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

• 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, 2 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.
• 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 and containing a pyrotechnic composition based on tungsten, barium chromate and potassium perchlorate, characterized in that it has a diameter less than or equal to 3 mm, the ratio of the outside diameter to the diameter of the core occupied by the pyrotechnic composition being between 1.4 and 2.0 and in that this pyrotechnic composition is free of silica and consists of 25 to 45% by weight of tungsten with a particle size between 2 and 6 ⁇ , from 45 to 65% in weight of barium chromate and 8 to 15% by weight of potassium perchlorate.
• 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.
• a woven sheath or an extruded synthetic material is also possible to use.
• 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 with 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 generally have an outside diameter of between 1.5 and 3 mm and a 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 greater than 500 ° C. Furthermore, their exceptionally low combustion speed taking into account the weakness of their diameter is only subject to very small variation as a function of 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.
• 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 on 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 speed 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)

Families Citing this family (10)

Family Cites Families (7)

• 1979
  • 1979-09-06 FR FR7922278A patent/FR2464932A1/fr active Granted
• 1980
  • 1980-08-20 DE DE8080401194T patent/DE3065888D1/de not_active Expired
  • 1980-08-20 EP EP80401194A patent/EP0025732B2/fr 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

Also Published As

Similar Documents

Legal Events