Foundry production is the main procurement base for mechanical engineering. About 40% of all workpieces used in mechanical engineering are produced by casting. However, Foundry is one of the most environmentally unfavorable.
More than 100 technological processes, more than 40 types of binders, and more than 200 non-stick coatings are used in foundry production.
This has led to the fact that up to 50 regulated hazardous substances are found in the air of the working area. sanitary standards. When producing 1t of cast iron castings, the following is released:
10..30 kg - dust;
200..300 kg - carbon monoxide;
1..2 kg - nitrogen oxide and sulfur;
0.5..1.5 g - phenol, formaldehyde, cyanide, etc.;
3 m 3 - polluted Wastewater may enter the water basin;
0.7..1.2 t - waste mixtures to the dump.
The bulk of foundry waste consists of spent molding and core mixtures and slag. Disposal of these foundry wastes is most relevant, because... Several hundred hectares of the earth's surface are occupied by mixtures transported annually to a dump in the Odessa region.
In order to reduce soil pollution by various industrial wastes, the following measures are envisaged in the practice of land resource protection:
disposal;
neutralization by burning;
burial in special landfills;
organization of improved landfills.
The choice of method for neutralization and disposal of waste depends on its chemical composition and the degree of impact on the environment.
Thus, waste from the metalworking, metallurgical, and coal industries contains sand particles, rocks and mechanical impurities. Therefore, dumps change the structure, physicochemical properties and mechanical composition of soils.
These wastes are used in the construction of roads, backfilling pits and exhausted quarries after dewatering. At the same time, waste from engineering plants and chemical enterprises containing heavy metal salts, cyanides, toxic organic and inorganic compounds cannot be disposed of. These types of waste are collected in sludge pits, after which they are backfilled, compacted and the burial site is landscaped.
Phenol- the most dangerous toxic compound found in molding and core mixtures. At the same time, studies show that the bulk of phenol-containing mixtures that have been poured contain practically no phenol and do not pose a hazard to the environment. In addition, phenol, despite its high toxicity, quickly decomposes in soil. Spectral analysis of spent mixtures using other types of binders showed the absence of particularly hazardous elements: Hg, Pb, As, F and heavy metals. That is, as calculations from these studies show, spent molding sands do not pose a hazard to the environment and do not require any special measures for their disposal. Negative factor is the very existence of dumps, which create an unsightly landscape and disturb the landscape. In addition, dust blown from dumps by the wind pollutes the environment. However, it cannot be said that the problem of dumps is not being solved. In the foundry industry there are a number of technological equipment, allowing for the regeneration of molding sands and their use in the production cycle repeatedly. Existing methods regenerations are traditionally divided into mechanical, pneumatic, thermal, hydraulic and combined.
According to the International Sand Reclamation Commission, in 1980, out of 70 foundries surveyed Western Europe and Japan 45 used mechanical recovery units.
At the same time, foundry waste mixtures are good raw materials for building materials: bricks, silicate concrete, and products made from it, mortars, asphalt concrete for road surfaces, for backfilling. railways.
Research by Sverdlovsk scientists (Russia) has shown that foundry waste has unique properties: they can be used to treat sewage sludge (existing foundry dumps are suitable for this); protect steel structures from soil corrosion. Specialists from the Cheboksary Industrial Tractor Plant (Russia) used dust-like regeneration waste as an additive (up to 10%) in the production of sand-lime brick.
Many foundry dumps are used as secondary raw materials in the foundry itself. For example, acid slag from steel production and ferrochrome slag are used in slip forming technology for investment casting.
In some cases, waste from mechanical engineering and metallurgical industries contains a significant amount of chemical compounds that can be valuable as raw materials and used as an addition to the charge.
The considered issues of improving the environmental situation in the production of cast parts allows us to conclude that in foundry production it is possible to comprehensively solve very complex environmental problems.
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LiteproductionOchildhood, one of the industries whose products are castings obtained in foundry molds by filling them with liquid alloy. On average, about 40% (by weight) of machine parts blanks are produced using casting methods, and in some branches of mechanical engineering, for example in machine tool building, the share of cast products is 80%. Of all cast billets produced, mechanical engineering consumes approximately 70%, the metallurgical industry - 20%, and the production of sanitary equipment - 10%. Cast parts are used in metalworking machines, internal combustion engines, compressors, pumps, electric motors, steam and hydraulic turbines, rolling mills, and agriculture. cars, automobiles, tractors, locomotives, carriages. The widespread use of castings is explained by the fact that their shape is easier to approximate the configuration of finished products than the shape of blanks produced by other methods, such as forging. Casting can produce workpieces of varying complexity with small allowances, which reduces metal consumption, reduces machining costs and, ultimately, reduces the cost of products. Casting can produce products of almost any weight - from several G up to hundreds T, with walls thickness of tenths mm up to several m. The main alloys from which castings are made are: gray, malleable and alloyed cast iron (up to 75% of all castings by weight), carbon and alloy steels (over 20%) and non-ferrous alloys (copper, aluminum, zinc and magnesium). The scope of application of cast parts is constantly expanding.
Foundry waste.
Classification of production waste is possible according to various criteria, among which the following can be considered the main ones:
by industry - ferrous and non-ferrous metallurgy, ore and coal mining, oil and gas, etc.
by phase composition - solid (dust, sludge, slag), liquid (solutions, emulsions, suspensions), gaseous (carbon oxides, nitrogen oxides, sulfur compounds, etc.)
by production cycles - in the extraction of raw materials (overburden and oval rocks), in enrichment (tailings, sludge, waste), in pyrometallurgy (slag, sludge, dust, gases), in hydrometallurgy (solutions, sediments, gases).
At a metallurgical plant with a closed cycle (cast iron - steel - rolled products), solid waste can be of two types - dust and slag. Quite often wet gas cleaning is used, then instead of dust the waste is sludge. The most valuable for ferrous metallurgy are iron-containing wastes (dust, sludge, scale), while slags are mainly used in other industries.
During the operation of the main metallurgical units, a large amount of fine dust is formed, consisting of oxides of various elements. The latter is captured by gas treatment facilities and then either fed into a sludge storage tank or sent for subsequent processing (mainly as a component of the sinter charge).
Examples of foundry waste:
Foundry burnt sand
Arc furnace slag
Scrap of non-ferrous and ferrous metals
Oil waste (waste oils, greases)
Burnt molding sand (molding earth) is foundry waste, with physical and mechanical properties approaching sandy loam. It is formed as a result of the sand casting method. It consists mainly of quartz sand, bentonite (10%), carbonate additives (up to 5%).
I chose this type of waste because the issue of recycling waste sand is one of the important issues of foundry production from an environmental point of view.
Molding materials must have mainly fire resistance, gas permeability and ductility.
The refractoriness of a molding material is its ability not to fuse and sinter when in contact with molten metal. The most accessible and cheapest molding material is quartz sand (SiO2), which is sufficiently refractory for casting the most refractory metals and alloys. Of the impurities accompanying SiO2, the most undesirable are alkalis, which, acting on SiO2 like fluxes, form low-melting compounds (silicates) with it, burning to the casting and making it difficult to clean. When melting cast iron and bronze, harmful impurities in quartz sand should not exceed 5-7%, and for steel - 1.5-2%.
The gas permeability of a molding material is its ability to allow gases to pass through. If the molding earth has poor gas permeability, gas pockets (usually spherical in shape) can form in the casting and cause casting failure. The cavities are discovered during subsequent machining of the casting when the top layer of metal is removed. The gas permeability of the molding earth depends on its porosity between individual grains of sand, on the shape and size of these grains, on their uniformity and on the amount of clay and moisture in it.
Sand with rounded grains has greater gas permeability than sand with rounded grains. Small grains, located between large ones, also reduce the gas permeability of the mixture, reducing porosity and creating small winding channels that make it difficult for gases to escape. Clay, having extremely fine grains, clogs pores. Excess water also clogs the pores and, in addition, evaporating upon contact with the hot metal poured into the mold, increases the amount of gases that must pass through the walls of the mold.
The strength of the molding mixture lies in the ability to maintain the shape given to it, resisting the action of external forces (shocks, impact of a jet of liquid metal, static pressure of metal poured into the mold, pressure of gases released from the mold and metal during pouring, pressure from shrinkage of the metal, etc. .).
The strength of the molding sand increases as the moisture content increases to a certain limit. With a further increase in the amount of moisture, the strength decreases. If there is an admixture of clay in the molding sand ("liquid sand"), the strength increases. Oily sand requires a higher moisture content than sand with low clay content ("lean sand"). The finer the sand grain and the more angular its shape, the greater the strength of the molding sand. A thin binding layer between individual sand grains is achieved by thorough and prolonged mixing of sand and clay.
The plasticity of a molding sand is the ability to easily perceive and accurately maintain the shape of a model. Plasticity is especially necessary in the production of artistic and complex castings to reproduce the smallest details of the model and preserve their imprints during the filling of the mold with metal. The finer the grains of sand and the more uniformly they are surrounded by a layer of clay, the better they fill the smallest details of the model’s surface and retain their shape. With excessive moisture, the binder clay liquefies and plasticity decreases sharply.
When used molding sands are stored in a landfill, dust and environmental pollution occur.
To solve this problem, it is proposed to regenerate spent molding sands.
Special additives. One of the most common types of casting defects is the burning of the molding and core mixture to the casting. The reasons that cause burns are varied: insufficient fire resistance of the mixture, coarse-grained composition of the mixture, incorrect selection of non-stick paints, lack of special non-stick additives in the mixture, poor-quality painting of molds, etc. There are three types of burns: thermal, mechanical and chemical.
Thermal burns are relatively easily removed when cleaning castings.
Mechanical burns are formed as a result of the penetration of the melt into the pores of the molding mixture and can be removed along with the alloy crust containing interspersed grains of the molding material.
Chemical burnout is a formation cemented by fusible compounds such as slag, which arise during the interaction of molding materials with the melt or its oxides.
Mechanical and chemical burns are either removed from the surface of the castings (a lot of energy is required), or the castings are finally rejected. Prevention of burning is based on the introduction of special additives into the molding or core mixture: ground coal, asbestos chips, fuel oil, etc., as well as coating the working surfaces of the molds and cores with non-stick paints, dusts, rubs or pastes containing highly refractory materials (graphite, talc), which do not interact with high temperatures with melt oxides, or materials that create a reducing environment (ground coal, fuel oil) in the mold when pouring it.
Stirring and moistening. The components of the molding mixture are thoroughly mixed in dry form in order to evenly distribute clay particles throughout the entire mass of sand. Then the mixture is moistened by adding the required amount of water and mixed again so that each of the sand particles is covered with a film of clay or other binder. It is not recommended to moisten the components of the mixture before mixing, since in this case sands with a high clay content roll into small balls that are difficult to loosen. Mixing large quantities of materials by hand is a large and labor-intensive job. In modern foundries, the components of the mixture are mixed in screw mixers or mixing runners during its preparation.
Special additives for molding sands. Special additives are introduced into molding and core mixtures to provide special properties of the mixture. For example, cast iron shot introduced into the molding sand increases its thermal conductivity and prevents the formation of shrinkage looseness in massive casting units during their solidification. Sawdust and peat are added to mixtures intended for the manufacture of forms and cores that are subjected to drying. After drying, these additives, decreasing in volume, increase the gas permeability and pliability of the molds and cores. Caustic soda is introduced into molding quick-hardening mixtures on liquid glass to increase the durability of the mixture (caking of the mixture is eliminated).
Preparation of molding sands. The quality of artistic casting largely depends on the quality of the molding mixture from which its casting mold is prepared. Therefore, the selection of molding materials for the mixture and its preparation in the technological process of obtaining a casting is important. The molding sand can be prepared using fresh molding materials and spent sand with a small addition of fresh materials.
The process of preparing molding mixtures from fresh molding materials consists of the following operations: preparing the mixture (selection of molding materials), mixing the components of the mixture in dry form, moistening, mixing after moistening, aging, loosening.
Compilation. It is known that molding sands that meet all the technological properties of the molding sand are rare under natural conditions. Therefore, mixtures are usually prepared by selecting sands with different clay contents, so that the resulting mixture contains the required amount of clay and has the necessary technological properties. This selection of materials for preparing a mixture is called mixing.
Stirring and moistening. The components of the molding mixture are thoroughly mixed in dry form in order to evenly distribute clay particles throughout the entire mass of sand. Then the mixture is moistened by adding the required amount of water and mixed again so that each of the sand particles is covered with a film of clay or other binder. It is not recommended to moisten the components of the mixture before mixing, since in this case sands with a high clay content roll into small balls that are difficult to loosen. Mixing large quantities of materials by hand is a large and labor-intensive job. In modern foundries, the components of the mixture during its preparation are mixed in screw mixers or mixing runners.
Mixing runners have a fixed bowl and two smooth rollers sitting on the horizontal axis of a vertical shaft connected by a bevel gear to an electric motor gearbox. An adjustable gap is made between the rollers and the bottom of the bowl to prevent the rollers from crushing the grains of the mixture - plasticity, gas permeability and fire resistance. To restore lost properties, 5-35% of fresh molding materials are added to the mixture. This operation when preparing the molding sand is usually called refreshing the mixture.
The process of preparing a molding sand using a spent mixture consists of the following operations: preparing the spent sand, adding fresh molding materials to the waste sand, dry mixing, moistening, mixing the components after moistening, aging, loosening.
The existing company Heinrich Wagner Sinto of the Sinto concern is mass-producing the new generation of molding lines of the FBO series. New machines produce flaskless molds with a horizontal parting plane. More than 200 of these machines are successfully operating in Japan, the USA and other countries of the world.” With mold sizes ranging from 500 x 400 mm to 900 x 700 mm, FBO molding machines can produce from 80 to 160 molds per hour.
The closed design avoids sand spills and ensures comfortable conditions and cleanliness in the workplace. When developing the compaction system and transport devices, great attention was paid to keeping noise levels to a minimum. FBO installations meet all environmental requirements for new equipment.
The mixture filling system allows the production of precise molds using molding mixture with a bentonite binder. The automatic pressure control mechanism of the sand feeding and pressing device ensures uniform compaction of the mixture and guarantees high-quality production of complex castings with deep pockets and thin walls. This compaction process allows the height of the upper and lower mold halves to be varied independently of each other. This ensures significantly lower mixture consumption, which means more economical production due to the optimal metal-to-mold ratio.
Based on their composition and degree of impact on the environment, waste molding and core mixtures are divided into three hazard categories:
I – practically inert. Mixtures containing clay, bentonite, cement as a binder;
II – waste containing biochemically oxidizable substances. These are mixtures after pouring, the binders in which are synthetic and natural compositions;
III – waste containing low-toxic substances that are slightly soluble in water. These are liquid-glass mixtures, unannealed sand-resin mixtures, mixtures cured with compounds of non-ferrous and heavy metals.
When storing or disposing of waste mixtures separately, landfills should be located in separate, free from development areas that allow for the implementation of measures that exclude the possibility of contamination of populated areas. Landfills should be located in areas with weakly filtering soils (clay, sulinok, shale).
Spent molding sand, knocked out of the flasks, before reuse must be pre-processed. In non-mechanized foundries, it is sifted on a conventional sieve or on a mobile mixing plant, where metal particles and other impurities are separated. In mechanized workshops, the spent mixture is fed from under the knockout grid by a belt conveyor to the mixture preparation department. Large lumps of the mixture formed after knocking out forms are usually kneaded with smooth or grooved rollers. Metal particles are separated by magnetic separators installed in areas where the waste mixture is transferred from one conveyor to another.
Regeneration of burnt earth
Ecology remains a serious problem in foundry production, since during the production of one ton of castings from ferrous and non-ferrous alloys, about 50 kg of dust, 250 kg of carbon monoxide, 1.5-2.0 kg of sulfur oxide, 1 kg of hydrocarbons are released.
With the advent of shaping technologies using mixtures with binders made from synthetic resins of different classes, the release of phenols, aromatic hydrocarbons, formaldehydes, carcinogenic and ammonia benzopyrene is especially dangerous. The improvement of foundry production must be aimed not only at solving economic problems, but also, to no less extent, at creating conditions for human activity and habitation. According to expert estimates, today these technologies create up to 70% of environmental pollution from foundries.
Obviously, in the conditions of foundry production, an unfavorable cumulative effect of a complex factor manifests itself, in which the harmful impact of each individual ingredient (dust, gases, temperature, vibration, noise) increases sharply.
Modernization measures in foundry production include the following:
replacement of cupola furnaces with low-frequency induction furnaces (at the same time, the amount of harmful emissions is reduced: dust and carbon dioxide by approximately 12 times, sulfur dioxide by 35 times)
introduction into production of low-toxic and non-toxic mixture compositions
installation effective systems trapping and neutralizing released harmful substances
debugging efficient work ventilation systems
use of modern equipment with reduced vibration
regeneration of waste mixtures at the places of their formation
The amount of phenols in waste mixtures exceeds the content of other toxic substances. Phenols and formaldehydes are formed during the thermal destruction of molding and core mixtures in which synthetic resins are the binder. These substances are highly soluble in water, which creates a risk of them entering water bodies when washed out by surface (rain) or groundwater.
It is economically and environmentally unprofitable to throw away the spent molding sand after beating into dumps. The most rational solution is the regeneration of cold-hardening mixtures. The main purpose of regeneration is to remove binder films from quartz sand grains.
The most widespread is the mechanical regeneration method, in which binder films are separated from quartz sand grains due to mechanical grinding of the mixture. The binder films are destroyed, turned into dust and removed. The reclaimed sand is supplied for further use.
Technological diagram of the mechanical regeneration process:
knocking out the mold (The poured mold is fed onto the canvas of the knockout grid, where it is destroyed due to vibration impacts.);
crushing pieces of molding sand and mechanical grinding of the mixture (The mixture that has passed through the knockout grid enters a system of grinding sieves: a steel screen for large lumps, a sieve with wedge-shaped holes and a fine grinding sieve-classifier. The built-in system of sieves grinds the molding sand to the required size and screens out metal particles and other large inclusions.);
regenerate cooling (A vibration elevator ensures the transportation of hot sand to the cooler/deduster.);
pneumatic transmission of regenerated sand to the molding area.
Mechanical regeneration technology makes it possible to reuse from 60-70% (Alpha-set process) to 90-95% (Furan process) of reclaimed sand. If for the Furan process these indicators are optimal, then for the Alpha-set process the reuse of regenerate only at the level of 60-70% is insufficient and does not solve environmental and economic issues. To increase the percentage of use of regenerated sand, it is possible to use thermal regeneration of mixtures. Regenerated sand is not inferior in quality to fresh sand and even surpasses it due to the activation of the surface of the grains and the blowing out of dusty fractions. Thermal recovery furnaces operate on the fluidized bed principle. The regenerated material is heated by side burners. The heat from the flue gases is used to heat the air supplied to form the fluidized bed and to burn gas to heat the regenerated sand. To cool the regenerated sands, fluidized bed units equipped with water heat exchangers are used.
During thermal regeneration, mixtures are heated in an oxidizing environment at a temperature of 750-950 ºС. In this case, films of organic substances burn out from the surface of sand grains. Despite the high efficiency of the process (it is possible to use up to 100% regenerated mixture), it has the following disadvantages: complexity of the equipment, high energy consumption, low productivity, high cost.
All mixtures undergo preliminary preparation before regeneration: magnetic separation (other types of cleaning from non-magnetic scrap), crushing (if necessary), sifting.
When implementing the regeneration process, the amount solid waste, thrown into the dump, is reduced several times (sometimes they are completely eliminated). The amount of harmful emissions into the air with flue gases and dust-laden air from the foundry does not increase. This is due, firstly, to a fairly high degree of combustion of harmful components during thermal regeneration, and secondly, to a high degree of purification of flue gases and exhaust air from dust. For all types of regeneration, double purification of flue gases and exhaust air is used: for thermal - centrifugal cyclones and wet dust cleaners, for mechanical - centrifugal cyclones and bag filters.
Many machine-building enterprises have their own foundry, which uses molding earth for the production of casting molds and cores in the production of molded cast metal parts. After using casting molds, burnt earth is formed, the disposal of which is of great economic importance. The molding earth consists of 90-95% of high-quality quartz sand and small quantities of various additives: bentonite, ground coal, caustic soda, liquid glass, asbestos, etc.
Regeneration of burnt earth formed after casting of products consists of removing dust, small fractions and clay that has lost its binding properties under the influence of high temperature when filling the mold with metal. There are three ways to regenerate burnt earth:
electrocorona.
Wet method.
With the wet regeneration method, the burnt earth enters a system of sequential settling tanks with running water. When passing through settling tanks, sand settles at the bottom of the pool, and fine fractions are carried away by water. The sand is then dried and returned to production to make casting molds. Water is supplied for filtration and purification and is also returned to production.
Dry method.
The dry method of regenerating burnt earth consists of two sequential operations: separating sand from binding additives, which is achieved by blowing air into a drum with earth, and removing dust and small particles by sucking them out of the drum along with air. The air leaving the drum containing dust particles is cleaned using filters.
Electrocorona method.
With electrocorona regeneration, the waste mixture is divided into particles of different sizes using high voltage. Sand grains placed in the field of an electric corona discharge are charged with negative charges. If the electrical forces acting on a grain of sand and attracting it to the collecting electrode are greater than gravity, then the grains of sand settle on the surface of the electrode. By changing the voltage on the electrodes, it is possible to separate the sand passing between them into fractions.
The regeneration of molding mixtures with liquid glass is carried out in a special way, since with repeated use of the mixture, more than 1-1.3% of alkali accumulates in it, which increases the burn, especially on cast iron castings. The mixture and pebbles are simultaneously fed into the rotating drum of the regeneration unit, which, pouring from the blades onto the walls of the drum, mechanically destroy the film of liquid glass on the sand grains. Through adjustable blinds, air enters the drum and is sucked out along with dust into a wet dust collector. Then the sand together with pebbles is fed into a drum sieve to sift out pebbles and large grains with films. Useful sand from the sieve is transported to the warehouse.
Foundry production is characterized by the presence of toxic air emissions, wastewater and solid waste.
An acute problem in foundry production is the unsatisfactory condition of the air environment. Chemicalization of foundry production, contributing to the creation of progressive technology, simultaneously poses the task of improving the health of the air environment. Largest quantity dust is emitted from punching and core punching equipment. Cyclones are used to clean dust emissions different types, hollow scrubbers and cyclone washers. The cleaning efficiency in these devices is in the range of 20-95%. The use of synthetic binders in foundry production poses a particularly acute problem of purifying air emissions from toxic substances, mainly from organic compounds of phenol, formaldehyde, carbon oxides, benzene, etc. To neutralize organic vapors from foundry production, various methods are used: thermal combustion, catalytic afterburning, adsorption activated carbon, ozone oxidation, biopurification, etc.
The source of wastewater in foundries is mainly installations for hydraulic and electro-hydraulic casting cleaning, wet air cleaning, and hydrogeneration of spent molding sands. The recycling of wastewater and sludge is of great economic importance for the national economy. The amount of wastewater can be significantly reduced by using water recycling.
Solid waste from foundries entering the dumps consists mainly of waste foundry sands. A small part (less than 10%) consists of metal waste, ceramics, defective cores and molds, refractories, paper and wood waste.
The main direction of reducing the amount of solid waste in dumps should be considered the regeneration of waste foundry sands. The use of a regenerator reduces the consumption of fresh sand, as well as binders and catalysts. The developed technological regeneration processes make it possible to regenerate sand from good quality and high yield of the target product.
In the absence of regeneration, spent molding sands, as well as slag, must be used in other industries: waste sand - in road construction as ballast material for leveling the relief and constructing embankments; waste sand-resin mixtures - for the production of cold and hot asphalt concrete; fine fraction of waste molding sands - for the production of building materials: cement, brick, facing tiles; waste liquid glass mixtures - raw materials for construction cement mortars and concrete; foundry slag - for road construction as crushed stone; fine fraction - as fertilizer.
It is advisable to dispose of solid waste from foundry production in ravines, exhausted quarries and mines.
CASTING ALLOYS
IN modern technology They use cast parts from a wide variety of alloys. Currently, in the USSR, the share of steel casting in the total balance of castings is approximately 23%, and cast iron - 72%. Castings from non-ferrous metal alloys about 5%.
Cast iron and cast bronzes are “traditional” casting alloys that have been used since ancient times. They do not have sufficient ductility for pressure processing; products from them are produced by casting. At the same time, wrought alloys, such as steel, are also widely used to produce castings. The possibility of using an alloy to produce castings is determined by its casting properties.
3/2011_MGSU TNIK
DISPOSAL OF LITHIUM PRODUCTION WASTE DURING THE MANUFACTURE OF CONSTRUCTION PRODUCTS
RECYCLING OF THE WASTE OF FOUNDRY MANUFACTURE AT MANUFACTURING OF BUILDING PRODUCTS
B.B. Zharikov, B.A. Yezersky, H.B. Kuznetsova, I.I. Sterkhov V. V. Zharikov, V.A. Yezersky, N.V. Kuznetsova, I.I. Sterhov
This research examines the possibility of recycling waste molding sand when using it in the production of composite building materials and products. Recipes of building materials recommended for producing building blocks are proposed.
In the present researches the possibility of recycling of the fulfilled forming admixture is surveyed at its use in manufacture of composite building materials and products. The compounds of building materials recommended for reception building blocks are offered.
Introduction.
During the technological process, foundry production is accompanied by the formation of waste, the main volume of which consists of spent molding (OPM) and core mixtures and slag. Currently, up to 70% of this waste is disposed of annually. Warehousing becomes economically unfeasible industrial waste and for the enterprises themselves, since due to the tightening of environmental laws, for 1 ton of waste you have to pay an environmental tax, the amount of which depends on the type of waste stored. In this regard, the problem of disposal of accumulated waste arises. One of the options for solving this problem is the use of OFS as an alternative to natural raw materials in the production of composite building materials and products.
The use of waste in the construction industry will reduce the environmental load on the territory of landfills and eliminate direct contact of waste with environment, as well as increase the efficiency of use of material resources (electricity, fuel, raw materials). In addition, the materials and products produced using waste meet the requirements of environmental and hygienic safety, since cement stone and concrete are detoxicants for many harmful ingredients, including even ash from waste incineration containing dioxins.
The purpose of this work is to select the compositions of multicomponent composite building materials with physical and technical parameters -
NEWSLETTER 3/2011
mi, comparable to materials produced using natural raw materials.
Experimental study of the physical and mechanical characteristics of composite building materials.
The components of composite building materials are: spent molding mixture (fineness modulus Mk = 1.88), which is a mixture of binder (Ethyl silicate-40) and filler (quartz sand of various fractions), used to completely or partially replace fine aggregate in a composite mixture material; Portland cement M400 (GOST 10178-85); quartz sand with Mk=1.77; water; superplasticizer S-3, which helps reduce the water demand of the concrete mixture and improve the structure of the material.
Experimental studies of the physical and mechanical characteristics of a cement composite material using OFS were carried out using the experimental design method.
The following indicators were selected as response functions: compressive strength (U), water absorption (U2), frost resistance (!z), which were determined according to the methods accordingly. This choice is due to the fact that, given the presented characteristics of the resulting new composite building material you can determine the scope of its application and the feasibility of use.
The following were considered as influencing factors: the proportion of crushed OFS content in the filler (x1); water/binder ratio (x2); aggregate/binder ratio (x3); amount of plasticizer additive S-3 (x4).
When planning the experiment, the ranges of changes in factors were taken based on the maximum and minimum possible values of the corresponding parameters (Table 1).
Table 1. - Variation intervals for factors
Factors Range of factor changes
x, 100% sand 50% sand + 50% crushed OFS 100% crushed OFS
x4, wt.% binder 0 1.5 3
Changing the mixing factors will make it possible to obtain materials with a wide range of construction and technical properties.
It was assumed that the dependence of physical and mechanical characteristics can be described by a reduced polynomial of incomplete third order, the coefficients of which depend on the values of the levels of mixing factors (x1, x2, x3, x4) and are described, in turn, by a second-order polynomial.
As a result of the experiments, matrices of response function values Vb, V2, V3 were formed. Taking into account the values of repeated experiments, 24*3=72 values were obtained for each function.
Estimates of the unknown parameters of the models were found using the least squares method, that is, by minimizing the sum of squared deviations of the values of Y from those calculated by the model. To describe the dependences Y=Dx2, x3, x4), normal equations of the least squares method were used:
)=Хт ■ У, from where:<0 = [хт X ХтУ,
where 0 is the matrix of estimates of unknown model parameters; X - coefficient matrix; X - transposed coefficient matrix; Y is the vector of observation results.
To calculate the parameters of the dependences Y=Dx2, x3, x4), the formulas given in for plans of type N were used.
In models at a significance level of a=0.05, the significance of regression coefficients was checked using the Student’s ¿-test. The final form of the mathematical models was determined by excluding insignificant coefficients.
Analysis of physical and mechanical characteristics of composite building materials.
Of greatest practical interest are the dependencies of compressive strength, water absorption and frost resistance of composite building materials with the following fixed factors: W/C ratio - 0.6 (x2=1) and the amount of filler in relation to the binder - 3:1 (x3=-1) . The models of the studied dependencies have the form: compressive strength
y1 = 85.6 + 11.8 x1 + 4.07 x4 + 5.69 x1 - 0.46 x1 + 6.52 x1 x4 - 5.37 x4 +1.78 x4 -
1.91- x2 + 3.09 x42 water absorption
y3 = 10.02 - 2.57 x1 - 0.91-x4 -1.82 x1 + 0.96 x1 -1.38 x1 x4 + 0.08 x4 + 0.47 x4 +
3.01- x1 - 5.06 x4 frost resistance
y6 = 25.93 + 4.83 x1 + 2.28 x4 +1.06 x1 +1.56 x1 + 4.44 x1 x4 - 2.94 x4 +1.56 x4 + + 1.56 x2 + 3, 56 x42
To interpret the obtained mathematical models, graphical dependences of the target functions on two factors were constructed, with fixed values of the other two factors.
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Figure - 1 Isolines of the compressive strength of a composite building material, kgf/cm2, depending on the proportion of OFS (X1) in the filler and the amount of superplasticizer (x4).
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Figure - 2 Isolines of water absorption of composite building material, % by weight, depending on the proportion of OPC (x\) in the filler and the amount of superplasticizer (x4).
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Figure - 3 Isolines of frost resistance of composite building material, cycles, depending on the proportion of OPS (xx) in the filler and the amount of superplasticizer (x4).
Analysis of surfaces showed that when the OPS content in the filler changes from 0 to 100%, an average increase in the strength of materials is observed by 45%, a decrease in water absorption by 67% and an increase in frost resistance by 2 times. When the amount of superplasticizer C-3 changes from 0 to 3 (wt.%), an average increase in strength by 12% is observed; water absorption by mass varies from 10.38% to 16.46%; with a filler consisting of 100% OFS, frost resistance increases by 30%, but with a filler consisting of 100% quartz sand, frost resistance decreases by 35%.
Practical implementation of experimental results.
By analyzing the obtained mathematical models, it is possible to identify not only the compositions of materials with increased strength characteristics (Table 2), but also to determine the compositions of composite materials with predetermined physical and mechanical characteristics with a decrease in the proportion of binder in the composition (Table 3).
After an analysis of the physical and mechanical characteristics of the main building products, it was revealed that the formulations of the resulting compositions of composite materials using waste from the foundry industry are suitable for the production of wall blocks. The compositions of composite materials, which are given in Table 4, meet these requirements.
X1 (filler composition,%) X2 (W/C) X3 (filler/binder) X4 (super plasticizer, %) ^com, kgf/cm2 W, % Frost resistance, cycles
OFS sand
100 % 0,4 3 1 3 93 10,28 40
100 % 0,6 3 1 3 110 2,8 44
100 % 0,6 3 1 - 97 6,28 33
50 % 50 % 0,6 3 1 - 88 5,32 28
50 % 50 % 0,6 3 1 3 96 3,4 34
100 % 0,6 3 1 - 96 2,8 33
100 % 0,52 3 1 3 100 4,24 40
100 % 0,6 3,3:1 3 100 4,45 40
Table 3 - Materials with predetermined physical and mechanical _characteristics_
X! (filler composition, %) x2 (W/C) x3 (filler/binder) x4 (superplasticizer, %) Lszh, kgf/cm2
OFS sand
100 % - 0,4 3:1 2,7 65
50 % 50 % 0,4 3,3:1 2,4 65
100 % 0,6 4,5:1 2,4 65
100 % 0,4 6:1 3 65
Table 4 Physical and mechanical characteristics of building composites
materials using waste from the foundry industry
x1 (filler composition,%) x2 (W/C) x3 (filler/binder) x4 (super plasticizer, %) ^szh, kgf/cm2 w, % P, g/cm3 Frost resistance, cycles
OFS sand
100 % 0,6 3:1 3 110 2,8 1,5 44
100 % 0,52 3:1 3 100 4,24 1,35 40
100 % 0,6 3,3:1 3 100 4,45 1,52 40
Table 5 - Technical and economic characteristics of wall blocks
Construction products Technical requirements for wall blocks according to GOST 19010-82 Price, rub/piece
Compressive strength, kgf/cm2 Thermal conductivity coefficient, X, W/m0 C Average density, kg/m3 Water absorption, % by weight Frost resistance, brand
100 according to the manufacturer’s specifications >1300 according to the manufacturer’s specifications according to the manufacturer’s specifications
Sand concrete block Tam-bovBusinessStroy LLC 100 0.76 1840 4.3 I00 35
Block 1 using OFS 100 0.627 1520 4.45 B200 25
Block 2 using OFS 110 0.829 1500 2.8 B200 27
NEWSLETTER 3/2011
A method has been proposed for involving technogenic waste instead of natural raw materials in the production of composite building materials;
The main physical and mechanical characteristics of composite building materials using foundry waste have been studied;
Compositions of equal-strength composite building products with reduced cement consumption by 20% have been developed;
The compositions of mixtures for the manufacture of building products, for example, wall blocks, have been determined.
Literature
1. GOST 10060.0-95 Concrete. Methods for determining frost resistance.
2. GOST 10180-90 Concrete. Methods for determining strength using control samples.
3. GOST 12730.3-78 Concrete. Method for determining water absorption.
4. Zazhigaev L.S., Kishyan A.A., Romanikov Yu.I. Methods of planning and processing the results of a physical experiment. - M.: Atomizdat, 1978. - 232 p.
5. Krasovsky G.I., Filaretov G.F. Planning an experiment. - Mn.: BSU Publishing House, 1982. -302 p.
6. Malkova M.Yu., Ivanov A.S. Environmental problems of foundry dumps // Bulletin of Mechanical Engineering. 2005. No. 12. P.21-23.
1. GOST 10060.0-95 Concrete. Methods of definition of frost resistance.
2. GOST 10180-90 Concrete. Methods durability definition on control samples.
3. GOST 12730.3-78 Concrete. A method of definition of water absorption.
4. Zajigaev L.S., Kishjan A.A., Romanikov JU.I. Method of planning and processing of results of physical experiment. - Mn: Atomizdat, 1978. - 232 p.
5. Krasovsky G.I, Filaretov G.F. Experiment planning. - Mn.: Publishing house BGU, 1982. - 302
6. Malkova M. Ju., Ivanov A. S. Environmental problem of sailings of foundry manufacture//the mechanical engineering Bulletin. 2005. No. 12. p.21-23.
Key words: ecology in construction, resource saving, waste molding sand, composite building materials, predetermined physical and mechanical characteristics, experimental planning method, response function, building blocks.
Keywords: a bionomics in building, resource saving, the fulfilled forming admixture, the composite building materials, in advance set physicomechanical characteristics, method of planning of experiment, response function, building blocks.
