US3838645A

US3838645A - Proximity fuze improvement

Info

Publication number: US3838645A
Application number: US00302456A
Authority: US
Inventors: D Finger; G Wood; R High; E Harrison
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1972-10-31
Filing date: 1972-10-31
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01

Abstract

Projectiles utilizing proximity fuzes wherein the windshield structure thereof is capable of withstanding the buildup of static electrical charges on the surface thereof resulting in the prevention of premature functioning of said fuzes comprising in combination a conical windshield portion and a cylindrical base portion. The conical windshield comprises an electrically conductive surface capable of withstanding and rapidly dispersing electrical charges on the surface and having a surface resistivity of between about 1.0 and 200 megohms per square.

Description

United States Finger et a1.

atent [1 1 [451 Oct. 1, 1974 1 PROXIMITY FUZE IMPROVEMENT [75] Inventors: Daniel W. Finger; Gwendolyn B.

Wood, both of Bethesda, Md; Roy F. High, Washington, DC; Edwin H. Harrison, Jr., Arlington, Va.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

22 Filed: Oct. 31, 1972 21 Appl. No.: 302,456

[52] US. Cl. 102/70.2 P, 102/105, 343/841, 343/872 [51] Int. Cl. F42c 19/04, HOlq 1/42 [58] Field of Search l02/70.2 P, 105; 325/357; 343/841, 842, 872, 873

[56] References Cited UNITED STATES PATENTS 2,509,903 5/1950 Brode et al l02/70.2 P 2,583,540 l/l952 Bennett 343/841 2,962,717 11/1960 Kofoid 343/872 3,152,547 10/1964 Kyle l02/70.2 P

3,292,544 12/1966 Caldwell et al. 102/105 3,336,873 8/1967 Wilford l 102/105 3,555,550 1/1971 Walters 102/105 3,616,140 10/1971 Copeland et a1 102/105 R25,417 7/1963 Amason 343/872 Primary Examiner-Benjamin A. Borchelt Assistant ExaminerC. T. Jordan Attorney, Agent, or Firm-Edward J. Kelly; Saul Elbaum [5 7 ABSTRACT Projectiles utilizing proximity fuzes wherein the windshield structure thereof is capable of withstanding the buildup of static electrical charges on the surface thereof resulting in the prevention of premature functioning of said fuzes comprisingin combination a conical windshield portion and a cylindrical base portion. The conical windshield comprises an electrically conductive surface capable of withstanding and rapidly dispersing electrical charges on the surface and having a surface resistivity of between about 1.0 and 200 megohms per square.

12 Claims, 1 Drawing Figure PROXIMITY FUZE IMPROVEMENT 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 royalty thereon.

BACKGROUND OF THE INVENTION This invention relates essentially to projectiles utilizing proximity fuzes and more particularly to projectiles wherein the Windshields thereof are constructed in such a manner so as to prevent misfirings of proximity fuzes located therein.

The use of proximity fuzes in artillery projectiles have not been too successful due to significant numbers of premature firings. These problems were believed to be due to the buildup of static electricity on the surface of the windshield and projectile thereby causing the misfirings.

Attempts to overcome these problems have not been successful up until this time. Recent laboratory tests indicate that an artillery projectile strikes numerous particles during flight, e.g., dust particles and ice crystals, which comprise some clouds, thereby causing the projectile to become electrically (i.e., either positively or negatively) charged. As the electric potential increases to a point on the order of about 100 to 700 kilovolts, a corona discharge occurs at the sharpest points on the projectile, e.g., points A and B, as illustrated in the accompanying drawings (at B if windshield is conductive, at A and B if windshield is insulator or semiconductor).

When a corona discharge occurs at position B, as per the attached drawings illustrating a typical artillery projectile having a metal fuze body 4 and steel projectile casing 5, it has been found that arcing results at the various gaps l in the segmented antenna 2. This arcing creates high amplitude fast rise time pulses which pass into the fuze firing circuit, thereby causing premature functioning of the projectile.

The effects of the buildup of electrical charges on the surface of artillery projectiles is entirely different from the effects of electrical charge buildup on plastic enclosures or radomes of aircraft. In the latter, radar and other directional equipment are usually stored for navigational purposes within the radome of an aircraft. When electrical charges build up on the surface of a radome, this buildup usually results in the emission of signals tending to have adverse effects on the navigation of the aircraft. In order to avoid these problems and control the electrical charge buildup on the surface of aircraft, and particularly radomes, certain methods have been employed for reducing the electrical charges in a controlled manner, e.g., by placing discharge wicks on the wings, stroke guiding systems, exposed grounded metal buttons, stroke diverting rods, diverter strips across radome surface (thin metal strips), etc. However, these methods have never been adapted to preventing or modifying corona discharges on projectiles or missiles containing proximity fuzes because the cause of misfirings have never been found to be due to the buildup of electrical charges on the surface of nose cones, but only recently, to an entirely different phenomena as will be discussed herein. When corona discharges result due to the buildup of electrical charges on the surface of the nose cone, various coatings and methods conventionally utilized to dissipate the electrical charges on aircraft radomes cannot be adapted for use on projectiles due to the inability of these coatings to withstand high temperatures and velocities. In this regard, it is noted that coatings on aircraft radomes are not satisfactorily resistant to withstand high temperatures on the order of 450-C. and velocities on the order of 3,000 feet per second. In fact, the conventional urethane coatings employed on aircraft radomes are not sufficiently ablation resistant for use on artillery projectiles and missiles.

A great need therefore exists for the development of artillery projectiles and missiles utilizing proximity fuzes that are capable of functioning without premature functioning of the fuze firing circuit.

OBJECTS OF THE INVENTION Accordingly, it is a significant object of the present invention to provide an artillery projectile or missile having a proximity fuze therein which is capable of being utilized without sufficient electrostatic charge buildup on the nose cone thereof, thereby causing the premature functioning of the proximity fuzes.

Consistent with the primary object of this invention, it is also a significant object of this invention to provide a means for dissipating the electrostaticcharge buildup on the nose cone of an artillery projectile or missile thereby preventing the arcing phenomena from occurring at the various gaps in the segmented antenna system due to corona discharges at the front portion of the nose cone.

Another closely related but yet still significant object of this invention is the provision of a nose cone for proximity fuzes which is capable of preventing premature functioning of fuzes due to corona discharges.

A still further object of this invention is the provision of a windshield for proximity fuzes having a coating thereon and capable of withstanding high temperatures encountered during flight and having sufficient erosion resistance to the air during flight.

An additional object of the invention is the provision of a coated windshield for proximity fuzes wherein the coating can be applied and cured at low temperatures thereby not causing any damage to electrical components and/or the proximity fuze located within the nose cone.

The invention will be better understood and objects other than those set forth above will become apparent after reading the following detailed description of preferred, yet illustrative, embodiments hereof.

BRIEF SUMMARY OF THE INVENTION It has now been discovered that these and other objects may be accomplished by employing a windshield structure for proximity fuzes capable of rendering harmless corona discharges therefrom due to the buildup of static electrical charge on the surface thereof resulting in the premature functioningof said fuzes which comprises, in combination, a conical nose portion and a cylindrical base portion. The conical windshield comprises an electrically conductive surface capable of withstanding and rapidly dispersing electrical charges on said surface and having a surface resistivity of generally between 1 and 200 megohms per square and usually between about 1 and 40 megohms per square.

The provisions of partially conducting surfaces for Windshields containing proximity fuzes therein is particularly significant because the dissipation of static charges on the surface of the nose cone results in the corona discharge becoming harmless thereby avoiding premature firings of the fuze circuit due to arcing on the segmented antenna located within the nose cone.

DETAILED DESCRIPTION OF THE INVENTION The conductive coating applied to the nose cone is a resin-based material containing a conductive material, e.g., carbon. The resin selected according to this preferred embodiment of the invention should satisfy the following criteria:

1. Can be dispersed with the conductive material;

2. Can be rendered slightly electrically conductive;

3. Can be easily adhered to the surface of the windshield;

4. Does not degrade over long periods of time, etc.

launcher;

6. Not soften or vaporize during the first few seconds when the windshield will see about 450 C. in flight from the gun barrel. (A heat deflection temperature of about 150 C. helps withstand this initial high temperature environment.)

Although resins having the above properties can be readily determined by those skilled in the art, one resin which has been found to be particularly useful in the practice of this embodiment of the invention includes epoxy based resins, e.g., Epon 828 or Epon 1001 (i.e., condensation products of epichlorohydrin and bisphenol-A). Other resins which are believed to be useful in the practice of this invention include (1) phenolic based resins, e.g., Electro-Science Labs phenolic resin in RS150 series (i.e., condensation reaction of a phenol and an aldehyde plus an acid or base catalyst; (2) butyl based resins, e.g., butyl rubber or buna-S rubber; (3) silicone based resins, e.g., Dow-Comings 806A Resin (i.e., cohydrolyzing mixtures of RxSiCly where R is usually methyl, phenyl or vinyl and x y 4); and (4) polyimide based resins, e.g., DuPonts SP1 or PI- 2501 or Monsantos AF-R2009 or Skybond 700 (i.e., reaction between an aromatic dianhydride and an aromatic diamine).

In order to impart the desired properties to nose cones, a preferred embodiment of this invention relates to the coatings of the surface ofa nose cone. According to this preferred embodiment of the invention, compositions useful for coating the nose cone comprise l) a base resin having the properties set forth above, (2) an inert volatile solvent, (3) a curing agent for said resin capable of imparting a heat deflection temperature for the cured coating of at least about 120 C. and preferably between about 150 C. and 400 C., and (4) a powdered or fibrous conductive material.

The inert volative diluents or solvents are utilized to facilitate the application of smooth and even coatings on a substrate by means of conventional coating techniques including painting, spraying, dipping, screening, etc. Suitable diluents or solvents include ketones (e.g., methyl ethyl ketone and methyl isobutyl ketone), aromatics (e.g., benzene, toluene, xylene), alcohols (e.g., butanol and isopropanol), esters (e.g., ethyl acetate and butyl acetate), saturated hydrocarbons, cyclic hydrocarbons and mixtures thereof. These may be used in amounts of up to about 33 to 67 percent of the weight of the composition, depending on how the coating is to be applied and the resin used. (About 50 percent is preferred).

The curing agents useful in the preferred epoxy resin based compositions of the present invention in order to form the desired coatings on nose cones include various types with the selection of the particular curing agent dependent upon the desired pot life of the resin and imparting a suitable heat deflection temperature to the cured temperature of at least about 150 C. The curing agent selected should also enable cures at low temperatures, e.g., cone-surface temperature of 130 C. for several minutes produced by infrared lamps, where necessary, in order to protect any sensitive equipment located within the nose cone. Such low temperature cures' are particularly important when coatings are being applied to nose cones having proximity fuzes located therein and otherwise ready for use. When coatings are applied to the windshield prior to fuze assemblage, longer curing times are permissible. Depending on the resistance of the windshield material to continuous heat, higher curing temperatures may be permissible.

Examples of suitable curing agents for epoxy resins include diethylenetriamine, 2-ethyl-4-methylimidazole, diethylaminopropylamine and other conventionally used curing agents for epoxy resins. Cross-linking or final polymerization of phenolic resins are produced by catalysts or may require heat. Cures of butyl based resins, silicone based resins and polyimide based resins can be achieved in accordance with conventional methods to produce a resin having the various desired properties discussed above.

When curing agents are employed in the practice of this invention, they are essentially conventionally used curing agents for the particular resin employed in the practice of this invention. The curing agents are employed in amounts effective for obtaining the desired cured resin having a heat deflection temperature of at least about C., but preferably higher. The amount of curing agent employed is also dependent upon the amount of conductive material employed. For example, the amount of curing agent will be increased according to the amount of carbon employed as the conductive material. Carbon has a high surface area and adsorbs the curing agent thereby necessitating the use of additional amounts thereof.

The conductive material employed in the coating compositions of this invention for application to the surface 3 of the windshield or incorporated directly into the surface material of the nose cone without application of any coating thereon, includes a highly conductive material in a powdered or fibrous form, e.g., carbon black. A particularly useful form of carbon black is oil furnace carbon black having a high surface area.

The amount of carbon employed is generally sufficient to impart a resistivity of from at least about 1.0 megohm to no more than 40 megohms on the surface of the windshield. Generally, from about 1 to about parts of carbon areused per 100 parts by weight of 5 tion shown and described herein for obvious modificaresin and preferably between about 2 and 4 parts of tions will occur to persons skilled in the art. carbon per 100 parts by weight of resin when an epoxy Accordingly, what is claimed is: resin is used in the practice of this invention. 1. A windshield for proximity fuzes capable of with- When resin coatings are applied to the surfaces of standing the buildup of static electrical charges on the Windshields, it is usually desired to first clean the windto surface thereof resultingin the premature functioning shield. This can be accomplished by first rubbing the of said fuzes, comprising in combination a conical windshield with acetone for degreasing the cone and windshield portion and a cylindrical base portion, said thereafter rubbing said windshield with a cheese cloth conical windshield portion comprising an electrically soaked with a liquid coating composition in order to inconductive surface capable of withstanding and rapidly sure even wetting and coverage of the windshield surl5 dispersing electrical charges on said surface and having face. a surface resistivity of between about 1 and 200 megohms per square. EXAMPLES 2. A windshield structure of claim 1 wherein said The formulations set forth in the table below are ilconical windshield portion has a surface resistivity of lustrative of several preferred epoxy based resin comabout 1.0 to megohms per square and a heat deflecpositions that can be applied to Windshields in order to tlon temperature of atleast ab out llQf C. obtain the desired properties discussed hereinabove. Q Ihe windshield structure of claim l where in the TABLE Formulation 1A 1B 1c lD ll m w V VI Number of Components to gun l l l l l l l 1 First Component Mixture Resin type Epon Epon 828 Epon 828 Epon 828 Epon I001 Epon l00l Epon i001 Epon i001 Epon i001 828 Solvent mixture MIBK MIBK MIBK- MIBK- MlBK- MIBK- MIBK- MIBK- MIBK- lBA lBA lBA/X lBA/X IBA/X /BA/X lBA/X (/50) (50/50) (35/15/50 (35/15/50 (35/ 15/50 35/15/50) (35/ 15/50 Solvent/100 100 50 pts l00 50 pts 200 pts 200 pts 120 pts 90 pts [l5 pts parts resin pts pts Carbon/lOO 4 pts 4 pts 4 pts 4 pts 4 pts 4 pts 3 pts 3 pts 3.3 pts parts I'BSln Curing agent/100 EMl EMl EMl EMl DETA EMl EMl EM] parts resin (l0) (10 pts) (10 pts) (10 pts) (5 pts) (10 pts) (10 pts) (10 pts) pts Flow agent/I00 5 pts 5 pts 5 pts 5 pts 5 pts parts resin Defoamer/IOO 0.3 pts 0.3 pts 0.3 pts 0.3 pts 0.24 pts parts I'ESH'I Second Component Mixture Solvent/100 75 pts parts resin Curing agcnt/lOO EMl parts resin (25 pts) MIBK methylisobutylketone BA hutylalcohol X xylene EMl 2,4-ethylmethylimidazole DETA dicthylenetriaminc Carbon conductive (Vulcan XC-72R) Flow Agent Beetle 216-8 Defoamer PC4344 a flow agent to control the flow of coating over the surface of the nose cone and prevent cratering.

It should be understood that the invention is not limited to the exact details of construction and formulaelectrically conductive surface of said conical windshield portion consists essentially of a conductive material dispersed throughout the surface of said windshield.

4. The windshield structure of claim 1 wherein said conical windshield portion comprises a coating of a temperature resistant, electrical insulating plastic material having a conductive material dispersed therein, said coating covering at least a portion of the surface of said windshield.

5. The windshield structure of claim 4 wherein said plastic material is selected from the group consisting of epoxy, phenolic, butyl, silicone, and polyimide based resins.

6. A composition useful for forming a coating on Windshields for proximity fuzes comprising: (1) a base resin which can be easily adhered to the surface of the windwhield and does not degrade over long periods of time; (2) an inert volatile solvent; and (3) a powdered or fibrous conductive material. I

7. A composition according to claim 6 wherein said base resin is an epoxy resin.

8. A composition according to claim 7 further comprising a curing agent for said resin and capable of imparting a heat deflection temperature for the cured coating of at least about 120 C.

9. A composition according to claim 8 wherein said curing agent is selected from the group consisting of diethylenetriamine, 2-ethyl-4-methylimidazole or diethylaminopropylamine.

10. A composition according to claim 6 wherein said inert volatile solvent is selected from the group consist- 1. a solid epoxy resin;

2. 1 15 parts per parts resin of a solvent mixture consisting of about 35 percent methylisobutylketone, 15 percent butyl alcohol and 50 percent xylene;

3. about 3.3 parts carbon black per 100 parts resin;

4. about 10 parts 2,4-ethylmethylimidazole per 100 parts resin;

5. about 5 parts of a flowing agent per 100 parts resin; and

6. about 0.24 parts defoaming agent per 100 parts resin.

Claims

1. A windshield for proximity fuzes capable of withstanding the buildup of static electrical charges on the surface thereof resulting in the premature functioning of said fuzes, comprising in combination a conical windshield portion and a cylindrical base portion, said conical windshield portion comprising an electrically conductive surface capable of withstanding and rapidly dispersing electrical charges on said surface and having a surface resistivity of between about 1 and 200 megohms per square.

2. 115 parts per 100 parts resin of a solvent mixture consisting of about 35 percent methylisobutylketone, 15 percent butyl alcohol and 50 percent xylene;

2. A windshield structure of claim 1 wherein said conical windshield portion has a surface resistivity of about 1.0 to 40 megohms per square and a heat deflection temperature of at least about 120* C.

3. The windshield structure of claim 1 wherein the electrically conductive surface of said conical windshield portion consists essentially of a conductive material dispersed throughout the surface of said windshield.

3. about 3.3 parts carbon black per 100 parts resin;

4. about 10 parts 2,4-ethylmethylimidazole per 100 parts resin;

5. about 5 parts of a flowing agent per 100 parts resin; and

6. about 0.24 parts defoaming agent per 100 parts resin.

6. A composition useful for forming a coating on windshields for proximity fuzes comprising: (1) a base resin which can be easily adhered to the surface of the windwhield and does not degrade over long periods of time; (2) an inert volatile solvent; and (3) a powdered or fibrous conductive material.

8. A composition according to claim 7 further comprising a curing agent for said resin and capable of imparting a heat deflection temperature for the cured coating of at least about 120* C.

10. A composition according to claim 6 wherein said inert volatile solvent is selected from the group consisting of ketones, aromatics, esters, saturated hydrocarbons, cyclic hydrocarbons, alcohols and mixtures thereof.

11. A composition according to claim 6 wherein said conductive material is carbon black.

12. A composition according to claim 6 comprising: