US2891476A - Delay blasting devices - Google Patents

Description

June 23, 1959 w. FORSYTH DELAY BLASTING DEVICES Filed March 15, 1956 DELAY BLASTING DEVICES William Forsyth, Stevenston, Scotland,assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Application March 15, 1956, Serial No. 571,739 Claims priority, application Great Britain June 22, 1955 3 Claims. (Cl. 102-27) The present invention relates to a new or improved form of delay blasting device adapted for use when it is desired that a plurality of blasting explosive charges connected together by a detonating fuse should detonate at predetermined time intervals between the detonations insteadof simultaneously. t

In British patent specification No. 708,422 there is described and claimed inter alia a device comprising two metallic tubular sheathing elements connected by a length of tubing of distensible resilient shock absorbing flexible material in which device one sheathing element retains therein in fixed position an instantaneous detonator and the other a delay detonator so that the closed end of the instantaneous detonator and the open end of the delay detonator each point toward said tubing, said tubing being of narrower diameter than that of the tube of the instantaneous detonator,'and each sheathing element at its end remote from said length of tubing of flexible ma terial being open and of such diameter as to permit the insertion of a length of detonating fuse.

The object of the present invention is to provide a delay blasting device of the kind which includes a length of tubing of distensible resilient shock absorbing flexible material between two detonators which in contradistinction to the device of British patent specification No. 708,422 is reversible and which is simpler in construction, is more reliable and is safer to handle than the device of British patent specification No. 708,422.

In contradistinction to the reversible delay blasting device disclosed in German patent specification No. 915,197 the present invention does not sufier from the disadvantage of having a delay composition juxtaposed to the detonating explosive intended to ignite it because instead of being ignited said delay composition may be blown away without initiating the next explosive charge or may burn at a rate much higher than expected from its behaviour when ignited by non-detonating means. The device of the invention permits consistent and reliable delay times of the order of for instance to 100 milliseconds to be obtained as are required in so-called short delay blasting operations.

The device according to the invention comprises two delay detonators of like delay characteristics each retained in a thin walled tubular sheathing element in which device the mouths of the casings of said detonators are connected by a length of tubing of distensible resilient shock absorbing flexible material of narrower external diameter than the internal diameter of said mouths and each sheathing element at its end remote from said length of tubing of flexible material is open and of such diameter as to permit the insertion of a length of detonating fuse.

Preferably in each of said delay detonators the delay composition in the delay element is positioned at the end further removed from the primary charge of the detonator.

Said lengths of tubing of distensible resilient shock absorbing flexible material may be for example of natural ted States Patent .0 F

detonator.

2,891,476 Patented June 23, 1959 rubber, polymerized chloroprene (neoprene), polymerized butadiene or interpolymers of butadiene or acrylomtrile.

Each delay detonator is retained in position in the tubular sheathing element preferably by crimping.

If the delay detonator casings are to be attached by crimping to the tubing of distensible resilient shock absorbing material it is desirable to provide a short length end of the device as hereinbefore defined. The attachment of the lengths of detonating fuse may conveniently be achieved by crimping.

When the device of the invention has attached at each end a length of detonating fuse and one of these lengths is detonated at its end further away from the device the wave of detonation will upon arrival at the device initiate the detonation of the explosive charge in the delay detonator at that end and the detonated explosive charge will ignite the delay fuse composition in the same delay The flame gases and hot particles thus produced then pass through the tubing of distensible resilient shock absorbing material which presents to them a constricted but expansible passage adapted to minimise the shock to the delay element of the second delay detonator whose delay fuse composition will be ignited and, after the expiry of its proper and characteristic time delay, will initiate the main explosive charge in said second delay detonator, and this detonated explosive charge in turn will initiate the detonation of the other length of detonating fuse.

The invention is illustrated by way of example with reference to the diagrammatic drawing accompanying the specification which represents a longitudinal section showing a device in accordance with one form of the invention interposed in a line of detonating fuse.

In the diagrammatic drawing, 1, 1 are tubular sheaths made of metal capable of being crimped and are of a somewhat smaller diameter at one end than the other. 2, 2 are metal detonator casings each with its closed end facing the narrower end of its sheath 1. 3, 3 are lengths of flexible textile covered and externally waterproofed detonating fuses having a core of pentaerythritol tetranitrate. Each metal detonator casing 2 is charged with a primary initiating explosive charge 4 consisting of lead azide and a pre-mixed lead azide lead styphnate and aluminiurn powder composition 5 adjoining said primary charge 4 on the side further from the closed end of the detonator casing 2. Abutting each of said compositions 5, 5 there is provided a thick walled metal tube 6 having pressed into its bore at the end removed from the primary charge 4 a deflagrating delay composition 7 consisting of lead dinitroresorcinate with a samll proportion of graphite. Each of the aforesaid metal tubes 6, 6 is a press fit inside its detonator casing 2.

8 is a thick walled neoprene tube having at each end a short rigid metal tube 9. The thick walled neoprene tube 8 is crimped at each end into a detonator casing 2 at 10. The tubes 9, 9 are too short to abut when inserted into tube 8.

Each of the flexible textile covered and externally waterproofed detonating fuses 3, 3 is crimped into one of the tubular sheaths 1, 1 at 11.

The blasting device so formed is symmetrical about a line A--A drawn through the centre of the thick walled neoprene tube 8 at right angles to its bore.

In assembling the device a delay detonator (2, 4, 5, 6, 7) is inserted into the end of larger diameter of a tubular sheath 1, with its closed end first, as far as it will go, and a length of thick walled neoprene tube 8, cut to the requiredusiz'e and witha tube-9 in position at each end thereof,--is insertedhalf way into the detonator (2, 4, 5, 6, 7). A second delay detonator (2, 4, 5, 6, 7) is-inserted into itstubular sheath 1 in the same way as the first mentioned detonator (2, 4, 5, 6, 7) into-its sheath 1 and into this second mentioned detonator theother elnd'of the thick walled neoprene tube 8 is inserted. The thick walled neoprene tube 8 is of such length that when inserted into the two detonators only a small clearance is left between each of the thick walled metal tubes 6, 6 and the respective end of said length of thick walled neoprene tube 8. Each tubular sheath 1 is crimped at 10 to the length of thick walled neoprene tube 8.

Theireliability of the device of the invention is shown by way. of example by the following results. It is found for 100 devices of the invention, each device having its two delay detonators each of 17 milliseconds delay time, that when each device is formed into an assembly by connecting each of its ends to a length of detonating fuseand the. assembly fired the delay time for each devicelliesbetween l4 and 19 milliseconds as determined byan electronic tinre-interval measuring instrument.

Whatwe claim is:

l. A, flexible delay connector for lengths of detonating fuse including: a pair of like tubular delay detonators, each of said detonators having an open mouth at one end thereof and a closed base at the other end thereof, said mouthsbeing arranged in spaced opposed relation, a length of thick walled flexible tubing joining said detonators and extending through said mouths and into saiddetotnators, the major portion of said flexible tubing-being contained within said detonators, and the exposed portion of said flexible tubing between the open mouths of said detonators being of such short length as to preventsubstantial bending; an open ended sheath surrounding each of said detonators, said sheaths each being provided with an inwardly extending shoulder against which the base of the ensheathed detonator abuts, a short tubular tail on each of said sheaths of reduced but surficient diameter to accommodate the end of a length of detocnating fuse; and a waist portion in each half of the delay connector, said waist portion being disposed intermediate the length of each of said sheaths and being defined by'reduced transverse sections in said flexible tubing, said detonator, and said sheath.

2. The structure defined in claim 1 wherein a detonating charge is arranged in eachof said detonators adjacent the base thereof, anda delay composition arranged in each of said detonators in spaced relation to the detonating charge therein.

3. A flexible delay connector for lengths of detonating fuse including: a pair of like tubular delay detonators, each of said detonators having an open mouth at one end thereof and a closed base at the other end thereof, said mouths being arranged in spaced opposed relation, a length of thick Walled flexible tubing joining said detonators and extending through said mouths and into said detonators, the major portion of said flexible tubing being contained within said detonators, and the exposed portion-of said flexible tubing between the open mouths of said detonators being of such short length as to prevent substantial bending; a short length of rigid tubing disposed-within each endiof'the flexible tube; an open ended sheath surrounding each of said detonators, each of. said sheaths being provided with an inwardly directed shoulder against which the base of the ensheathed detonator abuts, a short tubular tail on each of said sheaths of reducedbut suflicient diameter to accommodate the end of a length of detonating-fuse; and a waist portion in each half of the delay connector, said waist portion being disposed intermediate the length of each of said sheaths and being defined by reduced sections in said flexible tubing, said detonator, and said sheath.

ReferencesCited in the fileof this patent UNITED STATES PATENTS 2,736,263 Lewis etal. Feb. 28, 1956 2,750,831 Long June 19, 1956 2,757,566 ToWellet al. Aug. 7, 1956 2,796,834, McCaflErey et a1 June 25, 1957 FOREIGN PATENTS 708,422 Great Britain May 5, 1954 915,197 Germany July 15, 1954

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