EA028489B1 - Molding composition and molding mixture comprising said composition - Google Patents

Abstract

A molding composition and a molding mixture comprising said composition relate to the field of foundry production, namely to compositions of molding compositions used in the molding mixtures in the manufacture of raw single molds from sand-clay (or bentonite) mixtures for castings from ferrous alloys. It is characterized by the fact that the molding composition containing the clay binder (bentonite or kaolinite clay) and the zeolite additionally contains schungite at the following component ratio, weight parts: clay binder - 65-90, zeolite - 8.9-32, schungite - 1.8-3.2, and the molding mixture on the basis of quartz sand and water additionally contains a molding composition of the above formulation with the following component ratio, weight parts: molding composition - 5-15, quartz sand - 85-95, water - 2.5-5.0. The technical result of usage of the proposed formulation of the mixture based on the joint use of zeolite and schungite provides obtaining technologically resistant to moisture content changes (at moisture levels elevated to 5%) formulation of a high-strength high-flow ductile molding mixture with increased thermal stability due to maintaining activity of the bentonite binder, irrespective of a method for compacting molds, type and temperature of the metal being poured (cast iron or steel), which promotes increase of resistance of the compacted mold to additional irreversible deformations affecting the integrity of the mold during broaching and accuracy of obtained casting, as well as reduction of consumption of the binder.

Description

The invention relates to the field of foundry, and in particular to compositions of molding compositions used in molding mixtures in the manufacture of raw single molds from sand clay (or bentonite) mixtures for castings from ferrous alloys (cast iron or steel).

A characteristic feature of the proposed molding composition is the presence in its composition of only inorganic components.

It is known from the prior art to use a mineral additive — zeolite in molding mixtures as a separate additive for additional activation of sodium bentonite [IPC B22C 1/18, IE No. 4331697 A1, publication 1995.03.23], and as part of a non-stick additive with graphite or as part of a non-stick compositions with graphite and bentonite [ΕΝνίΒΟΝΌ mixture, Cornelius Grefhorst, Rudolf Grepac, Materials of casting molds for casting iron with binders based on bentonite without organic additives, Foundry and foundry technology, 2006, pp. 8-16].

The specified coal-free molding materials are environmentally friendly, highly susceptible to water, which is ensured by the presence of zeolite in them, and the presence of graphite in the materials causes a slight increase in the strength, density and fluidity of molding mixtures based on them. However, the presence in the compositions of zeolite mixtures contributes to a certain decrease in their plastic properties.

Zeolites are minerals from the group of aqueous aluminosilicates of alkaline and alkaline-earth elements with a tetrahedral and structural skeleton, including cavities occupied by cations and water molecules. Zeolite is a porous crystal with a rigid frame. The cations filling the cavities are surrounded by hydration shells and are relatively easy to ion exchange. It is characteristic that the parameters of this skeleton change little during dehydration as a result of heating to a sufficiently high temperature (more than 500 ° C).

Also known from the prior art is the use of mineral shungite additives. Shungite is a natural carbon-containing rock, which is a composite consisting of shungite carbon (30%) and highly dispersed particles of silicates, mainly silica.

Shungite carbon is unusual in its structure, properties and interaction with silicate components: it has an amorphous structure, is resistant to graphitization, and is characterized by high sorption properties and reactivity. Crystalline carbon in shungite rock is present in very small quantities.

For example, a molding composition of the following composition is known, parts by weight: ground coal - 10-75, component carrier of brilliant carbon - 3-20, carbon black - 0.2-2, bentonite - 5-75, shungite 2-12 [IPC B22C 1/20, EA No. 017009, publication 2012.09.28].

The presence in the specified molding composition of a clay binder (bentonite) in an amount of 5-75 parts by weight allows you to develop compositions of molding mixtures with high strength without additional input of a binder (see table and position 3 in the specified patent).

However, the specified composition of the molding composition does not imply its use in molding sand for the manufacture of steel casting, since it is mainly a non-stick anti-shrink material for producing cast iron castings. On the contrary, the proposed molding composition forms the entire structure of the mixture and the whole complex of basic technological properties necessary to obtain both steel and iron castings.

Based on the technical nature and the achieved result, according to the authors, the prototype of the claimed molding composition is a non-stick composition - bentonite, graphite, zeolite - ΕΝνΕΝ.

The main disadvantage of using this composition in the composition of the molding sand is its inability to provide a sufficiently high level of plastic properties of the molding sand. It is known that in order to obtain high-quality molds and castings using modern models of complex configuration on modern automatic molding lines (AFL), the molding mixture must have high rates of both strength and ductility (fluidity). However, it was precisely the loss of plasticity of the moldable mixture containing the specified non-stick composition (ΕΝνίΒΟΝΟ mixture) that was noted during its testing at the I18A plant. [Cornelius Grefhorst, Rudolf Grepac, Foundry materials for casting iron with binders based on bentonite without organic additives, Foundry and foundry technology, 2006, p. 8-16].

The prototype of the claimed composition of the molding mixture, according to the authors, is the molding mixture for the manufacture of single raw molds for castings from black cast alloys of the following composition (wt.%):

bentonite - 5-10.

shungite - 2-5 of the bentonite content, quartz sand - the rest is up to 100%, water - 2.5-3.5 in excess of 100%.

[IPC B22C 1/20, EA No. 017010, publication 09/28/12].

The introduction of shungite positively affects such technological properties of the molding sand as fluidity by a stepwise test, tensile strength when wet, and formability index

- 1 028489 and bulk density.

The most significant drawback of this composition of the moldable mixture with shungite is the lack of stabilizing properties of the moldable mixture with respect to humidity, especially at its increased values (4-5%) and insufficient increase in strength at break in the moisture condensation zone.

An object of the invention is to develop the composition of the molding composition and the molding sand based on this composition without additional input components used in the manufacture of raw single forms of sand-clay mixtures, eliminating the disadvantages of the prototype, providing a high level of the complex technological properties of the mixture at high humidity, as well as obtaining high-quality molds and castings according to models of complex configuration for both iron and steel castings, regardless of the compaction method.

The technical result of solving the problem is to increase the strength properties of the mixture in the wet state both during compression, rupture and cleavage, and during rupture in the moisture condensation zone without increasing the binder content;

ensuring technological stability of the properties of the mixture to changes in moisture content at high humidity up to 5%;

increasing the thermal stability of the molding sand by maintaining the activity of the clay binder;

ensuring a positive effect on the behavior of the mixture, regardless of the method of compaction of the molds, as well as the type and temperature of the poured metal (cast iron or steel);

improving the sanitary and hygienic situation in the foundry by reducing the dust level and consumption of molding materials due to increased thermal stability of the molding mixture, as well as simplifying the process of preparing the molding mixture by eliminating the supply of individual components of the molding composition in the molding composition.

The required technical result is achieved by the fact that the molding composition containing a clay binder (bentonite or kaolinite clay) and zeolite additionally contains shungite in the following ratio of components, parts by weight: clay binder - 65-90, zeolite - 8.9-32, schungite 1.8-3.2, and the molding mixture based on quartz sand and water additionally contains a molding composition of the above composition with the following ratio of components, in wt.%): molding composition - 5-15%, quartz sand up to 100%, water - 2.5-5.0 in excess of 100%.

The binder content in the molding composition is less than 65 parts by weight. does not provide a sufficient level of strength properties of the molding sand. The binder content of more than 90 parts by weight requires an increased water content, which leads to an increase in the gas-generating ability of the mixture and contributes to the formation of burns and squids

The increase in the content of the molding composition of the zeolite above 32 wt.h. and shungite above 3.2 wt.h. impractical due to the lack of an additional effect of influence on the main technological properties of the molding sand.

The decrease in the zeolite content below 8.9 parts by weight and shungite below 1.8 wt.h. impractical due to the reduction of the effect of a positive effect on the compressive strength and tensile strength in the wet state, as well as the tensile strength in the moisture condensation zone and fluidity, determined by the stepwise test.

The content of the molding composition in the composition of the molding sand of less than 5 wt.% Does not provide a sufficient level of the complex technological properties of the molding sand. The content of the molding composition in the composition of the molding mixture of more than 15 wt.% Requires an increased water content, which can contribute to an increase in marriage of castings due to gas defects, burnout and bumps.

The amount of moisture (moisture indicator) in the mixture will depend on the amount and nature of the binder, ambient temperature, etc. The optimal amount of water introduced into the mixture is 2.5-5.0 wt.%.

The decrease in moisture content in the mixture below 2.5 wt.% Increases the fragility and crumbling of forms. The increase in moisture content above 5.0 wt.%. adversely affects the properties of the mixture and the surface quality of the castings (suppers, burns).

In the examples, Khakassky activated bentonite and Nizhne-Uvelskaya kaolinite clay were used as a binder for molding sand. The composition evaluation was carried out in accordance with GOST 2817789, GOST 23409, as well as additional methods.

Preparation of molding mixtures and determination of technological properties was carried out mainly using the Polish set of laboratory equipment (f. \ Uabar). Strength in the zone of moisture condensation was determined using a model 05212M device (Kharkov).

It is known that to assess the behavior of a clay binder in a mixture under thermal loads, the determination of heat resistance according to GOST 28177-89 (the ratio of the compressive strength after calcination and before calcination) is necessary, but insufficient. For a more complete assessment of heat resistance, for example, when changing the composition of the molding sand, it is necessary to determine the effect of the introduced additives on the preservation of the active binder after thermal loading. Comparative

- 2 028489 studies of compressive strength and tensile strength in the wet state, tensile strength in the moisture condensation zone, as well as the sorption ability of molding mixtures of different compositions before and after heat treatment of the binder and mineral additives. For this, the corresponding samples were processed in a furnace at a temperature of 550 ° C for 1 h, then the heat-treated minerals were used to prepare the molding mixtures according to GOST 28177-89 and determine these parameters.

In addition to standard methods for determining the fluidity of a mixture by a stepwise sample by measuring the hardness with a ball hardness tester, the hardness and fluidity of the samples was measured by an electronic hardness tester PPP f. Shshrkop Oegoka. The device measures the force corresponding to the penetration resistance of the pin element into the mold surface. The readings of an electronic hardness tester are a complex characteristic that determines the hardness, density and surface strength of a mold (sample), as well as allowing an additional assessment of the plasticity (fluidity) of a mixture using a stepwise test (fluidity of PPP).

The results of the above studies are given in table. 1-3.

In the table. 1 presents an assessment of the properties of molding compounds according to GOST 28177-89 before and after heat treatment of a bentonite binder with zeolite and shungite, separately and together. In addition to the properties specified in GOST 28177-89, such properties of the molding mixture as tensile strength in the wet state and sorption ability before and after heat treatment were determined.

As can be seen from the material presented in table. 1, the introduction of mineral additives in the molding mixture has a positive effect on the quality of the bentonite binder, in particular on the basic strength properties of the mixture and sorption ability. When one zeolite is introduced into the mixture, an increase in the compressive strength of the molding sand is increased by 19%, the tensile strength at break in the wet state by 25%, the tensile strength at break in the moisture condensation zone by 20%, and sorption ability by 15%. The introduction of shungite in the mixture helps to increase the tensile strength at break in the wet state by 25%, the tensile strength at break in the zone of moisture condensation by 12%, and sorption ability by 15%.

The best result on the effect on the strength properties of the mixture and sorption ability was shown by the use of the proposed molding composition — an increase in the strength and sorption capacity of the mixture is on average 25-30%.

In addition, it can be seen from the presented material (Table 1) that in a comprehensive assessment of the thermal stability of a bentonite binder (determination of compressive strength, wet gap, gap in the moisture condensation zone, and also the sorption ability of the mixture before and after calcination) the proposed molding composition to a greater extent contributes to the preservation of the active binder in the mixture than the use of mineral additives (schungite or zeolite) in the mixture separately. Apparently, this is facilitated by the combination of the presence of a zeolite in the moldable mixture, on the one hand, having a rigid framework, which does not practically change its parameters during dehydration as a result of heating, and, on the other hand, shungite, whose structure includes shungite carbon, characterized by high sorption properties and reactivity. It should be noted once again that only the combined use of zeolite and schungite as a part of the mixture helps to preserve the whole complex of properties of the molding sand after heat treatment.

- 3,028,489

Table 1

The influence of the proposed molding composition and the mineral additives included in its composition on the tensile strength and sorption ability of molding compounds

The content of the molding composition in the mixture, wt.% The content of mineral additives in the molding composition, mass parts Before heat treatment After heat treatment Heat resistance in accordance with GOST 28177-89 bentonite shungite zeolite The compressive strength in the wet state, kg / cm ² The tensile strength at break in the wet state, kg / cm ² The tensile strength at break in the zone of moisture condensation, g / cm ² Sorption capacity, ml / 5 mg The compressive strength in the wet state, kg / cm ² The tensile strength at break in the wet state, kg / cm ² The tensile strength at break in the zone of moisture condensation, g / cm ² Sorption capacity, ml / 5 mg BY compression by break by gap in the zone moisture condensation by sorption abilities 5 75 0 0 0.95 0.12 25 twenty 0.95 0.12 twenty nineteen one one 0.80 0.95 7 75 0 thirty 1.13 0.15 thirty 23 1.13 0.15 26 23 one one 0.87 one 5.15 75 2,3 0 0.96 0.15 28 23 0.96 0.14 23 nineteen one 0.93 0.82 0.83 7.15 75 2,3 thirty 1.25 0.16 32 25 1.25 0.16 32 25 one one one one

The experimental data presented in table. 2, indicate that the combined use of zeolite and shungite in the molding mixture enhances the stabilizing effect compared with a mixture containing only zeolite or only shungite. Moreover, the introduction of only shungite at high humidity has a minimal positive effect on the complex of technological properties of the molding mixture. Zeolite as a result of the stabilizing effect on the properties of the mixture increases the set of technological properties at high humidity. The greatest stabilizing effect is achieved when using the proposed molding composition. Compared with a mixture containing separately zeolite or shungite, there is an increase in the level of the following properties of the mixture:

compressive strength in the wet state by 14% (with humidity 5%) and 26% (with humidity

3%);

tensile strength in the wet state by 35% (with a moisture content of 5%) and 18% (with a moisture content of 3%);

strength when cleaved in the wet state by 30% (with humidity 5%) and 32% (with humidity

3%);

formability by 32% (at a moisture content of 5%) and 59% (at a moisture content of 3%); stepwise fluidity of 18% (at a moisture content of 5%) and 12% (at a moisture content of 3%); the strength of the RTR (block) by 21% (with a moisture content of 5%) and 2 times (with a moisture content of 3%); strength of the RTR (frontal surface) by 19% (with a moisture content of 5%) and 14% (with a moisture content of 3%); RTR yield by 27% (at a moisture content of 5%) and 74% (at a moisture content of 3%).

Thus, due to the combined use of mineral additives — zeolite and schungite — in the proposed molding composition, the molding mixture acquires increased RTR flow values. In combination with an increase in the quality indicators of the molding mixture, such as stepwise fluidity and wet tensile strength, the introduction of the proposed composition has a positive effect on the process of mold compaction and, in particular, on the quality of the model’s print, and enhances the endurance of the compacted mold to additional irreversible deformations, affecting the preservation of the integrity of the form during broaching the model and the accuracy of the obtained castings.

- 4,028,489

table 2

The influence of the proposed molding composition and mineral additives included in its composition on the complex of technological properties of the mixture at high humidity

The content of the molding composition in the mixture, wt.% 10 10.3 12 12.3 The content of mineral additives in the molding composition, mass, h bentonite 75 75 75 75 shungite 0 2,3 0 2,3 zeolite 0 0 fifteen fifteen Properties of the sand Humidity% 5.03 3.02 4.95 3.0 5,0 3.0 5,0 3.3 Sealability,% 70 60 70 60 69 fifty 69 thirty Bulk weight, g 90 112 91 122 95 130 80 199 Formability Index,% fifteen 59 17 82 twenty one hundred 25 145 Stepwise fluidity,% fifty 70 56 76 60 76 74 85 The strength of the PPP boob sample step, N / cm ² 1,0 2,5 1.3 4,5 1,5 5 1.7 9.5 Strength PPP of the frontal surface of the step sample, N / cm ' 12 twenty thirteen 25 14 26 sixteen 29th The turnover of PPP,% 8 thirteen 10 eighteen eleven nineteen 14 33 The compressive strength in the wet state, kg / cm ² 0.98 1,50 0.99 1.80 1.15 2.0 1.22 2,4 The tensile strength in the wet state, kg / 'cm ² 0.15 0.22 0.16 0.28 0.18 0.28 0.23 0.33 Strength at a chip when wet, kg / cm ' 0.25 0.33 0.26 0.35 0.28 0.40 0.35 0.49

Table 3

The compositions of the proposed molding composition and the level of basic technological properties of molding compounds provided by them

The composition of the molding composition, mass.h The composition of the molding mixture, mass. % Properties of the sand clay binder n IN § n in and IN G B about 8 from 3 with At one and K ig oz 2 in 1 about m About e 2 Ξ & 1 e * δ 2 about δ Ξ £ X and O. Oh and In co 5 "H (=: o so oa The compressive strength in the wet state, kg / cm ² The tensile strength in the wet state, kg / cm ² The tensile strength in the zone of moisture condensation, g / cm ² Fluidity by step sample,% 65 (bentonite) 8.9 1.8 95 5 2,5 1.20 0.15 thirty 80 90 (clay) 32 3.2 85 fifteen 5,0 0.80 0.12 10 65

Thus, the use of the proposed composition of the molding composition for the manufacture of raw single sandy-clay molds provides an increase in the strength properties of the mixture in the wet state both during compression, rupture and cleavage, as well as rupture in the moisture condensation zone without increasing the binder content;

technological stability of the properties of the mixture to changes in moisture content at high humidity up to 5%;

increasing the thermal stability of the molding sand by maintaining the activity of the bentonite binder;

the effect on the behavior of the mixture, regardless of the method of compaction of the molds, as well as the type and temperature of the poured metal (cast iron or steel).

It should be noted that when applying the proposed composition, the effect of increasing the heat resistance of the binder, as well as the fluidity of the RTP, is achieved, which confirms the positive effect of the joint use in the proposed composition of the molding composition of two mineral additives - zeolite and shungite.

The combination of these properties helps to increase the endurance of the compacted mold to additional irreversible deformations, which affect the preservation of the integrity of the mold during broaching the model and the accuracy of the castings obtained, reduce the consumption of molding materials (binder), obtain a high-quality print of models of critical castings of complex configuration, and also provide an impact on the behavior of the molding mixtures regardless of the method of compaction of the forms, type and temperature of the poured metal and improves sanitary and hygienic conditions Slovenia of labor.

Claims (2)

CLAIM 1. A molding composition comprising a clay binder (bentonite or kaolinite clay) and a zeolite, characterized in that it further comprises shungite in the following ratio of components, parts by weight: clay binder - 65-90, zeolite - 8.9-32, shungite - 1.8-3.2. 2. The molding mixture, including quartz sand and water, characterized in that it further comprises a molding composition with a composition according to claim 1 in the following ratio of components, parts by weight: molding composition - 5-15, quartz sand - 85-95, water - 2.5-5.0.