US2400103A - Detonator or blasting cap - Google Patents

Description

May 14, 1946. w.V M. COBB DETONATOR ORIBLASTIG CAP Fired April les, 1'941 mvENToR William M- Cubi BY Patented May 14, 1946 DETONATOR B BLASTING GAP William M. Cobb, United States Army,

' Daytona Beach, Fla.

Application April 16, 1941, Serial No. 388,761

2 Claims. (Gl. 1022-28) (oi-amai under umso@ or Marca s, iets, as amended April 30, i928; 370 0. G. '157) The invention describedherein may be manu factured and used by or iorthe Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to means for bringing about the detonation of relatively insensitive' characteristics Vfor use in detonators may be divided roughly into three groups:

First, compounds such as lead azide, fulminate of mercury, diazo-dinitrophenol and nitromannitol used to prime or initiate other explosives. Explosives in this group furnish the initiating ingredient of most commercial detonators and are sometimes called fulminating or cap compounds. Such compositions detonate on ignition and are extremely sensitive to blows and friction.

Second, compounds such as tetryl or P. E. T. N. (pentaerythritol tetran'itrate) which are usually used as base charges in detonatorsand as booster charges for the priming of insensitive compounds and are sometimes known as booster compounds. Explosives of this class are moderately sensitive to blows, are fairly difcult to ignite, and will not usually detonate when ignition is produced by ordinary means. Usually they must be initiated by compounds of the rst group.

Third, compounds such as trinitrotoluene, picric acid. and ammonium picrate, which are widely used as military demolition explosives and shellA fillers. Compounds of this class are quite insensitive to shock, are dimcult to ignite, and will usually burn without detonation when ignited in any normal manner. Conventionally they are exploded by a booster, which is initiated by a blasting cap or detonator.

Conventional blasting caps and detonators use one of the dangerously sensitive compositions of the iirst group as the initiating ingredient of their explosive mixture. Detonators are also known in which base charges from the second group or the more sensitive of those oi the third group have been used in conjunction with initiators from the L nist group. However it is not thought that a successful blasting cap has heretofore been produced using a substance or a combination of substances all of the same order of sensitivity as those of the second or third groups.

It is an object of this invention to providev means of exploding.insensitivefcompounds without requiring the u`se of dangerously sensitive initiators.

It is a further object of this invention to provide a novel form of detonator.

An ideal blasting cap would be one which could not ordinarily be exploded by accidental means. The initiating element should be very sensitive to heat 'or flame such as that produced by the spit of a safety fuse or from the fusing bridge wire or match head of conventional electrical fuse f heads. At the same time it should be relatively insensitive to blows, crushing, shock, sudden penetration, or probing. Such an ideal detonator could be approximated if an initiating element could be obtained which had the heat and flame sensitiveness of the fulminating compounds and a sensitivity to shock comparable to that of shell lling explosives.

Although the explosives of the second and third groups will not usually detonate yfrom heat or re as ordinarily applied, the basic principle of this invention lies in my discovery that these explosives will detonate consistently and completely if intense heat is applied to them over an extremely short interval of time. To supply this intense heat I use substances which are not ordinarily considered explosive, or at least are no more sensitive. than the explosives of the second or third groups. Such substances may be thermite, magnesium powder and barium peroxide. or other metallic powder and a suitable oxidizing agent.

'Rie specic nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred em- As an explosive or base charge 2 I may use any one of the explosive compounds of the seoond or third group, for example, tetiivl, P. E. 17. N.. 'l'. N. T., piene d, or t infranti picrate. En

' mite or any suitable metallic powder and an oxidizing agent. Such substances are substantially non-explosive but combine to produce extreme temperatures in a very short interval of time. Some of these heat producing agents may be ignited reliably by conventional means, but where I use those which cannot` be so ignited the use of an igniter charge I may be required. Such substances should be easily inflamed but should be chosen from among materials which will not increase the impact or abrasion sensitivity above the sensitiveness imparted toit by the base charge either by virtue of the inherent characteristics of the compound chosen or by virtue of the manner in which the compound is charged into the cap. For example nitrocellulose powder in granular form or in combination with suitable binding agents, collo'ided nitrocellulose, or mixtures such as that of selenium, barium peroxide, and nitrostarch may beemployed as igniters.

Specifically Figure 1 represents a blasting cap for use with safety fuse in which I is a conventional shell of metal or othe;` material and 2 the base charge of T. N. T. or the like. A sultable heat`producing charge 3 is placed directly over the base charge and in contact with it. Retaining the heating charge in place and serving to ignite it is a wafer -4' of nitrocellulose, pressed in plastic form into the cap shell.

In some cases it is desirableto insulate the container from the heating charge to prevent the decomposition of the container before detonation of the base charge has taken place. Figure 2 illustrates one such expedient wherein vention to an electric detonator of the cavity plug type. In this modication the lead wires 9, having a fusible bridge wire II, are sealed into a ceramic plug I2. Ihis plug is so formed as to include a cavity I3 in which the igniter charge 4 and heating charge 3 maybe loaded with consequent insulation of the shell wall from 'the heat generated. Sealing may be accomplished in vany well-known manner, as by use of the sealing compound I4 and sulphur plug Il.

Obviously a match head or any other electric ignition device may be employed in the practice of the invention. It is also contemplated that the heating charge or a part thereof may be the shell I is provided with an inner shell 5 of inert insulating material or is intern'ally coated with a layer of ceramic or insulating material. The base charge 2 and heating charge 3 are loaded as in Figure 1. heating charge is of the type Which can be ignited directly by the spit of a safety fuse and may be retained in place by the application of' nitrocellulose lacquer 6 or the like to the surface or by a perforated metal cap or thimble.

A similar expedient is illustrated in Figure 3. In this modification a thimble or cup 'I of ceramic or other insulating material is loaded with igniting charge 4 and heating charge 3 and pressed into the shell I being retained therein in contact with the base charge 2 by frictional engagement with the wall of the shell. The

perforation 8 exposes the igniter composition 4 A In this modification the mixed with the base charge.

In the modication of the invention shown in Fig. 6 a substantially spherical detonator is formed b y coating a bridge wire II with an ignlting charge 4 and surrounding this with the heating charge I. The base charge is thenv molded around the assembly and the assembly placed in a container or coated with a suitable protective substance I6. materials may be used in molding the charges into the desired shapes.

Figure 'I shows a modification somewhat similar to that of Figure 6. In this modification-the lead wires 9 are molded into a supporting plug lI'I and provided in the usual manner with a bridge wire II. The igniting composition 4 is molded about the bridge wire and the heatin charge 3 is formed thereagainst. Surrounding the heating charge and plug is the base charge 2. The Whole may be surrounded with a protective coating I6 as in Figure 6. A detonator of the form shown in Figures 6 or 'l in addition -to the obvious 'advantage of its simplicity of construction will have the advantage that the detonation wave will be propagated uniformly in all directions rather than exhibitl ing the sharply directional eiect ofthe convenv 1. In a substantially spherical electric det` onator having an electric ignition device, an initiator molded on and concentric with said ignition device, a charge of detonating explosive formed about said initiator and concentric therewith and a protective coating enclosing the detonator.

2. In a substantially spherical electric detonator,v a hemispherical plug of inert material supporting an electric ignition device, a hemispherical initiator charge formed against said plug, a detonating explosive formed about and concentric with said charge and plug and a protective coating enclosing the detonator.

' wnmAM M. COBB.

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