Abstract:
An inflatable air tube includes a sleeve member arranged concentrically about the upper end portion of the air tube to define a receptacle chamber for receiving a quantity of bulk explosive blasting powder, thereby to add weight to the air tube for positioning and stabilizing the same in the bulk explosive powder during the depositing of the powder into a blasting hole drilled into the ground. According to the method of the present invention, a plurality of accurate blasting patterns may be provided in the blasting powder column by timing the manual or mechanical insertion of the air tubes into the bulk blasting powder relative to the rate of supply of the powder from a source thereof.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    An inflatable air tube includes a sleeve member arranged concentrically about the upper end portion of the air tube to define a receptacle chamber for receiving a quantity of bulk explosive blasting powder, thereby to add weight to the air tube for positioning and stabilizing the same in the bulk explosive powder during the depositing of the powder into a blasting hole drilled into the ground. A plurality of accurate blasting patterns may be provided in the blasting powder column by timing the manual or mechanical insertion of the air tubes into the bulk blasting powder relative to the rate of supply of the powder from a source thereof. 
         [0003]    2. Description of Related Art 
         [0004]    In the prior art air tube construction disclosed in the Robert Australian patent No. AU 2004200940 required tedious loading requirements. Briefly, these requirements include loading layers of explosives, then installing the air tubes, then loading explosives around the air tube and then another layer of explosives and so on. These steps were necessary due to the light weight and buoyancy of the air filled tube. Even when these loading steps were followed, the tube would move from its installed position when the explosives layer was loaded on and around it. Random and imprecise positioning was the result. 
         [0005]    The improved design of the present invention was developed to provide an air tube having a sleeved top which facilitates automatic weighting of the air tube when it is inserted into the discharge of bulk explosives (by auger or pump) into the borehole (drill hole). Because of the added weight, the need for the tedious loading steps is eliminated and the loading time of a blast hole is substantially decreased from the ease of the resulting process. This new process incorporates the loading of the explosives and the air tubes at the same time. As the explosives are being loaded into the blast hole the air tube with sleeve is placed in the stream (discharge) of bulk explosives. The bulk explosives are caught in the cup cavity or chamber created at the top of the air tube by the sleeve; the now weighted air tube is displaced downwardly in a stabilized manner into the blast hole and is embedded in the explosive column at the precise predetermined location. Multiple air tubes can be installed by following the same process in series. 
         [0006]    Since the axial air-gaps from the sleeved air tubes are to be consumed in the detonation and the reduction of explosives in precise vertical areas are the focus, the requirement of special precautions to ensure concentric or horizontal aligned is not of specific consequence to the blast result. In fact in certain instances the air gaps created from the sleeved air tubes may overlap to maintain the desired explosive reduction. 
         [0007]    The previous design resulted in inaccurate positioning of the air tubes in a column of explosives. With the improved design, near exact placement of the air tube can be achieved. The result of accurate placement has yielded expanded applications of the product and the axial air-gapping technique. Previously the predominant application for axial air-gapping was for overall explosive reduction and ultimately cost savings. With the improved accuracy of placement from the sleeved air tube, specific tasks can be accomplished, resulting from an exact reduction of explosives in certain parts of the explosive charge column. The axial air gapping creates a core of air within the column of blasting agent that is consumed in the detonation. Standard air-gapping separates the column into multiple charges that are interrupted by the air-gapping device. 
         [0008]    The Kang U.S. Pat. Nos. 6,330,860 and 6,631,684 discloses the use of a similar air tube, but for a distinctly different purpose. In the first Kang patent, air tubes, having the same diameter or slightly smaller than the blast hole, are used to create a gap, separating the blasting agent column. This separation creates a “medium for sympathetic detonation” within the blast hole between the separated charges. Conversely, the air tubes of the present invention are a part of, and a consumable in, the blasting agent column and are consumed in the detonation. As a general rule, the diameter of the new air tube is equal to or less than 60% of the diameter of the blast hole. For example, an eight (8) inch blast hole would utilize an air tube that would be approx. 4.8″ in diameter (8.0″×0.6). The Kang patent has further constraints in regard to the length of an air tube. The air tube of the present invention overcomes this limitation. 
         [0009]    Furthermore, the aforementioned Kang patent contains fairly complicated calculations to determine the length of the air tube. These calculations and resulting lengths are used to ensure the occurrence of sympathetic detonation. Depending upon the diameter of the blast hole, if the length of the Kang tube is too long the occurrence of sympathetic detonation will not propagate from one charge to the next. Our improvement is not limited by the confines of sympathetic detonation. The air tube of the present invention generally promotes a standard four foot length in any size hole for user convenience; however, any length that does not exceed the length of the blasting agent column will still work and will be consumed with the detonation of the blasting agent column. 
         [0010]    For a better understanding of the Kang technique, the definition of sympathetic detonation/propagation is “The detonation of an explosive material as the result of receiving an impulse from another detonation through air, earth or water.” This definition comes from Explosives and Rock Blasting (copyright  1987 ) by the Atlas Powder Company. 
         [0011]    In the second Kang patent, the diameter sizes of the air tubes are reduced for ease of installation into the blast hole. In this change, the sympathetic detonation technique and the relating equations and size limitations still exist. Applicant&#39;s distinction is maintained in its consumable air tube against the Kang medium for sympathetic detonation. 
       SUMMARY OF THE INVENTION 
       [0012]    According to a primary object of the present invention, an inflatable air tube is provided including a sleeve member arranged concentrically about the upper end portion of the air tube to define a receptacle chamber for receiving a quantity of bulk explosive blasting powder, thereby to add weight to the air tube for positioning and stabilizing the same in the bulk explosive powder during the depositing of the powder into a blasting hole drilled into the ground. 
         [0013]    According to a further object of the invention, a method is provided for achieving a plurality of accurate blasting patterns in the blasting powder column formed in a blasting hole by timing the manual or mechanical insertion of the air tubes into the bulk blasting powder being deposited into the blasting hole relative to the rate of supply of the powder from a source thereof. 
         [0014]    The air tube initially has a compressed un-inflated flat condition defining in the intermediate portion of the tube between the ends thereof a pair of side walls. The sleeve member is also flattened and extends concentrically about the upper end of the compressed air tube, with the sleeve secured to at least one of the side walls, whereby upon inflation of the air tube, the sleeve cooperates with the dome-shaped end portion of the air tube to define a receptacle chamber for receiving the bulk explosive blasting powder. Owing to the initial compressed state of the air tube and sleeve member assembly, the sleeved air tube may be easily transported and stored with a minimal amount of space. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Other objects and advantages of the invention will become apparent from a study of the following specification, when viewed in the light of the accompanying drawing, in which: 
           [0016]      FIG. 1  is a partly sectioned view of the improved air tube of the present invention when in the initial collapsed condition, and  FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 ; 
           [0017]      FIG. 3  is a partly sectioned view of the air tube of  FIG. 1  when in the inflated condition, and  FIG. 4  is a sectional view taken along line  4 - 4  of  FIG. 3 ; 
           [0018]      FIG. 5  is a sectional view taken along line  5 - 5  of  FIG. 1 , and  FIG. 6  is a sectional view taken along line  6 - 6  of  FIG. 3 ; 
           [0019]      FIG. 7  is a diagrammatic sectional view illustrating the method for introducing the weighted air tubes into the blast hole together with the flow of the explosive blasting powder; and 
           [0020]      FIGS. 8-12  illustrate various selective patterns of arrangement of the air tubes in the blast hole. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring first more particularly to  FIGS. 1 and 2 , the air tube  2  is illustrated in the collapsed flat condition and includes an upper end portion  2   a , a vertically arranged intermediate portion  2   b , and a lower end portion  2   c . Prior to the introduction of air into the chamber  6  defined between the parallel air tube side walls  2   d  and  2   e , the upper and lower ends of the air tube have a generally arch-shaped configuration. As shown in  FIG. 1 . In accordance with a characterizing feature of the present invention, a tubular sleeve member  8  is arranged concentrically about the air tube upper end portion  2   a , which sleeve in the collapsed condition of  FIGS. 1 and 2  is flat and is secured to the air tube side wall  2   e  by a fastening strip  10 , such a heat seal seam, an adhesive strip, an adhesive layer between the sleeve member and the air tube, or the like. Preferably the upper edge  8   a  of the sleeve member is even with the adjacent edge of the arch-shaped end portion  2   a , as shown in  FIG. 1 . The air tube and the sleeve are each formed from a durable flexible synthetic plastic material. 
         [0022]    When air is introduced into chamber  6  via the air valve stem  12 , the air tube is expanded to the inflated condition of  FIGS. 3 and 4 , and the air valve stem is closed to maintain the air tube in the inflated condition. The upper end portion  2   a  of the air tube now has a generally dome-shaped configuration, and the sleeve  8  is expanded toward its tubular configuration and cooperates with the outer surface of the air tube end portion  2   a  to define a receptacle chamber  14 . The lower inner periphery of the sleeve member is in contiguous tight engagement with the outer surface of the air tube, thereby to seal the bottom of the receptacle chamber  14 . 
         [0023]    Referring now to  FIG. 7 , as is conventional in the art, bulk explosive blasting powder  20  is supplied from a source  22  by variable-speed auger or pump means  24  or the like and is deposited by gravity into the blasting or bore hole  26  that has been drilled into the ground  28 . At a given time during the supply of the blasting powder, an inflated air tube is manually or mechanically inserted into the flow of blasting powder to cause the receptacle chamber  14  defined by the sleeve  8  to be filled with the blasting powder, thereby to add weight to the air tube and to reduce the floating thereof within the blasting powder flow. The inflated and weighted air tube is then introduced into the blasting hole  26  together with the blasting powder flow. Additional inflated air tubes may be similarly weighted by insertion within the blasting powder flow  20  for introduction in a predetermined timed sequence into the blasting hole  26 . 
         [0024]    In practice, blasting agent is delivered to the drill pattern (blast holes) by a “bulk truck”. This truck has bins for storage of blasting agent. The blasting agent is augered from the bins through a discharge tube or auger arm and into the blast hole. Rates of discharge vary greatly from truck to truck. A typical range of 100 to 1000 pounds of blasting agent discharged (loaded) per minute exists. 
         [0025]    According to applicant&#39;s invention, precise placement of the air tube can be achieved through the weighted sleeve. To accomplish exact placement, discharge per minute, by the bulk truck and blast hole loading rate must be considered. The loading rate of a blast hole is determined by the hole diameter and the density of the blasting agent. Blasting agents range in density from 0.82 g/cc to 1.32 g/cc. The most widely used is ANFO at a density of 0.87 g/cc. Using ANFO as an example in an 8″ blast hole the loading rate would be determined as follows: 
         [0000]      Hole diameter×hole diameter×0.3402×product density=loading rate in pounds/foot 
         [0000]      8×8×0.3402×0.87=18.9 pounds per foot 
         [0026]    Knowing the loading rate of 18.9 pounds per foot and assuming a truck discharge rate of 200 pounds per minute, it can be determined that 10.6 feet of blasting agent column will be loaded into the blast hole in one minute. 
         [0000]      Pounds per minute—divided by—Pounds per foot=feet loaded per minute 
         [0000]      200/18.9=10.6 feet loaded per minute 
         [0027]    Using this same example, if an air tube is designed to be at 15 feet intervals throughout a blast hole then each air tube would be installed at a rate of every 90 seconds. 
         [0028]    Referring to  FIG. 8 , it will be seen that three inflated weighted air tubes  2  have been introduce in vertically staggered relation within the explosive blasting powder  20  that is introduced into the blasting hole  26  that extends downwardly toward the coal seam  30  contained in the ground  28 . Conventional stemming material  32 , such as a layer of dirt, closes the upper end of the blasting hole. In this application, a solution is provided for meeting the concern of many blasting operations that the damage to the coal or ore seam that is being mined from the blasting of the rock or overburden to be removed above the seams. For this application, with the precise placement of the sleeved air tubes, an exact reduction of explosives can be reduced in the specific area of the explosive charge. Reducing the explosive charge near the seam to be mined and recovered will reduce the damage to this seam. 
         [0029]    Referring to  FIG. 9 , when material is blasted for excavation, the perimeter around the blasted and excavated area remains as a wall  36  (commonly referred to as a “highwall”). Because other mining functions take place beneath this wall, reducing the damage to this undisturbed area is a concern for the safety of those operations. Generally a blast is designed with a target powder factor (a relationship of pounds of explosives to yards of material to be blasted) that will achieve a desired blast result. In many cases this designed powder factor will over shoot or damage the resulting wall. 
         [0030]    A reduction of the explosives in the perimeter (outside) blast holes will reduce the damage to this wall. With the accurate placement of the sleeved air tubes  2  in the blasting powder  20 , the exact reduction precisely in the area of the wall that is subject to damage can be achieved. Overall reductions between 15% to 25% of the explosive charge reduce the damage to perimeter walls. 
         [0031]    According to a further advantage of the invention, improved fragmentation may be achieved through a raised stem height. Referring to  FIG. 10 , An explosive charge  20  in a blast hole  26  must be confined by filling the top portion of the blast hole with an inert material  32  such as gravel or drill cutting produced from drilling the blast hole (commonly referred to as “stemming”). This confinement helps direct the explosive force to fracture the bank of material to be blasted instead of the energy being released out the top of the hole. However, in some cases the amount of needed material for adequate confinement also creates a considerable amount of poorly blasted material throughout the area of inert material. With the use of the sleeved air tubes  2 , explosives can be reduced in the top of the explosive column reducing the amount of needed inert confining material and consequently improving the result of blasted material. 
         [0032]    In the blasting procedure shown in  FIG. 11 , the advantage is obtained of correct loading through weak areas  40  of overburden. Banks of material to be blasted generally are made up of various type of material. In some case there is a great variance in the types of material. In instances where the variances create weak or soft areas that require considerably less explosives than the remaining bank, substantially reducing the explosives used in this area is desirable. Utilizing the sleeved air tubes  2  with the ability of precise placement, a pre-determined amount of explosive  20  can be reduced in the weak areas of the bank being blasted. The remaining areas  42  of the bank can receive the full load as designed. 
         [0033]    Referring now to  FIG. 12 , a further advantage of the present invention is the ability to achieve greater explosive reduction for control blasting. Control Blasting refers to situations were rock must be blasted but movement of the blasted material must be limited. In these cases a significantly reduced amount of explosives must be distributed throughout the rock to be blasted. The precise placement of the sleeved air tubes  2  can accomplish this task. Because of the large amount of reduction necessary to accomplish this, sleeved air tubes may overlap in the blast hole. 
         [0034]    According to a further advantage, the sleeved air tubes may be use in horizontal blasting; which is generally utilized underground with smaller diameter holes. When bulk explosives are used it is necessary to blow or pump the explosives into the horizontal blast hole. The sleeved air tube allows for the bulk explosive to catch and force the air tube into the horizontal blast hole and embed in place. The previous air tube had no means of conveyance in this type of loading. 
         [0035]    As distinguished from the prior art devices which required time consuming loading functions and, even if the steps were closely followed the vertical position of the air tube was not completely assured, the improvement of the sleeved top, for the purpose of weighting the air tube, in order to embed the air tube in precise vertical location within an explosive loaded blast hole, has resulted in the axial air gap technique being applied to numerous situations that the prior devices could not easily accommodate. 
         [0036]    While in accordance with the provisions of the Patent Statutes the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that changes may be made without deviating from the invention described above.