Method of charging holes with explosives

May 15, 1956 r. b. aitchison etal 2,745,346

METHOD OF CHARGING HOLES WITH EXPLOSIVES

Filed May 11, 1953

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United States Patent Office

2,745,346

Patented May 15, 1956

2,745,346

METHOD OF CHARGING HOLES WITH EXPLOSIVES

Robert B. Aitchison, New York, and Stanley B. Kirk New Rochelle, N. Y., assignors to Union Carbide and Carbon Corporation, a corporation of New York

Application May 11,1953, Serial No. 354,174

Claims. (Cl. 102—23)

The present invention relates to a method for charging blast holes with explosives and, more particularly, to a method for charging bored or flame pierced blast holes with an explosive.

Heretofore, blast holes have been prepared by either drilling or rock piercing to depths greater than one hundred feet. These holes are then charged with conventional cartridges of explosive which are to be detonated in the hole. Certain difficulties are often encountered when this prior art method is employed. Seepage water has filled such holes to substantial depths. Fissures in the strata surrounding the hole have added to the difficulties. In the case of holes produced by flame piercing, additional difficulty may be encountered by virtue of the fact that the walls of the hole are not perfectly regular and could cause a temporary jamming of explosive cartridge in the hole thereby preventing their insertion to the bottom and forming an air pocket beneath and around the cartridge should this condition be left uncorrected. In consequence, it is, therefore, often the practice to flame ream blast holes iii loose blocky formation and, if the explosive is contained in a rigid container, to utilize a slightly smaller size than is ideal for the job. Such procedures reduce the efficiency of the blast.

It is, therefore, an object of the present invention to provide a method of charging blast holes with explosives in such a manner that the effect of water seepage is obviated and the contour of the hole is of no consequence and has no effect on the charging of the hole.

Another object is to provide a method of charging blast holes, particularly flame pierced blast holes, so that the possibility of forming dead air pockets will be eliminated.

A further object is to provide a safer method for charging blast holes with explosives so that prior to or during introduction of the explosive into the hole, the danger of a premature explosion is greatly minimized.

A still further object is to provide a method suitable for deck loading and expanded section loading of blast holes so that the full efficiency of the explosive may be realized and the explosive charge may be placed in rock strata where it will be most advantageous.

In the drawing:

Fig. 1 is a vertical sectional view through a rock pierced blast hole;

Fig. 2 is a vertical sectional view through a rock pierced blast hole which has been expanded at the base;

Fig. 3 is a vertical sectional view of a rock pierced blast hole which has been expanded at predetermined locations to provide for deck loading of the explosive charge;

Fig. 4 is a vertical sectional view of a rock pierced blast hole, as shown in Fig. 1, showing one embodiment of the invention in which an end-weighted collapsed expansible impervious tube is being lowered into the hole;

Fig. 5 is a sectional view of the blast hole of Fig. 4 showing the inflation of the tube; and

Fig. 6 is a sectional view of the blast hole of Fig. 4 showing a dispensing unit depositing an explosive charge in the inflated tube.

In accordance with the method of the present invention a thin, elongated, collapsed, inflatable, expansible, im5 pervious tube of suitable length is lowered into the blast hole to any predetermined depth. The end of this tube is, of necessity, closed off and, preferably, weighted to facilitate lowering the tube into the hole. The collapsed tube may be provided in roll form for ease of handling 10 and lowering.

When the tube has been lowered to the proper depth within the hole it is severed from the roll and attached to a suitable supply of gas. The gas serves to inflate and expand the collapsed tube thereby causing it to contact 13 and cling securely to the side walls of the blast hole. Thereupon, the tube is securely closed off at the surface and removed from the gas supply. The loose neck is then hooked up to a dispenser capable of dispensing a free flowing explosive into the inflated tube.

As the inflated tube becomes filled with explosive charge, the inflating gas is displaced from the tube and is discharged to the atmosphere through valves provided in the dispenser.

The only special characteristic required of the ex25 plosive charge is that it be free flowing at the operating temperature.

One type of explosive charge especially adaptable to the method of the present invention is that type commonly referred to as liquid oxygen explosive. This explosive 30 consists of carbon soaked with liquid oxygen. As is required of the explosive charge generally, for the present method, it is imperative that a liquid oxygen explosive be employed which is freely flowable at the operating temperature (about —183° C.). When the method of the 35 present invention is employed to charge blast holes with such liquid oxygen explosive, an added benefit is achieved, in that, as the liquid oxygenated carbon is dispersed in the inflated tube it very quickly freezes the walls of the tube to the side walls of the blast hole and, in this manner, 40 provides a very effective insulating seal for the charge.

We have discovered that regardless of the type of explosive employed it is beneficial to employ rugged, collapsed, inflatable, impervious tube to insure against puncture by irregularities in the side walls of the blast hole. A 45 thin tube of polyethylene has been tested and found suitable for such application. It has been found that a double-ply thin tube is more effective in resisting puncture by irregularities in the side walls than is a single-ply tube equal in thickness to the sum of the thicknesses of the 50 two single plies.

It has been found that generally the collapsed, inflatable impervious tube of the present invention may be inflated with any gas that is not reactive with the explosive charge to be dispensed therein. In the case where liquid 55 oxygenated carbon explosive is to be used, it is imperative that the inflating gas employed, in addition to being itself non-reactive with the elements of the explosive, js additionally bone dry and oil free. Gases such as nitrogen fulfill all of these requirements, while gases such as com60 pressed air, without treatment, are moist and oily and, as such, in the presence of liquid oxygen may cause preignition in the hole.

The procedure which is followed when the desired amount of free flowing explosive is dispensed into the tube 65 is to allow the gas to freely discharge from the tube to the atmosphere. Then, suitable ignition means is positioned in desirable proximity to the charge and the unfilled portion of the blast hole may be filled with loose and otherwise suitable stemming.

γθ The present invention is especially important in its applicability to charging blast holes which have been sprung, or chambered, to increased diameters. The hole

2,745,346 mixture into said inflated tube thereby concurrently displacing said inert gas from said tube.

8. A method in accordance with claim 7 wherein said inflatable expansible tube of substantially impervious ma5 terial is a polyethylene tube.

9. A method in accordance with claim 7 wherein said free flowing explosive is pelletized carbon soaked in liquid oxygen.

10. A method of charging a blast hole with explosive 10 comprising inserting into said hole to the bottom thereof an elevated collapsed inflatable expansible tube of substantially impervious material having its lower end closed off and weighted, inflating said tube into contact with the side walls of said hole by introducing an inert gas into 15 said tube preparing liquid oxygen-soaked carbon pellets near the top of said hole, and dispensing a quantity of said, liquid oxygen-soaked carbon into said inflated tube while concurrently displacing said inert gas from said inflated tube.

11- A method in accordance with claim 10 wherein said inflatable expansible tube of substantially impervious material is a polyethylene tube.

12. A method of charging a blast hole having more than one chambered portion of increased diameter com25 prising the steps of inserting into said hole to the bottom thereof a first elongated collapsed inflatable expansible tube of substantially impervious material having its lower end closed off and weighted; inflating said first tube into contact with the side walls of said hole; introducing a 30 free flowing explosive at atmospheric temperature and pressure into said first inflated tube until said hole is charged up to approximately the upper end of the first encountered increased diameter portion; deflating the uncharged portion of said first inflated tube and inserting 35 suitable means for igniting said charge; providing suitable stemming in said hole between said first charge and the lower end of the second encountered increased diameter portion of said hole; inserting into said hole to approximately said lower end of said second encountered in40 creased diameter portion a second elongated collapsed inflatable expansible tube of substantially impervious material having its lower end closed off and weighted; inflating said second tube into contact with the side walls of said hole, including said second encountered increased ₄₅ diameter portion; introducing a free flowing explosive at atmospheric temperatures and pressure into said second inflated tube until said increased diameter portion of said hole is charged; deflating the uncharged portion of said second inflatable tube and inserting suitable means for _θ igniting said charge; and thereafter repeating said inserting, inflating, introducing deflating and stemming steps with other inflatable tubes whenever a further change in blast hole diameter resulting from chambering is encountered.

_rr 13.. A method in accordance with claim 12 wherein said inflatable expansible tube of substantially impervious material is a polyethylene tube.

14. A method in accordance with claim 12 wherein said free flowing explosive is powdered carbon soaked ₆₀ in liquid oxygen.

15. A method of charging a blast hole having more than one chambered portion of increased diameter comprising the steps of inserting into said hole to the bottom thereof a first elongated collapsed inflatable expansible _sg tube of substantially impervious material having its lower end closed off and weighted; inflating said first tube into contact with the side walls of said hole; introducing a free flowing liquid oxygenated carbon explosive into said first inflated tube until said hole is charged up to approximately _θ the upper end of the first encountered increased diameter portion; inserting ignition means in suitable proximity to said charge; providing suitable stemming in said hole between said first charge and approximately the lower end of the second encountered increased diameter portion; 75 introducing a further amount of free flowing liquid shown in Fig. 2 has been sprung at its base to produce a wider diameter to accommodate a larger charge of explosive. The blast hole shown in Fig. 3 has been sprung, or chambered, in two places to accommodate what is known as a deck loaded explosive charge.

In charging a blast hole, such as shown in Fig. 3, with conventional explosive charge, an inflatable tube would be lowered to the bottom of the hole and the procedure described hereinabove followed until the lower deck is properly charged with explosive and suitable detonating means. The portion of the hole between the lower deck and the upper deck is then filled with charge, or with stemming, and the method of the present, invention is then repeated to charge the upper deck of the blast hole with explosive. In this manner the bulk of explosive charge can be placed, wherever desired, in such quantity as is necessary, thereby obtaining the utmost efficiency from the explosive charge.

More specifically, a blast hole having mere than one chambered portion of increased diameter, such as shown in Fig. 3, may be charged by inserting a first collapsed inflatable expansible tube of substantially impervious material to the bottom, inflating said tube and introducing explosive until the hole is charged to the upper end of the first (lower) enlarged diameter portion whereupon the first tube is deflated and the hole is stemmed up to the next portion of increased diameter whereupon a second tube is inserted, expanded and charged up to the top of that portion and then deflated. This procedure may be repeated for each, chambered portion, using a separate tube for each charging.

The dispenser employed in the practice of the present invention is very simple in construction when a conventional free flowing explosive charge is to be dispensed. The gravity feed principle may be employed and prevision is made for the discharge of the displaced inflating gas through valves at the top of the dispenser.

When a liquid oxygenated carbon explosive is to be employed, the dispenser is combined with a soaking box for soaking the pelleted carbon in liquid oxygen. Such soaking box-dispenser should preferably be contained in a properly heat-insulated container to reduce evaporation losses.