EP0300112A1

EP0300112A1 - All plastic cartridge case and method and machine for its manufacture

Info

Publication number: EP0300112A1
Application number: EP87850233A
Authority: EP
Inventors: Henning Vasegaard; Ivan Vagner
Original assignee: DANVAG AS
Current assignee: DANVAG AS
Priority date: 1986-01-29
Filing date: 1987-07-21
Publication date: 1989-01-25
Also published as: DK44786A; DK44786D0

Abstract

A plastic cartridge case (1) for shot cartridges having both the cylindrical, tube-shaped case part (2) of uniform wall thickness and the cap-shaped part (3) placed at the bottom made in thermoplastic materials, e.g. in two different types of thermoplastic materials.

The case is charged the usual way with a percussion cap (8), a powder charge (7) and a buffer (6) containing a shot charge (5). Then the cartridge is closed, e.g. by means of a star-shaped closure (4).

A method for the manufacture of the case and a tool therefor are also indicated.

Description

The present invention relates to a plastic cartridge case of the kind indicated in the generic part of claim 1.
For many years it has been sought to manufacture a plastic cartridge case made entirely of plastic so that the problems that arise with respect to corrosion when using metal parts are avoided. Furthermore, the seminoble metals, such as brass alloys in general used for the reinforcement of the bottom part of the cartridge case, contribute to the increase in both the price of the materials for the cartridge and the price of its manufacture.
The specification of US patent No. 4,481,885 discloses a plastic cartridge case in which the bottom part is reinforced by means of a metal jacket or cap. The case is made of polytethylene which is thermoplastic and easy to process and shape but does not have the sufficient strength, whence a reinforcement is needed. In the specification of US patent No. 4,276,830 it is sought to avoid the corrosion problems associated with the metal reinforcement of the bottom of the case by completely embedding the metal reinforcement in the bottom of the case. Still, this gives a difficult and costly process of manufacture, and this cartridge case has been no success on account of the price.
The specification of US patent No. 4,020,763 discloses a cartridge case made entirely of plastic by placing a piece of extruded pipe together with a part of reinforcement that also may be made of plastic in a mould for injection moulding and then joining the parts by means of an injection moulding. Hereby a case made entirely of plastic is obtained, and by selection of the individual materials reasonable ratios of strength may be obtained. However, this case is difficult to manufacture because the two premanufactured parts have to be placed in the mould prior to the injection moulding and heated to a suitable temperature so that all the parts will stick together in a correct manner. Moreover, the amount of material used is also much too great so that the case becomes a little too expensive and the space within the cartridge for the charge just on the small side.
Finally, other persons have, e.g. according to the specification of US patent No. 3,673,965, used other thermoplastic materials, e.g. polycarbonate that has a greater strength so that a case made entirely of plastic can be manufactured. This material is considerably more expensive than polyethylene, and besides it is stiffer so that the forward directed opening of the cartridge cannot in general be closed by a usual star-shaped closure, but a closing plug has to be used which makes the cartridge more expensive.
The object of the invention is to provide a plastic cartridge case for shot cartridges made entirely of plastic and designed in such a way that the drawbacks of the cases of the prior art are completely avoided without implying the use of materials or methods of manufacture that will make the case more expensive compared to the cases of the prior art.
This object is achieved by designing the case according to the present invention as specified in the characterising part of claim 1. A cap-shaped reinforcement part made of plastic is placed at the location of the case where the influences are greatest. The cap-shaped part may be placed within the case or on the outside of the case as specified in the characterising part of claim 2.
The two parts of which the case is manufactured both consist of thermoplastic materials as specified in the characterising part of claim 3 and may be manufactured of two different kinds of thermoplastic material as indicated in the characterising part of claim 4 so that each of the parts may be seperately optimizied with respect to properties as to strength and with respect to form by a suitable selection of thermoplastic materials.
Hereby a plastic cartridge case can be manufactured totally without metal parts and particular reinforcement parts and still, a case can be obtained that may be closed by means of a usual star-shaped closure and this cartridge case may be reused several times by recharging.
Especially if the case according to the present invention is designed as indicated in the characterising part of claim 5, highly increased strength properties are obtained, and thightening problems as regards the gas pressure between the percussion cap and the case never occur. Such plastic cartridge cases can be recharged 10-20 times.
If the plastic cartridge case is designed as indicated in the characterising part of claim 6 it may be used with no problems in weapons having a case ejector in that the ejection rim is then made of a material that can withstand the grasp of the ejector mechanism. This very point is a weakness of many of the plastic cartridge cases belonging to the prior art, and they are therefore often provided with a metal cap so that the ejector mechanism does not tear the case to pieces. It has been found that the case according to the present invention is able to withstand even those ejector mechanism constructions that produce the strongest grasp on the bottom part of the case.
The present invention also relates to a method for the manufacture of a plastic cartridge case made entirely of plastic. By proceeding as indicated in the characterising part of claim 7, it is possible to manufacture a case in one single work process which reduces the price of manufacture significantly. In addition, no superfluous material is used and thus no waste results. First, the bottom of the case is injection moulded using e.g. polyethylene, and then the cap-shaped part is injection moulded, e.g. of polycarbonate, and only then is the case removed from the mould. Hence, the manufacturer has all possibilities of a speedy and fully automatic production process and of a process in which the two materials stick together optimally, because the blank is not being cooled too much between the first and the second moulding.
The present invention also relates to a tool for carrying out the method according to the present invention and as indicated in the characterising part of claim 8. Hereby a relatively simple tool is obtained having relatively few moving parts and in which the necessary rearrangements of the tool can be carried out during the production process.
The rearrangement of the tool is preferably carried out according to a pattern of movements as indicated in the characterising part of claim 9. Thus merely simple and uncomplicated movements of the parts of the tool have to be carried out.
The invention will now be explained in closer detail with reference to the drawing, wherein

fig. 1 shows a longitudinal section of an example of a cartridge having a case according to the invention,
fig. 2 shows a plane cross section in fig. 1 seen in the direction II-II,
fig. 3 shows an example of a tool for use in the manufacture of the cartridge case during the first moulding, and
fig. 4 shows the same tool rearranged for the second moulding.

Figs. 1 and 2 show a shot cartridge 1 having a plastic cartridge case according to the invention. The case consists of a cylindrical, tube-shaped part 2 of uniform wall thickness and having a closure end 4 closed in the manner of a usual star-shaped closure. As a matter of course it is possible to close the cartridge case in other ways, e.g. by a plate-shaped closure part that is put in place after charging the cartridge. In the cartridge there is placed an ordinary powder charge 7, a buffer 6, and a shot charge 5, all of generally known kind, and there is also mounted a generally known percussion cap 8 in the bottom of the case 10 which is designed with a central, cylindrical part 10′′ and ribs 10′ radially between the cylindrical parts 2 and 10′′. The whole case part 2, 10, 10′, 10′′ is made as a unitary body of thermoplastic material, e.g. polyethylene.
On the outside of, or possibly within, the case bottom there is placed a cap-shaped part 3 having a rim 9 made as a unit manufactured of a thermoplastic material, e.g. polycarbonate. This part is closely fastened to the bottom of the case 10, e.g. fused together with the bottom of the case.
The percussion cap 8 is mounted and secured frictionwise both in the part 10′′ and the part 3 so that a double tightening is obtained so that there is provided a complete tightening as regards the gas pressure from the powder charge 7. This double tightening ensures that no part of the gas pressure can be passed on backwards and reduce the effect of the charge of powder.
The radially outward directed rim 9 has the usual form so that it can be grasped by the generally known ejector mechanisms for firearms for shot cartridges.
A cartridge of this kind may be recharged a countless number of times, if so desired, because the cap shaped part 3, 9 gives the case sufficient strength so that it is not destroyed neither during the firing nor during the ejection.
The cartridge case according to the present invention may be manufactured, e.g. by means of a tool such as the tool shown in figs. 3 and 4 in the drawing. Fig. 3 shows the principle of a tool for moulding plastics comprising a mould 11 that can be heated and cooled in the usual way associated with a process for the injection moulding of plastics. In the mould 11 there are openings in which there has been placed moving mould parts 12 and 17, 20. The shape of the mould part 12 is as that of the interior cavity of a cartridge case, but having a nose 13 that can engage a cavity or bottom hole 19 corresponding hereto in the other moving mould part 17. In addition, the foremost end 14 of the mould part 12 is designed in such a way that it shapes the cylindrical part 10′′ of the bottom of the case and the ribs 10′ and the bottom plate 10. The double arrows 22 and 18 show the pattern of movement of the two mould parts. Moreover, the mould part 17 is provided with a ring-shaped, cylindrical part 20 having a projecting ring-shaped part 21. The parts 17 and 20 are in general kept together in a fixed position, but can be separated for cleaning, repair and so on. When the mould parts have been arranged as shown in fig. 8, the first moulding can be carried out in that the part 2, 10, 10′, 10′′ is moulded using the first moulding material. As a matter of course, the mould parts and the moulding material have to be heated in the usual manner before the injection moulding, and after the moulding the parts are cooled exactly to the extent that the moulding material solidifies.
Next, the position of the mould parts are changed to the position shown in fig. 4 as the moving core 17, 20 is pulled downwards and a set of moving jaws 15 that are movable in the directions of the arrows 16, are brought together so that they meet the nose 13. Now, a new mould cavity is produced and the cap- shaped part 3, 9 can be injection moulded in a second moulding using a second moulding material that may be the same material as the first material or another material, e.g. polycarbonate. The front edge of the mould 21 has been made exactly in such a way that it can close or fill the mould cavity (see fig. 3) at the bottom of the case not to be used in the first moulding.
Then the mould parts are cooled in the usual manner, the jaws 15 are pulled back to the position shown in fig. 3 and the mould is opened, and by means of the moving mould part 12 the finished case 1 can be brought out of the mould, completely without waste and without sprues and the like to be removed.
It is evident to a person skilled in the present art that the mould may be adapted in such a way that many, e.g. 12 or 24, cases per process, are moulded so that a rational production results.
It is likewise evident to a person skilled in the present art that figs. 3 and 4 in the drawing only show the principle of the tool according to the present invention, and that the drawings are not drawn to measure.
The materials that are used may be any material being a plastic and also being suited for injection moulding and they may have any desired colour so that different cartridges may have case parts 2 of different colours, but e.g. cap part 3 of the same colour or vice versa. Moreover, the cap part 3 may be manufactured of brass-coloured plastic, e.g. brass-coloured polycarbonate.

Claims

1. Plastic cartridge case for shot cartridges comprising a cylindrical, tube-shaped case part (2) of uniform wall thickness and having a closure end (4) and a part (10) shaped as the bottom provided with an opening for the placement of a percussion cap (8), characterised in that the part shaped as the bottom is provided with a cap-shaped part (3) made of plastic and having a central opening for the percussion cap.

2. Plastic cartridge case according to claim 1, characterised in that the cap-shaped part (3) is placed on the outside of the tube-shaped part (6).

3. Plastic cartridge case according to claim 1 or 2, characterised in that both the case part (2) and the cap-shaped part (3) are made of a thermoplastic material.

4. Plastic cartride case according to any of the claims 1-3, characterised in that the two parts are made of thermoplastic materials having different properties, the case part (2) preferably being made of polyethylene and the cap-shaped part (3) preferably being made of polycarbonate.

5. Plastic cartridge case according to any of the claims 1-4, characterised in that the end shaped as the bottom (10) is provided with ribs of reinforcement (10′) that radiate radially from an inward directed cylindrical flange part (10′′) made to secure the percussion cap (8), and to the outer cylindrical part (2), the said parts being designed without interruption in a unit.

6. Plastic cartridge case according to any of the claims 1-5, characterised in that the cap-shaped part (3) is made with an encircling, radially outward directed rim (9) at the bottom of the case.

7. Method for the manufacture of a plastic cartridge case according to claims 1-6, characterised in that first the case part (2, 10, 10′ , 10′′) is injection moulded in a mould cavity in a mould, and next - without removing the case part from the mould for injection moulding - the parts of the mould are changed so that a mould cavity corresponding to the cap-shaped part (3, 9) is produced and after that an injection moulding is performed once more, and then the completely finished case is removed.

8. Tool for use in carrying out the method according to claim 7, characterised in that it comprises a mould (11) having a cavity for moving mould parts made up of

1) a moving mould part (12) designed corresponding to the interior of the case and a central cylindrical nose (13) for the formation of an opening for the percussion cap,

2) a moving mould part (17, 20) provided with an opening (19) corresponding to the nose (13) and with a mould front edge shaping the outside end of the case bottom and an encircling mould part (21) that surrounds the case bottom, and

3) a number of radially movable jaws (15) used when performing the injection moulding of the cap-shaped part as they form the bottom of the mould for that part.

9. Tool according to claim 8, characterised in that the moving parts (12, 17, 20) are moved axially with respect to each other, and that the moving jaws (15) are moved radially with respect hereto.