SU1190420A1 - Method of manufacturing blanks of resistive elements from electroconducting concrete - Google Patents

Abstract

METHOD FOR PRODUCING PREPARATIONS resistive element of electrically conductive CONCRETE comprising forming, hydrothermal treatment and drying workpieces, on t l and h ayuschiys in that, in order to increase the reliability in operation, after the preform drying operation poured powder heat-treated carbonaceous material such as anthracite and performing em heat the workpieces at 350-600 C for 1-40 hours i

Description

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1C 1 The invention relates to electrical engineering, in particular, to methods for manufacturing composite resistors based on mineral substances, such as cement, liquid glass, etc. The purpose of the invention is to increase the reliability of resistors by increasing the specific energy dissipation, block voltage and stability of electrical characteristics . The thickness of the backfill must be at least 15 mm to ensure the prevention of free access of air and a sufficient amount of carbon dioxide. The increase in specific energy dissipation, voltage overlap and stability of electrical resistance is achieved due to the fact that at 350-600 ° C there is an irreversible removal of water released during the decomposition of cement stone compounds. The filling of products with powder from anthracite and the exclusion of free access of air to them prevents the burning of the conductive phase and the occurrence of oxidative processes characteristic of a given temperature. At the same time, the hot anthracite and free carbon dioxide that forms with it promotes the transition of unstable compounds of the products of the dehydration of the cement stone into new, stable, insoluble in water. The physicotechnical processes occurring in electrically conductive concrete during its heat treatment in carbon bed are as follows. When the furnace is heated, in which there are billets of resistive elements filled with anthrax powder, the temperature of the product substantially deviates from the temperature of the furnace and zasska. In the initial period of heating, the air that leaves the container, as in the latter, an overpressure is created, is partially emitted from the deli and lambing. Upon further heating, the powder reaches a temperature at which CO and CO gases evolve while the product is still at a lower temperature. 02 The CO and C02 gases formed in the powder penetrate through the pores of the preform into its central part due to the presence of a temperature gradient and thereby promote carbonization throughout the entire precursor resistive element volume. (OH) 2CaCO + KjO. The possibility of heat treatment at such a high temperature leads to the dehydration of some unstable compounds, ЗСаО-А120з-ЗСа504-3 Н20 and CaS04 0.5Н20 + CaS04-ZHjO -1-1,5 HgOT Freeing water contributes to the further hydration of unreacted cement particles. Thus, the following processes take place in the high-temperature treatment in powder from anthracite: removal of water from microcapillaries (physically bound water), gel and part of physico-chemically bound water, dehydration of sulfo-containing and hydroaluminate phases (complete dehydration CaO-Al Oj-3CaS04 -, completely dehydrates at 250400 C); Ca dehydration (should start at 350-500t. Ca (OH) iCaO + HjO-15.5 kcal CaO + C02CaOC3 or Ca (OK) +00 CaCOj + HjO; it is dehydrated from water and reacts with cement; carbonization of CaO + + CO CaCO f t-HjO (the presence of the carbonization process confirms the results of the thermo-weight analysis; the concentration of cement stone, which promotes the convergence of carbonaceous particles and the improvement of their contacts, which leads to a decrease in electrical resistance. The proposed method of manufacturing precursors of resistive elements was tested experimentally on samples made They are based on Portland cement and have an electrical resistivity of 50 and 175 Ohm-cm. The samples are manufactured in the following way. At first, the dry components of the mixture are mixed for 15 minutes in a mixer.

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water is then added and the mixture is stirred for another 5 minutes, after which blanks are molded from it by pressing with a force of 250 kgf / cm. The blanks are kept at room temperature for 20 hours, and then steamed at 98 ° C for 6 hours. After steaming, the blanks are placed in a special container, covered with a 20 mm baked anthracite with a particle size of 0.1-2.0 mm on all sides. and placed in an oven, where they are dried for 6 hours and then container

the ner is closed by the kryika and the temperature rises to At this temperature, the blanks are kept for 4 hours, after which they are cooled together with the furnace.

The test results of resistive elements made by the proposed and known methods are shown in the table.

The time of application of the electric load for blanks with 50 OC-cm is 0.04 s, and for blanks with 175 Ohm-cm 0.2 s.

The specific energy dissipated.

J / cm3 430

640,800

Change email resistance after 20 load impulses,%

The data in the table show that the proposed method of manufacture allows a significant increase in the characteristics of resistive elements, an increase in the dissipated energy by 20–30%, and an overlap voltage of 2–257. In addition, the stability of the electrical characteristics, which is expressed in During the high volt testing process, resistive elements made by a known method, after 20 load pulses, change the electrical resistance by 13-13 / 5%,

420

560

695

620

13.5 6.5

and samples made by the proposed method - only 5.7-6.55

Control measurements showed that the change in the electrical resistance of electrically conductive concrete in the central part of the product and on its surface as a result of heat treatment in the anthracite powder is the same.

The technical and economic effect of the proposed method lies in the fact that its use allows reducing the size of resistive

5 1190420ft

elements, which leads to savings in electrical service life of resistive element-conducting porcelain concrete, me-t.

tallish reinforcement and other on-the proposed method can recotoyalov, going to their manufacture, j is recommended not only for processing

about 12-30%. of the resistive elements.

In addition, it increases the reliability and, consequently, of the heating elements, for the processing of workpieces.

Claims (1)

METHOD FOR MANUFACTURING PREPARATIONS OF RESISTIVE ELEMENTS FROM ELECTRIC WIRED CONCRETE, including molding, hydrothermal treatment and drying of preforms, with the aim of increasing the reliability of the work, after the drying of the preform, the powder is coated with heat-treated carbon powder , for example anthracite, and carry out heat treatment of workpieces at 350-600 ° C for 1-40 hours