US2469421A - Heat-action explosive pyrotechnic marker - Google Patents

Description

May 10, 1949. I R. L TUVE HEAT-ACTIONEXPLOSIVE PYROTECHNIC MARKER Filed April 15, 1944 amen 1M RICHARD L. TUVE atented May 10, 1949 ittAZi HEAT-ACTION EXPLO SIVE' PYROTECHNIC MARK-ER (Granted under the act of' March 3', 1883, as amended April 30, 1928; 370 0. G. 75.7)

5 Claims.

This invention relates to the art of making pyrotechnic devices and-projectilesof general military utility. Itis particularly concerned with high explosive projectiles which are characterized by the appearance on bursting of a smoke cloud having a distinguishing color.

In the past various attempts have been made to color thesmoke or cloud. of gases which is formed by a bursting shell, but with no appreciable success. Many attempts to produce colcred bursts have been mad'e'by mixing dyestufis or inorganic pigments'with' the explosive powder or by filling a core with a dyestufi or pigment and. placing it in the center of the charge. All of these schemes have proved unsatisfactory because no appreciable color was produced if a high explosive charge was employed. The methods using inorganic pigments gave no-appreciable color even with low explosives. Where colored bursts were obtained; a very weak explosive charge was used. In such cases theshell became merely an-inefiective marker;

It is often highly desirable for purposes of accurate aiming in military actions to be able to distinguish the hits on .atarget made by shells from difierent guns. This is particularly true when many guns are'hurl ing shells'into the same general area. The value of shellswhich would give bursts of intensely colored smoke in antiaircraft defense or inthe bombardment of shore installations by ship-borne batteries is apparent.

The object of this invention is to provide high explosive shells which produce colored bursts of predetermined intense color.

A- second object ofthe invention is'to provide explosive shells characterized by the striking color of their bursts and the iact' that their explosive power is not substantially less than that of standard high explosive shells of the same calibre.

A thirdobject ofth'e invention is to provide novel means for coloring the bursts of display fireworkssuch as those obtained with large firecrackers, rockets, and. similar pyrotechnic devices.

A further object of the invention is to provide means for adding 'thec'oloring matter, in the form of a coating composition, to=the interior of the shell.

Other objects of the invention will in part be obvious =and in=part appear hereinafter.

Thisinvention is based onthe discovery that the coloring material inthe cloud created by the burst must be in'an" extremely finely divided solid or'liduid' state, such as'smoke or mist, and must be widely dispersed upon bursting of the projectile. In addition the cloud must be comparatively free of other light-absorbing material, particularly colloidal carbon which appears as a black smoke.

In the practice of this invention a "fine dispersion of the coloring matter is obtained by employing organic dyestuffs, so placed Within the explosive shell that, upon bursting of the shell, they are vaporized and the vapor widely dispersed in the-cloud of explosion products. Contact with the relatively cold air causes the dyestuffs to condense or solidify in the form of a fine smoke having an intense color. In order for the colored smoke to be clearly visible, an explosive must'b'e used which does not produce adark cloud on detonation. There are a number of well-known highexplosives of this type, but two explosives which are especially good are nitroguanidine and; a mixture comprising ammoniurn pier-ate and ammonium nitrate.

A mixtureof the nitrate and picrate containing from about 40% to about ammonium nitrate gives excellent performance. When the nitrateis present in an amount of only 40%, some-carbon is apparent in the burst, as the uncolored cloud is'of agreyish cast instead of white. However; this slight greyness is not enough to mask the'coloring of the dyestuli to any marked extent. For a perfectly white'burst from the explosive mixture alone stoichiometric proportions of the picrate and nitrate are theoretically suflicient, according to the following equation:

However, as indicated above, the proportions are not critical. Since the picrate is easier to handle and preserve in the shell than the nitrate,. it is advantageous-to use less than the stoichiometric amount of the nitrate. I'hese mixtures have approximately the same explosive power as the picrate alone.

The d'yestufi" may be of any color and composition desired, provided it is solid at ordinary temperatures and that it will vaporize or sublime without decomposition on being heated. Dyestufis melting as low as C. are less common than others, but they are perfectly satisfactory.

The'placement of the dyestuii without the shell, in relation to the explosive, is exceedingly important' because the temperatures reached by high explosives ondetonation may exceed three thousand degrees. mixed with the explosive or it will be dec0mposed in the detonation. At the same time, hoW-' Thus, the dyestuff cannot be as ever, it must be vaporized and dispersed in the air or cooler gases surrounding the point of detonation. This is accomplished by placing the dye stuff between the shell casing and the explosive.

The construction of a shell embodying my invention is readily understood from the accompanying simplified drawing in which a casing 53 is shown internally coated with a coloring layer II and filled with explosive charge i2. cases an inert separator or insulator 13 between charge l2 and color coating II is of value but ordinarily it is not necessary. ,After coating the inside of the shell casing In as described below the explosive charge I2 is inserted along with the standard time fuz e or contact detonator M and the shell casing is closed.

The method of applying the color coating to the inside of the shell can be worked out according to the convenience of the manufacturer. Rotation of the shell with the molten coloring matter therein and letting it solidify gradually has been found satisfactory. Likewise mixing the coloring matter with wax or thermoplastic resin of fairly low melting point such as ordinary paraifln or methyl methacrylate and applying the mixture to the inner wall of the shell by rotation of the casing containing the fluid mixture is quite satisfactory. A solution of the wax or resin and dye in a volatile solvent applied as outlined also gives satisfactory results. familiar to any chemist and it is unnecessary to describe them in any greater detail,

It has been found that a solution of an organic hinder or resin like methyl methacrylate in toluene with the dyestufi as pigment forms a very satisfactory paint for coating the inner surface of the shell. For example a solution of about 20% methyl methacrylate in toluene acting as Vehicle for the dyestufi forms a paint which forms a good adherent coating for the inside of the shell. This method of applying the color is an effective substitute for melting the dyestuif itself in the shell casing.

Although many different satisfactory dyestufi's can be found by testing them for evaporation or sublimation by dropping them in the form of powder on a hot plate, the following dyestuffs are typical of those which have been tested and found to give excellent results: for a red or orange smoke, xylene azo beta naphthol, benzene azo beta naphthol, diethyl m-amino phenolphthalein hydrochloride; for a yellow smoke, amino azo toluene and benzene azo dimethylaniline; for a blue smoke, quinazarin blue, alizarine cyanine green, anthraquinone violet. This list could be expanded greatly by means of the simple preliminary test indicated above. Likewise the colors of bursts can be varied by using mixtures of the dyes but since sharp diiferences in colors of bursts are generally desired it is not expected that great attention will be paid to shading of the bursts.

Many test projectiles of the 3 inch and 5 inch anti-aircraft type were made and fired, at both high and low elevation and against various kinds of backgrounds. All bursts were in sunlight. The bursts for the 3 inch shells were set for 5 seconds after firing, and the 5 inch shells were set for 15 seconds. At these distances all the colors were distinguishable but the yellows and greens faded rapidly. The red-orange bursts were relatively permanent and were diluted to a pink only after about three minutes. The 5 inch shell bursts were particularly striking. Generally, about of the total charge in the shell was dyestuif, which was put in place either by melting and coating These techniques are quite In some the shell sides as described or coating the shells with a solution of a binder in which the dye was dispersed. These tests revealed the following facts:

1. It is important, for maximum color, that the greater part of the dyestuif be placed on the sides of the shell and not on the bottom.

2. Increasing the proportion of dye used while keeping the coated area constant, results in an I increase in volume of the color cloud.

3. The use of a thick paint comprising an organic resinous binder and a volatile solvent as vehicle for the dye for coating the inside of the shell results in an effective substitute for the melting of the dyestuff itself in the shell casing.

4. Those dyestuffs which have a low melting point and high volatility give the greatest volume of color cloud per unit weight of dyestuff used.

5. The temperatures reached in the detonation do not adversely effect even the most readily oxidizable dyestuffs when they are coated on the inner wall of the shell casing.

Since certain changes can be made in the projectile or pyrotechnic device described and different embodiments of the invention could be made without departing from the scope of this invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

The invention described herein 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 01' therefor.

Iclaim:

l. A pyrotechnic device comprising a hollow casing, an explosive charge within the casing and a normally solid, vaporizable azo dye having a melting point not over 0., said dye being volatilizable at the explosion temperatures of the charge and condensible in colored aggregates at atmospheric temperatures, said dye being positioned between the explosive charge and the casing and applied as a coating to the inside wall of the casing.

2. An explosive marker shell comprising a hollow casing, a sheet of azo dye covering and adhering to the inside Wall of the casing, said dye being vaporizable and condensible in the atmosphere without substantial degradation and having a melting point below 150 0., the dye sheet operative on detonation of the explosive and rupture of the casing to vaporize and disseminate for atmospheric condensation in colored aggregates.

3. An explosive marker shell characterized by its ability to produce a colored burst of smoke which comprises a hollow casing, a charge of explosive within said casing and a normally solid coating of an azo dye having a melting point not over 150 C. adhering to the inside wall of the casing, said dye being volatilizable at the explosion temperatures of the charge and condensible in colored aggregates at atmospheric temperatures, said explosive charge being a, mixture of about 40% to about 75% ammonium nitrate and the balance ammonium picrate.

4. An explosive marker shell characterized by its ability to produce a colored burst of smoke which comprises a hollow casing, a charge of explosive within said casing and a normally solid coating of an azo dye having a melting point not over 150 C. adhering to the inside wall of the casing, said coating bonded by a methyl methacrylate resin, said dye being volatilizable at the explosion temperatures of the charge and condensible in colored aggregates at atmospheric temperatures and said explosive charge being a mixture of about 40% to about 75% ammonium nitrate and the balance ammonium picrate.

5. An explosive marker shell characterized by its abilit to produce a colored burst of smoke which comprises a hollow casing, a charge of explosive within said casing and a normally solid coating of an azo dye having a melting point not over 150 C. adhering to the inside wall of the casing, said coating bonded by a paraffin, said dye being volatilizable at the explosion temperatures of the charge and condensible in colored aggregates at atmospheric temperatures and said explosive charge being a mixture of about 40% to about 75% ammonium nitrate and the balance ammonium picrate.

RICHARD L. TUVE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 262,440 Linton Aug. 8, 1882 675,472 Ford June 4, 1901 1,428,011 Dahn Sept. 5, 1922 1,451,395 Hustvedt et a1 Apr. 10, 1923 2,108,019 Neukirch Feb. 8, 1938 FOREIGN PATENTS Number Country Date 17,788 Great Britain (1908)- Feb. 11, 1909 126,740 Great Britain May 22, 1919 128,986 Great Britain July 10, 1919 745,599 France Feb. 21, 1933

Images