EP0113402B1 - Process and apparatus for the manufacture of a monobase or plural base propellant - Google Patents

Abstract

Single- or multi-base propellants are produced in a solvent process from their starting components, of which at least one is moistened with alcohol, using a twin-shaft screw extruder, that has an inlet zone run at a raised temperature, then nextly a mixing and kneading zone and lastly an outlet zone. The temperature in the kneading and mixing zone and in the outlet zones is kept at a value that is higher than in the inlet zone. Furthermore there is a temperature drop towards the outlet zone.

Description

The invention relates to a method and a device for producing single or multi-base propellant charge powders in strand form by means of a twin-screw extruder with a feed zone for the starting components, at least one of which is moistened with alcohol, followed by mixing and kneading zones with solvent addition for plasticizing and an exit zone adjoining the screws with a molding head for one or more strands, the feed zone being kept at an elevated temperature.

Thermoplastic molding processes or shaping using volatile solvents are used to produce single-base propellant charge powder (nitrocellulose), dibasic (nitrocellulse + nitroglycerin or other explosive oils) and also triple-base propellant charge powder (nitrocellulose + nitroglycerin + nitroguanidine), the latter method being preferred, the latter method being preferred. Ketones, alcohols, ethers or mixtures thereof are generally used as solvents and gelling agents. Compared to thermoplastic molding, this method has the safety advantage that the processing temperature can be kept relatively low due to the addition of solvents. For example, pasted nitrocellulose can be extruded into one or more strands in a screw press (DE-AS 2825567, DE-OS 3044577), with one or more channels being molded into the strand depending on the application for the purpose of extrusion by means of a needle die.

In this molding process, elevated temperatures arise within the screw extruder due to the internal friction, which were previously achieved either by a disproportionate addition of solvent or by cooling the extruder in the kneading and mixing zones and in the exit zone (DE-AS 2 825 567) on one tried to keep safe value. In the former case, the extruded strand has to be subjected to a pre-drying process because of the remaining solvent before it can be processed further. The dimensional stability and thus the shape retention of the channels is not always given here. In both of the aforementioned cases, the quality of the end product, in particular its density and homogeneity, is unsatisfactory. It is precisely these factors, namely shape stability, density and homogeneity, which have a significant influence on the ballistic behavior. With a controlled addition of solvent (DE-OS 3044577) it is possible to achieve considerably better results, but the mass throughput is not satisfactory.

The invention has for its object to provide a method and an apparatus which allow propellant charge powder of homogeneous composition to be obtained in dimensionally stable strands with increased throughput.

Starting from the prior art described at the outset, in which the twin-screw extruder has a feed zone with elevated temperature, this object is achieved in terms of process technology in that the kneading and mixing zone and the exit zone are kept at a constant temperature which is higher than that of the feed zone .

The invention is based on the knowledge that the cooling provided in the prior art behind the heated feed zone leads to the formation of a layer on the housing wall. Shear forces develop between this and the neighboring inner product layers, which in addition to the mixing and kneading forces lead to uncontrolled temperature increases in the mass. These effects seem to be decisive for the inhomogeneity of the end product. In practice, this also leads to the formation of clots and thus to an uneven product leakage. Although attempts have been made to retain this inhomogeneity by arranging sieve inserts in front of the exit die (DE-OS 3042662), these sieves are installed very quickly, so that the extruder often has to be dismantled and cleaned.

The aforementioned effects are avoided by carrying out the process according to the invention. At the elevated temperature in the kneading and mixing zone, a better gel structure and thus a better flow behavior are achieved, which should be responsible for the better homogeneity found. For safety reasons, cooling of the extruder is inevitable, but practical studies have shown that the process can be carried out for days at elevated temperatures, which in any case must be below the evaporation temperature of the solvents. The throughput can also be increased significantly.

According to the invention, the higher safety-related risk in the case of propellant powders with two or more bases is taken into account in that the kneading and mixing zone is divided into sections with a temperature falling in the conveying direction but constant within the sections.

The product therefore passes through a section of elevated temperature in the feed zone, a section of even higher temperature in the first area of the kneading and mixing zone and then sections of falling temperature, which is still above that in the feed zone.

For the production of single-base propellant charge powders, even with small additions of explosive oils and dinitrotoluene, according to a preferred embodiment it is provided that the housing temperature in the area near the screw in the feed zone to 40 ± 3 ° C, in the kneading and mixing zone to 56 ± 3 ° C and in the exit zone is held so that the melt temperature is 64 ± 3 ° C.

In contrast, for the production of multi-base, in particular three-base, propellant powders, a preferred embodiment provides that the housing temperature in the area near the screw in the feed zone is 35 ± 5 ° C, in the kneading and mixing zone in the conveying direction from 50 ± 3 ° C to 45 ± 3 ° C drops and is 40 ± 3 ° C in the exit zone.

• a) Gleichläufer (gleichlaufende Schneckenwellen):
  
• b) Gegenläufer (gegenläufige Schneckenwellen):
  

To carry out the method according to the invention, twin-screw extruders of known type (DE-B 2825567, DE-A 3044577) are used which are designed as single or counter-rotors for single-base propellant charge powders, and advantageously only as co-rotators for multi-base propellant charge powders. In a preferred embodiment for single-base propellant charge powder, the following relationship between length L (total length minus length of the exit zone) and the inner diameter D of the screw extruder applies to the individual zones:

• a) Co-rotating (co-rotating worm shafts):
  
• b) Counter-rotating (counter-rotating worm shafts):
  

In the case of a co-rotating screw extruder for the production of multi-base, in particular three-base, propellant charge powder, according to a preferred embodiment with a total length of L = 23 D plus the length of the exit zone for the individual zones, the following dependency between the length L and the inside diameter D of the screw extruder applies:

In both of the above-mentioned embodiments, the length of the exit zone is irrelevant, since it is always approximately the same length. It is only necessary to ensure that the temperature limits specified in connection with the described methods are observed.

In all embodiments, it is advisable to provide the housing with one or more degassing openings, which should be arranged above all in the area of the mixing and kneading zones, in order to allow the evaporating solvents to be drawn off and, in particular, to avoid gas inclusions within the product line is coming. Likewise, in all embodiments, the housing of the screw extruder is connected to a fluid circuit which, controlled by thermostats, by cooling or heating ensures that the required constant temperature limits in the individual zones are maintained.

example 1

Single-base propellant powder: 100 kg nitrocellulose (dry weight) moistened with 25 to 30 kg alcohol, approx. 1.7 to 2 wt.% Stabilizer and sodium oxalate are processed with 16.5 to 27 kg acetone in a co-rotating or counter-rotating extruder. In the feed zone, the housing temperature is t ₁ = 40 ± 3 ° C in the area close to the wall and t ₂ = 56 ± 3 ° C in the kneading and mixing zone, while the melt temperature is kept at t ₃ = 64 ± 3 ° C in the outlet section. The speed of the screw shafts is 20 to 120 rpm for a multi-strand extrusion, each strand being able to be provided with one or more channels with the aid of a needle die in order to obtain strands for propellant powder of customary geometry.

The strands obtained in this way had a transparent appearance with a smooth surface and could be cut immediately without an additional drying process and then surface-treated without the shape stability suffering.

Example 2

A three-base propellant powder is made from a premix with a dry weight of 100 kg of 47 ± 1% by weight nitroguanidine, 28 ± 1% by weight nitrocellulose, 23 ± 1% by weight nitroglycerin, 1.5 ± 0.1% by weight Stabilizer, approx. 0.3% by weight cryolite and 6 to 8 kg alcohol and 18 to 22 kg acetone processed in a co-rotating twin-screw extruder. The housing temperature in the feed and metering area is at t ₁ = 35 ± 5 ° C, in a first section of the mixing and kneading zone to t ₂ '= 50 ± 3 ° C and in a second section of the kneading and mixing zone to t ₂ "= 45 ± 3 ° C, while in the exit zone the housing temperature is t ₃ = 40 ± 3 ° C at a melt temperature of 62 ± 5 ° C. The screw speed is again 20 to 120 rpm with multi-strand outlet and one or more channels per strand.

Single component dosing into the extruder is also possible, nitroglycerin being phlegmatized with nitrocellulose. In this case too, 18 to 22 kg of acetone were required for plasticizing.

• Figur 1 einen schematischen Längsschnitt durch einen Doppelwellen-Schneckenextruder als Gegenläufer und
• Figur 2 einen Doppelwellen-Schneckenextruder als Gleichläufer.

The invention is described below with reference to two embodiments shown in the drawing. The drawing shows:

• 1 shows a schematic longitudinal section through a twin-screw extruder as a counter-rotor and
• Figure 2 shows a twin-screw extruder as a co-rotor.

The extruder shown in Figure 1 has a Ge housing, which is composed of several segments 2, which are clamped together by end flanges 3. On the drive side 4, two parallel, counter-rotating worm shafts 5 are inserted into the housing, which extend to the front end flange 3 and end there in tips. A molding head 17 connects to the last housing segment 2. This screw extruder is used to produce single-base propellant powder.

The first drive-side housing segment 2 is provided with an addition opening 6 for the solid components, namely nitrocellulose and additives. Stabilizers can also be added at this point, all components being added individually or in a premix. The downstream segment 2 is provided with a nozzle channel 7, through which the solvent, if necessary in a mixture with the stabilizers, is metered in. Finally, the penultimate housing segment 2 in the conveying direction has a cutout 8, which serves on the one hand for degassing the product and on the other hand for photo-optical recording of the surface of the product passing the cutout 8. A camera 9 is arranged above the opening 8 and is connected to a monitor 10. Based on the recording on the monitor 10, the solvent added via the nozzle channel 7 is metered. The extruder described above is known (DE-OS 3 044 577).

The two symmetrical worm shafts 5 initially have a conveyor section 11 on the drive side, which is of a single-start design. This is followed in the area of the nozzle channel 7 by a further multi-course conveyor section 12 a, 12 b. A first kneading section 13 and a second kneading section 14 and then a baffle plate 15 are connected to the latter. Following the baffle plate 15 and directly in the area of the degassing and observation opening 8, a three-course conveying section 12 is again provided, which is finally closed off from the die by a further kneading section 13.

Between the individual conveyor sections 12 and between them and the kneading sections 13, as well as the baffle plate 15, calming zones 16 are provided, in which there are no displacement elements on the screw shafts. In the exemplary embodiment shown, the forming head 17 consists of a perforated die, a perforated plate adjoining it, and dies with needle carriers for producing the channels in the strand.

As can be seen from the drawing, the conveyor sections 11 and 12 extend approximately over the first three housing segments 2. These form the feed zone with the length L ₁ . The length L ₁ corresponds to approximately 11 D, where D is the inside diameter of the housing. In the area of this feed zone, a temperature of t _l = 40 ± 3 ° C is maintained during the production of a single-base propellant powder.

The adjoining four housing segments 2 form the kneading and mixing zone L _Z , in which a housing temperature of t ₂ = 56 ± 3 ° C is maintained. The length L ₂ corresponds to approximately 15 D. Finally, the melt temperature should be t ₃ = 64 ± 3 ° C in the exit zone with the die.

The co-rotating twin-screw screw extruder shown in FIG. 2 likewise has an essentially known structure, so that a detailed description can be dispensed with here. In the area of the feed zone, the screw shafts mainly have sections serving for conveying, in the adjoining area mainly serving sections for kneading and mixing, although the transitions can be fluid. Here, as in the previously described embodiment, the degassing openings are preferably arranged in the region of the conveying sections of the screws, as is shown by means of the degassing opening 8.

The conditions for the production of a single-base propellant powder are shown immediately below the drawing. Here, the feed zone L _{1 is} approximately equal to 9 D at a constant housing temperature t ₁ = 40 ± 3 ° C., while the length L _{2 of} the kneading and mixing zone is approximately 14 D. A temperature t ₂ = 56 ± 3 ° C is maintained in this zone. In the outlet part, the melt temperature of the single-base propellant powder is 64 ± 3 ° C.

Here, too, the outlet part is formed by a perforated die, which is optionally provided with a needle insert. Furthermore, at least one degassing opening is also provided in the kneading and mixing zone L ₂ .

Below are the conditions for the production of a three-base propellant powder. Since a multi-step temperature control is provided here, the individual zones do not exactly match the zones previously described in connection with the single-base propellant powder. The feed zone L ₁ corresponds here to approximately 5 D. A temperature of t ₁ = 35 ± 5 ° C is maintained there. The subsequent first section of the kneading and mixing zone L _Z corresponds to approximately 9 D with a constant temperature control of 50 ± 3 ° C. This is followed by another section L ₂ "of the kneading and mixing zone, where the housing temperature is 45 ± 3 ° C. This corresponds to a melt temperature of about 62 ± 5 ° C. Finally, a temperature t ₃ of 40 is reached in the outlet part with the dies Maintain ± 3 ° C.

Claims (7)

1. Process for the manufacture of singlebasic or polybasic propellant powders in strand form by means of a twin shaft screw extruder with a feed zone for the starting components, whereof at least one is moistened with alcohol, following mixing and kneading zones with solvent addition for plastification and an outlet zone following onto the screws with a moulding head for one or more strands, the feed zone being kept at an elevated temperature, characterized in that the kneading and mixing zones, as well as the outlet zone are kept at a roughly constant temperature which is higher than that of the feed zone.

2. Process according to claim 1, for the manufacture of double and polybasic propellant powders, characterized in that the kneading and mixing zone is subdivided into portions with a temperature falling in the feed direction, but which is constant within the portions.

3. Process according to claim 1, for the manufacture of singlebasic propellant powders, characterized in that the housing temperature in the screw-near region is 40±3°C in the feed zone, 56±3°C in the kneading and mixing zone and in the outlet zone is such that the material temperature is 64±3°C.

4. Process according to claims 1 or 2 for the manufacture of polybasic, particularly triple base propellant powders, characterized in that the housing temperature in the screw-near region is 35±5°C in the feed zone, between 50±3°C and 45±3°C in the kneading and mixing zone and 40±3°C in the outlet zone.

5. Process according to claim 4, characterized in that the housing temperature in the mixing and kneading zone drops in the feed direction from 50t3°C to 45±3°C.

6. Process according to claims 1 or 3 for the manufacture of singlebasic propellant powders, characterized in that for the individual zones there is roughly the following dependency between the length L (total length, less the length of the outlet zone) and the internal diameter D of the screw extruder:

a) Screw shafts rotating in the same direction:

b) Screw shafts rotating in opposite directions:

7. Process according to claims 1 or 4 for the manufacture of triplebasic propellant powders using a screw extruder with screw shafts rotating in the same direction, characterized in that for a total length of the screw shafts rotating in the same direction of L = 23 D plus the length of the outlet zone for the individual zones, roughly the following dependency exists between the length Land internal diameter D of the screw extruder:

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