Patent Publication Number: US-4727811-A

Title: Smoke canister with capillary bores

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a smoke canister of the type which includes a casing to contain a smoke-generating charge and which includes a lid for the casing, the lid containing ignition and propellant charges and having a periphery with electrical contact rings. 
     Smoke canisters of the species described in more detail at the outset are known from German Laid-Open application DE-OS No. 15 78 348. Their main purpose is the self-protection of vehicles of every kind, especially combat tanks, and they are therefore carried on such vehicles and are fired from launchers externally attached to the vehicle. Customary launchers, distributed in large numbers, are designed for a maximum gas pressure of about 13.5 Bar, so that only a propellant charge mostly consisting of black powder (which generates a low gas pressure) can be used for the launching of smoke canisters. It would be desirable, because of the achievable increase in protection, to launch smoke canisters having a larger smoke-generating charge from the vehicles seeking protection. However, this is not easily possible with customary launchers because of their comparatively low resistance to pressure. Furthermore, the black powder propellant charges usually employed have the disadvantage that they foul the electrical contacts for the firing of the smoke canisters to a high degree. 
     Especially when it is impossible to clean immediately after the launching of the smoke canisters, heavy corrosion effects occur, leading to difficulties with the contacts and, at the least, making repeated launches of the smoke canisters more difficult. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved smoke canister which makes assured self-protection possible at greater speed a with customary smoke canisters, and which avoids fouling of the contacts. Such fouling would impair the assurance of operation. 
     This object is attained, based on a smoke canister of the species described at the outset in more detail, by providing a container having first and second end faces and having a high-pressure proof propellant chamber between the end faces, the container being mounted in the lid with the first end face oriented toward the smoke-generating charge, the first end face having a capillary bore and the second end face having a single capillary bore, the diameter of the second capillary bore ranging from about 1 mm to about 1.4 mm, wherein the propellant and ignition charges are disposed in the propellant chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view through the smoke canister; 
     FIG. 2 is a longitudinal sectional view through the base of the smoke canister; 
     FIG. 3 is a plan view of the base of the propellant chamber shown in expanded scale; 
     FIG. 4 is a longitudinal sectional view through the base of the propellant chamber. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows in a longitudinal section view a smoke canister 1, comprising a casing 10 preferably made by the deep drawing method, into which is injected the smoke-generating charge 12. The casing 10 is closed by a lid 14 having on its circumference two contact rings 13 separated by an insulating ring (see FIG. 2). The launcher, not shown here, consists in general of a cylindrical jacket and a base, and at the height of the said contact rings 13 the launcher has contact pins which are disposed in the launcher jacket in a spring-loaded and insulated manner. During firing the launcher&#39;s contact pins apply voltage to the smoke canister 1. This voltage is applied via electrical wiring 19a, connected with the contact rings 13, to an ignition charge 19, which is in the form of a electrical priming cap (FIG. 1, FIG. 2). The customary black powder propellant charge is also ignited in this manner and it creates propellant gases to launch the smoke canister 1, the pressure level of which does not exceed the pressure stability of the launcher. However, customary black powder propellants foul the contact means to a high degree and thereby decrease the operational assurance. 
     The object of the invention is to improve self-protection by launching smoke canisters with a greater smoke charge, without exceeding the permissible pressure level and with greatly increased assurance of operation. This is accomplished by a novel propulsion system described in detail below. 
     After ignition of traditional black powder propellant charges a prescribed pressure level, which does not exceed the maximum pressure stability of the launcher, is created, and this pressure level steadily decreases after the start of the acceleration phase of the smoke canister up to the point where the canister is discharged. In contrast, the invention provides that a constant pressure level, not exceeding the maximum pressure stability of the launcher, is created in the launcher in spite of the acceleration of the smoke canister. The constant pressure level is maintained practically to the point of the final discharge of the smoke canister, whereby the launched smoke canister is steadily accelerated. For this purpose the smoke canister 1 in accordance with the invention has a high-pressure resistant propellant chamber 20 wherein a high-caloric, reduced-smoke generating powder 21 (for example, a nitro powder) is disposed as propellant. Powder 21 is electrically fired by the ignition charge 19. The propellant chamber 20, inserted in the lid 14 of the smoke canister 1, consists of a generally cup-shaped housing 20d which is closed by means of a screw-on lid 20a to form a container. In both end faces of the propellant chamber 20 capillary bores 20b and 20c, respectively, are disposed. To improve the storage life, bores 20b and 20c are covered with covers 18a and 18b, for example a self-adhesive foil of metal or plastic. Covers 18a and 18b prevent the entry of moisture into the propellant charge 21. After ignition of the propellant charge 21 by the electrical ignition of the ignition charge 19 via the contact rings 13 and the connecting wires 19a, a comparatively high pressure of a magnitude of approximately 1,000 Bar builds up in the propellant chamber 20 because of the conversion of the propellant powder 21. The propellant gases under high pressure in the propellant chamber 20 enter the bore 20b, rip the lid 18b apart, and then enter a moat-like indentation which is delimited by the outer wall of the launcher and a support spike rising in its center, on which the ready-to-be-launched smoke canister 1 rests. By proper dimensioning of the bore 20b the propellant gases under high pressure are throttled in such a way that inside the launcher only such a pressure level arises which does not exceed its maximum pressure stability. However, since propellant gas is steadily fed via the bore 20b even after the start of acceleration of the smoke canister 1, this pressure level is maintained inside the launcher until the smoke canister 1 has completely vacated the launcher. In this manner is created--contrary to traditional smoke canisters--a constant acceleration inside the launcher during the dwell time of the smoke canister 1 inside the launcher, whereby the same launch distances can be achieved with heavier smoke canisters. The bore 20b is appropriately disposed at an angle, preferably at an angle α of between 18° and 25°, preferably 20°, to the longitudinal axis 40 (FIG. 4) of the propellant chamber 20, so as to let the propellant gases reach the annular indentation of the launcher (not shown). The diameter of the bore 20b is between 1 mm and 1.4 mm. In an especially advantageous exemplary embodiment of the invention the diameter of the bore 20b is 1.2 mm. 
     The capillary bore 20c is disposed in the front face of the propellant chamber 20 facing the smoke-generating charge 12, and the cover 18a is provided for storage purposes. After ignition of the propellant charge 21 the hot propellant gases also enter the bore 20c, penetrate the cover 18a, and ignite the smoke-generating charge 12 in an area 12a adjacent the bore 20c, where the smoke-generating charge 12 surrounds an indentation 12b. Due to the ignition of the smoke-generating charge 12 in area 12a  a very high pressure builds up between the smoke-generating charge 12 and the lid 14 of the smoke canister 1 which closes the casing 10. This pressure finally causes the thread 14a, by means of which the lid 14 is fastened to the smoke canister, to begin to give and finally to tear, so that an annular slit is formed between the lid 14 and the cross section of the smoke canister 1 covered by it, the pent-up smoke clouds can exit through the slit. In this way a dense curtain of smoke offering initial protection is already created during the flight of the smoke canister 1 by the conically extending trail of smoke. The lid 14 is completely blown off during the flight. After the smoke canister 1 lands, the smoke generated by the burning smoke-generating charge 12 can exit through openings 10a, disposed evenly around the periphery of the smoke canister 1, without hindrance, so that a wall of smoke, offering concealment, is quickly formed. 
     The tearing of the thread 14a and the removal of the lid 14 are promoted by the fact that part of the lid 14 surrounding the high-pressure proof steel propellant chamber 20, especially the outer thread 14a contained therein, consists of plastic, while the inner thread, connected with the casing 10, is made of steel. 
     The propellant chamber 20, made of steel, insulates in an advantageous and sure way the electrically activatable ignition charge 19 against electro-magnetic impulses, which otherwise could cause an unwanted firing. 
     The propellant gases created from the propellant charge 21 which--as previously described--enter the launcher via the bore 20b, do not cause a noticeable fouling or corrosion of the contact pins disposed in the launcher. Accordingly safe reloading of the launcher and firing of smoke canisters 1 are possible without special cleaning measures being needed. In this way maintenance costs are considerably reduced and assurance of function is assured.