SU1027922A1 - Heat insulating mixture - Google Patents

Abstract

HEAT-INSULATING MIXTURE for steel casting, including hydrolytic lignin, ash and carbonaceous substance, characterized in that, in order to increase the quality of ingots by increasing the heat-insulating properties of the mixture, as a carbonaceous substance, the mixture contains carbon black in the following ratio of ingredients, wt. %: Hydrolytic lignin-30 Soot10-30 Ash. The rest (L

Description

1 The invention relates to ferrous metallurgy, specifically to the compositions of slag-forming mixtures used in steel casting, and methods for their preparation. The known heat-insulating mixture for steel casting, containing calcium fluoride, graphite, coal ash, and domain slag 1. Such a mixture in contact with the liquid metal quickly melts the presence of 8-13% calcium fluoride and a small (1-6%) amount of graphite which results to reduce its insulating properties. Heat-insulating and slag-forming mixtures containing powdered aluminum, graphite, wood flour, and refractory storages 2 are also known. The disadvantage of these mixtures is the use of components that pollute the environment (alkalis, fluorides), and also scarce and expensive aluminum and graphite. It is also known to use a briquette to protect the molds and the metal mirror of the hydrolytic lignin Gz J. However, due to the fact that combustible material-lignin is used together with other combustible organic substances 1 1I, the residue after burning on the metal mirror is unsuitable for thermal insulation of metal . Known slag-forming mixture for steel casting, containing 7585% ash and up to 5% soda, graphite - the rest is AJ, But in the known mixture, thermal insulation of liquid metal mirrors is not sufficiently effective due to the relatively high density of the ash-graphite mixture and heat loss of the metal to heat mixes. The absence of a stable reducing atmosphere and heat and heat through the bare metal parts in the tiller causes a thickening of the shlak which leads to a decrease in the surface quality of the steel ingot. The heat-insulating mixture for casting steel, including lignin, ash and carbonaceous substance 5, is closest to the invention in terms of its technical essence and effect. However, this mixture does not provide sufficiently high thermal insulation of the metal mirror. 222 The aim of the invention is to improve the quality of ingots by increasing the heat-insulating properties of the j mixture. To achieve this goal, the heat-insulating mixture for casting steel, including hydrolyzed lignin, ash and carbonaceous matter, contains carbon black as the carbonaceous substance in the following ratio of ingredients, wt.%: Hydrolyzed lignin5-30 Soot 10-30 Ash The remaining soot is an incomplete solid fine product combustion or thermal decomposition of organic matter containing more than 98% carbon. Low bulk density (0.06 + 0.28 t / m), small particle diameter (0.01 + 0.35 microns), large geometric specific surface (100-300) determine its high heat-insulating and protective lubricating properties compared to graphite. properties. Hydrolyzed lignin is a waste product from wood processing, yeast hydrolysis, starch and other industries. High exothermicity (3-4 thousand kcal / kg), low ignition temperatures (350-400 s) contribute to the rapid heating and melting of the mixture, and the release of gaseous products of the lignin combustion reaction makes it loosening and, accordingly, improves the heat insulating properties. When burning in a reducing atmosphere, lignin releases carbon black, which serves as an additional lubricant between the wall of the mold and the surface of the ingot. Lignin is cheap; when preparing for use, it does not require grinding, its use will reduce environmental pollution by waste. Selection of the above ratios of ingredients included in the heat insulating mixture reduces the ingestion of the mixture layer on the metal mirror, by using soot and loosening when releasing gaseous products of lignin combustion, accelerates slag formation by emitting heat when burning lignin, ensures casting of steel in a reducing atmosphere, reduce friction between the mold and the ingot surface due to the use of a fine carbonaceous product — soot and release of soot carbon The burning of lignin under conditions of lack of acid. The optimal composition of the slag-forming mixture is as follows,%: ash 65, lignin 15, soot 20. Soot content below 10% is unacceptable because of the need to protect the ash from melting, there is a danger of 30% soot The carbonization of metal of low carbon grades has become. The limits of hydrolytic lignin content were determined based on the fact that when its content is less than 5%, the mixture is not sufficiently loosening and melting, the presence of lignin in the mixture above 30 causes, in a number of cases, the metal to boil around the walls of the mold, strongly choosing a flame from the mold. The ash content limits should provide a sufficiently thick layer of slag on the metal surface and protect this layer of slag from melting by adding no less than 10% of carbon black. Heat insulating mixtures are made by crushing the initial components to a particle size of less than .1 mm, then mixing and drying to less moisture. To protect the mixtures from moisture during transportation and packaging, they are packed in plastic or paper bags. Both p and p 1. When siphon casting of calm steel into a 7-ton mold, a heat-insulating mixture is placed at the bottom of the latter in paper bags of 13 kg of the following composition,%: ash 50, carbon black 30 and hydr. lignin 20. In the process of mold filling, this mixture is uniformly distributed over the ingot mirror. PRI mme pZ. In siphon steel, into a 15-ton mold of two gold bags of 14 kg of MIXTURE are suspended at a distance of 250 mm from the bottom of the mold. The composition of the mixture: 85% ash, 10% carbon black, 5% lignin. Example 3. When casting calm steel, 16 kg of heat-insulating mixture of the following composition are deposited on top of a 7-tonne curvature of heat insulating mixture,%: ash 62.5, carbon black 20, lignin 17.5. Thermal insulation mixtures offered. The composition was tested when casting calm steel. The burning rate of the mixtures on the ingot surface was 0.1-0.5 kg / min. The mixture on the metal mirror kept its dark color until the beginning of stripper ingots. The acceleration of slag formation on the metal surface is obtained, a decrease in the amount of dust generated from. molds in the process of casting, improving the quality of the surface of the ingots. The invention is illustrated by the compositions and properties of the mixtures, which are listed respectively in Table I-2. From the data table. 2 it follows that as a result of applying the proposed mixture. In comparison with the known amount of flake, the cracks and the captivity on the ingot are reduced by 3 times, Such; the ingot requires less stripping before rolling. The effect of using lignin in the proposed mixture as compared to the mixture in the prototype is that the lignin in the soot shell does not burn, but smolders, which increases the heat release time in the mixture and, accordingly, improves the thermal insulation of the metal mirror, and the volatiles released from the lignin in the process of its smoldering reduce the emission of dust and smoke, and the candle end burns after the combustion of the lignin and ash. the soot shell, which reduces their melting and, accordingly, eliminates the heat insulation of the metal mirror. The mixture according to the invention during tests during the casting of steel showed extremely high thermal insulation properties. For example, when the thickness of the mixture layer on. 140 mm metal mirror for 40 minutes from the end of the casting, the surface temperature of the mixture was 50 ° C, while its lower surface was in contact with the liquid metal. The thermal conductivity of the mixture according to the invention is 0.05 W / m.trade, and the prototype is 1.18-1.27 W / mtrad. For comparison, K. perlite-graphite mixture is 0.23-0.32, ash graphite 0 , 52-0.57 W / mrad. The heat capacity of the mixture is determined by the heat capacity of its components and the composition

S10279226

ls 0.1-0.2 kcal / kg C, depending on the mixtures on the metallurgical chavoot of a specific composition, dah is a gol.ks account

The economic effect of the use of more-cheap machines from the proposed insulation of 0.35 rubles / ton.

The composition of the heat-insulating mixtures, wt.% Ingredient ll№2№3№4

40 30 30

50 20 30

62.5 20

17.5

T a b .11 and c a 1

8085

80

1010

105

18 2 №5№6IN-

table 2

Claims (1)

THERMAL INSULATING MIXTURE for steel casting, including hydrolysis lignin, ashes and carbonaceous matter, characterized in that, in order to improve the quality of ingots by improving the heat-insulating properties of the mixture, the mixture contains carbon black as a carbonaceous substance in the following ratio of ingredients, wt. %: Hydrolytic lignin ^ -30 Soot 10-30 Ash rest <e SU .. „1027922 '1027922