RU2385849C1 - Method of making ceramic objects based on wollastonite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the ceramic industry and more specifically to making lining for assemblies and foundry equipment for metallurgy of aluminium alloys. The method of making ceramic objects based on wollastonite involves preparation of a moulding compound through simultaneous wet-grinding of the following compounds in the following ratio, wt %: natural wollastonite concentrate - 70-80, kaolin - 10-20, clay - 5-10 with addition of water in amount of 27-32% of the mass of dry components and stabilisers of liquid glass and calcined soda to grinding fineness with 0063 sieve residue - 5-23%, moulding objects through slip casting in porous moulds, drying and calcinations at temperature 950-1000°C for 1-3 hours. Before moulding, the moulding compound is mixed with crushed rejects based on wollastonite (fraction of up to 2.5 mm) while moistening to moisture of 20-27%, where the said crushed rejects are taken in amount of 20-30% of over 100% of the mass of dry components.

EFFECT: recycling production wastes of materials based on wollastonite, increased heat resistance of the objects.

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Description

The invention relates to the ceramic industry, in particular to the manufacture of lining of aggregates and foundry equipment for the metallurgy of aluminum alloys, in which asbestos-containing refractory materials with carcinogenic properties have been recently replaced by more environmentally friendly wollastonite materials, characterized by high chemical inertness to molten aluminum .

A known method of producing a sheet of thermal insulation material based on wollastonite, RF patent No. 2132829 С04В 28/18, publ. 07/10/99, including:

- joint dry grinding of quicklime 6-12% and quartz sand 24-38%;

- moistening the mixture after grinding to a moisture content of 40% in order to extinguish lime;

- mixing wollastonite 50-70% with an aqueous suspension of aluminum powder (≈0.3%);

- mixing a mixture of hydrated lime, quartz sand, wollastonite and aluminum powder while moistening the mixture to a moisture content of 35-40%;

- forming sheet material by vibrating method;

- steaming wet molded material in an autoclave at a saturated steam pressure of 1-2.6 MPa and a temperature of 180-250 ° C for 12-24 hours;

- drying at 250-350 ° C for 1.5-3 hours;

- firing at 850-900 ° C for 4-6 hours

This method allows to obtain sheet thermal insulation material with a density of 0.75-1.15 g / cm ³ and a compressive strength of 4-6 MPa. The material can be used in contact with aluminum alloy at temperatures up to 1000 ° C.

The disadvantages of this technical solution are:

- the need to use complex, expensive equipment, such as high pressure autoclaves;

- the impossibility of manufacturing complex products;

- low material strength;

- the difficulty of preparing the initial wollastonite;

- the formation of significant alkaline effluents;

- the need for expensive treatment of effluents from alkali,

and when they (drains) are involved in the production process, the need for complex adjustment of the dosage of lime, as with an excess or insufficient content of lime in the formulation of the material, the hardening process during autoclaving is disrupted.

A known technology for producing composite materials for the aluminum industry from a natural wollastonite concentrate with the addition of sintering activators and inorganic fibers (kaolin, mullite-siliceous, siliceous), which is introduced into the material in an amount of 20-50% to increase its heat-insulating characteristics and heat resistance. This technology, described in an article by Romashin A.G. et al. Wollastonite-based ceramics developed at ONPP Technology, New Refractories, 2004, No. 1, pp. 43-47, includes: preparation of a charge, molding of a workpiece by semi-dry pressing, followed by drying, firing and machining.

The material obtained by this method has a density of 0.5-1.9 g / cm ³ , static bending strength of 0.5-30 MPa, heat resistance up to 25 heat exchangers from 800 to 20 ° C (air), chemically resistant to melt aluminum.

The main disadvantages of the described method are the dustiness of jobs associated with the preparation of molding materials and filling molds, and the inability to obtain complex profile overall products.

Closest to the claimed solution is a method of producing ceramic products based on wollastonite, RF patent No. 2298537 С04В 33/28, С04В 33/00, publ. 05/10/2007, including:

- preparation of the molding mass by simultaneous wet grinding of natural wollastonite concentrate 70-80%, kaolin 10-20% and clay 5-10% with the addition of water in an amount of 27-32% by weight of dry components, water glass and soda ash as stabilizers to grinding fineness with a residue on sieve 0063 - 5-23%;

- molding products by slip casting into porous molds;

- drying products at a temperature of 100-150 ° C for 2-5 hours;

- firing products at a temperature of 950-1000 ° C for 1-3 hours

This method allows to obtain a material with a density of 1.45-1.65 g / cm ³ , strength with a static bend of 8-25 MPa, heat resistance up to 12 heat exchangers from 850 to 20 ° C in air, chemically resistant to aluminum alloys to a temperature of 1000 ° FROM.

All of the described analogues do not address the extremely important problem of the disposal of waste ceramic materials based on wollastonite. This problem is important from a technical and economic point of view, as well as in the aspect of environmental protection. Large volumes of defective and long-lived refractories replenish numerous landfills, while they are valuable raw materials and can be used for recycling.

The objective of the invention is the disposal of industrial waste materials based on wollastonite.

This goal is achieved by the fact that the proposed method for producing ceramic products based on wollastonite, including the preparation of the molding material, by simultaneously wet grinding the following components in the ratio of wt.%: Natural wollastonite concentrate - 70-80, kaolin - 10-20, clay - 5- 10 with the addition of water in an amount of 27-32% by weight of dry components and stabilizers of liquid glass and soda ash to a fineness of grinding with a residue on a sieve 0063 - 5-23%, molding products by slip casting into porous forms, drying and firing when at a temperature of 950-1000 ° C for 1-3 hours, characterized in that before molding the molding material is mixed with a battle of 20-27% moistened to a moisture content of defective wollastonite-based products (fraction up to 2.5 mm), taken in an amount of 20- 30% in excess of 100% by weight of dry components.

The advantages of this method are:

- disposal of defective products based on wollastonite.

- increase the heat resistance of the material.

The presence in the slip and coarse-grained filler of more than 70 wt.% Natural wollastonite provides chemical resistance of the material to aluminum alloys up to 1000 ° C.

The presence in the slip of the plastic components of kaolin and clay, as well as stabilizers of water glass and soda ash, provides a high adaptability of the slip. These components play the role of a bond in the material, which allows you to move the molded product to subsequent technological operations without destruction.

In the process of firing, clay and kaolin in the presence of fluxes, including stabilizers and tiny particles of wollastonite, formed as a result of abrasion during grinding, form a glass phase and contribute to sintering and hardening of the material.

The introduction of a coarse-grained filler into the molding mass, which is proposed to use the battle of defective and uncontaminated spent wollastonite products, allows to increase the heat resistance of the material, which is associated with the peculiar structure of coarse-grained material. The presence of microcracks and gaps in it near large grains of the refiner gives the structure the character of “point adhesion” in these places, which creates the possibility of local stress discharge due to the mutual displacement of individual parts of the material.

With the introduction of coarse filler of less than 20%, there is no increase in heat resistance. An increase in the filler content of more than 30% leads to a structural change, which is associated with the formation of an endless cluster of filler particles (filler particles are in contact with each other), therefore, the strength and heat resistance of the material are reduced.

The use of fractions up to 2.5 mm in battle of defective products is optimal both in strength and heat resistance of the material, and in the processability of the molding material. An increase in the dispersion of the filler entails an increase in the water demand of the molding material. A decrease in the dispersion of the filler entails a decrease in the casting properties of the molding material.

Maintaining the shape of the product is facilitated by low shrinkage of the material (1-4%), which is explained by the formation of a framework of multidirectional needle-fibrous wollastonite crystals that do not interact with the liquid phase at a firing temperature of up to 1000 ° C. Firing at temperatures above 1000 ° C leads to a sharp increase in the glass phase in the material, in the formation of which not only the fine fraction of wollastonite formed during grinding takes part, but also the surface of large particles of wollastonite dissolves, which increases shrinkage, reduces deformation resistance and heat resistance.

Lowering the firing temperature below 950 ° C does not allow to obtain high strength material.

The products are molded by slip casting into porous forms. This molding method allows to obtain complex and large-sized products. When pouring the mass into the mold, if necessary, apply vibration to better fill the mold with the molding mass. After drying and drying at 100-150 ° C for 2-5 hours, the products are fired at a temperature of 950-1000 ° C for 1-3 hours.

Obtained by the proposed method, the material has a density of 1.45-1.60 g / cm ³ , heat resistance 18-25 heat transfer from 850 to 20 ° C (in air), chemically resistant to aluminum alloys to a temperature of 1000 ° C.

The use of coarse-grained filler from the battle of defective and uncontaminated waste products allows solving the urgent problem of waste disposal. These valuable materials in large quantities continue to replenish landfills, harming the environment, while they are a valuable raw material for the production of ceramics. The use of coarse-grained filler can also simultaneously increase the heat resistance of the material.

This set of features of the method provides waste disposal, obtaining complex, large-sized products based on natural wollastonite with high heat resistance.

Examples of the method

Example 1

Natural wollastonite concentrate 80 wt.%, Kaolin 15 wt.%, Clay 5 wt.% Is crushed in a ball mill with the addition of water in an amount of 27% by weight of the components. As stabilizers use liquid glass in an amount of 0.3% and soda ash in an amount of 0.2% by weight of the solid phase of the slip. The finished slip has a moisture content of 27 wt.%, Grinding fineness (residue on sieve 0063) is 23%.

The resulting slurry is mixed with a 20% battle of defective products moistened to humidity (fraction up to 2.5 mm), taken in an amount of 20% in excess of 100% by weight of the solid phase of the slip.

From the mass thus obtained, the bulk is molded in a plaster form into an insert in a mold for aluminum alloys, which is a cylinder with a diameter of 225 mm and a height of 35 mm. When pouring, vibration is used to fill the mold better. The set is carried out for 4 hours. After 8 hours from the start of molding, the preform is removed from the mold, dried for 48 hours, dried at 150 ° C for 2 hours and calcined at 1000 ° C for 1 hour.

The material has a density of 1.60 g / cm ³ , heat resistance - 18 cycles from 850 to 20 ° C (air). The material is inert to molten aluminum and can be used up to a temperature of 1000 ° C.

Example 2

Natural wollastonite concentrate 70 wt.%, Kaolin 20 wt.%, Clay 10 wt.% Is crushed in a ball mill with the addition of water in an amount of 30% by weight of the starting components. As stabilizers use liquid glass in an amount of 0.3% and soda ash in an amount of 0.2% by weight of the solid phase of the slip. The finished slip has a moisture content of 30 wt.%, Grinding fineness (residue on sieve 0063) is 10%.

The resulting slurry is mixed with 25% battle of defective products moistened to humidity (fraction up to 2.5 mm), taken in an amount of 25% in excess of 100% by weight of the solid phase of the slip.

From the mass obtained in this way, the filter container, which is a box without a bottom measuring 270 × 250 × 200 mm and a wall thickness of 25 mm, is molded in a plaster form with a core in bulk. When pouring, vibration is used to fill the mold better. The set is carried out for 6 hours. After 8 hours from the start of molding, the core is taken out of the mold, after 24 hours the mold is taken apart, the workpiece is taken out of the mold, dried for 48 hours, dried at 100 ° С for 5 hours and calcined at 980 ° С within 1 hour

The material has a density of 1.55 g / cm ³ , heat resistance - 20 cycles from 850 to 20 ° C (air). The material is inert to molten aluminum and can be used up to a temperature of 1000 ° C.

Example 3

Natural wollastonite concentrate - 75 wt.%, Kaolin - 15%, and clay - 10% are crushed in a ball mill with the addition of water in an amount of 32% by weight of the components. As stabilizers use liquid glass - 0.3% and soda ash in the amount of 0.2% by weight of the solid phase of the slip. The finished slip has a moisture content of -32 wt.%, Grinding fineness (residue on sieve 0063) - 5%.

The resulting slurry is mixed in a propeller mixer with a 27% battle of defective products moistened to humidity (fraction up to 2.5 mm), taken in an amount of 30% in excess of 100% by weight of the solid phase of the slip.

From the mass thus obtained, the bulk is molded in a plaster form into an insert in a mold for aluminum alloys. When pouring, vibration is used to fill the mold better. The set is carried out for 4 hours. After 8 hours from the start of molding, the preform is removed from the mold, dried for 48 hours, dried at 150 ° C for 2 hours and calcined at 950 ° C for 3 hours.

The material has a density of 1.45 g / cm ³ , heat resistance - 25 cycles from 850 to 20 ° C (air). The material is inert to molten aluminum and can be used up to a temperature of 1000 ° C.

As can be seen from the presented examples, the proposed method solves the problem of disposing of defective wollastonite products, creating a simple, environmentally friendly technology for producing complex, large-sized products based on wollastonite, with increased heat resistance and chemical resistance to aluminum alloys up to a temperature of 1000 ° C.

The proposed method allows to utilize ceramic waste, in addition, it allows to increase the heat resistance of the material while maintaining strength characteristics.

Information sources

1. RF patent No. 2132829 С04В 28/18, publ. 07/10/99, a Method for producing sheet thermal insulation material based on wollastonite.

2. Romashin A.G. et al. Wollastonite-based ceramics developed at ONPP Technologiya. “New Refractories”, 2004, No. 1, pp. 43-47.

3. RF patent No. 2298537 С04В 33/28, 33/00, publ. May 10, 2007. A method for producing ceramic products based on wollastonite is a prototype.

Claims (1)

A method of producing ceramic products based on wollastonite, including the preparation of a molding material by simultaneous wet grinding of the following components in the ratio, wt.%: Natural wollastonite concentrate 70-80, kaolin 10-20, clay 5-10 with the addition of water in an amount of 27-32% from the mass of dry components and stabilizers of liquid glass and soda ash to a fineness of grinding with a residue on a sieve 0063 - 5-23%, molding products by slip casting into porous forms, drying and firing at a temperature of 950-1000 ° C for 1-3 hours characterized in that before molding of articles molding mass is mixed with the humidified to a moisture content of 20-27% fight defective items on the basis of wollastonite (fraction up to 2.5 mm) taken in an amount of 20-30% excess of 100% by weight of the dry components.