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INVENTION
Patent of the Russian Federation RU2165817
MIXING FORMING FOR MANUFACTURING JEWELERY CASES

MIXING FORMING FOR MANUFACTURE OF JEWELERY CASTINGS. ORNAMENTS. JEWELRY. GOLD. PLATINUM. DIAMOND. BRILLIANT. KNOW HOW. TREATMENT. BREAKDOWN. PRECIOUS STONE. INTRODUCTION. PATENT. TECHNOLOGIES.

INVENTION. MIXING FORMING FOR MANUFACTURE OF JEWELERY CASTINGS. Patent of the Russian Federation RU2165817

Applicant's name: Closed Joint Stock Company "Investment and Finance Company" ROMEX-INVEST "
The name of the inventor: Kondakov EN
The name of the patent holder: Closed Joint Stock Company "Investment and Finance Company" ROMEX-INVEST "
Address for correspondence: 195220, St. Petersburg, PO Box 372, Stankovsky VM
Date of commencement of the patent: 2000.03.28

The mixture is intended for investment casting castings of jewelry made from precious and non-ferrous metal alloys. Powder mixture for making molds, which is closed by water during molding, contains cristobalite 48 - 78% by weight, high strength gypsum 20 to 50% by weight, potassium nitrate 0.5 to 2.0% by weight, and the balance to potassium dihydrogen phosphate. Cristobalite is used with admixture of tridymite and amorphous quartz not more than 20% or 40%, alkali metal oxides are not more than 2%. The mixture is finely dispersed and has high strength characteristics, which ensures high quality of the castings.

DESCRIPTION OF THE INVENTION

The invention relates to a casting process for investment casting for casting of jewelry from precious and non-ferrous metal alloys, in particular to compositions of molding mixtures.

Known domestic molding mixture "Jewelery" of the following composition, weight%, [1]:

Dinas ED - 60-64

Gypsum - 10-12

Orthophosphoric acid - 0.03-1.0

Water - Other

In order to improve the quality of the castings, an improved formulation of "Yu-KEN", weight%, was developed [2]:

Burnt quartzite - 52-57

Gypsum - 15-20

Dihydrogen phosphate 0-2.2

Water - Other

Forming mixture "Yu-KEN" is produced instead of the mixture "Jewelery".

The mixture of "Yu-KEN" instead of dinas, which has about 20% cristobalite, burned quartzite, in which 30-40% cristobalite and less harmful impurities. In addition, instead of liquid orthophosphoric acid, which was very accurately dosed into the water during molding, powdered dihydrogen phosphate was introduced into the powder mixture of calcined quartzite and gypsum. Thus, the powder molding mixture "Yu-KEN", as well as imported powder mixtures is closed with water without acids. The quality of the castings using the "Yu-KEN" mixture was still lower than that of the castings obtained from foreign mixtures, since pure cristobalite was used there.

In recent years, new foreign molding mixtures have appeared in Russia, (for example, the KERR molding mixture of Kerr Manufacturing Company, USA [3]), consisting of powder components of finer grinding, which makes it possible to obtain castings with a higher surface purity, which is very It is important for products made of precious metals, especially for gold. The higher the dispersion of the powder mixture (the thinner the grinding), the better the cleanliness of the surface of the castings (specularity) and, accordingly, less gold removal when polished and less gold is lost.

As a prototype, a mixture [4] was chosen for the manufacture of ceramic molds and rods for the production of castings of art and jewelry. The mixture contains, by weight: gypsum - 10,0-14, -0, dinas 50,0 - 63,0, pulverized sublimation of fireclay production - 3,7-7,0, alumochromophosphate binder 0,003-0,02 and the rest - Water. To reduce the viscosity of the gypsum mixture and increase the strength of the ceramic molds, the aqueous solution of the aluminochromophosphate binder is treated with nanosecond electromagnetic pulses prior to mixing the ingredients.

It is an object of the present invention to provide a composition of a fine dispersion molding mixture with high process parameters, namely, with improved strength characteristics, increased flowability, etc., which improve the quality of the castings.

This development became possible after the creation of a technology for the production of cristobalite from quartz sand [5] and the manufacture of a special mill lined with plates of uralite to obtain fine grinding of the components.

The task is achieved by the fact that in a mixture of a molding for manufacturing jewelry containing gypsum, a siliceous material, a technological additive, a new one according to the invention is the introduction of a high-strength - gypsum, the use of cristobalite as a siliceous material, and as a technological additive of potassium dihydrogen phosphate and additionally the introduction of potassium nitrate with the following ratio of components, mass%:

- Gypsum - 20-50

Cristobalite - 48-78

Potassium nitrate - 0,5-2,0

Potassium dihydrogen phosphate - Other

In this case, cristobalite with an admixture of trimidite and amorphous quartz does not exceed 20%, alkali metal oxides not more than 20%, and alkali metal oxides 0.2-2.0% by weight.

Water from the manufacturer to the powder mixture is not introduced, but only used by consumers in work.

Powder mixture - the mass part (M) at work is closed by distilled water - the water part (B) in proportion: for 1 kg of the powder part 0.38-0.40 l of the water part is introduced; In the certificate for the lot of the molding mixture is indicated as: V / M = 0.38 l / kg (ie the water-mass ratio of 380 ml of water per 1 kg of the powder mixture).

The action of the components of the powder molding mixture is as follows: gypsum - binder; Cristobalite (SiO 2 ) - shrinkage compensator of gypsum as a result of dehydration during firing the mold; Potassium dihydrogen phosphate (KH 2 PO 4 ) - provides the fluidity of the molding mixture; Potassium nitrate (KNO 3 ) - provides the necessary solidification time for the molding mixture in 14-40 minutes.

The percentage of the components of the molding mixture is determined by the required strength of the mold and the required solidification time of the mixture. So, for example, for casting filigree castings having thin sections (up to 0.3 mm), it is necessary to use molding compounds having low strength (low gypsum content), since castings are extracted from the mold by breaking it with a wooden hammer (kiyankoy); If the mold has high strength, then the thin sections of the castings are deformed or broken. For massive castings weighing 0.5 kg or more, it is necessary to have a high strength molding mixture, because a weak form when pouring large amounts of liquid metal is washed out and destroyed.

For evacuation from the air of large amounts of a molding mixture of 15-30 kg for the manufacture of large molds for casting massive castings, mixtures having a beginning of solidification on 30-40 minutes should be used, otherwise air bubbles will remain in the mold, which, when filled, will be filled with metal, and castings On the surface will have spherical metal influxes, which is an incorrigible marriage.

The new finely divided molding mixture has a particle size of 10 - 90 μm, which corresponds to the dispersion of the best foreign mixtures.

The technological properties of the molding mixture proposed in the application in comparison with the properties of the prototype mixture are illustrated by the tables:

- tab. 1 - compositions of the test mixtures (dry mixtures). Columns 1-4 show compositions according to the claimed invention, in columns 5-6 - according to RF patent 2129932 in terms of dry mix,

- tab. 2 - compositions of the test mixtures with a water sealant, i.e. Ready for use,

- tab. 3 - properties of the compositions presented in Table. 2.

As can be seen from Table. 3, the strength characteristics of the claimed mixture is significantly higher than in the prototype. In addition, when firing in casting molds, no cracks are formed from the claimed mixture, so there is no such kind of rejection of castings as oblong (thin deposits of metal on the surface of the castings). Mixtures of the application have a high fluidity - the diameter of the spread of 250 g of the mixture - 180-220 mm. When the mixtures are evacuated, air bubbles emerge actively from them, so that the defects in the castings are insignificant by ball influx. For comparison, a mixture made according to the prototype formula has a low fluidity (120-160 mm). As the inspection showed, the introduction of alumochromophosphate in the gypsum mixture in an amount of 0.003-0.2% does not allow to achieve fluidity above 140-160 mm.

The use of pure cristobalite instead of dinas, which has 5-6% harmful for molding mixtures of impurities (Fe, Ca, Mg), makes it possible to stabilize the obtaining of high technological properties (see Table 3) and the high quality of the castings. The composition of the claimed molding mixture is introduced with potassium nitrate, which acts as a regulator of solidification of gypsum entering the mixture. For the production of jewelry it is very important, because. The mixture is used to make both very small molds with a mixture amount of 0.5 kg and very large forms, with a mixture amount of up to 15-20 kg. With such a difference in shape by volume, the evacuation time varies from 5 to 30 minutes, and therefore the solidification time should differ substantially. The quantitative ratio of the ingredients used makes it possible to obtain the desired result.

In Table. 4-6 shows the characteristics of the claimed mixture in comparison with the analogues used in the industry.

As can be seen from Table. 4, when using the molding mixture of the present invention, in comparison with the molding mixture "KERR", the quality of castings of the filigree group having thin sections improves, which can be achieved by using molding mixtures with less strength. And the quality of the castings of a group of massive souvenirs with significantly higher weight (up to 10 kg) improves due to the use of high-strength mixtures containing up to 50% gypsum, which avoids the appearance of cracks in large molds.

In Table. 5 comparative data of molding mixtures on loss of gold on casting and polishing operations of castings are given. As can be seen from Table. 5, using the claimed mixture and using the "KERR" mixture, the loss of gold for casting and polishing of the castings is almost the same and almost 2 times less than when using the "Yu-KEN" mixture.

In Table. 6 data on the dispersion (fineness of grinding) of powder molding mixtures when sieved through a screen with different cell sizes are shown. The data of Table. 6 show that the dispersion and the level of rejects of the castings of the "KERR" mixture and of the molding mixture according to the proposed application are similar.

In this case, it is possible to produce molding mixtures with different strengths (with different content of gypsum), especially for casting groups: filigree castings - 4-5 kgf / cm 2 ; Medium castings (rings, earrings, pendants) - 6-10 kgf / cm 2 ; Massive castings (up to 10 kg and more) - 11-15 kgf / cm 2 .

INFORMATION SOURCES

1. Authorship certificate of the USSR N 904869, IPC B 22 C 1/16, 1980.

2. The patent of Russia 2105630, IPC B 22 C 1/00, 1993.

3. A prospectus of KERR Manufacturing Company (USA) for the molding mixture "KERR", 1991.

4. The patent of the Russian Federation 2129932, МПК B 22 C 1/18, 1999 - a prototype.

5. Patent of Russia N 2145948, IPC C 04 B 28/26, 2000, bul. N 6.

CLAIM

1. A molding mixture for making jewelry, comprising gypsum, a siliceous material, a processing aid, characterized in that it contains a high-strength Gypsum, cristobalite as a siliceous material, and potassium dihydrogenphosphate and additionally potassium nitrate as a technological additive with the following ratio of components, mass%:

-Gypes - 20 - 50

Cristobalite - 48 - 78

Potassium nitrate - 0,5 - 2,0

Potassium dihydrogen phosphate - Other

2. A mixture according to claim 1, characterized in that it contains cristobalite with an admixture of tridymite and amorphous quartz of not more than 20% by weight, and alkali metal oxides of 0.1-2.0% by weight.

3. A mixture according to claim 1, characterized in that it contains cristobalite with an admixture of tridymite and amorphous quartz of not more than 40% by weight, and alkali metal oxides of not more than 2% by weight.

print version
Date of publication 02.01.2007гг