Abstract:
The invention relates to a device and a method for explosive drilling. Explosive capsules are fired by a firing device at a material to be stripped. A high degree of safety is attained in that use is made of an explosive with liquid oxygen that is only produced immediately before its application.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device for explosive drilling by means of explosive capsules with a firing device for firing the explosive capsules at a material to be stripped, wherein at least one container with liquid oxygen and at least one container with at least one fuel component are provided. 
     The invention further relates to a method for explosive drilling. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR §§1.97 and 37 CFR 1.98 
     Devices and methods of this kind that are used for the explosive drilling of earth or rock formations have been known for a long time, as for example from U.S. Pat. No. 3,516,502 or from U.S. Pat. No. 3,605,918. Especially when boreholes are sunk in hard rock formations, such as granite, the specific application of explosive capsules for shattering the rock leads to excellent stripping performances. 
     However, up to now explosive drilling could not gain ground within a wide range of applications. One of the reasons for this can be found in particular in the extremely strict legal regulations concerning the transport, storage and use of explosives. Especially in the civil sectors these extremely rigorous restrictions for explosives stood in the way of an economic application of explosive drilling. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the object to provide a device and a method for explosive drilling, with which a safe and economic application of explosive drilling is rendered possible in a great variety of applications. 
     In accordance with the invention the object is solved on the one hand by a device in which a combining device is arranged for combining the fuel component with the liquid oxygen for the forming of the explosive capsules and a supply device is provided for supplying the formed explosive capsules to the firing device, and on the other hand by a method wherein an explosive with liquid oxygen is used. 
     The device for explosive drilling according to the invention is characterized in that at least one container with liquid oxygen and at least one container with at least one fuel component are provided, in that a combining device is arranged for combining the fuel component with the liquid oxygen for the forming of the explosive capsules and in that a supply device is provided for supplying the formed explosive capsules to the firing device. 
     A fundamental idea of the invention resides in the fact that the explosive capsules used for explosive drilling are produced immediately before their application directly on the device. Thereby, for the production of the explosive capsules components are employed that are as such practically non-hazardous, in particular they are not considered as explosives and do not fall under any legal restrictions. 
     According to a finding of the invention liquid oxygen explosives are especially suitable for this purpose. Explosives containing liquid oxygen have been known for many decades. Cryogenic liquid oxygen is a particularly strong oxidizing agent, which, on being mixed appropriately, leads to an explosive-like reaction even with low-reactive fuels. 
     From U.S. Pat. No. 1,508,185 a liquid oxygen explosive containing wood powder as a fuel is known for example. However, as fuel other types of compounds containing carbon, hydrocarbon, other organic compounds and even metal powder and other substances can also be used, which, when reacting with oxygen, have a sufficient exothermal reaction enthalpy. A mixing of these fuels, which are present in particular in a solid state, preferably in a powdery or loose state, with liquid oxygen leads to an almost optimal spatial arrangement of the reactants, so that a rapid combustion and therefore a detonating reaction is brought about. In particular, according to the invention fuels on the basis of hydrocarbon molecules are used which, by being free of any safety-related restrictions, can be transported and stored in any chosen quantity. Likewise, liquid oxygen is a widespread technical gas that is used on a large scale in the welding technique for example and can be acquired without problem via existing distribution systems. 
     For safe application in explosive drilling the use of liquid oxygen explosives according to the invention offers the additional advantage that under ambient conditions these explosives keep their explosive properties for a short period of time only, ranging approximately from some seconds up to a few minutes. The reason is that cryogenic liquid oxygen volatilizes very quickly so that the remaining fuel component regains its normal non-hazardous state. More particularly, the fuel component is also environmentally friendly so that even in the case of an unintended non-detonation no hazardous material with regard to both explosive properties and environmental compatibility remains in the ground. 
     From these freely available and generally non-hazardous basic components explosive capsules are produced in the machine according to the invention, which are then directly fired via a supply device at the material to be shattered, in particular at rock formations. 
     An advantageous embodiment of the device according to the invention resides in the fact that in the combining device the fuel component is present as a prefabricated shaped body or can be formed into shaped bodies, in which case the fuel component can be mixed with the liquid oxygen before or after the forming. The fuel component, which is preferably existent as a powder or granulated material, is formed e.g. through sintering or pressing into a desired shape. In particular, this shape can be cylindrical or substantially spherical, while special shapes, e.g. for forming a hollow charge, are possible, too. Following the formation, the shaped body consisting of the fuel component is preferably soaked with the liquid oxygen and is thereby activated. The explosive capsule thus produced can then be supplied directly to the firing device, by means of which the explosive capsules can be fired in a defined direction and with a defined energy at the rock to be stripped. When sinking predominantly vertically directed boreholes an acceleration of the explosive capsules can take place solely through gravity so that the firing device merely releases or deblocks the explosive capsules. 
     Another preferred embodiment of the invention resides in the fact that casing bodies, prefabricated capsules containing fuel, and/or ignition elements can be supplied to the combining device in order to form the explosive capsules. If the fuel components as such do not possess inherent stability, the components can also be filled into a casing body made for example of cardboard or metal. This casing body serves as a geometric mold or shape-giver for the explosive charge. Especially when use is made of casing bodies a desired increase in the detonation effect can be additionally adjusted. There is also the possibility of filling the fuel component together with the liquid oxygen as a kind of slurry into the casing bodies. In the following the bodies consisting of the explosive charges that are filled into the casing or shaped bodies shall also be referred to as explosive capsules. Basically, the explosive capsule can explode as a result of the impact, pressure or blow energy occurring during the impact on the rock to be shattered. However, to increase safety it may be useful to arrange also an ignition device in the capsule, such as a conventional impact igniter. For example in the explosive capsules a dynamic inertia plugging can be provided in the rear part as seen in the impact direction, which triggers the detonating reaction at the moment of impact and/or preferably enhances the effect of detonation in the forward direction. 
     For the production of boreholes it is particularly preferred according to the invention that a tube-shaped drilling body is provided, in the lower end portion of which at least one aperture of the firing device is arranged. This allows for the most precise application as possible of the explosive capsules onto the material to be stripped. It can be provided one central aperture or several apertures that are spaced from the drilling axis. In addition, it is possible to provide a drill head with a rotatable or pivotable aperture. 
     According to the invention a directional control or a control of the drilling progress can be implemented in that, depending on the angle of rotation of the drill head, that part of the working face is preferably fired at, into which the borehole is to be redirected. To this end the firing aperture can be arranged eccentrically to the drilling axis. In addition, an adjusting device for adjusting the aperture can be provided. 
     Furthermore, according to the invention a gas nozzle arrangement is designed in the vicinity of the aperture. The nozzle arrangement can in particular be a ring nozzle arrangement around the aperture. This can serve to stabilize the trajectory of the explosive capsule, in which case the trajectory can have a length ranging from a few centimeters to some meters. In addition, in the case of works carried out in suspension-filled boreholes via the gas nozzle arrangement can be created a free space for the explosive capsule in the suspension. 
     According to the invention an especially good stripping performance is achieved in that in the lower end portion of the drilling body stripping members, in particular cutting teeth and/or roller bits are arranged. With these stripping members shattered or partly loosened rock material can be stripped. The combination of explosive shattering and stripping of the rock by means of stripping members brings about a borehole having a wall with the precise shape. 
     Furthermore, according to the invention a discharging conveyor device, in particular an auger, is arranged for conveying away the material to be shattered. The auger can be arranged in a flight-shaped manner around the tubular drilling body, which is driven in a rotating manner by a rotary drive. Alternatively, the discharging the conveyor device can also comprise an air supply, whereby stripped soil material can be conveyed away from the borehole in the airlift method. 
     Basically, the firing device can comprise a mechanical, electromechanical or even an explosion system. In accordance with the invention an especially simple and practicable design resides in the fact that the firing device has a pneumatic or hydraulic feeding device. The feeding device can be connected to a compressed-air supply by which a flow of compressed air can be generated. By means of this compressed-air-flow explosive capsules can be pneumatically accelerated and fed individually or in a continuous manner in a tube for example. They are fired with a defined kinetic energy and in a defined direction at the material which is to be stripped. 
     The method for explosive drilling according to the invention is characterized in that an explosive with liquid oxygen is used. As a result, the previously described advantages are attained in explosive drilling with regard to safety and good environmental compatibility. 
     An especially high safety level is attained in accordance with the invention in that explosive capsules are formed of at least one fuel and the liquid oxygen immediately before being supplied to a firing device and in that the explosive capsules are fired by the firing device at a material to be stripped in order to explode thereon and shatter the material. In this method according to the invention the explosive is produced according to demand directly before being fired so that a storage of large quantities of the explosive in its potentially explosive state is not required. 
     In accordance with the invention a very good stripping performance is achieved in that the explosive capsule is fired with a frequency of 0.1 Hz to 500 Hz. Hence, depending on the firing frequency relatively small explosive capsules with a few grams of explosive material can be used which, in themselves, represent a very small danger potential only. As a result, the easy and safe application of explosive drilling according to the invention is increased further. 
     In accordance with the invention it is particularly preferred that an afore-described device is employed for explosive drilling. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the following the invention will be described further by way of preferred embodiments shown in an extremely schematized manner in the accompanying drawings, wherein: 
         FIG. 1  shows a schematic arrangement of a device for explosive drilling according to the invention; 
         FIG. 2  shows a schematic partially cross-sectional view of a device according to the invention; and 
         FIG. 3  shows a flow diagram concerning the method for explosive drilling according to the invention. 
         FIG. 3A  shows a flow diagram concerning an alternative to the method for explosive drilling according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a device  10  for explosive drilling according to the invention comprising a carrier implement  11 , in the rear part of which a vertically directed mast  15  is arranged. Along the mast  15  a tube-shaped drilling body  12  can be displaced vertically by means of a rotary drive  16  in order to sink a borehole in the ground. On the outside of the drilling body  12  an auger  14  is arranged in a known manner, in which case the drilling body  12  is arranged together with the auger  14  again in an encasing tube  17  to carry out cased drilling. Through rotation of the drilling body  12  with the auger  14  stripped soil and rock material can be conveyed away from the borehole. 
     Above the rotary drive  16  a combining device  30  for the production of explosive capsules is arranged. Via schematically depicted tubes, a powdery or granular fuel made from hydrocarbon molecules or prefabricated capsules containing the fuel are supplied from a container  34 . Spaced apart from this container  34  a further container  32  with liquid oxygen is provided, from which liquid oxygen is supplied to the combining device  30  according to demand. In the combining device  30  the solid fuel, if not provided in a prefabricated manner, is formed or configured into the desired capsule shape and is then soaked with the liquid oxygen. In doing so the explosive capsule is activated, which means that only then does the capsule gain its explosive properties. If required, a cooling device can be provided in order to prevent rapid volatilization of the cryogenic liquid oxygen in the combining device  30 . The explosive capsule thus produced is supplied immediately from the combining device  30  to a firing device  20  which is operated by means of a pneumatic feeding device  22  with a separate compressor and a pressure line containing compressed air. 
     By means of a control device not shown here the firing device  20  fires explosive capsules at a rate of approximately 1 Hz through the tube-shaped drilling body  12  in the down-ward direction at the bottom of the borehole in order to loosen there further soil and rock material. The drilling body  12  driven in a rotating manner is connected through a rotary coupling  26  with the stationary firing device  20 . Further, an adjusting device  27  can be provided, with which a selected part of the working face can be fired at for directional control or control of the drilling progress. 
     In an extremely schematized cross-sectional view according to  FIG. 2  the explosive capsules  50  can be seen that are produced in the combining device  30 . Through a tube-shaped supply device  28  the explosive capsules  50  are supplied to the firing device  20  that has an annular duct  23  connected to the compressed-air supply. Through nozzle orifices  25  compressed air can be selectively introduced in a ring-shaped manner into the drilling body  12  so as to thereby fire the explosive capsules  50  at a predetermined rate and with a defined kinetic energy from the aperture  24  of the drilling body  12  at the rock material to be shattered. The shattered material can be conveyed away upwards by an auger  14  interacting with stripping members  13  in the shape of cutting teeth located at the lower end of the auger  14 . 
     The flow diagram of  FIG. 3  illustrates that the explosive capsules are produced by mixing liquid oxygen (LOX) with a powdery and/or granular fuel. As shown in the flow diagram of  FIG. 3A , it is possible to fill the fuel component together with the LOX as a kind of slurry into casing bodies. It is only the combination of the fuel with the liquid oxygen that leads to the highly explosive property of the explosive capsules. The explosive capsules are supplied immediately to the firing device, by which the explosive capsules are then fired at the rock to be shattered. Due to the high volatility of liquid oxygen the explosive capsules keep their explosive properties for a short time only so that the safety during explosive drilling is increased. Therefore the produced explosive capsules have to be used rapidly without significant storage and fired immediately by the firing device at the rock. 
     All things considered, a particularly safe and environmentally compatible explosive drilling is rendered possible according to the invention.