DE2730797A1 - INJECTION MOLDING PROCESS FOR SCRAP CARTRIDGES - Google Patents

Description

273G797 - 5 -

DESCRIPTION

The invention relates to an injection molding process for shotgun shells.

It is already known to produce shot cartridges made exclusively of plastic by injection molding, See, for example, U.S. Patents 3,590,740, 3,591,898, 3,614,929, 3,673,965, 3,722,411, 3,722,412 and 3 752 434. The cartridges, previously made entirely of plastic, are not strong enough to be repeated to be loaded. The invention provides an injection molding process for pure plastic shotgun cartridges that significantly are more solid than known plastic cartridges and, in particular, can be filled or reloaded repeatedly.

In the injection molding art, it has traditionally been considered necessary to construct the injection molding apparatus and control the process conditions in such a way as to ensure a smooth laminar flow of the material injected into the mold. This practice has been practiced in the injection molding of all plastic shotgun shells.
The inventor has found, however, that only plastic shotshells of surprising strength can be injected by appropriately selecting the injection molding material and by avoiding the conventional practice of working with a smooth flow of the injection material into the mold.

The invention provides an injection molding process for a plastic shotshell with the following process steps:

A hollow shape is formed with an elongated hollow tube section which is closed at one end and at the other end into a disk-shaped and transverse to said other end of the cylinder section hollow section passes over;

thermoplastic material is heated in an injection molding machine;

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the molten thermoplastic material is injected into the mold under pressure through a large number of nozzle openings injected with the nozzle openings at the central part of the disc-shaped hollow portion in the circumferential direction are arranged distributed so that the molten thermoplastic material in a multitude of turbulent flows is directed by the disc-shaped section after exit outside into the hollow cylinder section; the injection of the thermoplastic material is continued until the cylindrical and the disk-shaped part of the hollow shape filled and the cylinder wall and the disk-shaped end face are shaped into a cartridge; and

the cartridge thus formed is separated from the hollow mold. It is preferably the thermoplastic Material is a polymer having a molecular weight of at least 1,250,000 and preferably greater than 1,500,000, where the entire effective cross-section of the nozzle openings in the

range from 2.5 to 9 mm, the pressure acting on the thermoplastic material in the range from 1,050 to 1,760 kg / cm ²

and the temperature of the thermoplastic material at

Injection into the mold is in the range of 210 to 360 ° C.

Preferably, the thermoplastic material enters the hollow mold through a tubular injection part that is inserted into the disk-shaped portion of the hollow shape protrudes, wherein the nozzle openings are formed in the peripheral wall of the injection part are.

In the method according to the invention, the temperature is at which the thermoplastic material is injected into the mold is much higher than would normally be recommended by conventional injection molding practice. Also, the material injected through a much smaller orifice area and at a higher pressure than according to the conventional theory of Case would be. The purpose of these departures from normal practice is to give the thermoplastic material to the mold in a variety of ways initiate of turbulent flows in a manner that deals with a spray of material into those molded parts lets compare in which the cartridge wall is shaped

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shall be. As it turned out, the cartridge walls significantly higher strength properties when using thermoplastic materials with high molecular weight of a type commonly used in blow molding (but not injection molding) to them Way is injected into the mold. Without specifying the causes of these increased strength properties To limit theory or explanation, it is believed that the increased strength is due to the phenomenon of biaxial orientation is based, due to which the thermoplastic material is in a rigid network instead of the ordinary Laminate structure is fixed. This leads to the "weld lines" that occur after conventional injection molding processes produced cartridges occur and significantly weaken the impact resistance of the cartridge wall, largely be eliminated. By injecting the thermoplastic material into the mold in such a way that it sprays out in a turbulent manner the thermoplastic material coming into the cylindrical part of the hollow mold leads to a random distribution Movement that causes the molecules in the material to randomly orientate until the material moves into solidified in an unusually strong stable network structure.

The invention is described in the following description a special injection molding device based on the results of the molding of shotgun shells with the aid of this device were achieved, explained in more detail in connection with the drawings. Show in the drawings Figure 1 is a longitudinal section through part of the device showing the manner in which the plastic injected into the hollow mold formed between a stationary mold part and a movable mold part will;

FIG. 2 shows a representation similar to FIG. 1, but in which the molded parts are separated after a molding process are shown;

Figure 3 is a perspective view of that part

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the device through which the plastic is injected into the hollow mold, on an enlarged scale; and

Figure 4 to 10 diagrams with the test results as they when forming shotshells with the device

according to Figure 1 to 3 have been achieved. According to the drawing, the device comprises a mold 10 with a stationary part 11 and a movable part 12, the parts 11 and 12 being attached to the stationary part in a conventional manner or the movable pressure piece of a standard injection molding machine are attached. The movable part 12 can bring to carry out an injection molding process according to Figure 1 in abutment with the stationary part 11 and after Withdraw the injection process into the position shown in FIG.

The movable mold part 12 comprises a hollow block 13 with a central, generally cylindrical opening 14 and a mandrel-like core 15 protruding into the opening. In In the closed state shown in FIG. 1, the mold encloses a cavity 16 with the shape of the one to be produced Shotshell. The cavity 16 includes an elongated tubular hollow portion 17 between the wall the opening 14 and the outer wall of the core 15 is formed, as well as a disk-shaped hollow section 18, which is attached to the section 17 connects and runs transversely to this. Of the disc-shaped cavity section 18 is between the stationary Molded part 11 and the end face of the core 15 facing this in the end of the cylindrical opening 14 of the Hollow blocks 13 are formed. The other end of the tubular mold portion 17 is through the interlocking of the core 15 and the hollow block 13 are permanently closed in the injection position.

As is customary with injection molds, the hollow block is 13 provided with cooling water ducts 20, so that it is cooled with the help of water circulating through the ducts Water can be cooled to a constant temperature

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the solidification of the thermoplastic injected into the hollow mold Control materials.

Preferably, the outer wall of the core 15 is slightly conical, the diameter decreasing towards the free end, by the To facilitate demolding of the cartridge produced in the injection molding process. The tubular wall of the cartridge produced is therefore correspondingly conical.

At the end of the cylindrical opening U in the hollow block 13 facing the stationary molded part 11 there is a recess 19 provided, which results in the usual bead on the finished shotgun cartridge.

The stationary molded part 11 is provided with an outlet sleeve

21, through which the thermoplastic injection molding material is passed from the conventional injection nozzle 22 of an injection molding machine into the cavity 16. The outlet bushing 21 is generally tubular and has a stepped outer surface 23 and a central plastic feedthrough 2h , which leads to the spray nozzle

22 converges so that when a finished shotgun cartridge is removed, the sprue is easily pulled out with it and the injected material breaks off at or within the hot nozzle tip.

The discharge end of the spout 21 is provided with a tip 25 which extends into the central part of the disk-shaped Section 18 of the cavity 16 protrudes. The design of this tip 25 can be seen most clearly from FIG. It comprises a cylindrical collar 26, the outer end 27 of which is distributed over the circumference by four at regular intervals radial slots 28 is divided. In the closed state of the mold, the outer end 27 of the collar 26 is in contact the end face of the core 15, which closes the outer ends of the slots 28 to four rectangular openings, the Distributed over the circumference in the central area of the disk-shaped Section 18 of the cavity 16 are arranged and through which the thermoplastic material of the central passage 24 of the outlet bushing 21 to the outside is injected into the cavity 16 of the mold.

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The shape of the shotshell produced in the injection molding process can best be seen in FIG which shows the shape in the open state, with the shotgun cartridge still protruding into the outlet sleeve 21 through a Sprue is held on the stationary mold part 11. The cartridge v / eist a tubular wall 31 and a disc-shaped end wall 32 with the usual edge flange or bead 33 on. Because the tip 25 of the outlet socket 21 protrudes into the cavity 16 of the mold, the end wall 32 of the cartridge has after removal of the sprue a central cylindrical opening for receiving a primer. The tip 25 of the outlet bushing 21 is with it an annular projection 29 provided with a sawtooth-shaped cross-section, which in the outer end of said opening forms a retaining groove for the primer.

The spray nozzle 22 forms the nozzle of an injection molding cylinder system. This cylinder system can be of a conventional type and is not shown in the drawing. Preferred white it is a screw feed system with a heated tube in which the thermoplastic material is placed feeding from a funnel at one end of the tube to the spray nozzle 22 at the other end of the tube Conveyor screw is arranged.

It has been shown that shotshells with increased strength can be produced with the aid of the device shown leave, if a suitable plastic is used, the injection openings formed by the slots 28 in the outlet sleeve 21 have a suitable cross-section and the process conditions during the injection molding process according to present invention can be controlled.

With regard to the thermoplastic material to be used, it has been found that this has a high molecular weight, preferably in conjunction with a relatively low melt index, to have shotgun shells obtained that allow multiple loading or refilling. In particular, the thermoplastic material should

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have a molecular weight of at least 1,250,000, preferably in the range 1,500,000 to 2,000,000, the latter number representing the upper limit for the materials available today in commercially available quantities. High-density polyethylenes with low voltages and a molecular weight in the specified range are particularly suitable. A small percentage of copolymer, for example with 5 % butylene, is permissible. This can be beneficial in that it provides a degree of elasticity for flanging the

End of the shotshell when filling is desired.

Examples of suitable materials are those from Union Carbide under the names DMPL 1155 (a copolymer with 95 % ethylene and 5 % butylene with essentially linear molecules) and DMDL 3103 (a copolymer with 95 % ethylene and 5 % butylene with essentially linear molecules but a higher melt index). Both materials are high density materials commonly used in blow molding processes but not in injection molding processes. Another one A suitable material is a rubber-modified, high-polymer, high-density polyethylene manufactured by Allied Chemicals is available under the name PLASKON Shotshell Quality 6/34.

In Figs. K to 10 are the results of experiments

shown using the apparatus shown in Figures 1 to 3 on a normal 2 ounce injection molding machine from Johns have been carried out. The mold was for the production of 12-caliber shotshells with a length of 70 mm, a diameter of 20 mm, an average pipe wall thickness 1.20 mm and an end wall thickness of 2.54 mm. These cartridges had an average weight of 5.8 g. An extensive test program has shown that optimum results have been achieved with a spout that has a tip with an outside diameter of 3.05 mm and four end slots were achieved, each slot having an opening of 1.9 mm χ 0.76 mm, resulting in a total injection opening cross-section of 5.8 mm, and the thermoplastic

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Material was fed through the spray nozzle 22 under a pressure of 1406 kg / cm at a temperature of 300 ° C. To show the importance of the correct choice of conditions according to the present invention, illustrate FIGS. 4 to 9 show the effects that result when a parameter or a condition changes and the other conditions are kept at the experimentally determined optimum. In the individual figures the strength of the cartridge obtained is plotted on the ordinate, measured as the number of refills, which can be done before the cartridge fails.

FIG. 4 shows the results for thermoplastics Materials of different molecular weights, the device otherwise under optimal conditions was operated. As can be seen, it is expedient to use a material with the highest possible molecular weight. If one assumes the possibility of a sixfold refill as a minimum requirement, then it is necessary - as can be seen, to use a thermoplastic material whose molecular weight is at least 1 million and is preferably on the order of 1,800,000 to 2,000,000.

Figure 5 shows the results obtained when the temperature of the injected material is changed, from which it can be seen that to achieve at least six refills this temperature should be in a range of 210 to 350 ° C, and that optimal results are achieved if the temperature is between 250 and 300 ° C. It is believed that at If the temperature is too low, the spray effect at the injection openings is not achieved, while if the temperature is too high, a Decrease in the molecular weight of the thermoplastic material takes place which leads to a weakening of the finished shotshell leads.

Figure 6 shows the effect of changes in pressure on the thermoplastic material, measured

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at the passage of the injection tube, that is to say in the pressure exerted on the inlet of the spray nozzle 22. As can be seen, to achieve at least six refills, this pressure should be kept in the range of 843 to 1757 kg / cm, with optimal results being obtained when the pressure is kept very close to 1406 kg / cm.

It has been found that the injection time to Filling the cavity 16 of the mold at the optimal pressure is 7 seconds. At the lower limit of the permissible pressure range the injection time increased to 9 s, which Injection speed of 0.6 g / s results while it is reduced to 5 s at the uppermost permissible pressure, which corresponds to an injection speed of 1.2 g / s. It it can therefore be said that to achieve the desired Spray-injection effect in the manufacture of a shotshell, the pressure must be chosen so that it results in an injection speed between 0.6 and 1.2 g / s.

FIG. 7 illustrates the effect that the cooling of the hollow block 13 has, the measured at various Temperatures of the hollow block obtained results are plotted. It has been found that the optimum temperature of the hollow block depends on the thickness of the tubular wall the shot shell produced. The temperature must be low enough to allow the thermo to effect plastic material; definitely should Temperature below about 18 ° C. As discussed above, the thickness of the tubular wall can be between about 0.74 and Sway 1.8 m. When producing cartridges whose wall thickness is at the lower limit of this range, has It has been shown that the temperature of the hollow block should not be below 8 ° C, as too rapid cooling would lead to this can clog the cavity of the mold before a full batch of material has been injected. When forming However, thicker walled cartridges can achieve good results at temperature.

a temperature of the hollow block of down to 2 ° C

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^{"Τ η} Figures 8 and 9 are shown the effects that result when the number or the size of the injection slots is changed 28th As can be seen, there should be at least two slots, preferably 4.5 or 6 slots, and the total effective cross-sectional area of the slots should be in the range of 0.25-0.9 mm, with optimum results being achieved when the total cross-sectional area is about Is 0.645 mm.

Figure 10 shows the effects of changes in the time interval while the molded shotshell of which is held in the cooled form before it is ejected. As can be seen, the cooling time should be at least 8s and preferably 13s. Is the cooling time longer than about 18 s, the individual production runs will be different Results are obtained because the material being fed must remain in the injection tube for extended periods of time is exposed to high temperatures for these periods of time and suffers a decrease in molecular weight. To such a thing To avoid a decrease in molecular weight due to excessive heating in the injection tube, it is also important that the tube is not loaded with too much material. It has in particular has shown that when the amount of material in the injection tube is kept below 200 g, cartridges are uniform high strength can be produced, while fluctuating results can occur if the pipe is over this amount addition is loaded.

The thickness of the tubular cartridge wall must be chosen that it has the combination of strength and flexibility needed for flanging, sealing, and the like multiple refills is required. In general, the Cartridge flared at a point 1/2 to 1/4 of the diameter of the cartridge from the open end of the cartridge Has. As has been shown, the wall thickness in this zone should be in the range from 0.74 to 1.8 mm. Around The front wall should ensure adequate strength and a high muzzle velocity when firing

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of the cartridge must be at least 2 mm thick.

FIGS. 4 to 10 show the results of a large number of experiments in a very concise form. To the more complete Presentation of the results as they can be achieved with the aid of the method according to the invention in the following details of several special test runs are given. Each of these trials was carried out with a Johns 2 ounce injection molding machine using a 609ram long snail carried out. The tip of the bleacher had an outside diameter of 3.05 mm and had four end slots each 1.9 mm long, 0.76 mm wide and 0.69 mm deep. In the injection molding machine was about 1 kg of thermoplastic material is heated, whereby the weight of the cartridges manufactured in the individual passes is approximately Was 5.8 g.

Pass 1

Material: HX538

Injection chamber temperature: inlet end 270 ° C

Middle 280 ° C

₉ End of ejection 285 ° C

Temperature of the sprayed material: 280 ° C spray pressure: 1757 kg / cm
Injection time: 7 seconds
Cooling down time: 8 seconds
Temperature of the hollow block: 2 ° C

Number of refills achieved: 27

Pass 2

Material: HX538 Incoming 290 ° C. Injection chamber temperature: center 300 ° C. Ejecting end 320 ° C.

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Temperature of the sprayed material: 300 ° C ^{Injection pressure: 1757 kg / cm 2} Injection time: 7 seconds Cooling time: 18 seconds Temperature of the hollow block: 12 ° C Number of refills achieved:

Pass 3

Material: DMDL31O3 Temperature of the injection chamber: inlet end 280 ° C Middle 290 ° C

End of injection 300 ° C

Temperature of the injected material: 290 ° C ^{Injection pressure: 1757 kg / cm 2} Injection time: 7 seconds Cooling time: 25 seconds Temperature of the hollow block: 12 ° C Number of refills achieved:

Pass h

Material DMDL1 155 290 ° C. Temperature of Injection chamber: 300 ° C. 320 ° C. Temperature of Injection pressure: : Incoming center Ejecting end injected material: 300 ° C 1757 kg / cm ²

Injection time: 7 seconds, cooling time: 27 seconds, temperature of the hollow block: 12 ° C Number of refills achieved:

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So the above results show that it is possible to use only plastic shotshells with surprising strength to produce by a thermoplastic Material is used that has not previously been used for injection molding processes. Essentially these results are achieved by the thermoplastic material through a group of small openings or Slitting is injected under such pressure and temperature conditions that the material is injected into the cavity of the mold is sprayed outwards. The test results presented above are for the manufacture of standard shotgun shells 12 gauge has been obtained; however, it has been found that other shotgun shells are used for making shotgun shells Caliber no significant changes in the conditions of opening, size, temperature and pressure occur. When producing larger or smaller cartridges, there is a corresponding slight increase or decrease the injection time to fill the mold; the process conditions that cause the turbulence in the in-mold Feed material, but remain the same.

The device shown above has only been given as an example and could be varied considerably. For example, as readily apparent, the invention is also applicable to machines with multiple cavity molds, the invention in accordance with certain parameters apply to the injection of material into each mold. Furthermore , the type of configuration of the hollow shape and the structure defining the injection openings within the hollow shape could be varied.

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Claims (14)

2 7 j J 7 9 7 PATtN "ANWAlTt SCHIFF ν. FÜNER STREHL SCHÜBEL-HOPF EBBINGHAUS FINCK MARIAHILFPl.ATZ 2 4 3, MDNCHEN 9O POSTAL ADDRESS: POST BOX 95 Ol 6O, D-8OOO MUNICH 95 LARRY SORENSON 7, Jun-54 1977 Injection molding process for shotgun parts. PATENT CLAIMS 1 injection molding method for plastic shotgun shells, wherein a hollow shape having an elongated tubular hollow portion is formed which is closed at one end and merges at its other end in a direction transverse to said other end disk-shaped hollow portion in an injection molding machine a thermoplastic material is heated, the molten thermoplastic material is injected under pressure into the hollow mold, the injection of the thermoplastic material is continued until the tubular and. the disk-shaped section of the hollow mold to form a cylindrical wall and a disc-shaped end wall of a cartridge are filled, and the cartridge thus formed is separated from the cavity mold, characterized g e - kennze ichnet that the thermoplastic material injected into the mold through a plurality of injection ports being, which is at the central part of the disc-shaped 7 O 9 B 8 3 / ORIGINAL INSPECTED hollow section are arranged distributed in the circumferential direction, so that the melted thermoplastic material in a plurality of turbulent flows is directed from the disc-shaped hollow section to the tubular hollow section to extend radially outward. 2. The method according to claim 1, characterized in that the entire effective cross section of the Openings in the range of 2.5 to 9 mm and that the thermoplastic material is at a temperature in the range from 210 to 360 ° C and with a throughput between 0.5 and 1.0 g / s is injected into the mold. 3. The method according to claim 2, characterized in that g e k e η η ze rejects that between 4 and 7 g of thermoplastic Material can be injected into the mold within an injection time in the range of 5 to 9 s. 4. The method according to any one of claims 1 to 3 »characterized in that as a thermoplastic Material a polymer with a molecular weight of at least 1,250,000 is selected and that on the thermoplastichehe Material a pressure in the range of 1050 to 1760 kg / cm is exerted. 5. The method according to any one of claims 1 to 4, characterized in that the thermoplastic rejects Material is passed into the hollow mold through a tubular injection part which runs along the central axis of the hollow mold 700683/086 2 protrudes into the disk-shaped portion of the mold, wherein the injection openings are formed in the peripheral wall of the injection part. 6. The method according to claim 5, characterized in that the hollow shape by a mold with a central core piece is formed and that in the formation of the hollow shape the central core piece with the injection part is brought into the stop. 7. The method according to claim 6, characterized in that g e k e η η, that the injection openings of open at their ends slots in the end of the in the formation of Hollow shape on the core piece resting tubular injection part are formed. 8. The method according to any one of the preceding claims, characterized in that at least four openings are regularly distributed in the circumferential direction and each opening has an effective cross section in the range of 1.29 to 1.95 mm ² . 9. The method according to any one of the preceding claims, characterized in that a thermoplastic material having a molecular weight in the range of 1,500,000 to 2,000,000 is elected. 709883/0862 10. The method according to any one of the preceding claims, characterized in that a thermoplastic material is selected which contains at least 90 % high density polyethylene. 11. The method according to any one of the preceding claims, characterized in that the temperature of the thermoplastic material is set to the range of 250 to 320 ° C when injected into the hollow mold. 12. The method according to any one of the preceding claims, characterized in that it rejects the hollow shape forming mold block is cooled to a temperature of less than 18 ° C. 13. The method according to any one of the preceding claims, characterized in that the cartridge in the hollow mold is cooled for at least 8 s before demolding. 14. The method according to any one of the preceding claims, characterized in that the thickness of the tubular Cartridge wall in the zone that is about 1/2 tube diameter from the open end, in the area from 0.74 to 1.8 mm. 709883 / 08Θ2