US2935948A - Rocket igniter pellets - Google Patents

Description

S. J. PORTER ROCKET IGNITER PELLETS May 10, 1960 Filed Feb. 14, 1958 INVENTOR. Samuel J- Porfer ECKHOFF 75 .SZ/CK 5 4T RNEYs 5M A MEMBER OF THE PIE are' felect'rically -actuated;"After the'pellets V ignited, theyare dispersed onto the grain surface of the curs, .-y- Y U e t s Pa n 2,935,948 R'OCKET IGNITER PELLEIS Samuel .lliiorter, Scituate, Mass, assignor. to American ;;Potashz herni eal Qorporatipm-a corporation of Dela- Application February 14, 1958, Serial No. 715,421 2 Claims. 01.102-70 invention relates in generalfto pellets used for viduals are alsosuitable. The jacket must be consumed .1 at the. ignition --temperature' of the igniter pellet. The

use of. such a jacket or cup eliminates breakage and the formation of large-quantities of powder and dust during handlingof: the pellets and thus insures the tolledb ni The pellet may be entirely covered, one or two end.

surfaceslbeing' protected with very thin disks or sheetsof-metallic material of such'a thickness that the applica-- tion: ofnheat byvmeans of a squib of the type customarily employedin conjunction with igniters will cause destruc- -tion1of,thesurfacerprotecting disk or sheet. Alterna-- thepurpose of igniting themainpropellant charge of a rocketdevice, and more rocket igniter pellets.

' It is customary, practice in the rocket ignition arttov cause'ignition of the main propellant charge by burning a qt f1 tity'of' readily ignitable' pellets which are enclosed .ingthf igniter prior to firingand'ignited by squibsjwhich "e become particularly to a coating. for'thes'e rockegp'owder where they continue to-burn and cause ignition of the rocket propellant. These pellets ordi- 'narily jconsist .of antignition mixture suchas potassium perchlorate, 1 barium. nitrate and zirconium nickel alloy tively, a flat pellet surface may be left exposed, and the-- remaining surfaces and edges, which are normally more subject to chipping and breakage, covered with a suitable protective jacket or sleeve.

More particularly, it has been found that the igniter pellets ordinarily used in rocket igniters may .be pro- I tected,, moisture absorption controlled and improved quality control in terms of size and weight during manufacture obtained by .the simple expedient of. covering all or mostly all of the s urfaces of the pellets with a thin with a small amount of a binder ;'such as ethyl cellulose.

Thepellets have reasonable mechanical strength, comparable {to-ordinary. aspirin tablets, whichthey may resembledn sizeand shape. However, in. practice it has beenJfqundthatsince these pellets are usually packed in the igniter, they. tend, during handling and; transp'orta:

tion, to rub and strike against eachotherwithtresultant: attrition- ,and breakage. 1 The elfect {of this .1 is. that considerable dust. formation lioccurs. with consequent" large increase in total surface -of' the; ignition-mixtures Thus, i. when the igniter functions; it. very oftengexplodesgrather-z than ;burns in a controlled fashion jsincethere is :much

more ig'nitable surface than originally;intended. .In aothera 'i instances if considerable breakage and dust formation results, ,enoughgpackinga down ofthe material aroundthe-fi squibs m'q yuoccur that the fire from the squibs does DOLE? hit the i Further considerable wearon the dies used. v V I lfinally, since the pellets customarilyaree ter material, as intended ,and non-ignition: oc-

, I hemtheigniter.pelletsareformed into. as-.; p fisr' iz d,,cy i er u form z and w h s. om what difiicult to maintain and if the pellet compositions? contain such abrasive metalpowders as boron, there is.

posed. to.,.

the atmosphere for a period of timebefore use, they may absorb a certain amount their operation; I

Still another object of this invention is to provide for pellets and to provide a product which is moisture-resistant-and which will withstand rough handling;

Broadly, it:has been 'foundnthat rocket ignition devices wherein a' plurality of pellets are provided for dispersion. ontofa rocket grain surface after the ignition of the pellets may be improved substantially by providing exposed surface of the pellet, the metal being such a 'igreaterquality control in the -manufact-ure'ofigniter'" jacket pf metallie aterial, preferablyaluminum, magnesium or t itanium. lf all surfaces of each pellet are to be. pretected and none left exposed, a surface ,of sub-' stantial size,.such as one of the flat surfaces of an ordi-- f nary cylindrical pellet, should becovered with a metallic disk or sheet of a thickness no greater than about 0.005 inch and preferably 0.001 inch so that the heat supplied by the squib will cause destruction of this protective disk. or sheetrfol lowed by ignition of the pellet. The jacket (exclus ive.of thedisk or flat sheet protecting the single surface aforementionedishould be of athickness ofbetweelilabout.(LQOiandQQlO inch. To serve effectivelyitsifp'rifiiary purpose that is, to protect the pellet from physical damage duringhandling, it needbe of no greater ,-thickne ss;., than this. Additional metal merely reduces volume.

the ntirnber of pellets which; can be placed ina given burning, the metallic jacket itself is consumed mama-i tributes to. the igniter performance. be ignitable at or below theburning temperature of the igiiter composition, and thedisk fitted over one or both ends of the pellet must-be capable of igniting at a temperatu're which can be produced -by thesquib-fiame.

Hence, theigniter composition has been modified to include in-the formulation the metal represented by the jacket ahd, Where the igniter composition ordinarily in- ,cludes one of the metals. listed above, as part ofthe 'adrnixtd amount; of"

metallrepresented by the jacket. A prethe ,fdisk' -'covering the. flat surface of the; pellet, fab

ferreglthicknes'fs for thefjacket is-about 0.010 inch and for V excepthn efiaflsurfacey Figure z ho'ws"a'simuarpeuet provided with a 4 ""as' wiell as themetal jacket on the othersurfac'es';and

. a metallic jacket surrounding all or a largepartof the Figure 1,. wherein thepellet, generally 10, is sh0Wn-pr0-- vided with' the most elementary forfm jof protection cont,

or i sgnium. n h! a All s t e. fi indi- Fi-gui'e 3 is an isometric view-of the-rocket 'igniter =55 assembly,.partially cut away,sh'o wing the placementof the igizitersquib and the individual pellets surrounding the Gonsidering now the drawings wherein like characters reteritb v like parts throughout, attention is directed to I Patented May I O, 19cc desired con- "afores't'atedgthe jacket is composed, of titanium, magn uin, 'aluminum, zirconium or alloys of these Alse' suitable are the zirconium nickel alloys. Thus, on i The metal used must the. quantity thereof may be decreased by the thin 7 V aluminumi pr otective disk on the upper surface thereof from the pellet to show the interior structure thereof. The ignited mix of the pellet, designated 12, is protected on its lower surface and on the peripheral circumferential walls thereof with a metallic cup 14. The nppersurface is left entirelyunprotected since it is the curved edges which have the greatest tendency to chip and break off; Of course, it is possible to leave both flat ends of; the cylinder unprotected, the most essential feature being the protection of the more readily damaged curved walls of the pellet.

A modification of the invention is set forth inFigure-ZQ Metallic cup 16 covers the lower flat surface of the pellet and the peripheral circumferential walls, and isprovidd at the upper lip thereof with a fiang'e 18 which seryes '-'to fasten in place the fiat disk 20 provided for the of the upper surface of the pellet.

Figure 3 shows the entire igniter assembly, the base 22 having a squib initiator 24 of conventionals'ti'uotufe posi tioned upright in the center thereof-. 'Means 26 are provided for supplying an electrical itnp'ulsetothe squib initiator 24. The assembly is provided a" cover basket 28 which seats upon the base 22 andse'i'ves to hold the individual pellets, in the fashion shown, clustered about the squib. V The structure of the igniter assembly is conventional and need not be described in greater detailhe're. Also, various pellet compositions are knownto those in the art, and it is to be understood that any ofthse may be used. That is, any of the known pellet compositions may be used provided that it is desired only to take advantage of the protection-affording features of the jacket. However, in the preferred embodiment of the invention, the composition used in combination with the jacket is: one which ordinarily incorporates a metal or alloy as a portion of the customary formula. Thus, use of the jackets of this invention allows a substantial reduction in the quantity of metal used in'the'powder sinceth'e jacket itself is considered a portion of the formulation.

The placement of the metal has been shiftedlfrom the; interior of the pellet to the exterior thereof and hence it serves a twofold function simultaneously without adding any weight to the pellet. For example, a preferred embodiment of the invention involves an aluminumsleeve of 0.005 inch thickness filled with an igniter composi on The total width of the pellet including the sleeve is 0.290 inch and the thickness of the pellet is 0.125 inch,

The composition given above is to be contrastedwith the corresponding original igniter composition prepared foruse where an aluminum sleeve was lacking. Because of the absence of the aluminum in the form of the sleeve, the aluminum content of theigniter composition mustbe increased by the weight of the aluminum. inthe sleeve. Thus, the standard composition is as follows: 7

Ingredient: Percent by .weight Potassium perchlorate 62.30 Aluminum 12.50 50/ 50-zirconium/nickel c 12.50 Boron 8.70 Ethyl cellulose 4.00

A wide variety of igniter compositions are known .to those in the field which contain various metals suchas magnesium, aluminum, titanium, as weu'as zirconium (3) Loaded cups and zirconium-nickel alloys. For example, another very commonly used composition which may be modified readily by removing a portion of the zirconium-nickel alloy ordinarily contained in the composition and replacing it in the form of a protective sleeve, is the following composition:

Ingredient: Percent by weight Potassium perchlorate 30.00 Barium nitrate 16.00 Zirconium nickel alloy 49.00 Ethyl cellulose 5.00

In a series of tests, igniter pellets (hereinafter designated I276) were loaded into thin aluminum cups of 0.010 inch thickness and one end of each pellet remained exposed. These pellets were loadedinto an igniter basket of the type shown in the drawing and subjected toa regu lation jumble test for thirty minutes. 'The composition of the pellets tested was:

Ingredient: Percent by weight Barium peroxide 84.00 Toluidine, red pigment 0.50 Zinc stearate ...s 1.00 Magnesium powder 14.50

These pellets emergedxin better condition than did cel-- lulose nitrate-treated pellets similarly tested or uncoated pellets also tested in this fashion. p

In a further series of tests, these same pellets, following treatment as aforesaid, were ignited and the results compared. It was found that the pellets loaded into the aluminum cups burned with far less violence than did the other pellets. Details andresults of each of these tests are set forth below, i

The aforementioned igniter mix material for two of the tests was made into'pellets 0.280 inch in diameter and approximately 0.125 inch high. In one test, the uncoated pellets were used. In 'a' second test the pellets were coated with cellulose nitrate. This was applied by dipping the pellets twice in a 10% cellulose nitrate colloid in ethyl acetate. En the third test, the 1276 was consolidated into regular aluminum relay cups with the load'flush with the cup top. Approximately "grar'ns 'of each type, i.e., pellets, coated pellets, and jacketed pellets, were loaded into an igniter basket with cotton batting in the bottom and the top'sealed with a thin metal disk. The. loaded baskets were then subjected to the jumble test for 30 minutes. The results were as follows:

Type V Results I (I) Uncoated pellets bl early broken. I

Slight erosion of pellet edges.

(2) Coated pellets surface.

Each of the above three loaded baskets was assembled to an igniter base containing squibs and sustainer mix. Each was then fired in the results:

'Type' 1 Results A Quite a severe initial blow which moved the whole unit approximately five feet. The sustainer burned for 12.5 seconds.

Quite'a severe initial blow which moved the whole unit approximately three feet. Thesustainer burned for 11.5 seconds.

A mild initiallblow whichmov'ed the whole unit approximately one foot. The sus- 'tainer burnedt'or 10.5 seconds.

(1) Uncoated pellets (2) Coatedpellts (3) Loaded cups Additional tests have been conducted using titanium,

Only a few minute scratches on the powder open with the following magnesium, zirconium and alloys of these as well as zirconium nickel alloys, and it has been found that thicknesses substantially identical to those set forth above as suitable for aluminum may be employed with satisfactory results.

It is seen, therefore, that by the use of a sleeve, cup or totally encompassing jacket, it is possible to avoid the objectionable chipping discussed above as Well as securing a number of other advantages. In addition, when one of the metals suggested or an alloy thereof is used, such jacket will ignite and burn at a temperature less than theignition temperature of the igniter composition, and hence the. metalbecomes a part of the igniter I, formula.

However, it is necessary that the thickness of the metal sleeve and the disks used for covering the ends of the pelletsbe maintained to within therange of I thicknesses set forth earlier if the desired consumption of the metal is to be achieved Obviously many" modifications and variations of the invention as hereinbefore set forthfmay be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim: f.

1. In a rocket ignition device wherein a plurality of flat-ended cylindrical pellets consisting of an ignitable formulation containing at least one metal selected from the class, consisting of aluminum, magnesium, and titanium, loosely contact one anotherin a container therefor, atleast some of said pellets being juxtaposed to a minum, magnesium, titanium and alloys consisting solely I f. squib initiator therefor, the improvement comprising a sleeve of metal selected from the class consisting of alutial walls of each of said pellets, the thickness of said metal being at least about 0.005 inch and no greater than about 0.010 inch, either end of each of said pellets; re

m aining exposed, the metal of said sleeves servingas a portion of the total m'etal requirements ,of saidi'pelleted formulation, and entering into the burning mechanism If' the class consisting of aluminum, magnesium, and tita- 1 3 nium, loosely contact one another in a container there-,

for, at least some of said pellets being juxtaposedto a squib initiator therefor, the improvement comprising a cup of metal selected from the class consisting of aluminum, magnesium, titanium and alloys consisting solely of the foregoing metals encasing all but a single flat suref face of each of said pellets, the thickness of said metal 7 f cup being at least about 0.005 inch and no greater than about 0.010 inch, one end of each of said pellets remaining exposed, the metal of said cups serving as aportion of the total metal requirements of said pelleted formulation. v

References Cited in the file of this patent UNITED STATES PATENTS 1,036,176 Bichel Aug. 20, 1 912 7 2,072,671 Foulke Mar. 2 1937 2,124,201 Lewis July 19, 1938 2,561,670 Miller J. July 24, 1951 2,637,274 Taylor ;May 5, 1953 2,685,837 Sage Aug. 10, 1954' Spaulding Dec. 21, 19541

Claims (1)

1. IN A ROCKET IGNITION DEVICE WHEREIN A PLURALITY OF FLAT-ENDED CYLINDRICAL PELLETS CONSISTING OF AN IGNITABLE FORMULATION CONTAINING AT LEAST ONE METAL SELECTED FROM THE CLASS CONSISTING OF ALUMINUM, MAGNESIUM, AND TITANIUM, LOOSELY CONTACT ONE ANOTHER IN A CONTAINER THEREFOR, AT LEAST SOME OF SAID PELLETS BEING JUXTAPOSED TO A SQUIB INITIATOR THEREFOR, THE IMPROVEMENT COMPRISING A SLEEVE OF METAL SELECTED FROM THE CLASS CONSISTING OF ALUMINUM, MAGNESIUM, TITANIUM AND ALLOYS CONSISTING SOLELY OF THE FOREGOING METALS ENCASING SOLELY THE CIRCUMFRENTIAL WALLS OF EACH OF SAID PELLETS, THE THICKNESS OF SAID METAL BEING AT LEAST ABOUT 0.005 INCH AND NO GREATER THAN ABOUT 0.010 INCH, EITHER END OF EACH OF SAID PELLETS RE-

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