EP0424490B1 - Process and device for producing a tribasic propellent powder - Google Patents

Abstract

The invention relates to a process and a device for producing a tribasic propellent powder. To obtain reliable, continuous operation, a dibasic pre-gelatinized intermediate product is produced, initially without the use of solvent, from nitrocellulose and trinitroglycerine in a shearing rolling mill (1). The intermediate product is granulated and fed to an extruder (4) into which the third crystalline energy carrier and solvents are introduced. The powdered substance is mixed and extruded to form powder strands moistened with solvent.

Description

The invention relates to a method for producing a three-base propellant charge powder from nitrocellulose, explosive oil and a third, crystalline energy source and additives using a solvent, and to an apparatus for carrying out this method.

The three-base propellant powders are also known as "cold" powders. Compared to the usual, "hot" powders that do not contain a third, crystalline energy source, they have the advantage of greater protection of the pipe.

When producing propellant powder with explosive oil, the explosive oil acts as a gelatinator for the nitrocellulose. In the case of three-base propellant charge powders, the amount of the explosive oil is often not sufficient for complete gelatinization of the nitrocellulose and a uniform, homogeneous incorporation of the third, crystalline energy carrier into the powder mass, especially if the proportion of the crystalline energy carrier is high. In these cases, three-base propellant powder is produced using an organic solvent as a gelatinization aid. The solvent, for example a mixture of acetone and alcohol, is added when mixing the raw powder mass and is finally removed from the finished powder.

It is common to produce three-base propellant powder in batches. All components of the powder are mixed with the addition of the solvent to a solvent-moist powder mass and kneaded in a closed kneader until the powder mass is homogenized and gelatinized. The gelatinized powder mass is pressed in a pot press into powder strands which are then cut to length and freed from the solvent by drying. Because of the frequent manual handling of the powder mass, this process is very labor-intensive.

A continuously feasible process for the production of three-base propellant powder with solvent has also become known (DE-PS 24 61 646 and US-PS 4,051,207). In this method, a solvent-moist mixture of all components of the propellant charge powder is pre-plastified on an open, continuously working kneader, ie partially gelatinized. The mass usually passes through the kneader several times. The pre-plasticized, solvent-containing mass is then gelatinized in an extruder and converted into granulate form. The extruder should also be used several times be run through. The granules are then pressed in a further extruder to the desired powder strands, which are then cut to length and dried. This process is very complex in terms of the necessary mechanical equipment and in the process management, ie the setting and monitoring of the process parameters.

The invention is based on the object of specifying an improved, continuously executable method of the type mentioned at the outset which, in particular, requires less mechanical effort than previously and the course of which is easily adjustable and controllable. In addition, a device for performing this method is to be specified.

• a) Aus wasserfeuchter Nitrozellulose und Sprengöl vorgemischte wasserfeuchte Rohmasse wird auf einer kontinuierlich arbeitenden, offenen Knetvorrichtung gelatiniert und dabei getrocknet, wobei der Knetvorgang so eingestellt wird, daß die Rohmasse beim Verlassen der Knetvorrichtung in ein fertig gelatiniertes Zwischenprodukt mit einem Restwassergehalt von weniger als 3 % überfuhrt ist;
• b) das Zwischenprodukt wird beim Verlassen der Knetvorrichtung granuliert;
• c) das granulierte Zwischenprodukt (Granulat) und der dritte kristalline Energieträger sowie das Lösungsmittel werden einem kontinuierlich arbeitenden, geschlossenen Extruder zugeführt und in diesem durch Kneten homogenisiert und zu lösungsmittelfeuchten Pulversträngen extrudiert, wobei in Arbeitsrichtung des Extruders zuerst gemeinsam das Granulat und der kristalline Energieträger und nachfolgend das Lösungsmittel zugegeben werden;
• d) die lösungsmittelfeuchten Pulverstränge werden auf Länge geschnitten und getrocknet; gelöst.

Based on the method of the type mentioned at the outset, this object is achieved according to the invention a method for producing a three-base propellant charge powder from nitrocellulose, explosive oil and a third, crystalline energy source and additives using a solvent,
characterized by the following steps:

• a) Water-moist raw mass premixed from water-moist nitrocellulose and explosive oil is gelatinized on a continuously working, open kneading device and dried, the kneading process being set such that the raw mass when leaving the kneading device into a finished gelatinized intermediate product with a residual water content of less than 3% is convicted;
• b) the intermediate product is granulated on leaving the kneading device;
• c) the granulated intermediate product (granulate) and the third crystalline energy source and the solvent are fed to a continuously operating, closed extruder and homogenized in this by kneading and extruded to solvent-moist powder strands, the granules and the crystalline energy source first being jointly working in the direction of the extruder subsequently the solvent is added;
• d) the solvent-moist powder strands are cut to length and dried; solved.

Explosive oil in the context of this application is to be understood as the explosive oils usually used for propellant charge powder, in particular nitroglycerin and diglycol dinitrate, as well as mixtures of the aforementioned explosive oils.

The third, crystalline energy source is usually nitroguanidine (Nigu; NQ). However, hexogen (RDX) or octogen (HMX) or nitropenta (PETN) as well as other crystalline energy sources and mixtures of the aforementioned energy sources are also possible.

The additives are those customary in powder production, in particular plasticizers and stabilizers, which are present in the powder mixture in relatively small proportions by weight.

Drying the powder strands means any measure customary in powder production with which the solvent can be removed from the powder strands practically completely.

The process according to the invention is characterized in that not all components of the three-base propellant charge powder are mixed with one another from the outset. Rather, a finished gelatinized intermediate product is initially only produced from nitrocellulose and explosive oil, which are premixed into a water-moist raw mass, in a single pass on an open kneading device without the use of solvent.

This gelatinized and therefore dry intermediate product is granulated and fed as granules together with the third, crystalline energy source to a closed extruder, the solvent being added only now. Kneading in a closed extruder creates a homogeneous, doughy mass in which the crystalline energy source is uniformly and finely distributed. This solvent-moist mass is extruded from the kneading into powder strands in the same extruder, which are then cut to length and dried in the usual manner.

Overall, the method according to the invention can be carried out continuously. To carry it out, it only requires two essential machines, namely the open kneading device and the closed extruder, in addition a pelletizing device downstream of the open kneading device and a means for transporting the pellets to the extruder. The procedure is simple. Each machine only needs to be run once. Even if the recipes are changed frequently, it is not difficult to adjust the respective process parameters in a new and correct manner and to monitor their compliance. An advantage in this context is the fact that the first part of the process, the processing of the raw mass on the open kneading device, runs little differently than in the usual production of dibasic propellant powders, so that the routines and experience of this production method can be used in this respect . This also guarantees a high level of security. Until the nitrocellulose is completely gelatinized by the Explosive oil is particularly at high risk of self-ignition of the powder mass in every production, for example due to excretion of explosive oil from the raw mass. In this phase, however, the method according to the invention only works on the open kneading device, where the consequences of any self-ignition are far more harmless than in a closed processing device, for example an extruder. In the extruder, in turn, the risk of explosion is significantly reduced by the addition of the solvent in the process according to the invention. Finally, the method according to the invention manages with a significantly smaller amount than the solvent in terms of the production volume than the conventional manufacturing method and the losses of solvent during drying of the extruded powder strands are correspondingly lower, which increases the economy and makes a contribution to environmental protection. For the same reason, the drying effort compared to the usual method is considerably lower.

A shear roller mill, which is known per se for the homogenization and plasticization of non-explosive thermoplastic materials, for example plastics, is preferably used as the open kneading device (EP-A 0 148 966 or US Pat. No. 4,605,309). With regard to the details of such a shear roller mill, reference is expressly made to the two publications mentioned. The shear roller mill has two independently drivable rollers, between which there is an adjustable roller gap. The rollers are provided with spiral grooves, which ensure that the processed material is securely drawn into the gap and at the same time generate an axial transport movement in the nip from one end of the pair of rollers to the other end. In the method according to the invention, the water-moist raw mass is continuously fed onto the two rollers of the shear roller mill at one end and then gradually transported to the other end of the two rollers with kneading and intensive shearing. The raw material arriving at the other end is then gelatinized. To enable gelatinization, the water must be removed from the raw mass. This is done by squeezing in the roller gap and also by evaporating the water, since the rollers of the shear roller mill are heated. The raw powder mass fed to the shear roller mill preferably has a water moisture content of 20% to 30%. The removal of this water and thus the increasing gelatinization of the raw material takes place gradually during the migration of the raw material along the rollers. By adjusting the roller gap and the speeds of the two rollers, the process can be controlled in such a way that the raw mass at the discharge end of the roller pair is practically dry and thus gelatinized, which means that the residual water content is less than 3% and preferably less than 1%, for example 0.5%. The finished gelatinized raw material is located on one of the two rollers and can be removed there continuously with simultaneous granulation, for example with a granulating head.

The process according to the invention also has the advantage that the recipes can be adhered to very precisely and the production of various propellant powders can therefore be reproduced exactly because Both the intermediate product due to its granular form and the third crystalline energy source can both be fed to the extruder in precisely metered form, for example with the aid of suitable metering devices. There are several options for adding to the extruder. If the granules and the crystalline energy carrier are added together in the working direction of the extruder, and then the solvent is added, the design of the extruder required is particularly simple because only a common input opening for granules and crystalline energy carriers is necessary. By adding the solvent in the working direction behind the place of addition of granules and energy carriers, bridging and clogging in the inlet opening for granules and energy carriers are avoided. It has been shown that the homogeneity of the powder strand is still somewhat better if first the granulate, then the solvent and then the crystalline energy source are added in the working direction of the extruder. For this purpose, the extruder requires a first filling opening for the granules in the working direction, then an opening for the supply of the solvent and then an opening for the supply of the crystalline energy source under pressure, which is technically somewhat more complex.

The additives can already be fed to the kneading device together with the premixed water-moist raw material. Alternatively, it is possible to add the additives to the extruder together with the granules and / or the crystalline energy carrier. The joint application of both options can be done in In individual cases, ie depending on the particular recipe, it may be useful, for example, in such a way that certain additives are only fed to the kneading device and the remaining additives to the extruder.

The raw mass fed to the shear roller usually comprises 40% to 60% and preferably 45% to 55% nitrocellulose. The crystalline energy source is metered into the extruder in an amount of 10% to 55% and preferably in an amount between 40% and 55% of the granules supplied.

The solvent is expediently fed to the extruder in an amount of 60 to 130 grams per kilogram of the solids fed (granules + crystalline energy source). This means a saving in solvent of 30% to 60% compared to conventional manufacturing processes. Examples of solvents are Alcohol or acetone in question. The selection depends, among other things. on the degree of nitration of the nitrocellulose used. The higher the degree of nitration, the more or the sharper the solvent is generally necessary.

A device for carrying out the method according to the invention is characterized by an open shear roller mill, a downstream granulating device, a transport device and a closed extruder.

The invention is explained in more detail below with further advantageous details using a schematically illustrated exemplary embodiment. The only Figure shows a schematic representation of a device for producing three-base propellant powder.

The device shown comprises an open shear roller mill 1, as is known, for example, from US Pat. No. 4,605,309. The shear roller mill has two independently drivable rollers, between which a roller gap is formed. At one end of the two rollers, the pre-mixed, water-moist raw powder mixture of water-moist nitrocellulose and explosive oil is fed to the shear roller mill. The feed is indicated in the drawing by a feed hopper and an arrow. The raw mass is kneaded in the shear roller mill and thereby gelatinized while removing the water. During processing, it moves to the other end of the two rollers, the raw material arriving at the other end being completely gelatinized. A pelletizing device 2 is assigned to this end of the two rolls, with which the gelatinized raw material or the intermediate product is removed from one of the two rolls and thereby pelletized. The granulated intermediate product (granulate) reaches the input opening 5 of a closed extruder 4 by means of a transport device 3. The third, crystalline energy carrier is fed to the same input opening 5. The granulate and the third energy carrier are expediently supplied in each case via a metering device (not shown in more detail). In the working direction behind the filling opening 5, an addition device 6 is provided on the extruder 4 for the addition of solvent. Alternatively, a further filling opening 7 can be provided behind the feed device 6, via which the crystalline energy carrier is introduced into the extruder separately from the granulate. This must then be done under pressure because a pressure has already built up in the area of the filling opening 7 inside the extruder.

The extruder 4 is provided in the usual way with one or two screws 8, which are rotatably mounted in the housing of the extruder and are only indicated schematically here. At the outlet area 9 of the extruder there is a die, not shown, through which the material is extruded into powder strands. Due to the kneading action inside the extruder, the granulate and the third energy source in connection with the solvent, e.g. Alcohol, a pasty powder mass in which the third, crystalline energy source is homogeneously finely distributed. This solvent-containing mass is finally passed through the die of the extruder e.g. extruded into a 7-hole powder strand. The powder strands emerging from the extruder are cut to length in a conventional manner, not shown, and suitably, e.g. in a drying facility, freed from the solvent.

The two rollers of the shear roller mill can be heated to temperatures between 80 ^o C and 120 ^o C. The adjustable speed range of the two rollers is between 40 and 70 rpm. The gap between the two rollers is usually set to less than 2 mm . The granulating device 2 delivers a granulate in the size of 3 to 6 mm. The extruder 4 is typically designed with a length to diameter ratio of 20 to 24. The temperature inside is between 20 ^o C and 50 ^o C. The screw speed can be set between 30 and 80 rpm.

In the production of a certain three-base propellant charge powder 1 mixed raw mass of 46% nitrocellulose (N₂ = ¹3.1%), 46% nitroglycerin, 8% Centralit I and 0.7% cryolite is processed on the shear roller mill. The temperature of one roller of the shear roller mill is 90 ^o C and its speed is 68 rpm. The temperature of the second roller is 80 ^o C and its speed is 58 rpm. The average throughput on the shear roller mill is 52 kg of water-moist mass per hour. The finished gelatinized raw material, the intermediate product, on the granulating device 2 has a water content of less than 0.5%. The dry granules and nitroguanidine as the third energy source are metered into the extruder in a weight ratio of 45% granules and 55% nitroguanidine, where they are homogenized with the aid of solvents and extruded into a 7-hole powder. The throughput here is 40 kilograms per hour at a screw speed of 60 rpm and an extruder head pressure of 23 bar.

To produce another three-base propellant charge powder, a mixed raw mass of 62% nitrocellulose, 37% nitroglycerin, 0.3% centralite, 0.5% acardite, 0.1% magnesium oxide and 0.1% graphite with an initial water content is placed on the shear roller mill 1 processed by 28%. The temperature of the first roller is 110 ^° C. and its speed is 50 rpm, the temperature the second roller 90 ^o C and its speed 45 rpm. This results in a throughput of 42 kilograms of dry mass per hour with a water content of approx. 0.7% at the granulating device. The granules and nitroguanidine are metered into the extruder in a weight ratio of 60%: 40% and processed there with acetone as solvent in an amount of 3 liters per hour and extruded to form a 7-hole bulk powder. The screw speed is 40 rpm, the head pressure is 27 bar and the head temperature is 48 ^o C. The throughput is 30 kg per hour.

Claims (9)

1. A method of preparing a tribasic propellant charge powder of nitrocellulose, blasting oil, and a third, crystalline energy carrier, as well as additives, including the use of a solvent, characterized by the following steps:

   (a) raw stock moist with water and premixed of nitro-cellulose, which is moist with water, and blasting oil is gelatinized in a continuously working, open kneading apparatus, while being dried at the same time, the kneading process being adjusted such that the raw stock, upon leaving the kneading apparatus, has been converted into a fully gelatinized intermediate product having a residual water content of leass than 3 %;

   (b) the intermediate product is granulated as it leaves the kneading apparatus;

   (c) the granulated intermediate product (granular material) and the third crystalline energy carrier as well as the solvent are supplied to a continuously working, closed extruder in which they are homogenized by kneading and extruded in the form of powder strands which are moist with solvent, the feeding being realized, in operating direction of the extruder, by first jointly adding the granular material and the crystalline energy carrier and subsequently the solvent;

   (d) the powder strands moist with solvent are cut to length and dried.
2. The method as claimed in claim 1, characterized in that an open shearing mill is used as kneading apparatus.
3. The method as claimed in claim 1 or 2, characterized in that additives are fed to kneading apparatus together with the premixed raw stock which is moist with water.
4. The method as claimed in claim 1, 2 or 3, characterized in that additives are fed to the extruder together with the granular material and the crystalline energy carrier.
5. The method as claimed in any one of claims 1 to 4, characterized in that the raw stock supplied to the shearing roller comprises from 40 % to 60 % of nitrocellulose.
6. The method as claimed in any one of claims 1 to 5, characterized in that the raw stock supplied to the shearing roller contains from 20 % to 30 % of water moisture.
7. The method as claimed in any one of claims 1 to 6, characterized in that the crystalline energy carrier is fed to the extruder in an amount of from 10 % to 55 % of the granular material supplied.
8. The method as claimed in any one of claims 1 to 7, characterized in that the solvent is fed to the extruder in an amount of from 60 to 130 g per kg of the solids supplied (granular material + crystalline energy carrier).
9. An apparatus for carrying out the method as claimed in any one of claims 1 to 8, characterized by an open shearing mill, a downstream granulating means, a conveying means, and a closed extruder which comprises, in the direction of operation, a first feed opening for the granular material and the crystalline energy carrier and then an opening for supply of the solvent.