US 2497387 A
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MANUFACTURE-F FUSE rown'iiit AND FUSES Henryk Zenftman, Saltcoats, Scotland, assig'nor to Imperial Chemical Industries Limited, a cor 7 poration of Great Britain No Drawing. Application October 6, 1944, Serial No. 557,560. In Great Britain October 6, 1943 10 Claims. (01. 52- 2) considerable variation in their burning properties according to the prevailing atmospheric pressure,
which frequently causes inconvenience in -blast-" ing at high altitudes and in the production of military fuses. Mixtures of oxidising and reducing agents that react together with the formation of little or no gaseous products are free from this objection, and it has been proposed to em ploy as fuse compositions mixtures consisting of red lead and silicon. The reaction may be represented by the equation Unfortunately the range of fuse speeds that can be obtained in mixtures of red lead and silicon by variation in the relative proportions of two ingredients is very limited, and the burning speed at atmospheric pressure of fuses made from even the slowest burning mixtures composed of 'red lead and silicon is substantially faster than that of ordinary black powder fuse.
It is known that mixtures of silicon and potassium nitrate are capable of reacting exothermically when they are strongly heated, but they cannot be used as fuse compositions sincethey are incapable of propagating the reactionprogressively through a train of small cross sectional area. This reaction proceeds with the evolution" of gas and the formation of a glowing residue, and may be represented as follows: a
I have now found that by using potassium nitrate and red lead together as oxidising agents for silicon fuse compositions, fuses capable of burning vigorously at a wide rangeof burning speeds are obtained, and more particularly-the production of fuses burning vigorously atlowerspeeds than those that can be obtained by the use of mixtures of red lead and silicon alone, is
According to the present inventlon fus-co rnpositions comprise a pulverulent mixture of potas sium nitrate, red lead and silicon, g
The amounts of potassium nitrate, red leada d silicon can lie between 50-15%, 30-60% and 10-40%, respectively, and preferably between -55 tion in the atmospheric pressure.
40-20%, 40-60% and 20-30%, respectively.
The burning speeds of the resulting fus powders depend both on the relative amounts of potassium nitrate and red lead present in the oxidising component of the mixture, and on the silicon content of the composition. The minimum fuse speeds that can be attained become progressively slower as the potassium nitrate content of the oxidising component is increased towards the limit that can be tolerated without rendering the composition incapable of propagating the reaction along the fuse. Up to a point the effect of excess of silicon over the stoichiometric proportion, calculated from the foregoing equations, is to increase the fuse speeds; but as the excess of silicon is progressively increased the resulting fuse speeds approach a maximum, and may become slower before sufficient silicon has been included in the composition to render the fuse incapable of burning steadily.
For any particular proportion of potassium nitrate in the oxidising component it is preferable to employ a composition containing the less of any two excesses of silicon that will give a fuse of the desired speed, since the resulting fuse composition will be the more vigorously burning of the two.
But the presence of progressively increasing proportions of potassium nitrate renders it possible to include progressively higher amounts of excess silicon in the mixture.
When the ratio of'the amount of potassium nitrate to that of red. lead is low, no excess of silicon over the stoichiometric proportion need be employed, or it may even be permissible that there should be a slight deficiency of silicon, but as the potassium nitrate content of the oxidising component is increased it becomes necessary to employ a progressively increasing excess of silicon to render the fuse powder capable of propagating the reaction. The maximurn excess of silicon that can be used without rendering the fuse incapable of propagating the reaction also increases.
The fuse compositions produced according to the present invention yield a certain amount of gas amongst the products of their combustion, thus providing for end spit, a characteristic absolutely indispensable in non-detonating fuse in order that it may be operative to set off a detonator into which it may be crimped. But, by means of the invention, it is possible to obtain fuse compositions burning at speeds comparable with those obtained from black powder fuse compositions, that are substantially less liable to variation in their burning properties with varia- This is bei cause, in the new fuse compositions, the gaseous component of the products of combustion can be so much smaller in proportion to the total amount of said products than is the case with black powder fuse.
In putting the invention into effect the pulverulent ingredients may be mixed together in any order but preferably the pulverulent mixture is produced by first admixing potassium nitrate and red lead and thereafter admixing this mix-r ture with silicon. The fuses may be made with a core of the pulverulent fuse composition in powder or rod form containing .a binding agent, or preferably with corned granules containing gum, nitrocellulose or an artificial resin, in the customary fashion; but the composition may also be made into an imporgus mass bymeans of a thermoplastic binding agent, for instance a gelatinised nitrocellulose composition, -.so that it can be extruded at arsuitably raised temperature to forma core around which anenvelope is applied. It will be understood that the burning speed of the fuse so produced may differ considerably-from that of fusehaving a core of the powder or corned :fuse composition.
For the purposeof studyand-comparison of the burning speedsof these compositions, a testing method known as the lead fuse test may be used.
In this test, lead tubes of specified size and weight are filled with thefuse powder to'be tested, and are sealedand drawn through dies until they have-been reduced to aspecified standard diameter. -middle portion ofthe filled and drawn tube, and
Measured=lengthstare then cut from the the speed of burning of these lengths is then measured at any-desired pressure.
Since the lead sheath is melted bythe heat of combustion of the fuse powder, thegaseous combustion-products aresubstantially unconfined and the burning takes placeunder-the prevailing barometrio pressure.
The burningspeedsof the fuse made in accordance with the present invention maybe somewhat increasedby embeddinginthe .core a soft =metalwire, for instance of 20 19040 standard wire gauge diameter.
' The invention is illustrated :by the following -examples,- in which the parts are parts: by weight:
Exampl 1 .Thefu e powder i m de b m siee ed l ficatiqn s eve. ndsili ons v sl t pass a itis Standard ecifica on Sieve In t jesidis ns. com onen t redl ad and t e po s- .sium nitrate r resent in h pro o tion 78.52 1 nd hen ili a in var u ron on f om i met c u wa s- .Th lea fuse .speeds of the resulti g fuse powders at one atmosphere pressure are approximately as follows:
The; ingredients usednare the-same as,in Example ..;1, but th red eadandnot ssiu nitrate i e 1*. we sees 31 are used in the proportions 71.422815. The lead fuse speeds of the resulting fuse powders at one atmosphere pressure are approximately as follows:
Percentage S Silicon r-gconds Excess Per Yard :In we ab e cen an 9i sil o h l fuse-failstopropa ate.
E mp eh ingre ie ts u ed are thesa e a n EX- nle bu th red ea and P ta si n t are used in-theproportions of 55.534 5. The lead fus -s eeds .qf h resnltiqs f se wqde s t n atm sphere P eset? .ep mxima el a 1.-
-:9 spqn2 n ls diyse speeds e iuse 991E1- ro iti ps-rnadswith es 1 1 and si con on .:ra-. ee'.-fm.a 32 st second .ner a d with .1 excess silico to ab. t 131; seconds per yard with 35 .ate Thec n ssiti s .QtEx mrfle 1 containi om tow-pe entexcssss at s ,qqmpe iiiqns Ex m leq nta s supl 60 e cent. assess sil lcnnrand' these o conta nin u to oi exc lle tqual- .ity .whenihet zm wi .ORS e nss lwith sum a provided t wate w n ted text l envelqps after thefashion custom rily employed for the manufacture of safety-fuse from black powder.
ss ssg silken that see he ;cllid. d is .ws than-tin the eas 9f lea fus hus wh n ll lfl p red ead onota smm u e huminsstees et a ou can be ob a ne b use of a eitdffseciid's per :3.% excess. of silicon,
100 C. The red lead and the potassium nitrate are present in the proportions 55.5:44.5. The ratio of the amounts of powder to binding agent is 70:20, and the approximate diameter of the extruded fuse core is 0.06 inch. In the pulverulent ingredients the silicon is present in an excess of 12.5 per cent over the theoretical. The extruded core composition is coated with a textile covering spun around it and the envelope is waterproofed. The resulting fuse has a speed of about 320 seconds per yard at one atmosphere pressure.
Example 5 The procedure is the same as in Example 4, but the diameter of the extruded core is .08 inch. The relative proportions of red lead and potassium nitrate and the ratio of powder to binding agent are the same as in Example 4, but the excess of silicon is 8 per cent. The burning speed of the resulting fuse is about 475 seconds per yard at one atmosphere pressure.
Example 6 The procedure is the same as in Example 4. The diameter of the core is .08 inch and the proportions of red lead to potassium nitrate and of powder to binding agent are the same as in Example 4, but the excess of silicon is 4 per cent. The burning speed of the resulting fuse is about 660 seconds per yard.
Example 7 The procedure is the same as in Example 4, except that the core is extruded around a. 30 standard wire gauge copper wire passing centrally through the die. The diameter of the core is .05 inch, the red lead and the potassium nitrate are present in the ratio 71.4:28.6 and the silicon is present in an excess of 23 per cent. The ratio of powder to binding agent is 75:20. The resulting fuse has a speed of approximately 33 seconds per yard at atmospheric pressure and 38 seconds per yard at one third of an atmosphere pressure.
1. Fuse compositions comprising a pulverulent mixture of potassium nitrate, red lead and silicon, wherein the proportions by weight of the ingredients in the order named lie between 50-15%, 30-60 and 10-40 respectively.
2. Fuse compositions as claimed in claim 1 wherein the amounts of potassium nitrate, red
6 lead and silicon lie between 40-20%, 40-50% and 20-30%, respectively.
3. Fuse compositions as claimed in claim 1 wherein the said pulverulent mixture is in the form of corned granules containing a binding agent.
4. Fuse compositions as claimed in claim 1 wherein the said pulverulent mixture is bound together in rod form by means of a binding agent.
5. Fuse compositions as claimed in claim 1 wherein the said pulverulent mixture is in homogeneous admixture with a suflicient quantity of a thermoplastic binding agent to form an imporous plastic mass capable of extrusion.
6. Fuse compositions as claimed in claim 1 wherein the said pulverulent mixture is in the form of corned granules containing a binding agent, and the proportions of potassium nitrate, red lead and silicon lie between 40-20%, 40-50% and 20-30%, respectively.
7. Fuse compositions as claimed in claim 1 wherein the said pulverulent mixture is bound together in rod form by means of a binding agent, and the proportions of potassium nitrate, red lead and silicon lie between 40-20%, 40-50% and 20-30%, respectively.
8. Fuse compositions as claimed in claim 1 wherein the said pulverulent mixture is in homogeneous admixture with a sufiicient quantity of a thermoplastic binding agent to form an imporous plastic mass capable of extrusion, and the proportions of potassium nitrate, red lead and silicon lie between 40-20%, 40-50% and 20-30%, respectively.
9. Non-detonating fuse containing the fuse composition set forth in claim 1.
10. Non-detonating fuse containing the fuse composition set forth in claim 1, wherein the proportions of potassium nitrate, red lead and silicon lie between 40- 0%, 40-50% and 20-30%,
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS