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INVENTION
Patent of the Russian Federation RU2252103
MIXTURE FOREQUARTERS AND FIRES FOR MANUFACTURING CASTINGS ON PERFORMED MODELS

MIXTURE Self-hardening self-pouring mix for molds and rods in casting over cast models. ORNAMENTS. JEWELRY. GOLD. PLATINUM. DIAMOND. BRILLIANT. KNOW HOW. TREATMENT. BREAKDOWN. PRECIOUS STONE. DIAMOND. INTRODUCTION. PATENT. TECHNOLOGIES.

INVENTION. MIXTURE Self-hardening self-pouring mix for molds and rods in casting over cast models. Patent of the Russian Federation RU2252103

Applicant's Name: South Ural State University (RU)
The name of the inventor: Dubrovin V.K. (RU); Kulakov B.A. (RU); Karpinsky A.V. (RU); Znamensky L.G. (RU); Erdakov I.N. (RU); Ivochkina O.V. (RU)
The name of the patent holder: South Ural State University (RU)
Address for correspondence: 454080, Chelyabinsk, pr-kt them. IN AND. Lenina, 76, SUSU, technical department
Date of commencement of the patent: 2004.02.16

The invention can be used in the production of artistic, jewelry and technical castings from non-ferrous and ferrous alloys by casting on investment models. Portland cement is used as a binder in the mixture, fine quartz sand is used as the filler. To improve the rheological and technological properties, the additive - aluminum nitrate 9 - is used. The shutter is water. The components are taken in the following ratio, weight: Portland cement 12.72 ... 17.90, fine quartz sand 53.00 ... 58.80, aluminum nitrate nine-water 1.79 ... 3.18, water - the rest.

DESCRIPTION OF THE INVENTION

The invention relates to the field of foundry production and can be used in the manufacture of molds and rods in the production of both artistic and jewelry, as well as technical castings of non-ferrous and ferrous alloys obtained by investment casting (LWM).

At present, in art and jewelry casting, mixtures with a gypsum binder (1 / a) and mixtures based on hydrolysed ethylsilicate (ETC) / 2 / are most widely used.

However, the former do not allow the production of castings of ferrous metals with a high pouring temperature. Gypsum is unstable at temperatures above 1200 ° C, and iron is the catalyst for its decomposition; therefore, when casting, for example, cast iron, gypsum decomposes with the release of gaseous reaction products (SO 3 , SO 2 ), which affect the castings with gas shells over the entire surface.

The production of castings in shell molds based on ETS has a number of disadvantages:

  • Duration and multi-stage formation of a multilayer shell;
  • Expensive components of the binder - ethyl silicate and alcohol;
  • Harmful and fire hazardous working conditions in connection with the use of ethyl silicate binder.

The closest in technical essence is the self-curing mixture with cement as a binder (3, p.116). According to the aforementioned prototype, the mixture includes quartz sand, Portland cement, surfactant, aluminum sulfate, sodium silicate and water with the following ratio of the ingredients, by weight:

  • Portland cement 12.72 ... 17.90;
  • Fine quartz sand 53,00 ... 58,80;
  • Aluminum nitrate nine-fold 1.79 ... 3.18;
  • Water - the rest.

The principle of manufacturing volumetric molds in casting for investment models is that the finished model unit installed in the flask is poured with a molding mass. Therefore, in its consistency, the molding mass must be a slurry with a good liquidity. The same technical solution contains a small amount of a water curtain, which does not provide the necessary fluidity of the molding mixture, which allows filling all the undercuts of the model.

The molding mixture of this composition makes it possible to obtain castings from ferrous alloys in industrial production by constant models.

At the same time, the prototype has the following significant drawbacks:

  • Unsatisfactory rheological properties of the mixture as applied to investment casting, its inability to completely fill the working volume of the flask and the internal cavity of the model (to form a rod), especially in the manufacture of difficult-profile castings with a developed surface, the presence of undercuts, hard-to-pour cavities due to low fluidity of the mixture.
  • The prototype mixture does not provide for heating, and after calcination it has low strength, hence the form is destroyed when it is poured with metal, and as a result, the castings are brazenly clogged, distorted in shape and geometric dimensions and, ultimately, impossible to obtain a high-quality casting by casting Melted models.
  • The presence of a coke on the castings of ferrous metals due to the interaction of the cast alloy with the liquid glass.
  • The use of unmilled quartz sand in the mixture gives castings with an increased roughness of the surface.

Multicomponent mixture implies the complexity of the process of its preparation. Thus, the mixture of the prototype does not allow to obtain high-quality castings from both black and non-ferrous alloys by the method of investment casting.

The aim of the invention is to create such self-priming self-hardening mixture for manufacturing castings from ferrous and non-ferrous alloys for investment models that would ensure the production of high-quality castings, mainly difficult-profile ones due to optimal technological and physical-mechanical properties of shapes and rods (rheology, strength, crack resistance , Temperature coefficient of linear expansion, knockout) and the stability of the manufacturing process. The new technological process should be less labor-intensive, while the cost of manufacturing products should be lower than in similar methods.

This aim is achieved by the fact that a mixture of self-hardening for making molds and rods in the manufacture of castings for investment models, including a fine filler based on silica, portland cement and water, according to the invention, contains nine nitrate aluminum nitrate with the following ratio of said ingredients, by weight:

  • Portland cement 12.72 ... 17.90;
  • Fine quartz sand 53,00 ... 58,80;
  • Aluminum nitrate nine-fold 1.79 ... 3.18;
  • Water - the rest.

Aluminum nitrate nine-GOST 3757-75 is introduced by dissolving it in tap water or distilled water during the preparation of the molding mixture. The additive shortens the time of thickening of the mixture, since aluminum nitrate accelerates the process of the formation of crystalline hydrates of cement, and acts as a binder itself, enveloping the filler particles. This leads to the absence of sedimentation in the aqueous quench, ensuring the stability of the properties of the slurry on the cement binder, and the simplicity of its composition and ease of introduction of aluminum nitrate simplify the process compared to the prototype. When calcining forms, aluminum nitrate decomposes in the temperature range 150-200 ° C with the formation of nitrogen oxides and Al 2 O 3 , which increases the porosity of the forms and prevents cracking. And the additive improves the knockoutability of the molding mixture by both increasing the porosity and by decreasing the residual strength, most likely due to a change in the growth pattern of the crystal hydrates. At the same time, the strength remains at a sufficient level, ensuring the pouring of metal and the high quality of the molds.

In the claimed technical solution, in comparison with the prototype, the content of the shutter is increased by almost four times, which makes the mixture a suspension in a consistency suitable for manufacturing liquid bulk molds for casting both small and large-sized products.

Dispersing of quartz sand particles to grain size of 50 ... 160 μm provides high quality of the print of forms on the cement binder, as well as their required physical and mechanical characteristics. In this case, the dispersion can be carried out by simple grinding of quartz sand, for example grades 3K 3 O 2 O 3 or 5K 3 O 2 O 3 (GOST 213 8-91).

The use of Portland cement as a binder allows to obtain castings from ferrous alloys with a high pouring temperature, because cement, in contrast to gypsum, is much more resistant to high temperatures.

Preparation of the claimed mixture for the manufacture of molds and rods on a cement binder in the manufacture of castings from non-ferrous, black and precious alloys is carried out as follows. An estimated amount of Portland cement and dispersed quartz sand is hung. Then, the necessary amount of water is measured and the necessary amount of aluminum nitrate is dissolved therein.

Before the manufacture of molds and rods in a previously prepared shutter, 360 ... 380 ml of the shutter per 1 kg of dry constituents are covered with portland cement, mixed for 0.5-1 minutes and then sand is poured. The mixture is then thoroughly mixed at a rotational speed of 3000 ... 6000 rpm. After that, the slurry is used to make shapes and rods. If a mixture of a sufficient level of fluidity is lost, it is possible to dilute it again with additional stirring. After manufacturing, the mold is dried, then the model composition is extruded (removed) by hot air at a temperature of 120-160 ° C and mold calcination at 550 ° -700 ° C. The temperature of the molds before casting the metal is reduced to 400-500 ° C.

The content in the proposed mixture of portland cement is less than 12.72% by weight, leads to an increase in the time of its thickening, which in turn negatively affects the strength, the precipitability of the finished forms and the sedimentation stability of the molding mixture itself, and to the quality of the surface of the finished casting. The reason for this is the lack of binder material in the molding mixture. On the contrary, the content of Portland cement is more than 17.90% by weight, leads to an excessive increase in strength and deterioration in knockout, and a rise in the cost of the molding mixture.

The amount of nitrate of nine-lead aluminum in the mixture of 1.79 ... 3.18% by weight is optimal from the point of view of mixture survivability, maximum sedimentation stability of the slurry, low mold sagging and easy knocking out of the molding mixture. The content in the mixture of aluminum nitrate less than 1.79% by weight leads to an excessive increase in the time of the beginning of solidification of the mixture, its stratification, as well as the difficulty in knocking mold castings out of the high strength of the mixture after casting them with metal. The content of aluminum nitrate more than 3.18% leads to a rapid setting of the mixture, that is, to a loss of the ability to mix, fill the cavity of the flask and, consequently, the impossibility of obtaining high-quality castings.

And these properties of the suspension and the finished form are affected by the shutter (water), the optimum amount of which is in the range of 36-38 wt. By 100% by weight. H of the dry components of the mixture.

In the claimed composition it is recommended to use portland cement according to GOST 10178-85.

The proposed composition of a mixture for making molds and rods on a cement binder is illustrated by the following example.

Example. Prepare a dry mixture of portland cement grade PC-400 (GOST 10178-85) and dispersed quartz sand. Then we weigh the aluminum nitrate and dissolve it in the distilled water, then add the dry mixture itself, followed by stirring for 1.5-2 minutes.

In parallel, to obtain comparative data, the mixture is prepared on a cement binder according to the prior art. Compositions of the mixtures are given in Table 1.

Prepared mixtures are used to make molds and rods on a cement binder with fixation of their physico-mechanical properties.

The parameters for comparison are the coefficient of thermal linear expansion (KTLR) of the mixture in the temperature range 20 ... 700 ° С, the compressive strength of the molds after drying and after calcination, the incidence of the molding mixture after calcining the molds, the roughness of the surface of the castings obtained in these molds.

KTLR was determined on a PAULIK dilatometer using samples 5 mm in diameter and 30 mm in height.

The strength of the molds was determined by compressing standard samples with a diameter and height of 50 mm after holding in air after 24 and 72 hours, after calcination (700 ° C, 3 hours) and cooling to room temperature.

The sintering of the molding mixture was evaluated according to the standard procedure on a Model 056 instrument for determining the shedding of molding mixtures.

The roughness of bronze castings of BrO5C5S5 was determined on the profilometer of model 296.

The results of the tests of the mixtures are given in Table 2.

The test results show that, in comparison with the prototype, the claimed composition of the mixture makes it possible to reduce the KTLR by 1.2-1.5 times, increase the strength of the molds after calcination by 6-10 times to a level that ensures the production of high-quality castings and prevents the destruction of the mold during pouring Metal, reduce the sagging of molds after calcining and improve the quality of the casting surface by 2-16 times.

The mixture passed industrial tests at CJSC "Ural Bronze" (Chelyabinsk) on a wide range of artistic castings weighing from 50 g to 80 kg. Qualitative castings were obtained, the cost price of which is 1.8-2 times lower than when produced in shell molds based on hydrolysed ethylsilicate.

Considering the improved complex of technological properties of the mixture, its universal nature, the claimed composition can be used in precise casting practically at any enterprise of the country.

BIBLIOGRAPHY

1. Patent of the Russian Federation No. 2175909. Mixture for the manufacture of molds and rods on a gypsum binder for the production of castings from non-ferrous and precious alloys / Erdakov IN, Znamensky LG, Kulakov BA, Dubrovin VK, etc. Bul. № 32, 2000.

2. Magnitsky ON, Pirainen V.Yu. Artistic casting. - St. Petersburg: Politechnica, 1996. - 213 p.

3. Doroshenko S.P., Vashchenko K.I. Наливная формовка: Monograph .: - Киев: Вища школа. Head Publishing House, 1980. - 176 p.

CLAIM

Mixture self-hardening for making molds and rods in the production of castings for investment models, including a fine filler based on silica, Portland cement and water, characterized in that it additionally contains nine-aqueous aluminum nitrate with the following ratio of the indicated ingredients, mass%:

  • Portland cement 12,72-17,90
  • Fine quartz sand 53,00-58,80
  • Aluminum nitrate nine-lead 1,79-3,18
  • Water Other

print version
Date of publication 03.01.2007gg