contiguous zones, capable of undergoing axial deformation.

Preferably the number, the dimensions and the shapes of the zones capable of undergoing radial or axial deformation are so chosen that increases or decreases in individual zonal volumes compensate one another when the cartridge, filled with a substantially incompressible fluid or another substantially incompressible material, is subjected to pressure. Thus, if a radial pressure is exerted on one or more zones capable of undergoing radial deformation, the decrease in volume which results can (in the present preferred case) be compensated by an increase in volume corresponding to lengthening of the zone(s) capable of undergoing axial deformation.

The capacity of a cartridge according to the invention may suitably be a function of the nominal diameter of the blasting hole which is to be sealed.

The total height of the cartridge is usually between 2 and 15 times, and most frequently between 4 and 8 times its greatest transverse dimension.

The material of which a cartridge according to the invention is composed should desirably be suffi cientlyelasticto permit the axial and radial deformation of the zones capable of undergoing radial or axial deformation respectively. However, it is prefer ably not too elastic, i.e. not too easily deformed, since it is desirable that the plugs should be easily positioned. Finally, the material preferably possesses an adequate abrasion resistance and a low coefficient of sliding friction. In general, thermoplastics materials are very suitable for producing cartridges according to the invention.Thus, it is possibleto use: polyolefins,e.g. high-density or lowdensity polyethylene, polypropylene, and ethylene and/or propylene copolymers; polystyrene; vinly resins, e.g. rigid or semi-rigid polyvinyl chloride, vinyl chloride copolymers and polyvinylidene fluoride; polyamides; polycarbonates; and thermoplastic polyesters, e.g. poly-(ethylene glycol) terephthalate. Good results have been obtained with polyolefins and more particularly with polypropylene or polyethylene.

A cartridge according to the invention can be produced by any applicable moulding technique, and, in particular, by blow-moulding from extruded tubular parisons or from injection-moulded preforms.

The thickness of the walls should naturally be adequate to give the desired leaktightness. Usually it is between 0.2 and 2 mm.

The invention will be explained in greater detail with reference to the accompanying drawings, in which: Figure 1 is a view in elevation of a cartridge according to the invention, and Figure 2 is a view in section on the line A-A of Figure 1.

As shown in the figures, the cartridge 1, which has been produced by blow-moulding a portion of a tubular polypropylene or polyethylene parison, possesses a side wall 2 of cylindrical shape, a closed base 3 of rounded shape, and a screw-threaded neck 4 which can be hermetically sealed by means of a screw-threaded cap which is not shown.

Starting from the base 3, the sidewall 2 of the cartridge successively posseses a smooth cylindrical zoneS, two contiguous zones 6 and 7 capable of undergoing radial deformation, and a zone 8 capable of undergoing axial deformation, the latter zone being adjacent to the screw-threaded neck 4. The cylindrical zone 5 is relatively short.

Each of the zones 6 and 7 comprises four identical hollow enlargements of constant width, which are uniformly distributed around the circumference of the cartridge and which are separated by longitudinal grooves 9, the angle of opening of which is about 1.5 radians.

The envelope of each of the zones 6 and 7 comprises a divergent portion 12 and a convergent portion 13, which are both in the shape of truncated cones and which are bridged by a short cylindrical portion 11.

The zones 6 and 7 are joined to one another by means of a short cylindrical portion 10.

The zone 8 possesses five identical annular channel 14, which are arranged so as to form a bellows.

The maximum diameter of the cylindrical portions 11 of the zones 6 and 7 is greater than that of the zone 8, and greater than that of the smooth cylindric al zone 5.

The outer surface of the cartridge 1 exhibits no sharp angles.

The cartridge 1 is employed in the following manner four plugging explosive charges placed in blasting holes.

The cartridge is filled with a material (which can be a liquid or a paste or solid, e.g. a powder) which is appropriate for plugging purposes in this field.

Water, glycols, mixtures of water and a gelling substance, aqueous solutions of calcium chloride, and calcium chloride flakes are examples of materials which can be used forfilling the cartridge. Very good results are obtained with plain water. The cartridge is sealed by means of a screw-threaded cap engaging the neck 4. The plug is preferably introduced cap first.

The plug formed in this way is suitable for use in blasting holes having a nominal diameter which is slightly smaller, for example less than 10% smaller, and preferably less than 5% smaller, than the diameter of the cylindrical portions 11, the said nominal diameter thus being greater than the diameters of the zone 8 and of the smooth cylindrical zone 5.

When the plug is forcibly introduced (cap first) by the use of a tamper, the zones 6 and 7 are compressed as they come into contact with the wall of the blasting hole, and contract, whereas the zone 8 becomes extended. When the cap is in contact with the explosive charge, the tamper is withdrawn, leaving the plug wedged in position by engagement of the zones 6 and 7, the hole thus being suitably sealed.

When the explosion takes place, the shock wave exerts an axial pressure whose initial effect is to shorten the zone 8, causing the zones 6 and 7 to expand and ensuring that the plug is still more firmly held in the blasting hole. Subsequently, however, the shock wave causes the bursting of the cartridge and the atomisation of its contents.

The plugs formed by means of cartridges according to the invention are suitable for inter alia all mine blasting in which the explosive charge is placed at the distal end of a hole of circular cross-section. By virtue of their high performance, they are very particularly suitable for use in coal mines.

Claims (13)

1. Cartridge of generally cylindrical shape, composed of an elastically deformable material, for plugging blasting holes, characterised in that it possesses at least one zone (6 or 7) capable of undergoing radial deformation and at least one zone (8) capable of undergoing axial defcrmation as a result of a radial or axial pressure being exerted on the cartridge or as a result of a variation in the internal pressure.

2. Cartridge according to claim 1, characterised in that the largest diameter of the zone(s) capable of undergoing radial deformation is greaterthan the largest diameter of the zone(s) capable of undergoing axial deformation.

3. Cartridge according to claim 1 or 2, characterised in that the zone(s) capable of undergoing radial deformation is or are provided with longitudinal channels or grooves (9).

4. Cartridge according to claim 3, characterised in that the longitudinal grooves are of triangular cross-section, the approximate angle of opening of which is 1 to 2 radians.

5. Cartridge according to any of claims 1 to 4, characterised in that the envelope of the zone(s) capable of undergoing radial deformation còmpris- es, at one end, a portion (12) in the shape of a truncated cone, which diverges from that end.

6. Cartridge according to claim 5, characterised in that the said envelope also comprises, at the other end, a portion (13) in the shape of a truncated cone, which converges towards that end.

7. Cartridge according to any of claims 1 to 6, characterised in that the (or each) zone capable of undergoing axial deformation is provided with hollow annular channels (14) disposed so as to form a bellows.

8. Cartridge according to any of claims 1 to 7, characterised in that it is provided with a filling neck (4) adjacent to the (or a) zone capable of undergoing axial deformation.

9. Cartridge according to any of claims 1 to 8, characterised in that the filling neck is screwthreaded.

10. Cartridge according to any of claims 1 to 9, characterised in that it is produced from a polyolefin.

11. Cartridge according to any of claims 1 to 10, characterised in that it comprises 1, 2 or 3 zones capable of undergoing axial deformation.

12. Cartridge according to any of claims 1 to 11, characterised in that the number, the dimensions and the shapes of the zones capable of undergoing radial or axial deformation are so chosen that increases or decreases in the individual zonal volumes compensate one another when the cartridge, filled with a substantially incompressible fluid or another substantially incompressible material, is subjected to pressure.

13. Cartridge according to claim 1, substantially as described with reference to the accompanying drawing.