Patent Application
20090277354
1. Field of the Invention
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.
2. Description of Related Art
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.
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.
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.
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.
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.
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.
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.
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's distinction is maintained in its consumable air tube against the Kang medium for sympathetic detonation.
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.
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.
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.
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:
Referring first more particularly to
When air is introduced into chamber 6 via the air valve stem 12, the air tube is expanded to the inflated condition of
Referring now to
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.
According to applicant'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:
Hole diameter×hole diameter×0.3402×product density=loading rate in pounds/foot
8×8×0.3402×0.87=18.9 pounds per foot
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.
Pounds per minute—divided by—Pounds per foot=feet loaded per minute
200/18.9=10.6 feet loaded per minute
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.
Referring to
Referring to
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.
According to a further advantage of the invention, improved fragmentation may be achieved through a raised stem height. Referring to
In the blasting procedure shown in
Referring now to
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.
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.
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.
