WO2026012527A1

WO2026012527A1 - A process for manufacturing a plastic cartridge case having a bottle-like shape

Info

Publication number: WO2026012527A1
Application number: PCT/CZ2024/050046
Authority: WO
Inventors: Igor SEVCENKO; Oleg VYBORNYI; Tomas PODLENA; Andrii VASIN; Oleksandr BEREZKIN
Original assignee: Ag Chemi Group SRO
Current assignee: Ag Chemi Group SRO
Priority date: 2024-07-12
Filing date: 2024-07-12
Publication date: 2026-01-15
Anticipated expiration: 2027-01-12

Abstract

The object of the invention is a process for manufacturing a plastic cartridge case (1) with metal reinforcements (4) and bottle-like shape using a modified water-soluble polymer. A water-soluble inner mold (3) of the water-soluble polymer is applied to a template, wherein the water-soluble polymer is modified by adding a maximum of 30% by weight of saccharides and/or inorganic clays or ceramics, and the shape of the water-soluble inner mold (3) corresponds to the inner shape of the cartridge case (1). Further the metal reinforcements (4) are fitted onto the inner mold and a polymer layer (6) of the cartridge case (1) using injection molding is created. After the completion of injection molding the template is removed and the water-soluble inner mold (3) is dissolved.

Description

A process for manufacturing a plastic cartridge case having a bottle-like shape

Field of the Invention

The invention relates to weapon industry, in particular to manufacturing ammunition cartridges for automatic guns and rifles (caliber 5.45 mm, 5.56 mm, 7.62 mm, 12.7 mm). More particularly, the present invention relates to a multi-part ammunition cartridge case body wherein at least the cartridge case body is made from nanocomposite thermoplastic polymer.

Background of the Invention

Small cartridges are typically made of brass. High performance polymers are considered a cost effective and light weight alternative for metal. The most suitable technology for the production of polymer casing is a molding technology, that is a filling of the mold of specific shape with melt of suitable polymer. However, there are still some unsolved technological challenges. The problems that need to be solved can be divided into two general groups: (1 ) technical problem of the production procedure, and (2) selection of a proper polymer material.

Taking into account the specific bottle-like shape of the cartridge caliber 5.45 mm, 5.56 mm, 7.62 mm, 12.7 mm, namely the presence of the so-called neck with diameter smaller than diameter of the main body, it is technically impossible to extract the molded casing from the mold. The problem is illustrated in the Fig. 1 . This is one of the reasons that plastic cartridge has a sectional structure and is composed of at least two parts.

Another reason for the multicomponent structure of the case is that the bottom part of the cartridge (head), should be made of metal because this part of the cartridge is subjected to extremely high mechanical impact during preparation, handling, firing and extraction after firing. The main idea of the production of such multicomponent case is illustrated in the Fig. 2. The cartridge body can be divided into metal base (head), main body and bullet end (neck).

Despite the long history of this idea dating back to 1950s (US patent No. 2,654,319) there is still no universal technical solutions to the related problems. The major drawback of the concept lies in the multi-component cartridge structure and the necessity to find reliable bonding techniques, using adhesives or welding processes, to ensure the integrity of the cartridge.

To date, several patents related to the production of polymer-based ammunition cartridges have been published. Most of them focus on solving one of the specific problems described above. For example, patent US8561543 outlines a generic design for polymeric ammunition cartridges, featuring a cylindrical insert connected to a polymeric middle body. This design incorporates elements such as primer recesses, flash holes, and flanges for improved functionality. The middle body, constructed from ductile polymers or fiber-reinforced composites, provides durability and strength. The patent also covers methods for forming these cartridges, utilizing a wide range of polymers and bonding techniques.

The patent US9091516 introduces a three-part ammunition cartridge design featuring a head portion, a case portion, and a cap portion, each made with specific materials and configurations. The case and cap portion integrates a nanocomposite material comprising nanoclay dispersed in a polyamide resin matrix and similar nanocomposite material together with glass fibers, providing additional reinforcement. Despite its innovative aspects, challenges may arise from the relatively low glass transition temperature of the polyamide matrix. During the firing, the temperature inside the chamber can be higher than the glass transition temperature of the polyamide which can lead to the cook-off of the cartridges.

Polymer material of the main body of the cartridge should meet several requirements. Melting point of the material should be quite high to withstand thermal impact during explosion/shot. Other critical requirement is mechanical strength: material should withstand not only thermobaric impact during explosion, but also be mechanically resistant to mechanical handling during preparation and operation of automatic gun like installing caps, charging/recharging handling, etc. Patent US1 1434368B2 discloses thermally more stable polymer material for casing body as a polyphenylene sulfide (PPS). Pure PPS is quite brittle material, and the patent suggests using impact modification to improve mechanical durability of the casing body. Epoxy - functionalized polymer - is suggested as impact modifier.

The document EP4283242 describes an innovative solution to address challenges in producing polymeric ammunition cases. The technology enables creation of a monolithic case during thermoplastic injection, employing a fusible or consumable metal alloy core. The patent highlights the design of the resulting ammunition case, emphasizing its single-piece structure with a reinforced head portion containing the metallic insert.

Previous patent application of the applicant, PCT/CZ2023/050051 , presents the process of manufacturing a plastic cartridge case with increased strength and electrical conductivity achieved by polymer material enriched with nanoparticles and of production consisting of injection into a hot mold at a temperature higher than the melting point of the given polymer material. Furthermore, the production process is characterized by leaving the polymer in the form under pressure and at a temperature higher than the melting point of the given polymer.

However, the production of such a cartridge does not allow the use of commonly available water-soluble polymers to create the internal template, as these polymers are not able to withstand the necessary temperature and pressure applied during the production process.

It would therefore be desirable to come up with a solution that would allow the production of durable plastic cartridges with a narrowed neck.

Summary of the Invention

The shortcomings of the solutions known in the prior art are to some extent eliminated by a process for manufacturing a plastic cartridge case using a modified water- soluble polymer, comprising the steps of (i) applying an inner mold of the water-soluble polymer to a template, wherein the water-soluble polymer is modified by adding a maximum of 30% by weight of saccharides and/or inorganic clays or ceramics,

(ii) fitting of metal reinforcements,

(iii) creating a polymer layer of the cartridge case using injection molding,

(iv) removing the template,

(v) dissolving the water-soluble inner mold.

For the purposes of the present invention the term “cartridge” refers to a type of pre-assembled firearm ammunition comprising a projectile, a propellant substance and an ignition device within a metallic, paper, or plastic case, wherein the case is the main defining component of the cartridge. The case defines the shape of the cartridge and serves as the integrating housing for other functional components, it acts as a container for the propellant powders and also serves as a protective shell against the elements. In other words, the cartridge case is the envelope/container of the cartridge.

To overcome disadvantages of the state of the art, it is proposed to use injection molding technology for the production of multicomponent polymer cartridges cases composed of metal reinforcement parts and polymer body. The metal reinforcement parts are integrated in the polymer layer which create the final shape of cartridge case. Due to the specific shape of the small caliber cartridge, namely the the bottle-like shape with neck diameter smaller than diameter of the main body, this method has to overcome problem of removing an inner mold creating an internal volume after molding, i.e., the problem of extraction of the molded product from the mold. The proposed solution is to use water-soluble thermoplastic polymer to form the inner space of the cartridge case. This polymer shape is formed on the template, which can be a cylinder-shaped metal rod, by molding and followed by overmolding the resulting volume by a layer of hard plastic which makes the final shape of the cartridge case. The metal rod can be easily removed after the molding is completed and the polymer core is still hot, with the soluble core being dissolved in water after cooling of the case. The diameter and cross-section of the metal rod corresponds to the inner diameter of the neck of the cartridge case. The water-soluble polymer for use in the plastic production comprises a water- soluble polymer modified by addition of a saccharide, wherein the content is up to 30% by weight.

The saccharide used for modification is preferably isomalt, sucrose or sorbitol. Other options comprise any other saccharides including monosaccharides, polysaccharides, saccharide derivatives, with saccharide alcohols being particularly preferred.

The water-soluble polymer can be further modified by inorganic clays or ceramics, wherein the total content of saccharides and inorganic clays/ceramics is up to 30% by weight.

Inorganic clays or ceramics are metakaolin, silica nano- or microparticles, montmorillonite.

The water-soluble core is composed of a polymer material that is soluble in water. Examples of suitable water-soluble polymers include polyvinyl alcohol (PVA), polyethylene glycol (PEG), and starch-based polymers. The polymer material is selected based on its compatibility with the injection molding process and its ability to dissolve rapidly and completely in water without leaving any residue.

Water-soluble polymer, such as PVA, starch-based polymers or those commercially available based on polyvinyl alcohol, can be used. For example, there is a commercial solution under the Mowiflex brand. Depending on the case body material used, the most suitable water-soluble polymer is Mowiflex C17. This hydrophilic polymer can be used in its pure form or modified to prepare the water-soluble core. The Mowiflex can be modified by mechanical mixing of the melt in an extruder. As the additives can be used a sugar derivatives, such as isomalt, sucrose, sorbitol, and others, as well as additives of inorganic clays and ceramics, for example, talc, metakaolin, montmorillonite, and others in amount up to 30%. The additives can modify the thermomechanical properties of the core and ultimately to improve the final procedure, i.e., to remove the inner mold by means of water. The most suitable composition is a mixture consisting of 72% Mowiflex C17, 25% Isomalt, and 3% Metakaolin. This mixture is obtained by extrusion using any suitable equipment. The resulting mixture has improved dissolution properties in water and an increased elastic modulus. The addition of Isomalt and nanoclay (for example metakaolin or montmorillonite) increases the elastic modulus. With the same mixture composition, metakaolin has a higher elastic modulus and thermal stability than montmorillonite. As the metakaolin content increases (from 3% to 10%), the elastic modulus increases significantly, but the melt viscosity also increases. Data on the elastic modulus values of pure Mowiflex C17 and modified mixtures are illustrated in Table 1. The values were obtained by measurement on a DMA machine. The table also shows the dissolution time of fiber with the same dimensions (thickness and length), made from different materials. The temperature of the aqueous solution in all experiments was 50 °C. By modifying Mowiflex C17, it is thus possible to obtain blends with better solubility and to use these blends in the injection molding machine.

In the table below, the elastic modulus of pure Mowiflex C17 and modified mixtures thereof, as well as the corresponding time of dissolution in static conditions, can be seen. Dynamic mechanical analysis measurements were performed using three-point method at frequency 1 Hz and 20 microns amplitude.

The bottom part (head) of the cartridge is subjected to the strongest mechanical impacts during handling and explosion/shot and no known polymer can withstand such conditions. Therefore, metal inserts are commonly used as an overmolded bottom inserts/metal base.

In case of using water-soluble core as a part of the mold, the requirements for the polymer material of polymer layer of the main body are very strict. In addition to mechanical strength and thermal shock resistance, there is a strict requirement for the melt of the polymer. Melting point and viscosity of the melt of the material should not be very high to avoid damages of the soluble core during molding of the case body. But it should not be very low either, to withstand thermal impact during explosion/shot.

Another critical requirement is mechanical strength. The material should withstand not only thermobaric impact during explosion, but also be mechanically resistant to mechanical handling during preparation and operation of automatic gun like installing caps, charging/recharging handling, etc.

For this purpose, nanocomposite based on the impact modified polyphenylene sulfide (PPS) is used. Impact modification can be performed by blending with impact modifiers or by copolymerization with polymer component having high impact strength. As the impact modification by soft modifier commonly causes undesirable decrease of the toughness, the invention suggests using carbon nanotubes (CNTs) as nanofiller that improve impact strength as well as toughness of the modified PPS. CNT nanofiller also improves thermal conductivity of the PPS in melt and in solid state, improving processing quality. Thus, the combination of inherent high-performance properties of the PPS with advantages of the impact modifier and CNT nanofiller offers exceptional combination of high impact strength, heat resistance, and toughness in solid state, while maintaining good quality of melt during technological process.

Another great advantage of the PPS-CNT nanocomposite as the basic material is the possibility to convert the electrically insulating polymer matrix into an electrically conductive one. Such conversion can be achieved at the molding injection stage providing increase of the mold temperature up to the melting point of the polymer composite.

Many plastic cartridges suppliers/manufacturers have recently started to require antistatic properties of the inner surface of the cartridge case, which is related to the safe production process. CNTs are considered an electrically conductive additive for increasing electrical conductivity of the naturally insulating polymers. However, strong shear stresses in the polymer melt during the injection molding process destroy electrically conductive percolation network of CNTs resulting in a loss of the electrical conductivity in the moving melt flow. If the temperature of the mold is lower than the melting point of the thermoplastic, the nonconductive structure of the polymer composite is “frozen” and therefore the molded product has high electrical resistivity.

These problems can be avoided by injecting the polymer melt into the mold heated up to the melting point of the polymer. Such procedure provides formation of the electrically conductive percolation network of CNTs in the bulk of the polymer body as well as on the surface of the product.

For optimal properties of the polymer case body, it is suggested to strengthen the bottom part (head) and the neck by metal inserts. Such structure is well adopted to the injection molding procedure with water-soluble core and provides high mechanical strength and integrity of the overall structure. Metal inserts can be made of stainless steel or softer alloys like ZnAICu alloys.

Description of Drawings

A summary of the technical solution is further clarified using exemplary embodiments thereof, which are described with reference to the accompanying drawings, in which:

Fig. 1 shows a cartridge case from the state of art and an inner mold which cannot be removed after the molding, i.e., the technical problem solved by this invention,

Fig. 2a, 2b shows a structure of cartridge case from the state of art with metal base, main body and bullet end,

Fig. 3a shows a metal rod,

Fig. 3b shows the metal rod with applied water-soluble inner mold,

Fig. 3c shows the application of metal reinforcements,

Fig. 3d shows the applied polymer layer,

Fig. 3e shows the cartridge case after removal of the metal rod,

Fig. 3f shows the cartridge case dissolving the water-soluble inner mold. Embodiments of the Invention

Example 1

The first exemplary embodiment of the invention is a process for manufacturing a polymer cartridge case 1 for caliber 7-62. PVA:isomalt in a weight ratio 15:3 is used as the water-soluble polymer creating the water-soluble inner mold 3. PPS Ryton reinforced by 0.5 weight % of branched multiwall carbon nanotubes is used as the polymer of the polymer layer 6 of the case body.

The water-soluble inner mold 3 is formed on a template, which can be a cylindershaped metal rod 2 (Fig. 3a), by molding, as can be seen in Fig. 3b.

After application of the water-soluble inner mold 3 (Fig. 3b), metal reinforcement 4 parts are applied to the water-soluble inner mold 3 (Fig. 3c). At least a metal base is always used, in other cases, metal reinforcement 4 of the cartridge neck 5 can also be used.

The metal rod 2 with water-soluble inner mold 3 and the metal reinforcements 4 is inserted into the mold for the injection molding, followed by overmolding of the resulting volume by hard plastic which makes the polymer layer 6 which create final shape of the cartridge case 1 (Fig. 3d).

The metal rod 2 can be easily removed after the molding is completed (Fig. 3e) and the polymer core is still hot, while the water-soluble inner mold 3 is dissolved in water after cooling of the cartridge case 1 (Fig. 3f).

Example 2

The modified water-soluble polymer is prepared by mechanical mixing of the melt in an extruder. 75% by weight of PVA is mixed with 25% by weight of isomalt. The process for manufacturing the cartridge case 1 is the same as in Example 1 . Example 3

The modified water-soluble polymer is prepared by mechanical mixing of the melt in an extruder. 72% by weight of Mowiflex C 17 is mixed with 25% by weight of isomalt and 3% by weight of metakaolin. The process for manufacturing the cartridge case 1 is the same as in Example 1 .

Example 4

Another example of the manufacture of the cartridge case 1 according to this invention is the same as Example 1 , but the water-soluble polymer used is a material composed of Mowiflex C17, isomalt and metakaolin in a weight ratio of 15:3:2.

After application of the water-soluble inner mold 3 (Fig. 3b), metal reinforcement 4 parts are applied to the water-soluble inner mold 3 (Fig. 3c). At least a metal base is always used, in other cases, metal reinforcement 4 of the cartridge neck 5 can also be used. The metal reinforcement 4 part is applied to the water-soluble inner mold 3 so that the edges of the metal reinforcement 4 part overlap the edges of the water-soluble inner mold 3. The metal reinforcement 4 part can fit tightly to the water-soluble inner mold 3, or a gap can be left between the water-soluble inner mold 3 and the metal reinforcement 4 part, or the metal reinforcement 4 part can touch the water-soluble inner mold 3 with part of its inner surface, while its edges are distant from the surface of the water-soluble inner mold 3, as can be seen in Fig. 3c.

Then, the template with the water-soluble inner mold 3 and metal reinforcements 4 is inserted into the mold for injection molding and the polymer material is applied (Fig. 3d) which made the polymer layer 6 which create final shape of the cartridge case 1.

After curing the polymer of the cartridge case 1, the cartridge case 1 mold is removed, the metal rod 2 is removed (Fig. 3e), and the water-soluble inner mold 3 is dissolved in water (Fig. 3f). Example 5

Another example of cartridge manufacture according to this invention is the same as the first one, but the used water-soluble polymer is a material composed of Mowiflex C17:isomalt:montmorillonite in a weight ratio of 75:25:3.

After application of the water-soluble inner mold 3 (Fig. 3b), metal reinforcement 4 parts are applied to the water-soluble inner mold 3 (Fig. 3c). At least a metal base is always used, in other cases, metal reinforcement 4 of the cartridge neck 5 can also be used. The metal reinforcement 4 part is applied to the water-soluble inner mold 3 so that the edges of the reinforcement 4 part overlap the edges of the water-soluble inner mold 3. The metal reinforcement 4 part can fit tightly to the water-soluble inner mold 3, or a gap 7 can be left between the water-soluble inner mold 3 and the metal reinforcement 4 part, or the metal reinforcement 4 part can touch the water-soluble inner mold 3 with part of its inner surface, while its edges are distant from the surface of the water-soluble inner mold 3, as can be seen in Fig. 3c.

Then, the template with the water-soluble inner mold 3 and metal reinforcements 4 is inserted into the mold for injection molding and the polymer material is applied (Fig. 3d) which made the polymer layer 6 which create final shape of the cartridge case 1. The polymer is applied to the hot mold, with the mold temperature not lower than the melting point of the polymer to create the electrical conductivity of the polymer.

After curing the polymer of the cartridge case 1, the cartridge case 1 mold is removed, the metal rod 2 is removed (Fig. 3e), and the water-soluble inner mold 3 is dissolved in water (Fig. 3f).

List of Reference Signs

1 - Cartridge case

2 - Metal rod

3 - Water-soluble inner mold

4 - Metal reinforcement

5 - Neck

6 - Polymer layer

Claims

PATENT CLAIMS

1. A process for manufacturing a plastic cartridge case (1 ) with metal reinforcements (4) and bottle-like shape using a modified water-soluble polymer characterized in that the process comprises the steps of

(i) applying a water-soluble inner mold (3) of the water-soluble polymer to a template, wherein the water-soluble polymer is modified by adding a maximum of 30% by weight of saccharides and/or inorganic clays or ceramics, and the shape of the water-soluble inner mold (3) corresponds to the inner shape of the cartridge case (1 ),

(ii) fitting of metal reinforcements (4) onto the inner mold,

(iii) creating a polymer layer (6) of the cartridge case (1 ) using injection molding,

(iv) removing the template after completion of step (iii),

(v) dissolving the water-soluble inner mold (3).

2. The process for manufacturing a plastic cartridge case according to claim 1 characterized in that the template used in step (i) is a metal rod (2).

3. The process for manufacturing a plastic cartridge case according to claims 1 and 2 characterized in that the saccharide is isomalt, sucrose or sorbitol.

4. The process for manufacturing a plastic cartridge case according to claims 1 to 3 characterized in that the inorganic clays or ceramics are metakaolin, silica nanoparticles or microparticles or montmorillonite.

5. The process for manufacturing a plastic cartridge case according to claims 1 to 4, characterized in that the metal reinforcements (4) are fitted with an overlap over the edges of the water-soluble inner mold (3).

6. The process for manufacturing a plastic cartridge case according to claims 1 to 5 characterized in that the polymer layer (6) of the cartridge case (1 ) is polyphenylene sulfide reinforced by carbon nanotubes.

7. The process for manufacturing a plastic cartridge case according to claims 1 to 6 characterized in that the polymer layer (6) is achieved by using hot mold during the injection molding stage, wherein the temperature of the mold should not be lower than the melting point of the polymer used.

8. The process for manufacturing a plastic cartridge case according to claims 1 to 7 characterized in that the metal reinforcement (4) is made of stainless steel or softer alloys like ZnAICu alloys.