UA141852U - METHOD OF MANUFACTURE OF FOAM-CERAMIC FILTERS AND POROUS MATERIALS - Google Patents

Abstract

A method of manufacturing foam ceramic filters and porous materials includes mixing loose bulk filler, binder, pore former and other technological impurities, compaction of the formed mixture in the molding equipment, removal of the pore generator, drying and heat treatment of the molded product. In this case, granular ice in the amount of 8-90% by weight of the mixture is used as a pore former, the removal of which is performed by melting, standing at room temperature or by heating the mixture or product.

Description

The useful model belongs to foundry production and can be used to obtain foam ceramic filters, which are used for filtering molten metals and alloys. Foam ceramic filters allow to improve the quality of cleaning of metal melts and reduce the lack of castings. In this way, it is also possible to obtain foam concrete porous materials for construction or wall insulation, or fire-resistant materials with high gas or liquid permeability for casting molds or composite products by pouring molten metal into the pores.

There is a known method of forming with filtration of water from melting ice into a sand forming mixture and creating solid sand shells of a casting mold or cavities in a sand rod in it according to ice models (1Й. During the standing of the casting mold or rod, three operations are achieved involuntarily: melting of the ice model, filtration its melting into a loose sand mixture and solidification of this mixture, which takes place due to the chemical reaction of water (from the melt of the model) with hydration binders (gypsum or cement), which are mixed into the loose mixture during its preparation. To accelerate such solidification, a mold or the rod is heated to a temperature of 40-100 "С.

A similar hardening mechanism is used for a free-flowing molding mixture, the hydration of which is performed by melting the free-flowing granular ice introduced into this mixture (21.

At the same time, involuntary capillary movement of moisture in the pores of the mixture is used. The composition of the mixture, according to the example, includes a hydration binder - semi-aqueous gypsum 10-40 95 (by mass) and loose granular ice for hydration - 4-8 95, the rest - dispersed filler (sand).

These methods make it possible to create sand products with cavities formed according to ice models that melt and are removed from the cavities, and to use free-flowing self-hardening sand mixtures with granular ice, the hardening and hardening of which occurs due to the reaction of melt water with a powder binder in the composition of these mixtures The free-flowing nature of these mixtures allows them to be easily mixed, poured into the forming equipment and quickly compacted, in particular by vibration. Such resource-efficient technologies with the spontaneous melting of ice during the formation of sand cavities at the same time as the self-hardening nature of the hardening of the forming mixture to a monolithic solid state can serve as analogs of the claimed method, but they are not used for the manufacture of foam ceramic filters and porous

From materials, in particular for foundry and metallurgical technologies and the building materials industry.

A well-known fire-resistant composite concrete mixture (|Z) containing a fire-resistant filler, binder - high-alumina cement and an admixture, with the following ratio of components, wt. 9o: refractory aggregate - 62-65, high-alumina cement - 15-20, admixture (finely ground material) - 17-20. The fire resistance of products from such a mixture is 1500-1530 "С.

This refractory mixture contains high-alumina cement that hardens after moistening with water, the mixture is suitable for use in the foundry and metallurgical industry, has increased strength in products at high temperatures, but does not contain a pore former for the production of foam ceramic filters and porous materials.

Currently, foam ceramic filters are widely used, the peculiarity of which is that, having a relatively large pore size (0.5-5.0 mm) and a porosity of up to 90 95, thanks to their three-dimensional labyrinth structure, they retain by adsorption particles of inclusions up to up to micron sizes (4, 5|Y. The high permeability of these materials is determined by the capillary structure, foam ceramic filters contain continuous solid and gaseous phases.

The closest to the declared one is the method of manufacturing foam ceramic filters, which includes the manufacture of a ceramic slip with finely dispersed filler and binder |b).

Pore formation is carried out by impregnating organic foam with a ceramic slip in the sequence that this slip is homogenized, with the calculated amount of this slip, depending on the thickness of the ceramic bridges in the foam ceramic filter, fill the container with a blank made of organic foam, impregnate the blank in the mode of cyclic deformations until the ceramic slip is completely absorbed , carry out drying and burning of organic foam. The method describes the impregnation of a workpiece made of polyurethane foam with a size of 5x5x1.5 cm and a volume of 37.5 cm3. The pores of the resulting foam filter are 1.0-1.5 mm in size.

The disadvantages of this method are the use of organic foam - polyurethane foam for pore formation and impregnation of the workpiece in the mode of cyclic deformations until complete absorption of the aqueous ceramic slip. The industrial use of polyurethane foam as a pore former, as indicated in work I/|), gives pore sizes of no more than 2.5 mm, thereby limiting technological possibilities, the sizes of filters and porous material obtained by impregnation, in addition, it is difficult to stably obtain the same functional properties on it. because it is not easy to obtain a foam with the same pores, membranes or walls with each foaming. because the equipment for impregnating the workpiece with such foam in the mode of cyclic deformations until the absorption of aqueous ceramic slip is quite complex and is not suitable for foundry shops, but only for specialized production. The production of foam ceramic and porous materials in this way is limited by the rather small size of the pores and the low stability of the characteristics of the products due to the presence of various cells and walls, which affects the nature of the permeability of the filters.

Also, combustion of organic foam can produce soot residues on the filter walls, which is undesirable for filtering alloys limited in carbon content; and the process of thermal destruction of organic polymers requires means of neutralization of the resulting harmful products, which, for example, is not inherent in the melting of inorganic low-melting pore-forming materials.

The purpose of the useful model is to simplify the production of foam ceramic filters and porous materials, to increase the pore size above 2.5 mm, and to increase stability while achieving the same porosity of the products.

The task is solved by the fact that in the method of manufacturing foam ceramic filters and porous materials, which includes mixing of loose fine-dispersed filler, binder, foaming agent and other technological additives, compaction of the resulting mixture in the molding equipment, removal of the foaming agent, drying and heat treatment of the formed product, according to a useful model, as a pore former, granular ice is used in the amount of 8-90 96 by mass of the mixture, which is removed by melting by standing at room temperature or by heating the mixture or the product. Also, a hydration binder can be introduced into the mixture when mixing the loose fine-dispersed components, which is moistened by the melt of the pore former introduced into the mixture, and as a result of this moistening, the mixture is hardened and hardened to a monolithic state by the formation of crystal hydrates. In addition, while the mixture is standing in the molding equipment, it can be heated to a temperature of 400-100 C, water or an aqueous solution at this or room temperature can be supplied to the upper surface of the mixture, or water or an aqueous solution can be supplied to the upper surface of the mixture, and from the lower surface of the mixture through the holes in the bottom of the equipment, this mixture is vacuumed in the periods before the beginning of the melting of granular ice or (and) after the mixture solidifies to squeeze out excess water from the formed product.

If in the method Ib) foam is used as a one-time model that is permeated (in the pores) with a slip and fired, then in the proposed method for the formation of cavities of foam-like materials

Melting models are used. The method was implemented based on the experience of forming ice models || and taking into account forming methods using granular or loose ice |2, 8, 9|Ї, in which a number of examples of its application in foundry production are described. At the current stage of the development of refrigeration technology, water ice has a relatively low cost, is fully compatible with the environment, which leads to the wide use of ice and water-ice solutions in agriculture, food industry, trade, air conditioning systems, construction, etc. Ice is obtained both by refrigeration units, ice generators, and by using the natural cold of the environment. More than 1 million tons of artificial ice, both technical and food, are produced annually in the world |10Y. Modern small and medium-sized stores buy ice generators with a capacity of 120-300 kg of ice per day, and hypermarkets use units that produce up to 2.5 tons of ice. With the help of ice generators and ice crushers, which are serially produced in dozens of types and sizes, different sizes and shapes of ice grains are obtained. There are also dozens of ways, including domestic ones, of obtaining loose or granular ice. Flaky, granulated ice and ice crumb were used, taking into account the pores that should be obtained in foam ceramic or porous products. Granular ice was sifted or collected according to the granulometric composition.

The implementation of the method is based on the fact that the mixture is mixed from loose components, it is easier than preparing a moistened mixture, because water creates bonds with the particles of the components.

This mixture is transferred from a loose to a bound state by granular ice and a hydration binder, which are mixed into the loose mixture during its preparation, and during the standing of the mixture in the equipment, they achieve spontaneous melting of ice, filtration of its melt into the mixture, and solidification of the sand mixture in contact with this melt due to the chemical reaction of water (from melting ice) with hydration binders such as gypsum or cement. Granular ice in the mixture contains 8-90 95 by mass of the mixture, which is more than method |2| and capable of forming pores, was limited to the upper limit of 90 95. Since foam ceramics with a limit porosity of 95 95 (11) are known, then with an ice density of about 0.92 g/cm" and a much higher density of the solid framework in the range of 1.71-4.0 g/cm3 of components based on AI2Oz (12), the mass fraction in the ice mixture of 90 95 to create pores will allow to create voids (porosity) of about 95 95 and higher by volume fraction. The indicated limits of 8-90 95 can be considered approximate, they only characterize for this method the maximum possible interval of the volume of pores formed by the removed ice, the specific composition of the mixture is determined by the manufacturer of porous products.

For example, if, according to method (1), sand shells (with cavities) are made based on ice models in the form of several or many spheres, or sand rods whose internal cavities are made according to ice models in the form of several or many spheres or according to models of another geometric shape, then such products can be considered porous products. But the difference is that the claimed method achieves results that exceed the features of the I6Y method, in particular, due to the use of a pore-forming material as a reagent for solidification of a loose mixture, and an increase in the pore size range above 2.5 mm, simple porosity regulation and replacement with ice organic pore formers.

As in the method (1), technological additives (of the order of 0.5-5 905), which are surface-active substances (for example, liquid soap), can be introduced into the composition of the aqueous solution (or loose mixture) from which granular ice is frozen facilitate the spreading of ice melt on the surface of dispersed filler particles, introduce hardening accelerators of hydration binders, or gelling agents. For example, liquid glass in an aqueous solution (for freezing into ice) is both an effective accelerator of such hardening and a gelling agent, widely used in foundry production for the manufacture of sand molds, lining of ladles, etc. Also, powder technological additives are even easier to introduce when mixing loose components for porous or foam products.

The general scheme of the method of forming according to a useful model includes the preparation of a loose mixture by known methods and pouring it into a tool for forming. In particular, after preliminary mixing of the mineral base, the simplest composition of which is a finely dispersed filler - granular corundum, sand, cement or gypsum in different dosages, in one of the options (2)| pouring the loose mixture into the cavity of the tool, it is also possible to introduce into this mixture free-flowing granular ice when mixing two jets by pouring the jet of ice grains with the jet of the free-flowing mineral base of the forming mixture into one stream and performing vibration of the tool. This mixing option allows you to quickly mix the grains in a loose form and compact them in the forming equipment without melting the ice. Rapid mixing of mineral sands and powders with granular ice in a concrete mixer was also used.

З When the loose mixture is compacted by vibration in the equipment (forming brick), the sand grains of the components continue to move between each other, nesting with each other to the maximum possible density of the mixture; a rigid frame is formed from optimally stacked grains with the placement of powder technological particles and a binder between them. Vibration reduces the internal friction of sand grains, bringing the loose material to the state of "pseudo-liquid".

The method is implemented due to the fact that the force interaction of melt water (from granular ice) with particles of finely dispersed mineral components is determined by the hydrophilicity of these particles. After the ice melts, water is absorbed and retained by adsorption-capillary forces in the medium of finely dispersed components. If more water enters the layer of these components than it can hold by these forces, the excess moisture flows through the pores into the layer below it. Standing for hardening is mostly inherent in the manufacture of concrete products, in which the hardening operation proceeds spontaneously for a certain time. During the formation, the action of adsorption-capillary forces for particles with a hydrophilic surface was combined with chemisorption for particles of a hydration binder.

Granular ice, as a pore former, consists of frozen water or an aqueous composition, usually at a temperature of -20...-15 "C. After vibration compaction of the mixture in the equipment, the ice is heated by the surrounding material and after some time (usually up to several minutes) begins to melt , coming out as a self-flow through the pores of the mixture, then the melting continues for about a few minutes or longer depending on the amount and temperature of the ice.

The method uses the following phenomena of filtration, hardening and solidification of the mixture. When wetting and filtering a dry, free-flowing ambient mixture with a molten liquid, the components of this liquid and the mixture form a binding self-hardening composition, which leads to the hardening of the mixture.

Hydrophilicity of mineral (most often aluminosilicate, quartz) grains leads to their envelopment with water or an aqueous solution and electro-molecular coupling between them and sands. If, in one of the variants, the dispersed material contained dry sand with cement or gypsum powder, the melt water from the ice during capillary absorption by the walls of this material served as a cement or gypsum hardener and increased the strength of its adhesion (adhesion) to the grains of sand. At the same time, hardening consisted in the transformation of a dispersed system into a "condensed" state - the formation of an interphase structure from dispersed heterogeneous particles (13). With quartz or aluminosilicate grains, water has a high surface tension and is a weak binder. The action of surface forces affects the retention of the ceiling (shells) of sand pores from ice grains, the stronger the smaller the radius of these pores. If the strength properties of many binders (clay, cement, gypsum, liquid glass, etc.) are acquired only in the presence of water, then the use of an ice-dispersed foaming agent with the supply of water during its melting belongs to the advantages used in the claimed method of manufacturing foam filters.

Adhesion requires close contact between the adhesive and the substrate, such contact between the dispersed material and the adhesive product that sticks it together is provided by melt water or an aqueous composition, and the mechanism of hardening of hydration binders is hydrate formation (and structure formation (formation of crystal hydrates), as synthesis strength of the material of the final product 131.

Standing the mixture in the equipment for a time no less than sufficient to melt the ice, seeping its melt through the mixture and creating a solid frame of foam ceramic filters and porous materials is the solution that allows you to achieve the planned technical result. After standing the mixture in the tool, further technological actions with it are performed when a sufficiently solid product is formed, the actions of which will not violate its integrity, it is freed from the remains of liquid products of the model (if any) and after additional hardening, drying, and, if necessary, heat treatment (firing , firing, etc.) or other known processing operations are sent to the point of use.

In the version of the method, acceleration of the solidification of the mixture by heating to a temperature of 40-100 "С is provided for accelerating the turnover of the equipment, increasing the productivity of the process and the efficiency of the use of equipment similarly (1|. Simplifying production and reducing the probability of defects also contributed to pouring water, an aqueous solution or applying them with an aerosol (including at such a temperature) on the surface of the mixture, which accelerated the hardening and hardening of the upper layer (as a stabilizing base), or thanks to filtration, the entire thickness of the formed product was permeated even before the ice began to melt. The option was also worked out when water or aqueous solution on the upper surface of the mixture, and from the lower surface of the mixture through the holes in the bottom of the equipment, this mixture was vacuumed in the periods before the beginning of the melting of granular ice or (and) after the solidification of the mixture in order to squeeze out excess water from the formed product. It was vacuumed by a known method and equipment traditional for foundries with vacuum molding ( VPF) or for casting in sand vacuum molds according to

With models that are gasified (LGM process). Vents were previously installed in the bottom of the equipment, to which vacuum from a vacuum pump was supplied through a pipeline. Water poured onto the surface of the mixture was pumped for several seconds. The mixture was moistened before the ice grains began to melt and began to harden and harden, providing a stable porous structure.

The essentiality of the sign of the method - the resistance of the mixture, explains the fact that at this time the local supports for the loose filler - ice grains - melt, and the mixture around them, which is moistened, gains strength. Preservation in a static state of vibration-compacted grains of fine-dispersed filler provides moisture, which itself glues the grains with limited strength, and the presence of a hydration binder in the mixture - gypsum and/or cement in contact with moisture gives a semi-hard shell (film or crust) in which begins hardening (setting) of the indicated binders when they lose their fluidity (fluidity) under the action of gravitational forces. Also used is the fact that after vibration compaction in the optimal mode, grains of dispersed material are preferably placed in such a way that they jam each other, preventing mutual movement. This phenomenon is called "appearance of arched structures" (14). In the arch, each individual element cannot move in the direction of the action of the external force, because it is clamped in the gap by neighboring elements, to which it transmits the active load and acquires the properties of a solid body, which allows a fairly thin hardening shell to withstand the weight of the upper layers of loose material in a static state. Usually, products were cured during the second and third shifts, filling the equipment with a mixture with compaction on the first shift. On the second day or within 24 hours, the molded products acquired sufficient strength for further operations.

Thus, to preserve the pores during the melting of pore-forming ice, the role of three factors was used: internal friction (rest) of compacted hard grains, which are wedged with their protrusions and have a powder of hydration binder - gypsum and/or cement - in the pores between them; moistening of the pores between the grains with the binding role of water; and hardening of the hydration binder with the beginning of the formation of crystal hydrates, followed by hardening to the state of possibility of removal from the equipment, carrying out drying and heat treatment operations. The water that was not retained in the foam, flowed through the pores and flowed out of the tool through holes in the bottom of the tool.

Note that, among dozens of experiments on choosing the optimal composition of the mixture (when inspecting the sprayed filters), rare cases were obtained when the ceiling and adjacent walls because of individual large pores were deformed (sunk, floated) when the ice melted, in all cases only partially (not more by 10-15 95) reduced the pore volume from ice. In the case of deformation of the wall, the grains of ice touched, got wet from it with melt water, which reacted with the binder, which began to harden, water also came from the upper layers, to this was added the fact that the vibrated sand grains of the walls lose their optimal arrangement of grains during their displacement and these wall layers expand, which stops the deformation of the walls with a concave surface. The expansion of the gaps between the grains increases the fine pores between them, and in general the degree of porosity does not decrease.

Filter chambers can also be formed by the claimed method, for example, for in-mold modification of metals. The side walls of the chamber are made of sand-crystal hydrate mixtures with an admixture of granular ice less than 8 95 (similarly to (21), and they serve as a supporting base for loading the modifier, and the outlet is covered with a filter from the mixture and granular ice 8-90 vol.

As examples of the implementation of a useful model, foam ceramic filters were made from a refractory mixture, the composition of the solid component of which is similar to the closest analogue |b6)Y, and the binder is high-alumina cement, used similarly to the refractory composite concrete mixture IZ), the fire resistance of products from which is 1500-1530 " C. The mixture contains a refractory filler, binder (binder) - high-alumina cement and impurities - finely ground material of the oxidal type, as well as kaolin, with a ratio of components, weight 95 (table). At a temperature of -157C, ice has a density of 0.919 g/cmu, and the filter frame has a density of 21.71 g/cmu, then the volume fraction of ice is greater than the mass fraction, as shown in the table.

Table

Mixture components and pore sizes

Oksidalmas. 77777711 111140 1150.

Kaolin, mass 77777711 111108 1170 11te (Total fillers, mass 9ei | 1400 | 500 | 600

Ice grains of a given size were sifted using standard sieves according to DSTU IBO 3310-1:2017. "Sieves. Technical requirements and tests". The sizes of the ice grains or its grain composition, which corresponds to the nominal sizes of the sieve openings, are indicated in the table. with sizes rounded to the first decimal place. The pore sizes in accordance with the sizes of the ice grains for the three compositions of the mixture were 2.2-3.4 mm, which is higher than in the closest analogue |b) - 1.0-1.5 mm. The pore sizes are determined by the size of ice particles as a pore former, which can be stably selected and be 0.2-22.4 mm in size, and even with much wider limits of this interval, since

From DSTU IBO 3310-1:2017 defines the nominal sizes of sieve openings in the range of 0.02-125.00 mm for determining the grain composition of loose materials. This definition is a typical standardized operation of control of loose materials for molding laboratories of foundries and enterprises manufacturing building materials. Large (» 5 mm) ice particles of the same size can be frozen from water in household freezers in shaker molds with cells of various configurations. However, it is quite difficult to obtain identical or large cells of polyurethane foam or similar foamed polymers.

The simplification of the production of foam ceramic filters and porous materials consists in the fact that mixing, pouring into the equipment and compacting the mixture takes place in its loose state, which is simpler than operations for water slickers according to the closest analogue |b)|; also according to the main variants of the method of removing the pore former, it took place spontaneously, melting - primarily under the influence of the ambient temperature, and outflow - due to filtration under the influence of capillary and gravitational forces. Impregnation of the foam blank is not required in the mode of cyclic deformations until absorption of the aqueous ceramic slip. Options for accelerating the removal of the foaming agent simultaneously with hardening and initial solidification of the loose mixture are given.

In addition to fire-resistant foam ceramic filters, according to the stated method, the production of porous materials, in particular foam concrete, using construction grades of Portland cement and gypsum is recommended. In the composition of binders, it is recommended to mix 15 95 gypsum with cement -

85 95. Gypsum accelerates hardening and hardening, and cement gives water resistance to the hardening mixture, preventing it from splashing or deformation in case of excessive moisture.

Among the advantages of pore formation with ice grains is also the fact that the thickness and size of the final product can be quite large and is practically determined by the size of the equipment, the amount of mixture and the oven for drying or heat treatment, if necessary. From thick blocks of foam filters, various shaped products can be cut by mechanical processing, or many identical plate filters can also be formed into shaped filter products. At the same time, according to the closest analogue, it is difficult to impregnate polyurethane foam with a thick layer of water slicker, therefore, according to the description (b), a filter with dimensions of 5x5x1.5 cm was made.

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Claims (2)

USEFUL MODEL FORMULA 1. The method of manufacturing foam ceramic filters and porous materials, which includes mixing of loose fine-dispersed filler, binder, pore former and other technological impurities, compaction of the resulting mixture in the molding equipment, removal of the pore former, drying and heat treatment of the formed product, which is distinguished by the fact that as a pore former use granular ice in the amount of 8-90 96 by mass of the mixture, the removal of which is performed by melting, standing at room temperature or by heating the mixture or product. 2. The method according to claim 1, which is distinguished by the fact that a hydration binder is introduced into the mixture when mixing the loose, finely dispersed components, which is moistened by the melt of the foaming agent introduced into the mixture, and as a result of this moistening, the mixture is hardened and solidified to a monolithic state by the formation of crystal hydrates. C. The method according to claim 1, which is distinguished by the fact that during the standing of the mixture in the molding equipment, it is heated to a temperature of 40...100 "С, water or an aqueous solution with this or room temperature is supplied to the upper surface of the mixture, or water is supplied or aqueous solution on the upper surface of the mixture, and from the lower surface of the mixture through the holes in the bottom of the equipment, this mixture is vacuumed in the periods before the beginning of the melting of granular ice or/and after the mixture solidifies to squeeze out excess water from the formed product. economy, trade and agriculture of Ukraine, St. M. Hrushevskyi, 12/2, Kyiv, 01008, Ukraine SE "Ukrainian Institute of Intellectual Property", str. Glazunova, 1, Kyiv - 42, 01601 (c;