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INVENTION
Russian Federation Patent RU2129932
Mixture for ceramic molds and cores AT production of castings from ferrous and precious alloy and method of its preparation
Name of applicant: Chelyabinsk State Technical University
Name of the inventor: LG Znamensky .; Kulakov, BA .; Krymsky VV .; Smolko VA .; Dubrovin VK .; Erdakov IN
The name of the patentee: Chelyabinsk State Technical University
Address for correspondence: 454080, Chelyabinsk, Lenina, 76, CSTU, Technical Department
Starting date of the patent: 1998.03.02
The invention relates to foundry and can be used mainly in the production of castings of art and jewelry. The mixture contains, by weight. %: 10,0-14,0 gypsum, Dinas 50,0-63,0, powdered sublimate 3,7-7,0 fireclay production, alyumohromfosfatnoe 0,003-0,02 binder and -water else. Before mixing the ingredients to make processing of aqueous binder alyumohromfosfatnogo nanosecond electromagnetic pulses. This reduces the viscosity of the gypsum mixture. Provides increased durability and precision ceramic molds and cores, and thus the quality of castings.
DESCRIPTION OF THE INVENTION
The invention relates to the field of foundry and may be used in the manufacture of ceramic molds and cores, mainly in the production of castings art and jewelery of precious and non-ferrous alloys.
Currently, art and jewelery casting alloys, non-ferrous and precious metals most widely imported gypsum mixture "K-90", "Superkast" "Satinkast", "Ultravest" / 1, 2 /. Such mixtures are characterized by molding processability operations knockout and cleaning castings. However, these mixtures are expensive, and a high content of gypsum, having a tendency to degrade at 650 o C or higher results in a reduction of strength of ceramic forms at high temperatures.
The closest in technical essence is the method of preparation and composition of a mixture for the manufacture of ceramic molds comprising mixing gypsum DINACYT, orthophosphoric acid and water followed by treatment vibrovakuumnoy mixture with the following ratio of ingredients, wt% / 3 /.:
gypsum - 10 ... 12;
Dinas - 60 ... 64;
Phosphoric acid - 0.03 ... 1.0;
water - the rest.
The known solution provides stability rheological properties of the mixture.
However, the prototype has the following significant drawbacks:
- unsatisfactory level of strength and precision ceramic molds and cores, particularly for the manufacture of large-sized armchair art and jewelry castings;
- expansion of gypsum-earths mixture in the temperature range 150 ... 300 o C, uncompensated shrinkage plaster, violates the accuracy of the ceramic molds and cores;
- reduced level of strength values of the mixture after its vibrovakuumnoy processing that reduces fidelity microrelief patterns;
- increased sedimentation of the mixture, causing the non-technological operations forming tonkorelefnyh castings;
- decrease in strength of the mixture while hot from the decomposition of gypsum - a single binder.
Insufficient strength and rheological properties of the mixture and its method of preparation, taken as a prototype, determine the decline in the quality and increased marriage armchair art and jewelry castings increasing their weight and complexity of the configuration.
The object of the invention to create such a mixture and a method of preparation that would provide higher strength and precision ceramic molds and cores, especially in hot conditions, and thus improved the quality of manufacturing very complex configuration of art and jewelry castings, non-ferrous and precious alloys.
This problem is solved in such a way that the mixture for the manufacture of ceramic molds and cores used mainly in the production of castings art and jewelery of precious and base alloy comprising gypsum, dynasties and a mixing a phosphorus additive and water, according to the invention further comprises a fumed sublimate fireclay production, and as phosphorus-containing additives a mixing alyumohromfosfatnoe binder (AHFS) with the following ratio of ingredients, wt.%:
gypsum - 10 ... 14;
Dinas - 50 ... 63;
sublimate powdered fireclay production - 3.7 ... 7.0;
alyumohromfosfatnoe binder - 0.003 ... 0.02;
water - the rest.
Providing a mixture of pulverized chamotte sublimate production due to the additional expansion compensation DINACYT gypsum by heating reduces the thermal linear expansion coefficient (thermal linear expansion factor) molds and cores, improving their accuracy and strength due to high dispersion values, and the specific surface area of said processing aid.
Reduced thermal linear expansion factor and improved at the expense of precision ceramic molds and cores during casting of non-ferrous and precious alloys are largely determined mullitization pulverized sublimate fireclay production flows according to X-ray diffraction (DRON-4) at a temperature calcination (700 ... 750 o C) under the catalytic action of CaO, gypsum formed in the decomposition during heating.
The chemical composition of the sublimate pulverized refractory production is shown in Table 1.
The pulverized sublimate fireclay production is going on in the system electrostatic kiln for the production of refractory products, nedefitsiten, available in large enough quantities.
Introduction of the binder mixture alyumohromfosfatnogo (AHFS) being a high temperature binder material, creates the conditions for the formation of high strength and precision ceramic plaster molds and cores, especially at elevated temperatures.
Use as a mixing an aqueous solution of AHFS having an acidic environment provides the required survivability plaster mixes (15 ... 25 minutes) to enable it to effectively carry out treatment to remove vibrovakuumnuyu complicit in the air and a good seal in a snap.
This object is achieved by the fact that in the process of preparing the mixture for the manufacture of ceramic molds and cores used mainly in the production of castings art and jewelery of precious and base alloy, comprising mixing ingredients mixture and vibrovakuumirovanie according to the invention, prior to mixing, the processing a mixing mixture nanosecond electromagnetic impulses (NEMI). Moreover NEMI AHFS treated aqueous solution for 15 ... 25 min.
Impact NEMI destroys the hydration shell of the colloidal particles AHFS and significantly reduces the viscosity of a mixing plaster mixture. As a result, it is possible for a given flow of the gypsum slurry to increase its filling, reducing vodomassovoe ratio, which increases the strength and crack resistance of ceramic molds and cores.
In addition, due to "liquefy" the gypsum slurry under the influence of NEMI manages at constant vodomassovom respect to increase the fluidity of the mixture and thereby improve the reproducibility tonkorelefnoy surface models and workmanship and artistic jewelry castings.
Preparing a mixture for the manufacture of ceramic molds and cores as follows. Estimated number of AHFS (TU 6-18-166-78) and water is stirred and treated NEMI for 15 ... 25 min.
NEMI exposure duration of less than 15 minutes does not lead to the desired level of processing aid mixture as well in excess of 25 minutes a mixing processing of a further marked increase physical and mechanical properties of molds and cores virtually not observed.
Then, prepare a dry mixture of plaster and pulverized sublimate Dinas refractory production by mixing these ingredients.
Before the actual manufacturing of molds and cores are introduced into a mixing dry mixture - prepared aqueous solution AHFS treated NEMI in an amount of 360 ... 400 ml per 1 kg of dry components. The mixture was stirred and vibrovakuumnoy treated for 3 ... 4 m. Then the mixture may be used for making molds and cores.
The content of the proposed mixture of pulverized sublimate fireclay production is less than 3.7 wt.% Is not sufficient to significantly reduce the thermal linear expansion factor and increase the accuracy of ceramic molds and cores during calcination. The introduction of highly dispersed mixture of said processing aid in an amount of more than 7 wt.% Is necessary to increase the content of a mixing to achieve the desired flowability of the mixture, which adversely affects the crack resistance of ceramic molds and cores.
Number of AHFS in the mixture -. 0.003 ... 0.02% by weight is optimal from the standpoint of obtaining the required strength characteristics of ceramic molds and cores and the optimal duration of curing mixture needed to fill it with the aim of improving the quality of the surface tonkorelefnoy art and jewelry castings.
The developed composition and method of preparation is preferable to use a mixture of high-strength gypsum marks 250 ... 300 Samara Plaster kombinata and Dinas brand ED Pervouralsk Silica Plant. Furthermore, it may be used crushed and sieved fight silica brick, which is waste product when replacing the lining of metallurgical furnaces.
The proposed composition and method of preparing a mixture for the manufacture of ceramic molds and cores are illustrated by the following examples.
example 1
Prepare a dry mixture of plaster and pulverized sublimate Dinas refractory production. Before the production of molds and cores in a mixing mixture is introduced - AHFS previously prepared aqueous solution in an amount of 380 ml per 1 kg of dry constituents, followed by stirring and vibrovakuumnoy treatment for 3 ... 4 m.
Apply with a vibration amplitude of 0.3 ... 0.55 mm and a frequency of 50 Hz. Vacuum is maintained in the vessel with gypsum suspension with a residual air pressure of 1400 Pa / 2 /.
Parallel to obtain comparative data is carried out according to the preparation of a mixture of plaster prototype, observing the same content of the suspension and the indicated parameters vibrovakuumnoy mixture processing.
The prepared mixture is used for determining the rheological properties, producing ceramic molds and cores with fixing their physico-mechanical properties.
The indicators for comparison are the flow and duration of hardening of the gypsum slurry, the coefficients of thermal linear expansion (thermal linear expansion factor) in the temperature range 20 ... 300 o C, the strength and osypaemost ceramic samples.
Flowability was evaluated using the procedure Suttarda, diameter rastecheniya 250 ml of suspension in a standard lifting sleeve (height and diameter 50 mm) with a mixture of gypsum, after which mixing took 8 minutes / 4 /.
The curing of the gypsum slurry using fixed Vicat needle / 4 /.
Thermal linear expansion factor is determined on the dilatometer "PAULIK", using ceramic samples 5 mm in diameter and 30 mm height.
Durability was evaluated ceramics, testing on samples measuring bending (40x20x5) · 10 -3 m after drying in air and heated at a temperature of 700 o C.
Osypaemost determined on standard specimens height and a diameter of 50 mm in accordance with GOST 23409.9-78.
The test results are shown in Table mixtures. 3.
example 2
Analogously to Example 1, a mixture for the production of ceramic molds and cores from the 2 (see. Table 2) shows the optimum processing properties. However, a method podyutovki gypsum mixture, in which a mixing prior to introducing it into the dry ingredients treated elekromagnitnymi nanosecond pulses (NEMI).
To do this in a container of a mixing - aqueous AHFS establish an emitter connected to the generator NEMI / 5/1 MW in a pulse repetition frequency of 1000 Hz.
The radiator is made in the form of a pyramid size (10x10x15) · 10 -2 m of copper. The duration of treatment of an aqueous solution of AHFS nanosecond electromagnetic pulses varies: 15, 20 and 25 minutes. NEMI influence on the properties of plasters is shown in Table. 4.
Table. 4 shows the values of strength of ceramic samples made by the inventive method, when filling a gypsum slurry: 360 ml of a mixing 1 kg dry constituents.
NEMI treatment has the effect of "diluting" effect on a mixing, increasing its sedimentation stability due to the destruction of hydration shells of colloidal particles of an aqueous solution of AHFS. As a result, while maintaining optimal manages fluidity of the gypsum slurry (140 ... 160 mm) to reduce the amount of a mixing 1 kg of the dry ingredients and thereby provide a higher strength ceramic molds and cores.
The test results show that in comparison with the prototype and the method claimed composition allow preparation of a mixture of 40 ... 50% increase for the same fluidity suspension filling and maintaining optimal curing duration, 6 or more times to reduce the thermal linear expansion factor, and virtually eliminate osypaemost 1, 2.0 ... 5 times to increase the strength of ceramic molds and cores.
Mixture and method of its preparation have been tested in art and jewelery investment casting on the nomenclature of castings, characterized by an increased weight and complexity of the micro-relief, showing improvement in the quality of their production.
Thus, the inventive mixture and the method of preparation allows to obtain high-precision plaster molds and cores with improved physical and mechanical properties. Efficiency is achieved by special processing aids - not scarce low cost production of refractory waste (production pulverized chamotte sublimate) in combination with the designed composition and a mixing processing nanosecond electromagnetic pulses to provide improved rheological properties of the mixture.
The composition and method of preparation of the mixture is recommended for the production of castings of art and jewelry of precious and non-ferrous alloys. However, given the accuracy of the forms and their higher mechanical properties, a mixture and a method of its preparation may be used in dental practice, in the manufacture of other products in the precision casting of ferrous alloys.
BIBLIOGRAPHY
1. Urvachev VP, VV Kochetkov, Gorin NB Jewelry and art investment casting of copper alloys. - Chelyabinsk Metallurgy. -1991. To -168.
2. Magnitsky OP, Piraino VY Art Casting. - SPb .: Polytechnic. -1996. -213 With.
3. The copyright certificate N 904869. 15.02.82 B 22 C 1/16. The mixture for the manufacture of molds for investment casting / Kondakov EN, Smirnov AA, Starchenko IP et al. Bull. N 6, 1982. C. 59 (prototype). B 21 J 15/38.
4. Gutov LA Bablyak EL, Izoyko AP Art Casting of precious metals. - L .: Engineering, 1988. - 224 p.
5. Patent RF N 1757088. shaper of nanosecond pulses / Belkin BC, GI Shulzhenko Bull. N 31, 1992. - p. 226. 23.08.92 H 03 K 5/01, Institute of poison. f. SB RAS.
CLAIM
1. A mixture for the manufacture of ceramic molds and cores in the production of castings of non-ferrous and precious alloys, comprising gypsum, water and dynasties, characterized in that it further comprises a sublimate pulverized chamotte alyumohromfosfatnoe production and binder in the following ratio of ingredients, wt.%:
Gypsum - 10 - 14
Dinas - 50 - 63
The pulverized sublimate fireclay production - 3.7 - 7.0
Alyumohromfosfatnoe binder - 0.003 - 0.02
Water - The rest
2. A method for preparing a mixture for the manufacture of ceramic molds and cores in the production of castings of non-ferrous and precious alloys, comprising mixing ingredients vibrovakuumirovanie mixture and wherein the mixture has the following composition, wt.%:
Gypsum - 10 - 14
Dinas - 50 - 63
The pulverized sublimate fireclay production - 3.7 - 7.0
Alyumohromfosfatnoe binder - 0.003 - 0.02
Water - The rest
and before mixing the ingredients, the processing of an aqueous solution of the binder alyumohromfosfatnogo nanosecond electromagnetic pulses.
3. A method according to claim 2, characterized in that the treatment of the aqueous solution of the binder alyumohromfosfatnogo nanosecond electromagnetic pulses is carried out for 15 -. 25 min.
print version
Publication date 02.01.2007gg
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