RU2434833C1 - Method of producing working mix of powders - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention relates to composite solid propellants based on ammonium perchlorate with addition of components. Stringent requirements are specified for composite solid propellant production that relate to content of components and to ratio between individual fractions of ammonium perchlorate. Said requirements are governed by preset parameters of ballistic and physicomechanical characteristics. Method of preparing by two-roll vaned-shaft mixer working mixes of powders whereby fractions of ammonium perchlorate are batched in four steps into 1/4 of each fraction to be mixed for 5-7 minutes. First coarse fraction is batched, then fine fraction is batched, while, additional components are added in first step. In finale step, mixing is performed for 30-36 minutes. ^ EFFECT: optimum grain size composition. ^ 1 dwg, 2 tbl, 1 ex

Description

The invention relates to a technology for the preparation of powdered components and their mixtures based on ammonium perchlorate, used in the manufacture of charges from mixed solid rocket fuel (STRT) and can be used in the preparation of mixtures of powdered explosives and pyrotechnic compositions.

In STRT compositions, ammonium perchlorate is mainly used as an oxidizing agent in the form of a mixture of its various fractions with the introduction of additional powdery components for special purposes. This mixture is called the working mixture of powders (CSP). In RF patent No. 2317280, IPC С06В 21/00, priority dated August 10, 2006, "Installation for preparing a powder mixture based on ammonium perchlorate (PHA) used as an oxidizing agent for charging a solid-propellant rocket engine", the process design obtaining various fractions and mixtures thereof with additional components. The scheme shown in the aforementioned patent regarding dosing fractions, additional components, mixing them, unloading through a storage ring, sieving and packaging into containers is taken as a prototype.

The disadvantages of the prototype include the lack of dosing procedures for fine and large fractions, additional components and modes of mixing, which, in many respects, determine the quality of the resulting working mixture of powders required for STRT. Sections 1.7.1 and 1.7.3 in the "New reference book of a chemist and technologist" Processes and Apparatuses of Chemical Technologies ", Part 1, NPO Professional, St. Petersburg, 2004, are devoted to the mixing of various phases, including granular materials. this source indicates only general principles of the approach when choosing a mixing method, in particular, a significant influence on the time to achieve the required quality of the mixture, sequence and method of loading the initial mixed components is noted, but there is no specification of the process parameters.

The theory of mixing processes and a description of the most common equipment used in this operation are described in section 9.4 on pages 153-177 of the book by MB Generalov, “Main Processes and Apparatuses for Industrial Explosives Technology", Moscow, Akademkniga Research and Development Center, 2004 In the same section, on pages 176-177, a mixer is described that is similar in design to a twin-shaft mixer with blades used in the preparation of working powder mixtures. However, the operation of the mixer is described in isolation from the metering devices. In the book of authors N. A. Simbirtsev, Yu. M. Milekhin, V. M. Merkulov, Yu. B. Bonzuly "Fundamentals of the technology for the preparation of dispersed materials in the processing of energy condensed systems", Moscow, 2006, there is a special section 7 relating to mixing dispersed materials and preparing working mixtures of powders. This source also did not find reflection regarding specific recommendations for the qualitative mixing of different-sized fractions of granular materials with the introduction of a small amount of additional components.

In the manufacture of STRT, stringent requirements have been established both for ensuring the content of components and for the ratio of individual fractions of ammonium perchlorate. These requirements are due to the need to ensure the specified parameters for ballistic and physical-mechanical characteristics.

An object of the invention is to provide a high-quality working mixture of powders according to particle size distribution by optimizing the order of input fractions of ammonium perchlorate, additional components and their mixing time.

The technical results of the invention are the preparation of a high-quality working mixture of powders by mixing a large fraction of PHA with a particle size of 160-315 microns and a fine fraction with a particle size of PHA less than 50 microns in a twin-shaft mixer with blades in a ratio of 20/80 ... 80/20 wt.%, at the same time, first coarse and then fine fractions are dosed in 1/4 of them in four doses, in each dose they are mixed for 5-7 minutes while the mixer and the reversing screw are operated in the locking mode, and at the final stage the reversing screw is turned off They read and continue mixing in the mixer for up to 30-36 minutes, unload with the mixer running and the reversing screw turned on for unloading, transport it with the screws to the intermediate tank, from it to the separator, sift it into a container mounted on the scales. In the first dose, after loading large and small fractions of ammonium perchlorate, additional components are dosed.

In the manufacturing process for producing STRT, the dosage of semi-finished products is carried out in three flows: a working mixture of powders, a mixture of liquid-viscous components and a mixture of hardeners. The working mixture of powders is a carefully mixed mixture of fractions of ammonium perchlorate, differing in particle size, in a given ratio, as well as additional components. Currently, ammonium perchlorate fractions are mainly used:

- large with particle sizes of 160-315 microns, supplied by the manufacturer under the brand name D + 160-315,

a fine fraction "C" with particle sizes up to 50 microns under the brand name, manufactured at the STRT manufacturing plants.

Depending on the composition of the STRT and the requirements for ballistic and physical-mechanical characteristics, the ratio between the fractions of ammonium perchlorate is:

The content of each of the added additive components does not exceed 0.4%.

It is known from the theory and practice of mixing that the smaller the difference in the content of the mixed components, the faster their distribution among themselves. Therefore, with a low content of additional components, they must first be mixed with part of the main component - ammonium perchlorate.

The fine fraction of PHA has poor flowability, crumbles and coalesces. For this reason, when first loading the fine fraction, it will occupy the bottom of the mixer. Being in the gap between the bottom of the mixer and the blades, the fine fraction will mix poorly with the coarse fraction.

The coarse fraction has fluidity, does not crumple and does not cake. When loading the coarse fraction at the beginning of the process, and then the fine fraction, the conditions for mixing are improved. In this case, the small fraction passes into the gaps between the particles of the large fraction, which contributes to better mixing. Based on the above principles, a technological process for the preparation of a working mixture of powders has been developed.

The process diagram is shown in the drawing.

According to the above scheme, a coarse fraction with a particle size of 160-315 μm from the hopper 1 is fed by a screw feeder into a batch weighing batcher 3, configured to take% of this fraction and is poured into a twin-shaft mixer 5 with blades. Then a small fraction of PHA with a particle size of less than 50 microns from the hopper 2 with a tedder using a feeding screw is fed into a batch weighing batcher 3, configured to take 1/4 of the required portion of this fraction. A portion is poured into a twin-shaft mixer 5 with blades. Then the entire sample of additional components is dosed with dispenser 4 into a twin-shaft mixer 5 with blades. Turn on the reversing screw 6 for locking and the drive of the twin-shaft mixer 5 with blades for mixing for 5-7 minutes. During this period, the distribution of coarse and fine fractions and additional components occurs in the volume of the twin-shaft mixer 5 with blades. The blades on the shafts are fixed in such a way that they circulate the components being mixed, moving them from one half of the mixer to the other. Similarly, the second, third and fourth parts of the coarse and fine fractions of PHA are dosed. After loading the last portions of the coarse and fine fractions, they are mixed in a twin-shaft mixer with blades, after 5-7 minutes of mixing, the reversing screw is turned off and mixing is continued for 30–36 minutes. The working mixture of powders added in the above manner is discharged. To do this, turn on the drive of the twin-shaft mixer with blades, the reversing auger 6 for unloading mode, the transport auger 7. In this case, the working mixture of powders enters the hopper 8. After 5 minutes, include the separator 10, the transport auger 9, and the powdered working mixture sifted on the separator enters into the container 11. After the set mass of the working mixture of powders is set in the container 11, according to the indications of the weights 12, the separator and the transport auger are automatically switched off. The filled container is replaced with an empty one and the process is continued by turning on the separator 10 and the transport auger 9.

The selection of the optimal parameters of the method of preparation of the working mixture of powders is confirmed by the following example.

Example.

It is required to produce 1000 kg of a working mixture of powders at extreme values of the coarse and fine fractions - with the coarse fractions 80 wt.% And 20 wt.% Fine and 20 wt.% Coarse and 80 wt.% Fine fractions, as well as 0, 4% calcium phosphate - anti-caking additives.

To prepare a working mixture of powders, it is necessary in the first case to dose 800 kg of coarse and 200 kg fractions with a particle size of less than 50 μm, as well as 4 kg of calcium phosphate, and in the second case, 200 kg of coarse and 800 kg of fine. For loading in four doses, it is necessary to dose 200 kg of coarse and 50 kg of fine fraction in the first case and 50 kg of coarse and 200 kg of fine in the second case at each dose.

The modes of preparation of the working mixture of powders for these cases are shown in table 1.

Table 1 Correlation fractions Receptions Dosage kg The duration of mixing, min The duration of the reversing screw in the locking mode, min Coarse fraction PHA Fine fraction PHA Calcium phosphate one 2 3 four 5 6 7 80% coarse 20% shallow The first 200 fifty four 5 7 Second 200 fifty - 5 7 Third 200 fifty - 5 7 Fourth 200 fifty - 5 7 20% coarse 80% shallow The first fifty 200 four 7 5 Second fifty 200 - 7 5 Third fifty 200 - 7 5 Fourth fifty 200 - 7 5

With the visual observation modes shown in Table 1, a uniform distribution of fractions in the volume of the mixer and the absence of precipitation from the twin-shaft mixer through the reversing screw are ensured.

To establish the required mixing time in the fourth step, the influence of the duration of mixing on the quality of the working mixture of powders by granulometric composition was determined. In this case, the limiting values in the ratio between the fractions are taken, as the most difficult to mix, namely

Assessment of the quality of the preparation of the CPD in the above modes is shown in table 2.

table 2 Ratio of fractions Quality control The duration of mixing, min Grading, % The content of particles with a size of 160-315 microns, wt.% The content of particles with a size of less than 50 microns, wt.% 80% coarse 20% shallow Norm for scientific and technical documentation 66.5-80 17-20 According to analysis 25 64.0 21.1 According to analysis 28 65.0 20.5 According to analysis thirty 67.0 19.5 According to analysis 36 70.0 18.5 According to analysis 40 69.0 18.7 20% coarse 80% shallow Norm for scientific and technical documentation 17-20 66.5-80 According to analysis 26 22.0 63.5 According to analysis 29th 20.5 66.0 According to analysis thirty 19.5 68.0 According to analysis 36 19.5 70.0 According to analysis 40 19.3 69.5

According to the data in table 2, the minimum allowable mixing time, which ensures the production of working mixtures of powders with a given particle size distribution, is 30 minutes. An increase in mixing time leads to a decrease in the productivity of the process. Given the fulfillment of the technological requirements of the process, the maximum allowable mixing time is set to 36 minutes.

Claims (1)

A method of preparing a working mixture of powders, including dosing small and large fractions of ammonium perchlorate into a mixer, mixing, sieving and unloading into a container, characterized in that in a twin-shaft mixer with blades mixed PCA of a large fraction with a particle size of 160-315 μm and a fine fraction with particle size less than 50 microns in a ratio of 20/80 ... 80/20 wt.%, at the same time, first coarse and then fine fractions are dosed in 1/4 of them in four doses, in the first dose, after loading large and small fractions of PCA, additional Components, at each intake, the resulting mixture is stirred for 5-7 minutes while the mixer and the reversing screw are operating in the locking mode, at the final stage, the reversing screw is turned off and mixing is continued in the mixer for 30-36 minutes, unloaded with the mixer running and the reversing screw is switched on for unloading , transported by screws into an intermediate tank, from it to a separator, sieved into a container mounted on the scales.

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