US 3169478 A
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Feb. 16, 1965 H. L. SCHAAF 3,169,478
FOLDABLE EXPLOSIVE TAPE Filed July 23, 1962 2 Sheets-Sheet 1 INVENTOR. HERBERT L. SC HAAF BY y.-
Feb. 16, 1965 H. L. SCHAAF FOLDABLE EXPLOSIVE TAPE 2 Sheets-Sheet 2 Filed July 23. 1962 INVENTOR. HERBERT L. SCHAAF "5* courage tearing.
, 3,169,478 FOLDABLE EXPLOSIVE TAPE United States Patent O Herbert L. Schaaf, Wenonah, N..I., assignor to E. I. du
Pont de 'Nemours and Company, Wilmington, Del., a corporation of Delaware Filed July 23, 1962, Ser. No. 211,636 Claims. (Cl. 102-22) This invention relates to an explosive tape adapted to be folded at designated areas.
In recent years, explosive compositions which can be formed into flexible, non-resilient sheets have been de veloped. Compositions of this type and their preparation are described in detail in Us. Patents 2,999,743 and 2,992,087.
Unfortunately, the described compositions, and other compositions of crystalline high explosives in a binder matrix, are not of sufficient flexibility to permit a length of sheet, i.e., a tape, to be folded back on itself without forming a crack at the severe bend. The strength of a tape of such material can be increased by providing a backing of flexible material, e.g., cloth; however even when such backing is provided the stresses produced when the explosive tape is folded on itself result in tearing, discontinuities and hiatus of the explosive composition in the area of the fold. Obviously, propagation of detonation across these discontinuities is not reliable.
Accordingly, by the present invention, I provide an explosive structure adapted to be folded which comprises a length of tape of a deformable, self-supporting explosive composition comprising from about to about 92.5% by weight of a cap-sensitive crystalline explosive in admixture with an elastomeric binding agent, a plurality of slits, essentially equal in length, arranged in echelon across said tape, torsion bars being defined by the section of said tape lying between said slits, the width of each said torsion bars being essentially equal in magnitude to the thickness of said tape.
As used herein, the terms length of explosive and tape of explosive are synonymous and refer to a sheet of the self-supporting composition which is long in relationship to its width.
In a preferred embodiment of this invention, the length of self-supporting explosive composition (hereinafter referred to simply as tape) is mounted, e.g., for dimensional stability, on a flexible backing which is thin in relationship to said tape (approximately to the thickness of said tape) and which has a tensile strength at least 1.5 times that of the tape.
In another preferred embodiment of this invention minutecircles having a diameter slightly greater than the width of said slit are scribed on the ends of the slits. The provision of such circles dissipates stress placed upon the slits during the bending action.
By the term in echelon as used herein is meant an arrangementof slits drawn up in parallel lines, each somewhat to the right or left of the adjacent slits.
The term torsion bar as used herein refers to a strip of said explosive composition which is long in proportion to its depth and thickness and which is adapted to be subjected to twisting as the tape is being folded.
Of course, the plurality of slits arranged in echelon fashion along the tape are designed to facilitate folding of the tape with the avoidance of the normal stresses and strains normally attendant to such action. Thus, the'slits are arranged in echelon fashion to intersect the real or proposed crease of the tape. The angle formed by each slit with the crease must be greater than 0 and less than 60". An angle of 0 would induce great strain and en- Stresses and strains would be directed to those portions of the tape, along the crease, which had not been severed. An angle greater than 60 would result in increasing strain being imparted to the tape along the crease, upon folding, and result in the build up of stresses and strains at the crease of the fold rather than relieving these factors.
Additionally, each of the slits must extend through the crease or fold, when the tape isfolded, and into the section of explosive composition on either side of the crease a distance at least equal to twice the thickness of the tape.
As to the nature of the slit itself, it will completely sever, or cut, the explosive composition it is imposed upon; however, it need not sever the backing or support material which forms a part of the complete structure and gives it strength. The entire line defined by the slit can vary from a straight line to one defining a semi circle; however, that portion of the slit which will, or does, intersect the existing, or proposed, crease, must be substantially straight, i.e., run horizontal to the longitudinal axis of tape it intersects, at the point of intersection and for a very short distance therefrom, and the aforedefined angle must be formed by the slit and the crease.
In order to describe this invention in greater detail, reference is now made to the accompanying drawings wherein:
FIGURE 1 is a top view of the explosive tape adapted to be folded in accordance with this invention;
FIGURE 2 is a top view of the folded explosive tape in accordance with this invention;
FIGURE 3 is an end view of the folded explosive tape of this invention (slightly enlarged in dimension for clarity);
FIGURE 4 is a top view of an alternative embodiment of the explosive tape of this invention;
FIGURE 5 is a top view of the folded explosive tape of FIGURE 4;
FIGURE 6 is an end view of the explosive tape of FIGURE 4; and
FIGURE 7 is a view of an explosive tape having semicircular slits.
In FIGURE 1, 1 designates the explosive tape, 2 is the flexible backing for the tape and 3 the torsion bar formed between slits AA and B-B. C represents an initiation site for the tape. The line FF represents the crease along which the tape is to be folded, i.e., the fold plane of the tape.
In FIGURE 2 and FIGURE 3 the elements are as in FIGURE 1 with the exception that the tape is folded along crease FF.
In FIGURE 4, the elements are as in FIGURE 1 with the exception that the slits in the tape are designated by lines G-G', H-H, 1-1, 1-1, K-K', L-L, and M-M.
In FIGURE 5, the elements are as in FIGURE 4 with the exception that the tape is folded along crease F F.
FIGURE 6 is an end view taken along line FF of FIGURE 5 and shows the twist imparted to the torsion bars and the stress relief provided by the slits.
FIGURE 7 depicts a length of explosive tape provided with curvilinear slits designated by lines GG through QQ'- In use, the explosive tape is slit in accordance with this invention in the section in which it is desired to fold the tape along a crease line, which generally will form an angle of from 0 to with the longitudinal axis of the tape, and the tape bent simply by folding along this line, which, in practice, will generally pass through the midpoint of the torsion bars. As the tape is folded the ex plosive composition parts cleanly and easily along the slits with no tearing or fraying of the body of the explosive composition. The torsion bar between slits, e.g., AA and BB in FIGURE 1 is unitary with the unfolded sections asserts of the tape. By forming the echelon of slits in the explosive composition at a plurality of appropriate crease sites, which creases may be parallel, at angles, or even the package, it again assumes generally its original, un-
The explosive structure can beactuated, e.g.','by an initiator applied at points C or line wave generator applied along the edge of the tape, or ata point within the tape. Upon initiation the detonation impulse is propagated uninterrupted and at a uniform rate throughout the entire area of the pipe, the detonati'ng impulse in the slit portion(s)' of the tape being transmitted by the torsion bars.
Various factors and requirements'are involved inthe selection of the self-supporting explosive composition for use in the explosive structure of this invention. Naturally, the composition must have acceptable explosive properties. Namely, it must be capable of propagating the detonation impulse reliably even when the explosive loading is low. Secondly, it must have adequate sensitivity with respect to initiation, that is, the composition must be initiable by the customary initiation means, for example, the standard blasting caps or line wave generators as described in US. 2,943,571. its impact sensitiveness, which indicates the sensitivity of the explosive to mechanical shocks, desirably is low to enable machining and transportation. 1
in addition to the explosive properties prercquisites,the self-supporting composition must possess certain characteristics with regard to physical form. Its nature must be such that is can be readily formed into the'necessary configuration and will retain the desired formunder conditions of handling, transport and storage. That is, the configurations must not lose their dimensional stability inasmuch as changes in dimensions would result in undesirable variations in weight or" explosive per unit of area in the configuration, nor should the configuration be so soft stability, should be, relatively thin in relationship to the tape and should be-characteri'zed by a tensile strength at least 1.5,tirnes that of the explosive composition. in
general, this material will be a thin sheet or film of a I material inert to the explosive composition'in the sheet and will have a tensile strength, of at least 35 kg./ sq. mm.
:Exemplary materials for usein this backing material includes porous paper or fibers impregnated with and unified by a non-tackyca'ou'tc'houcic composition admixed with aresinous'composition or elastorneric films adhered to the explosive by a flexible adhesive. of any of the coni ventional types, particularly a pressure-sensitive adhesive.
The chemical composition of the backing material ob-j viously is notcritical as long-as the material has the desired physical characteristics, i.e.,fiexibility with relatively high tensile strength even in thin layers.
The following examples serve to illustrate specific embodiments of the explosive composition'of the present invention. t P
Example 1 Five tapes (4 inches by 2 inches by A3 inch) were formed of the explosive composition of Example 1 in U.S. Patent'2,999,743 and mounted on'a 4 inch by 2 inch film of porous paper impregnated and unified by a non-tacky cohesive blend of abroken-down rubber ad 7 mixed with a water-insoluble solid resin via a tacky,
angle of 45 with the longitudinal edges of the tape and an angle of 5 with a proposed crease which is at a 50. angle with the longitudinal edges of the tape were or friable, i;e., clay-like, that their dimensions, i.e., thickness, width or length, areeasily altered during handling to preclude uniformity of the explosive. The tapes should 7 be tough, i.e., strong or firm in texture, but flexible to V marily to the physical structure, the exact chemical cornposition of the explosive tapeis not critical.
The number of the slits formed in echelon along the crease will depend upon the width of the tape and the angle which each slit'in the echelon forms with the crease along which the tape is who folded. in general, we have found that it is preferable that an angle of about to about is enscribed between each of the. slits and the crease along which the tape is to be folded. With this degree of angle, an optimum'number of torsion bars will be formed across the width of the'tape to provide greater flexibility in the area to be bent and also to proslit, such as a knife or a blade, can be used in preparing the explosive structure of this'inventiom'or the desired slits can be made in a cutting die.
The backing material, whichis used for dimensional cut in echelon in the tape, as in FIGURE 1, opposite ends of each of the pair slits being inch from the edge of the tape. Each of the tapes couldbe flexed and bent easily. After eachtape had been flexed and bent along the crease '5 times, the tapes were initiated by applying a conventional number 6 blasting cap to one end of the tape. The detonationimpulse was easily propagated over the torsion bar between srits and the entire length of explosive detonated at a uniform rate.
Exam ple 2 Five tapes of the sheet explosive composition of Example 1 of US. 2,992,087 were cut to the dimensions 5 inches by 3.5 inches by A inch and mounted on a film such as described in Example labove. tape eight slits were cut in echeion as shown in FIG- URE 4. Each slit was l' /s inches long and formed an angle of 20 with a line forming an angle of with the-longitudinal axis of the tape. The slits did notcxtend through the film backing. The tapes were'folded through an angle of 180 along this 45 line repeatedly.
' The torsion'bars defined between theslits were not frayed nor ruptured in any way. When the tapes were initiated at one end by a conventional number 6 electric blasting cap, the detonation impulse was transmitted without interruption across the folded section and the tape detonated consistently at a velocity of .6700 metersper second. 1
Various modifications and alterations of this invention will be apparent to thoseskilled in the art without departing from the spirit and scope of this invention;
What is claimed is: v 1. A foldable explosive structure which comprises a length of tape of tough, flexible, self-supporting explosive composition comprising from about 15 to about 92.5% by weight of cap-sensitive crystalline explosive in admixturewith an elastomeric binding agent, a plurality of slits essentially equal in length extending through said explosive composition, said slits being arranged in echelon .between the sides of the tape at an angle greater than 0 and less than with respect to the line on which a said tape is to be folded, torsion bars being defined by the'sections of tape lying between said slits, the width of Two 1.5 inch long parallel v i slits separated by a distance of inch and forming an 7 In each 23 each torsion bar being essentially equal to the thickness of the tape, and each of said slits extending across said line and to each side thereof a distance at least equal to twice the thickness of the tape.
2. The explosive structure of claim 1 wherein the tape of explosive composition is mounted on a flexible backing, said backing being thin in relationship to said tape and having a tensile strength at least 1.5 times that of said tape of explosive composition.
3. The explosive structure of claim 1 wherein circles having a diameter slightly greater than the Width of the slits are inscribed on the ends of the said slits.
4. The explosive structure of claim 1 wherein the slits are at an angle between 5 and 45 with respect to the line on which the tape is to be folded.
5. The explosive structure of claim 1 wherein the slits are at an angle between about 15 and 40 with respect to the line on which the tape is to be folded.
References Cited in the file of this patent UNITED STATES PATENTS 1,704,186 Garnmeter Mar. 5, 1929 2,181,164 Alexander Nov. 28, 1939 2,692,425 Martin Oct. 26, 1954 2,735,426 Claydon Feb. 21, 1956 2,750,884 Gaines June 19, 1956 2,992,087 Fassnacht et a1. July 11, 1961 2,999,743 Breza et a1. Sept. 12, 1961