US 2900242 A
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IGNITER FOR GAS GENERATOR GRAINS AND PROPELLANTS Application December 16, 1958 Serial No. 780,902 g a 3 Claims. (Cl. 52-14) (Granted under Title 35, US. Code (1952), see. 266) No Drawing.
The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to igniter materials for use in the ignition of solid propellants.
Conventional ignition of solid propellants involves a chain reaction whereby an electric squib ignites an igniter material which in turn ignites the propellent grain. Black powder has been widely used in the past for the igniter material but possesses certain disadvantages. Erratic behavior results from the use of black powder due to variations in particle size, water content, and density of the pressed grain. Such igniter grains were pressed into shape while the material was moist and thus the water content could easily vary.
Additionally, some of the prior igniters other than those using black powder delivered too sudden a shock to propellent grains, resulting sometimes in chipping and cracking of the grain.
Accordingly, it is an object of this invention to produce an igniter material which will exhibit stable reproducible behavior on ignition.
A further object is to produce an igniter material which builds up pressure relatively gradually so as not to cause the propellent grain to chip or crack.
The above objects are accomplished by a mixture comprising polytrifluorochlorethylene, boron, and ammonium perchlorate. The polytrifluorochloroethylene used is an elastomeric material having a molecular weight in the range of about 500,000 to 1,000,000 and serves as a binder for the other two materials, as well as an oxidizer for the metal. The ammonium perchlorate used in the present compositions is preferably micropulverized and ranges in particle size from 1 to about 5 microns. Amorphous boron is preferred but the crystalline variety is operable if ground to about the same size as the ammonium perchlorate.
The proportion of boron used ranges from about 5.5% to about 7.5%, and the other two ingredients comprising the remainder of the composition are present in about equal amounts by weight. The range of boron is critical for applicants purposes. With the aforestated range of boron, gaseous BF and BCl are produced in the exhaust. With less boron, however, the toxic gases HF and HCl are produced. Greater amounts of boron will produce the solid product B 0 The compositions are made by dissolving the polymer in acetone and adding the correct amounts of boron and 2,900,242 Patented Aug. 18, 1959 ammonium perchlorate. The resulting slurry is thoroughly mixed and vacuum dried. The rubbery sheet resulting is cut up and milled, using Dry Ice to keep the material brittle. The material which passes through a 60 mesh screen is ready for use.
The comminuted material is then pressed into desired shape at 80 C. and 10,000-l5,000 p.s.i. Typically, the material is pressed into a disk with a central perforation. The perforated disk is put into a container, and a squib inserted in the container and positioned in close proximity to the disk. The container is then ready to be positioned in the central perforation of a propellent grain.
The igniter material can be made to burn faster if the central perforation of the disk is packed with loose powder of the same composition as the disk. This loose pow der is much less dense than the pressed disk and readily burns, providing the heat necessary to rapidly burn the much more dense pressed material.
In Table I below are presented data on the behavior of an igniter composition of 5.82% boron, 47.28% ammonium perchlorate, and 46.90% polytrifluorochloroethylene with a conventional ammonium nitrate-rubber base propellent grain. All igniters were of the aforementioned disk type with the central perforations packed with loose powder. The igniters were positioned in the central perforation of a propellent grain in a combustion chamber and actuated. The data were obtained by techniques well known in the art.
Table I Quantity of Igniter, Grams Smooth ignition and burning resulted in all cases with no pressure peaks recorded such as would indicate a chipped or cracked grain.
The igniter compositions do not absorb moisture from the atmosphere and are decidedly inert chemically under any conditions which would be encountered in ordinary handling and storage.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
What is claimed is:
1. An igniter composition comprising from about 5.5 to about 7.5% boron and the remainder ammonium perchlorate and poly-trifiuorochloroethylene is substantially equal amounts, the latter having a molecular weight range of about 500,000 to 1,000,000.
2. The composition of claim 1 in which the ammonium perchlorate is present in an amount up to about 1% in excess of the poly-trifluorochloroethylene.
3. The composition of claim 1 in which the boron is amorphous, and the ammonium perchlorate particle size ranges from about 1 to 5 microns.
No references cited.