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INVENTION
Russian Federation Patent RU2163854
Mixture for making molds and cores, gypsum binder in the production of castings from nonferrous and precious alloys

Name of applicant: South Ural State University
Name of the inventor: Ivochkina OV .; LG Znamensky .; Dubrovin VK .; Kulakov, BA
The name of the patentee: South Ural State University
Address for correspondence: 454080, Chelyabinsk, etc. to them.. IN AND. Lenin 76, SUSU, Technical Department
Starting date of the patent: 2000.07.12

The invention relates to a foundry. The mixture contains, in weight%: gypsum 12 - 15 Silica powder 24 - 30, optical glass production waste 24 - 30, alyumoborfosfatny concentrate 0.02 - 0.04 0.03 oxalic acid - 0.08, water - the rest.. Introduction to the mixture of waste optical glass production due to expansion compensation Dinas during heating reduces the coefficient of thermal expansion of molds and cores. Increased accuracy and strength of molds and cores. Improves the surface quality of the jewelry and artistic castings differing tonkorelefnostyu.

DESCRIPTION OF THE INVENTION

The invention relates to the field of foundry and can be used in the manufacture of molds and cores in the gypsum binder, mainly in the production of tonkorelefnyh art and jewelry castings, non-ferrous and precious alloys obtained by casting, investment casting (DML).

Currently, art and jewelery casting the most widely used mixture on gypsum binder import "K-90", "Superkast", "Ultravest" [1, 2], and the domestic and "Jewelry-1" and "Jewelry-2" [ 2]. However, imports of road mix, and domestic have a reduced level of stress of the mixture which reduces the fidelity of the microrelief patterns. In addition, a decrease in the strength of the forms of these compounds in hot conditions as a result of the decomposition of gypsum - a single binder.

The closest the technical essence is a mixture for the production of ceramic molds and cores in the production of castings from ferrous and non-precious alloys [3]. The mixture includes gypsum Silica powder pulverized chamotte sublimate production alyumohromfosfatnoe binder and water in the following ratio of ingredients, wt.%:

• Gypsum - 10 ... 14
• Silica powder - 50 ... 63
• The pulverized sublimate fireclay production - 3.7 ... 7.0
• Alyumohromfosfatnoe binder - 0,003 ... 0,020
• Water - The rest

Known mixture provides the necessary level of rheological properties (flowability, solidification time) mixture for the production of art and jewelry casting, investment casting.

However, the prototype has the following significant drawbacks:

• increased coefficient of thermal expansion of the mixture when heated to calcining temperatures is the cause of cracking molds and cores;
• low sedimentation stability of the colloidal aqueous solution alyumohromfosfatnogo binder in the composition of the mixture of the prototype does not provide the stability and rheological properties of the mixture forms on gypsum binder;
• low wettability of aqueous gypsum slurry melted waxy models reduces the reproducibility of a mixture of their configuration and disturbance tonkorelefnoy quality surface of castings;
• unsatisfactory set of strength characteristics of molds and cores, particularly in the production of art and jewelry castings, characterized by complex-and tonkorelefnostyu;
• insufficient physical and mechanical properties of molds and cores cause an increase in the marriage of art and jewelry castings clog, sagging and surface roughness.

Furthermore, in the manufacture of a mixture for removing a mixture of the prototype developed tonkorelefnyh cavities of castings is difficult, which increases the complexity and stripping operations leads to irreversible losses of precious and non-ferrous alloys.

The object of the invention to create a mix that would ensure the improvement of the physical and mechanical properties of molds and cores in the gypsum binder and stability of the process of their manufacture, but also improve the quality of the surface of the jewelry and artistic castings differing tonkorelefnostyu.

This problem is solved in such a way that the mixture for the production of molds and cores in the gypsum binder, used in the manufacture of tonkorelefnyh art and jewelry castings, non-ferrous and precious alloys, including gypsum, Silica powder, phosphorus-containing additive and water, according to the invention as phosphorus-containing additives includes alyumoborfosfatny concentrate, and a further optical glass production waste and oxalic acid, with the following ratio of ingredients, wt.%:

• Gypsum - 12 ... 15
• Silica powder - 24 ... 30
• Wastes from the manufacture of optical glasses - 24 ... 30
• Alyumoborfosfatny concentrate - 0.02 ... 0.04
• Oxalic acid - 0.03 0.08 ...
• Water - The rest

Introduction into a mixture of waste producing optical glasses (OPOS) by more with gypsum expansion compensation DINACYT on heating reduces the thermal expansion coefficient (thermal linear expansion factor) molds and cores, improving their accuracy and strength due to a significant content of said processing aid having a high performance of dispersion and specific surface.

Reduction of thermal linear expansion factor can increase the intensity of the heat treatment molds and cores on a plaster binder without damage and cracking. As a result, it is possible to reduce energy consumption and the cost of production of castings.

Reduced thermal linear expansion factor and improved at the expense of precision molds and cores on gypsum binder is largely determined by the phase composition OPOS. According to X-ray diffraction (DRON-4), said processing aid contains 40 ... 50% quartz and 60 ... 50% cristobalite.

OPOS is formed during the manufacture of high purity glasses. Its chemical composition is shown in Table. 1.

Introduction of the mixture alyumoborfosfatnogo concentrate (ABFK) being a high temperature binder, contributes to the strength of molds and cores for the gypsum binder, especially when the calcination temperature and pouring nonferrous alloys and precious.

The high sedimentation stability ABFK aqueous colloidal solution used as a mixing mixture provides stability to slurry rheology gypsum binder.

Introduction of the oxalate mixture, having the properties of a surfactant reduces the surface tension of water and a mixing provides the desired surface wettability gypsum slurry of waxy cast models. Therefore, there is a high degree of reproducibility of form very complex configuration models and quality improvement is achieved tonkorelefnoy surface of art and jewelry castings.

Preparation of applications mixture for making molds and cores on gypsum binder in the production of castings from ferrous and non-precious alloys is as follows. Stir the estimated amount ABFK (TU 113-08-606-87), oxalic acid and water to give a mixing mixture. Then, prepare a dry mixture of plaster, Dinas and optical glass production waste by mixing these ingredients.

Before the actual manufacturing of molds and cores dry mixture is poured into a mixing previously prepared from 380 ... calculating a mixing 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 OPOS less than 24 wt.% Is insufficient to substantially reduce the thermal linear expansion factor when heated to calcining temperatures. The introduction of said additive mixture in an amount of more than 30% does not provide the required level of the gypsum slurry rheological properties (flowability, solidification time).

Number ABFK mixture consisting of 0.02 ... 0.04 wt.% Is optimum from the standpoint of obtaining required strength characteristics of the molds and cores for the gypsum binder, especially at elevated temperatures, and optimum length of the curing mixture.

The content of oxalic acid in the mixture in an amount of 0.03 ... 0.08 wt.% Causes a phenomenon of surface wettability waxy slurry cast models. Introduction of oxalic acid in an amount of more than 0.08% leads to the release of gases during the preparation for the gypsum slurry binder.

The inventive composition is preferable to use high-strength gypsum brands G-16 (GOST 125-79) and higher Samara Plaster Plant and Dinas Ed Markey (GOST 1566-71) 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 of the mixture for the production of molds and cores in the gypsum binder is illustrated by the following example.

Example
Prepare a dry mixture of plaster brand G-16 (GOST 125-79), of silica powder and waste production of optical glass. Before the production of molds and cores in the dry mixture is a mixing - previously prepared aqueous ABFK (TU 113-08-606-87) and oxalic acid - in an amount of 380 ml per 1 kg of dry constituents, followed by stirring and vibrovakuumnoy treatment for 3 .. .4 minutes. Applied vibration with an amplitude of 0.3. . .0,55 Mm and a frequency of 50 Hz. Maintain the vacuum in the vessel with gypsum suspension with a residual air pressure of 1400 Pa [2].

Parallel to obtain comparative data exercise preparing a mixture of gypsum binder according to the prototype, following the suspension of the same content and these parameters vibrovakuumnoy mixture processing. Compositions of the mixtures are shown in Table. 2.

The prepared mixture is used for making molds and cores for gypsum binder with fixing their physico-mechanical properties.

The indicators for comparison are the thermal coefficient of linear expansion (thermal linear expansion factor) of the mixture in the temperature range 20 ... 800 ^{o C,} wetting ability and a mixing sedimentation stability, strength in compression form after drying and the residual (characterizes vybivaemost mixture).

Thermal linear expansion factor is determined on the dilatometer "PAULIK", using a specimen of 5 mm in diameter and 30 mm height.

Wettability was evaluated by a mixing method known capillary impregnation of porous media. To this tube was measured 5 mm in diameter and 300 mm height equilibrium height impregnating a mixing preformed mixture of quartz sand 2K ₁₃ O 03 (GOST 2138-91) and pulverized quartz of grade A (GOST 9077-82) in the ratio 3: 1 by weight. The more the equilibrium height of a mixing impregnating the porous medium, the better its wetting ability and the higher the degree of playback on a mixture of gypsum binder tonkorelefnoy surface models.

A mixing Sedimentation was assessed in accordance with GOST 80772-78.

Durability forms were determined on compression testing standard specimens diameter and 50 mm in height after drying in air and after calcination (700 ^{o C,} 2 hours), and cool to room temperature.

The test results are shown in Table mixtures. 3.

The test results show that compared with the prior art composition of the mixture claimed allows more than two-fold decrease in thermal linear expansion factor, to provide a gypsum slurry tonkorelefnoy wettability of the surface models and the formation and stability of the rheological properties of the mixture due to a significant increase in a mixing sedimentation stability. and create conditions to improve the strength characteristics of the molds and cores by 30 ... 40% while improving their vybivaemosti.

The mixture was tested in art and jewelery investment casting to casting nomenclature differing tonkorelefnostyu and highly complex configuration, showing improvement in the quality of their production.

Given the improved processing properties of complex mixtures, the claimed composition can be used in the manufacture of complex foundry equipment, in dental practice in precision casting slozhnoprofilnyh engineering billets critical applications.

BIBLIOGRAPHY

1. Urvachev VP, VV Kochetkov, Gorin NB Jewelry and art investment casting of copper alloys. - Chelyabinsk: Metallurgy, 1991. - 168 p.

2. Magnitsky ON, Piraino VY Art Casting. - SPb .: University of Technology, 1996. - 213 p.

3. Patent RF N 2129932. A mixture for the manufacture of ceramic molds and cores in the production of castings from ferrous and non-precious alloys and the method of its preparation. / LG Znamensky, Kulakov, BA, Krymsky VV et al. Bull. N 13, 1999 (prototype).

CLAIM

The mixture for making molds and cores for gypsum binder in the production of castings of non-ferrous and precious alloys, comprising gypsum, Silica powder phosphorus additive and water, characterized in that it as a phosphorus additive comprises alyumoborfosfatny concentrate, but also additional waste production of optical glass and oxalic acid with the following ratio of ingredients, wt.%:

• Gypsum - 12-15
• Silica powder - 24-30
• Wastes from the production of optical glass - 24-30
• Alyumoborfosfatny concentrate - 0.02-0.04
• Oxalic acid - 0.03-0.08
• Water - The rest

print version
Publication date 28.11.2006gg

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