RU2555167C1 - Graphite-oxide firebrick - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: graphite-oxide firebrick including carbon containing component, periclase and binding substance, contains artificial graphite and crystalline graphite as carbon containing component, and polyphosphate binder with refractoriness up to 2000°C as binding substance, at the following components ratio in wt %: artificial graphite 36-50, crystalline graphite 14-20, periclase 20-30, polyphosphate binding substance - rest.

EFFECT: firebrick of improved heat resistance, oxidability and industrial safety.

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Description

The invention relates to metallurgy, and in particular to the production of carbon-containing refractories used in the production of casting crucibles and refractory castings.

Graphite-oxide refractories are widely used in the production of foundry crucibles, in the lining of metallurgical units for out-of-furnace treatment, and in the transportation of metal. Moreover, the graphite component provides resistance to thermal shock due to the small coefficient of thermal expansion of graphites, and the oxide component determines a higher heat resistance of refractories in comparison with graphite counterparts.

Known carbon-containing refractory (RF patent No. 2270179, С04В 35/103, 2006), made of a mass containing periclase and / or corundum, a carbon-containing component, an antioxidant and a binder, in the following ratio, wt.%:

corundum fractions less than 0.063 mm 16-20 periclase fraction 0.5-1.0 mm 4-12 graphite 6-10 metal aluminum 1-5 crystalline silicon 2-5 ethylene glycol 1.5-1.8 powder phenolic binder 2.7-3.3 corundum fr. 0.5-6 mm rest

This composition allows to obtain a refractory with such operational properties as low thermal expansion, sufficient mechanical strength and low oxidizability. However, it has a complex composition, and its manufacturing technology requires high-temperature annealing. In addition, the composition contains such a harmful substance as phenol that it is not recommended to use it according to EEC directives. All this complicates the use of this material in production oriented to the world market.

The closest to the invention in composition is a refractory (SU 510456, С04В 35/20, 06/11/1976) containing, wt.%: Magnesite fractions, mm: 1-0,2 - 40-50, 1-3 - 20-25, ≤0.06-15-25, flake graphite - 5-25, ligament - 8-10.

The known composition of the refractory is adopted as a prototype.

A magnesite-based refractory possesses the necessary strength, heat resistance, and low oxidizability.

The main disadvantages of this material include:

- during annealing, the formation of microcracks occurs due to the active interaction of magnesite with aluminophosphates of the binder, which negatively affects the durability of the products;

- the increased content of magnesium oxide in the composition leads to an increase in the coefficient of thermal expansion, to uneven physical and chemical properties in the volume of the resulting products, which negatively affects the mechanical strength and heat resistance of products from this refractory.

The main objective of the present invention is to develop a composition of refractory material for the production of casting crucibles and refractory coatings with high heat resistance, low oxidizability and industrial safety.

The technical result is achieved in that the graphite-oxide refractory, including crystalline graphite, a magnesian component and a binder containing aluminophosphates, according to the invention additionally contains artificial graphite, as a magnesia component of periclase, and as a binder, an inorganic polyphosphate binder with refractoriness up to 2000 ° C, in the following ratio of components, wt.%:

artificial graphite 36-50 crystalline graphite 14-20 periclase 20-30 inorganic polyphosphate binder with refractoriness up to 2000 ° C 10-20

As inorganic polyphosphate binder, aluminophosphate binders of the following composition were used: (1)

Refractoriness of the binder after polymerization reaches 2000 ° C, which is known from literature (Metallophosphate binders and mixtures: Monograph / I. Illarionov et al. Cheboksary: Publishing House at Chuvash University, 1995 - 524 s.) This property the binder provides high thermal stability for the inventive graphite-oxide refractory.

In addition, the inorganic polyphosphate binder provides high mechanical strength of both freshly formed and polymerized refractories due to irreversible hardening during self-heating with the formation of a dense binder frame. Self-hardening of the samples occurs due to the chemical interaction of the binder with periclase, because aluminum polyphosphates in the binder enter into interaction with magnesium oxide and with impurities contained in periclase. The ongoing exothermic reaction leads to heating of the refractory mixture, causing the binder to polymerize. This allows you to get durable samples without prior high-temperature annealing at a temperature of not more than 400 ° C.

Inorganic polyphosphate binder intensively interacts with chemical active centers on the surface of graphite particles, which significantly reduces the thermal oxidation of graphite and positively affects the heat resistance and durability of refractory products made of this material.

The choice of the boundary values indicated in the claims is due to the following.

A content of inorganic polyphosphate binder of less than 10% is not enough to moisten the mixture due to its active interaction with periclase, and the introduction of more than 25% overmoistens the mass and causes cracking of the overpress.

Periclase in the composition of the refractory provides the necessary packing density due to its higher density compared to graphites, and also reacts with a binder, thereby serving to ensure self-annealing of the samples. Moreover, when its content in the composition is less than 25%, the necessary exothermic reaction intensity is not achieved, and when the content is more than 34%, active polymerization and clumping of the powder composition occurs due to high heat generation, which complicates further pressing and shaping.

Crystalline graphite contained in the composition provides high thermal conductivity of the composition, low wettability by liquid metal due to the obvious crystalline structure of graphite. The increased thermal conductivity of the composition reduces thermal stresses in the volume of refractory ceramics based on the proposed composition, which increases the service life of the product and ensures the stability of physical and mechanical properties in the case of high-temperature drops.

It has been experimentally established that the content of crystalline graphites of less than 14% does not provide high thermal conductivity, and the content of more than 37% leads to delamination of refractory ceramics due to both low wettability of the binder and due to delamination of crystalline graphites, and as a result of a decrease in mutual friction between particles composition.

Examples of compositions for the manufacture of samples of graphite oxide refractory and their properties are shown in tables 1-2.

The following materials were used to obtain the refractory of the claimed composition: fused periclase (with an MgO content of 96.3%), artificial graphite (graphitized battle with a carbon content of up to 90%, sulfur no more than 0.5%) and crystalline (GL-2 grade), aluminophosphate binder by reference (1).

These components were dosed in the amounts given in the claims, mixed, molded products on a hydraulic press, while the heat treatment and polymerization of the samples occurred due to heat from the chemical interaction of the polyphosphate binder with periclase. After polymerization, the samples were subjected to fixing annealing at a temperature of 400 ° C.

The quality of the carbon-containing refractory was evaluated as follows: by oxidation and compressive strength, which were determined after molding and self-solidification of the samples in an oxidizing atmosphere at 1350 ° C for 1 hour. Oxidation was defined as the ratio of the amount of carbon remaining in the sample at a distance of 15 mm from its surface to its initial amount in percent. The compressive strength was determined according to GOST 4071.1-94.

Table 1. The mass composition of the proposed and known graphite oxide refractory

Composition number Content, wt.%: artificial graphite graphite crist. periclase polyphosphate. communication corundum Al soot pitch + FFS boron carbide Maud. additive prototype fifteen 40 25 four 5 7 one 3 one fifty twenty twenty 10 - - - - - - 2 43 17 25 fifteen - - - - - - 3 36 fourteen thirty twenty - - - - - -

Table 2. Properties of the proposed and known graphite oxide refractory

Composition number The compressive strength after heat treatment at 1350 ° C, N / mm ² Oxidation,% prototype 10 57 one 12.5 71 2 fifteen 68 3 fourteen 75

The table shows that the proposed refractory has high mechanical strength and heat resistance (oxidizability higher).

Graphite-oxide refractory, in addition to the listed advantages, has higher thermal conductivity, low wettability by liquid metal, low thermal expansion and maintains constancy of properties during prolonged contact with metal at elevated temperatures.

The combination of the advantages of magnesian carbon-containing and graphite refractories in this refractory allows it to be successfully used for the production of casting crucibles and refractory coatings for color casting, which was confirmed by the results of industrial tests.

Claims (1)

Graphite-oxide refractory, including crystalline graphite, magnesia component and a binder, characterized in that it additionally contains artificial graphite, periclase as a magnesia component, and an inorganic polyphosphate binder with refractoriness up to 2000 ° C in the following ratio of components, wt.%:
artificial graphite 36-50 crystalline graphite 14-20 periclase 20-30 inorganic polyphosphate binder with refractoriness up to 2000 ° С 10-20