US3621559A - Manufacture of detonating fuse cord - Google Patents

Abstract

DETONATING FUSE CORD HAVING ALONG ITS LENGTH ALTERNATING SECTIONS OF GREATER AND LESSER EXPLOSIVE ENERGY IS MANUFACTURED BY THE CONTROLLED EJECTION OF SLURRIED PARTICULATE EXPLOSIVE INTO A STOCKING AND THEREAFTER DRYING AND COVERING TFHE FILLED STOCKING.

Description

Nov. 23, 1971 WELSH 3,621,559

MANUFACTURE OF DETONATING FUSE CORD Filed Jan. 19, 1970 2 Shoots-Sheet 1 INVENTOR David Martin WELSH AGENT Nov. 23, 1971 Filed Jan. 19, 1970 D. M. WELSH MANUFACTURE OF DETONATING FUSE CORD 2 Sheets-Sheet 8 SUPPLY OF EXPLOSIVE PREPARATION OF EXPLOSIVE SLURRY WET FORMATION OF TEX E COVERED COLUM EXPLOSIVE DRYING OF WET COLUMN OF EXPLOSIVE EXAMINATION DRIED TEXTILE CO E E0 COLUMN OF EXPLOSIVE APPLICATION OF MOISTURE BARRIER OPTIONAL FINISHING OPERATIONS INVENTOR David Martin WELSH AGENT United States Patent 3,621,559 MANUFACTURE OF DETONATING FUSE CORD David Martin Welsh, Brownsburg, Quebec, Canada, as-

signor to Canadian Safety Fuse Company Limited, Montreal, Quebec, Canada Filed Jan. 19, 1970, Ser. No. 3,861 Claims priority, application Canada, May 6, 1969,

Int. ci. B2255 U.S. Cl. 29420 3 Claims ABSTRACT OF THE DISCLOSURE Detonating fuse cord having along its length alternating sections of greater and lesser explosive energy is manufactured by the controlled ejection of slurried particulate explosive into a stocking and thereafter drying and covering the filled stocking.

This invention relates to detonating cord and in particular, to the manufacture of a detonating cord having an explosive core of alternating core sections of controlled variations. Such a detonating cord has particular use in, for example, metal expansion applications.

As is known in the explosives art, detonating cords are normally produced in long or continuous lengths and comprise essentially a uniform core of explosive encased in a protective wrapping or sheath. Originally, the protective sheath consisted of a soft metal such as lead but these lead sheathed cords have now generally been superseded by those having sheaths consisting of Water resistant tape or textile wrappings, synthetic plastics and the like. The amount of explosive per foot of length in the core may vary from a small quantity of from 0.1 to about grains, as in low energy detonating cord (LEDC), to as much as 50 grains or more. Typical explosives employed as core material are, for example, pentaerythritoltetranitrate (PETN), cyclotrimethylenetrinitramine (RDX) nitromannite, lead azide, trinitrotoluene (TNT), cyclotatramethylenetetranitramine (HMX), lead stylphnate or tetryl and mixtures of these.

In the explosives industry detonating cords are manufactured by one or other of the dry or wet processes. In the dry process relatively coarse, particulate, dry explosive which comprises the core material of the cord is encased in a continuous column by means of a wrap of tape-like material and thereafter encircled by means of textile yarns or the like. The cord may thereafter be coated with a waterproofing surface layer of pitch, thermoplastic or the like. The dry process is normally employed in the manufacture of detonating cords having a core load of 25 grains or more of explosive per foot of length.

In the wet process, the core is formed from a thickened aqueous slurry of particulate explosive which is wrapped and covered in much the same manner as that employed in the dry process. Generally the wet process is employed in the manufacture of detonating cord having a core load of 4 grains or more of explosive per foot of length.

It has heretofore been the object and concern of the explosives industry to manufacture detonating cords having an absolute minumum of core load variation throughout the cord length in order to ensure constant detonation characteristics along the cord, in particular, uniform I lateral energy output. It has now been found that in 3,621,559 Patented Nov. 23, 1971 to provide a method of manufacture of detonating cord wherein the cord contains a continuous explosive core load, which core load comprises alternating sections of greater and lesser explosive energy.

Other objects of the invention will become obvious from a consideration of the following disclosure and claims.

The novel method of manufacture of the invention comprises the steps of continuously forming a braided textile stocking and directing a stream of slurried particulate explosive through an orifice in a continuous column into said' textile stocking in such a manner that regular, alternating sections of the explosives column within the stocking have different energy outputs.

The method of the invention and the product thereof may be more fully understood by reference to the accompanying drawings wherein:

FIG. 1 is a sectional view of one embodiment of a finished detonating cord made by the method of this invention;

FIG. 2 is an elevational diagrammatic view, of a portion of the apparatus suitable for use in the method of the invention;

FIG. 3 is an elevational diagrammatic view, partly in section of a portion of an alternative apparatus suitable for use in the method of the invention; and

FIG. 4 is a flow diagram of the process steps of the method of the invention.

Referring in detail to FIG. 1, there is shown a detonating cord 1 having an inner explosive core 2 which core comprises connected, alternating thick sections 3 and thin sections 4. Core 2 is encircled by braided textile stocking or sheath 5, which sheath has an outer covering 6 of, for example, a flexible thermoplastic material.

Referring to FIG. 2, there is shown pressurized storage containers 10 and 11, each containing a quantity of slurried, particulate explosive, for example, PETN. Leading from containers 10 and 11 are delivery lines 12 and 13 respectively, which lines terminate at air-operated valve 14. Air cylinder 15 is adapted to operate valve 14. Valve 14 comprises an exit line 16 having an orifice 17 to which the slurried exposive may be delivered from containers 10 and 11. Below orifice 17 is textile braiding head 18 by which means a braided textile stocking is formed on orifices 17 and is continuously withdrawn from orifice 17 as it is formed while at the same time the slurried particulate explosive is forced out of the center of orifice 17. Below braiding head 18, the textile covered cord 1 is delivered to a drying operation (not shown) preparatory to inspection and the application of an outer protective sheath or coating. Air lines 19 and 20 enter containers 10 and 11 respectively and pressurized air (from sources not shown) is directed into each of these containers. The pressure of the air in container 10 is different from the pressure of that of the air in container 11.

Referring to FIG. 3, there is shown an apparatus similar to that shown in FIG. 2 except that the valve 14 and air cylinder 15 of FIG. 2 are replaced by excentric cam 21 which is rotated by drive means (not shown) to activate pinch valves 22 and 23 which alternatively close off the flow of explosive slurry through lines 12 and 13 respectively.

Referring to FIG. 4, there is shown in sequential steps the various operations employed in the method of the present invention.

In one operation of the method of the invention employing the apparatus as shown in FIG. 2, a supply of typical detonating cord explosive, for example, PETN in suitable particulate form is prepared as an aqueous slurry by combining the PETN grains with a quantity of water and a suitable thickening agent such as, for example, hydroxy ethyl cellulose. A quantity of the PETN/water slurry is placed in each of containers and 11 and air pressure is applied to the surface of the slurry in each container through air lines 19 and 20. Air at, for example, 10 p.s.i. is applied to container 10 and air at, for example, 40 p.s.i. is applied to container 11. Air cylinder operates valve 14 in timed reciprocating motion by well known means (not shown) to allow delivery of the explosive slurry in alternating sequence from containers 10 and 11 and delivery 12 and 13 to exit line 16 and orifice 17. As the PETN slurry is forced from orifice 17 and into the braided stocking, it assumes a cohesive, string-like configuration having along its length regularly alternating thick and thin sections. The textile sheathed cord is then passed to a drying operation (not shown) and, after inspection, an outer covering of, for example, thermoplastic material is applied. The thus completed detonating cord may then be wound on a take-up spool for storage or shipment.

In the operation of the method of the invention employing the apparatus as shown in FIG. 3, all the steps described heretofore with respect to the apparatus of FIG. 2 are the same with the exception of the means employed to achieve an alternating or pulsating extrusion of the PETN slurry.

Referring to FIG. 3, it can be seen that when excentric cam 21 is rotated by a drive means (not shown) the flow of explosive slurry through line 12- and 13 is interrupted in a sequential manner by pinch valves 22 and 23 thus permitting the extrusion of the explosive slurry at orifice 17 in a column of thick and thin sections.

In the operation of the method employing either the apparatus of FIG. 2 or FIG. 3 and using a PETN explosive of grain size normally used for the manufacture of detonating cords of 4 grains or more of explosive per foot of length containing a small percentage of water and thickener, it has been found that air pressure of about 10 p.s.i. on container 10 or 11 produces a detonating cord section containing an average explosive load of 24 grains per foot of length when the orifice 17 has an internal cross section of 0.166 inch. An air pressure of about 40 p.s.i. produces an average core load of 52 grains of explosive per foot of length through the same orifice. Employing air pressure of 10 p.s.i. in container 10 and 40 p.s.i. in container 11 therefore produces alternating core loads in a continuous length of detonating cord of 24 and 52 grains per foot respectively. These core sections of greater and lesser quantity of explosive which take the form of thick and thin sections of core load may be any length as desired since the section length is a function of the length of time the slurry is permitted to flow from the alternative sources of supply. It will be obvious that the quantity of explosives in each of the thick and thin sections of the detonating cord can be varied depending on the thickness or density of the explosive slurry and on pressure of the air delivered to each of the storage containers. Too thin a slurry will generally result in an unsatisfactory product.

It will be obvious from the foregoing description that detonating cord comprising alternating connected sections of greater and lesser explosive energy may also be produced through the use of, for example, explosives having dilferent energy values or strengths. That is to say, the continuous column or core may comprise, for example, a section of PETN adjacent to a section of TNT with the sequence thereafter repeated. It will also be obvious that a combination of quantities and kinds of explosives may be used in the alternating core. For example, one section may comprise a core load of, say, 50 grains per foot of PETN and the adjacent section may comprise, say 25 grains per foot of TNT, or vice versa. The production of such cords using the apparatus shown in the figures of the drawing may be readily accomplished by placing a selected slurry of PETN in container 10 and a selected slurry of TNT in container 11. Application of appropriate air pressure to each container will provide extruded sections through orifice 17 of explosive of alternating explosive energy. Similarly the explosive adapted for use in the cord section of lesser energy may comprise a useful particulate explosive such as PETN mixed with an inert adulterant in order to further reduce the actual quantity of explosive present in the cord section and hence also reduce the explosive energy upon detonation of the cord.

It will be appreciated that a wide variety of slurriable particulate explosives and mixtures thereof may be utilized for the process described.

EXAMPLE To demonstrate that the detonating cord made by the method of the invention comprises areas of greater and lesser explosive energy, the following procedure was followed. A detonating cord similar in configuration to that shown in FIG. 1 of the drawing was prepared by the method hereinbefore described and the apparatus of FIG. 2 wherein the areas of lesser cord diameter contained 24 grains of PETN per foot of length and the areas of greater cord diameter contained 52 grains of PETN per foot of length. A length of this detonating cord was located along the central radial axis of a cold drawn Inconel (registered trademark) steel alloy tube having an outside diameter of 0.75 inch and a wall thickness of 0.056- inch. The open ends of the tube were stoppered after the space between the detonating cord and inner wall of the tube was filled with water. The cord was initiated by means of an electric blasting cap and the degree of expansion of the tube was then measured at points along its length. The tubing sections adjacent the 52 grains per foot sections of the cord were found to have expanded to an average diameter of 1.005 inch, an increase in diameter of 0.255 inch. The tubing sections adjacent the 24 grains per foot section of the cord expanded to an average diameter of 0.875 inch, an increase of 0.125 inch. Thus it could be seen that the cord of the invention comprised alternating areas or sections of greater and lesser explosive energy as measured by the expansion of the metal tube.

From the foregoing example it can be seen that the detonating cord produced by the method of the invention may be employed, for example, to expand a metal tube within a tube sheet where the tube apertures are of stepped, tapered, or uneven configuration. The expansion of a tube within both the narrower access or neck of the tube sheet aperture and the larger or wider area of the aperture by conventional mechanical tube expansion means is not possible. The detonating cord made by the process of the present invention, however, may be usefully employed for such purposes by the judicious location within the expandable tube of a detonating cord having alternating sections of dilferent explosive energy. Additionally, such a cord may be employed for purposes of expanding tubes into tube sheets by the method disclosed by Irwin Berman et al. in United States Pat. No. 3,411,198 granted Nov. 19, 1968.

I claim:

1. A method of continuously producing detonating fuse cord having along its length regular alternating sections of different potential energy outputs comprising the steps of:

(a) continuously forming a braided textile stocking;

(b) continuously ejecting a stream of slurried particulate explosive in regularly varying amounts through an orifice and into said textile stocking, thus forming into said stocking a continuous column of explosive having regularly alternating thick and thin sections; (c) drying the filled, braided stocking; and (d) covering the dried, filled, braided stocking with a protective sheath.

2. A method as claimed in claim 1 wherein the stream of slurried explosive is ejected by pneumatic force.

3. A method as claimed in claim 1 wherein the par- 3,318,242 5/1967 Griffith 102-27 X ticulate explosive is selected from the group consisting of 3,367,266 2/ 1968 Griffith 102-27 pentaerythritoltetranitrate, cyclotrimethylenetrinitramine, 3,382,802 5/1968 Prior et a1. l02-27 nitrornannite, lead azide, trinitrotoluene, cyclotetramethyl- 3,435,764 4/ 1969 Kelly et a]. 102-27 ene tetranitramine, lead stylphnate, tetryl and mixtures of 5 th JOHN F. CAMPBELL, Primary Examiner References Cited v. A. DIPALMA, Assistant Examiner UNITED STATES PATENTS US Cl XR 1,275,001 8/1918 Dormer 102-27 10 R 1,674,773 6/ 1928 Fritzsche 10227

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