Renewable Liquid Investment Seal

1. Field of the Invention

This invention relates to a liquid seal for combustion apparatus, especially adapted for use in liquid propellant, or caseless, or revolver type guns.

2. Prior Art

Annular seals are well known, and are shown, for example, in Hasek, U.S. Pat. No. 2,117,885; Asbury, U.S. Pat. No. 1,376,130; Gerdom, U.S. Pat. No. 539,733; Thierry, U.S. Pat. No. 3,006,254; Wankel, Germany DAS 1,096,697; and Ashley, U.S. Pat. No. 3,783,737. Each of these seals functions by stressing a ring into abutment with a bore to provide a close surface continuum, and is more or less effective for a limited number of firings.

Liquid propellant guns, other guns firing caseless ammunition, and revolver type guns must be provided with seals to prevent the escape of gas from the firing chamber during a repeated number of firings.

An object of this invention is to provide a seal for such guns which is effective during a repeated number of firings.

A feature of the invention is the provision of a liquid investment seal for the firing chamber of a gun which is renewed at the commencement of each firing.

FIG. 1 is a longitudinal cross-section of a firing chamber for a liquid propellant gun, of the type shown, for example, by Tassie in U.S. Pat. No. 3,763,739, issued Oct. 9, 1973, showing a bolt incorporating this invention in its closed and locked disposition;

FIG. 2 is a transverse cross-section of the chamber of FIG. 1, taken along the plane II--II;

FIG. 3 is a detail view, in longitudinal cross-section, of the chamber of FIG. 1, showing the bolt in its unlocked and propellant filling disposition;

FIG. 4 is an enlarged detail view, in longitudinal cross-section, of the bolt and the chamber of FIG. 1, showing the generation of the liquid investment seal;

FIG. 5 is a schematic of a portion of a revolver having a firing chamber and a portion of a gun barrel, incorporating this invention;

FIG. 6 is a longitudinal cross-section of portions of a firing chamber and a gun barrel incorporating the mechanism of FIG. 5;

FIG. 7 is a transverse cross-section of the mechanism of FIG. 5 taken along the plane VII--VII;

FIG. 8 is a chart showing chamber pressure and seal-piston stroke against time using "decalin" as an investment material; and,

FIG. 9 is a chart showing chamber pressure and seal-piston stroke against time using grease as an investment material.

In guns firing conventional cased ammunition, the interface between the combustion or firing chamber and the gun bolt is sealed by the cartridge case. A new case is provided for each firing. In many prior art guns utilizing liquid propellant to fire a projectile without a cartridge case, the interface between the chamber and the bolt is closed by a seal ring which is carried by the bolt. In most such guns, the seal ring is stressed by the combustion gas. There is a small initial leakage which causes heating and erosion of the seal ring, and often allows foreign particles to enter the gap and to interfere with the seating of the seal ring. In U.S. Pat. No. 3,783,737, which uses a pre-stressed ring seal, this problem is obviated; however, the metal-to-metal contact does eventually result in frictional wear, galling and fatigue.

To overcome all of these disadvantages this invention provides a liquid which is used to fill or to invest the joint or gap between the bolt and the combustion chamber at a pressure which is higher than the pressure of the combustion gas in the chamber, so that the investment liquid will flow into the chamber, rather than the combustion gas flowing into the joint. Flow control rings may be used to limit the rate of flow of the investment liquid to minimize the loss of the investment liquid.

FIG. 1 shows a combustion chamber 10 in a gun barrel 12 which is fixed to a barrel extension 14, having a longitudinal bore or antechamber 15 having a conical transition portion 16 and a reduced diameter portion 17. Two concentric sleeves 18 and 20 are disposed in the bore 15 which is capped by an L-ring 22 which is fixed to the extension 14 and extends within the bore 15. The L-ring 22 has a longitudinal bore 24, and an outer ring seal 26 and an inner ring seal 28. The outer sleeve 18 has a forward annular rib 30 with an outer ring seal 32 and an aft annular rib 34 with an outer ring seal 36, a forwardmost, inwardly projecting nose cone section 38, and a plurality of radially extending bores 40 located between the ribs. The inner sleeve 20 has an intermediate annular rib 42 having an outer ring seal 44 and an inner ring seal 46, and its aft end extends within the bore 24 against the ring seal 28.

The gun bolt 48, which may be locked to the barrel extension by conventional means, such as wing locks 49, is disposed within the bore 24, and within the inner sleeve 20, against the ring seal 46, and is reciprocatable into the aft portion of the combustion chamber 10. A transverse bore 50 extends through the gun barrel 12 into the aft portion of the combustion chamber, and a spark plug 52 is fixed therein.

An annular recess 54 may be provided in the interface between the gun barrel 12 and the extension 14 about the cahmber 10 with a drain passageway 56 and an annular relief valve 58.

The gun bolt 48 comprises a bolt aft body 60, a bolt forward body 62, and a tubular coupler 64 which fixes together the bodies 60 and 62. The composite body has a blind longitudinal bore 66 in which are disposed a helical compression spring 68 and a piston 70. The aft portion of the piston has a longitudinally extended, diametrical slot 72 in which is disposed a cross-pin 74 whose ends extend into a diametrical bore in the bolt body. The cross-pin thus captures the piston within the bore 66 while permitting limited reciprocation therein. The piston captures the spring 68 within the bore, while the spring biases the piston forwardly. The piston has a head which at its forwardmost end is disk-shaped as at 78 with a conical transition portion 80 leading to the stem 82. The forward portion of the bore 66 is enlarged in a cone-shape, as at 84, to mate with conical portion 80 of the piston head.

The longitudinal length of the sleeve 18, from its forwardmost portion 38 to its aftmost portion 34 is shorter than the longitudinal length of the bore 15 from its forwardmost conical surface 16 to its aftmost transverse surface provided by the ring 22. Thus the sleeve 18 is free to slide to and between a forwardmost position shown in FIG. 1 and an aftmost position shown in FIG. 3. Similarly, the longitudinal length of the sleeve 20 between it forwardmost end and the annular rib 42 is shorter than the open length of the bore 15. When both sleeves are in their forwardmost positions a void 90 is defined in which is received a quantity of gas under pressure, supplied from a source, not shown, via a conduit 91 assembly. This gas serves as a gas spring, biasing the sleeves towards their forwardmost positions.

The barrel extension 14 also has a radial bore 92 which opens into the bore 15 between the ribs 30 and 34 of the sleeve 18 when the sleeve 18 is in either its fore or aft position. The extension also has a radial bore 94 which opens into the bore 15 forward of the annular rib 30 when the sleeve 18 is in either its fore or aft position. In a liquid propellant gun of the type taught in U.S. Pat. No. 3,763,739, a measured quantity of liquid fuel is pumped through the bore 92 while a measured quantity of liquid oxidizer is pumped through the bore 94. These liquids force the sleeves aft, against the bias of the gas spring, so that fuel passes through the radial bores 40 in the sleeve 18, then forwardly between the sleeves, then around the head of the piston and into the combustion chamber; while oxidizer passes around the conical portion of the sleeve 18 into the combustion chamber. When the supply of fuel and oxidizer under pressure ceases, the gas spring biases the sleeves forwardly, as shown in FIG. 1, to provide a seal between the sleeves 20 and 18 and the barrel extension, forward of the supply bores 92 and 94. The annular flows of fuel and oxidizer guided by the sleeves 18 and 30 intermix to fill the combustion chamber with a relatively homogeneous mixture. A quantity of this liquid mixture is trapped in the annular void between the aft conical surface of the head of the piston and the mating conical surface of the bolt body. As shown in FIG. 4, a leakage interface Z exists between the bolt body and the piston stem, a leakage interface Y exists between the bolt body and the barrel, and a leakage interface X exists between the piston head and the barrel. To permit a more generous clearance between the bolt body and the chamber wall of the barrel, an L-ring seal 96 may be disposed in an annular notch 98 cut into the forward-outer corner of the bolt body. This ring differs from a conventional seal in that no preload against the chamber wall is necessary.

When ignition is provided by the spark plug, the mixture of fuel and oxidizer forward of the piston head adjacent the spark plug burns and generates combustion gas under relatively high pressure. This gas pressure is communicated to the piston head, biasing it aft against the return spring. The liquid trapped or invested behind the piston head is under a relatively higher pressure than the combustion gas, which is equal to the piston head transverse area divided by the difference of the piston head transverse area and the piston stem cross-sectional area, all multiplied by the combustion gas pressure. The invested liquid flows out of the interfaces X, Y, and Z at this relatively high pressure. This forward flow at X, being at a higher pressure than the liquid or gas pressure in the chamber forward of the piston head, precludes any flow aftward of combustion gas at X. The use of the L-ring seal 96 effectively precludes any significant flow of investment liquid at Y, which would otherwise ultimately pass to the atmosphere.

The invention may also be utilized to seal a revolver to a gun barrel. An exemplary revolver gun is shown in the Final Report, 19 Nov. 1953-31 Jan. 1956, under contract DA-36-034-ORD-1504RD, Project TS1-47-8, page 31, FIG. 16. As is schematically shown in FIG. 5, a revolver 100 has a transverse forward face 102 which is spaced by a leakage interface 104 from a transverse aft face 106 of a gun barrel 108. The inner wall 110 of a chamber 112 of the revolver is aligned with the inner wall 114 of the bore 116 of the gun barrel. Conventional means 117 provide combustion gas to the chamber 112, or the system shown in FIG. 1 may be utilized. A cylinder 118 is provided in the wall of the revolver and has a combustion gas inlet port 120. A piston 122 having a head 124 and a stem 126 is disposed in the cylinder. The cylinder also has an outlet port 130 which communicates with an annular recess 132 cut into the surface 102 and coaxial with the chamber 112. A pair of flow control L-shaped rings 134 and 136 may be disposed in the recess. The cylinder below the piston head is filled with a suitable investment liquid such as grease which can be pumped by the piston head through the recess and into the leakage interface 104. As before, the investment liquid will be pumped into the leakage interface at a pressure which is higher than the pressure of the combustion gas, and which is equal to the piston head transverse area divided by the difference of the piston head transverse area and the piston stem cross-sectional area, all multiplied by the combustion gas pressure.

As shown in FIGS. 6 and 7, the piston and the investment liquid may be retained in the cylinder by means of a plug 140. Suitable means for automatically charging the cylinder with a supply of grease between bursts of firing may be provided by an auxiliary pumping system, not shown.

The flow control rings are forced into the leakage interface 104. The rate of flow permitted by the rings is determined by surface conditions. Flow towards the atmosphere should be held to a minimum, while flow towards the chamber/bore should be more generous to fill the interface joint to preclude combustion gas from entering. Investment liquid, such as Molybdenum disulphide, should be selected to meet the high temperature and high pressure conditions provided by the combustion gas.

FIG. 8 shows piston stroke and chamber pressure versus time in a mechanism shown in FIG. 1 utilizing decalin as the investment liquid.

FIG. 9 is similar to FIG. 8, but utilizing a MIL-G-3278A grease.