AU619925B2 - Conducting primer compositions - Google Patents

Description

THE 4COMMONWENLTH OF 'AUSTRALIA 31 Slgna- lure of or Scal of C ompany and 2 linatures of 1 s A4.f 'les or Assoclatifn.

BY/

D/ RY L B. MISCHLEWSKI REGISTERED PATENT ATTORNEY 4' I~~jI] jr.ii ,i Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952.69 COMPLETE SPECFICATIJU (ORIGINAL) 619 Clans 10. Class Application Number: Lodged: PJ 1757 05.12.1988 Complete Specification Lodged: Accepted: Published: Priority:, Relatod Art: :Nplitec'f Applcant: Address of Applicant: THE (fl'M0WE ALTH OF AUSTRALIA C/o Departmrent of Defence, Assistanit Secretary Industry Operations, Anzvic Park West Building, CANB3ERRA, A,CT, 2600.

*Ae~i~ nvnor: JUfIN R, BENTLEY Addr s for Service: MW O Q M, WATEMARK PATENT TRADENAR ATJXJPNEYS, 2ndFlor, The'Atrium", 290 Burwood Rd, Hawthoo,Vctra Australia.

Complete Specification for the Invention entitled: 0440,"CONDUCTING PRMER C(XIPOSITIONS", Thelfollowing statement Is a full description of this Invqrntion, including the best minhod of performing It kiITOWn to0'PS' ,I Niln.r is the assignee of the said .ACTUA.L INVEN.TOR o[ AcLtual Inventor or ParngraPh 2 ulshould he I *completed by show ing de- D a 4. volutlon of DECLARED at title, he sad i .'th is .4t..

2- CONDUCTING PRIMER COMPOSITIONS This invention relates to conducting compositions for use in primers and for use in detonators.

Generally electrically activated explosives use bridge wire devices for actuation. Such devices are relatively are expensive and difficult to produce.

The present invention is particularly concerned with applications where power insensitivity is particularly o important.

US Patent 4,605,453 discloses a conducting composition for use in a firing cap which has high energy insensitivity. The power sensitivity however is particularly low. Devices containing these compositions can be initiated with power of less than one watt. It is important in designing primers and detonators that they comply with a requirement of being insensitive to both one amp or one watt.

It is an object of the pcesent invention to provide ia conducting composition which complies with these 20 requirements, To this end the present invention provides a "0 ',,.conducting composition suitable for use in a detonator consisting of 2 to 10 parts by weight of carbon black and or graphite 40 to 80 parts by weight of lead styphnate the 9* s balance being lead oxide or other explosive or non-explosive material said composition being formulated to epsure insensitivity to 30 one amp of current or one watt of power.

It is preferred that the conducting composition utilise normal lead styphnate which has a mean particle size not less than 5 microns in admixture with carbon black or graphite which has a mean aggregate size between 0.5 microns and 15 microns.

tr r 3t Howevev, a failing of the compositions taught in the US Patent is that they do not have good power or current insensitivity.

It is a preferred requirement of one aspect of the present invention that the content of carbon black is adjusted to provide resistance within the range of half to three ohms. This requirement compares with resistance levels ranging upwards from 16 ohms in US Patent 4,605,453.

In preparing compositions according to this aspect of the present invention, the voltage and current sensitivities are approximately the same and this can be achieved by preferably adjusting the composition to have a nominal resistance of approximately 1 ohm.

However, where resistance is lower the speed or firing time of devices containing the composition is relatively slow. Generally for resistances of 0.8 to 1.2 flH ohms ard a firing current of 5 amps timcs of greater than milliseconds are expected.

In another preferred aspect of this invention 4 20 compositions of firing times less than 50 milliseconds and preferably less than 8 milliseconds for a firing current of 5 amps are provided which still satisfy the one amp, one watt insensitivity requirement. This is achieved by using graphite which has a higher conductivity than carbon black and adjusting the final resistance to 1.3 3 ohms. The E graphite can replace all or some of the carbon black 4 *4

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1 depending on the desired functioning time. Preferably at least one percent by weight of graphite is used.

S' It is to be noted that the firing tinte decrease is achieved with an increase in resistance and thus the current insensitivity may approach the threshhold of one amlp if the 4 resistance is too high.

C The following are particular examples of preferred formulations of this invention.

Example 1 One preferred formulation of the present invention comprises a conducting composition having the following composition: ji~,j i i

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CA

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p .55 -4 Carbon black (Tintacarb) 7.5% by weight Lead Oxide 30.0% by weight Lead Styphnate 62.5% by weight The energy and power sensitivity was determined from Breucton tests. Results were as follows: ENERGY Capacitance 2.95PF Increment 0.05 (log units) Number Tester Mean 3.764 (5808pJ) S.Dev 0.041 (log units) Energy Threshold 3.98 mJ POWER Constant Current Supply Increment 0.1A Number Tested Mean 2.3A S.Dev 0.18A Threshold C .rrent 1.58A Threhold Power i 2 R min Example 2 Carbon Black (Tintacarb) 2% by weight Graphite 2% by weiyht Lead Styphnate 66% by weight Lead Oxide 34% by weight This composition had a firing time of less than 8 25 milliseconds and was insensitive to one amp of current and one watt of power.

Example 3 Carbon Black 3.5% by weight Graphite 1% by weight Lead Styphnate 64.5t by weight Lead Oxide 30% by weight This composition had a firing time of less than 8 milliseconds and was insensitive to one amp of current and one watt of, power.

*0 0 Si 0* S i ~1 ii~~ ii ~wi The compositions of the present invention are useful in any situation where bridge wire devices are required to be replaced by a cheaper yet power insensitive device. A typical application is in relation to automobile crash bags where an electrically activated explosive charge is required to initiate inflation of the protective bag and this risk of unintended initiation must be low.

These conducting compositions can be used wherever electrically initiated detonators or igniters are used and can be formulated for a wide range of firing times and still be insensitive to one amp of current or one watt of power.

From the above description it can be seen that the present invention provides a new and useful conducting primer composition which overcomes difficulties associated with alternative initiating devices.

t t It c I I t i

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Claims (4)

1. A conducting composition for use in a detonator consisting of 2 to 10 parts by weight of carbon black and or graphite to 80 parts by weight of lead styphnate the balance being lead oxide or other explosive or non-explosive material said composition being formulated to ensure insensitivity to one amp of current or one watt of power.

2. A composition as claimed in claim 1 wherein normal lead styphnate is used in conjunction with carbon black or graphite so that the resistance is between 0.5 ohms and 3 ohms.

3. An electrically Initiated detonator, primer or igniter Incorporating a conducting composition as claimed in claim 1 or 2.

4. A detonator primer or igniter as claimed In claim 3 in which the firing time is less than eight milliseconds and the composition incorporates at least one percent by weight of graphite. DATED this 14th day of November 1991 THE COMMONWEALTH OF AUSTRALIA WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA 14 Ir,,c, I..