RU1771863C - Suspension for preparation of ceramic envelope forms - Google Patents

Abstract

Usage: the invention relates to investment casting. SUBSTANCE: suspension contains, wt.%. ethyl silicate 9.0-14.0; water 21.0-26.0; hydrochloric acid 0.3-2.0; surfactant 0.05-0.3; amorphous silica - dust of electrostatic precipitators of silicon production 0.7-7.0; pulverized quartz - the rest Amorphous silica, which has a developed surface, enhances the thixogropic properties of suspensions. The increase in the strength characteristics of ceramics is due to the formation of silica in the suspension during the interaction of the finely divided part of silica and water. In addition, drying of ceramics is accelerated due to the presence of calcium and magnesium oxides in amorphous silica, which accelerate the transfer of CZR-containing sols into gel, and the water formed with this 1 is quickly removed from ceramics 3, thereby drying ceramics is accelerated 2 table. 1L

Description

The invention relates to foundry, in particular, to the manufacture of ceramic molds for smelted models.

The purpose of the invention is to accelerate drying and increase the strength of ceramic molds. The goal is achieved in that in a suspension containing ethyl silicate, water, hydrochloric acid, a surfactant and pulverized silica, amorphous silica is additionally introduced - dust from electrostatic precipitators of silicon production in the following ratio of components, wt.%: Ethyl silicate 9.0-14.0

Water 21.0-26.0

Salt for acid 0.3-2.0

Surfactant Amorphous Silica

0.05-0.3 07-7.0

Dusty quartz

Amorphous silica - dust electrostatic precipitators of silicon production - is a fine powder of the following chemical composition, wt.% Silicon oxide 75-95

Alumina 0.5-0.8

Oxides of calcium and magnesium 0.8-2.2

Iron Oxide 0.6-0.7

Free carbon 4.5-5.0

and particle size distribution: size, μm content,%

up to 85

up to 1010

more than 105

Amorphous silica, possessing a developed surface, enhances the thixogropic properties of suspensions. Native

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This bulk structure easily holds the refractory filler in suspension, giving the suspension increased sedimentation stability. The increase in the strength characteristics of ceramics is due to the formation of silica in the suspension during the interaction of the finely divided part of silica and water. The silicic acid thus formed enhances, together with ethyl silicate, the binding properties of the suspension.

The acceleration of drying of ceramics is explained by the presence in the amorphous silica of calcium and magnesium oxides, which accelerate the transfer of the binder ash into a gel, the resulting water being removed faster from the ceramic, thereby reducing the drying time of the ceramic.

With the introduction of amorphous silica in an amount of 0.7%, the drying time and strength of the ceramics remain at the level of the prototype. With the introduction of amorphous silica of more than 7 wt.%, The technological properties of the suspension deteriorate due to the high thixotropic properties, its mobility decreases, which leads to its uneven distribution over the model surface. In addition, strength is reduced, possibly due to a violation of the optimal particle size distribution of the refractory filler.

Example. The compositions of the suspensions are given in Table 1. The calculated amounts of water and acid were poured into the mixing tank, half of the calculated amount of refractory filler, which was a mixture of amorphous silica and pulverized silica, was poured and stirred for 30 minutes with a stirrer with a speed of 2800 rpm. Then ethyl silicate, the remaining amount of refractory filler, surfactant were added and the suspension was stirred for 30-40 minutes. The viscosity of the suspension with a VZ-4 viscometer for the first layer is 40-60 s, for subsequent layers 30-40 s. The suspension after applying 1 layer is diluted to the required viscosity with a hydrolyzed ethyl silicate solution with a viscosity of not more than 14 s. Each layer was dried in a drying chamber at a temperature of 27 ± 1 ° C and a relative humidity of 50-70% for 2 hours. Smelting of the model composition carried out in an autoclave at 120 ° C, a pressure of 2 atm., for 20 minutes The ceramics were calcined in an electric furnace at a temperature of 950 ± 10 ° C for 1 h. Determination of the bending strength after drying, model composition refining, and calcination was carried out on a tensile testing machine ТМ-30-1 according to the well-known technique of the Research Institute of Automotive Industry on 4-layer ceramic samples, size 20x75 mm. Strength at 950 ° C was determined using a 123IV-10 apparatus according to the method developed at the Institute of Nuclear Technology.

5O sedimentation stability of the suspension was judged by the amount of stratification of the suspension in the measuring cylinder for 3 hours according to the following formula

10

V1

V06

100%,

where S is the stratification value of the suspension,%; Vi is the volume of fluid released,

cm3;

V06 - total suspension volume, cm3. Drying kinetics was carried out for ceramics formed from a suspension with amorphous silica and was prepared for comparison

suspensions of the prototype. Drying kinetics decreased for 1, 3, and 5 layers of ceramic. The sampling interval for humidity was 0.5 hours. Humidity was determined according to GOST 2642.1-86.

Data on the properties of the suspension and ceramics are presented in table. 2. From the table. Figure 2 shows that a 2.5-fold increase in the sedimentation stability of the suspension compared to the prototype is observed with the introduction of 0.7% amorphous silica. At a higher content, the suspension does not delaminate within 5 days. The strength of ceramics is increased by 1.2-2 times. In ceramics with additives of 0.7-7% amorphous

silica, residual moisture after 1.5 hours of drying and residual moisture in ceramics prepared according to the prototype, after 2 hours of drying, is almost the same in all studied layers. The drying kinetics of ceramics with amorphous silica contents above 7% was not carried out due to the low technological quality of the suspension.

Thus, the introduction of 0.77% amorphous silica into the suspension makes it possible to reduce the drying time of each layer by 0.5 hours and increase the ceramic strength by 1.2-2 times.

Claims (1)

SUMMARY OF THE INVENTION A suspension for the manufacture of ceramic shell molds used in the production of investment castings, including ethyl silicate, water, hydrochloric acid, a surfactant, and artificial pulverized silica, characterized in that, in order to accelerate drying and increase strength, it additionally contains amorphous silica - dust of electrostatic precipitators of silicon production in the following ratio of components, wt.%: Ethyl Silicate 9.0-14.0 Water 21.0-26.0 Salt for acid 0.3-2.05 Surface active substance Amorphous silica - dust of electrostatic precipitators of silicon production Dust quartz Table I table 2