SU1281334A1 - Sand for making cast ceramic moulds and cores by permanent pattern - Google Patents

Abstract

The invention relates to compositions of mixtures for the manufacture of ceramic forms according to permanent models. The purpose of the invention is to increase the strength of the forms after calcining them and to reduce the time for cleaning castings from ceramics. This is achieved by addition of sodium polyphosphate of the composition (NaPOg ;, - with the molar ratio Na 0: P 0 1 and dispersion i1 mm with the following ratio of components, wt.%, Ethyl silicate, 1.33 ... 4, 93; water 17.29 ... 20.89; hydrochloric acid 0.004 ... 0.0488; ferrochrome slag 0.067 ... 0.10; sodium polyphosphate 0.3 ... 1.5; refractory filler - the rest Therefore, the high bending strength of ceramics after calcination allows to obtain shapes and rods of complex configuration. 1 1 table i i c so 00 00 4 4

Description

FIELD OF THE INVENTION The present invention relates to a foundry, in particular, to mixtures for the manufacture of ceramic molds and rods in permanent models.

The purpose of the invention is to increase the strength of the molds and cores after calcination and reduce the time for cleaning castings from ceramics.

Sodium polyphosphate of the general formula (NaPO h) H ,, 0 with a molar ratio of 0 1 (Graham salt) at a temperature above melts, fills microcracks in ceramics, and ce-gates filler grains. The degradation of sodium polyphosphate during the cleaning of castings in alkaline solutions is due to the fact that it dissolves in alkali and weakens the bonds between the filler grains, contributing to a more rapid dissolution of the ceramic mixture.

Sodium polyphosphate should have a particle size of mm, since it is only with such granularity that it completely dissolves in the hydrolyzed ethyl silicate solution (GRE), which ensures its diffusion when drying ceramic forms and rods from their working surfaces. As a result, on working surfaces it decreases. the content of such harmful elements as sodium and phosphorus.

The proposed mixture is prepared as follows.

Ethyl silicate-32 or ethyl silicate-4O is mixed with water, acidified with 0.3% hydrochloric acid (from the mass of a hydrolyzed solution of ethyl silicate) until a binder with a conditional silica content is obtained, respectively, 24.60-25.60 or 32.00 32.70%, which is diluted with water to obtain hydrolyzed ethyl silicate solutions containing conditionally 2-6% silica. GRA mixed with refractory filler in the ratio of 1: 3,5.

The ratio of powdered quartz brand KP-3 and molding sand brand 1K02A in refractory filler,

five

0

five

0

five

0

five

The composition of the mixture is 60:40, with this ratio ensuring sufficient density of the ceramics and low roughness of the ceramic forms and abraded ones.

GRE is first poured into the mixer at the speed of rotation of shaft 47, and then the refractory filler is loaded and the components are mixed for 4-6 minutes. After that ferrochromic slag is loaded and mixed for 30- 60 s. The sodium polyphosphate is introduced last into the mixer and mixed for 20-30 seconds.

The finished mixture is poured into a snap-in, in which ceramic rods are produced for insertion into the mold during the casting of electric motors under pressure. At the same time, ceramic samples of size 10) 15 60 and mm are made for testing, respectively, the strength of the samples in bending and for determining the phosphorus content in the surface layer of the casting. After extraction from the tooling, the ceramic core and ceramic samples are dried in air for 24 hours at room temperature.

Then the ceramic rods and the samples are calcined at 900 ° C for 2 hours.

In sand-liquid forms, using ceramic rods made of the proposed mixture, steel castings are obtained, which are first knocked out of the forms, and then, with the ceramics remaining on their surface, are placed in a bath with a 35% sodium hydroxide solution. 120 C, and maintain them in solution until the surface of the castings is completely cleaned. A track for complete cleaning of the castings from the kera.-1- th mixture is fixed with stopwatches. After cleaning the casting, chips are taken from its surface to a depth of 0.2 mm and a chemical analysis is made for the phosphorus content.

Mixture compositions, properties of ceramic samples, phosphorus content. at a depth of 0.2 mm from the surface of the casting, as well as the cleaning time of the reflux -. ki from ceramics are shown in the table.

- Refractory filler - the rest.

As can be seen from the data given in Table 25, the higher the content of sodium polyphosphate in the mixture, the higher the strength of the molds and the shorter the cleaning time of the castings. However, with an increase in the amount of polyphosphate, the phosphate content in the peripheral portions of the castings increases. Therefore, in the manufacture of steel castings, the content of sodium polyphosphate in the mixture should not exceed 1.0 wt.%. A mixture with a sodium polyphosphate content of up to 1.5 wt.% Can be used for castings from phosphorous cast irons.

and non-ferrous alloys.

35

The content of sodium polyphosphate in the mixture is less than 0.3. wt.% does not provide sufficient strength forms and rods of complex configuration, for example, with protruding thin elements. This also increases the duration of cleaning castings.

The proposed mixture allows to expand the field of application of mixtures without organic solvents for casting ceramic molds and cores.

reduce scrap castings and reduce the cycle of their manufacture.

Claims (1)

Invention Formula The mixture for the manufacture of casting ceramic molds and rods by permanent models, including ethyl silicate, water, hydrochloric acid, refractory filler and ferrochromic slag, characterized in that, in order to increase the strength of the molds and cores after calcination and shorten the cleaning time castings from. ceramics, it additionally contains sodium polyphosphate with a molar ratio of Nai2P: P5 dj; 1 and the dispersion of si mm in the following ratio, wt.%: five 0 Ethyl silicate Water Salt acid Ferrochromic slag Sodium polyphosphate refractory filler 1.33 ... 4.93 17.29 ... 20.89 0.004 ... 0.0148 Oh, 067 ... Oh, 10 0.3 ... 1.50 Rest