Waste foundry that applies. Foundry environmental problems and ways of their development
Foundries are characterized by the presence of toxic air emissions, waste water and solid waste.
The unsatisfactory condition of the air environment is considered an acute problem in the foundry industry. Chemicalization of the foundry, contributing to the creation of progressive technology, at the same time sets the task of improving the air environment. The largest amount of dust is emitted from the equipment for knocking out molds and cores. Various types of cyclones, hollow scrubbers and cyclone washers are used to clean dust emissions. The cleaning efficiency in these devices is in the range of 20-95%. The use of synthetic binders in foundry production raises the problem of cleaning air emissions from toxic substances, mainly from organic compounds of phenol, formaldehyde, carbon oxides, benzene, etc. different ways: thermal combustion, catalytic combustion, adsorption by activated carbon, ozone oxidation, bioremediation, etc.
The source of wastewater in foundries is mainly installations for hydraulic and electro-hydraulic cleaning of castings, wet air cleaning, and hydrogeneration of used molding sands. Great economic importance for National economy has a wastewater and sludge disposal. The amount of waste water can be significantly reduced by using recycled water supply.
Foundry solid waste, which goes to the dumps, is mainly waste foundry sands. An insignificant part (less than 10%) is made up of metal waste, ceramics, defective rods 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 provides a reduction in the consumption of fresh sand, as well as binders and catalysts. The developed technological processes of regeneration make it possible to regenerate sand from good quality and high yield of the target product.
In the absence of regeneration, the spent molding sands, as well as slags, must be used in other industries: waste sands - in road construction as ballast material for leveling the relief and arranging embankments; waste sand-resin mixtures - for the production of cold and hot asphalt concrete; fine fraction of spent molding sands - for the production of building materials: cement, bricks, facing tiles; spent liquid glass mixtures - raw materials for building cement mortars and concrete; foundry slag - for road construction as crushed stone; fine fraction - as fertilizer.
It is advisable to dispose of solid waste foundry in ravines, worked out pits and mines.
CASTING ALLOYS
V modern technology use cast parts from many alloys. At present, in the USSR, the share of steel casting in the total balance of castings is approximately 23%, cast iron - 72%. Castings from non-ferrous metal alloys about 5%.
Cast iron and foundry bronzes are the “traditional” foundry alloys used for a long time. They do not have sufficient plasticity for pressure treatment; products from them are obtained by casting. At the same time, wrought alloys, for example, steels, are widely used to obtain castings. The possibility of using an alloy to obtain castings is determined by its casting properties.
Foundry waste
foundry waste
English-Russian dictionary of technical terms. 2005 .
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The foundry uses waste from its own production (circulating resources) and waste coming from outside (commodity resources). When preparing waste, the following operations are performed: sorting, separation, cutting, packing, dehydration, degreasing, drying and briquetting. For re-melting of waste, induction furnaces are used. The remelting technology depends on the characteristics of the waste - the grade of the alloy, the size of the pieces, etc. Special attention it is necessary to pay attention to the remelting of the shavings.
ALUMINUM AND MAGNESIUM ALLOYS.
The largest group of aluminum waste is shavings. Its mass fraction in the total amount of waste reaches 40%. The first group of aluminum waste includes scrap and waste of unalloyed aluminum;
in the second group - scrap and waste of wrought alloys with a low magnesium content [up to 0.8% (wt. fraction)];
in the third - scrap and waste of wrought alloys with an increased (up to 1.8%) magnesium content;
in the fourth - wastes from foundry alloys with a low (up to 1.5%) copper content;
in the fifth - casting alloys with a high copper content;
in the sixth - deformable alloys with magnesium content up to 6.8%;
in the seventh - with the content of magnesium up to 13%;
in the eighth - wrought alloys with zinc content up to 7.0%;
in the ninth - casting alloys with zinc content up to 12%;
in the tenth - the rest of the alloys.
For remelting large lumpy waste, induction crucible and channel electric furnaces are used.
The sizes of charge pieces during melting in crucible induction furnaces should not be less than 8-10 cm, since it is with these sizes of charge pieces that the maximum power release occurs, due to the depth of current penetration. Therefore, it is not recommended to carry out melting in such furnaces using small charge and shavings, especially when melting with solid filling. Large waste of own production usually has an increased electrical resistance in comparison with the original primary metals, which determines the order of loading the charge and the sequence of the introduction of components in the smelting process. First, large lumpy waste from its own production is loaded, and then (as a liquid bath appears) - the rest of the components. When working with a limited nomenclature of alloys, the most economical and productive melting with a transfer liquid bath - in this case, it is possible to use small charge and shavings.
In induction channel furnaces, first grade wastes are remelted - defective parts, ingots, large semi-finished products. Wastes of the second grade (shavings, splashes) are pre-remelted in induction crucible or fuel furnaces with casting into ingots. These operations are performed in order to prevent intensive overgrowth of channels with oxides and deterioration of the furnace operation. Especially negatively affects the overgrowth of canals increased content in wastes of silicon, magnesium and iron. Electricity consumption when melting dense scrap and waste is 600-650 kWh / t.
The shavings of aluminum alloys are either remelted with subsequent casting into ingots, or added directly to the charge during the preparation of the working alloy.
When charging the base alloy, the chips are introduced into the melt either in briquettes or in bulk. Briquetting increases the metal yield by 1.0%, but the introduction of bulk chips is more economical. The introduction of more than 5.0% chips into the alloy is impractical.
The remelting of shavings with casting into ingots is carried out in induction furnaces with a "swamp" with a minimum overheating of the alloy above the liquidus temperature by 30-40 ° C. During the entire melting process, a flux is fed into the bath in small portions, most often of the following chemical composition,% (mass fraction): KCl -47, NaCl-30, NO3AlF6 -23. The flux consumption is 2.0-2.5% of the batch weight. When melting oxidized shavings, a large number of dry slag, the crucible becomes overgrown and the released active power decreases. The growth of slag with a thickness of 2.0-3.0 cm leads to a decrease in active power by 10.0-15.0%. The amount of pre-remelted chips used in the charge may be higher than with the direct addition of chips to the alloy.
REFRACTORY ALLOYS.
For remelting waste of refractory alloys, electron-beam and arc furnaces with a capacity of up to 600 kW are most often used. The most efficient technology is continuous remelting with overflow, when melting and refining are separated from the crystallization of the alloy, and the furnace contains four to five electron guns of various powers, distributed over the water-cooled hearth, mold and crystallizer. When titanium is remelted, the liquid bath is overheated by 150-200 ° C above the liquidus temperature; the drain spout of the mold is heated; the form can be stationary or rotating around its axis with a frequency of up to 500 rpm. Melting occurs at a residual pressure of 1.3-10 ~ 2 Pa. The smelting process begins with fusion of the skull, after which scrap and a consumable electrode are introduced.
When melting in arc furnaces, electrodes of two types are used: non-consumable and consumable. When using a non-consumable electrode, the charge is loaded into a crucible, most often a water-cooled copper or graphite; graphite, tungsten or other refractory metals are used as an electrode.
At a given power, melting of various metals differs in the melting rate and working vacuum. The melting is divided into two periods - the heating of the electrode with the crucible and the actual melting. The mass of the drained metal is 15–20% less than the mass of the loaded metal due to the formation of a skull. The waste of the main components is 4.0-6.0% (May share).
NICKEL, COPPER AND COPPER-NICKEL ALLOYS.
To obtain ferro-nickel, remelting of secondary raw materials of nickel alloys is carried out in electric arc furnaces. Quartz is used as a flux in an amount of 5-6% of the batch weight. As the mixture melts, the charge settles, therefore, it is necessary to reload the furnace, sometimes up to 10 times. The resulting slags have an increased content of nickel and other valuable metals (tungsten or molybdenum). Subsequently, these slags are processed together with oxidized nickel ore. The yield of ferronickel is about 60% of the mass of the solid charge.
For the processing of metal waste heat-resistant alloys, oxidation-sulfiding smelting or extracting smelting in magnesium is carried out. In the latter case, magnesium extracts nickel, practically not extracting tungsten, iron and molybdenum.
When processing waste copper and its alloys, bronze and brass are most often obtained. Smelting of tin bronzes is carried out in reverberatory furnaces; brasses - in induction. Melting is carried out in a transfer bath, the volume of which is 35-45% of the furnace volume. When melting brass, first of all, chips and flux are loaded. The yield of suitable metal is 23-25%, the yield of slags is 3-5% of the charge weight; electricity consumption varies from 300 to 370 kWh / t.
When smelting tin bronze, first of all, small charge is also loaded - shavings, stampings, meshes; last but not least - bulky scrap and lump waste. The temperature of the metal before casting is 1100-1150 ° C. Extraction of metal in finished products is 93-94.5%.
Tinless bronzes are melted in rotary reflective or induction furnaces. To prevent oxidation, use charcoal or cryolite, fluorspar and soda ash. The flow rate of the flux is 2-4% of the mass of the charge.
First of all, flux and alloying components are loaded into the furnace; last but not least - waste of bronze and copper.
Most of the harmful impurities in copper alloys are removed by blowing the bath with air, steam, or the introduction of copper scale. Phosphorus and lithium are used as deoxidizing agents. Phosphorus deoxidation of brass is not used because of the high affinity of zinc for oxygen. Degassing of copper alloys is reduced to the removal of hydrogen from the melt; carried out by blowing with inert gases.
For melting copper-nickel alloys, induction channel furnaces with acid lining are used. It is not recommended to add shavings and other small waste to the charge without preliminary remelting. The tendency of these alloys to carburization excludes the use of charcoal and other carbon-containing materials.
ZINC AND LIGHT-FUSION ALLOYS.
Remelting of zinc alloy waste (sprues, shavings, splashes) is carried out in reverberatory furnaces. Alloys are purified from non-metallic impurities by refining with chlorides, blowing with inert gases and filtering. When refining with chlorides, 0.1-0.2% (by weight) of ammonium chloride or 0.3-0.4% (by weight) of hexachloroethane is introduced into the melt using a bell at 450-470 ° C; in the same case, refining can be performed by stirring the melt until the separation of the reaction products stops. Then, a deeper purification of the melt is carried out by filtration through fine-grained filters made of magnesite, an alloy of magnesium and calcium fluorides, and sodium chloride. The temperature of the filtering layer is 500 ° C, its height is 70-100 mm, and the grain size is 2-3 mm.
Remelting of waste tin and lead alloys is carried out under a layer of charcoal in cast iron crucibles of furnaces with any heating. The resulting metal is refined from non-metallic impurities with ammonium chloride (add 0.1-0.5%) and filtered through granular filters.
Remelting of cadmium waste is carried out in cast iron or graphite-fireclay crucibles under a layer of charcoal. Magnesium is introduced to reduce oxidizability and losses of cadmium. The charcoal layer is changed several times.
It is necessary to observe the same safety measures as when melting cadmium alloys.
LiteproductionOdstvo, one of the industries, the products of which are castings obtained in casting molds when filled with a liquid alloy. On average, about 40% (by weight) of blanks of machine parts are manufactured by casting methods, and in some branches of mechanical engineering, for example, in machine-tool construction, the share of cast products is 80%. Of all the cast billets produced, mechanical engineering consumes about 70%, the metallurgical industry - 20%, 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 agricultural industries. cars, automobiles, tractors, locomotives, wagons. 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, for example, forging. Casting can produce workpieces of varying complexity with small allowances, which reduces metal consumption, reduces the cost of machining and, ultimately, reduces the cost of products. Casting can be used to manufacture products of almost any mass - from several G up to hundreds T, with walls from tenths of a fraction mm up to several m. The main alloys from which castings are made: gray, malleable and alloyed iron (up to 75% of all castings by weight), carbon and alloyed steels (over 20%) and non-ferrous alloys (copper, aluminum, zinc and magnesium). The field of application of cast parts is constantly expanding.
Foundry waste.
The classification of production wastes 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, sulfur compounds, etc.)
by production cycles - during the extraction of raw materials (overburden and oval rocks), during enrichment (tailings, sludge, sludge), in pyrometallurgy (slags, sludge, dust, gases), in hydrometallurgy (solutions, sediments, gases).
At a metallurgical plant with a closed cycle (cast iron - steel - rolled metal), solid waste can be of two types - dust and slag. Wet gas cleaning is often used, then sludge is the waste instead of dust. 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 greater amount of finely dispersed dust is formed, consisting of oxides of various elements. The latter is captured by gas treatment facilities and then either fed to a sludge collector or sent for further 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
Waste oil (waste oils, greases)
Molding burnt sand (molding earth) is foundry waste, which in terms of physical and mechanical properties is close to sandy loam. Formed as a result of the sand casting method. Consists mainly of quartz sand, bentonite (10%), carbonate additives (up to 5%).
I chose this type of waste because the disposal of used molding sand is one of the most important issues in foundry from an environmental point of view.
The molding materials must be mainly refractory, gas permeable and plastic.
Refractoriness of a molding material is its ability not to fuse and sinter when in contact with molten metal. The most accessible and cheap molding material is quartz sand (SiO2), which is sufficiently refractory for casting the most refractory metals and alloys. Of the impurities accompanying SiO2, alkalis are especially undesirable, which, acting on SiO2, like fluxes, form low-melting compounds (silicates) with it, which stick to the casting and make it difficult to clean. When melting cast iron and bronze, harmful impurities, harmful impurities in quartz sand should not exceed 5-7%, and for steel - 1.5-2%.
Gas permeability of a molding material is its ability to pass gases. With poor gas permeability of the molding earth, gas pockets (usually spherical) can form in the casting and cause casting defects. The shells are found during the subsequent machining of the casting when the top layer of the metal is removed. Gas permeability of the molding earth depends on its porosity between individual sand grains, on the shape and size of these grains, on their uniformity and on the amount of clay and moisture in it.
Sand with round grains has a higher gas permeability than sand with round grains. Small grains, located between large ones, also reduce the gas permeability of the mixture, reducing porosity and creating small tortuous channels that impede the escape of gases. Clay, with its extremely fine grains, clogs the pores. Excess water also clogs the pores and, in addition, evaporating on 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 consists in the ability to maintain the shape given to it, resisting the action of external forces (shock, impact of a jet of liquid metal, static pressure of the metal poured into the mold, pressure of gases released from the mold and metal during pouring, pressure from metal shrinkage, etc. .).
The strength of the molding sand increases with increasing moisture content up to a certain limit. With a further increase in the amount of moisture, the strength decreases. In the presence of clay impurities ("liquid sand") in the foundry sand, the strength increases. Greasy sand requires a higher moisture content than sand with a low clay content ("skinny sand"). The finer the sand grain and the more angular its shape, the greater the strength of the sand. A thin bonding layer between individual sand grains is achieved by thorough and continuous mixing of sand with clay.
The plasticity of the moldable mixture is the ability to easily perceive and accurately maintain the shape of the model. Plasticity is especially necessary in the manufacture of artistic and complex castings to reproduce the smallest details of the model and preserve their imprints during metal casting. The finer the sand grains and the more evenly they are surrounded by a layer of clay, the better they fill in the smallest details of the model's surface and retain their shape. With excessive moisture, the binding clay liquefies and the plasticity decreases sharply.
When storing waste molding sands in a landfill, dust and pollution of the environment occurs.
To solve this problem, it is proposed to regenerate the spent molding sands.
Special additives. One of the most common types of casting defects is the burn-in of the molding and core sand to the casting. The causes of burn-in are varied: insufficient refractoriness of the mixture, coarse-grained composition of the mixture, incorrect selection of non-stick paints, the absence of special non-stick additives in the mixture, poor-quality coloring of forms, etc. There are three types of burn-in: thermal, mechanical and chemical.
Thermal burn-in is relatively easy to remove when cleaning castings.
Mechanical burnt is formed as a result of the penetration of the melt into the pores of the molding mixture and can be removed together with the alloy crust containing the impregnated grains of the molding material.
Chemical burn-in is a formation cemented by low-melting slag-type compounds arising from 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 large expenditure of energy is required), or the castings are finally rejected. Burn-in prevention is based on the introduction of special additives into the molding or core mixture: ground coal, asbestos chips, fuel oil, etc. talc), not interacting when high temperatures with oxides of melts, or materials that create a reducing environment (ground coal, fuel oil) in the mold when it is poured.
Stirring and moisturizing. The components of the molding mixture are thoroughly mixed in a dry form in order to evenly distribute the clay particles throughout the entire mass of sand. Then the mixture is moistened by adding the correct amount of water, and again mixed 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 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 time-consuming job. In modern foundries, the constituent mixtures are mixed during its preparation in screw mixers or mixing runners.
Special additives in molding sands. Special additives are introduced into molding and core sands to ensure the special properties of the mixture. So, for example, cast iron shot, introduced into the molding mixture, increases its thermal conductivity and prevents the formation of shrinkage looseness in massive castings during their solidification. Wood sawdust and peat are introduced into mixtures intended for the manufacture of molds and rods that are subjected to drying. After drying, these additives, decreasing in volume, increase the gas permeability and pliability of molds and cores. Caustic soda is introduced into molding quick-hardening mixtures on liquid glass to increase the durability of the mixture (the mixture caking 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 of great importance. The moldable mixture can be prepared from fresh moldable materials and used molds with a small addition of fresh materials.
The process of preparing molding mixtures from fresh molding materials consists of the following operations: mixture preparation (selection of molding materials), mixing the components of the mixture in dry form, moistening, mixing after moistening, aging, loosening.
Compilation. It is known that foundry sands that meet all the technological properties of the molding sand are rarely found in natural conditions. Therefore, mixtures, as a rule, are prepared by selecting sands with different clay contents, so that the resulting mixture contains the required amount of clay and has the required processing properties. This selection of materials for preparing a mixture is called mixing.
Stirring and moisturizing. The components of the molding mixture are thoroughly mixed in a dry form in order to evenly distribute the clay particles throughout the entire mass of sand. Then the mixture is moistened by adding the correct amount of water, and again mixed 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 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 time-consuming job. In modern foundries, the components of the mixture during its preparation are mixed in screw mixers or mixing runners.
The 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, which prevents the rollers from crushing the grains of the mixture plasticity, gas permeability and fire resistance. To restore the lost properties, 5-35% of fresh molding materials are added to the mixture. Such an operation in the preparation of the molding sand is usually called the refreshing of the mixture.
The process of preparing the molding sand using the spent mixture consists of the following operations: preparing the spent mixture, adding fresh molding materials to the spent mixture, mixing in dry form, moistening, mixing the components after moistening, curing, loosening.
The existing company Heinrich Wagner Sinto of the Sinto concern serially produces the new generation of molding lines of the FBO series. On new machines, flaskless molds with a horizontal split plane are produced. More than 200 of these machines are successfully operating in Japan, the USA and other countries of the world. " With mold sizes 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 a comfortable and clean workplace. In the development of the sealing system and transport devices, great care has been taken to keep noise levels to a minimum. FBO plants meet all the environmental requirements for new equipment.
The sand filling system allows precise molds to be produced using bentonite binder sand. 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 low wall thickness. This compaction process allows the height of the upper and lower mold halves to be varied independently of each other. This provides a significantly lower mixture consumption, which means more economical production due to the optimal metal-to-mold ratio.
According to its composition and the degree of environmental impact, spent molding and core sands are divided into three categories of hazard:
I are practically inert. Mixtures containing clay, bentonite, cement as a binder;
II - waste containing biochemically oxidizable substances. These are mixtures after pouring, in which synthetic and natural compositions are the binder;
III - wastes containing low-toxic substances, slightly soluble in water. These are liquid glass mixtures, unannealed sand - resin mixtures, mixtures cured with compounds of non-ferrous and heavy metals.
In case of separate storage or burial, landfills of waste mixtures should be located in isolated, free from building places that allow the implementation of measures that exclude the possibility of pollution of settlements. Landfills should be placed in areas with poorly filtering soils (clay, sulinka, shale).
The spent molding sand, knocked out of the flasks, must be pre-processed before reuse. In non-mechanized foundries, it is sieved on an ordinary 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 knock-out grate by a belt conveyor to the mixture preparation department. Large lumps of the mixture formed after beating the molds are usually kneaded with smooth or grooved rollers. Metal particles are separated by magnetic separators installed in the areas where the spent mixture is transferred from one conveyor to another.
Burned earth regeneration
Ecology remains a serious problem for foundry, as in 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 emitted.
With the advent of shaping technologies using mixtures with binders made of synthetic resins of different classes, the release of phenols, aromatic hydrocarbons, formaldehydes, carcinogenic and ammonia benzopyrene is especially dangerous. The improvement of foundry must be aimed not only at resolving economic problems, but also at least at creating conditions for human activity and living. According to expert estimates, today these technologies create up to 70% of environmental pollution from foundries.
Obviously, in the conditions of foundry, an unfavorable cumulative effect of a complex factor manifests itself, in which the harmful effect of each individual ingredient (dust, gases, temperature, vibration, noise) increases sharply.
The modernizing measures in the foundry are as follows:
replacement of cupolas with low-frequency induction furnaces (while the size of harmful emissions decreases: dust and carbon dioxide by about 12 times, sulfur dioxide by 35 times)
introduction into production of low-toxic and non-toxic mixtures
installation of effective systems for capturing and neutralizing emitted harmful substances
debugging the efficient operation of ventilation systems
use of modern equipment with reduced vibration
regeneration of spent mixtures at the places of their formation
The amount of phenols in dump mixtures exceeds the content of other toxic substances. Phenols and formaldehydes are formed during the thermal destruction of molding and core sands in which synthetic resins are the binder. These substances are highly soluble in water, which creates the danger of their getting into water bodies when washed out by surface (rain) or groundwater.
It is economically and environmentally unprofitable to dispose of the spent molding sand after being knocked out into the dumps. The most rational solution is the regeneration of cold-hardening mixtures. The main purpose of the regeneration is to remove the binder films from the quartz sand grains.
The most widespread is the mechanical method of regeneration, in which the separation of the binder films from the quartz sand grains occurs due to the mechanical grinding of the mixture. The binder films break down, turn into dust and are removed. The reclaimed sand goes for further use.
Mechanical regeneration process flow chart:
mold knockout (The cast mold is fed to the knock-out lattice cloth, where it is destroyed due to vibration shocks.);
crushing of pieces of molding sand and mechanical grinding of the mixture (The mixture passed through the knock-out grate enters the scrubbing sieve system: a steel screen for large lumps, a wedge-shaped sieve and a fine scrubbing sieve-classifier. The built-in sieve system grinds the molding sand to the required size and sifts out metal particles and other large inclusions.);
cooling of the regenerate (Vibrating elevator provides transportation of hot sand to the cooler / dedusting unit.);
pneumatic transfer of the reclaimed sand to the molding section.
Mechanical regeneration technology provides the possibility of 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 the regenerate only at the level of 60-70% is insufficient and does not solve environmental and economic issues. To increase the percentage of reclaimed sand utilization, it is possible to use thermal reclaiming of mixtures. The quality of regenerated sand is not inferior to fresh sand and even surpasses it due to the activation of the surface of the grains and the blowing of dust-like fractions. Thermal regeneration furnaces operate on the fluidized bed principle. The recovered material is heated by side burners. The heat of the flue gases is used to heat the air supplied to the formation of the fluidized bed and to the combustion of gas to heat the regenerated sand. Fluidized bed installations equipped with water heat exchangers are used to cool the regenerated sands.
During thermal regeneration, the mixtures are heated in an oxidizing environment at a temperature of 750-950 ºС. In this case, the burnout of films of organic substances from the surface of the sand grains occurs. Despite the high efficiency of the process (it is possible to use up to 100% of the regenerated mixture), it has the following disadvantages: equipment complexity, high energy consumption, low productivity, high cost.
Before regeneration, all mixtures undergo preliminary preparation: magnetic separation (other types of cleaning from non-magnetic scrap), crushing (if necessary), sieving.
With the introduction of the regeneration process, the amount of solid waste thrown into the dump is reduced by several times (sometimes they are completely eliminated). The amount of harmful emissions into the air atmosphere with flue gases and dusty 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 cleaning 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 that uses in the manufacture of molded cast metal parts molding earth for the manufacture of casting molds and cores. After the use of casting molds, burnt earth is formed, the utilization of which is of great economic importance. Forming earth consists of 90-95% of high quality quartz sand and small amounts of various additives: bentonite, ground coal, caustic soda, liquid glass, asbestos, etc.
Regeneration of the burnt earth formed after the casting of products consists in the removal of dust, fine fractions and clay, which 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:
electro-crown.
Wet way.
With the wet method of regeneration, the burnt earth enters the system of successive sedimentation tanks with running water... When passing through the settling tanks, sand settles at the bottom of the pool, and small fractions are carried away by the water. The sand is then dried and returned to production for making casting molds. Water goes to filtration and purification and also returns to production.
Dry method.
The dry method of regenerating burnt earth consists of two sequential operations: separating sand from binder additives, which is achieved by blowing air into the drum with the earth, and removing dust and small particles by sucking them out of the drum along with air. Air escaping from the drum, containing dust particles, is cleaned by filters.
Electrocoronary method.
With electro-crown regeneration, the spent mixture is separated into particles of different sizes using high voltage. Grains of sand placed in the field of an electrocorona discharge are charged with negative charges. If the electric forces acting on a grain of sand and attracting it to the collecting electrode are greater than the force of gravity, then the grains of sand settle on the surface of the electrode. By changing the voltage across the electrodes, it is possible to separate the sand passing between them into fractions.
Regeneration of molding sands 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 burn-in, especially on cast iron castings. Mix and pebbles are simultaneously fed into the rotating drum of the regeneration unit, which, being poured from the blades onto the walls of the drum, mechanically destroy the liquid glass film on the sand grains. Through adjustable louvers, air enters the drum, which is sucked together with dust into a wet dust collector. Then the sand, together with the pebbles, is fed into a drum sieve to sift out pebbles and large grains with films. Good sand from the sieve is transported to the warehouse.
3 / 2011_MGSu TNIK
DISPOSAL OF WASTE OF LITHUANIAN PRODUCTION WHEN MANUFACTURING 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
In the present studies, the possibility of utilizing the spent molding sand when using it in the production of composite building materials and products is considered. Formulations of building materials recommended for obtaining building blocks are proposed.
In the present researches possibility of recycling of the fulfilled forming admixture is surveyed at its use in manufacture of composite building materials and products. The compoundings of building materials recommended for reception building blocks are offered.
Introduction.
In the course of the technological process, the foundry is accompanied by the formation of waste, the main volume of which is spent molding (OFS) and core mixtures and slag. Currently, up to 70% of this waste is disposed of annually. It becomes economically inexpedient to store industrial waste for the enterprises themselves, since due to the tightening of environmental laws, one ton of waste has to pay an environmental tax, the amount of which depends on the type of waste stored. In this regard, there is a problem of disposal of the accumulated waste. 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 exclude direct contact of waste with environment, as well as to increase the efficiency of the 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 detoxifying agents for many harmful ingredients, including even incineration ash containing dioxins.
The purpose of this work is the selection of compositions of multicomponent composite building materials with physical and technical parameters -
BULLETIN 3/2011
m, 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 a binder (Ethylsilicate-40) and an aggregate (quartz sand of various fractions), used for complete or partial replacement of 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 to reduce the water demand of the concrete mixture and improve the structure of the material.
Experimental studies of the physical and mechanical characteristics of the cement composite material using the OFS were carried out using the method of planning the experiment.
The following indicators were chosen as the response functions: compressive strength (Y), water absorption (V2), frost resistance (! S), which were determined by the methods, respectively. This choice is due to the fact that in the presence of the presented characteristics of the resulting new composite building material it is possible to determine the scope of its application and the appropriateness of its use.
The following factors were considered as influencing factors: the proportion of the content of the crushed OFS in the aggregate (x1); water / binder ratio (x2); aggregate / binder ratio (x3); the amount of addition of the plasticizer C-3 (x4).
When planning the experiment, the ranges of the factors were taken on the basis of the maximum and minimum possible values of the corresponding parameters (Table 1).
Table 1. - Intervals of variation of factors
Factors Factors variation range
x, 100% sand 50% sand + 50% crushed OFS 100% crushed OFS
x4,% of the mass. 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 the 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 the mixing factors (x1, x2, x3, x4) and are described, in turn, by a polynomial of the second order.
As a result of the experiments, matrices of values of the response functions V1, V2, V3 were formed. Taking into account the values of repeated experiments for each function, 24 * 3 = 72 values were obtained.
The estimates of the unknown parameters of the models were found using the method least squares, that is, by minimizing the sum of the squares of the deviations of the Y values from those calculated by the model. To describe the dependencies Y = Dx1 x2, x3, x4), the normal equations of the least squares method were used:
) = Xm ■ Y, whence:<0 = [хт X ХтУ,
where 0 is a matrix of estimates of unknown parameters of the model; X is a matrix of coefficients; X - transposed matrix of coefficients; Y is the vector of observation results.
To calculate the parameters of the dependencies Y = Dx1 x2, x3, x4), the formulas given in for plans of type N were used.
In the models with a significance level of a = 0.05, the significance of the regression coefficients was checked using the Student's t-test. The exclusion of insignificant coefficients was determined by the final form of mathematical models.
Analysis of the physical and mechanical characteristics of composite building materials.
Of greatest practical interest are the dependences of the 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 aggregate in relation to the binder - 3: 1 (x3 = -1) ... Models of the investigated 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 objective functions on two factors were built, with fixed values of two other factors.
"2L-40 PL-M
Figure - 1 Isolines of the compressive strength of a composite building material, kgf / cm2, depending on the proportion of CFC (X1) in the aggregate and the amount of superplasticizer (x4).
I C | 1u | Mk1 ^ | L1 || mi..1 ||| (| 9 ^ ______ 1 | ЫИ<1ФС
Figure - 2 Isolines of water absorption of a composite building material,% by weight, depending on the proportion of OFS (x \) in the aggregate and the amount of superplasticizer (x4).
□ zmo ■ zo-E5
□ 1EI5 ■ NN) V 0-5
Figure - 3 Isolines of frost resistance of a composite building material, cycles, depending on the proportion of CFC (xx) in the aggregate and the amount of superplasticizer (x4).
The analysis of the surfaces showed that when the content of OPS in the aggregate changes from 0 to 100%, there is an average increase in the strength of materials 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 is observed by 12%; water absorption by weight varies from 10.38% to 16.46%; with an aggregate consisting of 100% OFS, frost resistance increases by 30%, but with an aggregate consisting of 100% quartz sand, frost resistance decreases by 35%.
Practical implementation of the experimental results.
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 the binder (Table 3).
After the analysis of the physical and mechanical characteristics of the main building products, it was revealed that the formulations of the obtained compositions of composite materials using waste from the foundry industry are suitable for the production of wall blocks. Compositions of composite materials, which are shown in Table 4, correspond to these requirements.
X1 (aggregate composition,%) x2 (W / C) X3 (aggregate / binder) x4 (super plasticizer,%) ^ comp, kgf / cm2 W,% Frost resistance, cycles
sand OFS
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_
NS! (aggregate composition,%) x2 (W / C) x3 (aggregate / binder) x4 (superplasticizer,%) Lszh, kgf / cm2
sand OFS
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 composite
materials using waste from the foundry industry
х1 (aggregate composition,%) х2 (W / C) х3 (aggregate / binder) х4 (super plasticizer,%) ^ comp, kgf / cm2 w,% P, g / cm3 Frost resistance, cycles
sand OFS
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 in accordance with GOST 19010-82 Price, rub / piece
Compressive strength, kgf / cm2 Thermal conductivity coefficient, X, W / m 0 С Average density, kg / m3 Water absorption,% by weight Frost resistance, grade
100 according to manufacturer's specifications> 1300 according to manufacturer's specifications according to 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
BULLETIN 3/2011
A method is 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 with the use of foundry waste have been investigated;
Compositions of equal-strength composite building products with a 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 the strength of control samples.
3. GOST 12730.3-78 Concrete. Method for determining water absorption.
4. Zazhigaev L.S., Kishyan A.A., Romanikov Yu.I. Methods for planning and processing the results of a physical experiment.- Moscow: Atomizdat, 1978.- 232 p.
5. Krasovsky G.I., Filaretov G.F. Planning an experiment, Minsk: BSU Publishing House, 1982, 302 p.
6. Malkova M.Yu., Ivanov A.S. Environmental problems of casting dumps // Vestnik mashinostroeniya. 2005. No. 12. S.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, experiment planning method, response function, building blocks.
Keywords: a bionomics in building, resource conservation, the fulfilled forming admixture, the composite building materials, in advance set physicomechanical characteristics, method of planning of experiment, response function, building blocks.
