US3760729A

US3760729A - Hermetically sealed plastic cartridge case/cap system

Info

Publication number: US3760729A
Application number: US00210535A
Authority: US
Inventors: D Freeman
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1971-12-21
Filing date: 1971-12-21
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25

Abstract

A container, such as a cartridge case for an illuminant star signal, comprises a molded case of fiberglass reinforced rigid thermoplastic resin possessing a cap of similar but unreinforced resin ultrasonically welded thereto to provide a hermetically sealed unit. Due to the dissimilarity in fiberglass content of the cap and case materials, the cartridge possesses a line of reproducible weakness along the weld line. Signal cartridges of this type are capable of failing reliably along said weld line to achieve a highly reproducible narrow altitude range of star trajectory and reliable star ignition.

Description

0 limited States Patent 1191 [111 3,76%,729 Freeman Sept, 25, 119731 [54] HERMETICALLY SEALED PLASTIC 3,537,397 11/1970 Ripley et al lO2/37.8

CARTRIDGE CASE/CAP SYSTEM FOREIGN PATENTS 0R APPLICATIONS [75] Inventor: Donald J. Freeman, Parsippany, 858,560 1/1961 Great Britain 102/43 P NJ. WT: f Primary Examiner-Robert F. Stahl [73] Asslgnee. The United States of America as Atmmey Harry saragovitz et a1 represented by the Secretary of the Army [57] ABSTRACT [22] Filed: Dec. 21, 19711 A container, such as a cartridge case for an illuminant star signal, comprises a molded case of fiberglass rein- [211 App! 210535 forced rigid thermoplastic resin possessing a cap of similar but unreinforced resin ultrasonically welded [52] 11.8. C1. 102/32, l02/37.6, 102/43 P, thereto to provide a hermetically sealed unit. Due to 102/43 C the dissimilarity in fiberglass content of the cap and [51] Int. Cl C06d 11/00 case materials, the cartridge possesses a line of repro- [58] Field of Search 156/370, 580, 581; ducible weakness along the weld line. Signal cartridges 102/39, 43, 43 P, 32, 43 C of this type are capable of failing reliably along said weld line to achieve a highly reproducible narrow alti- [5 6] References Cited tude range of star trajectory and reliable star ignition.

UNITED STATES PATENTS 3,099,958 8/1963 Daubenspeck et al. 102 43 P 9 Umms 4 WWW 3,468,731 9/1969 Obeda 3,144,827 8/1964 Boutwell..... 3,298,311 l/l967 Catlin 102/37.8 X

HERMETICALLY SEALED PLASTIC CARTRIDGE.

governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION The present invention relates to a novel capped, hermetically sealed, organic plastic container, e.g. a cartridge case suitable for use with illuminant compositions for signalling, marking and like purposes.

In the past, illuminant compositions, such as stars, flares and tracers, have been employed by the military for signalling from air to air, air to ground (or ship), ground to ground, and ground to air, for the purpose of distress signalling, warning, position marking, radiosilence communication and maneuver coordination. Generally, such illuminant compositions were contained in a capped cartridge case together with a propellant charge of black powder for ejecting the illuminant and a primer for igniting the propellant. The cartridge was inserted into a suitable weapon, e.g. pistol or mortar, and the breech closed. When the trigger was pulled, the firing pin struck the primer which ignited the black powder charge, which in turn provided the flame to ignite the illuminant as well as gases to blow off the cap and propel the burning illuminant from the cartridge case to an altitude of 150 feet or more.

Cartridge cases employed for such illuminant flares etc. have possessed a number of deficiencies. Thus, an early type of signal developed by the U.S. Army during World War II employed a brass-based paper cartridge case roll crimped over a cardboard disc cap closure. This signal was susceptible to deterioration by moisture, which caused degradation of the primer and black powder and physical distortion or even destruction of the paper cartridge case, and also reacted with the causing magnesium in the illuminant to produce hydrogen gas, resulting in pressure buildup and premature blow-off of the cap. The principal protection from moisture afforded such signals was provided by the packing containers therefor; and if the container was inadequate or opened, the storage life of the signal was seriously impaired.

The paper cartridge was replaced by a 2 piece case composed of an aluminum base snapped onto a steel tube provided with a pressed steel cap closure. Although this case was an improvement, moisture at times penetrated the aluminum-steel joints at the base and at the cap. Further, inclusion of moisture in the signal due to inadequate moisture control during manufacture generated hydrogen gas from reaction of water with powdered magnesium present in the illuminant composition, causing premature popping of caps and separation of the case into two parts, misfiring and erratic performance of the signal. The two piece aluminum case was supplanted by a one piece impactextruded aluminum case, which together with improved moisture control during manufacture of the signal has minimized many of the chronic storage and functioning difficulties, However, the seating and sealing of the steel cap in the latter cartridge case has given several manufacturers problems which have been resolved fairly satisfactorily but at the expense of production delays, acceptance of substandard production lots, etc., all with attendant increased costs.

Thus, since specifications require that the signal star or stars fired from the cartridge reach a minimum altitude of 150 feet, manufacturers must set minimum standards of 200 feet to be reasonably certain of meeting specification requirements, and maximum altitudes may reach 350 feet or more. Hence, the range between minimum and maximum altitudes for a normal production lot of signals is usually about 150 feet, which represents essentially a percent variation in altitude and indicates erratic performances at best. Such as wide range of altitudes indicates a wide range of pressure buildup to reach the corresponding altitude followed by a sudden pressure drop to about atmospheric pressure when the cap and stars are ejected. Ballistic tests have shown that ignition difficulties result from attainment of such high altitudes, apparently by snuffing out the burning faces of the star or stars.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel capped cartridge case or similar container or ridid thermoplastic resin, wherein the cap is welded to the case to form a hermetically sealed unit, which is capable of rupturing reliably aong the weld line on functioning of the cartridge, thereby resulting in highly reproducible and reliable star ignition and altitude of trajectory.

Another object is to provide a cartridge case of rigid thermoplastic resin possessing high tensile strength, yield strength and elastic limit over a wide range or temperatures so that the case will not crack or jam in the barrel of the weapon upon functioning.

A further object is to provide a capped cartridge case, which will not permit internal gas pressure buildup due to hydrogen gas generation.

A still further object is to provide a capped cartridge case having economic and manufacturingadvantages over previous cartridge cases.

Other objects will appear or be obvious from the following description of the invention in conjunction with the drawings.

These objects of the present invention are achieved and the aforesaid deficiencies of the prior art are obviated by a novel cartridge case suitable for use with signals and related items of ammunition, which comprises a molded case of fiberglass reinforced, rigid thermoplastic resin possessing a molded cap of similar thermoplastic resin containing substantially less or no fiberglass, which is thermally welded to said case to provide a hermetically sealed unit. Due to the dissimilarity in composition and structural strength between the materials thus joined, resulting essentially from the presence of substantial fiberglass reinforcing in the case and the substantially lesser amount of absence theeof in the cap, the sealed unit possesses a line of reproducible weakness along the weld line, whereby the cartridge on functioning is capable of failing reliably along said weld line to achieve a highly reproducible, narrow altitude range of star trajectory and reliable star ignition.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention is illustrated in the drawings, wherein:

FIG. I illustrates a longitudinal section of a cylindrical cartridge case of fiberglass reinforced rigid thermoplastic resin.

FIG. 2 illustrates a cross-sectional view of a flanged cap of similar unreinforced rigid thermoplastic resin.

FIG. 3 shows an enlarged detailed view of the cap flange section illustrated in FIG. 2.

FIG. 4 shows a longitudinal section of a loaded signal cartridge case with a welded cap.

Similar numbers refer to similar parts throughout the several views.

DETAILED DESCRIPTION OF THE INVENTION The rigid thermoplastic resin material employed to fabricate containers and cartridge cases for signals of the aforesaid type must possess a unique combination of physical properties. Since it is expected that the signal may be fired from several different weapons of various calibers, the case resin must possess a sufficiently high tensile strength preferably at least about 1,3000 psi so as not to crack or rupture when functioned, even without any gun barrel support at all, over a temperature range from 65F. to +160F. For example, one type of standard U. S. Army aircraft signal cartridge will develop a peak internal pressure of about 1,100 psi, which translates to a hoop stress of about 10,000 psi considering the dimensions of the case. Also, the thermoplastic resin material must possess low moisture absorption, low coefficient of thermal expansion, high impact strength and high thermal stability.

According to the present invention glass fiber reinforced rigid thermoplastic resins suitable for fabricating cartridge cases possessing the aforesaid physical properties include commercially available rigid thermoplastic resins, such as polyphenylene oxide resins including modified polyphenylene oxide resins, as well as polycarbonate resins, acrylontrile-butadiene-styrene (ABS) resins, polystyrene resins and styreneacrylonitrile copolymer resins. Depending on the tensile strength desired for the case, the percentage of fiberglass in the fiberglass reinforced resin can vary widely and usually ranges from about percent to about 50 percent, preferably from about 20% to about 40% by weight. The cap for the cartridge case is fabricated from the same or similar rigid thermoplastic resin as the case itself except that it contains substantially less than preferably none of the fiberglass reinforcing. The cap and case, due to their content of the same or similar thermoplastic resin, can be readily joined together by thermal welding to provide a band, which effectively seals out air and moisture. At the same time, the cartridge case possesses a line of reproducible weakness along the weld line due to the difference in structural strength between the case and cap, which can be suitably adjusted by the use of sufficiently less or none of the fiberglass reinforcing in the resin of the cap than in the resin of the case.

Ultrasonic welding is the preferred method for sealing the cap to the case, although other known methods of thermal welding can be employed with good results, e.g. spinwelding. Solvent welding and adhesive bonding are slow, and messy and provide bonds that are less reliable and satisfactory than those obtained by thermal welding e.g. ultrasonic and spinwelding.

Referring to the drawing, FIG. 1 shows a cylindrical cartridge case 1 approximately 1.5 inches in diameter and 3.7 inches long of molded fiberglass reinforced polyphenylene oxide resin. The case has a thick, heavy, rimmed base 2 and a tubular thin wall section 3 approximately 0.05 in. thick terminating in a flat rim 4 at its open end. The base 2 of case 1 is provided with coring 5 for the following reasons:

l. to avoid uneven cooling and sinking" of the molded case;

2. to avoid long molding cycles required by cooling of the thick base;

3. to avoid physical weakness at the juncture of the thick'base with the thin wall of the case.

The base/wall thickness ratio is preferably kept as low as possible (close to 2:1) to achieve uniform molding and maximum strength. The radius 6 of the section where the base 2 meets the thin case wall 3, is preferably as large as practicable to prevent failure of the case as a result of flexure of the thin wall while the base remains rigid. The walls of the case and mold are slightly tapered to permit removal of the case from the mold, as usual. The base has a center hole 7 for receiving a primer charge (not shown).

FIG. 2 shows a cap 8 of shallow cup configuration of approximately 0.040 in. wall thickness, having a circumferential flange 9 approximately 0.020 in. thick adapted to mate with the rim 4!- of the case shown in FIG. 1. The bottom surface of flange 9 designed to seat on the case rim 3, possesses a 360 triangular wedge 10, shown in greater detail in FIG. 3, which serves as an energy director to facilitate ultrasonic welding of the cap to the case. Also, the center of the cap has a thickened, convex-shaped circular section 11 to prevent the tendency of the cap to crack during ultrasonic welding.

The case 1 was injection molded by center gating the resin into the base of a mold corresponding to the case configuration. The resin used was a mixture of parts of modified polyphenylene oxide resin (marketed under the tradename of NORYL resin by General Electric Co., Polymer Products Operation, Selkirk, N. Y.) and 30 parts of fiberglass filler. (A similar fiberglass reinforced modified polyphenylene oxide resin is marketed under the name of modified polypheylene oxide resin, catalogue number ZF-l006, marketed by Liquid Nitrogen Processing Co., Malvern, Pa.) The tensile strengths of the aforementioned unreinforced and fiberglass reinforced molded resins are about 9,000 psi and about 18,000 to 22,000 psi, resp.

The cap 8 was injection molded by center gating the aforementioned modified polyphenylene oxide resin containing no fiberglass filler into a suitable mold.

The following illustrates suitable conditions for injection molding the case (wt. approximately 1.6 oz.) and cap from the aforementioned resin materials. The equipment employed was a New Britain Reciprocal Screw Molding Machine, 10 02. capacity, made by The New Britain Manufacturing Co., New Britain, Conn.

CASE CAP Adjustable holding press time 15 sec. 1 1 sec. Cooling time 15 sec. 11 sec. Injection cylinder temperature:

Front: 550F 550F Middle: 530F 5 l 0F Rear: 490F 490F Mold temperature 220? 220F Injection pressure 9000 psi 9000 psi A hole 7 for inserting the primer was drilled into the center of the base of cartridge case 1 obtained in the above manner.

The cartridge case obtained above was loaded in conventional manner to produce a standard illuminant signal as shown in FIG. 4, wherein the case ll contained a primer shown in hole 7, 2 grams of a black powder propellant charge 12, two stars each consisting of a standard red star illuminant charge 13 in aluminum container 14, felt wads and chipboard discs 16. The black powder propellant charge 12 was held in place by means of onionskin paper 17 glued to the bottom of lower felt wad 15. The illuminant charges 13, aluminum containers 14, felt wads 15 and lower chipboard diss 16 each possessed a center hole, forming passage 19. The stars were obtained by compressing powdered illuminant charge 13 with black powder igniter charges 18 at both ends into cylindrical aluminum container 14 provided with conventional quick match igniter cord 20 (to ensure ignition of black powder igniter charge 18 and illuminant charge 13) threaded through holes 21, followed by placing thereon disc 22 having a center hole corresponding to passage 19 and provided with quick match igniter cord 23, which is threaded through holes 24 and positioned in passage 19, and crimping the edge 25 of container 14 to clamp disc 22 onto illuminant charge 13.

The assembly was then completed by placing the loaded case in a nest on an ultrasonic sealing machine of suitable size equipped with the proper booster horn and properly designed sealinng horn. The cap 8 obtained above was then positioned with flange 9 and wedge 10 seating on the flat rim 4 of case 1, and sealed by use of the appropriate weld time, holding and welding pressure. The following illustrates suitable ultrasonic welding conditions using a Branson 227 Stand, and a J 32 Power Supply, manufactured by Branson Sonic Power Co. Inc., Danbury, Conn. at 20,000 cycles per sec:

Weld time 0.7 sec. Hold time 0.5 sec. Weld pressure 35 psi In operation, for tests summarized below, the signal cartridge is inserted into a suitable weapon and the breech closed. When the trigger is pulled, the firing pin strikes the primer, which ignites the black powder charge 12, which in turn provides flame through passage 19 to ignite the

igniter cords

20 and 23 and illuminant charges 13 as well as hot gases to blow off the cap 8 and propel the aluminum containers 14 containing the burning star illuminants out of the cartridge case ll.

TEST RESULTS The NORYL resin cased signals obtained in the manner described above were functioned at 65F., ambient temperature (between +60 and +80F.) and 160F. without any incidence of cracked cases. The caps separated from the cases along the weld line at the juncture of the cap and case with reliable consistency, as indicated by altitude ranges of from approximately 225 ft. min. to 275 ft. max. attained by the star illuminants in vertical trajectory, in contrast to altitude ranges of about 150 ft. min. to 300 ft. max. usually attained with corresponding aluminum cased signals. Further, no failures resulted when the novel resin cased signals were subjected to 14 day temperature-humidity cycling (i.e. cycled daily between 65lF and 160F. at 95 percent relative humidity) which was indicative of a hermetically sealed cartridge (the only effect was a slight about a 5 percent decrease in average altitude). in contrast, the corresponding aluminum cased signals, when subjected to similar 14 day temperaturehumidity cycling, resulted in many functioning failures. Also, the novel resin cased signals were unaffected by h days storage at 165F both in the conditioning phase and in the ballistic functioning phase.

In similar manner, the present invention can be employed to produce a wide variety of capped, hermetically sealed cartridge cases of rigid, thermoplastic resin having the unique and valuable characteristics described above, including miniature hand-held, smoke and flare signals developed in recent years.

It is thus evident that the invention represents a significant advance in the art and provides a number of important advantages over previous cartridge cases, notably:

1. The method of sealing the cap to the case and the materials used for their fabriction provide an effective, positive moisture barrier and a reliable failure point during normal functioning of the signal. The similarity of the basic resin in both cap and case permits a thermal welding together of cap and case to provide a hermetically sealed cartridge, and the fiberglass reinforcement in the case results in a plane of lower strength along the line where the two parts are welded together.

2. The rigid thermoplastic resins used will not absorb moisture nor allow moisture to pass through.

3. The rigid thermoplastic resins used are permeable to hydrogen gas, so that hydrogen gas generated by the reaction of magnesium in the illuminant composition with any inadvertently included moisture will pass through the case wall, thereby preventing buildup of hydrogen pressure and premature displacement of the cap.

4. The novel materials of construction and weldsealing of cap to case employed in the invention results in a narrower range of altitudes for apex of star trajectory. This narrower range of altitudes results in a narrower range of post-ignition case pressures, which minimizes star ignition difficulties caused by snuffing out of the burning star due to a large drop in pressure as the cap separates from the case.

5. The novel plastic cartridge cases can be manufactured readily and economically by thousands of plastic molders possessing injection molding machines, whereas the manufacture of impact extruded aluminum cases previously used requires heavy, expensive industrial machinery operated by at most a dozen manufacturers in the United States. Also, the plastic cartridge case of fiberglass reinforced rigid thermoplastic resin is less costly to fabricate than the aluminum case. Further, the plastic caps are less costly than the present steel caps and can be ultrasonically welded to the case more rapdily, cleanly and economically than the present seating of the steel cap in the aluminum case and sealing with a castor oil-nitrocellulose composition.

6. A molded case of fiberglass reinforced rigid thermoplastic resin, particularly a polyphenylene oxide resin, is tough and strong, the resin possessing a tensile strength of more than 15-20,000 psi. When loaded with a standard military signal charge and sealed with a welded on plastic cap, as described above, it can be fired from weapons of various calibers even in the absence of any gun barrel support at all as long as the case can be seated in the weapon for functioning, without cracking or rupture.

I wish it to be understood that I do not desire to be limited to the exact method and detail of construction described for obvious modification will occur to persons skilled in the art.

What is claimed is:

1. A signal cartridge which comprises a cylindrical, one piece, molded case consisting essentially of fiberglass reinforced, rigid thermoplastic resin, an illuminant signal and propellant therefor contained in said case, and a molded cap consisting essentially of similar resin containing substantially less fiberglass and being structurally weaker than said case, wherein said cap is thermally welded to said case by fusion of the similar base resin in said cap and case to provide a hermetically sealed unit, said unit possessing a line of weakness along said weld line due to the difference in structural strengths of said cap and case, whereby the cartridge on functioning of the propellant fails along said weld line and provides a highly reproducible, narrow altitude range of illuminant trajectory and reliable illuminant signal ignition.

2. A cartridge according to claim 1, wherein said cap is ultrasonically welded to said case.

3. A cartridge according to claim 2, wherein the rigid thermoplastic resin is selected from the group consisting of polyphenylene oxide resins, polycarbonate resins, polystyrene resins, and styrene-acrylonitrile resins.

4. A cartridge according to claim 3, wherein the amount of fiberglass in the fiberglass reinforced resin of said case is between about 5 percent and about 50 percent by weight.

5. A cartridge according to claim 4, wherein the fiberglass reinforced resin of said case possesses a tensile strength of at least about 13,000 psi over the temperature range of -65F to 160F. and the cap resin possesses a tensile strength at least about 5000 psi less than that of the case.

6. A cartridge according to claim 4, wherein the case consists essentially of between about 60 and 80 percent by weight of polyphenylene oxide resin and between about and 40 percent by weight of fiberglass and the cap consists essentially of the same resin containing substantially no fiberglass.

7. A cartridge according to claim 1, wherein the case possesses a thick cored base and the ratio of base thickness to case wall thickness is not substantially greater than 2.

8. A cartridge according to claim 7, wherein the cap is a concave disc having a circumferential flange and a thickened center section for preventing cracking of the cap during ultrasonic welding thereof to the case, said flange being seated on and ultrasonically welded to the rim of said case with the concave side of the cap facing outwardly of the case.

9. A cartridge according to claim 8, wherein the resin is a polyphenylene oxide resin.

Claims

5. A cartridge according to claim 4, wherein the fiberglass reinforced resin of said case possesses a tensile strength of at least about 13,000 psi over the temperature range of -65*F to + 160*F. and the cap resin possesses a tensile strength at least about 5000 psi less than that of the case.

6. A cartridge according to claim 4, wherein the case consists essentially of between about 60 and 80 percent by weight of polyphenylene oxide resin and between about 20 and 40 percent by weight of fiberglass and the cap consists essentially of the same resin containing substantially no fiberglass.