US2678603A - Delayed action explosive munition - Google Patents

Description

y 18, 1954 L. M. PRINCE, JR., ETAL 2,678,603

DELAYED ACTION EXPLOSIVE MUNITION Filed Aug. 15, 1944 2 Sheets-Sheet 1 LEON N. PRINCE) L/R. Log/1s G, W/LLKE y 8, 1954 M. PRINCE, JR., ETAL 2,678,603

DELAYED ACTION EXPLOSIVE MUNITION Filed Aug. 15, 1944 2 Sheets-Sheet? Louis 6, W/LL E- 1 501v PRINCE; L/R.

Patented May 18, 1954 DELAYED ACTION EXPLOSIVE MUNITION Leon M. Prince, Jr., New York, N. Y., and Louis G. Willke, United States Army, Edgewood Arsenal, Md., assignors to the United States of America as represented by the Secretary of War Application August 15, 1944, Serial No. 549,602

(Granted under Title 35, U. S. Code (1.952),

sec. 266) 3 Claims.

The invention described herein may be manufactured and used by or for the Government, for governmental purposes without the payment to us of any royalty thereon.

This invention relates to munitions and particularly to bombs having a delayed action burster or fragmentation unit.

Munitions with which this invention is particularly concerned are incendiary aircraft bombs of the intensive type, e. g., thermit filled bombs for causing disruption of military importance. This type of bomb is intended to cause a conflagration by a concentrated high temperature burning as a unit until consumed.

Explosive incendiary bombs were developed to discourage fire fighting action. At first, explosive incendiaries were made by incorporating a small burster charge of black powder into the noses of the bombs to have an explosion occur when the incendiary charges burned down. These bombs failed to give more than a small explosion, just a puff, and resulted only in harass ing or frightening fire fighters. Later, attempts were made to use high explosives as burster charges, but difficulties were encountered in obtaining satisfactory tactical results, since without proper delay action the high explosive, in functioning too soon after impact, scatters the incendiary filling before incendiary action occurs, reveals the location of the incendiaries, and fails to act as a delayed restraint against fire fighting efforts. Similarly, if the explosion is consistently delayed to the end of the burning of the incendiary, the surprise factor is reduced. A common difficulty in designing explosive incendiaries has been in using high explosive charge in standardized incendiary bombs with positive but variable delayed detonation after impact on target surfaces of various degrees of hardness, e. g., on the ground or on concrete.

To obtain improved explosive incendiary bombs which avoid previous difficulties, this invention has amongother objects those of providing incendiary bombs with high explosive bursters without necessitating any substantial changes in the appearance, weight or ballistics of the bombs. It is concerned with providing the bombs with a fragmentation burster having a high explosive charge of lethal proportions in combination with a detonating means which is portioning and constructing the burster unit in such a manner that the high explosive is satisfactorily protected against premature ignition or decomposition by high temperature heat generated in the bomb before such heat effects the functioning of the detonator so that the explosion is made to occur through the functioning of the detonator. It has the additional object of providing an explosive bomb constructed so as not to interfere with the assembling, loading, handling, clustering, aiming, and functioning of the bombs.

The foregoing and further objects of the invention will be understood from the following detailed description in conjunction with the accompanying drawings and claims. I

Without being limited thereto, the invention is described with reference to several practical embodiments illustrated in the accompanying drawing, in which;

Figure l is a longitudinal sectional view of one type of incendiary bomb with a delayed action explosive unit.

Fig. 2 is an elevational view of the tail end of the bomb on a larger scale;

Fig. 3 is a cross sectional view taken on line 33 of Fig. l on a larger scale;

Fig. 4 is an elevational view of the nose end of the bomb shown in Fig. 1 on a larger scale;

Fig. 5 is a longitudinal sectional view of a nose end portion of another type of explosive incendiary bomb;

Fig. 6 is a longitudinal sectional view of a nose end portion of a 3rd type of an explosive incendiary bomb;

Fig. 7 is a longitudinal sectional view of a 4th type of delayed action explosive incendiary bomb;

Fig. 8 is a cross-sectional view of a truncated cone delay element which may be alternately used in place of a disc or other shape of delay element interposed between a thermit filling and the top end of a live detonator in a burster.

' It will be understood from the following dcscription that this invention is concerned with the utilization of various shapes, sizes and kinds of metal delay elements for influencing the time required for transmission of heat from a burning incendiary agent in a bomb in suiiicient intensity to activate a suitable heat-sensitive detonator and, in turn, a high explosive burster charge in predetermined time ranges.

change in construction and appearance;

(2) Positive functioning of the explosive charge under all climatic conditions and with different kinds of impact;

(3) Variable delay in explosion from a few secondsto about 10 minutes after impact; and

(4) Capability of producing casualties and damage over a substantial area.

In general, the assembly of the burster, detonator, and delay elements is'torbexlocated munition where heat can be conducted at a suitable rate from a burning chargein the inunition through the delay element to the detonator. With explosive incendiary bombs-of .tlie thermit-type, the practice is to place this assembly at the nose end of the bombs. "It iszdesirable to fill the bomb casing with a thermit-type incendiary agent, commonly known as thermit, pressed in from the top of the casing'andito irn sert the burster and detonator from the nose and following the thermit loading.

Referring particularly to Fig. 'l of the draw- .ings,.an explosive, incendiary bomb formingone embodiment of this invention comprises a body .5, made of cast magnesium or magnesium alloy, hexagonally shaped, .and'filled with a thermit chargefi. A 'cast iron or steel nose I, mortised intothe nose (lower) end of body 5 serves as a .bursteroase and also serves to make the-bomb plummet with suitable'velooity in an uprightpo- -sition-when dropped from aircraft.

A first fire charge 8 is loaded through the tail (upper) end of body'5. The first fire charge 8 is pressed into a truncated conicalprojection 9 .tofill 'a-corresponding-shaped recess at the-end of thermit charge :6. A small depression In is .formed :in-the center of the exposed'surface of :the first firecharge 8 toaidignitionthereof.

The first fire charge 8 is formulated to be readily ignited by a standard'type of primer cap 11, spaced therefrom and held in a primer cap :holder [2 of steel or "aluminum which seats agaigist the shoulder !3 formed in,the:boclycasting;

The primer cap is adapted-to be fired by afiring pin I 4 disposed ina-firingpin holder 15. The firing pin 14 may be-made of aluminum or steel :and includes "a weight portion H5. The firing piniweight portion [6 has a'projection l8 of re- :duced diameter adapted to set within a turnedin flange 19 of the-firing pin'holder'l5. The'firing pin I4 is normally retained :in the position shown'by means TOfELSClGW .2 and a cross-shaped bracememberi l. The cross-shaped member'z'l is made of brass or other deformablematerials, :so that 'upon a predetermined impact of the "bombythe crossed strips'of this-member willyfold up and permit the firing pin I4 to slide toward the primer cap l l.

The -firing pin "assembly is held in place by screws-22. A safety pin .23 is provided with "a :spring'24 fitting therearound to tend to force'the safety :pin 23 in a-zwithdrawn or armed position. This type of bomb'is adapted to beloadedinto :clusterssothat anumber of bombs, for example,

:50 or more, 'fit against one another to press the 7 safety pins 23, into-an unarmedposition, wherein the safetypins 23-pushed under the firing pins 44 prevent accidental movement of the firing pins toward the-primer caps l I.

Lhexagonally shaped tail 215 is attached to the tail (upper) end of the body and is held in place Iby'the screws 22. The tail 25 stabilizes the downward flight of the bomb. Vent .holes .noropenings 2S are'formedin:thebodynasting 5 between the primer cap holder .12 :and theifirst Crv from the burning charge.

plugs 2'1.

"tratediin Fig.;1,'which has been standardized, has

fire charge 8. The outer ends of the holes 26 are counterbored so as to receive plugs or stoppers 2?, which may be made of rubber, fibre board or metal cups, which are blown out by gases evolved Inxorder .to make the bomb waterproof, the outer surfaces of the plugs .2! are coated with a waterproof cement or lacquer, preferably, the inner surfaces of the holes 26 are-also lacquered before the insertion of the One practical form of the bomb illusatotal weight of about four lbs. and an overall length .of about 21% inches. The magnesium alloy casting 5 has a weight of about 1 lb. 4 oz.,

ra lengthof: aboutll inches and for the greater part of its length, has a thickness of about 1%". A suitable thermit mixture for forming the .corexihargefi :has the following composition in percentage by weight:

Per cent Aluminum,. granular .15.? to 16.3 .Iron oxide .scaleor .iron ore 43.5 to 144:5 Aluminum, grained -8.8-to .92 Barium nitrate 28.6 to 29.4 Sulfur 1.9 ,to 2.1

The weight of the chargefiin a bomb weighingabout 4 lbs. is about 265 grams. The therlnate charge 6 is preferablyloadedinto the body 5 in four approximately equal increments .under a dead loadpressure of 6,000 to 7,000 lbs. using a ram shaped to formatruncated conica1 \depression corresponding to the shape of .the truncated projection 9 of thefirst firecharge-fl.

The firstfire charge ,8 for a-ZGSgram-thermit charge should weigh about :19 to.21 grams and may be pressed on top the charge v6 underadead load'of 6000 to 7000 lbs. 'using'a .ram shaped .to form arounded depression ID. A suitable first fire charge composition comprises 25% mag- .nesiumrpowdenand barium chromate.

Next, referring more particularly-to the nose end assembly shown in Fig. 1, the steel or iron nose cup 1 is mortised into the nose end of the body ;5, and has integral parts/28 and 29 of .reduced-cross-section :at'its inner end. The nose cup 1 base relatively large -.ho1low chamber 30 for containing a suitablelhighexplosive. .At its frontend-opening, the nose cup .l-is threadedto receive'a closure plug alprovided'with-drill holes 32 for receivingaspanner wrench in tightening the pluginto position. A fibrous or felt pad .3-3

.isplaced adjacent the plug 3| in closing thaexplosion chamber after it has been loaded with high explosive and witha detonator .tube 13-4 inserted into a central bore 35 through the-reduced cross section extension :29. -A metal or plastic disc =36 may be placed in the explosion chamber "38 ;-at the base of :the detonator tube 34 .to offer resistance :to the movement -.of the detonator tube when the bomb issubjected to impact. -A delay element disc .3-1 .-is interposed at .theendof the .nose cupextension .29 between the thermate'filling'fi andtheopen inner end of the-,detonator tube 134. The materiaLshapeand size of this disc 3'l is.-a factor in determiningrthe delay period for transmission :of heat from the burningpart of the bomb to the detonator ior initiating detonation of the high explosion in chamber .30.

Ina bomb having substantially the construction illustrated in Fig. 1 asteel disc approximately 0.960" in diameter and 0.0.6 sthick .may

be dropped .into the body from .the tail .end prior to loading .of :the body with nthermit .and :first dire charge. Following the loading with the nose cup 1 in position, the detonator 34 may then be inserted through the open end with plug 3| removed until the open end of the detonator tube contacts with the underside of the steel disc 31.

With a suitable detonator tube thus in place, and a suitable high explosive, such as tetranitromethylaniline, filling the explosion chamber 30, the nose cup is closed by screwing in the threaded plug 3i.

In a bombing operation, when a cluster of the bombs is released from aircraft, bands which hold the bombs in the clusters are broken so as to permit the individual bombs to fall separately in a pattern toward the target. As the bombs separate from one another, the safety pins 23 which were pressed inwardly in the cluster are released to the position shown in Fig. 3 so as to arm the bombs. Upon impact of the nose end of a bomb, the inertia movement of the weight portion !8 of the firing pin !4 acts to deform the retaining cross shaped member 2i so as to allow the firing pin I4 to strike the primer cap I I. The primer cap II flashes into the depression III of the first fire charge 8, thereby igniting this charge. The gases produced by the combustion of the ignited first fire charge 8 develop sufficient pressure to blow out the vent hole plug 21, thus leaving a passage for escape of combustion gases evolved by the burnin incendiary charge so as to prevent explosion of the incendiary unit before the delayed explosive unit functions.

The first fire charge 8 burns at a temperature sufficiently high to ignite the thermate charge 6, which in turn ignites the adjacent body 5 of the bomb where an intense incendiary action is obtained. A portion of the heat tends to flow through the bomb body toward the nose end where the burster unit is located. The intensity of the heat which reaches the burster unit depends on the proximity of the burning portion of the incendiary charge 6, the burning advancing gradually toward the nose end of the bomb.

When bombs assembled as described were tested by static firing, delays from about 1 minute up to 12 minutes and longer, from the instant the thermate began to burn until the explosion, were obtained. On dropping these bombs from a plane at 1,000 feet and 4,300 feet onto concrete, the average delays were even longer on account of the tendency of the detonator to be set back a short distance from the steel disc 31 and, accordingly, the variable delay range was somewhat increased but Without misfires of the explosive,

Statically fired, the average delay was about 1 minute 45 seconds, and on dropping onto concrete the average delay was approximately 2 minutes 30 seconds measured from the instant of impact till the explosion. A rough approximation of the percentages of explosions in varied delay ranges were: 10% in l to 2 minutes; 50% in 2 to 3 minutes; in 3 to 4 minutes; 10% in i to 5 minutes; and 5% in 5 to 12 minutes.

Thus, it was determined that a very satisfactory variation in delay is obtainable with substantially no failures in explosion.

Investigation shows that a number of readily available high explosives could be used satisfactorily in the nose cup. Tetryl was generally satisfactory. Trinitrotoluene, particularly in pellet form, Tetrytol and Hexalite gave good results even though they were at first suspected of being too sensitive to thermal decomposition for such a use and the chamber may be charged with til O the jacket 38.

one or more of these explosives instead of tetryl. It is thus indicated that construction with suitable delay elements and a proper detonator serves to preserve the high explosive until the detonation action is initiated in the detonator through delayed heat transmission thereto, even after the incendiary agent in the bomb has been consumed.

The detonator tube 34, in general, comprises a slow burning train of non-explosive powder leading to a primer and a booster explosive enclosed in a flexible metallic jacket. A detonator of this type has an aluminum or copper gildingmetal jacket 38, 0.274 inch 0. D., open at the top where the delay train is exposed and closed at the bottom. The delay train powder 39 com- ;prising preferably a readily reducible metal oxide, and a readily oxidizable element is compressed in a lead tubing 40 staked tightly within At the open end of the jacket 38, the delay powder is extruded flush with the-top of the jacket. A delay powder comprising barium peroxide and silicon ignites at approximately 300 C. and undergoes practically gasless autocombustion, at a rate of approximately 5 seconds per inch, thus burning from end to end in about 1 to 3 seconds. This delay train terminates in an ignition charge M of a -30 mixture of lead ortho-cresol and potassium chlorate, diazo-dinitrophenol, or the like. Three rains of this charge 4i pressed at 200 lbs.,'ignites at about 270 C. The ignition charge is pressed against a primer charge 42 comprising lead azide, or the like, disposed next to a bottom booster charge 43 made up of 14 grains of tetryl, preferably phelgmatized.

Following the principles set forth, the detonator may have varied ingredients. This type of detonator occupies a very small space. It is satisfactorily stable against shock and against changes by varied climatic conditions. The thin flexible metal container or jacket is subject to some deformation on impact of the bomb, but this deformation does not interfere with the functioning of the detonator but rather tends to increase the delay in the action of the detonator. 1

In the type of bomb having a nose as illustrated in Fig. 5, the detonator tube I34 inserted in the neck or extension 29 of the steel nose 1 has a flanged top 44 which serves to hold the detonator tube I34 in position against the metallic delay element I31. In place of a steel disc, a magnesium disc about 0.064" thick may act as the partitioning delay element I31. The magnesium disc acts to protect the detonator while the thermate is being loaded. When the thermate nearly burns down to this magnesium disc, the magnesium disc burns quickly and promptly initiates the burning of the delay powder train in the detonator I34. The desirability of this action lies in the fact that this bomb may be mistaken as a long delay bomb and those who attempt to extinguish the bomb before a delayed explosion will be injured or killed. In actual tests, of the explosions occurred in 60 to '70 seconds after impact, and the remaining 25% before a minutes.

In the type of bomb nose assembly illustrated in Fig. 6, the metallic delay element 231 is cast integral with the bomb body 5. The detonator tube 234 is inserted into a hole drilled into the partitioning member 231 which is cast integral with the body 5, but a 4;" thickness of magnesium separates the top of the detonator from amen i? am zthermate; sand :this ithiekness -;of magnesium #acts in the ssame-iway as 0.j06"- steeLdisc. iltmrewants iflame :frem reaching the :detonator rand eservesto delaythe flow-of heatto-the detonator. fSevcral-perforated discs :46 of high meltin 'point rplastic,;such as phenol-iormaldehydezresin, may the ad sposed ,to collar the detonator :tube 34 ato "serve as an insulation and guide for furtherproztection=-y of the detonator and the highexplosive iin-zthis-typeoi construction.

:By; forming the integral vdela-y partition mem- :ber-i331ain theshape of a truncated cone,asishown in SEE. -7, tl-iede1ay peri0d may be shortened moreauniformly, for when the thermit surroundsing theconegbegins to burn-the cone is readily ignited and-thereuponheat is quickly transferred to the detonator tuhe234. However, a separate conical disc element43l' (see Figr8) maybe used ,',-instead of "an integral partition member should {fiffShOItQi jdelay be desired. Bombs with -theconi qcal delay element produced 85% of the explos-ions :35 to 60 seconds after impactandtheaemaining 15% of explosions were distributedfrom el'atoi3zminute'intervals after impact.

-'I -heoretical principles "which -may "be considered as involved in the functioning of the heat itra-nsmit-ting delay elements are:

v('1) {The delayaelementsserving to protect the 'detonator from the flame and heat generated:by stheburning thermate for aperiod after impact are capable vof conducting heat of sufllcienteinrtensit-y "to initiate "the action of the 'detonator hefore :heat conducted to the nose cup can-affect itheihigh explosive therein;

(12) The delay in heat transmission to there plosive in the nose cupand-to'thephargeinthe detonator is a function ofathe distance that.:;the :heat must travel to reach these charges.

.zA ;-f avora-ble characteristic of --the detonato r giS ;that;it permits the high explosive'charge itOEbe icept 1 intact until fired by detonation. -In=the -;delayed :action detonating means described, ethere :are .no Zmoving parts and its elements are :not {fractured under; the :strains and shocks imposed :apon impact 20f the high :velocity bomb. The ntypes'of delay -Vmeans used eeliminate theineed of any pyrotechnic delays which are suscelltible to -jdamaging ,by the shock incurred, and "which xmustbe provided with elongated connecting-links H 'avhichvreguire excessive ;spacetand :work :in as- :sembling. The. delay elements-zus,edrintthepres- -ent invention are simple andddeally suited for large (scale production with ravlninimum whence ior difficulties.

L'ItiiS r130 be=understood -that-theinvention:is;not

3 etc gbeilimited iby .theiorms or embodiments ede- ;-.SO1' -ib.d nor ;by;'any theory of: mechanismof their operation, but that modifications come :within the spirit and scope thereof.

1. ,A bombincluding a=casing, a recessednose ,portiommortised into the front end-10f ithe Leasing, said nose portion containing a ,high iexplorsive-cha-rge: in its front end portion and "an F6101).-

gated detonator tube to the rearzofsaidqcharge, :saidcasing containinga slidabiy mounted firing min; a primer cap-holder spaced apart ,fromand in frontof saidfiring pin, afirstfiring charge spaced apart "from "and in 'front of said ,firing :primer capholder, athermit charge in front-of ssaid firing :charge, said .first firing charge, -,and --.said:.therrnit charge being highlycompacted together after being loaded in the casingysaid jdetonator tube :beingopen "at its rear send por "tion-and'havingan ignition charge in .its front vend -portion and a-delay powder-train forignit- :m said ignition charge. Y

2. The-bombof-cl-aim 17in which the rear .end -p0rtion-of-the firstifiring charge iszrecessedpand its :front end portion-is rammed into a a recess in therea-rendportion of said thermit-charge.

:3. The bomb of claim 1 in which thefiring charge consistsof an:admixture of magnesium :poWder-and -barium chromateand the thermit charge consists essentially ofa highly compacted gadmixturejof sulphur, grained aluminum,;granular aluminum, barium vnitrate and -a compound 'ofxironrandnxygen.

References :oGited in thefileof this patent UNITED STATES PATEN-TS {Number .Name Date 1329.8;222 Kane V .Mar. "25,, 19.19 ,,1 ,36l','2i86 ,Ratrick V. r Dec. 2,;1920 1 ,43 6,24;8 Hammond" N0v.'21, 192.2 I2.', O9 3,35 3 "Geitmann Sept. 14,193? 42,316,656 rWa1ker F Apr. 13, 19.43 12,318,994 Helmhold r e May '11, 11943 FOREIGN :PATENTS "Number Country Date 1,250,271 Great Britain 0017.21, 1926 669,007 Germany Dec. '14, {1938 66,996 Norway Oct. 25,1943

OTHER REFERENCES :Popula-rfiSciencejMarch 1943, page 115. (Copy

Images