RU2433100C2 - Method of making ceramic articles - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of producing ceramic articles. The method of producing ceramic articles involves grinding dried raw material followed by semidry moulding without firing. During the process of grinding the raw material to fine fractions, moulding powder is removed from the grinding equipment using an air stream and then deposited from this stream. The obtained moulding powder is used while loose for semidry moulding by replacing air therein with steam.

EFFECT: high efficiency and cost effectiveness of the equipment, simple and improved operation of said equipment and high frost resistance of the articles.

2 cl, 1 dwg

Description

The invention relates to the production of ceramic products, both rough wall ceramics, including building bricks, and fine ceramics.

The production of ceramic products consists of the operations of manufacturing unfired products - raw and its subsequent firing. In the production of raw materials, two main methods are used - plastic molding and semi-dry compression pressing. In the production of building bricks, plastic molding is the most common, occupying about 95% of all production volumes. Semi-dry pressing accounts for about 5% of production volumes (1, p. 2), despite the fact that the equipment is simpler, and the labor input and production costs are lower (2, p. 349).

There are two main reasons. Plastic molding from high quality clay raw materials allows to obtain products more efficient: with higher thermal insulation properties, facilitated by voids, having large dimensions, as well as more frost-resistant. However, for plastic molding, the reserves of high-quality raw materials are increasingly depleted, and this forces either to complicate the processing of raw materials, or to switch to semi-dry pressing, eliminating its disadvantages.

One of these complications was the processing of raw materials by slip technology, in which the clay was stirred with water until it was separated into primary mineral particles and until a fluid mass was obtained. Then, the moisture content of this mass was reduced by extraction on filter presses with subsequent drying of the cakes obtained during the extraction, or in one operation — by drying small drops of slip when they settled in tower spray dryers. The press powder was either dried in semi-dry pressing (as in the Obolsky brick factory in Belarus), or again wetted for plastic molding (as in the Gusinsky factory of drainage pipes in the Smolensk region). Due to the high energy intensity, this method of averaging and purification of raw materials for rough ceramics is not widespread. For fine ceramics, it is still used today.

The prototype of the claimed method is a known semi-dry pressing. Semi-dry pressing bricks now often do not withstand the minimum required by the norms of 15 cycles of freezing and thawing and are suitable only for internal wall structures or internal parts of external walls. There are two main reasons for decreasing the frost resistance of semi-dry pressed bricks: cracking due to pressing in raw air and insufficient averaging of the composition of the fresh powder, mineralogical and physical heterogeneity of its granules.

To increase the frost resistance of semi-pressed pressing bricks, through technological voids are used to facilitate the exit of air from the pressed raw material, optimization of the particle size distribution of the fresh powder for the same purpose, as well as soft drying of the raw material before firing, in order to weaken the formation of cracks due to the heterogeneity of the fresh powder and excessive mechanical stresses arising at a finish combined with firing (2, p. 367-386, 402-409). For special ceramics, vacuum powder is also used in the pressing process, however, for the production of wall materials this technique is too complicated (2, p. 384).

In addition, with the known methods of grinding dried raw materials, the productivity of grinding equipment and the energy consumption for grinding are overestimated due to the ever-increasing share of small fractions that uselessly absorb energy and prevent grinding of large fractions.

The aim of the invention is to increase the productivity and efficiency of equipment, its simplification and improvement of work, as well as improving product quality, expanding the raw material base and the scope of the proposed method.

This goal is achieved by the fact that air is removed from the pre-powder before pressing, replacing, replacing with water or other steam at a final temperature of steam and powder, which ensures balancing the pressure of the pressure of the surrounding atmosphere, which prevents the secondary penetration of air into the pre-powder (for water vapor it is + 100 ° C at normal atmospheric pressure 765 mm Hg).

In this case, the replacement of air by steam should not be confused with the known operations of processing raw materials with steam and with vacuum during plastic molding, in which the steam condenses and the air either remains or is forced out of the voids between the particles of the raw material that are closed as a result of steam condensation or pressing (see 3 and 4).

Replacing air with steam not only eliminates the pressing of air, eliminating the main reason for reducing the frost resistance of semi-dry pressing bricks, but also allows for an acceleration of the pressing process, up to impact pressing, and this allows to significantly simplify the pressing equipment, up to the use of simple pile drivers, piling machines, pneumatic hammers etc. The wear resistance of compression molds can also be increased, since during shock pressing due to inertia forces of the powder, proppants exerted by the powder onto the mold walls are reduced. Due to this, the uniformity in height of the compacts (raw) is simultaneously increased. The steam condenses during the pressing process, moistening the surfaces of the pressed particles, thereby improving their adhesion and without creating high pressure, which is dangerous for the integrity of the raw material. At the same time, the humidity optimal for pressing will decrease, the raw material will turn out to be hot inside, which contributes to its natural drying and will allow combining the final drying of the raw material with firing without compromising the quality of the finished product, and obtaining raw material of a higher quality will simplify and improve its firing.

Air can be replaced by steam, either by directly blowing the powder off with steam from top to bottom, or by filling the powder with steam after removing air from it by vacuum, i.e. using known methods of replacing air with steam (gravitational and forevacuum - see 5). Since the volume of air not exceeding the volume of indelible voids (porosity) of the shard is harmless, the degree of evacuation and pressure reduction relative to the normal atmosphere is usual for ceramic production - 90-98% (680-750 mm Hg).

The exclusion of air pressing allows you to significantly simplify the processing of raw materials and improve its quality, since the grinding of raw materials can be done up to the primary particles of raw materials, as in the slip method. At the same time, during the grinding process, small fractions are removed from the grinding equipment by an air stream, which eliminates energy losses and weakening the forces of grinding media on large fractions, increasing productivity and efficiency of grinding equipment, and also allows to achieve averaging and cleaning of raw materials similar to averaging and cleaning during slip method, providing a significant increase in product quality. Additional possibilities appear: selection of the smallest fractions during the grinding process (i.e., regulation of the fineness of grinding) and separation of fractions when they are separated from the air stream. Pneumatic transportation allows you to abandon belt conveyors and bucket elevators, and this greatly simplifies the equipment and reduces or eliminates the dustiness of the premises. To eliminate the entrainment of fine fractions and dusting the environment, air in the powder extraction system from the grinding equipment should be used according to the circulation scheme, without emission to the atmosphere.

The fine fractions removed by the air stream are precipitated from this stream and used directly for semi-dry pressing, and pre-moistened for plastic molding. Large fractions, if these are harmful rocky inclusions, are either sieved on sieves or crushed to obtain particles of safe size.

An example of the method. The attached drawing shows a block diagram of a brick factory that implements the claimed method in the version with full mantle of large fractions and stony inclusions. The diagram shows an indoor (“warm”) clay storage 1 equipped with a crane beam with a clamshell bucket, a drawer feeder with ribbed (stone extraction) rollers 2 installed under it, a drying drum 3, a rod mixer 4, a powder storage hopper 5, vacuum -gateway 6, hot storage hopper 7 and press 8, which make up the main path of processing raw materials into raw materials. To select the crushed powder from the mixer 4 and transport it to the hopper 5, pipe 9 and pipes 10 and 11 are used, in which air circulates under the influence of a suction blower 12. Also shown is a raw machine-stacker 13, two crane beams on common supports 14, a furnace with a removable vault 15 and an exhibition area 16.

Work on the scheme. The delivery of raw materials from the quarry to alumina 1 is provided by road. The grab bucket, dropping onto the clay cone of the storage tank 1, grabs a portion of the raw material and transfers it to the batcher with rollers 2, from where the lumpy raw materials are fed into the drying drum 3 by a conveyor belt 17, where they are dried, then they are conveyed by a conveyor belt 18 to a core mixer 4, where they are crushed to as long as the crushed particles are not picked up by the flow of air pumped into the mixer and sucked from the mixer by the suction-blower 12 through pipelines 9-11. The fine fractions taken away from the mixer 4 enter the hopper 5, where, as a result of the deceleration of the air flow due to the larger cross-section of the hopper than the cross-sections of the pipelines 9 and 10, the fine fractions settle. It is also possible to use a cyclone. Portions of powder are filled from hopper 5 into gateway 6. After filling each portion, the gateway is sealed, air is pumped out from it by a vacuum pump 19, then the vacuum is turned off and superheated steam is supplied from the steam generator 20. The steam should have a pressure slightly higher than the pressure of the surrounding atmosphere ( to prevent air from entering the steam path) and be slightly overheated (to avoid condensation, to compensate for heat loss). After filling the airlock 6 with steam, it is opened from below and the powder is poured under its own weight into a hot storage hopper 7 (constantly heated externally under thermal insulation with steam from the steam generator 20), from where it is poured into the hopper of the press 7. As necessary 8 also constantly add steam from the generator 20.

Of the equipment currently manufactured, you can use crane beams, clamshell grips for firing bags, a batcher (for example, СМ260, a drying drum (for example, СМ-45А) with a chain curtain, a torch and a countercurrent, a rod mixer (for example, СК20), retrofitted with pipelines , as well as any press for semi-dry pressing of clay or fireclay bricks (СМ1085, СМ301, etc.). The press is equipped with a warmed bell that is closed from above and not sealed from below (steam is lighter than air), separating the pressing zone from the surrounding atmosphere Thera. advisability of developing and using percussion press. The equipment used after the press goes beyond the claimed method is not described.

The above shows that the proposed method can be fully used in plastic molding, including the production of fine ceramics, allowing you to replace the energy-intensive slip method. Its simplicity, efficiency and the ability to control the quality of raw materials can significantly expand the raw material base, which is especially important for the modernization of old plants that have developed nearby reserves of high-quality raw materials. Complex processing of deposits is also possible, for example, into clay and gravel, for fine and rough ceramics, etc.

Literature

1. The production of ceramic wall products by semi-dry pressing. M, VNIIESM, 1990

2. Kondratenko V.A. Ceramic wall materials. M .: Composite, 2005

3.SU 655687

4. SU1813647

5.http: // vinar / publikation / test /

Claims (2)

1. A method of manufacturing ceramic products containing the operation of grinding dried raw materials, semi-dry pressing and firing, characterized in that during the grinding of raw materials, fine fractions of the powder powder are removed from the grinding equipment by an air stream, then they are precipitated from this stream and the obtained powder powder is used in bulk for semi-dry pressing, replacing the air in it with steam. 2. The method according to claim 1, characterized in that the air before the semi-dry pressing in the powder is replaced by steam by blowing the powder with steam or after evacuation of the powder.

Images