US2559275A - Cellular plastic wad - Google Patents

Description

July 3, 1951 J. T. BROWN EI'AL.

CELLULAR PLASIIC IAD Filed Juil.)v 3, 1947 INVENTOR dbf/,lv THOMPSON @Rauw Patented July 3, 1951 CELLULAR PLASTIC WAD John Thompson Brown, Montchanin, Del., and Benjamin K. Daubenspeck, Stratford, Conn.,

assignors to Remington Arms Company, Inc.,

Bridgeport, Conn., a corporation of Delaware Application July 3, 1947, Serial No. 758,832

12 Claims. (Ci. 102-42) This invention relates to ammunition, and more particularly to ller wads for shot shells.

The function of the filler wad or wad column, which in a shot shell separates the propellant powder from the shot mass, is twofold. First, the wadding functions as a gas seal, being propelled forward by the gas pressure behind it and transmitting this pressure to the shot charge, preferably without any leakage.V of gas through or around the wadding and into the shot charge; second, the wadding should cushion the impact of the suddenly generatedpowder gas against the shot in such a way that the shot is pushed and gradually accelerated, instead of being struck a sudden hammer` blow. In a 12 gauge shot shell, the shot charge has a weight of 1 to 1% oz.; hence, a substantial inertia. Moreover, the sudden generation of a large quantity of gas in the confined space behind the wadding is productive of undesirably high pressures unless the wadding is susceptible to substantial compression, thereby enabling a certain expansion of the gas before and during the initial movement of the shot charge.

".I'he two functions of the wadding are to a certain extent contradictory. A rigidgtightly barrel sealing body is required to prevent gas leakage, while at the same time a highly compressible body is desirable to prevent excessive peak pressures and enable'a more gradual acceleration of the shot. Certain attempts have heretofore been made to provide a wad column of two or more diiferent elements of diierent properties, one having a gas sealing function and another being of compressible character. However, prior attempts to provide a-highly compressible wad have not been satisfactory, by reason of the dimculty in providing a suiiiciently compressible medium which Iwill not be disintegrated under firing stresses. The maximum pressure generated in the ring of an ordinary shot shell is of the order of 10,000 pounds per square inch, and this pressure is transmitted from the powder chamber through the wadding to the inert shot charge. Such compressible materials as have been used hitherto disintegrate under these high pressures into fragments which at gun muzzle are dispersed into a cloud which obscures the shooters view and may be blown back in his face.

The present invention comprises the discovery of a class of materials which can be easily and cheaply formed into one-piece wads which are very highly compressible and on compression are packed into a thin disk that is projected from the shotgun barrel with little or no fragmentation.

These materials are of a group which for the purpose of this specification will be called cellular plastics. They are also known by such terms as foam plastics or expanded plastics.

In the drawings:

Fig. 1 is a side view of a shot shell, a portion of the body wall being broken away to illustrate a wad according to the invention.

Fig. 2 is an enlarged fragmentary side view of an unflred wad.

Fig. 3 is a fragmentary, sectional elevation of a fired wad, enlarged in the same proportions as Fig. 2 so that Figs. 2 and v3 show the comparative lengths of the unred and ilred wad.

Fig. 4 is an enlarged fragmentary cross-section of a wad embodying the invention, being substantially a copy of a photo-micrograph.

For the purpose of this specification, the term plastic or its plural form of plastics are used as nouns indentifying generally t at class of synthetic organic polymers which a e susceptible to formation and/or shaping in a iluid or semi-duid condition and upon proper processing yield bodies which at ordinary te peratures are continuous and rigid at least the extent of being self-sustaining. A variety f addition agents for enhancing particular properties may be included. Such plastics include phenolics, aminoplasts, vinyls, acrylics, polyamids, polystyrene, polyethylene, polyesters," and cellulose esters and ethers. The plastics in their ordinary form are continuous and substantially homogeneous bodies. It has recently been found that plastics generally are susceptible to formation into a cellular structure of greatly reduced apparent density as compared with their density in their normal condition. The specific gravity of the solid plastics varies from about .9 to about 1.33. these figures corresponding-'to a density range of from about 56 pounds per "cubic foot to about 82 pounds per cubic foot. When produced in cellular form, the apparent density may be as low as 1.5 pounds per cubic foot or even less. Such cellular plastics having an apparent density as high as 1l pounds per cubic foothave been made into satisfactory shot shell wads.

Taking cellulose acetate as an example, its density in its common commercial form ranges from about '79 pounds per cubic foot to somewhat over 82 pounds per cubic foot. By proper treatment. it can be expanded into substantially rigid and coherent bodies having densities from 1.5 pounds per cubic foot 'to about 8 pounds per cubic foot. One method of accomplishing this may be outlined as follows:

A pulverulent or granular material comprising 97% or 98% unplasticized cellulose acetate, the remainder being chiefly water, is admixed with 9% to 20% of a volatile liquid which is nonsolvent for the cellulose derivative at '10 F. and

` a solvent therefor above about 160 F., say an admixture of ethyl alcohol and acetone. This composite is extruded from an extrusion machine at a temperature between 350 F. and 400 F. with a back pressure of at least 300 pounds per square inch. Under these conditions of temperature and pressure the mass has the consistency of a stiff paste or dough. As the mass is extruded through a small orifice, there is a sudden decrease in pressure which permits the superheated solvent to flash vaporize and form the expanded body. The exposure of the expanded body to the atmosphere after expansion permits cooling and evaporation of the remaining solvent to rigidify the material. The expanded body consists of a great multiplicity of uncommunieating cells separated by a honeycomb web or lattice of the solid material. A more uniform texture can be secured by the addition to the mixture of a suitable quantity of a solid pulverulent material which is insoluble in the solvent and is inert to the plastic, such as barium sulfate, powdered copper, powdered aluminum, aluminum oxide, mica, fullers earth, zinc oxide, etc. The solid grains act as nuclei for the formation of the gas bubbles which establish the individual and uncommunicating cells. Bodies of a desired cross-sectional configuration can be secured by associating a short guide of the desired cross-section with the extruding orice. For example, a rod of a diameter of 3A" may be secured by placing adjacent an orifice of a diameter of the order of 0.09 to 0.145", a tube of an interior diameter of 3/4 and about 3" or 4" long. 'Ihe material expands and rigidifies with such rapidity that a longer guide tube is unnecessary. The porosity or density of the product is a function of the amount of solvent used in the mixture. The greater the amount of solvent the lower the density of the product. 'I'he lower density limit for a product suitable for the purposes of this application appears to be about 1.5 pounds per cubic foot, corresponding to a solvent content in the mixture of about Lower density materials are subject to undesirable fragmentation under shot shell firing pressures. The rigidity and coherency of the low density product may be augmented by adding to the starting material an appropriate amount, say 1 to 10% of a suitably dispersed fibrous material which is insoluble in the solvents and will withstand the rigorous temperature conditions, such for example, as glass fiber. i

Other methods of preparing cellular plastics comprise the admixture with the pulverulent plastic of volatile or decomposable solids, or of soluble salts subsequently leached out by the use of a solvent, or the generation of steam by the heat of reaction of the constituents of a plastic such as urea formaldehyde in admixture with a catalyst.

A product comprising separate non-communicating cells is preferable for the purpose of the present invention. A structure of communicating cells, such as that produced by the use of soluble salts, is less coherent and more easily disintegrated. A typical individual cell plastic, such as cellular cellulose acetate, will be crushed or permanently compressed under firing pressures to about 13% of its original length with f 4 little if any fragmentation. After firing, the compressed wads, each bearing a dimpled shot pattern and having an average length of about .06". can be recovered substantially intact.

The cellular plastic wad is preferably used in conjunction with a gas sealing Wad which is of conventional design, for example a felted fibrous construction as disclosed in the patent to Burghardt, No. 1,834,377, December 1, 1931, except that, since it need not be compressible, it may be so compacted and impregnated with a high melting sealing and lubricating material as to form a superior and substantially perfect gas seal.

To obviate bore friction and abrasion, the cellular plastic wad is preferably surface lubricated, and the non-communicating cellular structure is effective to present unwanted penetration of the wad body by the lubricant, confining the lubricant to the surface, where it is useful.

Referring to the drawings, numeral I0 is a head of a shot shell comprising a body Il which contains a charge of shot l2, a charge of powder I3, a gas sealing wad I4, and a compressible cellular wad I5 of the present invention. The cellular structure of the Wad is clearly illustrated in Fig. 4, which is substantially a copy of a photo-micrograph. The comparative lengths of the wad l5 as loaded and the same wad I5' after ring are shown in Figs. 2 and 3 which are on the same scale, each being enlarged approximately three times the dimensions used for a 12 gauge shot shell. In firing, the length and volume of the wad are reduced to not over about 13% of the original length and volume. For a 12 gauge shot shell, the original wad length is substantially 1/2", the pattern of the adjacent shot is impressed in its forward face on firing, and its length is reduced to a maximum of about .09" at the crests adjoining the shot cavities to a minimum of about .04" at the bottom of the shot cavities. 'I'he average length is about .06", which means that a powder expansion space having a length of about .44 and a volume of 87% of the original wad volume has been provided.

By the use of a highly compressible cellular plastic wad, it becomes possible to materially improve and perfect the gas sealing Wad. Gas leakage into and past the wad column facilitates wad break-up and is ballistically detrimental. Prior to the present invention, improvement in gas sealing has been handicapped by the necessity for making the gas sealing wad somewhat compressible. No material hitherto proposed as a cushion Wad has been susceptible to an amount of compression whicn would enable the use of a substantially ncn-compressible gas-sealing wad without producing excessive pressures. With the wad of this invention, complete gas sealing and standard velocity can be secured with pressures materially lower than accepted standards. Shot shells containing a cellular cellulose acetate wad and a gas sealing wad have been shot in comparison with a commercial imperfectly sealing wad column and with experimental shells containing a commercial wad and a gas sealing wad, with the following results:

Cellular Plastic Commercial with oas seal with oas seal Comme'cal v P v P v P S84 9, 40o ses 11,000 ass 10,100 871 9, soo ses 11, ooo 856 9, 10o 874 9, 400 882 1o, 60o ssi 1o, 40o

acudan Each of the above gures is an average for 25 shots, and velocities the usual average over a range of 25 yards. A11 components of each compared groupof shells except the wad column were identical. It will be seen that as compared with conventional and commercially acceptable Wadding, the wadding of this invention gives pressures which are not only lower but more unihform, with no material difference in velocity, also that the tendency of a tight gas seal to cause excessive pressure has been completely overcome.

What is claimed is:

1. A shot shell wad comprising a unitary, substantially circular cylindrical body having substantially the diameter of the inside of a shot shell, said body consisting of a single piece. substantially the full size of said body, of a cellular, expanded, plastic containing a multiplicity of non-communicating empty cells separated by permanently crushable, relatively thin, Vwalls of the solid plastic.

2. A shot shell wad according to claim 1, having a lubricated surface, the lubricant being conned to the surface portion by the non-communicating cell structure.

3. A shot shell wad according to claim 1. in which the cell defining material is an admixture of a plastic with 1% to 10% of a hardening and strengthening agent.

4. A shot shell wad according to claim 3, in which the hardening agent is ber glass.

5. A shot shell wad according to claim 1, said single piece of cellular expanded plastic having. before crushing, an apparent density of not over 11 pounds per cubic foot.

6. A shot shell wad according to claim 1, in which the cellular expanded plastic is cellular cellulose acetate.

7. A shot shell wad according to claim l, in which the cellular expanded plastic is cellular styrene.

8. A shot shell wad according to claim i, in which the cellular expanded plastic is cellular phenol formaldehyde.

9. A shot shell containing a charge of a propellent powder and a shot charge separated from said powder charge by a wad column comprising at least one cushion wad formed of a single piece of a cellular expanded plastic containing a multiplicity of non-communicating empty cells separated by permanently crushable, relatively thin walls of the solid plastic.

10. A shot shell according to claim 9, in which the cellular expanded plastic cushion wad is surface lubricated. i

11. A shot shell containing a charge of a propellent powder and a shot charge separated from said powder charge by a wad column comprising a cushion wad of permanently crushable cellular cellulose acetate plastic and a gas sealing wad.

12. A shot shell according to claim 11, in which the gas sealing wad is a felted brous material impregnated with a high-melting-point lubricant.

JOHN THOMPSON BROWN. BENJAMIN K. DAUBENSPECK.

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

UNITED STATES PATENTS

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