RU2301707C2 - Method for grinding of solid particles - Google Patents

Abstract

FIELD: processes for grinding of solid particles, including grinding of oxidizer in production of mixed solid rocket fuel for obtaining of ultradispersed fraction.

SUBSTANCE: method involves continuously grinding suspension in two-rotor grinder; feeding suspension to grinder by means of pump from the bottom to the top; draining ground suspension from grinder through readily detachable filter via one channel by alternatively changing-over suspension flow for feeding into emptied mixer whose bottom valve is closed, and for consuming of suspension from filled mixer, whose bottom valve is opened. Remote and simultaneous changing-over of suspension flow and bottom valves is performed upon pressure drop occurred downstream of pump.

EFFECT: increased efficiency and safe grinding of solid particles.

1 dwg

Description

The invention relates to the field of grinding of organic and inorganic substances, which are solid particles. It can be used in many industries. For example, in the manufacture of mixed solid rocket fuel charges, an ultrafine fraction of an oxidizing agent or explosives with a particle size of 2 or less microns is used along with particles from 300 to 700 microns.

The ultrafine fraction of the oxidizing agent is obtained by grinding in bead mills in the presence, as grinding media, of glass beads (see patent RU No. 2247101 C2, IPC ⁷ C06B 21/00, B02C 17/16). Grinding methods using bead mills are widely used in the technological process for the manufacture of paints, pigments and are described in the book by P. I. Ermilov "Dispersion of pigments", Moscow, Chemistry, 1971

The most promising scheme for grinding solid particles in an apparatus similar to bead mills is proposed in UK patent No. 1374214, MKI V02C 17/16, adopted as a prototype. According to this patent, the grinding of solid particles is carried out by feeding the suspension vertically upwards into a cylindrical chamber with a rotating shaft with disks mounted in the center thereof and filled with balls. Suspension is circulated by a pump with supply from one tank and reception after the chopper into another tank. After emptying the first tank, the circulation is continued with the suspension being fed from the second tank and received after the chopper in the first tank. According to this scheme, work is continued until the required dispersion of the crushed material is obtained. To keep the balls in the grinder, nets are installed at the inlet and outlet of the suspension from it.

However, the scheme described in the above patent is not fully acceptable for use in the grinding of oxidizing agents and explosives for the following reasons. Suspensions of oxidizing agents and explosives have the ability to structure. In this state, they lose mobility without the application of mechanical stress. For this reason, in the circulation line in the stagnant zones when working according to the scheme described in the patent, it is possible to stop the movement of the suspension. In the prototype, such zones in the suspension circulation line are:

- the pipeline from the grinder to the valve in line to the tank from which the suspension is used, since this valve is closed during this period;

- the bottom of the tank filled with suspension, and the pipeline from it to the pump.

To resume the movement of the suspension in stagnant zones after switching to draining it from the grinder to an empty tank and spending it from a filled tank, it will be necessary to purge the line or apply vibrating actions, which is not safe when working with oxidizing agents and explosives sensitive to mechanical influences. The mesh in the upper area of the grinder is in suspension. In the case of clogging, which is not excluded, for its cleaning and replacement it is necessary to drain part of the suspension, partially disassemble the apparatus, which also poses a certain danger when working with oxidizing agents and explosives.

The technical task of this invention is to ensure safe conduct of the process, continuous circulation of the suspension and the intensification of grinding of the oxidizing agent and explosives. The technical result when grinding solid particles by circulating a suspension through a grinder filled with balls held by nets at the inlet and outlet of it, and alternating filling of the mixers with crushed particles is achieved by continuously grinding the suspension in a two-rotor grinder, while the suspension is supplied with a pump from bottom to top, and discharge from the grinder is carried out through an easily removable filter by means of one channel by alternately switching the suspension flow to the supply to the nny meshatel, bottom valve is closed, and flow of the slurry filled meshatelya, a bottom valve which is opened, is carried out at pressure levels fall after the pump with the remote and the simultaneous switching of slurry flow and bottom valves.

The description of the technological process of grinding the oxidizing agent and explosives shown in the drawing with the implementation of the proposed method is given below.

When the bottom bottom valve 3a is closed from the measuring device 2, the specified sample of a dispersion medium not dissolving the oxidizing agent or explosive is poured into the mixer 1a, then, when the mixer is working, a sample of the oxidizer or explosive is loaded through the hatch from the container 4. The ratio of the oxidizing agent and the dispersion medium is 1: 4, and for explosive the ratio is 1: 6. Turn on the peristaltic pump 5 for circulation of the suspension. Before turning on the pump, the bottom valve 3a is opened, and the flow switch 6 with the pneumatic cylinder 7 is set to the position of the suspension in the mixer 1b with the closing of the bottom valve 3b. In this case, the suspension from the mixer 1a by a peristaltic pump 5 is continuously pumped through a filter 9 (a grill with round holes) into a two-rotor grinder 8 filled with glass balls. When the rotors with the disks are turned on, the glass balls are in constant motion. The solid particles of an oxidizing agent or explosive, passing through the space between the balls, are subjected to friction and impact, and they are crushed. The suspension with crushed particles through an easily removable cartridge slit filter 10 is continuously poured into the mixer 1b. When the pressure level drops after the pump, which indicates the complete transfer of the suspension from the mixer 1a to the mixer 1b, remote and simultaneous switching of the flow of the suspension and bottom valves is carried out. For this, the valve 3a under the mixer 1a is closed, and open under the mixer 1b, and the flow switch 6 sends the suspension after the grinder 8 into the freed mixer 1a. Thus, the circulation of the suspension is continued until the desired particle size is obtained. The suspension obtained is transferred by a peristaltic pump to the operation of removing the dispersion medium, i.e., drying.

In the claimed invention, a two-rotor grinder is used as a grinding apparatus. It was established by experimental work that when using a two-rotor grinder, the desired particle size is achieved from 1.5 to 2.0 times faster with the same working volume than when using a single-rotor apparatus. In a two-rotor grinder, the disks of one rotor are located in the gap between the disks of the other rotor.

Structured suspensions characteristic of oxidizing agents and explosives lose their mobility due to the developed cohesion between particles, which leads to an increase in the viscosity of the system. Only when shear forces are applied to structured systems do they acquire mobility. In this regard, mixers are installed in containers for receiving and spending slurry in the circulation line, that is, mixers are used.

In the prototype, the suspension from the grinder is poured into each of the two tanks through an independent pipeline with a valve. When working according to this scheme, the valve in the pipeline to the container from which the suspension is spent is closed, that is, the remaining suspension in the pipeline in the section up to the valve is without movement, that is, it is in the stagnant zone. In this regard, it is not guaranteed that the discharge of the suspension into this container is restored upon subsequent opening of the valve.

- образной формы. При этом конец сливного трубопровода соединяют гибкой насадкой, которую, в свою очередь, сообщают со штоком пневмоцилиндра. По датчику давления, установленному после насоса, и оповещающему при снижении давления о конце перекачки всей массы суспензии из мешателя прием суспензии переключают в этот мешатель с закрытием донного клапана под этим мешателем. Для этого при помощи пневмоцилиндра гибкую насадку переводят на прием суспензии в опорожненный мешатель. Расходование суспензии продолжают из другого мешателя, для чего одновременно с закрытием донного клапана под опорожненным мешателем проводят открывание донного клапана под другим заполненным суспензией мешателем. Вышеуказанные операции по переключению потока суспензии и донных клапанов проводят дистанционно и одновременно для обеспечения непрерывной циркуляции суспензии до получения заданного размера твердых частиц.This disadvantage is eliminated if the suspension is drained through one channel. In this case, the suspension is in constant motion without the formation of a stagnant zone. Switching the flow of the suspension to its supply from one mixer to another and vice versa can be done using a simple device through pipelines

- shaped. In this case, the end of the drain pipe is connected by a flexible nozzle, which, in turn, is communicated with the rod of the pneumatic cylinder. According to the pressure sensor installed after the pump, and notifying when the pressure decreases about the end of pumping the entire mass of the suspension from the mixer, the reception of the suspension is switched to this mixer with the bottom valve closing under this mixer. To do this, with the help of a pneumatic cylinder, the flexible nozzle is transferred to the reception of the suspension in an empty mixer. The consumption of the suspension is continued from another mixer, for which, simultaneously with the closing of the bottom valve under the empty mixer, the bottom valve is opened under another mixer filled with suspension. The above operations for switching the flow of the suspension and bottom valves are carried out remotely and at the same time to ensure continuous circulation of the suspension to obtain a given size of solid particles.

The presence of the bottom valve in its closed position prevents the suspension from entering the pipeline under the valve with structure formation, excluding clogging when the circulation resumes. An easily removable slotted cartridge filter is installed to the grinder pipe in the suspension discharge line in the internal cavity of the grinder. This option allows the filter to be replaced and cleaned if it is clogged without disassembling the grinder.

The grinding method with signs that differ from the prototype was tested with positive results at the experimental chemical plant FSUE NIIPM.

Claims (1)

A method of grinding solid particles, including pump circulation of a suspension through a grinder filled with balls held by nets at the inlet and outlet of it, and alternately filling the mixers with crushed particles of the suspension, characterized in that the grinding of the suspension is carried out continuously in a two-rotor grinder, while feeding the suspension into it provide the pump from the bottom up, and the discharge from the grinder is carried out through an easily removable filter through a single channel by alternately switching the flow of the suspension the flow to the emptied mixer, the bottom valve of which is closed, and to the flow of the suspension from the filled mixer, the bottom clan of which is opened, while remote and simultaneous switching of the flow of the suspension and bottom valves is carried out when the pressure level after the pump drops.