US2525397A - Blasting initiator - Google Patents

Description

Oct. 10, 1950 R. w. CAIRNS ETAI. 2,525,397

Bms'rmc INITIATOR 2 Sheets-Sheet 1 Filed Dec. 27, 1945 FIG.

AGENT Oct. 10, 1950 RQW. CAIRNS EI'AL 2,525,397

BLASIING mrm-roa Filed Dec. 27, 1945 2 Sheets-Sheet z INVENTUkS AGENT FIG. 4

M PW" illi/l1!!! ll! 14/ FIG.

Patented Oct. 10, 1950 2,525,397 BLASTING INITIATOR Robert W. Cairns and Robert W. Lawrence, Wilmington, Del., assignors to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application December 27, 1945, Serial No. 637,384

Claims.

This invention relates to blasting initiators and more particularly to blasting initiators of improved initiating power.

It is well known that blasting gelatin which consists of nitroglycerin gelatinized with about 7% by weight of nitrocellulose tends to become very insensitive on storage. This insensitiveness has usually been associated with the increased density which results from the gradual loss of air bubbles incorporated in the gelatin mix during manufacture. near its maximum density, i. e., between 1.58 and 1.61 g./cc., it is quite resistant to detonation by standard commercial blasting caps. However, when detonated at a high rate, high density blasting gelatin acquires a greater velocity than low density blasting gelatin and. it is therefore desirable to employ a blasting gelatin with as high a density as possible.

When blasting gelatin of low density is detonated, it has been found that itwill start with a low rate of detonation (2500-3000 m./sec.) and will then accelerate sharply to a high rate (about 7800 m./sec.). When blasting gelatin of high density is detonated, acceleration of a low. rate When the blasting gelatin is if a fuse cap is desired or by an ignition assembly if an electric blasting cap is desired.

Having now indicated in a general way the nature of this invention, there follows a more detailed description of preferred embodiments thereof with reference to" the accompanying drawings wherein reference symbols refer to like parts wherever they occur and in which: A

Fig. 1 is a vertical, sectional view of a standard commercial electric blasting cap;

Fig. 2 is a vertical, sectional view of an electric blasting cap in accordance with this invention;

Fig. 3 is a vertical, sectional view of a standard commercial fuse blasting cap; and v Fig. 4 is aivertical, sectional view of a fuse blasting cap in accordance with this invention.

The commercial'electric blasting cap of Fig. 1 includes a 0.30 caliber shell I, which has an inside diameter of 0.77 cm., a bottom 0.053 cm. thick. and a wall 0.015 cm. thick. having a base charge 2 of high explosive pressedto a density less than 1.4'5 g./cc. Superimposed upon the base charge 2 of detonation to a high rate of detonation does not often occur. Thus, the problem of detonating high density gelatin has appeared to be one of producing an initial high rate of detonation. In an effort to accomplish this, the density of the base charge in the blasting initiator has been increased, thus obtaining a high energy density and improving its brisance. However, this expedient has not entirely solved the problem, for

even with use of such initiators insensitive blasting gelatin has, in general, been detonated only at comparatively low rates or has failed to propagate detonation.

Now, in accordance with this invention, blasting initiators have been prepared which are capable of detonating insensitive explosive materials at a high rate. This is accomplished by employing an initiator carrying a base explosive charge of high density in a shell having a bottom weight less than the bottom weight in a standard commercial blasting initiator or cap.

The blasting initiators or caps in accordance with this invention may be prepared employing secondary or base explosives known to the art, such as pentaerythritol tetranitrate, nitromannite, cyclonite, mannitol hexanitrate, nitrolactose, and nitrosucrose. The explosive is placed in a shell whose bottom has a weight not more than about 0.10 gram, and pressed to a high density. A charge of priming explosive is added and the open end of the shell closed by a capsule is aloose priming charge 3 of initiating explosive. The shell is fitted with a plug 4 through which are inserted two leg wires5. A bridge wire 6 is soldered to the leg wires 5. The bridge wire 8 is embedded in the loose priming charge 3. The shell I is madewaterproof by a seal 1 composed of a waterproofing compound, and is provided with a crimp 8 to hold a sulfur seal 9 firmly in the shell. p

The commercial electric blasting cap vof Fig. 1 is distinguished from the blasting capo! Fig. 2 by the base charge 2 of greater height, due to its lower density, and the shell I with a-bottom III of greater thickness and, accordingly, greater weight. V A

The electric blasting cap. of Fig. 2 includes a 0.30 caliber shell II, which has an nside diameter of 0.77 cm., a bottom 0.023cm. thick, and a wall 0 0.015 cm. thick, havinga base charge l2 of high explosive pressed to a density more than 1.45

g./cc.

A primin charge 3, plug I, leg wires 5, bridge wire 6, seal 1, crimp 8, and sulfur seal 9 are provided for the can and consist of the same materials applied in the same manner as described for the can de ict d in Fig.1.

This electric blasting can is di tin ui hed from that of Fig. 1 and other standard commercial bla ting caps by the base charge l2 of greater den ity, as indicated by its smaller height in the shell, and the sh ll II with a bottom I 3 of reduced thickness and. accordingly, reduced weight. The commercialfuse blasting can of Fig. 3 includes a 0.22 caliber shell 20, which has an inside diameter of 0.56 cm., a bottom 0.043 cm. thick, and a wall 0.015 cm. thick, having a base charge 2| of high explosive pressed to a density less than 1.45 g./cc. A Pr r O! 1111- tiating explosive is disposed over the base charge. A gilding metal capsule 23 with an aperture 24 therein and a wafer charge 25, respectively, are provided in the shell.

The commercial fuse blasting cap of Fig. 3 is distinguished from the cap of Fig. 4 by the base charge 2| of greater height, due to its lower density, and the shell 20 with a bottom 28 of greater thickness and, accordingly, greater weight.

The fuse blasting cap of Fig. 4 includes a 0.22 caliber shell 21, which has an inside diameter of 0.56 cm., a bottom 0.023 cm. thick, and a wall 0.015 cm. thick, having a base charge 28 of high explosive pressed to a density of more than 1.45 g./cc. A priming charge 22, capsule 23, and wafer charge 25 are provided for the cap and consist of the some materials applied in the same manner as described for the cap depicted in Fig. 3.

This fuse blasting cap is distinguished from that of Fig. 3 and other standard commercial blasting caps by the base charge 12 of greater density, as indicated by its smaller height in the shell, and the shell 21 with a bottom 29 of reduced thickness and, accordingly, reduced weight.

The following examples illustrate the practical application of this invention:

EXAMPLEI Copper shells of 0.30 caliber (#6 commercial cap size) having an inside diameter of 0.77 cm. with a 0.015 cm. wall thickness and having various'bottom thicknesses were charged with pentaerythritol tetranitrate pressed to various densities. These shells were further charged with 0.4 gram of a loose priming mixture containing 75% diazodinitrophenol and 25% potassium chlorate. A conventional ignition assembly such as that described for Fig. 1 was provided for each shell, thus providing a complete electric blasting cap. The detonating power of these caps was tested as follows: A column of glycerin trinitrate was placed in a glass tube of 19 mm. inside diameter. The cap being tested was inserted through a rubber stopper until the base charge was entirely surrounded by the explosive. The cap was then initiated by a suitable source of electric current. The detonation rate was determined by using a high speed camera. Since both the high and the low rates are characteristic, approximately 7700 m./sec. for the high -rate and approximately 1700 m./sec. for the low rate, the data in the following tables merely show whether the rate of detonation was high (indicated by H) or low (indicated by L). The results of testing the caps of Example 1 are given in Table I:

Table I 4 EXAMPLE 2 the priming explosive mixture was added and pressed at the same pressure as the priming charge. The detonating power of these caps were tested as follows: A column of glycerin trinitrate was placed in a. glass tube of 19 mm. inside diameter. The cap being tested was inserted through a rubber stopper until the base charge was entirely surrounded by the explosive. cap was then initiated by a. suitable fuse and the detonation rate was determined by using a high speed camera. The results are given in Table II:

Table II PETN BASE CHARGESCOPPER SHELLS Thickness Density of Rate of Weight of Weight of of Bottom Charge, Detonacm Bottom, g. Charge, g. Mac. on

0. 010 0. 025 0. 25 l. 47 H 0. 010 0. 025 0. 25 1. 44 L 0. 015 0. 037 0. 25 l. 48 H 0. 015 0. 037 0. 25 1. 43 L 0. 023 0. 055 0. 10 1. 65 H 0.023 0. 055 0. 25 1. 52 H 0. 023 0. 055 0. 25 1.50 H 0. 035 0. 086 0.10 l. 65 H 0. 035. 0. 086 0. 25 1. 48 H 0. 085 0. 086 0. 25 l. 41 L 0. 043 0. l. 00 l. 69 L 0. 043 0. 105 0. 50 1. 59 L 0. 043 0.105 0. 25 l. 57 L 0. 0B 0. 105 0. 20 l. 40 L EXAMPLE 3 Cellulose acetate shells of 0.22 caliber having an inside diameter of 0.56 cm. with a 0.076 cm. wall thickness and having various bottom thicknesses were charged with 0.25 gram of pentaerythritol tetranitrate pressed to various densities. These shells were further charged with 0.3 gram of a loose priming mixture containing 75% diazodinitrophenol and 25% potassium chlorate. A conventional ignition assembly such as that described for Fig. 1 was provided for each shell, thus providing a complete electric blasting cap. The detonating power of these caps was determined by the same procedure as utilized for testing the caps of Example 1. The results are given in Table III:

The

Tlable III PETN BASE CHABGESCELLULOSE ACETATE SHELLS Thickness Density of Rate of Weight of Weight of 0! 32 Bottom, g. Charge, g. 27:5 g gg 1 0. 064 0. 033 0. 25 1. 47 H 2 0. 0. 083 0. 25 1. 57 H 3 0. 160 0. 083 0. 25 1. 40 L 4------ 0. zoo 0. 117 0. 25 l. 57 L With reference to the above tables, it will be seen that a high rate of detonation is obtained only by a combination of weight of shell bottom not greater than 0.10 gram and a base charge having a density greater than 1.45 g./cc. for pentaerythtritol tetranitrate. Further, it will be seen that a weight of charge as much as 1.00 gram pressed to a high density was ineffective to give a high rate of detonation when the weight of shell bottom was greater than 0.10 gram. On the other hand, a weight of charge as low as 0.10 gram pressed to a high density was effective to give a high rate of detonation when the weight of shell bottom was less than 0.10 gram. Still further it will be seen that identical caps as to weight of bottom less than 0.10 gram and weight of charge will not give a high rate of detonation unless the density is above a certain minimum for a given base charge.

In order to determine whether the strength or weakness of the shell bottom was important, the bottoms (0.043 cm. thick) were cut oil a number of standard #6 copper shells. The bottoms were then sealed to the shell tube with rubber cement,

producing a. very weak joint. The shells were filled with explosive as in Example 2 and the caps were tested as in Example 2. It was found that these caps were no more effective in producing a high rate of detonation than standard.

#6 blasting cap shells. In other tests on copper shells, copper was cut from the junction of shell bottom and shell wall until it was only 0.0l0'crn. thick at this junction. Even this weakening of the shell did not result in any improvement in initiating eificiency in tests similar to the above.

Shells without bottoms are not satisfactory due to obvious handling problems and the impossibility of waterproofing bottomless shells.

Approximately 25% of the available energy in a 0.25 gram base charge is used in givin rapid motion to the bottom and wall shell fragments in the initial explosive action. This corresponds to about all the energy actually available while the explosive gases are expanding to twice their volume. On the other hand, the energy needed to burst the shell itself it probably less than 1% of that available. It is hypothesized that this is why the weight of the shell bottom adjacent to the base explosive is of importance while the weakness or the thinness of the shell at these points is relatively unimportant.

From the examples, it is seen that the effectiveness of the blasting caps in accordance with this invention are governed by several factors, namely, the weight of the shell bottom, the density of the base charge, and the particular base charge used. These are each interdependent. However, it is possible to fully define an operable blasting cap in accordance with this invention by specifying only the weight of the shell bottom and the density of the base charge. The weight of base charge ordinarily employed in commercial caps does not vary greatly and even if varied greatly as illustrated herein does not materially affect the rate of detonation. Ordinarily, the weight of base charge utilized in fuse type caps is from about 0.15 to about 0.25 gram for #6, from about 0.5 to about 0.6 gram for #8, from about 0.9 to about 1.0 gram for Army Engineer cap, and for electric type caps from about 0.25 to about 0.40 gram for #6, from about 0.45 to about 0.55 gram for #8, from about 0.9 to about 1.0 gram for Army Engineer cap. The relative detonating power of most common explosives is well known, hence the ranges of weight and charge density for various base charges may be determined from those of pentaerythritol tetranitrate by correction using a factor which represents such relative detonating power compared to pentaerythritol tetranitrate.

Thus, the density of the explo -g d h;

such that it gives approximately the same strength' (explosive energy per unit volume) as pentaerythritol tetranitr'ate at a density 011.45

g./cc. For example, cyclonite, nitromannite,

mannitol hexanitrate, nitrolactos e; and nitrosucrose are"substantiallyequivalent to penta erythritol tetranitrate when pressed to the den: sity indicated. The pressing "of various 'explosives'to obtain a density that'gives auesirea bulk' strengthis well understood in the art and is not further elaborated here.

' Therefore, in accordance with the present'inthe shell bottom should be v The weight .should be not more than about 0.10 gram, preferably from about 0.02 to about 0.09 gram. The base'charge utilized maybe secondary,explosives, such as" vention, the weight of as low as practical.

pentaerythritol tetranitrate, cyclonite, Y nitro,-'

nitrosucrose, and the like.

as pentaerythritol .tetranitratef at the same den sity. Preferably, shouldhave .a density of from about 1 .50 to about 1.70g./cc.

Various priming explosives such as lead azide, silver azide, mercury fulminate, mixturesofsul-r ,1

fur nitride with potassium chlorate or lead azide, etc., in addition to diazodinitrophenol or the diazodinitrophenol potassium chlorate mixture shown in the examples, may be used. Materials used in the shells of this invention may include copper, aluminum, zinc, steel and other metals, cellulose acetate, ethyl cellulose, phenol-formaldehyde resins, and other plastics. The plugs for electric blasting caps may be formed of sulfur, rubber or plastic materials such as phenol-formaldehyde resins, polystyrene, ethyl cellulose, porcelain, etc. If desired, the plugs may be sealed in the caps using a sealing or waterproofing compound such as sulfur, asphalt, wax, or other material. The lead wires may be of any electrical conductive material and may be insulated us ng enamel, cotton or plastic materials. The bridge wire connecting the terminal ends of the leg wires may be electrically-resistant wire composed of noble or base metals or alloys thereof, such as platinum, Nichrome, copper-nickel, etc.

Where in the specification and appended claims the term "bottom is used, the entire base is meant, in other words, the outside diameter of the blasting cap shell at its base is equivalent to the diameter of the bottom, and the weight is determined from the area thereof times the thickness of the material forming the base times the weight of such material in grams.

The improved blasting initiators according to this invention have been found particularly useful for. insuring the detonating of blasting gelatin of extremely high density at its maximum rate. It thus provides for propagation of the explosion under the severe conditions of use met in firing under high liquid heads in oil well shooting and geophysical prospecting.

these secondary explosives. 1

What we claim and desire to protect by Letters Patent is:

1. In a blasting initiator, the combination of a shell having a bottom whose weight is not more than 0.10 gram, and a base charge of a secondary explosive having an explosive energy per unit volume equivalent to pentaerythritol tetranitrate at a density of 1.45 g./cc.

2. In a blasting initiator, the combination of a shell having a bottom whose weight is from 0.02 to 0.09 gram, and a base charge of a secondary explosive having an explosive energy per unit volume equivalent to pentaerythritol tetranitrate at a density of 1.45 g./cc.

3. In a blasting initiator, the combination of a shell having a bottom whose weight is from 0.02 to 0.09 gram, and a base charge of pentaerythritol tetranitrate having a density of more than 1.45 g./cc.,

4. In a blasting initiator, the combination of a shell having a bottom whose weight is from 0.02 to 0.09 gram, and a base charge of cyclonite having a density of more than 1.45 g./cc.

5. In a blasting initiator, the combination of a shell having a bottom whose weight is from 0.02 to 0.09 gram, and a base charge of nitrolactose having a density of more than 1.45 g./cc.

6. In a blasting initiator, the combination of a shell having a bottom whose weight is from 0.02 to 0.09 gram, and a base charge of pentaerythritol tetranitrate having a density from 1.50'to 1.70 g./cc.

7. In a blasting initiator, the combination of a shell having a bottom whose weight is from 0.02 to 0.09 gram, and a base charge of cyclo- 3 nite having a density from 1.50 to 1.70 g./cc.

8. In a blasting initiator, the combination of a shell having a bottom whose weight is from 0.02 to 0.09 gram, and a base charge of nitrolactose having a density from 1.50 to 1.70 g./cc.

9. In a #6 commercial blasting cap, the combination of a shell having a bottom whose weight is not more than 0.10 gram, and a base charge of a secondary explosive having an explosive energy per unit volume equivalent to pentaerythritol tetranitrate at a density of 1.45 g./cc.

10. In a #8 commercial blasting cap, the combination of a shell having a bottom whose weight is not more than 0.10 gram, and a base charge of a*secondary explosive having an explosive energy per unit volume equivalent to pentaerythritol tetranitrate at a density of 1.45 g./cc.

ROBERT W. CAIRNS. ROBERT W. LAWRENCE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STA'I'ES'PA'I'ENTS Number Name Date 323,524 Paulus Aug. 4, 1885 1,743,739 Turek Jan. 14, 1930 2,363,254 Lawrence Nov. 21, 1944 FOREIGN PATENTS Number Country Date 145,791 Great Britain Mar. 17, 1921 172,914 Great Britain Dec. 22, 1921

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