UA122235C2 - METHOD OF MANUFACTURE OF COMBINED MULTILAYER CERAMIC COVER FORMS - Google Patents

Abstract

The invention relates to foundry production, namely to the manufacture of combined multilayer ceramic shell molds for casting on melted models. A method of manufacturing combined multilayer ceramic shell molds includes sequential alternate application and drying on a model block of layers of refractory suspensions, the first two layers of ceramic shell molds being made of the same suspension based on liquid glass and powdered quartz. After drying, the first layer is chemically fixed with an aqueous solution of acid salt (pH <7) and re-dried. The method prevents the occurrence of surface defects such as gas bubbles and clogging of chemical origin on castings.

Description

The invention belongs to foundry production, namely, it relates to methods of manufacturing multilayer ceramic shell molds obtained by melting or firing models.

There is a known method of manufacturing ceramic shell molds (CO), which includes the sequential application and sprinkling of each layer of refractory coating on a model block with a refractory material, the paired layers of which are performed using a suspension based on an aqueous solution of alcohol or acetone in a ratio of 1:1 to 1: 3 by volume and the value of the hydrogen indicator pH-7, for odd layers - a suspension based on an aqueous solution of liquid glass or an aluminochrome phosphate binder with a density of 1200...1300 kg/muU, respectively, with a value of pH7 and pH7, and drying the layers carried out after applying all layers of coating |A. with. 1682031 AI

USSR, publ. 07.10.91.

The main disadvantage of this method is the low fire resistance of CO based on liquid glass and the saturation of the surface of steel castings with phosphorus from the material of CO, which are made on the basis of aluminochrome phosphate binder. The result of this shortcoming is the instability of the dimensional accuracy and the accuracy of the geometric shape of the castings obtained in the KO based on liquid glass, and the inconsistency with regard to the requirements for the metal of steel castings in terms of the phosphorus content in their surface layers in the case of their production in the KO based on an aluminochrome phosphate binder. In addition, this technology requires the use of flammable toxic materials (alcohol, acetone, etc.).

The closest in terms of technical essence and the effect achieved is the manufacturing method

KO, which includes the alternate application of layers of refractory suspensions on the model block, where each subsequent layer of suspension chemically fixes the previous one, since the layer on sodium liquid glass (the binder of the material has alkaline properties, and the fixative is a layer of orthophosphoric acid, which has acidic properties (Pat. of Ukraine Mo 108654, published 05/25/2015).

The main disadvantage of this method is the formation on the working surface of the ceramic shell mold during its firing of compounds based on iron, sodium and phosphorus, the source of which are materials that were used for the manufacture of paired layers (layers based on orthophosphoric acid) of the KO. The presence of such compounds leads to the emergence of lithuania

From surface defects in the form of gas bubbles and clogging of chemical origin.

The basis of the invention is the task of improving the quality of casting.

The technical result is that thanks to the proposed invention, the appearance of surface defects is prevented. The first two layers of ceramic shell molds are made from the same suspension based on liquid glass and pulverized quartz, and after drying, the first layer is chemically fixed with an aqueous solution of acidic salt (pHe7) and its re-drying is carried out. The proposed method allows to increase the water-absorbing capacity of the layer of liquid glass coating between the front surface of the KO and the layer containing crystal hydrates. When heating the CO, this prevents the release of aqueous solutions formed in the third layer of the CO to its working surface and, accordingly, the appearance of the above-mentioned defects.

The task is solved due to the fact that in the method of manufacturing ceramic shell molds, which includes sequential application and drying on the model block of layers of refractory suspensions, according to the invention, the first two layers of ceramic shell molds are made from the same suspension based on liquid glass and dusty quartz, and after drying, the first layer is chemically fixed with an aqueous solution of acidic salt (pH«e7) and it is re-dried.

Gas bubbles and clogging in castings are the result of the formation of aqueous solutions of salts and liquid glass in crystal hydrates and water, which is present and released in a free state from the layer of acidic binder, its migration, release on the working surface of CO in the form of droplets and their dehydration. That is, during heating and roasting, the process of formation and removal of solutions of sodium metasilicate and iron sulfate with crystal hydrate water from the inner layers to the working surface of the boiler takes place.

Based on the fact that the amount of free crystalline hydrate water is limited by the conditions of production of the CO according to the adopted scheme, then increasing the thickness of the liquid glass layer between the working surface of the CO and its layer based on orthophosphoric acid prevents the occurrence of gas bubbles and clogging of chemical origin, due to the absorption of the material of the interlayer of emerging solutions.

An example of implementation. The following materials were used for the manufacture of CU: - quartz sand 2KzO1016; - quartz ground powder form PK-1 (GOST 9077-82); 60 - technical water;

- aluminum sulfuric acid 16 water (GOST 12966-85); - liquid sodium glass with silicate module Mviog-2.9...3.1 (GOST 13078-81); - orthophosphoric acid technical grade B with a density of 1500 kg/m3 (TU U 6-05766356.037-98); - surfactant (surfactant); - fly ash of the Dnieper thermal power plant.

For chemical fixation of the first layer of CO, an aqueous solution of aluminum sulfate saturated at 25 "C (pHN.3, 1) was prepared.

To perform the first and second layers of CO, a suspension was prepared on the basis of liquid glass with a density of 1135...1147 kg/m3, pulverized quartz and surfactant (suspension with conditional number Mo 12).

Conditional viscosity of Mo 12 suspension was 48...60 s according to viscometer B3-4 (GOST 9070-75).

A suspension based on orthophosphoric acid and sawdust (suspension with conventional number Me 3) was used to perform the third and subsequent odd-numbered layers of CO. Conditional viscosity of Mo Z suspension was 27...30 s according to viscometer B3-4.

To perform the fourth and subsequent paired layers of CO, a suspension of Mo 4 (suspension based on liquid glass with a density of 1270...1300 kg/m) and pulverized quartz (suspension with a conventional number of Mo 4) was used. Conditional viscosity of Me4 suspension was 28...30 s according to viscometer 3-4.

The ceramic shell mold on the surface of the model block was made as follows.

The model block was completely immersed in Mo 12 suspension, taken out and turned for 20...40 s in different directions at an angle of 20...60 degrees. to the horizon for the excess suspension to run off and its uniform distribution over the surface of the model block, after which it was sprinkled with quartz sand.

Drying of the first layer was carried out for 45...60 minutes under conditions of forced air movement with a temperature of 28...32 76.

After drying, the first layer was chemically fixed with an aqueous solution of aluminum sulfate by spraying the first layer on the model block from a spray gun.

The second layer of CO was applied to the model block according to the scheme of applying the first layer followed by drying for 90...180 minutes under conditions of forced air movement with a temperature of 28...32 76.

For the production of the third layer of CO, the model block was immersed in a MoZ suspension (a suspension based on orthophosphoric acid and ash), removed from the suspension, turned for 10...20 seconds in different directions at an angle of 20...60 degrees. to the horizon to drain off excess suspension and sprinkled with quartz sand. The layer was dried for 180 waves with forced air movement at a temperature of 28...32 76.

The following layers were applied to the model block in the given sequence, followed by drying for at least 3 hours for each layer.

Melting of the model composition with CO was carried out with hot air at a temperature of 165:2-15 "C for 60...90 minutes (until the flow of the model composition with CO stopped). After melting, the CO was roasted according to the following regime: - temperature in the furnace when loading CO 20 ...250 C; - heating up to 930220 "C at a rate of 170...250 "C/hour; - isothermal holding at 930220 "C for 1...2 hours.

In order to determine the main properties and compare the proposed technology for obtaining ceramic shell forms with the prototype, samples were made to determine the strength limit during static bending (V.N. LytbE by fusible models / V.N. Ivanov, S.A.

Kazennov, V.S. Kurchman and others; under the municipality ed. Ya.I. Shklennyka, V.A. Ozerova. - 3rd edition, revised. and additional - M.: Mashinostroenie, 1984. - P. 199-200.

As a result of changing the order of application of layers of refractory coating on the model block, a combined CO with the properties given in the table is formed.

Table

Properties of combined KO

For Proposed

Indicators and a prototype method

The presence of gas bubbles on the castings is absent

The presence of clogging on the castings is absent

Strength limit during static bending (at 20 "С), MPa 7.2...8.5 7.8...8.9

Gas permeability, unit 0.17...0.22 0.17...0.22

Gas-forming capacity at 950 "С, cm3/100 g 45...47 45...47

From the analysis of the obtained data, it follows that the CUs manufactured by the proposed method compared to the prototype have somewhat greater strength and allow to prevent the appearance of surface defects such as gas bubbles and clogging of chemical origin on the castings.

Claims (1)

FORMULA OF THE INVENTION The method of manufacturing combined multi-layer ceramic shell molds, which includes the sequential application and drying on the model block of layers of refractory suspensions, which is characterized by the fact that the first two layers of ceramic shell molds are made from the same suspension based on liquid glass and pulverized quartz, at the same time, after drying, the first layer is chemically fixed with an aqueous solution of acidic salt (pHe7) and its repeated drying is carried out.