SU1107948A1 - Binder for making ceramic investment moulds and method of preparing same - Google Patents

Abstract

1. Binder for the manufacture of casting ceramic molds in high-grade models, including liquid glass with a density indicator

Description

 one

The invention relates to foundry production, in particular to the manufacture of casting molds for smelted e fcIM models, and can be used in the manufacture of precision castings.

A binder is known, which is a hydrolyzed solution of ethyl silicate in organic polar solvents, the use of which provides the high strength properties of the resulting ceramic SP

However, at the same time, the specified binder is characterized by toxicity, high cost, difficulty of preparation (hydrolysis) and, in addition, long-term drying of each refractory layer (up to 4 hours) and fire and explosion hazards in the shops for precise casting.

Therefore, recently, inorganic binding materials with an aqueous solvent, which, unlike organic ones, do not have these disadvantages, are becoming more common.

In the manufacture of ceramic molds based on melted models, it is known, in particular, a binder, which is a product of sodium hydrosilicate (liquid glass) gelation 12. This results in a reduction in the shaping time by 6-8 times as compared with ethyl silicate G2.

However, the strength properties of manufactured ceramics are 2-3 times lower than when using ethyl silicate.

It is also known aluminosilicate binder, which is formed as a result of exposure to liquid glass, aluminum oxychlorides (solution of aluminum chloride) and 31.

Form coats made using the specified binder have sufficient bending strength (up to 5.5 MPa). However, at the same time, the shaping process is prolonged as a result of insufficient drying of the refractory layers (drying of each layer to 2.5 hours). The removal of aluminochloride in organic solvents of L floors increases the production and increases the risk of explosion and explosion at the forging site.

The closest to the invention of the technical nature and reach079482

My result is a C5l binder for the manufacture of casting ceramic molds on melted models, consisting of liquid glass with a density indicator (1.4 ± + 0.02) 10 kg / m, water and phosphoric acid, and the content of these ingredients, wt.%: 10 Liquid glass. 76.92

Orthophosphorus

acid combined

with water23,08

The closest to the invention of the technical essence and the achieved result is also a method of preparing a bond for fabricated ceramic ceramic forms according to melted models, which consists in diluting a liquid glass with water, followed by neutralization with an aqueous solution of phosphoric acid with stirring tSl Using this reference to create this glass with water followed by neutralization with an aqueous solution of orthophosphoric acid while mixing tSl Use this reference to create this glass with water followed by neutralization with an aqueous solution of orthophosphoric acid while stirring tSl Using this reference will create this connection with water, followed by neutralization with an aqueous solution of orthophosphoric acid under stirring tSl Using this reference will result in this glass that will be connected and neutralized with an aqueous solution of orthophosphoric acid while stirring with tSl. it will be possible to obtain fairly stable properties of ceramics, increase productivity at the shaping site and significantly improve sanitary and hygiene cal conditions of work in the shop.

However, 5 since the industrial liquid stem has a narrow interval of difference in modulus (2.0–3.0), the amount of orthophoresoric acid that can be introduced into the binder is limited by the coagulation threshold of the suspension. In this connection, the amount of silicophosphates, which are formed during calcination and reinforce the ceramic matrix, is not enough, which does not allow obtaining the high strength of the shells in hot and calcined conditions.

In addition, fluctuations in the viscosity of the suspensions are observed on the basis of the described binder prepared in this way with the same amount of filler.

The purpose of the invention is to improve the quality of the molds by increasing their strength during the calcination process and after calcining and stabilizing the properties of the binder.

In order to achieve this goal, the binder for the manufacture of 5 casting ceramic molds on melted models, including liquid glass with a density indicator (1.4 + 0.02), water and orthophosphoric acid, additionally contains alkali in the following ratio of ingredients, wt.%: Liquid glass with a density indicator (1.4 + 0, Q2) X 10 kg / m 52-60 Alkaline11-21 Phosphoric acid18-20 Water 8.0-10 ,, 7 As an alkali, the binder according to the invention contains potassium hydroxide. As base, the binder contains sodium hydroxide. To achieve this goal, there is also a method of preparing a binder for making casting ceramic molds using melted models, which includes diluting a water glass with water and then neutralizing it with an aqueous solution of orthophosphoric acid with stirring, according to which a previously prepared water solution is introduced into the diluted water glass. alkalis, and neutralization with an aqueous solution of orthophosphoric acid is carried out by mixing with it at a speed of 35–40 rad / s for 240–300 s, followed by water cooling with stirring to a temperature of 293-298 K. In the process of oxidation preparation of the binder according to the invention, a large amount of sodium or potassium phosphates is formed in its composition, some of which form strong bonds with liquid impurities even at room temperature. glass At the stage of fixing the binder, silica gel is expelled in the form of a capillary-porous body. During calcination, dehydration of the gel occurs with the release of amorphous silica, which at calcination temperatures (1073–1273 K) interacts with sodium or potassium phosphates trapped in the pores of the form. As a result, hydrogen bonds are formed between the phosphates and the surface of the silica. This results in a very strong silicophosphate binder. The preliminary alkalization of liquid glass creates the possibility of increasing the amount of orthophosphoric acid introduced into the liquid glass. This contributes to an increase in the phosphate content in the shell and the emergence of a more developed reinforcing network of silicophosphates. The introduction of alkali into liquid glass leads to the destruction of silica-oxygen bonds. This stabilizes the viscosity of the suspensions made on its basis, since the subsequent partial polymerization under the action of orthophosphoric acid proceeds under practically the same conditions. The binder is made as follows. An aqueous solution of alkali is introduced into the initial liquid glass with a density of (1.38-1.42) 1 10 kg / m. Depending on the silicate module of the glass, the concentration and density of the alkali solution are selected (Table 1). Table 1

i

Regardless of the modulus of the liquid glass, the water content in the alkaline solution should be 0.15 kg per 1 kg of liquid glass. Thereafter, with vigorous stirring at a speed of 35-40 rad / s, the binder is partially neutralized with orthophosphoric acid of density (1.45-1.48) V 10 kg / m for 240-300 s. Intensive agitation is necessary to prevent silica lumps from falling out. The neutralization time is determined by the kinetics of the gel falling out. Amount of orthophosphoric acid, INPUTABLE

in solution, should always be equal to 0.35 kg per 1 kg of liquid glass. Since the neutralization temperature of the binder rises to 323-. 333 K, it must be cooled in order to avoid cracking during drying of the coating and disturbance of geo 7948

metric precision castings. For this purpose, water is o. 1) Continue mixing until the binder temperature 5 reaches 293-298 K.

The density of the silicophosphate binder, ready for use, must be (1.3 t 0.05) to 10 kg / m. The density adjustment with tap water is possible.

Increasing the alkali and orthophosphoric acid content above the specified limits does not lead to a further increase in the strength of ceramics, and if the content is below the specified limits, they have a smaller effect on the strength.

Liquid glass based binders with a different initial module were prepared for the test (Mrs .;)

The parameters for the preparation of the binder are shown in Table. 2. Table2

Compounds bounded to inventions Sodium hydroxide

are listed in Table. 3

ITABLE3

16,0

Phosphoric acid density

(1.46 t 0.01) x 10

G Silicate module of liquid glasses in the binding 2.4; 2.6; 2.8; 3.0; 3.0.

For comparison, marshalite forms were made on the basis of the proposed binder and prototype binder.

Marshallite molds for manufactured models were manufactured using the following technology. Based on the binders of the invention, a refractory slurry was prepared with KP-2 powdered quartz with a viscosity of 35 sec according to VZ-4. On the modules of model composition P-3, four layers of refractory coating were formed based on the specified bending strength of ceramics, MPa:

in hot condition

The viscosity of the suspension based on the proposed binder practically did not change when using liquid glass of different batches, and with a binder to marshalite ratio of 50:50 (parts by weight) was in the range of 34-35 s according to VZ-4

Continued table. 3 j

19.6

18,8

18.4

suspension with sanding sand KO315, mourned by technical ammonia in the amount of 0.03 kg per 1 kg of sand. Drying each layer 2400 s.

Vytopku models produced in the model mass. The strength of the samples for bending in the wet state was 3.5 MPa.

The results of the strength tests of form sheaths with binders 1-5 are given in Table. four.

Table 4

293 K. The viscosity of the suspension based on the binder of the prototype with the same ratio with marshalite ranged from 25 to 40 s.

Therefore, the binder according to the invention stabilizes the properties of the suspensions obtained. At 1-5, respectively, it is equal to: strength tests of ceramics were made from a suspension with a viscosity of 35 s for all variants. When testing ceramics obtained using the prototype binder, the following averaged indicators of flexural strength were recorded: In the hot state .5.0 MPa In the calcined state, 5.5 MPa In comparison with the prototype binder, the binder To the invention it allows to increase the strength of ceramics by 62-65% with stable properties of the binder and form shells. 810 Binder ethyl silicate and water glass were used as a base object, which are used to make ceramic molds at the Chel Instrument Factory. Replacing the base binder with a binding agent according to the invention (for the purity of the surface of the castings, one layer based on ethyl silicate remains), reduces the total scrap of the castings by 37–40%, eliminates ceramics maintenance at the calcining stage almost completely, reduce the consumption of ethyl silicate by 3 times. The estimated economic efficiency from the use of a binder is 50-60 thousand rubles. per year dp of one foundry with an annual program of 500 tons of precision cast billets.

Claims (4)

1. Binder for the manufacture of ceramic casting molds on investment casting, including liquid glass with a density index (1.4 + 0.02) x 10 ^ά kg / m ³ , water and phosphoric acid, characterized in that, 'in order to improve quality forms by increasing their strength during calcination and after calcination and stabilization of the properties of the binder, it additionally contains alkali in the following ratio of ingredients, wt.%: Liquid glass with a density index (1.4 ± 0.02) * * 10 ^? kg / m ³ Alkali Orthophosphoric acid Water 2. The binder according to claim 1, 52-60 11-21 18-20 8.0-10.7 characterized in that, as an alkali, it contains potassium hydroxide. 3. A binder according to claim 1, characterized in that it contains sodium hydroxide as an alkali. 4. A method of preparing a binder for the manufacture of ceramic casting molds according to investment casting, including diluting liquid glass with water, followed by neutralizing it with an aqueous solution of phosphoric acid with stirring, characterized in that, in order to improve the quality of the molds by increasing their strength during calcination and after calcining and stabilizing the properties of the binder, a previously prepared aqueous solution of alkali is introduced into liquid glass diluted with water, and neutralization with an aqueous solution of phosphoric acid is carried out by mixing with it at a speed. 35-40 rad / s for 240-300 s followed by water cooling with stirring to a binder temperature of 293-298 K.