SU1726451A1 - Method of producing heat resistant refractory products - Google Patents

Abstract

The invention relates to ferrous and non-ferrous metallurgy and can be used in the manufacture of ceramic tooling operating under long-term alternating thermal stresses. The aim of the invention is to increase the mechanical strength of the product after prolonged thermal cycling while reducing the sintering temperature. For this, a mixture of fine components (alumina, quartz glass and potassium fluoride) is first introduced into the mullite suspension, mixed, and then the granular components: electrocorundum and mullite at a ratio of components, wt.%: Finely ground mullite 32-34; electrocorundum 44-46; alumina GK fr. 0.063 mm 3.5, quartz glass FR. 0.063 mm 2-4; potassium fluoride 0.5-1; water 6-8; sodium silicate solution 0.1-0.2; granular mullite 1.8-12.4, -a calcination is carried out at 1200 or 1460 ° C. The resulting products have the following properties: open porosity,%: calcined at 1200 ° C 20.7-21.2; at 1460 ° C 19.0-19.2; compressive strength of unfired samples, MPa 3.8-4.0; compressive strength, MPa, 59-63, 138-142, residual strength after eight cycles of 20-1250 water,%: 99-100, 98-100, residual strength after forty cycles of 20-1250 ° C - water, %: 95-105, 70-76, shrinkage during firing,%: 0.3-0.4; 0.6-0.8. 2 tab.

Description

The invention relates to the field of ferrous and nonferrous metallurgy and can be used in the manufacture of ceramic tooling (crucibles, ducts, various funnels, cups), operated under conditions of long alternating thermal stresses.

The purpose of the invention is to increase the mechanical strength of products after prolonged thermal cycling while reducing the sintering temperature.

The effect of preserving strength after prolonged thermal cycling is achieved by the formation during thermal treatment of interconnected regular zones of secondary mullite, the crystals of which reinforce the primary mullite matrix and localize the cracks resulting from the discharge of thermal stresses. Regularity of formation of secondary mullite is ensured by the presence of a liquid phase during the reaction due to smooth potassium fluoride.

Example 1. Preparing samples using the following technology.

First, an aqueous suspension of mullite is prepared by wet grinding in a ball mill. Then a mixture of finely dispersed GK alumina, silica glass, and potassium fluoride is prepared, which is introduced into the aqueous suspension of mullite, and this slip is thoroughly mixed. The granular electrocorundum and mullite are kneaded last in the resulting slip. The resulting mass is filled with gypsum forms and vibrates them on the vibrostand for 1.5-2 minutes at a frequency of 2800 oscillations per minute and an amplitude of 0.5-1 mm. The vibrated products are dried in natural conditions, not removed from the molds, 2-3 hours, removed from the molds, dried at 80-100 ° C for 2-3 hours. Then heat treatment is carried out at 1200 and 1460 ° C with aging at the indicated temperatures. 2 h. The rate of temperature rise is 250 ° / h.

The composition of the samples, wt.%:

Mullite fine milled

(solid phase

suspensions) 33

Electrocorundum45

Alumina GC fraction

less than 0,063 mm4

Quartz glass fractions

less than 0,063 mm3

Potassium fluoride 0.75

Sodium silicate solution

(, 35 g / cm3) 0.15

Water (liquid phase

suspensions) 7

Granular mullit7,1

Moreover, electrocorundum and mullite are distributed in fractions as follows, wt%:

Mullite fraction, mm

. 3.0-1.013

1.0-059

Less than 0.578

Electrocorundum fraction, mm

3.0-1.075

1.0-0.525

In this and the following examples, traditional grain composition was used to prepare the mass.

Example 2. A mass of the composition specified in Example 1 was prepared by successively mixing the components: mullite slurry, alumina HA, quartz glass, potassium fluoride, granular electrocorundum and mullite. After mixing further processing, the wire according to example 1.

Example 3 The mass of the composition specified in example 1 is prepared as follows: a mixture of finely dispersed alumina HA and quartz is introduced into the mullite suspension.

glass and the resulting slurry is thoroughly mixed; then electrocorundum and mullite are mixed into it. Potassium fluoride was added last with careful mixing. After mixing, further processing is carried out according to Example 1.

The composition of the masses and the properties of the samples based on them are given in Tables 1 and 2, respectively.

The yield of finely ground mullite beyond the specified limits (32–34%) leads to a deterioration of the casting properties of the system (more than 34%) due to thickening of the slip or to a decrease in strength after prolonged thermal cycling (less than 32%) due to an increase in the relative water content ).

A change in the content of electrocorundum leads to a decrease in the mechanical strength of the samples, both in the case of an increase in its amount by more than 46% (due to the lack of the necessary amount of sintering finely ground mullite) and in the case of a decrease in its amount below 44% (due to an insufficient amount of structural aggregate of the matrix).

Failure to comply with the indicated amount of alumina HA leads to a decrease in mechanical strength due to a sharp increase in the free surface of the system and a lack of binder - builder - primary finely ground mullite, if the amount of alumina is more than 5%, or to a decrease in mechanical strength after prolonged thermal cycling due to the lack of alumina for the secondary mullite chain in reaction with quartz glass, if its amount is less than 3%.

For the same reason, a reduction in the amount of silica glass of less than 2% is unacceptable. The output of the amount of quartz glass beyond 4% leads to a decrease in the mechanical strength after prolonged thermocycling due to the presence of a free glass phase disrupting the regular crystal microstructure.

The output of potassium fluoride beyond both lower (less than 0.5%) and upwards (more than 1%) leads to a decrease in mechanical strength after prolonged thermal cycling due to the disruption of the regular arrangement of secondary mullite zones, which are formed in a certain way only when the presence of a set amount of the liquid phase (the liquid phase is provided by the introduction of potassium fluoride into the mass).

When the water content in the slurry is less than 6%, casting properties deteriorate, more

8% - increases porosity, which leads to a decrease in mechanical strength.

A solution of sodium silicate in the range of 0.1-0.2% with the traditionally used density helps to regulate the pH in order to obtain stable suspensions with satisfactory casting properties.

Residual strength after 8 and 40 cycles of 20-1250 ° C - water is defined as follows.

The sample is placed in an oven at 1250 ° C and heated for 10 minutes. Further, all operations are carried out according to a known method.

Claims (1)

Invention Formula A method of making heat resistant refractory products; including the preparation of a water suspension of finely dispersed mullite, mixing it with electrocorundum and granular mullite, vibroforming, drying and roasting, characterized in that, in order to increase the mechanical strength of the products after prolonged thermocycling while simultaneously reducing five 0 five In order to maintain the pH, a solution of sodium silicate with a density of 1.3-1.35 g / cm is introduced into the suspension of finely dispersed mullite before mixing it with granular electrocorundum and mullite; a mixture of alumina fraction less than 0.063 mm, quartz glass fraction less than 0.063 mm and potassium fluoride in the following ratio, wt.%: Fine mullit32-34 Electrocorundum44-46 Alumina fraction less than 0,063 mm3-5 Quartz glass fraction less 0.063 mm2-4 Potassium fluoride 0.5-1 Water6-8 Silicate solution sodium 0.1-0.2 Grainy mullit1,8-12,4 and the calcination is carried out at 1200 ° C or 1460 ° C. Table 1 Note. The numerator is the data for samples burned at, in the denominator at. Table 2