RU2793659C1 - Mixture for making moulds and cores - Google Patents

Abstract

FIELD: foundry production.

SUBSTANCE: mixture for the manufacture of moulds and cores contains, in % by weight: 5-6 liquid glass, 3-5 moulding clay, 1.5-2.0 crushed silicone rubber waste, 0.5-1.5 aqueous 4-8% polyvinyl alcohol solution and the rest is quartz sand. A solution of polyvinyl alcohol partially envelops the grains of sand and crushed waste silicone rubber with formation of an elastic film on their surface during drying, which strengthens the surface layer of the mould. Particles of crushed silicone rubber waste, evenly distributed in the composition of the liquid glass mixture, decompose when the mould is heated to form amorphous silicon dioxide and carbon dioxide, which destroys binder films on the surface of quartz sand grains.

EFFECT: reduction of friability and residual strength of the mixture and improvement of mould and core breakdown are provided.

2 cl, 5 tbl, 1 ex

Description

The invention relates to foundry production, namely, to the manufacture of molds and cores from sand mixtures on a liquid glass binder, cured by blowing with carbon dioxide.

Molding and core sand mixtures based on a liquid glass binder are widely used in the foundry industry. However, these mixtures have significant drawbacks. Among them are low raw (handling) strength, flaking after drying, and poor knockout from castings due to high residual strength. To eliminate these shortcomings, various organic and inorganic additives are introduced into the mixture.

The use of organic additives in the composition of sand mixtures on a liquid-glass binder helps to reduce the residual strength of the rods, and therefore improve their knock-out.

For example, a mixture containing 3.0-6.0%, wt. liquid glass, 1.0-3.0%, wt. sludge waste chemical cleaning of steel products, 0.5-1.0% of the mass. caustic soda and refractory filler based on silicon dioxide [1]. When the organic oil additive, which is part of the sludge waste from the chemical cleaning of steel products, burns out, gases are released, the pressure of which destroys the binder films, thereby contributing to the softening of the mixture. The main disadvantages of this mixture are a rather high residual strength and the fact that when the oil additive burns out, harmful toxic gases are released that pollute the atmosphere of the pouring and knockout sections of the foundry.

It is known that the inclusion of inorganic additives in the composition of the sand mixture on a liquid-glass binder does not lead to the release of harmful gases when the mold is poured with a melt [2]. At the same time, the introduction of such additives in small amounts does not have a significant softening effect, and an increase in their content in the mixture leads to a decrease in the strength properties of the rod.

For example, a mixture containing 6.0-6.5%, wt. liquid glass, 8.0-11.0%, wt. clay, calcined at a temperature of 800°C, 1.25-1.5%, wt. caustic soda and quartz sand as a refractory base [3]. The disadvantages of this mixture include significant crumbling and high residual strength.

Closest to the invention in terms of physical and chemical composition and the achieved technical result is a mixture consisting of 5.0-14.0%, wt. liquid glass, 7.0-26.0%, wt. waste of ceramic products containing clay, and quartz sand as a refractory base [4].

This mixture has high strength properties only with a high percentage of water glass and waste from the production of ceramic products. At the same time, the residual strength of the mixture is very high (>2 MPa) and, as a result, such a mixture is poorly knocked out of the castings. A mixture with a relatively low percentage of liquid glass and waste from the production of ceramic products has a low compressive strength in the wet state, high friability after drying, and insufficient knockout.

In addition, the rods made from the mixture of the prototype must be dried at a temperature of 180-220°C for a long time, which is also a disadvantage.

These shortcomings are eliminated by the proposed solution.

The problem of improving the manufacturability of the mixture is being solved.

EFFECT: obtaining a mixture for the manufacture of molds and cores on a liquid glass binder, which has a reduced friability and low residual strength.

The technical result is achieved by the fact that the mixture for the manufacture of molds and cores, containing liquid glass and quartz sand, according to the invention additionally contains molding clay, crushed silicone rubber waste and an aqueous solution of polyvinyl alcohol in the following ratio of ingredients, wt.%:

liquid glass 5.0-6.0 molding clay 3.0-5.0 shredded silicone rubber waste 1.5-2.0 aqueous 4-8% solution of polyvinyl alcohol 0.5-1.5 quartz sand rest

The essence of the invention is as follows.

Liquid glass is introduced into the mixture as a binder in the amount of 5.0-6.0%, wt. When the content of liquid glass in the mixture in an amount less than 5.0%, the strength of the rod in the cured state in compression and tensile strength decreases and the shattering increases, and when the content is greater than 6.0%, the knockout significantly deteriorates. This is confirmed by the preliminary tests carried out (Table 1).

Molding clay is added to the composition of the mixture in the amount of 3.0-5.0%, wt. to increase the raw (manipulatory) strength of the rod. The lower limit of the clay content is due to the fact that a smaller amount does not provide a significant increase in green strength. The upper limit is limited to 5.0%, wt., because with a higher clay content, the strength of the rod in the hardened (hardened) state decreases. This is confirmed by the preliminary tests carried out (Table 2).

Silicone rubber wastes are worn and decommissioned molds used for the manufacture of products from polyurethanes, artificial decorative stone, casting of low-temperature metals and alloys, as well as waste generated during the production of silicone molds. They are included in the federal waste classification catalog (“Waste of silicone in the manufacture of silicone molds” No. 33577111204).

In the claimed invention, it is proposed to grind these wastes and use them as a softening additive for molding and core sand mixtures on a liquid glass binder. Grinding and screening to obtain a certain fraction can be carried out using a cutting mill.

Particles of crushed waste silicone rubber, evenly distributed in the composition of the liquid glass mixture, when the mold or rod is heated to temperatures above 300 ° C, decompose with the formation of amorphous silicon dioxide and carbon dioxide, which, in turn, destroys the binder film on the surface of the grains of the refractory base - quartz sand, thereby helping to reduce the residual strength of the rod and improve its knockout.

The lower limit of the content of the additive of crushed waste silicone rubber (1.5%, wt.) is due to the fact that a smaller amount does not provide a significant softening effect (Table 3). The content of the additive of crushed waste silicone rubber in the composition of the mixture in an amount greater than 2.0%, wt., leads to an increase in the gas content of the mixture and, as a result, to the appearance of a defect in the castings - gas porosity.

The smaller the particle size of the crushed silicone rubber waste, the more uniformly they are distributed in the rod mass and the more intense the softening occurs (Table 4). However, the process of obtaining particles of fine fraction (<0.3 mm) is very long and economically unprofitable. The use of crushed silicone rubber waste particles larger than 0.5 mm leads to a deterioration in the surface quality of the rod due to its flaking.

To reduce friability and increase surface strength, an aqueous 4.0-8.0% solution of polyvinyl alcohol is added to the mixture.

A solution of polyvinyl alcohol partially envelops the grains of sand and the addition of crushed silicone rubber waste, forming an elastic film on their surface during drying, which strengthens the surface layer of the mold or core.

Based on preliminary tests for the introduction of polyvinyl alcohol into the mixture, a concentration of 4.0-8.0%, wt. At a concentration of less than 4.0%, wt. the stickiness of the rod to the tooling increases due to the increased water content in the mixture. The use of a solution with a concentration of more than 8.0%, wt. impractical due to an increase in its viscosity and, as a result, a decrease in the uniformity of distribution in the core mixture.

The lower limit of the content of an aqueous solution of polyvinyl alcohol (0.5 wt.%) is due to the fact that a smaller amount does not provide a significant reduction in the crumbling of the mixture (Table 5). The content of the solution of polyvinyl alcohol above 1.5 wt. % leads to an increase in the gas content of the mixture and the formation of gas porosity in the castings.

Example.

For comparison, samples were made from the proposed composition and from the known mixture - the prototype [4]. The composition of mixtures and physical and mechanical properties are given in table. 5.

The following materials were used to prepare the mixture: liquid sodium glass with a modulus of 2.6 and a density of 1.47 g/cm ³ (GOST 13078-81); quartz sand 2K ₁ O ₂ 02 (GOST 2138-91); molding clay P3 (GOST 3226-93); shredded silicone rubber waste; aqueous 4-8% solution of polyvinyl alcohol grade PVA, 6/1 grade 1 GOST 10779-78.

The core mixture was prepared as follows.

The model 02113 mixer was loaded with quartz sand, clay, crushed silicone rubber waste, previously prepared using a Retsch SM100 cutting mill, and mixed for 3 minutes. Then liquid glass was introduced into the mixture and stirred for 5 minutes. Next, an aqueous solution of polyvinyl alcohol was introduced into the mixture and finally mixed for 3 minutes.

The properties of the mixture were evaluated on standard samples. The samples were purged with carbon dioxide for 60 seconds at a flow rate of 30 dm ³ /min and a pressure of 0.1 MPa.

Tests of specimens for strength (compressive and tensile) were carried out in accordance with GOST 23409.7-78. Samples were tested for gas permeability according to GOST 23409.6-78. Samples were tested for flaking according to GOST 23409.9-78.

To determine the residual strength, the samples were preheated to 800°C for one hour (as in the patent for the invention taken as a prototype), then cooled in air to 20°C and then tested according to the method (GOST 23409.7-78). Thus, an imitation of the heating of the core mixture was carried out when it was exposed to the heat of the solidifying metal. At a temperature of 800°C, a fusible double eutectic is formed in the liquid-glass mixture, consisting of 21.6% Na ₂ O and 73% SiO ₂ , under the influence of which, after cooling, sand grains are cemented into a monolithic mass [5]. This case is the worst in terms of knocking out cores from castings.

Since one of the objectives of the claimed invention is to improve the knockout of rods from castings, then for comparison, example No. 2 with the lowest residual strength given in the description of the prototype invention was taken.

From Table. 5 shows that the proposed mixture (compositions No. 3, No. 4 and No. 5) in comparison with the prototype has higher physical and mechanical properties. The gas permeability of the prototype mixture is higher than that of the claimed mixture, however, the level of gas permeability of the proposed mixture compositions is quite high (about 200 units) and is quite sufficient to ensure the quality of castings due to gas defects [6]. At the same time, the proposed mixture has a friability lower by 1.4-5 times, and the residual strength is 2 times lower compared to the prototype.

Thus, the manufacturability of the mixture is improved. In addition, the use of crushed silicone rubber waste helps to reduce environmental pollution, since these wastes are not currently recycled on an industrial scale (they are dumped to landfills).

Information sources

1. Author's certificate of the USSR No. 1685586, class. B22C 1/02, publ. 10/23/1991.

2. Casting molding materials. Molding, core mixtures and coatings: reference book / A.N. Boldin, N.I. Davydov, S.S. Zhukovsky and others. M.: Mashinostroenie, 2006. 507 p.

3. Author's certificate of the USSR No. 366028, class. B22C 1/00, C04B 35/14, publ. 01/16/1973.

4. RF patent No. 2224619, class. B22C 1/18, publ. 02/27/2004.

5. Svarika A.A. Molding materials and mixtures: a reference book. K.: Tekhnika, 1983. 144 p.

6. Medvedev Ya.I., Valisovsky I.V. Technological testing of molding materials / Ya.I. Medvedev, I.V. Valisovsky. M.: Mashinostroenie, 1973. 312 p.

Table 1

No.
p/p Components and characteristics of mixtures Composition of mixtures, wt.% #1 #2 No. 3 #4 #5 #6 #7 1 2 3 4 5 6 7 8 9 1 Liquid glass 4.0 4.5 5.0 5.5 6.0 6.5 7.0 2 Quartz sand rest. rest. rest. rest. rest. rest. rest. 3 Wet compressive strength, MPa <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 4 Compressive strength in the cured state, MPa 1.85 1.92 2.10 2.22 2.30 2.34 2.36 5 Gas permeability, units 220 220 210 208 208 205 204 6 Ultimate tensile strength in the cured state, MPa 0.72 0.76 0.85 0.88 0.91 0.93 0.94 7 Peeling, % 0.26 0.26 0.24 0.23 0.21 0.21 0.21 8 Residual strength after calcination of samples at a temperature of 800°C, MPa 0.47 0.77 0.96 1.62 1.90 2.20 2.70 9 Gas porosity in the casting No No No No No No No

table 2

No.
p/p Components and characteristics of mixtures Composition of mixtures, wt.% #1 #2 No. 3 #4 #5 #6 #7 #8 #9 #10 1 2 1 2 3 4 5 6 7 8 9 10 1 Liquid glass 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 2 molding clay 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 3 Quartz sand rest. rest. rest. rest. rest. rest. rest. rest. rest. rest. 4 Wet compressive strength, MPa 0.02 0.02 0.04 0.04 0.05 0.05 0.05 0.06 0.06 0.06 5 Compressive strength in the cured state, MPa 2.26 2.21 2.14 2.06 2.00 1.95 1.88 1.81 1.73 1.67 6 Gas permeability, units 205 203 200 200 200 199 196 196 192 189 7 Ultimate tensile strength in the cured state, MPa 0.89 0.88 0.86 0.86 0.85 0.83 0.82 0.82 0.81 0.79 8 Peeling, % 0.20 0.21 0.21 0.20 0.20 0.21 0.20 0.23 0.24 0.25 9 Residual strength after calcination of samples at a temperature of 800°C, MPa 1.88 1.87 1.85 1.82 1.80 1.77 1.74 1.72 1.68 1.65 10 Gas porosity in the casting No No No No No No No No No No

Table 3

No.
p/n Components and characteristics of mixtures Composition of mixtures, wt.% #1 #2 No. 3 #4 #5 #6 1 2 3 4 5 6 7 8 1 Liquid glass 6.0 6.0 6.0 6.0 6.0 6.0 2 molding clay 4.0 4.0 4.0 4.0 4.0 4.0 3 Shredded silicone rubber waste (particle size 0.5 mm) 0.5 1.0 1.5 2.0 2.5 3.0 4 Quartz sand rest. rest. rest. rest. rest. rest. 5 Wet compressive strength, MPa 0.08 0.08 0.07 0.09 0.08 0.07 6 Compressive strength in the cured state, MPa 2.00 1.98 1.97 1.95 1.91 1.88 7 Gas permeability, units 200 203 200 200 200 200 8 Ultimate tensile strength in the cured state, MPa 0.85 0.84 0.84 0.83 0.81 0.79 9 Peeling, % 0.20 0.24 0.26 0.27 0.28 0.29 10 Residual strength after calcination of samples at a temperature of 800°C, MPa 0.42 0.34 0.31 0.20 0.20 0.19 eleven Gas porosity in the casting No No No No There is There is

Table 4

No.
p/p Components and characteristics of mixtures Composition of mixtures, wt.% #1 #2 No. 3 #4 #5 #6 #7 #8 1 2 3 4 5 6 7 8 9 10 1 Liquid glass 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 2 molding clay 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 3 Shredded silicone rubber waste 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 4 Particle size of crushed silicone rubber waste, mm 0.2 0.25 0.3 0.5 0.75 1.0 1.5 2.0 5 Quartz sand rest. rest. rest. rest. rest. rest. rest. rest. 6 Wet compressive strength, MPa 0.09 0.09 0.09 0.09 0.08 0.07 0.06 0.06 7 Compressive strength in the cured state, MPa 2.00 1.99 1.99 1.95 1.90 1.81 1.73 1.64 8 Gas permeability, units 194 195 198 200 202 204 205 205 9 Ultimate tensile strength in the cured state, MPa 0.87 0.87 0.86 0.83 0.81 0.77 0.74 0.70 10 Peeling, % 0.20 0.20 0.22 0.27 0.29 0.32 0.34 0.36 eleven Residual strength after calcination of samples at a temperature of 800°C, MPa 0.16 0.18 0.18 0.20 0.22 0.26 0.32 0.39 12 Gas porosity in the casting No No No No No No No No

Table 5

No.
p/p Components and characteristics of mixtures Composition of mixtures, wt.% #1
(prototype) #2 No. 3 #4 #5 #6 1 2 3 4 5 6 7 8 1 Liquid glass 5.0 6.0 6.0 6.0 6.0 6.0 2 molding clay - 4.0 4.0 4.0 4.0 4.0 3 Shredded silicone rubber waste (particle size 0.5 mm) - 2.0 2.0 2.0 2.0 2.0 4 Aqueous 4-8% solution of polyvinyl alcohol - 0.25 0.5 1.0 1.5 2.0 5 Waste from the production of ceramic products 7.0 - - - - - 6 Quartz sand rest. rest. rest. rest. rest. rest. 7 Wet compressive strength, MPa 0.03 0.08 0.09 0.08 0.09 0.09 8 Compressive strength in the cured state ^* , MPa 1.95 1.95 1.95 1.97 1.98 1.98 9 Gas permeability, units 380 200 202 200 200 198 10 Dry tensile strength ^** , MPa 0.82 0.83 0.83 0.84 0.84 0.85 eleven Peeling, % 0.10 0.10 0.07 0.04 0.02 0.02 12 Residual strength after calcination of samples at a temperature of 800°C, MPa 0.40 0.20 0.20 0.20 0.20 0.19 13 Gas porosity in the casting - No No No No There is ^* For the prototype mix, the cured compressive strength refers to the strength of the specimens after drying. For the claimed mixture, this is the strength after purging with carbon dioxide or exposure to air for 2-3 hours.
^** For the prototype mix, dry tensile strength means the tensile strength of the samples after drying. For the inventive mixture, this is the tensile strength after purging with carbon dioxide or exposure to air for 2-3 hours.

Claims (3)

1. A mixture for the manufacture of molds and cores containing liquid glass and quartz sand, characterized in that it additionally contains molding clay, as well as the addition of crushed silicone rubber waste and an aqueous 4-8% solution of polyvinyl alcohol, in the following ratio of components , wt.%: liquid glass 5.0-6.0 molding clay 3.0-5.0 shredded silicone rubber waste 1.5-2.0 aqueous 4-8% solution of polyvinyl alcohol 0.5-1.5 quartz sand rest 2. A mixture according to claim 1, characterized in that the particle size of the crushed silicone rubber waste is 0.3-0.5 mm.