US2604042A - Detonating explosive charge and method of impressing surfaces employing same - Google Patents

Description

y 9 J. H. COOK 2,604,042

DETONATING EXPLOSIVE CHARGE AND METHOD OF IMPRESSING SURFACES EMPLOYING SAME Filed July 30, 1948 3 Sheets-Sheet l II I I I/ l/II Attorneys y 9 2 J. H. cook 2,604,042.

TING LOSIVE CHARGE ETHOD DET OF BESS SURFACES EIIPL SAME Filed July 30. 1948 3 Sheets-Sheet 3 INVENTOR JOHN. HENRY COOK svzwawf $404M) ATTORNEYS Patented July 22, 1952 nairomrmo nxrtosivg cnaiges METHOD OF I'IltflRESSING .EMPI'JOYING SAME John .:Henry tGook Ayrshire, scotlandfassiginor" :to ImDerialUlremical Industries Limited, .a cor- :poration of Great Britain 7 Application'ZIuly 30, 194-8, Seria l"No.'4160'5 In Great Britain October 6, 1947 .9-Claims. (01. 101-4012) "The-present invention is concerned with-a new and improved l metho-d of explosively impressing markings in"low-irelief into=a metal opiate whereby impressed metal: plates suitable i fo risuchipurp'oses as e'mbossing or printingsheet=:materials:may:be "obtained. The inventionfurtherrelates to asn'ew 'form of explosive charge suitable io'r impressing in' l'ow relief on a m'etal'platemarkings simulating those provided by the -boundaries between sur- "faces of 1 differing relief in a item-plate interposed betweenit and the metal plate.

It as :a'n object of the invention t'o provide a pr'actic'alilemethod for the productionrof metal plates-"of at least several'square inches in area impressed with designso'r other markings in low relief suitable for embossing, printing orthe like --in a more expeditious inanner than by the usual -r'neth'ods. It is also an ob'ject of the invention -to "provide a new "or improved form of explosive charge having *a plane end of --subs'tantial area characterised "in that when its detonation is initi'ated from its opposite end the detonation wave "front-at'said plane'endfis substantially free from curvature Y Other Objects of the invention will appear hereinafter. i I It has-long been known that i by placing a coin -qn--a-=meta1 p1ate and initiating "detonation of an explosive charge superposed -on "the coin, the "design on 'the face of the coin presented to the metal 'plate 'can'bemoi'e "or less faithfully reproduced on the plate in reverse that- 1s to say the hollow portions of the design on the coin will i'appeara's raised portions inithe plate, and the relief portions of the d si n 'on the coin will be indented infthe plate; on -the other hand the sha e and markings of a .leaf, a piece of lace, or'llke flat object "of :small "area "made 'of soft jiie'structiblemateiial laid on a metal plate have been shownmarked on a metal plate in positive image by detonating a plane=ended explosive cartridge superposed on "the object. Hitherto however the .so .impressed plates have been regarded merely as scientific curiosities and no .jinilustrial applicationhas'been made of'thepossilbilities T01 impressing ,metal [plates with designs "by means oftexplosives.

Wh'enfia comparatively short cylinder or other plane fended columnar body of "detonating explosive having an axis perpendicular to its ends and thesame crosssection throughout its axial length hasfits -.detonation initiated ,from a ,point at one ,endof itsakis, the detonation wave front advancing through the column .is convex. Owing to this ,convexitypf the detonation wave. front, no design "-2 v impressed by-means'of anexplosivecolumn, whose detonation is initiated -by-a-detonator;-at its remote end, on azmetalgplatesfrom an;inte r.posedtemplate or :stencil cut with a design in low relief can the satisfactorily simulated, except in a :small area immediately around :the :;axis of the column ;,so that unless the cross'sectional area -ofaherexplosive :column andthe v design as 'a whole;;is .small :the rendering :of the :design becomes moreaand 'rmore fn'oticeably indistinct as the ;periphery of the cclisc is approacheiwith the results that the impressed metal plate obtained is vof inolpr-actical value.

This imperfection 10f impression "presents a problem IO which a practical solution is not easily found. 'fihusamultiple initiation by means of detonators spaced at ;intervals over the area of :the remote tend cof the :explosive column :does not usually effect the desired result, since the "resulting designr'on the metalaplate may-beimarrjed by blemishes repres'enting the .lines :where the convex detonation wave front surfaces intersect.

tirhile l the replacement zofia portion of, the length or the -column of explosive aby a tliscxofI-an explosive of highervlocity of ..'dtonation-than Ethat "plane -base-is uriintertupted by any recess for spro- -jection,-said conical forni being-if :desiredftnuhcated by one 'or more surfaces passing perpen- -dicula'rly through its base, and in deton'ation inducing relationship with said-explosive :charge, a covering of =a thickness of an explosive ofia higher Velocity of detonation extending over the whole of its-conical curved surface, the de'tonati'on initiating ineans bing -at the apes; the sine of the base angle of the cone being equal t'o the -quotientof the-velocity-ofdetonation-'o'f-theeizplosive of relatively lower "velocity amuse rbyoffthe'exp'losive of relatively higher velocity;

The detonation wave front transmitted to'and beyond the base of such "an explosive-charge is a plane parallel fto said 'base. The longer time than would be otherwise required for an nn iil'se tob'etransmitted'fiorn the"apical regiontv folly or, partly ialong the sloping length of the thickness of explosive'of higher velocityoif deton ti'o'n covering the core explosive than directly-along the axis to: the"'coneiis compensafmu for "bythe v reduced thickness ioffthefexplosive offlcwer velocity of detonation through which the impulse must be transmitted before it can reach the base, so that at every point of the base of the cone, whether or not this is truncated as aforesaid, there arrivesan impulse at the same instant of time.

In the method of explosively impressing low relief markings in a metal plate according to the present invention, the apically disposed initiating means detonates the composite explosive charge with a resultant plane detonation wave front. Between the base of the explosive charge and the metal plate there is'interposed a sheet of destructible compressible material having predetermined local variations in its thickness or in the nature of the material composing it. The aforesaid destructible compressible material causes absorption of the energy of detonation directed through it in correspondingly differing degrees at the respective parts of its area. If desired, further cushioning sheet material of uniform absorption capacity over its area may be employed to absorb the energy to an additional degree. The higher energy absorbing portions of the sheet of destructible compressible material cause the metal plate portions beneath them to be subjected to less energy of detonation than those portions of the metal plate underlying the lesser energy absorbing portions of the destructible sheet material. As

a result of this, as is explained more fully hereinafter, various designs may be impressed in the metal surfaces.

The aforesaid composite explosive charge preferably includes also as an element intern posed between said first mentioned element and the sheet of destructible compressible material a parallel plane-ended column of uniform cross section, having its columnar axis perpendicular to its plane ends, of an explosive composition whose detonation is initiated from one of its plane ends through the base of said first mentioned element, whereof the core explosive has a velocity of detonation not exceeding and preferably lower than that of the explosive of said parallel plane-ended column. By the method of the present invention designs extending over areas ranging up to some hundreds of square inches may be satisfactorily impressed.

The invention will be further understood by reference to the diagrammatic drawings accompanying the provisional specification, whereof Figure l is a vertical axial section and Figure 2 is a top plan view of an assembly for executing a design on a metal plate according to one form of the invention, Figure 3 is a plan view of a sheet of destructible compressible material bearing an ornamental design forming part of the aforesaid assembly, Figure 4 is aplan view of the metal plate having the ornamental design inlow relief obtained as a result of the detonation, Figure 5 is a vertical axial section of a modification of Figure 1, and Figure 6 is a top plan view of the modification of Figure 5.

In Figure 1, I is a steel anvil, 9 is a sheet of cushioning material such as cardboard, 8 is a brass plate, 6 is the smooth cardboard base and 3 the cardboard wall of a container. I, seen also in Figure 3, is a sheet of hard cardboard cut in stencil with the ornamental design shown in Figure 3. A and-'1 are thin partitions of stiff paper or the like. is a' cylindrical charge of an explosive of a velocity of detonation about 600 metres, per second and 5 is a conical charge of an explosiveof velocity of detonation about 2300 metres per second capable'of inducing the was detonation of the explosive 5 when it is itself detonated by a charge 5 of a velocity of detonation abotu 5800 metres per second constituing a layer of uniform thickness covering the coni= cal charge and capable of detonating the latter through the intervening thin sheet 4 i The base angle of the cone is 23 22. I I is a tetryl primer and I2 is an electric detonator.

When the electric detonator I2 is fired the primer II is detonated and the latter radially initiates the detonation of the explosive charge 5, which in turn initiates the detonation of the explosive charge 5 across the intervening sheet '4 The thickness of the explosive 5 of lower velocity of detonation than that of explosive 5 that has to be traversed before the detonation impulse meets the explosive 5 is greatest vertically below the apex of the cone, and the angle of the cone is such that the detonation impulse that has travelled down the outer layer explosive of higher velocity 5 arrives at the circumference of its base at precisely the same instant as that travelling axially arrives at the center of its base. At this instant a detonation impulse arrives at every point at the interface between the explosive 5 and 5 so that the detonation wave front at this interface is not convex but plane. Hence the detonation induced in the cylindrical explosive charge 5 travels through it with a plane wave front and everywhere on the sheet I the detonation impinges normal to its surface. The upstanding parts of the design on the sheet I however, absorb more of the energy of the detonation than the blank portions, so that the metal plate 8 is more deeply impressed beneath the blank portions than beneath the upstanding portions. The base 6 of the container absorbs some of the detonation energy before it reaches the sheet I. The cushioning sheet 9 helps to prevent the plate 8 from being bent or broken. It is a remarkable fact, however, that the design rendered on the plate 8 is as a whole somewhat larger. than that on the said sheet I, as is shown in Figures 3 and 4. The design is distinctly rendered on the plate over the whole area of the design. I

The greater the difference between the velocities of detonation of the core explosive and of the outer explosive in the conical portion of the charge, the flatter may be the shape of the cone and hence the less the amount of explosive material required to produce a plane detonation wave front. It may therefore be preferable to employ as the core explosive one that would have a substantially lower velocity of detonation than is usually desirable for impressing the markings effectively on a metal plate-so long as it' is capable of initiating the detonation of the parallel plane-ended column of 'theexplosive of velocity of detonation suitable for impressing the markings. Thus the core explosive in the conical portion of the charge may advantageously have a velocity of detonation for instance of about 2,000-2500 metres per second and that of the explosive of the parallel plane-ended column may range up to about 3300-3800 metres per second or more depending on the depth of impression required, and the nature of the material of the metal plate and the extent to which the explosive charge is cushioned. I

The velocity of detonation of the, explosive on the conically curved surface should theoretically be as high as possible but economical rangers doesfi-not-hecessarily follow that *the depth of the impressionsall-overthe surface workedupon will be identical, since the two explosives presinthe conical 'portion-may differ markedly in jpower or density so that the-energy transmitteii from the base of this gconical --structure will not-in::general"'be the same in amount aiwall parts of its surface. This differential effect, however, is minimised when the conical portion is somewhat truncated by one "or more surfaces normal to itsf'base, andyalso when this 'portion is "employed 'as the initiating "means .in conjunctionflwith a parallel plane-ended cylindrical column of explosive in the "aforesaid manner, especially'when the'explosive used =for-thecore of the ,conicaliporti-on isofa' substanti-ally -low'ervelocity of detonationthan that-of the explosive in said column and the velocity ofdetonation 'of the explosive on the -conically curved surface is substantially higher than that of the explosive in .said ,parallel plane-ended column.

Tn 'the 'case where a circular area is to be worked upon, the periphery o'f the -base of the cone may ibercomplete although jitjis iusually desirable, that the form. of the charge, or portion .of theldharge should be truncatedso that. at;least that portion of the cone lying outside .the truncated surface perpendicular .to the ;base' 'of the, complete cone and intersecting it .at .the

junction between the two explosives comprising the cone should be omitted, and it'is sometimes preferable that the truncation should be such asrto omit an annular-portion of the complete cone -lying outside a cylindrical surface perpendicular to and intersecting the base somewhat nearerthe-axis-ofthe cone; In the case where a non-:circular arealis :to ;be worked amen, it will in generallbe.gadvisablesthatthe truncation of the cone should be such as to omit those portions of the complete cone that lie outside the surface or surfaces perpendicular to the base of the complete cone and intersecting it at the outline of the working area, the area of the base of the complete cone being large enough to circumscribe or even extend everywhere beyond the outline of the working area. This enables the base of this portion of the explosive to be superimposed on the plane end of a column of explosive of the required shape without overhanging it. Such truncations are without any adverse effect on the plane detonation wave front characteristics of the charge. An example of a composite explosive charge suitable for working on a non-circular area in accordance with this invention is shown in Figures and 6, where like numerals as those used in Figures 1 and 2 represent like parts. The composite explosive charge of Figures 5 and 6 for working on a square area is formed by truncating the cone-shaped explosive charge 5 so as to form four equal length surfaces l3 at right angles to each other and normal to the base of the conical explosive charge 5 The portion of the explosive charge in the form of the plane ended column may for instance consist of an 80:20 mixture by weight of trinitrotoluene and sodium chloride milled to a fine grist.

The explosive constituting the core of the coned portion may advantageously have a velocity of detonation not exceeding about 2300 metres per second and the explosive constituting the outer thickness a velocity of detonation 6 considerably "higher, e. g. 3060: -metres :per sec end. The core explosive-may consist -for lin stance of *Denaby Bowder --whioh consists of "a mixture comprising 12% 59% ammonium mtrate, 6% sodium nitrate, 20% sodium onic-- ride, and 3% cellulosic material and theouter thickness explosive may "consist for instance :of cyclotrimethylene trinitramine. The ini-tiating means at the-apexof the cone maybe a primeradapted to receive a detonator, =an'd may be :included as a permanent part of the charge, :er supplied separately "like the -detonator :itself. "to be "assembled with the rest of the charge when it is to lie-exploded. r 1

Tt'w'ill be understood thatin'making up the explosive charge a *casing -suitably compartmented by'means-of structures-of l-ight material is desirably employed, and that the base of the casing will serve -*as=cushioning'material between the explosive and thezsheet of ides'truetiblercompressible material which may, if desired, ihave thelow relie'f markings penetrating-through the whole of its thickness :in the fashion :of .a :stencil or through only va apart 10f bits zthickness. :Ihe sharpness .:of :the :markings on the :metal ;plate may be modified as desired ..by =interposing :fur ther cushioning .r-material :preferably melow :the sheet of destructible compressible; material. -.The sheet of :ldestructible compressible rrnaterialzand further:cnshioningsmaterialshonldbe cigar-charactor .=such ithat :-.they :will not :become mermanently :attached. to the metal plate rafter-the detonation. .7 woodipaper. :c rdboard or the like may the used. -;A sheet :of cushioning material may .;;also :be zinternosedrbetween the metal plate and ithe :anvil rsulqnorting -.it.

.I aclaim: ,Agcomposite rexplesive :charge ,capablesof producing :a gplane. detonation gwavie :flQIlt .comprising ;a right angle ;.cone+shape,d rexplosive charge arranged :for detonation by 22, thickness of a priming charge of higher velocity of detonation extending over the whole of said conically curved surface, the apex of said thickness of charge of higher velocity of detonation being adapted for receiving detonation initiating means, and the sine of the base angle of the right angled cone-shaped explosive charge being equal to the quotient of the velocity of detonation of the charge of relatively lower velocity divided by the velocity of detonation of the charge of relatively higher velocity.

2. A composite explosive charge capable of producing a plane detonation wave front as set forth in claim 1 wherein the base surface of said cone-shaped explosive charge is arranged for initiating detonation of one end of an explosive composition in the form of a planeended column of uniform cross section having its columnar axis perpendicular to its plane ends, the velocity of detonation of said conical detonating charge being not greater than that of the velocity of said explosive of said planeended column.

3. A composite explosive charge capable of producing a plane detonation wave front as set forth in claim 1 wherein said composite charge is truncated by at least one surface normal to the base of the cone-shaped explosive charge.

4. A composite explosive charge capable of producing a, plane detonation wave front comprising a right angle cone-shaped explosive charge arranged for detonation by a thickness of a priming charge of higher velocity of detonation extending over the whole of said conically curved surface and further arranged for concial detonating charge being not greater than that of the velocity of saidexplosive. of said column, and thesine of the base angle of said right angle cone-shaped explosive charge being equal to the quotient of the velocity of detonation of the charge of the right angle coneshaped explosive divided by the, velocity of detonation of the priming charge and having the apex of said thickness of said priming charge adapted for detonating initiating means. 1

5. A composite explosive charge capable of producing a plane detonation wave front as set forth in claim 4 wherein said composite explosive charge is truncated by at leastone surface normal to the base of the cone.

6. A method of impressing 10w relief mark: ings into a metal .plate which comprises interposing a sheet of destructible compressible material having predetermined local variations ofthe kind to cause corresponding differences in energy absorption of a detonation directed through it between the metal plate to be impressed and a composite explosive charge, said composite explosive charge comprising a right angle cone-shaped charge arranged for detonation by a thickness of a priming charge of higher velocity of detonation extending :overthe whole of said conically curved surface, the sine of the base angle of said cone being equal to the quotient of the velocity of detonation of the charge of relatively lower velocity divided by the velocity of detonation of the charge. of relatively higher velocity and having the apex of said thickness of charge of higher velocity of detonation provided with detonation initiating means, positioning the said explosive charge so that the said initiating means 'is' furthermost removed from said metal-plate, and detonating said initi ating means.

said composite explosive charge is truncated by at least one surface normal to the base of the cone. a v f 8. A method as set forth in claim.6 wherein the composite explosive charge includes as a portion thereof nearest to the sheet of destructible. compressible material a plane-ended explosive column of uniform cross section having its columnar axis perpendicular to its plane ends and one end thereof arranged for detonation by the base of said cone-shaped explosive charge, the velocity of detonation of said cone-shaped explosive charge being not more than that of the explosive of said column. v

9. A method as set forth in claim 6 wherein cushioning sheet material is interposed between the composite explosive charge and the sheet of destructible compressible material.

JOHN HENRY COOK;

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

UNITED STATES PATENTS OTHER REFERENCES Propelled Hollow Charges, Popular Science, February 1945, pages 66 and 67.

7. A method as set forth in claimG wherem'

Claims (1)

1. 6. A METHOD OF IMPRESSING LOW RELIEF MARKINGS INTO A METAL PLATE WHICH COMPRISES INTERPOSING A SHEET OF DESTRUCTIBLE COMPRESSIBLE MATERIAL HAVING PREDETERMINED LOCAL VARIATIONS OF THE KIND OF CAUSE CORRESPONDING DIFFERENCES IN ENERGY ABSORPTION OF A DETONATION DIRECTED THROUGH IT BETWEEN THE METAL PLATE TO BE IMPRESSED AND A COMPOSUTE EXPLOSIVE CHARGE, SAID COMPOSITE EXPLOSIVE CHARGE COMPRISING A RIGHT ANGLE CONE-SHAPED CHARGE ARRANGED FOR DETONATION BY A THICKNESS OF A PRIMING CHARGE OF HIGHER VELOCITY OF DETONATION EXTENDING OVER THE WHOLE OF SAID CONICALLY CURVED SURFACE, THE SINE OF THE BASE OF SAID CONE BEING EQUAL TO THE QUOTIENT OF THE VELOCITY OF DETONATION OF THE

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