RU2044587C1 - Clay material activation method - Google Patents

Abstract

FIELD: foundry, in particular, usage of calcic-magnesium clay materials, primarily bentonites. SUBSTANCE: method involves artificially substituting calcium, magnesium and iron cations by sodium cations by various activators; introducing sodium-bearing compound as activator into moistened clay material in two stages: at the first stage simple salts and/or sodium-bearing compound bases (calcined soda and/or caustic soda, and/or trisodiumphosphate) are introduced to provide substitution of calcium cations, adsorbed on clay surface by sodium cations; at the second activation stage, providing mixing while introducing complex-forming sodium compounds condensed phosphates (tripolyphosphate or sodium pyrophosphate) to effectuate substitution of magnesium and iron cations remaining in clay material by sodium cations. An amount of activators at each stage is determined by predetermined dependence between activator and calcium cation concentration or total concentration of magnesium and ferriferrous iron in 100 g of clay material. EFFECT: improved physical-mechanical properties of clay materials (breaking strength limit within moisture condensation zone and thermal stability), and, as a result, improved processing characteristics of sand mixtures reduced usage of materials and increased quality of casts. 3 cl, 2 tbl

Description

 The invention relates to foundry, namely to the manufacture of raw sand and clay molding sand.

 In modern foundry, various clay materials, primarily bentonites, are used to prepare molding sand. All clay materials in the exchange complex contain cations of sodium, potassium, calcium, magnesium, iron, the composition and total amount of which are determined by the natural features of the clay material. At the same time, the optimum physicomechanical and technological properties of clays for foundry production are tensile strength at break in the zone of moisture condensation, thermal stability is achieved only if the exchange complex contains mainly sodium cations. Therefore, when using calcium-magnesium clay materials, primarily bentonites, an activation operation is used, i.e. artificial replacement of cations of calcium, magnesium and iron by sodium cations.

There is a known method of activating bentonite, according to which a product of condensation of naphthalene sulfonic acids with formaldehyde neutralized with sodium hydroxide and a non-inogenous surfactant in the form of polyethylene glycol ether and alkyl phenols is sequentially introduced into a mixture of bentonite and soda ash, and grinding is carried out in a jet mill with a speed class in 1 min 600-1200 [1] The main disadvantage of this method is a significant reduction in the physicomechanical properties of the intermediate due to its over-grinding tions. There is a technical solution in accordance with which a suspension is prepared by sequentially loading clay, water and an activator into the mixer. As an activator, sodium tripolyphosphate in an amount of 0.29-1.5% (4-20 mg ^. Equiv. Per 100 g of clay) or sodium pyrophosphate in an amount of 0.57-3.0% (5-27 mg ^. Equiv ^. 100 g of clay) by weight of clay (in terms of dry matter) [2] The disadvantage of this solution is: the proposed content of activators does not provide optimal activation of bentonite clays, the sum of exchange cations in the exchange complex of which is 50-120 mg ^. eq. per 100 g; when bentonites are used for activation only phosphates in the amount necessary for the complete replacement of cations of calcium, magnesium and iron, i.e. significantly larger than that proposed in the indicated source, accumulation of phosphorus compounds in the mixture and, accordingly, undesirable saturation of surface layers of castings by it is possible. There is also a technical solution, according to which the activation of bentonite is carried out directly during the preparation of the molding mixture, while as an activator, a solution of three simple sodium compounds, soda ash, caustic soda (caustic soda), trisodium phosphate is introduced into the mixer [3] This technology also unsuitable for the activation of clay materials with a predominance of calcium and magnesium cations in the exchange complex.

 Closest to the proposed is the activation method, involving the mixing of bentonite clay with sodium salt while moistening the ingredients with water. As sodium salt, soda ash is used (4). The disadvantage of this method is that it is suitable for the activation of clay materials of the calcium type, i.e. when it is used, only the replacement of calcium cations is provided. If there is a significant amount of magnesium and iron cations in the exchange complex of clay material, their substitution does not occur and the maximum possible physical and mechanical properties of the product are not achieved.

 The aim of the invention is the complete replacement of cations of calcium, magnesium and iron in the exchange complex of clay material with sodium cations, which ensures the maximum possible value of tensile strength for a given material at break in the moisture condensation zone and, accordingly, technological properties.

The goal is achieved in that the activation process of clay materials is carried out in two stages. At the first stage, one or several simple sodium compounds are introduced into the clay material, for example, soda ash and / or sodium hydroxide and / or trisodium phosphate, and the clay is moistened to the state of a paste or suspension of the clay material or the molding mixture containing it with the ingredients introduced. At the second stage, the clay material preactivated with simple sodium compounds and moistened to the state of a paste or suspension is introduced to form alkaline earth and transition metal complex compounds with exchange cations of the clay material. As such compounds, condensed salts of phosphoric acids are used: trisodium phosphate or sodium pyrophosphate. The amounts of activators added at each stage depend on the composition and concentration of the exchange cations of the clay material. The concentration of each cation is determined in mg ^. equiv according to GOST 28177-89, and the number of activators is determined by the formulas.

For simple sodium compounds:
A ₁ (0.5 1.5) G ₁ K, (1) where A _{1 is the} amount of simple sodium-containing compounds;
G ₁ - the amount of activator in g, corresponding to one mg ^. equivalent;
To the concentration of calcium cations in 100 g of clay substance, mg ^. eq.

For complex-forming activators:
A ₂ (0.2 -1.5) G ₂ (M + F), (2) where A _{2 is the} number of condensed salts of phosphoric acids;
M concentration of magnesium cations in 100 g of clay substance, mg ^. eq;
F total concentration of cations and ferric iron per 100 g of clay substance ^mg. eq;
G _{2 the} amount of activator in g corresponding to its mg ^. equivalent.

 Thus, in accordance with the invention, in the first stage, the exchange of cations of calcium with sodium cations is carried out with sodium cations, and with magnesium and iron cations for the second. The simultaneous introduction of activators in one stage does not lead to an optimal result, since the complexing ability of, for example, compounds such as polyphosphates, decreases in the presence of sodium trisodium phosphate, etc. compounds.

 The proposed activation process is carried out depending on the type of mixer available. If a batch mixer is used, then after loading bentonite and, if necessary, moistening it, a simple salt is introduced, for example, soda ash in an amount corresponding to that determined by formula (1). After mixing, a complexing compound, for example sodium tripolyphosphate, is introduced in an amount determined by the formula (2).

 If the clay material was activated in a paste state, it is transported to a drying and further grinding unit; if the suspension is activated, then it is transferred to the aggregates for preparing the molding sand. When activating clay material in the composition of the molding mixture, all further operations are carried out in accordance with the usual technological process of mixing. When activating clay material in continuous mixers, two successive units are used, in each of which a calculated amount of the corresponding activator is introduced.

 As a result of the use of the present invention, clay materials and molding mixtures based on them are characterized by maximum physical and mechanical properties, tensile strength at break in the moisture condensation zone, heat resistance, and a minimum content of phosphorus compounds.

Assessment of the physicomechanical properties of clay materials activated by any method was carried out in accordance with the methods of GOST 28177-89, for which mixtures of 5 parts by weight were prepared. bentonite, 95 m.h. quartz sand Gremyachevsky quarry ZIL and water. The compressive strength of this bentonite, determined according to GOST 28177-89, was 1.15 kgf / cm ² .

The composition of the exchange cations, mg ^. equiv: Calcium 39.9 Magnesium 31.8 Potassium 3.1 Sodium 2.1 Iron (total) 4.3 Total: 81.2
The bentonite activated by the proposed method is characterized by a tensile strength at break in the moisture condensation zone of 0.032-0.034 kg / cm ² , which is twice as high as activated by the prototype method, its heat resistance was 0.83-0.85 with an allowable content of phosphorus compounds in the mixture. The obtained level of properties for this clay material (bentonite) is sufficient for the manufacture of castings on all modern automatic lines. A decrease in the amount of simple sodium compounds introduced in the first stage of activation below the level determined by the calculation according to formula (1) necessitates an increase in the number of activators introduced in the second stage. This leads to undesirable accumulation of phosphorus compounds in the mixture and is not economically feasible.

 An increase in the amount of simple sodium compounds introduced in the first stage of activation below the level calculated by formula (1) leads to a decrease in the tensile strength at break in the moisture condensation zone.

 A decrease in the amount of condensed salts of phosphoric acids introduced in the second stage of activation, forming complex compounds of alkaline-earth and transition metals with exchange cations of clay material, leads to a decrease in the strength at break in the moisture condensation zone and the heat resistance of the clay material.

 An increase in the amount of condensed salts of phosphoric acids introduced in the second stage of activation, forming complex compounds of alkaline-earth and transition metals with exchange cations of clay material, also leads to a decrease in the tensile strength at break in the moisture condensation zone of the clay material and undesirable accumulation of phosphorus compounds.

 EXAMPLE 1. Activation was carried out in a continuous laboratory screw mixer. In the first stage of activation, lumpy bentonite and soda ash were introduced into the mixer with continuous stirring. The moisture content of the paste was 25-30%. Then, the first stage of activation of bentonite was sent to the mixer again, while sodium tripolyphosphate was introduced. The amount of activating additives at each stage was determined according to formulas (1) and (2), respectively. After the second stage of activation was completed, the bentonite paste was dried, ground in a ball mill, and the powder was tested in the composition of molding mixtures in accordance with GOST 28177-89. The product thus obtained complies with the highest requirements.

 PRI me R 2. Activation was carried out in laboratory runners of periodic action during the preparation of the molding mixture of a standard sample for testing bentonite according to GOST 20177-89.

 At the first stage of activation, the amount of sodium hydroxide calculated by formula (1) was introduced into the mixer. After stirring the resulting mixture, the calculated amount of sodium pyrophosphate was introduced and the mixture was mixed again for 5 minutes. The test results of bentonite activated in this way confirmed its high quality.

 PRI me R 3. The operations are carried out analogously to example 1, but in the first stage of activation, soda ash, caustic soda and trisodium phosphate are introduced in the form of a spent degreasing solution of galvanic production. The total number of components of this solution was also determined by the formula (1).

 In the second stage of activation, the amount of sodium tripolyphosphate determined by formula (2) was introduced. The product obtained in this case has sufficiently high properties.

 PRI me R 4. Activation is carried out in one stage in one stage in a continuous screw mixer. Calculated by the formulas (1), (2), the quantities of activators of soda ash and sodium tripolyphosphate were introduced simultaneously. Further operations, as in example 1. The finished product is characterized by low strength in the zone of moisture condensation.

 PRI me R 5. The operations are carried out similarly to the example, but in the first stage, an excess compared to the estimated amount of soda ash is introduced. Activated bentonite is characterized by a lower tensile strength at break in the zone of moisture condensation and heat resistance.

 PRI me R 6. The operation is carried out analogously to example 1, but at the first stage of activation is introduced lower than the calculated by the formula (1) amount of soda ash. In this case, there is also a decrease in the tensile strength at break in the zone of moisture condensation and thermal stability of bentonite.

 PRI me R 7. The operation is carried out analogously to example 1, but in the second stage of activation, an excess amount of sodium tripolyphosphate activator is introduced in comparison with the calculated by formula (2). In this case, there is also a decrease in tensile strength at break in the moisture condensation zone and to a lesser degree of thermal stability of the product compared to the best option. In addition, the content of phosphorus compounds in the mixture increases.

 PRI me R 8. The operation is carried out analogously to example 1, but in the second stage of activation is introduced reduced in comparison with the calculated by formula (2) the amount of activator of sodium tripolyphosphate. In this case, there is also a decrease in tensile strength in the zone of moisture condensation and thermal stability of the clay material.

 PRI me R 9. Made for comparison according to the technology described in [3], ie, in the amount of activating sodium-containing additives used waste degreasing solution of galvanic production (the content in bentonite is given in terms of dry residue).

 PRI me R 10. Performed by a method analogous to the one-stage activation of bentonite paste with soda ash in an amount that provides the maximum tensile strength for this activator in the zone of moisture condensation. This technology is currently in widespread use. When using soda to activate calcium-magnesium clay materials (bentonites), it is impossible to significantly increase their tensile strength at break in the condensation zone.

 The activation modes and activators used in examples 1-10 are presented in table 1, and the test results in table 2.

 The proposed method allows to achieve a significant economic effect by increasing the physicomechanical properties of previously practically unused clay materials and involving them in the national economy. In addition, the consumption of molding materials is reduced, the quality of castings is improved and scrap is reduced.

 The proposed method is implemented on existing equipment, and therefore almost no additional costs are required.

Claims (3)

 1. METHOD OF ACTIVATION OF CLAY MATERIALS by introducing sodium-containing compounds as activators to replace the exchange cations of calcium, magnesium and iron of clay materials with sodium cations of the activator and mixing them with clay materials while moistening, characterized in that the sodium-containing compounds are introduced in two stages, moreover in the first stage, simple salts and / or bases are introduced as these compounds, and in the second stage, condensed salts of phosphoric acids. 2. The method according to p. 1, characterized in that as simple sodium-containing compounds use soda ash and / or sodium hydroxide, and / or trisodium phosphate, and their amount is determined by the formula
A ₁ (0.5 1.5) G ₁ · K
where A _{1 the} number of simple sodium-containing compounds;
G _{1 the} amount of activator corresponding to 1 mg · equiv, g;
To the concentration of calcium cations in 100 g of clay material, mg · equiv. 3. The method according to PP.1 and 2, characterized in that as the condensed salts of phosphoric acids using tripolyphosphate or sodium pyrophosphate, and their number is determined by the formula
A ₂ (0.2 1.5) D ₂ (M + F)
where A _{2 the} number of condensed salts of phosphoric acids;
G _{2 the} amount of activator corresponding to 1 mg · equiv, g;
M concentration of magnesium cations in 100 g of clay material, mg · equiv;
W the total concentration of cations of ferrous and ferric iron in 100 g of clay material, mg · equiv.

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