SU1115849A1 - Thermal insulating sand for bottom casting of steel - Google Patents

Abstract

HEAT-INSULATING MIXTURE FOR SIPHONIC STEEL CASTING, including graphite and expanded perlite, characterized in that, in order to improve the quality of the Danes ingot part by eliminating the mixture clodiness and entanglement of the mixture in the metal and reduce dusting, it additionally contains lignin in the following composition of the mixture in the metal and reduction of dusting, and additionally lignin in the following composition of the mixture in the metal and reduction of dusting, in addition to lignin in the following composition of the mixture in the metal and reduce dusting %: Graphite 20-45 Lignin5-30 Expanded perliteEverything W SP 00 4 CO

Description

The invention relates to the metallurgy of ferrous metals, in particular to steelmaking, and improves the compositions of heat insulating mixtures for casting steel. Thermal insulating mixtures used in siphon casting of quiescent steel are known, which provide an improvement in the quality of the surface of the ingots and an increase in the yield of a suitable metal during their rolling. In this case, the most widely used are two-component heat-insulating mixtures based on coal ash CHP or expanded perlite and carbon-containing material, most often graphite. A heat-insulating ash graphite mixture containing 7588% of coal ash from a CHP plant or a state district power station and 12-25% amorphous graphite 1 is known. Ash-based mixtures are also known, which, in addition to the carbon-containing material, contain 2-5% silicate lump 23. However, known mixtures do not contain provide the required quality of ingots. A heat-insulating mixture is also known, including ash, carbon black and hydrolyzed lignin ZD. However, this mixture does not ensure the production of high-quality castings, since it is more difficult; affects the cooling of the first portions of the metal entering the mold, and the decomposition of the lignin does not occur. A heat insulating mixture for producing briquettes is known, including ash, sawdust, liquid steel, lignin, and 4J refractory filler. However, this mixture could not be used for siphon casting of metal, since the lignin in it, improving its thermophysical properties, does not have the ability to decompose with the release of a large amount of volatile compounds, since there is also no instant contact of the mixture with the incoming liquid metal. Closest to the proposed technical essence and the achievable effect is a heat-insulating mixture for siphon steel casting, including graphite and expanded perlite f 5 J. The disadvantage of this mixture is its tendency to crumple, which during the initial casting of the ingot when the mixture contacts the incoming into the mold from below by a flowing stream of liquid metal leads to entanglement of the mixture in the metal and, under conditions of its accelerated hardening in the bottom (most narrow and massive) part of the mold, to the formation of defects structures at the bottom of the ingots. In addition, when casting steel under this mixture, the sanitary and hygienic conditions for workers in the pouring bay deteriorate due to increased dust extraction from the set. prostrate The aim of the invention is to improve the quality of the bottom part of the ingots by eliminating the clodability of the mixture and its entanglement in the metal, as well as reducing dust emission. This goal is achieved by the fact that the heat insulating mixture for siphon steel casting, including graphite and expanded perlite, additionally contains lignin in the following ratio, ingredients, May.%:. Graphite 20-45 Lignin 5-30 Expanded perlite Rest Elongated in the composition of the proposed insulating mixture, lignin is a natural polymer found in wood and other plant materials. Lignin is a yellow-brown amorphous substance, it is insoluble in water and organic solvents. In industry, lignin is produced as waste in the production of cellulose and the hydrolysis of plant materials. Thus, in samples of lignin obtained by hydrolysis of corn cobs (cob bases remaining after threshing grain), contains,% C 41-47, ash 23-25, volatile components 48-49, moisture 4.5-5 . In turn, zbla lignin contains,% :. Si02 75-76, 4.0-5.0, 3.2-3.3, CaO 1.6-1.7, MgO 2.4-2.5, S 2.8-2.9, P205 0 3-0.4. Bulk bulk

3

the mass of ligpium is 0.5 g / cm -. Lignin is a good combustible material, its calorific value is 30004000 kcal / kg.

The lignin mixes well with the expanded perlite, the lignin particles, like the particles of graphite, firmly adhere to the surface of the expanded perlite grains.

Entering the lignin into the composition of the heat-insulating mixture consisting of expanded pearlite and carbon-containing material eliminates its closeness, since at steel casting temperatures lignin decomposes with the release of a fairly significant amount of volatile compounds (up to 50% of its mass). This process contributes to the loosening of the mixture and eliminates the loss in volumes of the rapidly solidifying metal, which in turn reduces the number of macrostructure defects in the lower part of the ingots, which are classified as slag inclusions, nonmetallic inclusions, or a metal-crust.

Such an effect of lignin, introduced into the composition of the heat insulating mixture, based on expanded perlite, is a new, additional positive effect that is not achieved when using lignin in the composition of the heat insulating mixture based on coal ash. This is due to significant differences in the properties of the mixtures themselves. Mixtures based on coal ash are heavy because of the high bulk ash weight, which is ten times greater than the bulk bulk of the expanded perlite. In addition, due to the considerably thinning insulating properties of mixtures based on coal ash, their specific consumption (about 2 kg / ton of steel) is twice as high as the specific consumption of mixtures based on expanded perlite (about 1 kg / g of steel). Therefore, when the first portions of the metal entering the mold are in contact with a large mass of dense and heavy ash-based mixture, a noticeable increase in the metal occurs. Under these conditions at the time of testing

58494

When the ingot reaches the part, the decomposition of ignim with volatile release does not occur, the ash-based mixture is lumped, captured and fixed in volumes of the crystallized, hardened metal. The process of decomposition of the lignin based on the ash-based mixture, which promotes the dissolution of the mixture, develops only slightly during the casting period of the upper half of the ingot, when the ash-based mixture has enough time to warm up in its entire volume.

5 Increased dust release from the molds when casting steel under heat insulating mixtures based on expanded perlite is mainly caused by removal to the atmosphere

0 very light particles of expanded perlite. When lignin is introduced into such a mixture, its heavier particles, which are well mixed and retain on the strongly developed surface of the expanded perlite particles, prevent them from being captured by heated air flowing along the walls of the mold. In addition, hydrolyzed lignin always contains

0 in itself a certain amount of moisture (from 4-5% in airborne lignin to 20% or more in lignin stored in dumps under the open sky), due to which P11is a certain amount of moisture and relaxation of the expanded perlite particles. This combination of the properties of lignin, which is part of mixtures based on expanded perlite, provides

 a noticeable decrease in the level of dust from the splinters during casting became with these mixtures.

In bars produced using a known coal ash mixture, there is no reduction in the release of lignin when entering into their composition, since here the lightest particles are the lightest and they can precipitate more heavy ash particles. In addition, lignin is poorly mixed with coal ash particles that have a poorly developed smooth (melted) surface.

5 it is preferable to use amorphous graphite as the carbon-containing material in the proposed mixture, which best stabilizes the heat-insulating properties of BcnyjeHHoro perlite 51. Crystal graphite, fine ground coke, dust of anthracite coals and other materials can be used as a substitute for amorphous graphite. The ratio of the components of the mixture op. is determined by its purpose (ingot weight), as well as the characteristics of the expanded perlite used in the composition of the mixture. Thus, when casting ingots of small mass (up to 2-3 tons), which crystallize during a relatively short period of time, the mixture should contain a minimum (2022%) graphite content of other carbon-containing material, which provides stabilization of the heat insulating properties of the expanded pearlite. At the same time, to loosen such a mixture with an increased amount of expanded perlite and reduce the removal of its particles (their deposition), it is necessary to introduce lignin at the upper limit (28-30%). When casting large ingots (weighing up to 15–20 tons) that crystallize over a long period of time (several hours), the heat-melting mixture during this long period is at a temperature close to the steel crystallization temperature. For efficient operation of the mixture under such severe conditions, i.e. to preserve its high thermal insulation properties, during the long period of crystallization of large ingots, it should contain the maximum content of graphite or other carbon-containing material (at the level of 43-45%). Taking into account the reduced content of expanded perlite in such a mixture, the lignin content in it should be minimal (at the level of 5-7%). Between these extreme cases, depending on the weight of the ingots, intermediate mixtures are selected. Depending on the characteristics of the expanded-perlite heat insulating mixture used in the composition of the mixture, the following adjustments are made to its composition. When an expanded perlite with a bulk bulk (for example, a mass of 0.05–0.08 g / cm perlite from the Aragats deposit) is used for a heat insulating mixture of bulk (for example, a mass of 0.05–0.08 g / cm), the content of graphite in the mixture should be 2–3% higher % lower than the same mass of the mixture for casting ingots of the same mixture based on more uniformly expanded perlite (for example, perlite from the Transcarpathian field with a bulk bulk density of 0.150, 20 g / cm). The choice of extreme values for the content of graphite and lignin in the invented mixture is determined by the following. With a content of graphite less than -20%, the thermal insulation properties of the mixture deteriorate sharply due to its melting. With a graphite content of more than 45%, an uncontrolled process of non-carburizing metal develops strongly. When the content of lignin is less than 5%, its action from the point of view of eliminating the clodiness of the mixture is weak due to the very small amount of volatile compounds with such a small amount of lignin in the mixture. Conversely, when the content of lignin in the mixture is more than 30%, an excessively high release of volatile compounds is observed, leading to an increase in the number of surface defects on the sheets and to the deterioration of the working conditions of the spills. The proposed mixture is prepared by mechanically mixing the initial components. The packaged portions, corresponding to its consumption per ingot, the mixture in paper or plastic bags, are seated on the bottom of the mold or suspended from a distance of 150-200 mm from the bottom of the mold before the steel is cast. Mixture consumption is in pre-. They are 1.2–2.0 kg / ton of steel and are determined mainly by the mass and configuration of the ingots (ingots broadened upwards or downwards). Example. 1. When casting assorted ingots weighing 2.5 tons in uiirenny up molds with profitable extensions, a heat-insulating mixture of the following composition is used, wt.%: Graphite 20, lignin 30, expanded perlite 50. Mixture in an amount of 3.4 kg (specific consumption 1, 2 kg / ton of steel) in a paper bag is suspended in the mold until the steel casting begins. Example 2. In the casting of high-grade ingots weighing 7.0 tons, a heat-insulating mixture of the following composition, wt.%: Graphite 30, lignin .10, expanded perlite with a bulk bulk weight of 0.07 g / cm 60, are used to expand upward-extending molds with primitive extensions. A batch of 9 kg (specific consumption 1.3 kg / ton steel) in a paper bag is placed on the bottom of the mold before the steel is cast. Example 3. When casting ingots of a weight of 8.0 tons, heat-insulating mixture of the following composition, wt.%: Coal dust 27, lignin 13, expanded perlite with bulk volume of 0.16 g /, is used to heat down molds with insulating liners. cm 6 A mixture of 13 kg (specific consumption of 1.6 kg / t of steel) in a paper bag is placed on the bottom of the mold before the steel is cast. Example 4. When casting cast ingots weighing 17 tons, the heat-insulating mixture of the following composition, wt.%: Graphite 45, lignin 5, expanded perlite 50, is used for broadening up molds with profitable extensions. 34 kg of the mixture (specific consumption 2.0 kg / ton steel) in polyethylene bags is suspended in molds until the steel has begun. The invention is illustrated by the composition and properties of the mixtures, which are listed in Table. 1 and 2 respectively. Ingredients

Graphite

17 33 50 Lignin Expanded perlite

Table 1

30 10 60

45

47

50

3

five

50

50

50 Ingredients content, wt.%, In blend 1 (prototype) 98 Data on zashtenIsti air of the working area on the casting platform of the open-hearth shop at them. Petrovsky are given in table. 3. The best thermal insulation mixtures are mixtures 2-4, which provide the least damage to the workpieces by surface defects, U Including the workpieces obtained from the bottom parts of the ingots, as well as the minimum extent of shrinkage defects. The consumption of these mixtures is less than 1% to 10–15% than the mixture 6. The study of the filling above the mold shows that the dust emission during casting is 3 times less for the optimal mixture composition (composition 3) than for the ash-graphite mixture and 1 , 5 times less than for the mixture 6. The proposed heat-insulating mixture is an effective material for isolating steel during siphon casting, which allows to improve the quality of ingots and thereby increase the yield of rolled metal from them by 1-1.5%. The economic efficiency of the application of the proposed insulating mixture under the conditions of the Dnepropetrovsk Metallurgical Plant named after Petrovsky, when it replaces the used 3 slag-forming mixture, amounts to 0.27-0.45 p / t of steel, including 0.20-0.35 p / t ea due to an increase in the yield of rolled steel and ingots and 0.07-0 , 10 p / t due to a decrease in the mixture cost. With a possible volume of introduction of the proposed mixture in the casting of 1.2 million tons of calm steel, the annual economic effect is 320–540 thousand rubles.

table 2

Indicators The number of investigated rolls of ingots, pcs. Affection, billets by surface defects,% of the total number of blanks 12, Affection by surface defects of blanks obtained from the bottom part of the ingot, the ratio of the length of defects to the total length of the blanks,%

Run-up start values

% of the length of the roll from the top 10.6-10.8- 10.5 The average value of the beginning of the suitable metal,% of the length of the roll from the top

r IZIZl- J.iri 10 38

.10, .011, 5- 11,012, 0 13.0 13.0

12.0 12.0 12.5

11.4 11.4 11.5 1.1.8 12.0 11.7

Table 3 20 10 15 15 3,4 7.2 6.9 5.4 1.8 12 15 17 22

Claims (1)

THERMAL INSULATING MIXTURE FOR SIPHON CASTING OF STEEL, including graphite and expanded perlite, characterized in that, in order to improve the quality of the bottom of the ingots by eliminating the clumping of the mixture and entangling the mixture in the metal and reducing dust formation, it additionally contains lignin in the following ratio of ingredients, ma.e.Z : Graphite _h 20-45 Lignin 5-30 Expanded Perlite Else SU "„ 1115849