US3855381A

US3855381A - Method of making plastic cartridge casing

Info

Publication number: US3855381A
Application number: US00374336A
Authority: US
Inventors: G Eckstein; W Moyher
Original assignee: Remington Arms Co LLC
Current assignee: Remington Arms Co LLC
Priority date: 1971-11-18
Filing date: 1973-06-28
Publication date: 1974-12-17
Anticipated expiration: 1991-12-17
Also published as: US4065541A; US3786755A; JPS532000B2; AU4817472A; JPS4862869A; CA979288A; FR2161719A5; GB1403594A; AU464492B2; DE2253440A1

Abstract

A method of making a one-piece plastic shotgun shell, i.e. where the transverse base portion is integral with the tubular body portion. A tubular plastic slug is carried progressively through a series of dies to produce a shotgun shell having a body portion which is highly oriented and a head section of somewhat lesser orientation. An oriented, integral primer gas seal skirt is formed inside the primer opening.

Description

I f -States "atom Eckstein et all.

METHOD OF MAKING PLASTIC CARTRIDGE CASING [451 Dec. 17, 1974 3,185,095 5/1965 Mayer 102/44 3,205,290 9/1965 Covington 264/292 3,284,560 11/1966 King 264/323 X 3,492,387 1/1970 Larson... I 264/292 X 3,514,468 5/1970 Sutcliffe. 264/292 X Primary Examiner-Richard R. Kucia Attorney, Agent, 0r FirmJohn H. Lewis, Jr.; Nicholas Skovran [57] ABSTRACT A method of making a one-piece plastic shotgun shell, I i.e. where the transverse base portion is integral with the tubular body portion. A tubular plastic slug is carried progressively through a series of dies to produce a shotgun shell having a body portion which ishighly oriented and a head section of somewhat lesser orien' tation. An oriented, integral primer gas seal skirt is' formed inside the primer opening.

6 Claims, 19 Drawing Figures PATENTED DEC] 7 I974 sum 1 0r 3 METHOD OF MAKING PLASTIC CARTRIDGE CASING This application is a Division of co-pending application Ser.No. 199,913 filed by George R. Eckstein et al. on Nov. 18, 1971 now US. Pat. No. 3,786,755 issued Jan. 22, 1974.

This invention relates in general to an improved plastic cartridge casing and the method of making the casing. More specifically, the invention relates to a onepiece cartridge casing of thermoplastic material which is formed by expanding at least a portion of a plastic slug in two directions to form a highly bi-axially ori ented tubular body portion and a thickened rear section, which rear section is then substantially deformed to provide the base portion of a shotgun shell including a novel primer sealing means.

The use of bi-axially oriented plastic, i.e. high density polyethylene, in shotgun shells, began in this country in the early 1960s as a result of the invention claimed in the Covington et al. US. Pat. No. 3,103,170, issued Sept. 10, 1963. Today, all the major US. and Canadian manufacturers provide plastic shells with bi-axially oriented bodies. Since that time, the practice of the consumer reloading his shotshell casings has increased substantially so that ammunition being manufactured today must take the reloaderinto consideration.

The advantages of providing a one-piece plastic shell, i.e. with base portion integrally formed with the body portion, are well known and need not be repeated here. One-piece shells have been known for a long time. See US. Pat. No. 1,364,871 to Ernst dated Jan. 11, 1921; U.S. Pat. No. 2,232,634 to Roberts et 211. dated Feb. 18, 1941; US. Pat. No. 2,349,970 to Lambeek dated May 30, 1944; U.S. Pat. No. 3,171,350 to Metcalf dated Mar. 2, 1965; US. Pat. No. 3,284,560 to King et a1.

dated Nov. 8, 1966; US. Pat. No. 3,377,951 to Larson dated Apr. 16, 1968; and French Pat. No. 1,170,851 (Core) published on Jan. 20, 1959.

Some of the shells described in the Patents cited above are plastic shells having integral body and base portions which were developed from injection molded slugs or starting pieces and which require that the finished head and basewad portion remain in substantially as-molded condition, free from deformation and orientation. Unlike such shells, all portions of the basewad portion of the present invention undergo substantial degrees of cold plastic deformation with the usual results on the physical properties of the cold worked plastic.

The present process is an adaptation of a process originally used to make aluminum shotshell and center fire cases. See U.S. Pat. Flo-2,668,345 to G. R. Eckstein issued on Feb. 9, 1954. However, there are differences in working with plastic, some of which will be described during the explanation of the process below.

A particular point of novelty, in the present case, is the primer gas sealing means and the method of forming the gas sealing means. There are various means presently in use or proposed for use which call for gas sealing rings or skirts located at the front end of the primer bore which are in direct contact with the propellant means so that they are moved by the explosive combustion pressure in the shell to engage the front end of the primer to efiect gas sealing.

As long as these gas sealing rings remain intact, reasonable sealing of the explosive gases between the primer and the primer bore can be expected. However,

' plastic body with a thickened wall if the gas sealing ring becomes detached or broken, as sometimes happens when reloading a spent shell, the gas sealing means is rendered inoperative and the shell becomes useless for further reloading.

Because the primer sealing ring of the present invention is found inside the primer bore, it is protected to some degree from mis-aligned depriming pins and thus is less susceptible to being damaged.

It is a general object of this invention to provide a cartridge of thermoplastic material in which the tubular body portion and integral base portion are oriented, the tubular body portion to a high degree and the integral base portion to a substantially lesser degree. A particu lar object of the invention is to provide a novel primer sealing means which will be effective to seal a variety of lengths and diameters of primers.

These and other objects, features, and advantages of the invention will be more fully brought out in the following specification, claims and drawings in which:

FIG. 1 is a cross-sectional view of a one-piece plastic shotshell made according to thepresent invention.

FIG. 2 is an exploded cross-sectional view of the primer opening and the associated gas'sealing ring.

FIG. 2A is the same view as FIG. 2 except that a primer means is shown in place.

FIG. 3 is a cross-sectional view of the starting plastic slug.

FIG. 4 is a cross-sectional view of a radially expanded slug which has also been flared at one end.

FIG. 5 is a cross-sectional view of the impactextruded portion at one end of and on the exterior of the body. 1

FIG. 6 is a cross-sectional view of the extruded plastic body after the forward end is trimmed and the thickened rear end portion inverted so that the mass of plastic is now inside the body.

FIG. 7 is a cross-sectional view of the plastic body after the thickened rear end portion is deformed to form a cartridge base portion with a primer opening and an extruded ring surrounding the portion of the primer opening opposite the tubular body section.

FIG. 8 is a cross-sectional view of the plastic body of FIG. 7 after sizing.

FIG. 9 is a cross-sectional view of the punch and die arrangement for the preform step which results in an expanded and flared preform as shown in FIG. 4-.

FIG. 10 is a cross-sectional view of the punch and die arrangement for the impact extrusion step which results in an oriented body as shown in FIG. 5.

FIG. 11 is a schematic view of a trimming means which removes the lower end of the body member shown in FIG. 5.

FIG. 12 is a cross-sectional view of the shrouding hunter and support'meansof the folding or inverting step which results in the plastic cartridge casing shown in FIG. 6.

FIG. 13 is a cross-sectional view of the hunter and die means of the pre-heading step which resultsin the cartridge casing shown in FIG. 7.

FIG. 14 is a cross-sectional view of the plastic cartridge casing being pushed through a sizing die.

FIG. 15 is a cross-sectional view of the rearwardly extending extruded collar on the pre-headed plastic cartridge being impacted to form a forwardly extending annular ring which eventually becomes the primer sealing ring.

FIG. 16 is a cross-sectional view of feeding the metal cap to the plastic shell.

FIG. 17 is a cross-sectional view showing the first heading bunt in which the metal cap is attached to the plastic shell and the primer sealing ring is pushed into shape.

FIG. 18 is a cross-sectional view of the main or final bunt in which the metal-capped plastic shell is formed to final dimensions.

Referring now to the drawings, FIG. 1 shows a shotgun shell casing having a tubular body portion 12 which may be skiv ed to form a tapered end 14 at its mouth end and which has an integrally formed transverse base portion 16 at the breech end of the shell. The tubular body portion 12 is essentially of uniform wall thickness although the rear portion 18 tapers slightly near the base portion. A conventional metal head member 20, of brass, steel, or any other suitable metal, is attached to the base portion 16 primarilyby an annular rim 22 integral with the base portion 16 and by the annular metal skirt 24 which projects inwardly into the primer opening 26 of the base portion. Integral with the base portion 16 is a continuous gas sealing skirt 28 which projects inwardly towards the center of the opening to form an annular ring havinga bore which is less than the primer bore. An alternative method of attaching the metal cap to the plastic base portion is to provide a plurality of prongs (not shown) in place of the annular metal skirt 24 and embed the prongs in the plastic base portion.

A primer 30 is inserted by force fit into the primer bore and extends past the forward end of the primer sealing skirt 28 so that the skirt forms a continuous surface with the cylindrical wall surface 26A of the primer bore. (See FIG. 2A) It can be seen that the gas sealing skirt'does not come into direct contact with the combustion heat and gases which result from the ignition of the propellant means. Thus, it can be expected that there will be less erosion of the primer seal as a result of the hot combustion gases.

The gas sealing skirt 28 utilizes a collar of plastic drawn out to an oriented section and buttresses with a tight fitting primer bore to concentrate stresses across a thin band or line of contact between plastic and primer.

It should be recognized that the working or shaping of many thermoplastics, and especially polethylene, is an art as contrasted to the working of metals. In the case of polyethylene, the pieces of plastic shaped by tools bear little resemblance in profile and dimension to the tools that did the shaping. These tools must be so shaped to compensate for the high degree of dimensional recovery that is typical of polyethylene after a severe cold-forming operation. In general, any plastic that can be mechanically deformed below its melting point can be processed according to the present process.

The starting point of the process is to provide a tubular plastic slug 32. (See FIG. 3) This plastic slug can be made in various ways but from the standpoint of economy, it has been found that extruded plastic heavywalled tubing, cut to proper length, can be used very conveniently and economically.

The process which has been developed involvesthe utilization of operating die sets of the progressive transfer type so that the time interval between steps is measured in fractions of a second. For this reason, the configurations and shapes of the workpieces shown in the FIGS. 4 through 7 are not entirely correct since the plastic after deformation takes some time to recover to the dimensions shown in the FIGURES. It is impossible to accurately measure the shape of the plastic immediately after removal from the dies since the plastic is in the process of elastic recovery and change due to this memory. The FIGURES thus represent sketches of workpieces which have been withdrawn from the process at that particular point and allowed to cool and attain a stable value.

The processing described in the following text can be accomplished on slugs at ambient temperature. Although a single-action press with auxiliary motions for powering transfer bars and undermotion knockout sleeves was used for most of the development work, the production presses can be relatively high speed and large enough to handle multiple rows of tools.

Slugs 32 are fed to each row of tools end to end (not shown) and are positioned over the first mechanical working station called preform." There are two tools used in this station, a top punch 34 and a support die 36. (See FIG. 9) I An important function of the preform step is to stretch the slug radially and prepare it to fit accurately into the die bore of the next processing step (impact extrude). Since plastic has a large elastic recovery and a memory factor, it is necessary to select tool diameters of punch 34 so that .the slug is overstretched. The uppermost portion 34a of punch 34 establishes a top flare on the preform to add a safety factor for punch entrance in the next operation.

FIG. 9 shows tool positions at the bottom of the machine stroke. On the upstroke, the preform is lifted up and is stripped against a stationary bushing (not shown). v

The preform is then moved into axial alignment for the next operation called impact extrude. (See FIG. 10) Impact extrude is a severe mechanical operation and requires the greatest thrust of any of the steps in the process.

There are two tools used in this step, a die 40 and an extrusion punch42. Punch 42 has a series of important dimensions and profiles. Beginning at the lower extremity, it has a taper section 42a, then a straight cylindrical section 42b, an enlarged knob-shaped working punch land 42c, and finally the support shank 42d of the punch. I

Tapered section 42a enters the bore of preform 38 and expands it radially into contact with the extrusion die bore 40a. Preform 38 can be at room temperature or at an elevated temperature below the crystalline melt temperature for the plastic being used. The diameter of cylindrical section 42b of the punch and the bore 400 are so related that the preform does not wrinkle or buckle when the working punch land 42c begins the actual impact extrusion of the plastic. The diameter of working punch land 42c is selected to clear the die bore 40a by an amount which will produce the desired wall thickness in the body of the finished shell. However, because of the elastic recovery of the plastic, the actual clearance between the punch and die is much less than the shell wall thickness produced.

The support shank 42d of the punch is back tapered to minimize the area of shell in contact with the punch at the instant of extrusion since the thick collar at the top of the extrusion (which becomesthe base of the axial or longitudinal direction and that an impactextruded component 44 has been formed which has a substantially straight walled tubular body portion 440 and a thick walled rear end section 44b, which thick wall is on the exterior of the body member. The forward end 44c, shown between punch land 42c and die insert 40c, is important to keep the tools from striking each-other.

The next operation performed on the shell is to trim the excess portion 44c from the forward or mouth end of the shell. This can be done by lancing with a knife why any other well-known means. FIG. 11 shows the portion 44c detached from the component after the component has been moved past the lancing means 45. After the removal of the portion 440, the shell mouth of the trimmed component 46 is at complete open bore and can be supported with a full diameter stem within the next station which is called profile inversion.

Profile inversion is a gathering or inversion of plastic which has been positioned on the exterior of theworkpiece at its upper end. This operation serves to crudely form the shell head and prepare it for final forging. This operation uses two basic tools, a bunter 48 and a stem 50. (See FIG. 12).

Stem 50 has a precision profiled noseSOa and is inserted in the trimmed impact extruded component 46 to support the shell while shroud-like bunter 48, with its profiled bore, establishes the required bore and diameter of the head section in the component. In operation, the trimmed impact extrusion 46 is located in axial alignment with stem 50. The bunter 48 descends and drives the workpiece over the stem and effects a diameter reduction of the component top. At some instant in the stroke, the clearance between stem 50 and the bore of bunter 48 serves to lock and support the component for further compression and inward folding. The component 52 is then removed from the stem 50 and moved to the next station called pre-heading. (See FIG. 13)

It is the purpose of pre-heading to complete the dimensional and profile requirements for the head of the shell.

The pre-head stationutilizes. three main tools to support and forge theplastic workpiece or component, i.e. a bunter 54, a stem 56, and a diemeans 58. The component S2 is supported by a stem 56 and a die 58 and is compressed by a bunter 54 which has a complex series of contours to form the preheaded component 60. The counterbore 54a fashions the extruded collar 60a and the corner cutaway 54b produces the rim 60b. Extruded collar 60a surrounds the primer bore and subsequently will be deformed to become the primer gas seal. Rim 60b will be reformed to become the rim fill of the cap which is added in a later step of the process. In operation, the profile inversion component 52 is driven by thebunter 54 into the die 58 as well as over the stem 56. Preheading is a high-thrust operation in is vented. This flow makes it possible to form' the collar 60a and the rim 60b. The flow also verifiesthe tapered wall between the head and body sections of the shell.

FIG. 13 shows the tool position at the bottom of the stroke. Again the component is lifted from stem 56 and die 58 on the upstroke, preferably by means of a knockout sleeve- (not shown).

The pre-headed component 60 is then transferred into axial alignment with the last station in the progressive die set. It is a simple sizing operation. (See FIG. 14) There are two tools used, a die 64 and a punch 66. In operation, the pre-headed component 60 is pushed mouth down through the die 64. The position of the tools shown in FIG. 14 is a mid-point in the downstroke of the press.

The sizing operation serves as a corrective means, at-

tained with inexpensive tooling, for establishing a desired body diameter on the finished shell.

After mechanical processing, the sized components 62 are washed free of lubricant and simultaneously stabilized dimensionally by using a hot water wash. The temperature of the wash is selected to coincide with the maximum temperature expected in storage conditions for the finished shells. Higher temperatures at wash accomplish dimensional stability in shorter times. For this purpose, 170F for 20 minutes is suitable.

Components thus washed and stabilized are ready for the assembly with metallic caps and primers. Basically, the equipment includes a -stem 68 and a die 70. (See FIGS. 15-18) In practice, the support stem 68 is positioned to hold the component well above the heading which plastic flows and extrudes into all free space that die 70 for the first working station (FIG. 15) of this'series. A shroud-like bunter 72 with center punch 74 inverts the collar 60a (FIG. 7) into position 76 and the rim 60b FIG. 7) FIG. tapered inwardly for ease in applyingthe metal cap 20 in the following work station.

FIG. 16 shows the cap 20 in place. The cap 20 has been half headed, i.e. the preparation for theprimer and the rim bulge 78 made in a separate operation. A simple flat end punch 80 is used for seating the cap.

FIG. 17 shows the stem 68 dropped to'align the capped shell within the die 70 at matching position of die shoulder 70a with cap bulge 78. Bunter 82 with center punch 84 drives the shell into location. The inverted collar 76 is drawn outinto a thinner section and the rim material 60b is displaced into the cap bulge 78.

FIG. 18 shows the finishing bunting of the shell. Bunter 86 with center pin 88 is critically profiled to provide finished dimensions to the gas sealing collar and the primer bore. Also at this station, the metallic rim of the cap 20 is compressed to hold onto the plastic fill that has been prepared-in the previous station (FIG. 17). The top area on the cap which will receive the flange of the batterycup type primer is also verified at this station.

In all of FIGS. 15-18, the punches and bunters are shown at the bottom of the press stroke.

Priming the shell may be done by the conventional method of inserting and seating of a regulation batterycup type of shotshell primer. The location of the gas sealing collar 28' is such that it will function with a shorter battery cup usually found in European made shotshells or with longer battery-cup primers generally used in the United States.

Because of elastic recovery and memory, the extrudingof plastic between a punch and die does not result in a plastic article having the shape and dimensions of the space between the punch and die.

A substantial amount of deformation and movement of plastic is necessary to achieve the desired results in the present invention. For example, a slug as shown in FIG. 3 having an O. D. of 0.665 inch and an I. D. of 0.230 inch is expanded at the base end 44b in FIG. 5 in the impact extrude step to an CD. of 0.912 inch and an I. D. of 0.495 inch and finally forged, sized, etc. to a finished shell having a base 0. D. of 0.790 inch and a primer bore of 0.220 inch.

The impact extruded dimensions listed above are the cooled dimensions and are not the dimensions of the plastic workpieces at the time they are subjected to deformation in the die set. Accordingly, the tool dimensions are somewhat greater than those listed for the plastic since the plastic workpieces must be expanded before elastic recovery and memory takes over. However, the dimensions are relatively accurate so that some indication can be gained as to the amount of radial deformation of the plastic slug.

It can also be seen that the elongated, thickened endwall portion 44b (FIG. 5) is deformed substantially in order to finish as the base portion 16 of the final shell (FIG. 1). Thus, there are specific portions of the base portion 16 which are at least moderately oriented 0r deformed, e.g. primer seal ring 28 and annular rim 22. Other sections of the base portion, because of the substantial cold working of the plastic to achieve the shape and dimensions of the final shell, can be expected to be oriented and strengthened to some degree. The tubular body wall portion 12, of course, is highly oriented in a longitudinal as well as a circumferential direction.

What is claimed is:

l. A method of making a cartridge casing comprising the following steps:

1. Forming a slug of thermoplastic material having a tubular, thick-walled construction;

2. Expanding the slug radially to increase the inner and outer diameters of the tubular slug and to flare one of the ends of the slug outwardly;

3. Positioning the non-flared end of said radially expanded slug into the bore of an extrustion die and impacting said slug so as to form a highly oriented tube having an externally flanged end portion;

4. Trimming the plastic tube at the end opposite to,

the externally flanged end portion;

5. Forming the flanged end portion of the slug to change the profile thereof and prepare the section for proper finished dimensions and profile control, said profile changes comprising decreasing the outer diameter to a predetermined dimension in order to permit it to be inserted into thedie for the following step, repositioning and thickening the externally flanged portion so that the flange is on the inside of the tube and defining a central opening which is of predetermined diameter for the next step, said plastic slug at this point resembling a roughly formed cartridge casing;

6. Pre-heading the roughly formed cartridge casing by inserting the flanged slug into a die and compressing the flanged end into approximate final dimensions and including an extruded, continuous, annular lip means which extends rearwardly from the periphery of the central opening;

7. Pushing the shell mouth first through a sizing die in order to decrease the outer diameter of the shell and to correct irregularities in the processing;

8. Washing the plastic casings in hot fluid at the desired temperature to relax the stresses in the casing and to stabilize the dimensions at or below that temperature;

9. Inserting the pre-headed casing into a metallic cup means and heading the casing to final dimensions including the forcing of said annular extruded lip into the primer opening to form an oriented, continuous, gas sealing ring integral with the inside of the final primer opening.

2. A method of making a preferentially oriented plastic shotshell casing comprising providing a tubular slug of thermoplastic material, expanding the slug radially to increase the inner and outer diameter of the slug, inserting said expanded slug into a die and impacting the slug with a punch to rearwardly extrude a highly oriented tubular plastic body with a relatively thick flanged wall section located on the exterior of said tubular body, trimming the forward end of said tubular body to the desired length, progressively forging the flanged end of said plastic body to position the thick flanged wall section on the interior of the shell and to form a cartridge head with a primer opening therein, extruding an annular lip means to extend rearwardly from the primer opening and finally inserting the preheaded cartridge casing into a metallic cap and heading the casing to final dimensions to attach the casing to the cap while deforming the rearwardly extending lip means into the primer opening to form a continuous, oriented plastic sealing lip integral with and positioned intermediate the ends of the primer opening.

3. A method of making an oriented plastic cartridge casing as recited in claim 2 in which the thick walled plastic slug is a section of conventionally extruded thick walled tubing.

4. A method of making an oriented plastic cartridge casing as recited in claim 3 in which the radially expanded slug is flared at one end to facilitate the punch insertion and positioning in the impact extrusion step.

5. A method of making an oriented plastic cartridge casing as recited in claim 2 in which said plastic slug is at a temperature less than the crystalline melt temperature of the plastic when impact extruded.

6. A method of making an oriented plastic cartridge casing as recited in claim 2 in which the initial thick walled plastic slug has an outside diameter less than the outside diameter of the finished cartridge casing, said plastic slug being radially expanded to an outside diameter substantially greater than'the outside diameter of the finished casing.

22 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N 3.855.381 Dated DECEMBER 17, 1974 Inventing) GEORGE R. ECKSTEIN and WILLIAM G. MOYHER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Col. 6, Line 36 "FIG.tapere d" should read-"is tapered- Signed-and sea le'd "this 18th day' of March 1.975.

1 MARSHALL DANN RUTH .C. MASON 7 Commissioner of Patents Attesting .Officer and Trademarks

Claims

1. A method of making a cartridge casing comprising the following steps:

2. A method of making a preferentially oriented plastic shotshell casing comprising providing a tubular slug of thermoplastic material, expanding the slug radially to increase the inner and outer diameter of the slug, inserting said expanded slug into a die and impacting the slug with a punch to rearwardly extrude a highly oriented tubular plastic body with a relatively thick flanged wall section located on the exterior of said tubular body, trimming the forward end of said tubular body to the desired length, progressively forging the flanged end of said plastic body to position the thick flanged wall section on the interior of the shell and to form a cartridge head with a primer opening therein, extruding an annular lip means to extend rearwardly from the primer opening and finally inserting the pre-headed cartridge casing into a metallic cap and heading the casing to final dimensions to attach the casing to the cap while deforming the rearwardly extending lip means into the primer opening to form a continuous, oriented plastic sealing lip integral with and positioned intermediate the ends of the primer opening.

4. Trimming the plastic tube at the end opposite to the externally flanged end portion;

5. Forming the flanged end portion of the slug to change the profile thereof and prepare the section for proper finished dimensions and profile control, said profile changes comprising decreasing the outer diameter to a predetermined dimension in order to permit it to be inserted into the die for the following step, repositioning and thickening the externally flanged portion so that the flange is on the inside of the tube and defining a central opening which is of predetermined diameter for the next step, said plastic slug at this point resembling a roughly formed cartridge casing;

6. A method of making an oriented plastic cartridge casing as recited in claim 2 in which the initial thick walled plastic slug has an outside diameter less than the outside diameter of the finished cartridge casing, said plastic slug being radially expanded to an outside diameter substantially greater than the outside diameter of the finished casinG.