RU2385782C1 - Mix for manufacturing of shapes and rods in precision casting and method of its manufacturing - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the field of casting production. Mix contains the following components, wt %: alumina-boron-phosphate concentrate 15-20; fine-dispersed quartz sand 54-60; haydite 10-15; powdery hardener - periclase 1-2; water - the rest. Preliminarily aqueous solution of alumina-boron-phosphate concentrate is prepared with a density of 1250 - 1350 kg/m³. Fine-dispersed quartz sand and haydite are introduced in it. Treatment with nanosecond electromagnet pulses is carried out with a specific capacity of 600-1000 MW/m³ with further mixing of specified ingredients and introduction of powdery hardener of binder.

EFFECT: improved strength, gas permeability and crack resistance of shapes in process of tempering.

2 cl, 3 tbl, 2 ex

Description

The invention relates to the field of foundry and can be used in the manufacture of ceramic molds and cores in the production of non-ferrous and ferrous metals by investment casting (LWM) of art, jewelry and technical castings.

Currently, in art and jewelry casting, mixtures on a gypsum binder are most widely used (RU 2175902. A mixture for the manufacture of molds and cores on gypsum binder in the manufacture of castings from non-ferrous and precious alloys. Erdakov IN, Znamensky LG, Kulakov B.A. et al. Bulletin of Inventions No. 32, 2000), as well as mixtures based on hydrolyzed ethyl silicate (ETS) (Magnitsky ON, Pirainen V.Yu. Artistic casting. - St. Petersburg: Polytechnic, 1996. - S.151 ... 164).

However, the former do not allow producing castings from ferrous alloys with a high pouring temperature. Gypsum is unstable at temperatures above 1200 ° C, and iron and silica are the catalysts for its decomposition, therefore, when casting, for example, cast iron into gypsum-siliceous forms, gypsum decomposes with the release of gaseous reaction products (SO ₃ , SO ₂ ), which affect castings by gas shells throughout surface.

The production of shell ceramic forms based on ETS, widely used for computer-aided technical castings, has a number of disadvantages, such as:

- the use of expensive equipment (metal molds and core boxes), the duration and complexity of their manufacture, which makes the use of the process unprofitable in single and small-scale production;

- the duration, multioperation and increased complexity of manufacturing a multilayer ceramic shell;

- fire hazard and environmental degradation in the workshop when preparing a binder (hydrolysis of ETS) from components: ethyl silicate, alcohol, acid solutions, as well as the high cost of these materials.

The closest in technical essence is a self-hardening liquid mixture for the manufacture of molds and cores in the production of investment castings (RU No. 2252103. Self-hardening liquid bulk mixture for the manufacture of molds and cores in the production of investment castings. VK Dubrovin, B.A. Kulakov ., Karpinsky A.V. et al. Bulletin of inventions No. 14, 2005). In accordance with the specified prototype, the mixture includes Portland cement, fine quartz sand, aluminum nitrate and water in the following ratio of ingredients, wt.%:

Portland cement 12.72 ... 17.90 fine quartz sand 53.00 ... 58.80 aluminum nitrate 1.79 ... 3.18 water rest

The principle of manufacturing three-dimensional molds from such a mixture in investment casting is that the finished model block obtained in the rubber split mold installed in the flask is poured with a molding compound. Therefore, by its consistency, it should be a suspension with good fluidity.

The molding mixture of the composition of the prototype makes it possible to obtain castings from alloys of ferrous and non-ferrous metals in the production of investment casting.

However, the prototype has the following significant disadvantages:

- a long cycle of shaping;

- the need for long-term drying of molds and cores (at least 3 days);

- unsatisfactory gas permeability and strength characteristics of molds and cores, including their surface strength (shedding) after calcination, especially in the manufacture of large casting for investment casting;

- low crack resistance of ceramic molds and cores during their calcination and melt pouring;

- difficulty knocking out of ceramic molds of castings, in particular large-sized complex and thin-relief.

Thus, this mixture practically does not allow to obtain high-quality large-sized complex-shaped castings from both ferrous and non-ferrous alloys by investment casting.

A known method of preparing a mixture for the manufacture of ceramic rods and molds, in which the processing of nanosecond electromagnetic pulses (NEMI) is carried out in relation to one of the components of the mixture, in particular to an aqueous solution of aluminochromophosphate binder, which is a substitute for a gypsum-siliceous mixture (RU No. 2129932. A mixture for the manufacture of ceramic molds and rods in the manufacture of castings from non-ferrous and precious alloys and a method for its preparation. Znamensky LG, Kulakov BA, Krymsky VV, etc. Bulletin eteny number 13, 1999). This provides an improvement in the rheological properties of the mixture. However, there is no possibility of a complex effect on all ingredients of the proposed composition of the mixture, therefore, the method of preparing the mixture for the manufacture of ceramic molds and cores taken as a prototype does not significantly speed up the cycle of forming, increase the physicomechanical properties of the mixture for the manufacture of precision castings made from non-ferrous, and ferrous alloys.

The technical problem is the basis of the invention - to create such a composition and method for preparing a mixture that would provide an accelerated shaping cycle, increased gas permeability, strength and crack resistance of ceramic molds and rods during calcination, their easy knockout required to improve the quality of manufacturing by casting on large-sized complex-profile and high relief castings.

The specified technical problem is solved in that the mixture for the manufacture of molds and cores in precision casting, comprising a binder, water and finely dispersed quartz sand, according to the invention contains alumina-phosphate concentrate and an additional powder hardener to it, as well as expanded clay in the following ratio of ingredients, wt. .%:

aluminum phosphate concentrate 15 ... 20 fine quartz sand 54 ... 60 expanded clay 10 ... 15 powder hardener - periclase 1 ... 2 water rest

The problem is also solved by the fact that in the method of preparing the mixture for the manufacture of molds and rods in precision casting, including mixing the ingredients of the mixture and processing with nanosecond electromagnetic pulses, according to the invention, in the preparation of the mixture of the above composition, an aqueous solution of aluminum phosphate concentrate with a density of 1250 ... 1350 kg / m ^{3 is} preliminarily prepared , then finely dispersed quartz sand and expanded clay are introduced into it, and nanosecond electromagnetic pulses with a specific power of 600 ... 1000 MW / m ^{3 are} processed with further stirring of these ingredients, followed by the introduction of a powdered binder hardener and final mixing.

The use of an alumina-borophosphate concentrate (ABPK) and its hardener (periclase) as a binder aqueous solution provides an accelerated shaping cycle (20 ... 30 min) and eliminates drying of manufactured molds and cores due to chemical hardening of the mixture.

In this case, ABPA in an aqueous medium undergoes hydrolysis with the formation of a solution of phosphoric acid, which interacts with iron on particles of finely dispersed silica sand with the release of hydrogen. This process, which proceeds at the “binder-filler” interface, and the chemical solidification of the mixture ensure the formation of a uniform porous structure of ceramic molds and rods. This structure creates the conditions for increasing their gas permeability, including after calcination.

The increase in crack resistance is ensured by the introduction of a highly porous material - expanded clay, which creates a kind of barrier that blocks the occurrence and development of cracks. Therefore, in contrast to the prototype, a minimal tendency to crack forms and cores during their calcination is achieved.

The effect of nanosecond electromagnetic pulses on the mixture of ingredients before the introduction of the hardener (periclase) can significantly improve the rheological and physico-mechanical properties of the mixture due to its electrophysical activation.

The dispersion of quartz sand particles to a grain size of 10 ... 100 microns provides high quality imprint forms, as well as their required physical and mechanical characteristics. In this case, dispersion can be carried out by grinding the initial silica sand, for example, grades 3K ₃ O ₂ 03 or 5K ₃ O ₂ 03 (GOST 2138-91) in vibrating mills with the production of finely divided filler based on silica of manufactured molds and cores.

The preparation of the inventive mixture for the manufacture of molds and cores in the manufacture of castings of non-ferrous and ferrous alloys by investment casting is carried out as follows. The calculated amount of ABFC and hardener are hung to it, expanded clay and finely dispersed quartz sand. Then measure the required amount of water and prepare an aqueous solution of ABFC density of 1250 ... 1350 kg / m ³ .

Finely dispersed quartz sand, expanded clay are poured into a pre-prepared aqueous solution of ABFC and they are mixed for 15 ... 20 min at an impeller rotation speed of 3000 ... 6000 rpm.

To improve the rheological and physico-mechanical properties of the mixture, it is treated with NEMI simultaneously with the mixing of the ingredients. For this, a copper emitter connected to a NEMI generator with parameters: 1 MW per pulse, field strength 10 ⁵ ... 10 ⁷ V / m, duration of one pulse 10 ^-9 ... 10 ^-10 s is immersed in the suspension. The estimated amount of hardener is introduced into the suspension immediately before the manufacture of molds and cores.

The content in the proposed mixture ABFC less than 15 wt.% Adversely affects the strength and shedding of the finished form, and therefore leads to a decrease in the surface quality of the finished casting. The reason for this is the lack of a binder in the sand. On the contrary, the content of ABFC more than 20 wt.% Leads to an excessive increase in strength and deterioration of knockout, as well as the cost of the molding sand.

Preliminary preparation of an aqueous solution of ABFC density

1250 ... 1350 kg / m ³ provides the required rheological properties of the mixture at the molding stage. When the density of the solution is more than 1350 kg / m ³ , the viscosity of the suspension increases significantly, which makes it difficult to qualitatively reproduce the shape of the configuration of the models, especially complex and thin-relief, for example, for art castings. When the density of the aqueous ABFC solution is less than 1250 kg / m ³ , the shedding of molds and cores sharply increases after calcination in investment casting. In addition, this leads to a decrease in sedimentation stability and stratification of the suspension at the molding stage, which leads to the low-tech nature of this operation.

The use of expanded clay in the mixture provides increased crack resistance of ceramic molds and cores in the process of calcination. However, when the amount of expanded clay in the mixture is more than 15 wt.%, The viscosity of the suspension increases significantly, and when the expanded clay content is less than 10%, the effect of reducing the tendency to form cracks and rods during calcination is weakly expressed.

The amount of hardener of the ABFC-periclase solution in the composition of the mixture 1 ... 2 wt.% Is optimal from the standpoint of ensuring the required duration of its solidification. A content of periclase in the mixture of less than 1 wt.% Leads to an excessive increase in the duration of the solidification of the mixture and its separation. A periclase content of more than 2 wt.% Causes a quick setting of the mixture, i.e. loss of ability to mix, fill the cavity of the flask and, therefore, does not allow to obtain high-quality castings.

For investment casting of particularly complex configuration of thin-relief and large-size castings, a specific power of NEMI in the range of 600 ... 1000 MW / m ^{3 is} recommended for processing the proposed mixture in order to increase its cohesive strength and fluidity. With a specific power of NEMI less than 600 MW / m ^{3 it is} not possible to significantly affect the rheological and physicomechanical properties of the mixture, and when the level of 1000 MW / m ^{3 is} exceeded, energy costs unnecessarily increase.

The proposed composition of the mixture for the manufacture of molds and rods and the method of its preparation are illustrated by the following examples.

Example 1. Prepare a dry mixture of expanded clay (GOST 9757-90) and fine quartz sand. Then we weigh ABFC (TU 113-08-606-87), dissolve it in water. Next, a dry mixture of fine sand and expanded clay is introduced into the prepared aqueous solution of ABFC with a density of 1300 kg / m ³ , followed by stirring for 15 minutes.

In parallel to obtain comparative data, the mixture is prepared according to the prototype. The compositions of the mixtures are given in table 1.

Table 1 Mixtures Name of ingredients The number of ingredients, wt.%, In mixtures prototype one 2 3 four 5 Portland cement 14.23 - - - - - Fine quartz sand 56.14 60 57 54 57 57 Aluminum Nitrate 2.49 - - - - - ABFC - fifteen eighteen twenty eighteen eighteen Periclase - 1,5 1,5 1,5 one 2 Expanded clay - 13 13 10 13 fifteen Water Rest Rest

Prepared mixtures are used for the manufacture of molds and cores with fixation of their technological (service) properties. For this, the calculated amount of hardener is introduced and the obtained self-hardening suspension is poured into the flask with a model unit installed in it. After manufacturing, the mold is kept in air for at least one hour, then the model composition is extruded (removed) with hot air at a temperature of 120 ... 160 ° С and the molds are calcined at 550 ... 700 ° С. The temperature of the molds before pouring the metal is reduced to 400 ... 500 ° C. Indicators for comparison are the duration of the solidification of the mixture, gas permeability, gas production, compressive strength of molds at various time intervals from the time of their manufacture, including during calcination, the shedding and residual strength of ceramic molds and cores, their tendency to crack (COT).

The solidification time of the mixture was determined using a Vic needle. Strength (cold, hot, residual), gas permeability, and crumbling of forms were evaluated using standard samples with a diameter and height of 50 mm. The tendency to crack ceramic forms after calcination (700 ° C, 3 h) was quantified by the area of the cracks formed, referred to the unit mass of the sample, which has the shape of a parallelepiped 100 × 50 × 30 mm in size with stress concentrators inserted inside (2 pc. 10 × 10 × 40 mm). The gas content of the samples was evaluated according to GOST 23409.12-78.

The test results of the mixtures are given in table.2. The numbers of the mixtures correspond to those given in table 1.

Example 2. Prepare analogously to example 1, a mixture of composition 2 (see table 1), which showed the most rational combination of service properties (see table 2). In this case, before the introduction of a hardener (periclase), simultaneously with mixing the ingredients of the mixture, they are treated with NEMI for 15 minutes. To do this, an emitter connected to the NEMI generator (RU No. 2030097, MKI H03K 3/33, K3 / 45. Shaper of nanosecond electromagnetic pulses. Belkin B.C., Shulzhenko GI, application. January 17, 1992) is introduced into the suspension.

The influence of NEMI on the properties of the mixture are presented in table 3.

The impact of NEMI opens up the possibility of further improving the physicomechanical properties of the mixture, in particular, significantly reducing the solidification time of the mixture, hardening it during solidification, while maintaining an acceptable range of values improved compared to the prototype gas production, gas permeability, knockability of ceramic rods and molds and their practically zero SOT.

In general, the test results show that, compared with the prototype, the claimed composition of the mixture and the method of its preparation allow more than 3 times to accelerate the shaping cycle, prevent drying of molds and cores, increase their strength by more than 10 times to a level that provides high-quality bulky castings and prevents the destruction of the mold during pouring of metal, to practically eliminate crumbling and cracking of molds after calcination, to facilitate knockout of castings from ceramic molds by more than 2 times reduce gas production and increase 6 ... 10 times the gas permeability of molds and cores. This made it possible to significantly improve the surface quality of complex, thin-relief castings in investment casting.

The mixture and the method of its preparation successfully passed industrial tests at CJSC Ural Bronze (Chelyabinsk) on a wide range of artistic castings weighing from 50 g to 150 kg, produced by investment casting. Given the improved set of technological properties of the mixture, its universal nature, the claimed composition of the mixture and the method of its preparation can be used in precision casting at virtually any enterprise in the country.

Claims (2)

1. A mixture for the manufacture of molds and cores in precision casting containing a binder, water and fine quartz sand, characterized in that it additionally contains expanded clay and a powder hardener of the binder - periclase, and as a binder it contains alumina-phosphate concentrate in the following ratio of ingredients, wt. %:
aluminum phosphate concentrate 15-20 fine quartz sand 54-60 expanded clay 10-15 powder hardener - periclase 1-2 water rest 2. A method of preparing a mixture for the manufacture of molds and cores in precision casting, including mixing the ingredients of the mixture and processing with nanosecond electromagnetic pulses, characterized in that a mixture of the following composition is prepared, wt.%:
aluminum phosphate concentrate 15-20 fine quartz sand 54-60 expanded clay 10-15 powder hardener - periclase 1-2 water rest
in this case, an aqueous solution of alumina-borophosphate concentrate with a density of 1250-1350 kg / m ³ is preliminarily prepared, finely dispersed quartz sand and expanded clay are introduced into it, nanosecond electromagnetic pulses are processed with a specific power of 600-1000 MW / m ³ with further mixing of these ingredients with the subsequent introduction of powdered hardener binder and final mixing.