US2465467A

US2465467A - Electric blasting cap

Info

Publication number: US2465467A
Application number: US675865A
Authority: US
Inventors: John B Morton
Original assignee: Hercules Powder Co
Current assignee: Hercules Powder Co
Priority date: 1946-06-11
Filing date: 1946-06-11
Publication date: 1949-03-29
Anticipated expiration: 1966-03-29

Description

March 29, 1949. J. B. MORTON 2,455,467

' ELECTRIC BLASTING CAP Filed June 11, 1946 FIG! FIG-2 JOHN B. MORTON INVENTOR.

Patented Mar. 29, 1949 UNITE.

ELECTRIC BLASTING CAP John B. Morton, Hopewell, Va., assignor to Hercules Powder Company, Wilmington, DeL, a

corporation of Delaware Claims.

This invention relates to an improved electric blasting cap and, more particularly, to a safetytype electric blasting cap.

It is well known that an electric blasting cap of the safety type may have a base charge comprising a secondary explosive and a priming charge superimposed thereon comprising an explosive of the so-called safety type, such as the nitrated saccharides, nitromannite and nitrolactose. These priming charges are ignited by means of a deflagratable composition or by means of a semi-explosive burst from a matchhead-type assembly superimposed thereon. These caps are known to be less sensitive toward detonation upon the application of strong external heat than similar blasting caps having a primary charge comprising such explosives as mercury fulminate, diazodinitrophenol, lead azide, etc. Safety-type electric blasting caps have several disadvantages, one being that the ignition charge necessary to set off the safety-type primary charge must have unusually strong ignition characteristics, another being that the priming charge requires an added confinement comprising a reinforcing capsule or inner shell in order to be fully effective, and still another is that, in most instances, relatively greater amounts of the safetytype priming charge must be used in order to efiect proper detonation of the base charge.

Now in accordance with the present invention it has been discovered that when a high heatstable primary charge of lead azide is positioned centrally and in the upper portion of a heatunstable priming or explosive charge, such as nitrolactose which is in turn superimposed upon a base charge, the disadvantages found with prior art safety-type electric blasting caps are eliminated.

It is an object of this invention to provide an electric blasting cap which may be heated externally to a high temperature without causing detonation.

Another object of this invention is to provide a safety-type electric blasting cap that is simple in construction, economical to manufacture and reliable.

Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.

Preferred embodiments of this invention have been chosen for the purpose of illustration and description and are shown in the accompanying drawing, forming a part of the specification wherein:

Fig. 1 is an elevational view in partial section of the electric blasting cap in the course of construction; and

Fig. 2 is an elevational view in partial section of the completed cap.

An improved electric blasting cap was manufactured in accordance with the present invention by placing a base charge 1 comprising 0.20 gram of tetryl into a shell 2 of 0.30-inch inside diameter, and pressed with a flat pin under a pressure of 4000 pounds per square inch. A heat-unstable priming charge 3, consisting of 0.12 gram of nitrolactose, was superimposed on top of the tetryl base charge and pressed with a step-cut pin 4 under a pressure of 200 pounds per square inch. The use of the step-cut pin, shown in Fig. 1 being withdrawn from the shell 2, forms a cavity 5 centrally located in the priming charge 3 and located in the upper portion thereof. The dimensions of the cavity 5 may be changed in such a way as to vary the depth to which the cavity extends into the priming charge 3, depending upon the length of the column of priming charge being used. The cavity is positioned as near the center of the priming charge as is possible so as to provide the maximum amount of insulation and cushioning by that portion of the priming charge 3 indicated by the numerals 6 for a given amount of heat-stable primary charge.

A heat-stable primary charge 1 comprising 0.02 gram of lead azide is charged into the minimum volume cavity 5 after which the ignition charge and the priming charge are pressed simultaneously with a flat pin under a pressure of 2000 pounds per square inch. A bridge assembly, comprising a plug 8 having a cavity 9 at the lower end thereof and a pair of spaced leg wires I0 extending therethrough and terminating adjacent the cavity 9 in a pair of bridge wire supports connected by a bridge wire H, is moved into the open end of the shell 2. The cavity 9 was previously filled with an ignition charge l2 consisting of 19.0% diazodinitrophenol, 65.8% potassium chlorate, 13.2% charcoal, and 2.0% nitrostarch. Thus, the ignition charge is placed in juxtaposition to the primary charge as shown in Fig. 2. The shell was then closed against mois ture with a waterproofing compound 13 and a sealing compound M.

Electric blasting caps prepared in accordance with the above example give an excellent lead plate test in accordance with the standards set up by the U. S. Bureau of Mines.

Electric blasting caps prepared in accordance with the above example were tested to determine their sensitivity to ignition from extreme heat by placing the caps in a molten metal bath at various temperatures. The results of these tests are given in the table, column 1.

More electric blasting caps were made similar to the above example, except that the heat-stable primary charge, lead azide, was positioned in a layer over the entire top surface of the priming charge which consisted of 0.22 gram of nitrolactose. Ihese caps were also subjected to the same molten metal bath test and the results are given in column 2 of the table. Five caps of each type were tested at the temperature given in the table.

Temperature I Tune for Dsecomposition, AV

Sec.

' Time for Decomposition.

- Ulla momma-cc: town-named:

Total partia 2; column two, .5.

1 Partial shots.

2 Cap detonated completely.

shots, column '1, 2; column two, 6.

It is noted that the tendency toward detonation with increased external heat is less pronounced with caps in which the lead azide is centrally positioned on the top side of the priming charge than with caps in which the lead azide is positioned over the entire top surface of the priming charge. The charges in which the lead .azide was centrally positioned were decomposed. at a slower rate than those in which the lead azide was posi tioned over the entire top of the surface.

Tests of these two types of caps for purposes of determining the minimum priming charge necessary to detonate a base charge of tetryl indicate that, for a given amount of a priming charge of nitrolactose, a lesser Weight of primary charge of lead azide is necesary when the lead azide is carried in a minimum volume cavity positioned centrally and on the top side of the priming charge than when the lead azide is spread in the form of a wafer over the entire top side surface of the priming charge.

Suitable safety-type priming charges operable in accordance with this invention are solid nitrated saccharides, such as, for example, nitrolactose, nitromannite, nitrosucrose, nitroinositol, etc.

Suitable base charges are any of the base charges commonly used in electric blasting caps such as, for example, tetryl, trinitrotoluene, nitrost'arch, PETN, etc. The preferred combina tion of charges is a combination of charges wherein the base charge is tetryl, the priming charge is nitrolactose, and the primary charge is lead azide.

In U. S. Patent 1,928,207 to Large, it is shown that 0.05 gram of nitrolactose is necessary to detonate a tetryl base charge The caps prepared in accordance with this invention use 42% less nitrolactose when combined with lead aside in the manner disclosed to effect the same desirable detonation of the base charge of tetryl. In accordance with this invention, the minimum priming charge necessary to detonate the tetryl will vary in accordance with the proportional Total complete shots, column one,

In all other cases, cans miffed without vio ence,

electric blasting caps where primary charges of lead azide, diazodinitrophenol, mercury fulminate, etc., are used. In ccntradistinction to the strong ignition charges necessary in order to properly ignite a safety-type electric blasting cap, the present invention provides for the use of the conventional and well-known types of ignition compositions in juxtaposition to the primary charge.

From the foregoing description, it is apparent that the objects of this invention have been accomplished by providing a safety-type electric blasting cap comprising a primary charge of lead azide positioned in minimum volume cavity held in insulated and cushioned relationship with the shell of the detonator on the top side .of a heatunstable priming ch rge, whereby a minimum amount of priming charge is necessary in order to properly detonate the base charge.

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

1. An electric blasting cap having in combination a base charge, a heat-unstable priming charge superimposed on the base charge, a primary charge of lead azide disposed centrally in the upper portion of the priming charge, and an ignition charge in juxtaposition to the primary charge.

2. An electric blasting cap having in combination a base charge, a priming charge or a solid nitrated saocharide superimposed on the base charge, a primary charge of lead azide disposed centrally in the upper portion of the priming charge, and an ignition charge in juxtaposition to the primary charge.

3. An electric blasting cap having in combination a base charge, a priming charge of nitrolacetose superimposed on the base charge, a primary charge of lead azide disposed centrally in the upper portion of the priming charge, and an ignition charge in juxtaposition to the primar charge.

An electric blasting cap having in combination a base charge, a priming charge of ni- 5 tromannite superimposed on the base charge, a primary charge of lead azide disposed centrally in the upper portion of the priming charge, and an ignition charge in juxtaposition to the primary charge.

5. An electric blasting cap having in combination a base charge, a priming charge of nitrosucrose superimposed on the base charge, a primary charge of lead azide disposed centrally in the upper portion of the priming charge, and an ignition charge in juxtaposition to the primary charge.

6. An electric blasting cap having in combination a heat-unstable explosive charge, a charge of lead azide disposed centrally in the upper portion of the heat-unstable explosive charge, and an ignition charge in juxtaposition to the charge of lead azide.

7. An electric blasting cap having in combination a heat-unstable explosive charge of a solid nitrated saccharide, a charge of lead azide disposed centrally in the upper portion of the heatunstable explosive charge, and an ignition charge in juxtaposition to the charge of lead azide.

8. An electric blasting cap having in combination a heat-unstable explosive charge of nitrolactose, a charge of lead azide disposed cen- 6? trally in the upper portion of the heat-unstable explosive charge, and an ignition charge in juxtaposition to the charge of lead azide.

9. An electric blasting cap having in combination a heat-unstable explosive charge of nitromannite, a charge of lead azide disposed centrally in the upper portion of the heat unstable explosive charge, and an ignition charge in juxtaposition to the charge of lead azide.

10. An electric blasting cap having in combination a heat-unstable explosive charge of nitrosucrose, a charge of lead azide disposed centrally in the upper portion of the heat-unstable explosive charge, and an ignition charge in juxtaposition to the charge of lead azide.

JOHN B. MORTON.

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

UNITED STATES PATENTS Number Name Date 1,928,208 Large Sept. 26, 1933 2,086,532 Burrows July 13, 1937 2,350,172 Lawrence May 30, 1944 2,402,235 Burrows June 18, 1946 Certificate of Correction Patent No. 2,465,467. March 29, 1949.

JOHN B. MORTON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 67, for 0.05 gram read 0.50 gram; column 4, lines 68 and 69, for nitrolacetose read nitrolactose; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofilce.

Signed and sealed this 30th day of August, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction Patent No. 2,465,467. March 29, 1949.

Column 3, line 67, for 0.05 gram read 0.50 gram; column 4, lines 68 and 69, for nitrolacetose read nitrolactose;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 30th day of August, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.