BACKGROUND OF THE INVENTION

THIS invention relates to a method and a device for tamping a blast hole.

It is well known that in breaking of rock through blasting, holes are drilled into the rock and thereafter charged with explosives. It is further well known to insert material into the blast hole after the hole has been charged to confine the effects of the blast to some extent.

Upon detonation of the explosives, a large volume of explosion gas is rapidly produced. This explosion gas exerts a pressure on the inner walls of the hole, thereby breaking the rock. Inserting material into the blast hole, after the hole has been charged with explosives, increases the efficiency of the blast by substantially confining the explosion gas to the immediate blast hole area. The confinement of the explosion gas may significantly increase the performance of the explosives even though this period of confinement may be in the order of milliseconds. The practise of inserting material into blast holes to improve the efficiency of the blasting operation is often referred to as tamping or stemming. Several options are available for tamping of blast holes. Examples include: factory prepared tamps of clay or clay and sand mixtures, stone fragments which may be loose or contained in prefilled tubes, tubes filled with water in situ, factory prepared tubes containing gelatinised water, expanding rigid or semi-rigid foams sprayed into the blast hole, chemical mixtures that react in situ to form tamps and engineered devices with protuberances that restrain outward movement from the blast hole.

Each of the mentioned examples of tamping devices suffers from unique disadvantages. The method of tamping with clay or similar material suffers from the disadvantage that the tamping is relatively difficult to remove from the blast hole in the event of a misfire. Each of the factory prepared tamps mentioned, whether solid, liquid or gel, suffers from the disadvantage that they are relatively heavy and voluminous. This may result in high transport costs and could make handling challenging; space often being extremely limited in the immediate area of the blast hole. The engineered devices are lightweight but relatively expensive. The filling of tubes with water can be time consuming.

A further disadvantage associated with solid tamping devices is the risk that the solid tamping device may be ejected from the blast hole as a dangerous projectile during the blasting operation.

Each of the above mentioned examples of tamping devices also suffers from the further disadvantage that it remains a practical logistical challenge for operators to ensure that the correct ratio of explosive cartridges and tamping devices are simultaneously available and ready for use at the blast face at the required time. This logistical hurdle associated with tamping is often, considered the reason why mines accept to blast without tamping, thereby losing out on the associated increase in blast efficiency.lt is therefore an object of the present invention to provide a tamping method and a tamping device that is relatively lightweight, that is low in initial volume, that incurs comparatively lower transport costs, that is relatively safe to use, that requires minimal preparation prior to insertion into the blast ho!e and that is relatively simple to remove from the blast hole in the event of a misfire.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a tamp for tamping a blast hole, the tamp comprising a superabsorbent polymer component and a semi-permeable membrane.

The superabsorbent polymer may be capable of absorbing aqueous liquids to form a hydrogel.

Preferably, the superabsorbent polymer is selected from the group consisting of polyacrylamide, polyvinyl alcohol, cross-linked polyethylene oxide, polymethylacrylate and polyacrylate salt. The polyacrylate salt is preferably selected from sodium polyacrylate, potassium polyacrylate, lithium polyacrylate and ammonium polyacrylate.

Preferably, the superabsorbent polymer is cross-linked sodium polyacrylate.

The superabsorbent polymer component may be in particulate form but it will be appreciated that the superabsorbent polymer component may be wetted to some degree.

The semi-permeable membrane may be arranged to form a closed vessel, preferably a capsule, with the superabsorbent polymer component contained in the capsule.

Preferably, at least one end of the closed vessel is formed at an angle of about 45 degrees relative to a longitudinal axis of the closed vessel.

The superabsorbent polymer component is preferably substantially uniformly dispersed within the capsule. This may be achieved by rendering an inner surface of the capsule adhesive such that particulate granules adhere to the surface. The superabsorbent polymer component may be coated on an inner surface of the capsule, for example, applied by way of a coating solution or other layer.

The semi-permeable membrane is preferably a non-woven material.

Preferably, the tamp is charged with less than about 50% by volume of substantially dry superabsorbent polymer component of the volume of the expanded capsule, preferably less than about 25% by volume, preferably less than about 15% by volume, most preferably less than about 5% by volume.

According to a second aspect of the invention there is provided a method of tamping a blast hole wherein a tamp is inserted into the blast hole, the tamp comprising a superabsorbent polymer component and a semi-permeable membrane wherein the tamp is soaked with an aqueous liquid either before or after its insertion into the blast hole so that it expands into contact with the walls of the hole.

The tamp may be a capsule having a diameter slightly less than that of the blast hole into which it is introduced when the tamp is soaked with an aqueous liquid before its insertion into the blast hole.

The tamp may be a capsule having a diameter slightly more that of the blast hole into which it is introduced when the tamp is soaked with an aqueous liquid after its insertion into the blast hole.

BRIEF DESCRIPTION OF THE DRAWINGS

Without thereby iimiting the scope, the invention will now be described in more detail with reference to the following Figures and examples in which:

Figure 1 is a perspective view of a tamp according to the present invention before wetting; and

Figure 2 is a perspective view of a tamp according to the present invention after wetting. DESCRIPTION OF PREFERRED EMBODIMENTS

This invention provides for a tamp for tamping blast holes comprising an absorbent component and a semi-permeable membrane.

The semi-permeable membrane is preferably arranged to form a capsule. The length of the capsule may vary depending on the depth of the blast hole to be tamped. The width of the capsule may be selected in manner which will provide for a final diameter, after the tamp has been soaked in an aqueous liquid for a period of time which allows for the absorption and retention of aqueous liquid by the absorbent component, that is slightly less than the diameter of the blast hole to be tamped. The seams of the capsule may be formed by stitching, chemical bonding, heat sealing or any other means of physical closure. One or both of the ends of the capsule may be formed at a 45 degree angle relative to a longitudinal axis of the capsule. The angled end or ends facilitate an easy insertion of the capsule into the blast hole. If the end or ends of the tube are square, they tend to form protrusions that extend beyond the mean cross-section of the capsule which obstructs insertion in the blast hole.

The semi-permeable membrane is preferably non-woven material. None- woven material is a fabric like material made from long fibres bonded together by chemical, mechanical, heat and/or solvent treatment. Preferably, the semi-permeable membrane is non-woven polyester cloth. Even more preferably, the semi-permeable membrane is non-woven cloth comprising a mixture of polyethelene and polypropylene.

The absorbent component may be in particulate form. The absorbent component is preferably included in the capsule, even more preferably the absorbent component is substantially uniformly dispersed in the capsule and most preferably the absorbent component is coated on an inner surface of the capsule.

The absorbent component may also be in a compressed tablet form. The superabsorbent polymer tablet may be formulated to contain an agent that increases the rate of disintegration of the tablet, for example an effervescent agent.

The capsule is preferably charged with the absorbent component at a volume percentage of dry absorbent component relative to the volume of the expanded capsule of preferably less than about 50 %, even more preferably less than about 25 %, even more preferably less than about 5 % and most preferably less than about 5 %. It will be appreciated that the capsule may be substantially under filled thereby allowing the capsules to be packaged, and therefore transported, in an essentially horizontally flat configuration.

The capsule is preferably charged with the absorbent component at a weight percentage of dry absorbent component relative to the weight of the expanded capsule of preferably less than about 50 %, even more preferably less than about 25 %, even more preferably less than about 15 % and most preferably less than about 5 % by weight. It will be appreciated that the capsule may be substantially under filled thereby allowing the capsules to be packaged, and therefore transported, in an essentially flat compacted configuration which results in significant cost savings.

The absorbent component is preferably a superabsorbent polymer. Superabsorbent polymers are polymers that can absorb and retain extremely large amounts of a liquid relative to their own mass. The superabsorbent polymer may also be a superabsorbent polymer that absorbs aqueous liquids and retains water through hydrogen bonding within the structure of the polymer thereby forming what is known as a hydrogel.

Preferably, the superabsorbent polymer can absorb and retain more than about 10 times its own mass, more preferably more than about 50 times its own mass, even more preferably more than about 100 times its own mass, even more preferably more than about 200 times its own mass, even more preferably more than about 500 times its own mass and most preferably more than about 600 times its own mass. The substantially dry tamp is soaked in liquid prior to insertion into the already charged blast hole. The liquid may be an aqueous liquid. The tamp may be soaked in the liquid until it attains a diameter slightly less than that of the blast hole into which will be inserted. The substantially dry tamp may also be wetted after insertion into the blast hole. It will be appreciated that the period of soaking of the substantially dry tamp before it reaches the required degree of saturation will be dependent on several factors including: the nature of the semi-permeable membrane, the nature of the soaking liquid, the temperature of the soaking liquid, the nature of the absorbent component, the amount of absorbent component relative to the surface area of the capsule and the final tamp diameter required as defined by the diameter of the blast hole.

It will be appreciated that a tamp according to the present invention, once wetted, will eventually dry out after a period of time and may be reused by re-soaking in an aqueous liquid.

Advantages of the present invention include that low mass tamps (stemming plugs) can be conveniently manufactured in a factory and transported at lower cost and conveniently to the workplace. The final preparation is a simple soaking operation that can be done concurrently with other tasks, so not increasing the workload on the operators. In addition, the wetted tamp can be easily removed from the blast hole in the event of a misfire.

A further advantage of the present invention is that the tamps of this invention can be packed with the explosives to be used for blasting due to the low mass and volume of the tamps. Explosives cartridges are conventionally packed in crates having a final mass of about 25 kg, there being a resistance to crates with a heavier final mass due to the difficulties associated with carrying the crates in confined underground spaces. These crates typically contain about 200 to 300 cartridge units, the units each having a diameter of about 22 to about 32 mm and a length of about 200 to about 300 mm . Therefore, as a result of the low volume and mass, about 60 to 100 tamps can easily be accommodated within the same explosives crate. This configuration significantly reduces the logistical hurdles associated with having the explosives cartridges and tamping devices ready, at the required time and in the correct numbers, at the blast face.

A further advantage of the present invention is that the low volume and mass of the tamps reduces the cost of transportation, relative to tamping devices known in the art, to such an extent that export becomes potentially viable.

Example 1

The semi-permeable membrane (11/21 ) defining the elongate capsule (10/20) was non-woven polyester cloth of the type manufactured by Freudenberg Inc in South Africa. The longitudinal seam (13) of the capsule was formed by stitching the polyester cloth (11/21 ) together to form an elongated sheath of desired length and width. The one terminal end of the sheath was stitched closed (12/22) forming an elongate capsule with three stitched sides and one open terminal end. The one terminal end of the elongate capsule was left open to provide for charging of the capsule with the sodium polyacrylate superabsorbent polymer.

The capsule (10) was initially in the form of a substantially flat sachet wherein the sachet had a length of 240 mm and a width of 60 mm.

The capsule (10) was charged with 7 g of sodium polyacrylate superabsorbent polymer (Favorpak 230, sold by inova RSA under the trade mark Fosge!). This material is capable of absorbing and retaining (gelatinising) 200 times its mass in water. It will be appreciated that placing of the superabsorbent polymer couid be effected by bonding it to one side of the membrane prior to forming the sachet (capsule) or dispensing into pre-formed sachets (capsules) or by a form-fill-seal process as commonly found in the industry. After charging of the capsule (10) with the superabsorbent polymer the open terminal end of the capsule was stitched closed (14/24) to form the final, substantially dry, tamp (10). The total mass of the semi-permeable polyester cioth capsule and the superabsorbent sodium polyacrylate, forming the final tamp, was 8.5 g.

The internal volume of the sachet (capsule), when fully expanded into cylindrical form (20) is 272 cubic centimetres whereas the volume of the Fosgel is less than 3 cubic centimetres so the sachet is substantially underfilled and can be packed almost flat.

The tamp was submerged in water for a period of 2 minutes. The superabsorbent polymer had absorbed water through the semi-permeable membrane allowing the tamp to swell to a substantially cylindrical capsule (20) with a diameter of 38 mm and a length of 240 mm. The mass of the wetted tamp had increased from the dry mass of 8.5 g to 275 g.

The wetted tamp (20) was inserted into a charged blast hole as a tamping device (stemming plug).

Example 2

The semi-permeable membrane defining the elongate capsule was a bi- Component non-woven cioth comprising polyethelene and polypropyene manufactured by Freudenberg Nonwovens (Pty) Ltd in South Africa under the trade mark VILEDON ^® (style number: MB040).

Two capsules of 300 mm in length and 48 mm in diameter were formed and tested by soaking the capsules in water at 30°C. Both capsules were filled with ca. 3.8 g of superabsorbent polymer per capsule. The superabsorbent polymer used was cross-linked sodium polyacrylate sold under the trade mark FAVOR ^® -PAC 400 by Evonik Stockhausen GmbH.

In Capsule number 1 the superabsorbent polymer was contained at one terminal end of the capsule, while in Capsule number 2 the superabsorbent polymer was uniformly distributed along the length of the capsule. The capsules were immersed in water at 30°C in order to compare the effect of the distribution of the superabsorbent polymer on the soak time. The capsules were compared at time intervals of 1 , 1.5, 2, 3 and 3.5 minutes. After a visual evaluation a "% filled" number was assigned to each capsule.

Capsule 1 was judged to be filled at 80% after 1 minute, 90% after 2 minutes and 100% after 3.5 minutes with some manipulation. Capsule 2 (uniform distribution of superabsorbent polymer) was judged to be filled at 75% after 1 minute, greater than 95% after 1.5 minutes and 100% after 2 minutes.

Capsule 1 had a final mass of 449.1 g and Capsule 2 had a final mass of 452.4 g.

From the above comparative test of Capsules 1 and 2 it can be concluded that the distribution of the superabsorbent polymer in the capsule is a parameter of minor importance in terms of the soak time of the capsule.

Example 4

The semi-permeable membrane defining the elongate capsule was a bi- component non-woven cloth comprising polyethelene and polypropyene manufactured by Freudenberg Nonwovens (Pty) Ltd in South Africa under the trade mark VILEDON ^® (style number: MB040).

Two capsules of 45 mm diameter and two capsules of 38 mm diameter were formed and tested by soaking the capsules in water at 30°C. Both capsules had a length of 300 mm and both were filled with ca. 3.8 g of superabsorbent polymer per capsule. The superabsorbent polymer used was cross-linked sodium polyacrylate sold under the trade mark FAVOR ^® - PAC 400 by Evonik Stockhausen GmbH. All four capsules were formed having one terminal end of each capsule at about 45 degrees relative to a longitudinal axis of the capsule.

Capsules A and B had a diameter of 45 mm, while capsules C and D had a diameter of 38 mm. The superabsorbent polymer was contained at one terminal end of each capsule for capsules A and C, while it was uniformly distributed along the length of the capsule for capsules B and D. The capsules were immersed in water at 30°C in order to compare the effect of the distribution of the superabsorbent polymer on the soak time. The capsules were compared at time intervals of 1 , 3 and 5 minutes. After a visual evaluation a "% Filled" number was assignd to each capsule.

Capsule A was judged to be filled at 60 - 70% after 1 minute, at 80 - 85% after 2 minutes, at 100% after 3 minutes (one end softer), and at 100% with even distribution after 5 minutes. Capsule B was judged to be filled at 70% after 1 minute, at 90% after 2 minutes, at 100% after 3 minutes (one end softer), and at 100% with even distribution after 5 minutes.

Capsule C was judged to be filled at 60% after 1 minute, at 80% after 2 minutes, at 90% after 3 minutes, and at 00% with even distribution after 5 minutes. Capsule D was judged to be filled at 70% after 1 minute, and at 00% after 2 minutes, at 100% with even distribution after 2 minutes.

From the above comparative test of Capsules A - D it can be concluded that the distribution of the superabsorbent polymer in the capsule is a parameter of minor importance in terms of the soak time of capsules with a diameter of 45 mm or 38 mm.