The present invention relates to a method for tamping an explosive charge in a hole provided in a vein of a bedrock comprising the steps of inserting the explosive charge in the hole and sealing the hole with a sealant.

In the underground mining industry, explosive charges are used for the removal of valable veins from a bedrock. The veines may contain valable ores such as for example ores of gold, silver, platinum, chromium, iron.

In a currently used method, a plurality of holes is drilled in the ore carrying veins and mother loads. An explosive charge is inserted into each hole and sealed into the hole by tamping the hole.

Thereto various means can be used, such as for example a clay tamping bag which is saturated with water. After the clay bags have been allowed to dry, the charge is brought to explosion.

Because the water saturated clay bags are rather hard and heavy, and because they do not readily adapt to the shape of the hole, they must be driven into the pre-drilled holes by means of working tools, such as a hammer. The insertion of the clay bags into the drilled holes thus involves undesired hard labour, taking into account the often narrow space that is available to the work men and the relatively high temperatures.

It is the aim of the present invention to provide a method for tamping the holes which is less laborious.

This is achieved with the present invention in that in stead of water saturated clay bags as a sealant, use is made of a foam forming polymer which is inserted in the hole in the liquid state, whereafter the polymer is allowed to foam and to harden.

It has been found that after the polymer has been inserted in the hole, for example through injection, the polymer flows out in the hole. Since the liquid polymer is rather mobile and capable of penetrating even very small cavities and since the polymer is only allowed to foam after it has been inserted in the hole containing the explosive charge, the polymer is capable of filling the remaining space in the hole, of adapting its shape to the shape of the hole and the explosive charge and of effectively encapsulating the explosive charge. In that way an effective tamping of the hole can be obtained, provided of course the polymer is allowed to foam to a sufficient extent. After the polymer has been allowed to foam, the foamed polymer is hardened or cured depending on whether a thermoplastic or thermosetting polymer is used.

In case use is made of a thermosetting polymer, the polymer foam can be readily cured because of the relatively high temperature and humidity in the mine. The time needed for hardening or curing the polymer may vary depending on the type of polymer used, but curing times of approximately only 20 minutes can be achieved. The method of this invention thus allows to achieve a serious saving of time as compared to the known method. It has namely been found that when use is made of clay tamping bags, the bags first need to be dried before an explosion can be initiated if an explosion with a high yield is aimed at. This drying may take 3-4 hours or even more. The presence of moisture in a hole namely appeared to adversely effect the yield of the induced explosion.

Furthermore, the polymer foam appears to show an improved adhesion to the walls of the hole so that an improved

sealing of the interior of the hole from the outside can be achieved. It is believed that because of the improved adhesion of the foam to the walls of the hole and the improved sealing of the hole, not only a larger number of charges can be exploded, thus decreasing the number of misfires, but that also the over-all efficiency and yield of each individual explosion can be increased. It has been found that the method of this invention, the yield can be increased with approximately 10-20 %, so that a more economically feasible process can be obtained.

The polymer foam further presents the advantage that it can be easily removed from the hole, for example by cutting the foam in pieces and removing those pieces from the hole. This is especially important in case the explosive shows a defect, and does not explode upon ignition and needs to be removed from the drilled hole for safety reasons. By cutting the foam out of the hole, the explosive becomes easily accessible and can be removed from the hole.

A wide variety of foam forming polymers can be used in the method of this invention. For example, use can be made of thermoplastic materials or thermo selting resins. Suitable examples include foam forming polyurethane; poly-isocyanurate; silicone; silyl terminated polyurethane, polyether, polyester, for example polyacrylate, polyvinylchloride; polyethylene, polypropylene. If so desired, mixtures of two or more of those foam forming polymers can be used. In the method of this invention, preferably use is made of foam forming polyurethane.

Polyurethane has been found to show a stable cellular structure, a low density involving excellent filling properties, good adhesion to a lot of substrates, high cohesive strength, good insulating properties against heat and electricity.

The foam forming polymer can be used as a one component system or a two component system. In a two component system two components react with each other to give a polymer. Mixing of

the two components can be done in several ways, for example through a static mixer right before applying the product, or through activating the system in a can wherein the two components are stored separately and thereafter mixed, so that the polymer is formed in situ in the can. An example of a two component system is polyurethane which is obtained from the reaction of a polyol with a di-isocyanate.

The foam forming polymer used in the method of this invention preferably contains a dye that is visible in the dark, more particularly a phosphorescent or a fluorescent dye. The use of such a polymer allows to identify the position of the explosive charges, even in underground mines, where even artificial light is scarce. Examples of suitable dyes include fluoresceine and its derivatives, cumarin derivatives, coumestrol and derivatives thereof, and many others or mixtures of one or more of these compounds. This may be important to increase the visibility of unexploded charges that have to be removed.

To allow the polymer material to foam, the polymer contains a foam forming agent. Examples of suitable foam forming agents include propane, butane isomers, dimethylether, nitrous oxide, carbon dioxide, freon for example 1,1,2-trifluoroethane (R152a), 1,1,1,2-tetrafluoroethane (R134a) and mixtures thereof.

The foam forming polymer of this invention is preferably applied by means of a multi position distributor, so that the foam forming polymer can be applied under pressure and independent of the orientation of the distributor. This is important in underground mines where the drilled holes may not always be easily accessible.

The multi position distributor comprises a container for containing the foam forming polymer. The container is provided with a valve with a press on valve shaft mounted thereon. One end of the press on valve shaft is connected to the inside of the container through a passage so as to allow the liquid polymer to leave the container.

The other end of the valve shaft is connected to a flexible pressure bag which may contain a gas under pressure or a predetermined quantity of chemical compounds that are mixed with each other when the press on valve shaft is pressed to produce a predetermined volume of gas. When the valve shaft is pressed on, the pressure bag is filled with gas and expanded, and the polymer is forced to leave the container. The gas pressure is usually chosen such that it is sufficient to force approximately the whole amount of polymer to leave the container.

The invention is further illustrated in the attached figures, description of the figures and description of a preferred embodiment.

Figure 1 is a front view of a bedrock containing pre-drilled holes tamped with the foam of the present invention.

In figure 2, a cross section of a multi position foam distributor is shown.

As is shown in figure 1, in a bedrock, a plurality of holes 1 are drilled at more or less regular distances from each other in ore carrying veins 2. After inserting a detonator 3 in each hole 1, an amount of an explosive material 4 is inserted in each hole. As an explosive material, for example use can be nade of trinitrotoluene. The trinitrotoluene is preferably injected under pressure, as a dry powder. After the pre-drilled holes have been provided with the explosive, the holes are tamped so as to firmly secure the explosive charge in the hole and to achieve a maximum result, i. e. to blast free as much of the ore carrying vein as possible. After the pre-drilled holes have been temped, the ignition is initiated and the explosive is brought to explosion.

In the method of the present invention, use is made of a foam forming polymer for tamping the holes, preferably a foam forming polyurethane. The foam forming polymer is injected in the hole, often in the liquid state, allowed to foam and to cure. Because the foam

forming polymer shows a large expansion, which can be up to approximately 50 times its original volume, or even more, it will flow into and fit perfectly into all crevasses that may be present in the pre-drilled holes. It is believed that the improved sealing involves the observed increase of the yield when the explosive is blasted and the reduction of the number of unexploded charges. Yield increases of up to 10% or more have been found.

The polyurethane foam present the advantages that it shows a good adhesion to a wide variety of rocky materials, even when humid. It has a gross weight of less than 1 kilo and can thus easily be carried. The clay bag tampings known from the art would have a weight which is approximately 20 times higher for the same volume and take a volume which is 50 times the volume of the unfoamed mining foam.

Also the polyurethane is a self extinguishing material, and in case any unexploded charges may remain, they can be easily removed by cutting the foam out of the hole and removing the explosive.

The polymer foam can be injected into the pre- drilled holes by means of a wide variety of applicators. Preferably use is made of a multi position container with which polymer foam can be applied, irrespective of the position and angle in which the container is held. An embodiment of a multi position container for use in the present invention is shown in figure 2. The container 5 comprises a first compartment 6 which contains the foam forming polymer. Upon pressing the press-on valve 6, pressure bag 7 is filled with a gas which simultaneously functions as foam forming agent and propellant gas, the gas pressure increases and the foam forming polymer is forced to leave the container. Suitable foam forming agents include propane, butane isomers, dimethylether, nitrous oxide, carbon dioxide, freon for example 1,1,2-trifluoroethane (R152a), 1,1,1,2-tetrafluoroethane (R134a) and mixtures thereof. Some of these gasses are more or less inflammable.

Preferably use is made of non-flammable gasses so as to reduce explosion risks. The most preferred gas is R134a. Building of pressure in the pressure bag 7 can be achieved by for example (i) allowing gas to flow from a container 8 under high pressure towards the pressure bag, or (ii) bringing gas forming reactants into contact with each other upon suppressing the valve 6, so that a pressure is generated in the pressure bag 7 and the foam forming polymer is forced to leave the container.