US 2605703 A
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A119 5, 41952 w. E. LAWSON 2,605,703
LINER FoR HoLLow CHARGES Filed July e, 1944 @M c. YM #RJ/IRM www,
Patented Aug. 5, 1952 LINER FOR HOLLOW CHARGES Walter E. Lawson, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application July 6, 1944, Serial No. 543,714
1 This invention relates to a novel explosive assembly wherewith increased explosive execution `may be obtained and to a method of'utilizing this explosive assembly or device.-
Explosives are used frequently for demolition purposes and with the object of causing the greatest possible destructive workV locally. In such work it was an earlier practice to bring the explosive into as close contact as possible with the object or material to be blasted. While early practice of hollowing non-detonating charges was practiced, it was commonly considered desirable to compress -or tamp the high explosive very tightly against the surface of the material to be demolished. The last named practices have been followed in uses of disruptive explosives, generally until recently in placing demolition charges.
The Munroe effect has been described in the literature over a period of years, this term being applied to the heightened effect obtained when a detonating high explosive charge was hollowed out on the side toward the material to be blasted. By reason of this cavity (recently vaccompanied by a definite space relation between explosive and opposed material), explosive waves appeared to be focussed or localized in'such manner as to cause" increased destructiveness against the adjacent surface and body. This effect has been a matter of considerable interest and has received some practical application in disruptive operations. The present application is directed'to an extension of the Munroe principle whereby unusual execution results.
An object of the present invention is a novel and improved explosive device and assembly whereby Yenhanced destructive effects are obtained in the use of high velocity explosives. A further object is such an assembly with which a controlled and directed blasting effect of increased effectiveness results. This includes producing a focussedjet of comminuted particles moved` inthe fore front of the wave of detonation projected against Ythe work or target, to improve cleavage or fragmentation of the material worked on'. A still further object is such an arrangement allowing the deep penetration of said blasting effect into any abutting material. A further object is a method of operating such an explosive unit or assembly and securing the results described. Additional objects will Vbe 'disclosedas the invention is described more at length in the following. f
In the drawings lig,` l is an elevational view partly in section, illustratingl my invention in use in one formi.
Fig. 2 is a view of the work orgtarget material partly in section showing the execution effected by detonation of the charge appliedA as in Fig. l;
Fig. 3 is a fragmentary enlarged section of the liner involved in Fig. 1;
Fig. 4 is a sectional View of an extension of the liner;
Fig. 5 is a fragmentary section of a main charge with a modified form of recess;
Fig. 6 is a fragmentary representation of the face of a modied liner material;
. Fig. 7 is a sectional view of such material.
I have found that the foregoing objects are accomplished -when I prepare a charge of a vdetonating explosive of relatively high density, form a hollow or depression in said charge on one side, and introduce or form a rigid frangible lining structure in said depression intimately contacting, or united with the explosive. This lining may =be formed of a frangible body of rigid metal, or metallic compound, or other hard material which has been made up of particles of metal, metallic compound or other hardmaterial strongly bonded together. Under the influence of the explosion of the charge, this liner becomes disintegrated instantaneously into small granular particles, which may be its component particles. There have also been demonstrated lining elements comprising particles of glass, Car.. borundum, and other non-metallic materials including quartz sand, held together with a binder.
The use of the foregoing hollowed charge withV rigid frangible liner brings about an enhanced and directed or focussing effect of the explosive that causes greatly increased blasting execution. As stated, I employ a liner of frangible metalthat is, bonded particles of a metal or a compound thereof, or of other hard material rather than a single shaped piece of ordinary metal, because the use of the latter would under ordinary practice cause the formation of a solid metal slug rather than disintegration of the liner into particles, It is contemplated, however, that a more frangible, brittle metal thanvheretofore employed may become available, as well as other brittle material which may be produced as an integral body.
In carrying out the invention, I may make use of various types and forms of frangible metal, the requirement being that the liner be a rigid structure (in one form, of bonded particles), such that, under `the vforce of the explosion, said structure Will disintegrate into small particles. Metal pariron filings or other form of comminuted me- 3 tallic iron or steel, nickel particles, zinc, tin, and other metals, metal oxides such as zinc and tin oxides, such materials as tungsten carbide, and the like. Various lbinding agents may be used with the comminuted metals or metallic compounds, for example linseed oil,A starch, dextrin, gums, sodium silicate, etc. Plastics and cements, plaster of Paris etc. have been used as matrices to carry particles of hardermaterial,
for instance, glass, carborundum, quartz sand, and other material. While a cone or other hollowed structure of frangible material alone is particularly contemplated, I mayA use such frangible structure as a liner in conjunction with a one-piece solid liner of metal or other material, alone, or, for example, as an inner layer on such solid liner either along the whole structure or at the apex of the cone. A moulded glass liner is effective, as disclosed in a copending application of .Clyde Oliver Davis, Serial No. 477,379, led February 27, 1943, now abandoned, and owned by the same assignee as the present application.
As has been stated, the invention comprises the maintenance of a hollowed or depressed portion on rone side of the explosive charge and the lining of said hollowed portion with a frangible structure conforming substantially to the shape of this hollowed portion. I may, for example, use a frangible liner of curved or hemispherical shape and adapted to fit a concavty in the explosive charge. Preferably, however, I employ a liner in the form of a cone,since this gives highly effective results, lends itself well to controlled adjustment and is readily fabricated. Any shape of liner adapted to fit into .or to integrally or otherwise form a hard brittle tacev of a hollowed portion of the explosive charge may be used, Where the shape of the hollowed portion is determined to be effective for the purposes hereinafter indicated.
The following will serve as specific examples of assemblies prepared and tested in accordance with the invention:
Example 1 A high density charge of a 50-50 blendfof pentaerythritol tetranitrate and trinitrotoluene in the form of a cylinder inches long and 2 `inches inV diameter was prepared with a conical cavity at one end, into which was fitted a similarly shaped conical liner of 11/2 inches diameter, having an internal angle of 45. This charge weighed approximately one pound. This cone was fabricated from iron filings bonded together by a sufficient amount of linseed oil. This explosiveunit, comprising a hollowed cylinder of explosive with a frangible metal cone fltted into the cavity, was placed closely adjacent to a piece of homogeneous steel armor plate of 5 inches thickness, the conical cavity in the explosive facing the armor plate, and the recessed end of the explosive being separated from the armor by a slight distance. The explosive was then red'by means of an electric blasting cap inserted Within a booster charge of explosive tted within the main charge at its outer end. The blast caused the'formation of a small diameter hole of considerable depth in the armor plate, indicating an enhanced explosive effect. vThe weight of the explosive in the cylinder above referred to was approximately one pound. 'Y
- Example 2 A similar test was carried out using the vsame type of explosive in the form of: a cylinderv 5 4 inches in length and 2 inches in diameter. A conical cavity was formed at one end of the explosive charge, into which was fitted a cone 2 inches in diameter, prepared by coating the interior of a solid steel cone of 45 angle (the wall lof the steel cone beingapproximately .03 inch thick) with a layer of iron filings bonded together with linseed oil, constituting a coating of `f approximately .035 inch thickness on the metal cone. This explosive unit was likewise placed close to a test piece of the same type of armor plate as used in Example l, the conical cavity in the explosive facing the armor plate and be- Y ing spaced 11/2 inches therefrom. When the explosive was fired, a hole was formed in the armor plate 1 inch deep and having a volume of 5.8 cc.
Example 3 An explosive charge was formed of the same type of explosive in the form of a cylinder of 6 inches'lengthfand l1.o inches diameter. Into a conical cavity at one end of the y,charge was inserted a cone having a angle, formed by bonding particles of zinc oxide with linseed oil. Again the charge was placed close to a piece of steel armor plate with the conical cavity toward the plate and spaced 1%; inches away. When the explosive was fired, a hole was formed in the armor plate 1%. inches deep and having a volume of 5.5 cc. ,v
The invention may be seen more clearly by reference tothe accompanying drawing, in which Figure 1 is an elevation of the explosive charge on a steel plate I5 Which is to receive the explosive impact, while Figure 2 is an elevation cutaway, showing the perforation in the plate as a result of the explosion.
In Figure 1, I0 representsa cast block consist,- ing of one pound of aitblend of pentaerythritcl tetranitrate and trinitrotoluene. This block is substantially in the form of a cylinder 6 inches in height and 2 inches in diameter, but
' at one end hasa conical indentation II, into which fits a hollow cone I2, fabricated of particles of metallic iron bonded together by a suitable binder. The cone may have a wall of about 1/8 inch thickness, and at its base is formed with outturned support flanges I3 in suitable number. The explosive block and inserted cone with arms I3 are spaced one and one half inches to two inches away from the test piece or target 15 of,5- inch armor plate by a support I4 of suitable material, a cardboard hollow cylinder having been used, resting on the plate I5. A IO-gram charge IIB of compressed tetryl Vis inserted into the top of the cast block. An electric blasting cap I'I with leading wires I3 is introduced into the booster charge of tetryl.` Whenv the explosive is fired by means of the blasting capa deep perforation in the steel plate or target l5 results. Larger charges similarly proportioned or `proportioned in accordwith prior practice. will produce correspondingly increased destructive effect.
Figure 2 shows the penetrating and perforating effect of the explosive unit described,when fired according to the arrangement of Figli. The hol-e I9 of several inches depthv and about 1 inch diameter is cut cleanly, with smooth straight sides. v l
With the explosive units Yand. assemblies described in the foregoing, very striking and effective blasting effects result. Clean cut holes of perhaps 1 inch diameter and several inches deepin steel-1'; latesr may Vbe obtained, whereas the same` amount of explosivefby itself would Ascarcely.have perforated the plate but would only have marred .the surface.' lOther tests have shownthat -with `the same amount of explosive and with the conical cavity therein, but without the liner of my invention, the. effectiveness of the blast would have been greatly inferior. Conventional solidmetal liners used in the recess have resulted in only slightdenting of the surface;of thework or target. It will be understood that the novel'assembly has paplication inthe destruction and demolition of all types of structures; 'whether of metal, cement or other material.
In carrying out the invention in accordance with the examples cited, the main explosive charge lused comprised a high density blend of pentaerythritol tetranitrate with trinitrotoluene. Variousother explosives may be used, a requirementbeing that they be high velocitydetonating explosives, at high density, and capable of attainingimaximum detonating velocity very rapidly. Castv explosivesand compressed explo- 'sives of the rmilitary type are well adapted to such purposes. Such explosives as trinitrotoluene, pentaerythritol tetranitrate, cyclotrimethylen'etrinitramine'picric acid, tetryl, and ammonium picrate are suitable4 for use.V Trinitrotoluene anditsblends with pentaerythritol tetranitrate, cyclotrimethylenetetramine, tetryl and ethylenedinitramine arev favored particularly, as they are well adapted to casting, because of the low melting point of trinitrotoluene. Preferably I use V(for` the-main charge at least) such explosives at densities above 1.50, which will be assured wth cast explosives. detonation approximates or exceeds 20,000 feet per second,in the mixtures named, it is understood. Commercial high velocity and high density explosives may also be used, however, for example high strength straight dynamites, high velocity ammonium nitrate explosives containing a'sensitizer; and high velocity gelatin dynamites. In applying the explosive assemblies in accordance with' the invention, the initiator will bezinserted into the explosive at the end away from the one having the cavity, and desirably near .the center at Vsuch end.
JTests and results from the practice of this invention indicated that with charges of the size set forthin reference to the tests described, the process during detonation consists of a pulverulent, if not molecular fragmentation of the target material lfor a distance thereinto from the face of impact, with no indication of fusing or plasticization of the metal removed. In this respect it may function as an armor piercing device corresponding to and possibly preferable to or supplementary to points heretofore used on armor piercing shells. The material removed in the use of the invention recited was not recoverable and no verification of the assumption stated has been possible otherwise than as stated. It is believed that abrasive action may be a material factor ineffecting at least initiation of the fragmentation ofthe material atthe surface of the target.
While heavt7 weight in the particles formed by the destruction of the lining is thought desirable and may be a contributing factor in the net destructive eect it is not anrarbitrary requirement, andi it has not been possible to determine this. yi It hasbeen contemplated to use a molded glass liner` which will readily fracture and disperse over aV somewhat reduced area of the face of the target within the area of impact of the-wave produced by the explosive, and if desired such The rate-of propagation of the 6 glass liner body may be treated as Well known, to place it under permanent internal stresses which cause it to granulate readily.
It should be 4understood that the invention is not intended for use only for placed, stationary or immobile explosives, but use of the invention is contemplated in demolition, armor-piercing and other projectiles, including shells, bombs, rockets, and grenades. While small sizes of charges are referred to in the specic tests, knowledgel indicates that function of Alarger charges applied in the utilization of the Munroe effect may be correspondinglyy improved.
It has also been contemplated to form a lining of particles of iron, abrasives or other material held in -form by .a binder or bond of a plastic, which may include explosives, for instance, a double base powder, or which may consist of trinitrotoluene. The method of combining the particles and the explosive safely may be adapted to the requirements. Thus, the double base powder may be applied as a thin liquid coating into which the particles may be afterward sifted or thrown. Y
After another procedure a coating of a hardener may be applied to the cone face of the cast body of explosive ll), so that an integral shell or liner face of harder material is formed 0f the explosive body Il] itself, the thickness of which liner face may be determined by the quantityV or viscosity' of the applied binder coating material.
In the formation of the liner, wide latitude in the thickness of the facing has been found permissible. Thicknesses of as little as .036 inch have been found effective and thicknesses of oneeighth inch have also operated satisfactorily in charges of the sizes before indicated. It is believed that greater thicknesses should be used in the larger charges than in the smaller ones.
The angle of the cone faces may also be Varied, angles of 30 to 45 degrees having been used and heretofore greater angles (up to degrees) have been found useful especially in large charges used with my invention.
Thercast blocks referred to were produced and used without encasement other than the liner element in the Acavity and it is interesting to Ynote that, as to depth of penetration, no materialbenet has been obtained by fitting a case to the outer sides and outer end of the block, although the aggregate execution is much increased, resulting in a cavity of much greater area being formed in the material subjected to attack or causing other greater destructive effect, according to the amount of the principal charge.
While the specific instances of practice of the invention herein relate to the formation of apertures or holes in armor plate, this is merely taken as a convenient means of indicating comparative results following the incorporation of my invention with the material used, and the contribution of my invention to improvement of the destructive effects is proportionately manifest in conjunction with charges larger or smaller encased laterally and at the outer end and employed against masonry or other structure. Such encasement when used may conform to prior conventional practice, or any which may be devised.
It should be borne in mind that metal liners of pressed, stamped or rolled metal as heretofore known are outside the scope of this invention, as well as liners of continuous or uninterrupted metal of extremely soft or ductile metal, or of metals of such low melting point and thinness as to disintegrate by fusion, melting, or fluxing.
But while I have disclosed the invention in the best specific form known to me at this time, it will nevertheless `be understood that this is purely exemplary and that modifications of structure, for-m, arrangement, and. combination of elements including substitution ofy materials and equivalents,A structural or otherwise, in making use of my disclosure, may be made without departing from the spirit of the invention.
Thus in Fig. 4 I have indicated the possibility of forming a moulded or otherwise produced rigid cup 20 which may consist of a mixture of a' suitable matrix material anda desired proportion of an aggregate of particles of material of desired quality, as to hardness, specific gravity, abrasiveness, and the like, alternatively or in the aggregate as to these qualities, or as to other qualities, properties or characteristics. The liquied explosive may be cast and allowed to remain in vthis cup for use, suitable supports, booster and detonator being provided for in accordance with the earlier disclosure herein.
Fig. illustrates the use of a liner 2l which may be nearly or quite hemispherical or parabolic in form, produced from materials such as indicated herein as desirable.
Figs. 6 and 7 illustrate a method of utilizing integral sheet metal of qualities heretofore employed, by a special treatment, to render it frangible, to such extent that, while remaining safely integral in production,` shipment and handling prior to explosive use, it will fragmentate and be directed as will the earlier described forms here- This material 22 -may consist of rolled and/or pressed or stamped metal, such as steel, which may or may not have special metallurgical qualities rendering it more liable to fragmentate rather than merely become distorted and remain substantially integral under detonative impact. It is, however, worked or treated, to produce a multitude of weakened lines 23 crisscrossing the material on one or both sides, so that when an explosive with such a liner is detonated, the ma terial will separate along all the weakened lines, or along most of them, and the material ofthe lines will separate intoa multitude of small particles corresponding to those between the lines. These lines may consist of scorings or cuttings extending part way through the `thickness of the material 22 and in two or more parallel or otherwise arranged series, the lines of one series intersecting those of another series so as to form diamond-shaped, rectangular or other shapes or material between the lines.
It is intended that the term metal derivative as used in the claims shall include particles oi metal, or particles ofvmetallic compounds.
l. A shaped explosive charge having an outwardly-opening cavity in one wall thereof, and a liner' of solid material fitting said cavity and comprising particles 'of hard material and a binder disintegrable atthe temperatures engendered by explosion of said charge.
2. In an explosive unit, a shaped explosive charge having a regularly shaped cavity therein and opening through one wall thereof, and a liner tting said cavity, said liner comprising a solid homogeneous material oi hard metallic particles and a binder of material disintegrating in respense to detonation of said charge.
3. In an explosive device of the character described, a body of explosive having a cavity in one side and a liner in said cavity, said liner comprising an aggregate of hard particles and a binding material of low tensile strength less than that of said particles.
4. In an explosive device of the character described, a body of explosive having a cavity, and av liner for said cavity, said liner comprising a matrix of material of'low tensile strength capable of maintaining rigidity at climatic temperature, and particles of harder materiall of greater tensile strength than said matrix material.
5. In an explosive device of the character described, a body of explosive having a cavity therein opening through one wall thereof, and a liner for said cavity, said liner consisting of a matrix of material rigid at climatic temperatures and having low tensile strength, and particles of abrasive material therein.
6. An explosive unit comprising a solid shaped explosive charge having an outwardly diverging cavity opening through one surface thereof, and a liner tting said cavity and comprising a matrix rigid at climatic temperatures and of relatively low tensile strength, and particles of abrasive embedded in said matrix.
7. In an explosive device of the characterdescribed, a, body of explosive having a cavityV in one side and a liner tting said cavity and comprising a matrix and an aggregate of abrasive particles.
8. In an explosive device of the character described, a body of explosive having a cavity in one surface, and a liner tting said cavity, said liner comprising a `matrix and an aggregate of particles of hard dense material of greater specific gravity than said matrix.
9. An explosive device comprising a high densitycharge of a detonating explosive with a depressed portion on one side of said charge, and a rigid structure lining said depressed portion and conforming generally to the shape thereof, said lining structure comprising particles of hard material and a bond of lower tensile strength than said particles.
l0. An explosive device' comprising a high density charge of a detonating explosive with a depressed portion on one side of said charge, and a rigid structure lining said depressed portion and conforming generally to the shape thereof, said lining structure comprising particles of abrasive material and a bond of lower tensile strength than said particles.
WALTER E. LAWSON.
REFERENCES CITED The following references are of record in the Italy Sept. 29, 1934