US2959130A - Cartridge case plug - Google Patents

Description

Nov. 8, 1960 A. C. H. WEISS ET AL CARTRIDGE CASE PLUG Filed Jan. 20, 1948 I m F FIG. 2

awuoz/wfow ALEXANDER GH. WEISS RICHARD .5. FRENCH CARTRIDGE CASE PLUG Alexander C. H. Weiss, Chicago, Ill. (2211 Pennsylvania Ave. NW., Washington, D.C.), and Richard S. French, Keys Fibre Company, Waterville, Maine Filed Jan. 20, 1948, Ser. No. 3,264

v 2 Claims. 01. 102-95 (Granted under Title as, US. Code 1952 sec. 266) The present invention relates to cartridge case plugs, more particularly to an'improvement in powder cartridge caseplugs for use in semi-fixed ammunition; Semi-fixed ammunition is that type of ammunition in which the projectile and the propellant cartridge are manufactured and handled as separate units; it is generally employed in guns of 5 inch caliber or larger. In such ammunition the mouth of the powder cartridge must be sealed with a plug to retain the powder grains.

An object of this invention is to provide improved sealing members.

Another object of this invention is to provide improved plugs for ammunition.

A further object 'of this invention is to provide improved cartridge case plugs for semi-fixed ammunition used in naval guns of medium caliber.

.This invention contemplates cartridge case plugs of hard and impervious material and yet of controlled frangibility. Although strong and tough, the plugs must fragment into. comparatively small pieces in order to avoid endangering personnel and equipment at a considerable distance from the muzzle. Other features, especially structural details, will be more clearly brought out in the specification.

nited States Patent 0 Semi-fixed ammunition is employed in case guns which are commonly rapid-fire weapons equipped for semi-automatic operation. In this type of a gun a power-driven rammer is usually provided for loading the projectile and cartridge case into the breech of the gun in one stroke, whereupon the breech block closes automatically. When the gun is fired, it recoils and the empty cartridge case is ejected during counter-recoil.

In the past, cartridge case plugs have been made of granulated cork and a binder, and the plug was sealed to the mouth of the cartridge case with shellac. While they were the best available at the time, these cork plugs were not satisfactory as they possessed the following defects:

(A) The dusting back or settling of fine cork particles upon firing has occasionally deranged or interfered with the operation of precision equipment in the vicinity of the gun.

(B) Pieces of cork were frequently chipped from the plugs while in ammunition .hoists or in entering the breech of the gun. This has resulted in gunnery casualties such as failure of the breech block to close and improper functioning of hoists. I

(C) ,The cork plug possessed poor weathering characteristics, which were reflected in its poor dimensional stability.

(D) The, seal at the mouth of the cartridge case was frequently not gas tight due to shrinkage, etc., thereby permiting the loss of ether and alcohol vapors from the smokeless powder with the attendant fire hazard and with a change in the characteristics of the powder.

The reinforced plastic plugs of the present invention ice not only overcome all of the defects of the cork plug, also possess the following desirable features:

' I (a) They will not shear at the rabbetted joint of the p.ug.

(b) They have no corrosive effect upon'the rifting of the gun barrel.

(0) They are fireproof and will withstand high temperatures in the breech of the gun barrel.

' (d) They do not react with smokeless powder.

(e) They are strong enough to stand the entire weight of the cartridge while inverted and being hoisted in ammunition hoists.

(1) They have great impact resistance. A power ramrher cam ram a cartridge with a heavy projectile ahead of it into the breech of .a gun without damaging the plug.

(g) They fragment satisfactorily by breaking into smallpieces rather than either minute particles or large sections when the gun is fired.

" (11) They do not abrade the liner of a gun.

(i) They are provided with blow-out sections which allow the flaming powder gases to blow through the plug and ignite a tracer in the base of the projectile.

(j) A smaller bulk or volume of material is blown out of the gun since the greater strength of the plastic permits the plug to be constructed as a hollow shell instead of a solid disc.

In place of the solid cartridge case plugs of resilient materials heretofore used, the plugs of the present invention comprise hollow shells of smooth hardened plastic composition. To strengthen the plastic, fibrous materials are incorporated therein in such manner as to form a uniform admixture. After experimenting with a wide variety of resinous materials, it was discovered that better results were obtained with thermo-setting resins than with thermoplastic materials, inasmuch as the latter tended to soften considerably from the intense heat of the powder gases when the gun was fired.

It was further discovered that most of the fillers and reinforcing agents used in the plastic molding art were unsuitable for cartridge cases failing to meet the difficult requirements of high impact strength combined with controlledfrangibility. The use of wood flour, sawdust and paper fillers resulted in brittle articles. The

,. incorporation of canvas in a plastic plug yielded an article with unsatisfactory frangibility, as the plug shattered on firing but all large fragments were held together by the canvas reinforcement. Various fibers such as asbestos, tula, glass and sisal were tried with undesirable results.

. In the case of asbestos fibers and also when tula fibers were used, proper flows of the plastic resin through the mold could not be obtained.

The, reinforcing agents of the present invention which meet all of the unusual requirements were discovered to be wood pulp or paper pulp, especially kraft pulp, and chopped cloth. Both the species of fiber and its length are critical. For smaller lugs, unbleached kraft pulp is the preferred reinforcing fiber, since it is cheap; but where somewhat greater impact strength is essential, as in the larger. sizes of cartridges, the chopped cloth is used. The process employed in the preparation of the pulp.- resin plug material consists of defibering pulp in a beater and dispersing a finely-divided, powdered resin in the resultant slurry. After dilution the pulp-resin dispersion is felted out on a 60 mesh wire screen by vacuum dies to the size desired for the preform.

Unbleached kraft pulp either in rolls or laps is first re-pulpedwith water to the point that it can be put in a beater and circulated without plugging the roll. In large commercial beaters, dry or wet laps can be added di rectly, but in the smaller units re-pulping is necessary. The pulp is completely defibered; all fiber bundles being broken down by circulating in the beater with a very light brush on the roll (the beater roll just barely bearing on the bed plate but having no cutting action). When the fibers have been fully separated, the dry powdered resin is added directly to the pulp in the beater and thoroughly mixed. A dispersion of the resin in water may be used in place of the dry powder if preferred. A slightly acidic slurry is beneficial at this point to smooth out the dispersion. The pH value will vary with different resins, but for the resins recommended for plugs it would be approximately 6.0.

When a smooth dispersion of pulp and resin is obtained, the beater furnish may be pumped into either a storage chest or into dilution tanks where the consistency is regulated at approximately 1% solids by weight. It is kept agitated in such a way that the mix is not turbulent but is uniform. The desired consistency is as dense as possible so long as complete dispersion is attained. Preforms are accreted on conventional fiat pulp molding dies by lowering these dies into the dispersion tank and applying a vacuum to the die. After about 20 seconds the die is raised from the slurry, the vacuum remaining on until excess water has drained off. A pressing disc is sucked down onto the preform pad in the die to compress it, then the vacuum is cut off and compressed air turned on to blow the completed preform from the mold. Other compressing means well known in the pulp molding art may also be employed. The wet preform discs are about Ai-inch in thickness and the diameter is 1 to 2 inches less than the diameter of the final mold. Next, the preforms are dried to a rnoisture content of approximately 5% in drying ovens or other suitable means. Dried preforms are stored in a conditioning room, where constant conditions of 60 deg'rees F. and 50% relative humidity are maintained until the molding step is performed.

In molding the final article, the correct weight of preforms are stacked in registry in the cavity of a conventional apparatus for molding plastics in which the dies are contoured in the exact size and shape of the final article. The press is closed and the piece cured at 4000 pounds per square inch pressure at 300 F. temperature for minutes. This operation completely cures the molding compound so that the plastic material is hardened throughout the article. In this molding of fiat preforms into contoured articles of considerably greater dimensions, the preforms must flow to a large degree in filling all the contours of the mold. As the pulp and resin of the various preforms flow through the mold, the different preforms are amalgamated or integrated to such extent that a completely non-lamina article is produced. In the usual manner of molding pulp and plastic articles from a number of preforms, the preforms are accreted on dies which are contoured in the same manner as the final article so far as possible. In such processes, the articles are nested together, and by virtue of this preshaping, practically no fiow of the fibrous pulp and plastic occurs. There is evidence to believe that this results in an article which is composed of individual laminations bonded together only by the plastic resin, whereas the article of the present invention is bonded throughout by a homogenous mixture of fibrous pulp and resin. In the molding process, the finished molding is extracted hot and placed on a bench to cool. After cooling, excess flash at the partingline is trimmed off on a lathe, and the piece is checked for dimensions in rings go and no-go gages.

Molding a chopped cloth-resin mixture differs cons'iderably from the process described above as no accretion step is involved. Scrap material is utilized in the form of scraps of cloth impregnated with a suitable plastic. This is a common waste material resulting from trimming layers of impregnated cloth to size in molding laminated articles. The preferred impregnant is a phenol-formaldehyde resin; and this is in the partially cured stage on the cloth. As will be discussed later, the plastic impregnant should amount to 40 to 60% of the total weight of the impregnated cloth in order to provide satisfactory molding characteristics. As used in the present invention, the impregnated cloth scraps are first comminuted in a chopping machine to pieces having dimensions ranging from As-inch to one inch, the majority being A to /2-inch in width and length. The chopped cloth scrap in weighed quantity is then placed into the finishing mold and molded in the same manner as the pulp plastic preforms. Where necessary or convenient in reducing the bulk factor, the material may be first formed into a molding pill by pressing it in an unheated arbor press. This molding pill is then transferred to the finishing mold for the curing operation. In this curing step, the resin and the small pieces of cloth flow in a similar manner to the pulp fibers and plastic.

In instances where maximum impact strength is desired, as for example, in the larger sizes of cartridge cases and where the case must ride over a ledge or projection in the ramming stroke, the chopped cloth-resin mixture is the preferred molding composition.

As mentioned before, thermoplastic resins were found less suitable for making plugs than the thermo-setting resins. Of the thermo-setting resins, the phenol-formaldehyde type is preferred; and the preferred embodiment of the invention employs the molding composition known as Durez 13007. This composition is a mixture of equal parts by weight of Durez 10650" and Durez 11078.

The weight ratios of plastic materials to kraft pulp or chopped cloth are determined by the requirements of proper flow characteristics and non-segregation of fibers and plastic. When segregation occurs in any zones of the article that is zones occupied by the plastic material alone with no mixed fibers, there is a corresponding reduction of strength in the zones. Although acceptable results are usually secured using a molding mixture consisting of 40 to 60% plastic and the remainder fibrous material; keeping the plastic content within the limits 45 to 55% is safer, and the plugs regarder as the most satisfactory are produced from a mixture of equal weights of plastic material and either kraft pulp or chopped cloth.

Dimensional stability is a matter of vital concern in the manufacture ofcartridge case plugs inasmuch as any considerable degree of swelling or warping will cause jams when the cartridge cases are rammed into a gun. Plugs made as described herein possess extremely good dimensional stability for the purpose and their dimensions will not vary more than .01 inches under all normal conditions. Under an extreme test for plastic materials, prolonged immersion in water heated to F., it was found that the plugs did not expand or warp sutficiently to affect gunnery operations.

Experiments were made using lignin extenders mixed with a phenolic resin and the resultant products were found to be almost impossible to mold by reason of poor flow characteristics. This was equally true with vinsol plasticized lignin, with hydrolized wood and with lignin enriched fillers. In certain cases where flow was still high enough for molding, the resultant article showed that the strength had been adversely affected and dimensional stability lost.

Fig. 1 is a fragmentary perspective view, partly in cross-section, of one modification of the invention;

Fig. 2 is a similar View illustrating another modification of the invention.

The preferred embodiment of the invention suitable for use on ordnance in which the loading tray is exactly in line with the gun barrel is illustrated in Fig. l. The substantially cup shaped cartridge case plug molded from phenol-formaldehyde resin and fibers in equal weights has a forward wall or nose 11 with a flat face in order to afford suflicient bearing area for distributing the load in ramming theprojectile. Blowout section or recess 12 in the form of an outside truncated conical depression providing a thin walled section is the weakest portion of the plug. Upon the firing of the gun, flaming powder gases will blow through the blowout section and ignite a tracer in the base of a projectile. The proper design and location of the blowout section are important, as it was discovered that locating this recess on the inside of the forward wall 11 generally results in failure to ignite the tracer. The shoulder 13 of the plug is rounded for maximum strength and the avoidance of angles and chamfered shoulders in which stresses are concentrated and thereby Weaken the article. This shoulder is a striking improvement over the chamfered shoulder for cartridge cases designed for guns in which the case rides directly into the breech in straight line motion without climbing a ledge or projection in its travel. The skirt 14 of the plug consists of three distinct sections. The forward section 15 has a slight conical taper for easier entry into the breech of a gun. The middle section 16 is cylindrical, and the rear section 17 is also cylindrical but rabbeted at 18 in order to fit into the mouth of a cartridge case. The edge 19 is belevel for greater ease of insertion into the cartridge case. It will be noticed that the thickness of the plug decreases from the shoulder 13 to the rear section 17 of the skirt inasmuch as the stresses encountered at the rear of the skirt are considerably smaller than those at the shoulder. Fragmentation of the plug is controlled by three elements; the radial grooves 20, annular groove 21 and blowout section 12. The blowout section and the grooves have a depth of approximately onehalf the wall thickness of the plug. A plug of the type of Fig. 1 for a 6 inch gun and having a maximum thickness of 51 of an inch will yield fragments having a maximum dimension on the order of 1.5 inches. The exact number of radial grooves is a matter of choice, but 16 of these grooves have an optional feature which gives slightly better fragmentation; and best results are secured by locating them about halfway between the center and the skirt. As can be further noted from the drawings, some radial grooves 20 intersect the outer annular groove and terminate at the inner annular groove which is the boundary of the blowout section. The use of the ribs described later in connection with Fig. 2 is also optional in the article of Fig. 1. For example, molding the article in Fig. 1 in dies contoured to provide twelve ribs produces a 70% gain in impact strength. The rear of the skirt is chamfered for ease of assembly with a cartridge case.

Fig. 2 disclosed a chamfered type plug substantially cup shape which is preferred where the motion of the cartridge case on the loading tray into the barrel is not entirely straight-line motion. This applies where the cartridge case must ride up over a ledge or projection in its travel during the ramming stroke. This plug is provided with the forward wall 11 having a flat face and blow-out section 12, a skirt 22 and chamfered shoulder 23. The arrangement of the fragmentation grooves is the same as before. The principal difiference lies in the chamfered shoulder 23 which, by a Wedging action, permits the cartridge case to ride over the projections with a minimum amount of shock. The angular construction necessitated by the use of a chamfer 23 does not possess the strength of the rounded shoulder 13 of Fig. 1, hence the use of reinforcing ribs 24 is preferred in the type of construction in order to avoid increasing the wall thickness. Although either of the molding compositions disclosed may be used in manufacturing the chamfered plug, the chopped cloth-plastic mixture is preferred in view of its greater strength.

With the smokeless powder used at present, the sealing of cartridge cases is a matter of vital importance. The escape of volatiles, ether and alcohol vapors, from the powder results in' an appreciable change in the rate of combustion thereby changing the initial velocity imparted to a projectile. Moreover, the loss of volatiles accelerates the gradual decomposition of the powder which affects its characteristics further and in time renders the powder dangerous. Another undesirable result from the same cause is the extreme fire hazard presented by the presence of the highly inflammable vapors in the vicinity of the powder cartridges.

When the plugs of the present invention are used a completely satisfactory seal can be obtained between the plug and the mouth of the cartridge case by the use of adhesives whose base is an elastomer or rubberlike material. Good results are obtained by employing a Buna N type of cement. Shellac was found to be unsatisfactory for sealing the plastic plug to the case; be cause, first, it took a month or better to set, and secondly, as it was very brittle when set variations in temperature would break the bond. The elastomer cements mentioned attain maximum strength in approximately 7 days when bonding plastic to brass, and inasmuch as they never set to a brittle state, they will retain their strength through a range of all possible atmospheric temperatures. A slight difficulty in handling these cements is that both have an initial tack to brass. The excess cement squeezed out on the plug when inserted may be removed by one of two methodseither by solvents or by first coating with mineral oil the external areas of the brass case and plastic plug which will have the excess cement forced upon the outer surfaces during assembly. Solvents suitable for removing excess cement are methyl isobutyl ketone and also acetone. Assembling the plug to the cartridge case the cement is applied freely over the rabbeted section 17 of the skirt of the plug and also to the interior of the rim of the cartridge case. Cement is allowed to dry on these surfaces for a few minutes in order to partially evaporate the solvent, then the plug is forced into the case. The excess cement squeezed out should be wiped off at once. In the event that the cartridge case is slightly out of round, the plug should be inserted about /2 inch into the case, and the voids filled with cement by daubing the loose area with a brush. The plug is then immediately pushed in and the crevice filled. In case the plug is loose it will be necessary to apply a second coat of cement before inserting the plug into the case. It has been found that a IOOO-pound pull is necessary in order to remove a plug assembled in this manner once the cement has set.

From the foregoing description it is apparent that the invention has provided improved types of cartridge case plugs of strong, light, waterproof construction and having characteristics of controlled frangibility. It is to be understood that true and proper scope of the present inven tion is limited only by the appended claims and in no Wise by the specific embodiments disclosed herein.

The invention herein described 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 or therefor.

What is claimed is:

1. A cartridge case lug formed in substantially a cup shape from a composition compounded of.from 40-60% by weight of phenol formaldehyde resin and the remainder of kraft wood pulp as a fibrous reinforcing material, said plug having a plurality of fragmentation grooves provided in its interior surface including at least one annular groove, a plurality of radial grooves intersecting said annular groove, and a substantially flat portion constituting the nose of said plug, said portion being formed with a relatively thin walled blowout section at the boundary of which the innermost ends of the radial grooves terminate.

2.. A cartridge case plug formed in substantially a cup shape from a composition compounded of from 4060% by weight of phenol formaldehyde resin and the remainder of kraft wood pulp as a fibrous reinforcing material, said 7 plug having a plurality of grooves defined in its surface 2,189,889 for eifecting controlled fragmentation thereof, and hav- 2,237,048 ing a weakened blowout section formed in its nose. 2,299,904

References Cited in the file of this patent 5 UNITED STATES PATENTS 1 312 2,045,004 Vickers June 23, I936 783,688

8 Engel Feb. 13, 1940 Carter Apr. 1, 1941 Keeling Oct. 27, 1942 FOREIGN PATENTS Great Britain Aug. 25, 1903 France July 17, 1935

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