RU2604281C1 - Method of making shell ceramic molds - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly, to production of casts based on removable (melted, burnt out, gasified) models. Method involves layer by layer deposition on a model of shells by immersing model in a suspension of refractory filler and binder solution and subsequent dusting with granular material. In dusting material of each layer, except last, coacervate is introduced in an amount of 0.5-1.5 wt%. Models are removed and shells are calcined. Coacervate used is alum.

EFFECT: reduced drying time of each layer of shell mold.

1 cl, 1 ex

Description

The invention relates to foundry, and in particular to the production of castings for removable (smelted, burned out, gasified) models.

A known suspension for the manufacture of shell molds for investment castings, including a refractory filler based on silicon dioxide, a phosphate binder, water glass, water and sulfuric acid, characterized in that in order to reduce the drying time of the suspension and increase its strength after firing, it additionally contains aluminum potassium alum in the following ratio of ingredients, wt. %: phosphate binder 9.0-13.0; liquid glass 3.0-7.0; water 17.0-21.0; sulfuric acid 1.1-1.7; aluminum-potassium alum 0.05-0.15; silica-based refractory filler - the rest; Alumochromophosphate or aluminoborophosphate binder is used as a phosphate binder [1].

However, the suspension has several disadvantages. The introduction of aluminum-potassium alum into the suspension can create difficulties when applied to the model block, associated with the possible formation of lumps as a result of insufficiently complete dissolution of the alum in the suspension due to their low solubility in water without additional heating. In addition, aluminum-potassium alum can significantly reduce the wetting ability of the suspension due to its hydrophilicity.

A known method of drying shell forms by blowing layers of ceramic coating with two streams of air with different speeds and humidity of 10-60%, characterized in that in order to reduce drying time and reduce energy consumption, each layer, starting from the second, is blown at a speed of 4-9 m / s, and then at such a speed as for the first layer; the air speed for blowing the first layer of ceramic coating is taken equal to 1.5-3.5 m / s [2].

However, the known method has several disadvantages. The complexity of the drying operation of shell forms increases, due to the need to blow the layers of the form with air flows at different speeds. In addition, the use of special fans, regulators and instrumentation is required to maintain optimal air flow rates and control air humidity.

A known method of manufacturing multilayer shell molds for investment casting, including applying to the block of investment models a layer of suspension on an ethyl silicate binder and layers obtained on a liquid glass binder, sprinkling with grain refractory material of each layer, drying the layers, characterized in that as a refractory coating material use quartz sand with the addition of grain wollastonite or granulated slag from blast furnace or converter production, containing the advantages compounds of calcium and silicon oxides in the form of Ca ₃ [Si ₃ O ₉ ], in an amount of from 2.5 to 97.5 wt.% [3].

The known method is not without drawbacks. Natural wollastonite is a scarce material; it is mined in limited quantities on the territory of the Russian Federation. The composition of natural wollastonite includes up to 10% of iron oxides in the form of impurities, therefore, their removal and enrichment of this material is required. The production of synthetic wollastonite in Russia is currently pilot, therefore, there is a dependence on foreign supplies. In addition, granular slags of blast furnace or converter production included in the composition of the bulk refractory material contain a large amount of free iron and its oxides. In this regard, upon contact with the suspension, iron hydroxide may form in it, reducing its hiding power when applied to the model block, and also causing swelling and delamination of the mold walls during subsequent calcination of the shells and their filling with metal melt.

Closest to the invention is a method of manufacturing shell ceramic molds for the production of precision castings for removable models, comprising layer-by-layer coating of the shells by immersing the model in a suspension of refractory filler in a binder solution and subsequent sprinkling with granular material, removing models and calcining the shells, characterized in that after sprinkling produce coacervation of each layer, except the last [4].

However, the known method has disadvantages. The complexity of the technological process of manufacturing shell ceramic forms increases due to the introduction of additional operations - coacervation of shell layers associated with aerosol spraying of solutions of high molecular weight substances, as well as the preparation of these solutions. In addition, for the implementation of the method, it is necessary to use special equipment to provide aerosol, and the actual operation of spraying solutions of macromolecular substances reduces the environmental safety of the process. In addition, the coacervation effect is unstable, which is associated with difficulties in dosing the required amount of coacervate and preparing the solution to obtain the effect for a given time, as well as ensuring the required level of aerosol characteristics.

These shortcomings are eliminated by the proposed solution.

The problem of improving the technological process is solved in terms of the use of a material in the shell mold form, which ensures a reduction in the number of manufacturing operations for the manufacture of shell molds in comparison with the prototype and a reduction in the drying time of each layer of a multilayer shell mold in comparison with the traditional investment casting scheme involving exposure to air after applying each layer for a long time (2-4 hours when using dried with conditioning ozduha [5] and 5.6 hours ethyl-silicate binder and for at least 10 hours without using a binder zhidkostekolnyh dried when exposed outdoors for production data), which reduces the complexity of the process of investment casting as a whole.

The technical result is an increase in the environmental friendliness of the process due to the rejection of aerosol spraying of solutions of high molecular weight substances, a reduction in the number of manufacturing operations for the production of shell molds compared to the prototype, and a reduction in the production cycle for manufacturing molds compared to the traditional investment casting scheme while ensuring stable shell quality.

The technical result is achieved by the fact that according to the method of manufacturing shell ceramic molds for the production of precision castings according to removable models, including layer-by-layer coating of the shells by immersing the model in a suspension of refractory filler in a binder solution and subsequent sprinkling with granular material, coacervation of each layer, except the last, removing models and calcination of the shells, coacervate is introduced into the composition of the refractory sprinkling material in an amount of 0.5-1.5% of the mass .; Alum is used as a coacervate.

The introduction of the coacervate into the composition of the refractory sprinkling material makes it possible to exclude the additional operation of aerosol spraying of the coacervate solution after sprinkling each layer, except the last, to combine the gelation process with the sprinkling and to increase the environmental friendliness of the process. This eliminates the need for preliminary preparation of a coacervate solution.

или $$M^{+}{M}^{3+}{(S{O}_4)}_2^{2-}\cdot 12H_{2}O$$

, где M⁺ - один из щелочных металлов (литий, натрий, калий, рубидий или цезий), а M³⁺ - один из трехвалентных металлов (обычно алюминий, хром или железо(III)). В роли M⁺ могут также выступать ионы аммония ( $$N{H}_4^{+}$$

) или замещенные ионы аммония (например, $$C{H}_{3}N{H}_3^{+}$$

). Alum used as a coacervate are double salts, crystalline sulfates of tri- and monovalent metals of the general formula $$M_2^{+}S{O}_{\mathrm{four}}^{2-}{M}_2^{3+}{(S{O}_{\mathrm{four}})}_3^{2-}\cdot 24H_{2}O$$

or $$M^{+}{M}^{3+}{(S{O}_{\mathrm{four}})}_2^{2-}\cdot 12H_{2}O$$

where M ⁺ is one of the alkali metals (lithium, sodium, potassium, rubidium or cesium), and M ³⁺ is one of the trivalent metals (usually aluminum, chromium or iron (III)). Ammonium ions can also play the role of M ⁺ ( $$N{H}_{\mathrm{four}}^{+}$$

) or substituted ammonium ions (e.g. $$C{H}_{3}N{H}_3^{+}$$

)

The hydrophilicity of alum makes it possible to provide gel formation in the shortest possible time, thereby preventing washing off of the deposited layer upon subsequent immersion in a suspension of refractory filler in a binder solution. In this case, the chemical nature of the binder does not change, which preserves its adhesive ability and, as a result, provides high strength properties of the shell material. At the same time, the probability of swelling of the previous layer is minimized when it is wetted by the next layer, leading to warping and swelling of the shell.

In addition, during subsequent calcination of the shell mold, the presence of alum helps to achieve maximum mold strength due to the loss of crystallization water during thermal exposure.

The content of alum in an amount of less than 0.5% by weight of the dusting does not provide the indicated effects and sharply reduces the quality of the shell mold for warping and peeling. The content of alum in an amount of more than 1.5% by weight of the dusting contributes to the saturation of the mold material with sulfate compounds, reduces the environmental safety of the process and is not economically feasible.

An example of the method

 For the manufacture of a refractory slurry, a ready-made binder GS-20E TU 6-02-1-046-95 and marshalite (pulverized silica) of grade A and B according to GOST 9077-82 were used. If necessary, nitric acid was used to adjust the binder to the working viscosity.

As a granular material for dusting the first layer, quartz sand of grade 1K ₂ O ₂ 02 GOST 2138-91 with the addition of powder of alum-potassium alum GOST 15028-77 (chemical formula KAl (SO ₄ ) ₂ · 12H ₂ O) in an amount of 0.5- 1.5% by weight of dusting. For the manufacture of subsequent layers, in addition to the last, quartz sand of the grade 1K ₁ O ₁ 03 GOST 2138-91 with the addition of the same amount of alum-potassium powder was used. For the manufacture of the last layer, quartz sand of grade 1K ₁ O ₁ 03 GOST 2138-91 without adding alum was used.

Uniform coating of the surface of the model block with a refractory suspension was carried out layer by layer by 2-3 times immersing the block in the working capacity of the hydrolyzer in order to remove air bubbles from the surface of the block and allowing excess suspension to run off. Granular material was sprinkled with all layers of the shell form, except for the last, in a pseudo-boiling stream in a sandblast.

Each layer was dried in air at a temperature of 22-28 ° C and humidity not higher than 60%. The total number of shell-shaped layers is five.

During the formation of each layer of the form in air, potassium alum binds crystallization water for a relatively short time, which allows the layers to be applied one after another at time intervals for an exposure time of each layer of 2.0-2.5 hours.

The models were refined with hot water at a temperature of 90-99 ° С. Then, shell forms were formed into calcining flasks using shells as a filler of ground ceramic battle. Calcination of shell forms in the support filler was carried out in a calcining furnace СНО 8.16.5 / 10И2.

Tests have shown the effectiveness of the proposed method with high quality shell forms.

Information sources

1. USSR Copyright Certificate No. 1507510, class B22 C9 / 00, 9/12, 1989.

2. USSR copyright certificate No. 1445848, class. B22 C9 / 04, 9/12, 1988.

3. Patent for the invention of the Russian Federation No. 2368452, class. B22 C1 / 04, 2009.

4. Patent for the invention of the Russian Federation No. 2025192, class. B22 C9 / 04, 1994 - prototype.

5. Lost wax casting / Ya.I. Shklennik [et al.]; under the editorship of ME AND. Shklennika, V.A. Ozerova. - M .: Mashgiz, 1961 .-- 455 p.

Claims (2)

 1. A method of manufacturing shell ceramic molds for the production of precision castings according to removable models, including layer-by-layer coating of shells on a model by immersing the model in a suspension of refractory filler and a solution of a binder and subsequent sprinkling with granular material, coacervation of each layer except the last one, removing models and calcining the shells characterized in that the coacervate is introduced into the composition of the sprinkled granular material in an amount of 0.5-1.0 wt.%. 2. The method according to p. 1, characterized in that alum is used as a coacervate.