Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06C—DETONATING OR PRIMING DEVICES; FUSES; CHEMICAL LIGHTERS; PYROPHORIC COMPOSITIONS
  • C06C5/00—Fuses, e.g. fuse cords

Definitions

• the invention relates to delay cords, that is to say to cords containing a pyrotechnic composition with a relatively slow combustion rate, which is confined in a generally metallic sheath.
• these compositions mainly combine a reducing agent such as boron, magnesium, aluminum, silicon, titanium, manganese, chromium, zirconium, niobium, molybdenum, tungsten or thorium with an oxide of transition metal or to one or more oxygenated oxidizing salts of alkali or alkaline earth metals such as chlorates, perchlorates, nitrates, oxides, peroxides, chromates and dichromates of these metals.
• a non-negligible proportion of these compositions may consist of inert materials intended to reduce the liveliness of the composition.
• compositions of this type which are very conventionally used in relay-delays are defined by American military standards MIL-T-23132 of December 21, 1961 and 23132A of June 16, 1972. They are for example used in American patent 4 144 814 and consist of mixtures comprising from 30 to 60 % by weight of tungsten with a particle size between less than 1 micron and 10 microns, from 30 to 60% by weight of barium chromate, from 5 to 9% by weight of potassium perchlorate and approximately 5% of silica, in the form of diatomaceous earth.
• the delay relays are relatively large metal parts since the delay column, that is to say the part which contains the pyrotechnic composition, has a diameter of at least 5 mm therein, while the outside diameter of these devices is meanwhile at least 8 mm.
• a delay cord having an internal diameter of 1 mm in diameter can only have a combustion speed greater than about 10 mm / s for an outside diameter of at least 12 mm since any reduction in the thickness of the metal wall of the cord can only increase the combustion speed of the latter.
• the invention relates to a delay cord having a combustion speed less than or equal to 4 mm / s, characterized in that it has a diameter less than or equal to 3 mm and in that it contains a composition.
• pyrotechnic sition consisting of 25 to 45% by weight of tungsten with a particle size between 2 and 6 microns, preferably between 2 and 4 microns, from 45 to 65% by weight of an alkali or alkaline earth chromate or dichromate and from 8 to 15% by weight of alkaline or alkaline earth perchlorate.
• an alkaline or alkaline earth chromate is used in preference to an alkaline or alkaline earth dichromate and an alkaline earth chromate in preference to an alkaline chromate.
• the barium chromate is particularly preferred. Mixtures of different chromates or dichromates can be used.
• an alkaline perchlorate is used in preference to an alkaline earth perchlorate.
• Sodium perchlorate and, above all, potassium perchlorate are particularly preferred.
• Ammonium perchlorate is less advantageous because its use leads to an increase in the rate of combustion of the composition. Mixtures of different perchlorates can be used.
• tungsten is used having a particle size between 2 and 4 microns.
• a particle size greater than 4 microns and less than 6 microns is used, there is a risk of ignition defects in the composition, in particular when the latter contains less than 35% by weight of tungsten. Tungsten cannot be replaced entirely by any other metal.
• the filling composition of the delay cord comprises only from 28 to 35% by weight of tungsten with a particle size between 2 and 4 microns, from 55 to 62% by weight of chromate of barium and 9 to 12% by weight of potassium perchlorate.
• the incorporation of silica is unacceptable in the compositions used in the context of the invention.
• the outer envelope of the delay cords according to the invention is produced in a conventional manner from a metal or a metal alloy preferably ductile and with a low melting point.
• a metal or a metal alloy preferably ductile and with a low melting point.
• Lead and lead-based alloys especially those based on tin and / or antimony are very suitable.
• the delay cords according to the invention can be manufactured in a usual manner and known per se. For example, they can be obtained from a ductile metal cord of relatively large diameter (10-25 mm), containing the composition indicated above, by passing said cord through dies of decreasing diameters. The delay induced by the string can be precisely adjusted by measuring the rate of combustion of a fragment of the latter leaving the die.
• the cords according to the invention can also be obtained by progressive reduction of the diameter by successive passages in the various grooves of decreasing sections of a rolling mill or by a series of passes to the rolling mill followed by a series of passes in dies. A section reduction ratio at each pass of the order of 0.9, conventionally used, is suitable.
• the delay cords according to the invention have an outside diameter of between 1.5 and 3 mm and a ratio of the outside diameter of the delay cords to the diameter of the core occupied by the pyrotechnic composition of between 1.4 and 2.0 .
• the actual density. of the compositions which they contain is in practice much lower than the theoretical values and between 2.7 and 4.0 g / cm 3 , preferably between 3.0 and 3.4 g / cm 3 .
• the delay cords according to the invention also show excellent thermostability since their self-ignition temperature is commonly above 500 ° C. Furthermore, their exceptionally low combustion speed, given the smallness of their diameter, undergoes only a very small variation depending on the temperature: a variation of only 10% is commonly observed between - 60 ° C and + 75 ° C, which is considered remarkable.
• the delay cords according to the invention make it possible to ensure, with a excellent reliability and in a wide range of conditions, delays of a few tens of seconds to several minutes and even several hours while occupying a very small volume and releasing little combustion heat, which ultimately has the effect of considerably reducing the weight of thermal protections surrounding said delay cords, in pyrotechnic systems on board spacecraft or submarines.
• the delay cords according to the invention are illustrated by the following nonlimiting examples:
• a 5% antimony antimony lead tube 17 mm in outside diameter and 12 mm in inside diameter was filled with a composition consisting of 32% by weight of tungsten with a particle size of 2 microns, 58%. by weight of barium chromate and 10% of potassium perchlorate.
• the latter is done in small successive quantities of a few cm 3 and, after each introduction, the composition is compacted using a piston by applying a pressure of approximately 16 bars.
• the tube closed at each end by a lead plug is then transformed into a cord with an outside diameter of 2 mm by a series of passages in successive dies of decreasing diameters; the section reduction ratio at each pass is of the order of 0.9 so that 20 passes are necessary to obtain said delay cord whose internal diameter is 1.26 mm.
• This cord has a combustion speed of 3.4 mm / s. Just 20.4 cm of cord to induce a delay of 60 seconds in a pyrotechnic chain.
• the delay cord was further tested in accordance with Example 13.
• the density of the composition it contained was 3.2 g / cm 3 .
• Its combustion rate is surprisingly stable since it goes from 2.44 mm / s at room temperature to 2.31 mm / s at - 60 ° C and to 2.5 mm / s at + 70 ° C.
• the cord still works perfectly. It does not self-ignite until around 510 ° C.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Air Bags (AREA)
• Fuses (AREA)

Applications Claiming Priority (2)

Publications (4)

Family

ID=9229401

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (9)

Family Cites Families (7)

• 1979
  • 1979-09-06 FR FR7922278A patent/FR2464932A1/fr active Granted
• 1980
  • 1980-08-20 EP EP80401194A patent/EP0025732B2/de not_active Expired
  • 1980-08-20 DE DE8080401194T patent/DE3065888D1/de not_active Expired
  • 1980-08-21 US US06/179,973 patent/US4356768A/en not_active Expired - Lifetime
  • 1980-09-03 JP JP12126580A patent/JPS5641894A/ja active Granted

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