RU2843795C1 - Slag-forming mixture for heat insulation and protection of metal surface in intermediate ladle from secondary oxidation during continuous steel casting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy. Slag-forming mixture for heat insulation and protection of metal surface in intermediate ladle from secondary oxidation during continuous steel casting contains, wt. %: 0.1-5 marble, 17.5-21.5 graphite, 0.1-5 feldspar, 1-4 soda and up to 100 flue ash. Introduction of flue ash provides higher heat-insulating capacity of mixture, as well as density and strength of granules of mixture. Marble increases slag assimilating capacity and promotes stability of casting without slag foaming. Soda reduces melting temperature and viscosity of slag. Feldspar dissolves oxides on metal surface and covers the surface, thus preventing oxidation. Graphite is added to control the rate of melting of the mixture and formation of a reducing atmosphere.

EFFECT: high heat-insulating capacity of the mixture.

1 cl, 1 tbl, 3 ex

Description

The proposed invention relates to ferrous metallurgy, namely to compositions of heat-insulating slag-forming mixtures for use in an intermediate ladle during continuous casting of steel.

A slag-forming mixture is known for protecting steel in an intermediate ladle, containing Portland cement and a material based on silicon oxides, which additionally contains technical soda ash and rice husks in the following ratio of components, wt.%: Portland cement 40-50, material based on silicon oxides 30-38, technical soda ash 10-18, rice husks 4-10 (RU Patent No. 2574903, B22D 11/111, published 10.02.2016 Bulletin No. 4).

The disadvantages of the known mixture are its low thermal insulation properties.

The technical result of the proposed invention consists in increasing the heat-insulating capacity of the mixture.

The specified technical result is achieved by a slag-forming mixture for thermal insulation and protection of the metal surface in the intermediate ladle from secondary oxidation during continuous casting of steel containing soda, according to the invention, the mixture additionally contains fly ash, marble, graphite and feldspar in the following ratio of components, wt. %:

Marble 0.1-5 Graphite 17.5-21.5 Feldspar 0.1-5 Soda 1-4 Fly ash up to 100

Fly ash is used (TU 38.21.40-001-00105638-2022) to improve the technological properties, namely the density and strength of the mixture granules; fly ash increases the heat-insulating capacity of the mixture.

Marble (TU 5716-001-99242323) is a source of calcium oxide, which increases the assimilating capacity of slag and binds dissolved aluminates in the liquid steel melt, thereby ensuring a stable casting process without slag foaming and mixing it with the slag.

Graphite (GOST 527229-2007) is added to regulate the melting rate of the slag. Free carbon, located between solid particles and melt droplets, creates a kind of inert barrier. Carbon is not wetted by molten slag, so liquid slag globules cannot agglomerate until the carbon particle is oxidized. In addition, carbon forms a reducing atmosphere (CO) during combustion.

Soda (GOST 5110-85 – premium grade, GOST 10689-75 – 1,2,3 grade) reduces the melting point, and simultaneously with fluorspar reduces viscosity. In slag, it is capable of forming strong compounds with Al ₂ O ₃ and SiO ₂ .

Feldspar is introduced as a flux to facilitate the separation of metal from gangue. It dissolves oxides already present on the metal surface and acts as an oxygen barrier, coating the hot surface, preventing oxidation.

The range of cast steel includes all grades of steel, excluding ultra-low carbon steel.

In the process of continuous steel casting, the mixture performs the following main functions:

- isolates liquid metal from air, preventing its oxidation;

- assimilates non-metallic inclusions that float in liquid metal;

- thermally insulates the metal surface in the tundish and protects it from excessive cooling.

The mixture has the following chemical composition, wt. %:

With _common 17.0-21.0 _{Al2O3 ​} 17.0-23.0 MgO≤2 MgO≤2 _Na2O + _K2O≤4 O≤4 Fe _total ≤5 CaO≤10 CaO≤10 _SiO2 42.0-50.0

The preparation of the slag-forming mixture Thermoisolit ASM-2 for thermal insulation and protection of the metal mirror in the intermediate ladle from secondary oxidation during continuous casting of steel is carried out in two stages: preparation of the suspension in wet grinding mills (WGM) and drying of the suspension, and obtaining granules in a tower spray dryer (TSD).

Before preparing the suspension in the MMP, water in the required amount is poured through measuring tanks according to the batching. The prepared batch materials: marble 0.1-5 wt. %, graphite 17.5-21.5 wt. %, feldspar 0.1-5 wt. %, soda 1-4 wt. % and fly ash up to 100 wt. % are loaded into the MMP, where the materials are ground and mixed at the same time. Ceramic cylindrical bodies are used as grinding media. After combined grinding and mixing of all materials, the finished suspension is poured from the MMP by gravity into the receiving mixers, in which it is constantly mixed to prevent sedimentation and stratification. Then, samples of the suspension are taken from the receiving mixers to determine the density, which should be within 1.70-1.90 g / cm³ and chemical composition, the dried sample of the suspension is sent to the LAC KKC. After obtaining satisfactory results, the suspension from the receiving mixer is pumped using a slip pump into the feed mixer to create a reserve before the high-pressure pump and the quick-release mixer.

The production of granules of the GShOS is carried out in the BRS. The suspension is fed into the BRS by a plunger pump under pressure through a device in the form of a ring with nozzles. Spraying of the suspension and formation of granules is carried out in counter-current to the heat supplied to the BRS by injection-type burners. The tower spray dryer is heated by a mixture of natural gas and air.

The temperature in the working space of the spray dryer is 360-480°C. The dried granulated mixture should have a moisture content of no more than 0.5%. From the BRS, the mixture enters the cooler, where it is cooled and, using a belt elevator, is fed to the storage bin and packed into valve bags weighing about 10 kg, or into Big Bag type MKRs with an insert of no more than 1.0 ton.

To assess the quality of the mixture, a sample of the granulated mixture weighing about 0.3-0.5 kg is taken from the container and sent to the laboratory of physical and mechanical tests of the UShOS to determine the moisture content and granulometric composition, and to the LAC (CLC) of the KKC of PJSC MMK to determine the chemical composition according to the analytical control scheme approved by the head of the STC of PJSC MMK. If necessary, a sample of the GSHS is transferred to the FSBEI HE MSTU named after G.I. Nosov to determine the melting point.

The physical properties of the mixture are presented in Table 1.

Table 1. Physical properties

Parameter ASM-2 Form granules Bulk density, g/cm3 ±deviation 0.65 ±0.15 Melting point, ºС ±deviation 1300 ±30 Granulometric composition, %: Residue on sieve 1.0 mm Residue on sieve 0.2mm ≥ 65 Residue on sieve 0.063mm ≤ 25 Passing through sieve 0.063mm ≤ 10

Example 1.

In the MMP, water in the required quantity was poured through measuring tanks according to the batching. The prepared batch materials (0.1 wt. % marble, 17.5 wt. % graphite, 0.1 wt. % feldspar, 1 wt. % soda and 81.3 wt. % fly ash) were loaded into the MMP, where the materials were crushed with simultaneous mixing. Ceramic cylindrical bodies were used as grinding bodies. After combined grinding and mixing of all materials into a ready suspension, the MMP was drained by gravity into the receiving mixers, in which it was constantly mixed to prevent sedimentation and stratification. Then, samples of the suspension were taken from the receiving mixers to determine the density, which was 1.79 g / cm³.

Chemical composition of the dried suspension sample:

With _common 17.8 _{Al2O3 ​} 22.4 MgO 1.7 _Na2O + _K2O 2.9 Fe _total 1.6 CaO 4.2 _SiO2 49.4

After this, the suspension was pumped from the receiving mixer using a slip pump into the feed mixer to create a reserve before the high-pressure pump and the quick-release mixer.

The production of granules of the GShOS was carried out in the BRS. The suspension was fed into the BRS by a plunger pump under pressure through a device in the form of a ring with nozzles. Spraying of the suspension and formation of granules was carried out in counter-current to the heat supplied to the BRS by injection-type burners.

The temperature in the working space of the spray dryer was 460°C. The dried granulated mixture had a moisture content of 0.12%. From the BRS, the mixture entered the cooler, where it was cooled and, using a belt elevator, it was fed into a storage bin and packaged.

Example 2.

In the MMP, water in the required quantity was poured through measuring tanks according to the batching. The prepared batch materials (marble 5 wt. %, graphite 21.5 wt. %, feldspar 5 wt. %, soda 4 wt. % and fly ash 64.5 wt. %) were loaded into the MMP, where the materials were crushed with simultaneous mixing. Ceramic cylindrical bodies were used as grinding bodies. After combined grinding and mixing of all materials into a ready suspension, the MMP was drained by gravity into the receiving mixers, in which it was constantly mixed to prevent sedimentation and stratification. Then, samples of the suspension were taken from the receiving mixers to determine the density, which was 1.82 g / cm³.

Chemical composition of the dried suspension sample:

With _common 20.6 _{Al2O3 ​} 17.6 MgO 1.7 _Na2O + _K2O 3.5 Fe _total 4.6 CaO 9.7 _SiO2 42.3

After this, the suspension was pumped from the receiving mixer using a slip pump into the feed mixer to create a reserve before the high-pressure pump and the quick-release mixer.

The production of granules of the GShOS was carried out in the BRS. The suspension was fed into the BRS by a plunger pump under pressure through a device in the form of a ring with nozzles. Spraying of the suspension and formation of granules was carried out in counter-current to the heat supplied to the BRS by injection-type burners.

The temperature in the working space of the spray dryer was 360°C. The dried granulated mixture had a moisture content of 0.5%. From the BRS, the mixture entered the cooler, where it cooled and was fed into the storage bin using a belt elevator and packaged.

Example 3.

In the MMP, water in the required quantity was poured through measuring tanks according to the batching. The prepared batch materials (marble 4 wt. %, graphite 20 wt. %, feldspar 4 wt. %, soda 2 wt. % and fly ash 70 wt. %) were loaded into the MMP, where the materials were crushed with simultaneous mixing. Ceramic cylindrical bodies were used as grinding bodies. After combined grinding and mixing of all materials into a ready suspension, the MMP was drained by gravity into the receiving mixers, in which it was constantly mixed to prevent sedimentation and stratification. Then, samples of the suspension were taken from the receiving mixers to determine the density, which was 1.81 g / cm³.

Chemical composition of the dried suspension sample:

With _common 18.8 _{Al2O3 ​} 20.0 MgO 1.7 _Na2O + _K2O 3.4 Fe _total 4.1 CaO 6.1 _SiO2 45.9

After this, the suspension was pumped from the receiving mixer using a slip pump into the feed mixer to create a reserve before the high-pressure pump and the quick-release mixer.

The production of granules of the GShOS was carried out in the BRS. The suspension was fed into the BRS by a plunger pump under pressure through a device in the form of a ring with nozzles. Spraying of the suspension and formation of granules was carried out in counter-current to the heat supplied to the BRS by injection-type burners.

The temperature in the working space of the spray dryer was 480°C. The dried granulated mixture had a moisture content of 0.09%. From the BRS, the mixture entered the cooler, where it was cooled and, using a belt elevator, it was fed into a storage bin and packaged.

Thermoisolit ASM-2 mixture was used in the Electric Steelmaking Shop of PJSC MMK for casting the entire range of steel grades on continuous casting machines (CCMs) and slab casters.

The proposed mixture ensures the stability of the steel carburization process during casting due to the use of natural graphite, while possessing sufficiently high heat-insulating properties.

Claims (2)

A slag-forming mixture for thermal insulation and protection of the metal surface in the intermediate ladle from secondary oxidation during continuous casting of steel, containing soda, characterized in that it additionally contains fly ash, marble, graphite and feldspar, in the following ratio of components, wt.%: marble 0.1-5 graphite 17.5-21.5 feldspar 0.1-5 soda 1-4 fly ash up to 100