US2478501A - Ignition compositions - Google Patents

Description

Patented Aug. 9, 1949 UNITE IGNITION COMPOSITIDNS No Drawing. Application July 16, 194.6, Serial No. 683,976. In Great Britain August 1, 1945 2 Claims.

The present invention relates to new and improved compositions of the general character of fuze powders of the kind comprising inorganic oxidising and reducing agents in admixture and adapted on ignition to propagate through themselves an exothermic reaction, with the formation of non-volatile products but not of any considerable quantity of gaseous products.

The invention also relates to improved fuzes or other charged elements through which a high temperature reaction zone progresses, when charged with the aforesaid new and improved compositions, and to the production of the resulting fuzes or other elements.

The new or improved compositions provided according to the present invention, although applicable for use in other kinds of elements through which a high temperature reaction progresses, are especially valuable in the production of fast burning delay fuzes of the kind in which the fuze composition is compressed into a tube of rigid material, such as are used for military purposes, for instance aerial bomb delay fuzes.

According to the present invention the fuze powders comprise a mixture of zirconium and red lead in such proportions that fuzes can be formed by compressing the said powders in rigid tubes under a load of tons per square inch that burn at a rate of not more than 50 milliseconds per cm.

For the purpose of making extremely fast burning delay fuzes the zirconium should be of as fine a particle size as practicable, preferably of the nature of an impalpable powder, a zirconium powder having an average particle size less than 0.005 mm, is especially suitable. Before the use the zirconium is desirably dried and any lumpy aggregates should be crushed. The red lead should be free from impurities and should be sieved through a fine mesh screen, for instance a 240 British Standard Specification screen. The mixtures of zirconium of this particle size and red lead in accordance with the invention yield even faster fuzes when compressed into delay sleeves than are at present available, and they are less sensitive to friction and percussion than the basic lead salts of polynitrophenolic compounds usually employed for the production of fast burning delay fuzes. On the other hand, the sensitlveness of the compositions provided according to the invention to ignition by flame for instance by electric fuzeheads, p-ercussion caps or igniferous detonators is relatively high even when the compositions are compressed into delay tubes, so that no intermediate composition is required to effect their ignition. Moreover, the fact that they yield little or no gaseous products of decomposition makes their burning speed substantially independent of the prevailing gas pressure.

The mixtures of zirconium and red lead may be corned with the aid of a solution of an adhesive in order to improve their running properties, for instance by means of a solution of nitrocellulose in an organic solvent or of gum arabic in water. It is an advantage of the compositions according to the present invention that they do not tend to stick to the press-plunger when they are being compressed as is the case with most compositions yielding fast burning delay fuzes, and that accordingly it is unnecessary to lubricate the compositions with graphite, a substance which contributes to the gas volume produced as a result of the reaction.

By way of example, in the case of mixtures of less than 0.005 mm. average particle size zirconium powder and red lead passing a 240 British Standard Specification screen corned with one per cent of its weight of nitrocellulose in solution in a volatile organic solvent and compressed into aerial bomb delay fuze tubes under a load of 10 tons per square inch, the following delay periods were observed:

Gravimctric ratio Milliseconds of zirconium to per centimetre red lead length of the order of 25 to 50 milliseconds per centi- REFERENCES CITED meter when compacted in metal delay tubes The following references are of record in the sisting essentially of a mixture of finely divided me of this patent, zirconium of less than 0.005 mm. average particle size and red lead, wherein the gravimetric 5 UNITED STATES PATENTS ratio of the zirconium to the red lead is between Number Name Date 20:80 and 1,805,214 Hale May 12, 1931 2. Delay fuze powders as claimed in claim 1, ,971,502 Piccard Aug 2 1934 wherein the mixture is corned by means of an 2,008,366 Pickett July 16, 1935 adhesi e, 10 2,027,208 Sosson Jan. '2, 1936 2,309,978 Pratt Feb. 2, 1943 EDWARD M. PATTERSON. 2,416,639 Pearsall Feb. 25, 1947