US 2595960 A
Description (OCR text may contain errors)
May 6, 1952 R. w. LAWRENCE EXPLOSIVE DEVICE Filed Oct. 30, 1948 FIG.|
ROBERT W. LAWRENCE.
, ability to be cast.
Patented May 6, 1952 UNITED- STATES TENT OFFICE 2,595,966 EXPLOSIVE' DEVICE Application October 30, 1948, Serial No. 57,464
5 Claims. 1.
This invention relates to explosive devices of high eiliciency and. more particularly to blasting devices comprising. shaped charges of maximum density gelatinand the process for their preparation.
Since the discovery of Charles E. Munroe in 1888, it has been known that detonating'charges of explosive which have a cavity in their base have unusual penetrating power. In late years extensive military use has been made of this property of shaped charges in demolition explosives. It is known that the penetrating. efiiciency of such charges, depends on the strength and detonation velocity of the explosive,,and the shape and size of" the. cavity in the base, as well as on the use of metal liners for the cavities. The military explosives most extensively used, including trinitrotoluene and mixtures of trinitrotoluene with pentaerythritol tetranitrate'or cyclotrimethylenetrinitramine, were. especially useful in the preparationof military shaped charges because of this These explosives are, however, relatively expensive, and it is necessary to heat them to fairly high. temperatures before they can be poured in castin operations. With commercial explosives, such as dynamites and gelatin dynamites, it is most difficult to form charges with suitable cavities due to the nature of these explosives and the great difiiculty encountered in packing to high. and uniform. density, especially in the region of the cavity. Furthermore, these explosives for. the most part are substantially weaker and have considerably lower detonation velocities than the military explosives commonly used. Blasting. gelatin, however, which consists of nitroglycerin gelatinized with nitrocellulose, is equivalent or superior in strength to the. best military explosives- Blasting gelatin is normally prepared. by heating the glycerin trinitrate to about 100 to 130 F. and stirring. in the desired amount of nitrocellul'ose until a sticky, rubbery gel is formed. This gel is extremely diflicult to pack because of its rubbery nature. Moreover, during thev stirring operation.substantialquantities of air. areztrapped in. the mix and the. resulting bubbles reduce density and effect a corresponding diminution indetonation velocity and. brisance. Obviously, this rubberlike gelis even more difilcult to pack to a uniform density around a conical mold to form a shaped charge than the pulverulent commercial explosives.
NOW in. accordance. with. thepresent invention, it.has been. discovered; thathighly efiicient: explosive devicscanbeeasily producedwhichcontain.
2 shaped charges of blasting gelatin having aniaximum density.
Generally described, the invention comprises an explosive device having in combination. a container and a shaped chargedisposed therein, said 7 determined amount of nitrocellulose and an anttion does take place.
- sired cavity or cavities.
acid substance as a stabilizer for the explosive liquid nitric ester, pouring the cooled mixture into a container before gelatinization takes place and warming container and contents-until gelatiniza- The containers are previously equipped with a form to provide the de- If it is desired to line the cavity with a metal or other suitable type liner, it is preferred to so construct the form that it may be utilized as the cavity lining.
In Fig. 1 and Fig. 2 areshown sectional views of twoembodiments of unprimed devices of this invention which are especially adapted to drilling holes in the earth or in soft stone.
In Fig. 1 and Fig. 2, a spirally wrapped paper container 1 is provided with a spun copper cone 2- which forms the bottom of the container and which functions as a mold and a liner for the cavity of the shaped charge of blasting gelatin 3 cast within the container l. The top of the container is crimped over the charge to form a fluted portion d which contains a central orifice 5 for intion necessary tothoroughlymix. ofl thismixture: were. poured. into a. thin walled brass, tube having. a diameter of. 0.50. inch anda 1 sertion. of a suitable detonator 1. Prior to being so primed, the fluted portion 4' is sealed by a snugly fitting annular cardboard disc 5. If desired, the disc 6' maybe provided with a tab to facilitate its removal. The devices illustrated in Fig; 1 and Fig. 2 may beprovi'ded with the desired amount of standoff inany suitable manner.
The followin examples are presented in order to morefully illustrate the invention. In all cases the basal diameter'of each cone employed is equal to the basal diameter of the container in which it is used.
Erample'l A glycerin trinitrate-nitrocellulosechalk (91/8/1) mixture was preparedby cooling the glycerin trim'trate to 4 C. and stirring in the nitrocellulose-and chalk with. minimum of agita- Twelve grams ample 5. The charge-was allowedto gel.
67 cone of lead 0.02 inch thick inserted vertex first into one end thereof. After the mixture was allowed to gel, the tube was placed cone end down on a. steel plate inch thick and detonated with a special No. 8 electric blasting cap. A hole 0.25 inch in diameter was drilled through the plate.
Example 2 The end of a length of brass tube similar to that employed in Example 1 was sealed with cellulose acetate tape and 12 grams of the mixture of Example 1 were introduced into the open end. After the charge was gelled, the tube was placed taped end down on a steel plate inch thick and shot with a special No. 8 electric blasting cap. The plate was dented but not perforated.
Exampl 3 A 90 cellulose acetate cone was inserted vertex first into a length of the tube employed in Examples 1 and 2, and 3 grams of the mixture of Example 1 were poured into the open end. When the charge had gelled, the tube was placed cone end down on a steel plate inch thick and shot with a special No. 8 electric blasting cap. A hole 0.20 inch in diameter was drilled through the plate.
Example 4 A coaxial core inch in diameter was bored through substantially the full length of a thermosetting phenol-formaldehyde plastic cylinder 12 inches long and 5 inches in diameter. Five holes 1 inch in diameter were bored from various points of the periphery of the cylinder to the coreand a 70 cone of thin copper having a diameter of 1 inch was forced into the holes so that their apexes were toward the core and their bases were 1 inch from the periphery of the cylinder. The glycerin trinitrate-nitrocellulose-chalk mixture of Example 1' was poured down the central core until the cavities were filled, care being taken to eliminate air bubbles. When the mixture had gelled, the cylinder was inserted into a steel pipe having an inside diameter of 6 inches and a wall thickness of 0.5 inch. The charge was fired with a special No. 8 electric blasting cap. The plastic cylinder was disintegrated by the force of the explosion and the steel pipe was perforated opposite each hole in the cylinder as originally positioned.
Example 5 An explosive device 6 inches in height and 3% inches in diameter at its base, similar to that in Fig. 1, was prepared with a 70, 0.08 inch thick spun copper cone in its base. The container was fabricated from spirally wrapped paper and was charged with a glycerin trinitrate-nitrocellulosechalk (95/4/ 1) mixture prepared as in Example 1, and the charge was allowed to gel. The device, weighing 910 grams, was fired with a booster cap at a standoff of 7.5 inches above the ground. A hole inches deep and 3 inches in diameter was formed in the ground by the charge.
Example 6 An explosive device 9 inches in height and 8 inches in diameter at its base, similar to that shown in Fig. 2, was prepared with a 70, 0.18 inch thick conical copper cone in its base. The container was fabricated from spirally wrapped paper and was charged with the mixture of Ex- The device weighing 5059 grams, Wasfired with a booster cap at a standoff of 12 inches from the ground. The charge made a hole in the ground 10 inches in diameter at the top and 7 feet deep.
Example 7 A tin can, 3.5 inches in diameter and 5.5 inches long, was provided with a 3-inch metal cone in its bottom; the apex extending into the can. A second can, 3.5 inches in diameter and 6 inches long, was sealed to the bottom of the first to give a hermetically-sealed closed space below the cone. Four pounds of the mixture used in Example 5 were poured into the upper can and allowed to gel. This device was fired with a booster cap under 40 feet of water in a seismic prospecting operation with completely satisfactory results.
Example 8 A spirally wrapped paper container 3.5 inches long and 2 inches in diameter was provided with a 53, 0.05 inch thick spun steel cone 2 inches high in its bottom. One-half pound of a 92/7 1 mixture of glycerin trinitrate (containing 20% glycol dinitrate) nitrocellulose and chalk prepared as in Example 1 was poured into the container and allowed to gel. When detonated with a booster cap from a standolf of 3 inches a penetration was made through 5 /2 inches of steel.
The density of the blasting gelatin charges employed in this invention may be in the range of 1.50-1.60 g./cc., but should perferably be in the range of 1.55-1.60 g./cc. This density will give maximum bulk strength and detonation velocity. In the firing of the shaped charges described, it is essential thatthe blasting gelatin be primed strongly enough that it detonates at its high velocity of 7600-7800 m./sec. in the preferred density range. This high velocity of detonation may be obtained by detonating the charge with a booster cap such as one containing 5 to 10 grams of pressed pentaerythritol tetranitrate or with the caps described in copending application of R. W. Cairns and R. W. Lawrence, Serial No. 637,384, filed December 27, 1945 now Patent No. 2,525,397. The special No. 8 cap used in Examples ll had base charges of from 0.4-0.5 gram of pentaerythritol tetranitrate pressed to a density of at least 1.5 g./cc.
The copper shells were 0.30 caliber with a bottom thickness of not more than 0.008 inch. Special No. 6 caps with base charges of 025-03 gram of pentaerythritol tetranitrate in similar shells were also found tosatisfactorily detonate the devices of Examples 1-4 at the high detonation velocity of the blasting gelatin employed.
The blasting gelatin employed in the devices of this invention may contain from about 96% to about 90% of explosive liquid nitric ester, from about 4% to about 10% of nitrocellulose and an additive amount of at least 1% of an antacid such as chalk or zinc oxide for the explosive ester. However, the preferred composition will contain about 93% to about 96% of liquid explosive nitric ester, and from about 7% to about 4% nitrocellulose. Although for most applications, straight glycerin trinitrate is the preferred liquid explosive ester, mixtures of liquid explosive nitric esters are often desirable. In place of using straight glycerin trinitrate, it is sometimes advantageous to mix the glycerin trinitrate with glycol dinitrate to the extent of 20 to 60%, giving a density range of 1.50-1.57 g./cc. However, with the higher glycol dinitrate content, the ,charge should be cooled to 1 0 to 20 C. below zero, in order'to slow down the rate of advantages.
gelatinization. The glycerin trinitrate may also contain from to 30% of diglycerin tetranitrate which will assist in slowing down the rate of gelatinization, or diethylene glycol dinitrate. It may also contain dinitrotoluene and/or trinitrotoluene in small proportions to lower the freezing point. Up to of a crystalline explosive such as pentaerythritol tetranitrate or cyclotrimethylenetrinitramine may also be uniformly incorporated. However, in order to have such a mixture pourable for casting, not more than about 5% of nitricellulose should be used for gelation.
The containers for the shaped charges of blasting gelatin may be made of any suitable paper, metal or plastic. Because of the high water resistance of blasting gelatin, it is not necessary to take the extreme precaution against entry of moisture or water as in the case of water-soluble explosives. The container employed in the oil well casing perforator devices of this invention may be constructed from any suitable material. If made of metal, the gun must be of such strength as to withstand the explosion of the charge without bursting and sticking in the casing. High-grade steel has been found satisfactory in this application. However, it is preferred to construct these guns of a plastic, as in Example 4, which will be pulverized by the exploding charge. Such guns are preferably molded from an inexpensive thermosetting resinous material capable of resisting the advanced temperatures often encountered in deeper wells. As illustrated by the foregoing examples, the blasting devices of this invention have many By casting the blasting gelatin in the container, it is possible to conveniently prepare shaped charges from a commercial explosive which will have a maximum density, a maximum detonation velocity and a maximum bulk strength, which will be highly resistant to water and which will possess penetrating powers equivalent or superior to those of the best military explosives. A further advantage. in the preparation of the charge of this invention is that it is unnecessary to heat the mold so that the cast explosive will take the full shape of the form. Furthermore, the danger of entrapping air bubbles is minimized and a maximum density is thereby obtained. The shaped charge containing blasting cartridges of this invention may be used for drilling holes in earth, concrete. sandstone, or other rock; for drilling holes in metal plates; and, in suitable form, for perforating oil well casings. Other uses for the strong, relatively inexpensive explosive devices of this invention will be apparent to those skilled in the art.
What I claim and. desire to protect by Letters Patent is:
1. An explosive device comprising in combination a container and a shaped charge disposed therein, said shaped charge being a cast blasting 6 gelatin having a density of between 1.50 and 1.60 g./cc.; said gelatin comprising from about to about 96% of explosive liquid nitric ester, from about 4% to about 10% nitrocellulose, and having added thereto at least 1% of an antacid.
2. An explosive device comprising in combination a container and a shaped charge disposed therein, said shaped charge being a cast blasting gelatin having a density of between 1.50 and 1.60 g./cc.; said gelatin comprising from about 93% to about 96% of explosive liquid nitric ester, from about 4% to about 7% nitrocellulose, and having added thereto at least 1% of an antacid.
3. An explosive device comprising in combination a container and a shaped charge disposed therein, said shaped charge being a cast blasting gelatin having a density of between 1.50 and 1.60 g./cc.; said gelatin comprising from about 93% to about 96% of glycerin trinitrate, from about 4% to about 7% of nitrocellulose, and having added thereto at least 1% of chalk.
4. An explosive device comprising in combination a container and a shaped charge disposed therein, said shaped charge being a cast blasting gelatin having a density of between'1.50 and 1.60 g./cc.; said gelatin comprising from about 90% to about 96% of a mixture of glycerin trinitrate and glycol dinitrate, from about 4% to about 10% of nitrocellulose, and having added thereto at least 1% of chalk.
5. An explosive device comprising in combination a container and a shaped charge disposed therein, said shaped charge being a cast blasting gelatin having a density of between 1.50 and 1.60 g./cc.; said gelatin comprising explosive liquid nitric ester and nitrocellulose.
ROBERT W. LAWRENCE.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS OTHER REFERENCES Manual of Explosives, by Jules Bebie, copyright 1943, pages 35 and 36, the MacMillan Company, N. Y.
Explosives Engineer, July-August 1945, pages -163.
Explosives Engineer, November-December 1947, pages 171-173, 182 and 183.
Clark, Technical Publication No. 2157, American Institute of Mining and Metallurgical Engineers, preprint for N. Y. meeting, March 1947, 16 pages.