Liteother productaboutdstvo, one of the industries whose products are castings obtained in casting molds by filling them with a liquid alloy. Casting methods produce on average about 40% (by weight) of blanks for machine parts, and in some branches of 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 machine tools, internal combustion engines, compressors, pumps, electric motors, steam and hydraulic turbines, rolling mills, and agricultural products. machines, automobiles, tractors, locomotives, wagons. The widespread use of castings is explained by the fact that their shape is easier to approximate to the configuration of finished products than the shape of blanks produced by other methods, such as forging. By casting it is possible to obtain 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 produce products of almost any mass - from several G up to hundreds t, with walls with a 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 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 (oxides of carbon, nitrogen, sulfur compounds, etc.)
by production cycles - in the extraction of raw materials (overburden and oval rocks), in enrichment (tailings, sludge, plums), 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 larger amount of fine dust is formed, consisting of oxides of various elements. The latter is captured by gas cleaning facilities and then either fed into the sludge accumulator or sent for further processing (mainly as a component of the sinter charge).
Examples of foundry waste:
foundry burnt sand
Slag from arc furnace
Scrap of non-ferrous and ferrous metals
Oil waste (waste oils, lubricants)
Burnt molding sand (moulding earth) is foundry waste, which, in terms of physical and mechanical properties, approaches sandy loam. It is formed as a result of applying the method of casting in sand molds. Consists mainly of quartz sand, bentonite (10%), carbonate additives (up to 5%).
I chose this type of waste because the disposal of used sand is one of the most important issues in foundry production from an environmental point of view.
Molding materials must have mainly fire resistance, gas permeability and plasticity.
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 that accompany SiO2, alkalis are especially undesirable, which, acting on SiO2 like fluxes, form low-melting compounds (silicates) with it, sticking 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 pass gases. If the gas permeability of the molding earth is poor, gas pockets (usually spherical in shape) can form in the casting and cause casting rejects. Shells are found during subsequent machining of the casting when removing the top layer of metal. The gas permeability of 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 a higher 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 impede the release of gases. Clay, having extremely small 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 sand lies in the ability to maintain the shape given to it, resisting the action of external forces (shaking, 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 metal shrinkage, etc. .).
The strength of the sand increases as the moisture content increases to a certain limit. With a further increase in the amount of moisture, the strength decreases. In the presence of clay impurities in the foundry sand ("liquid sand"), the strength increases. Oily sand requires a higher moisture content than sand with a low clay content ("lean sand"). The finer the grain of sand and the more angular its shape, the greater the strength of the sand. A thin bonding layer between the individual grains of sand is achieved by thorough and prolonged mixing of sand with clay.
The plasticity of the molding sand 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 the casting of the 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 surface of the model and retain their shape. With excessive moisture, the binder clay liquefies and plasticity decreases sharply.
When storing waste molding sands in a landfill, dusting and environmental pollution occur.
To solve this problem, it is proposed to carry out the regeneration of spent molding sands.
Special supplements. One of the most common types of casting defects is burnt molding and core sand to the casting. The causes of burns are varied: insufficient fire resistance of the mixture, coarse-grained composition of the mixture, improper selection of non-stick paints, the absence of special non-stick additives in the mixture, poor-quality coloring of molds, etc. There are three types of burns: thermal, mechanical and chemical.
Thermal sticking is relatively easy to remove when cleaning castings.
The mechanical burn is formed as a result of the penetration of the melt into the pores of the sand and can be removed together with the crust of the alloy containing disseminated grains of the molding material.
A chemical burn is a formation cemented with low-melting compounds such as slags that occur during the interaction of molding materials with a 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 prevention 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 molds and cores with non-stick paints, sprays, rubbing or pastes containing highly refractory materials (graphite, talc), which do not interact at high temperatures with melt oxides, or materials that create a reducing environment (ground coal, fuel oil) in the mold when it is poured.
Preparation of molding compounds. The quality of an art casting largely depends on the quality of the molding sand from which its mold is made. 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 from fresh molding materials and used sand with a small addition of fresh materials.
The process of preparing molding sands from fresh molding materials consists of the following operations: mixture preparation (selection of molding materials), dry mixing of the mixture components, 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 in natural conditions. Therefore, mixtures, as a rule, are prepared by selecting sands with different clay content, so that the resulting mixture contains the right amount of clay and has the necessary technological properties. This selection of materials for the preparation of the mixture is called the composition of the mixture.
Stirring and moisturizing. The components of the molding mixture are thoroughly mixed in dry form in order to evenly distribute clay particles throughout the 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 time-consuming job. In modern foundries, the constituents 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, 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. This operation in the preparation of the molding sand is called the refreshment of the mixture.
Special additives in molding sands. Special additives are introduced into the molding and core sands to ensure the special properties of the mixture. So, for example, 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 introduced into mixtures intended for the manufacture of molds and cores to be dried. After drying, these additives, decreasing in volume, increase the gas permeability and compliance of molds and cores. Caustic soda is added to molding quick-hardening mixtures on liquid glass to increase the durability of the mixture (the clumping of the mixture is eliminated).
The process of preparing the molding sand using the used sand consists of the following operations: preparing the used sand, adding fresh molding materials to the used sand, mixing in dry form, moistening, mixing the components after wetting, aging, loosening.
The existing company Heinrich Wagner Sinto of the Sinto Group is mass-producing a new generation of molding lines of the FBO series. The 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 around the world.” With mold sizes ranging from 500 x 400 mm to 900 x 700 mm, FBO molding machines can produce 80 to 160 molds per hour.
The closed design avoids sand spills and ensures a comfortable and clean working environment. When developing the sealing system and transport devices, great care was taken to keep the noise level to a minimum. FBO units meet all environmental requirements for new equipment.
The sand filling system allows the production of precise molds using a sand 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 small wall thicknesses. This compaction process allows the height of the upper and lower molds to be varied independently of each other. This results in significantly lower mix consumption and therefore more economical production due to the optimum metal-to-mould ratio.
In terms of composition and degree of influence on environment spent molding and core sands 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, in which synthetic and natural compositions are a binder;
III - waste containing low-toxic, water-soluble substances. 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 disposal, waste mixtures landfills should be located in separate, free from development areas 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, sulin, shale).
The spent molding sand knocked out of the flasks must be pre-processed before reuse. In non-mechanized foundries, it is screened on a conventional sieve or on a mobile mixing plant, where metal particles and other impurities are separated. In mechanized shops, the spent mixture is fed from under the knockout grate by a belt conveyor to the mixture preparation department. Large lumps of the mixture formed after the molds are knocked out are usually kneaded with smooth or corrugated rollers. Metal particles are separated by magnetic separators installed in the areas of transfer of the spent mixture from one conveyor to another.
Burnt ground regeneration
Ecology remains a serious problem in foundry production, since the production of one ton of casting from ferrous and non-ferrous alloys releases about 50 kg of dust, 250 kg of carbon monoxide, 1.5-2.0 kg of sulfur oxide, 1 kg of hydrocarbons.
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 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 production, an unfavorable cumulative effect of a complex factor is manifested, in which harmful effect each individual ingredient (dust, gases, temperature, vibration, noise) increases dramatically.
Modernizing measures in the foundry industry 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 about 12 times, sulfur dioxide by 35 times)
introduction of low-toxic and non-toxic mixtures into production
installation of effective systems for trapping and neutralizing emitted harmful substances
debugging the efficient operation of 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 sands, in which synthetic resins are the binder. These substances are highly soluble in water, which creates a risk of their getting into water bodies when washed out by surface (rain) or groundwater.
It is economically and environmentally unprofitable to throw away the spent molding sand after knocking out 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 widely used mechanical method of regeneration, in which binder films are separated from quartz sand grains due to mechanical grinding of the mixture. The binder films break down, turn into dust and are removed. The reclaimed sand is sent for further use.
Technological scheme of the process of mechanical regeneration:
knockout of the form (The filled form is fed to the canvas of the knockout grid, where it is destroyed due to vibration shocks.);
crushing of pieces of the sand and mechanical grinding of the sand (The sand that has passed through the knockout grate enters the 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 sieve system grinds the sand to the required size and screens out metal particles and other large inclusions.);
cooling of the regenerate (Vibrating elevator provides transportation of hot sand to the cooler/deduster.);
pneumatic transfer of reclaimed sand to the molding area.
The technology of mechanical regeneration provides the possibility of reusing from 60-70% (Alfa-set process) to 90-95% (Furan-process) of reclaimed sand. If for the Furan process these indicators are optimal, then for the Alfa-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 use of reclaimed sand, it is possible to use thermal regeneration of mixtures. Regenerated sand is not inferior to fresh sand in quality and even surpasses it due to the activation of the surface of the grains and the blowing out of dusty fractions. Thermal regeneration furnaces operate on the fluidized bed principle. Heating of the regenerated material is carried out by side burners. The flue gas heat is used to heat the air that enters the formation of the fluidized bed and the combustion of gas to heat the reclaimed sand. Fluidized bed units equipped with water heat exchangers are used to cool the regenerated sands.
During thermal regeneration, mixtures are heated in an oxidizing environment at a temperature of 750-950 ºС. In this case, the 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% of the regenerated mixture), it has the following disadvantages: the complexity of the equipment, high flow energy, low performance, high cost.
All mixtures undergo preliminary preparation before regeneration: magnetic separation (other types of cleaning from non-magnetic scrap), crushing (if necessary), screening.
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 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, which uses molding earth for the manufacture of molds and cores in the manufacture of molded cast metal parts. After the use of casting molds, burnt earth is formed, the disposal of which is of great importance. economic importance. The molding earth consists of 90-95% high-quality quartz sand and small amounts of various additives: bentonite, ground coal, caustic soda, liquid glass, asbestos, etc.
The regeneration of the burnt earth formed after the casting of products consists in the removal of dust, fine 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 ground:
electrocorona.
Wet way.
With the wet method of regeneration, the burnt earth enters the system of successive settling tanks with running water. When passing the sedimentation tanks, the sand settles on the bottom of the pool, and fine fractions are carried away by water. The sand is then dried and returned to production to make molds. Water enters the filtration and purification and is also returned to production.
Dry way.
The dry method of regeneration of burnt earth consists of two successive operations: separating sand from binding additives, which is achieved by blowing air into the drum with earth, and removing dust and small particles by sucking them out of the drum together with air. The air leaving the drum containing dust particles is cleaned with the help of filters.
Electrocorona method.
In electrocorona regeneration, the waste mixture is separated into particles of different sizes using high voltage. Sand grains placed in the field of 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 on the electrodes, it is possible to separate the sand passing between them into fractions.
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 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 liquid glass film on the sand grains. Through adjustable shutters, air enters the drum, which is sucked out together with dust into a wet dust collector. Then the sand, together with pebbles, is fed into a drum sieve to screen out pebbles and large grains with films. Suitable sand from the sieve is transported to the warehouse.
In addition to the regeneration of burnt earth, it is also possible to use it in the manufacture of bricks. For this purpose, the forming elements are first destroyed, and the earth is passed through a magnetic separator, where metal particles are separated from it. The earth cleared of metal inclusions completely replaces quartz sand. The use of burnt earth increases the degree of sintering of the brick mass, since it contains liquid glass and alkali.
The operation of the magnetic separator is based on the difference between the magnetic properties of the various components of the mixture. The essence of the process lies in the fact that individual metallomagnetic particles are separated from the flow of a common moving mixture, which change their path in the direction of the magnetic force.
In addition, burnt earth is used in the production of concrete products. Raw materials (cement, sand, pigment, water, additive) enter the concrete mixing plant (BSU), namely, the forced planetary mixer, through a system of electronic scales and optical dispensers
Also, the spent molding sand is used in the production of cinder block.
Cinder blocks are made from a molding sand with a moisture content of up to 18%, with the addition of anhydrites, limestone and mixture setting accelerators.
Technology of production of cinder blocks.
A concrete mixture is prepared from the spent molding sand, slag, water and cement. Mixed in a concrete mixer.
The prepared slag concrete solution is loaded into a mold (matrix). Forms (matrices) come in different sizes. After laying the mixture in the matrix, it shrinks with the help of pressure and vibration, then the matrix rises, and the cinder block remains in the pallet. The resulting drying product keeps its shape due to the rigidity of the solution.
Strengthening process. The final cinder block hardens within a month. After the final hardening, the finished product is stored for further strength development, which, according to GOST, must be at least 50% of the design strength. Further, the cinder block is shipped to the consumer or used on its own site.
Germany.
Installations for regeneration of mix of the KGT brand. They provide the foundry industry with an environmentally and economically viable technology for the recycling of foundry sands. The reverse cycle reduces the consumption of fresh sand, auxiliary materials and the area for storing the used mixture.
Foundry production is the main procurement base of mechanical engineering. About 40% of all blanks used in mechanical engineering are obtained by casting. However, foundry production is one of the most environmentally unfriendly.
More than 100 technological processes, more than 40 types of binders, more than 200 non-stick coatings are used in foundry production.
This led to the fact that up to 50 harmful substances regulated by sanitary standards are found in the air of the working area. In the production of 1 ton 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, cyanides, etc.;
3 m 3 - contaminated Wastewater can enter the water basin;
0.7..1.2 t - waste mixtures to the dump.
The bulk of foundry production wastes are spent molding and core sands and slag. The disposal of these foundry wastes is the most relevant, because. several hundred hectares of land surface are occupied by mixtures exported annually to the dump, in the Odessa region.
In order to reduce soil pollution by various industrial waste The following measures are envisaged in the practice of land resources protection:
disposal;
neutralization by incineration;
burial at special landfills;
organization of improved landfills.
The choice of the method of disposal and disposal of waste depends on their chemical composition and the degree of impact on the environment.
So, wastes of metalworking, metallurgical, coal industries contain particles of sand, rocks and mechanical impurities. Therefore, dumps change the structure, physicochemical characteristics and mechanical composition of soils.
These wastes are used in the construction of roads, backfilling of pits and waste quarries after dehydration. At the same time, waste from machine-building plants and chemical enterprises containing salts of heavy metals, cyanides, toxic organic and inorganic compounds cannot be recycled. These types of waste are collected in sludge collectors, after which they are filled up, rammed and landscaped at the burial site.
Phenol- the most dangerous toxic compound found in molding and core sands. 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 danger to the environment. In addition, phenol, despite its high toxicity, quickly decomposes in the soil. Spectral analysis of spent mixtures on other types of binder showed the absence of particularly hazardous elements: Hg, Pb, As, F and heavy metals. That is, as calculations of these studies show, spent molding sands do not pose a danger to the environment and do not require any special measures for their disposal. The negative factor is the very existence of dumps, which create an unsightly landscape, disturb the landscape. In addition, wind-blown dust pollutes the environment. However, it cannot be said that the problem of dumps is not being solved. In the foundry, there is a whole range of technological equipment that allows for the regeneration of foundry sands and their repeated use in the production cycle. The existing methods of regeneration are traditionally divided into mechanical, pneumatic, thermal, hydraulic and combined.
According to International Commission for sand regeneration, in 1980, out of 70 surveyed foundries in Western Europe and Japan, 45 used mechanical regeneration plants.
At the same time, foundry waste mixtures are good raw materials for building materials: bricks, silicate concrete, and products from it, mortars, asphalt concrete for road surfaces, for filling railway tracks.
Studies by Sverdlovsk scientists (Russia) have shown that foundry waste has unique properties: it can process sewage sludge (existing foundry dumps are suitable for this); protect steel structures from soil corrosion. Specialists of the Cheboksary Plant of Industrial Tractors (Russia) used pulverized regeneration waste as an additive (up to 10%) in the production of silicate brick.
Many foundry blades are used as secondary raw materials in the foundry itself. So, for example, acidic slag from steel production and ferrochromium slag are used in the technology of slip shaping in investment casting.
In some cases, waste from machine-building and metallurgical industries contains a significant amount of chemical compounds that can be valuable as raw materials and used as a supplement to the charge.
The considered issues of improving the environmental situation in the production of cast parts allows us to conclude that in the foundry it is possible to comprehensively solve very complex environmental problems.
The proposed method consists in the fact that preliminary crushing of the source material is carried out selectively and oriented with a concentrated force from 900 to 1200 J. In the process of processing, the selected dusty fractions are enclosed in a closed volume and exert a mechanical effect on them until a finely dispersed powder with a specific surface area of at least 5000 cm 2 /g. The installation for implementing this method includes a device for crushing and screening, made in the form of a remote-controlled manipulator, on which a hydropneumatic impact mechanism is installed. In addition, the installation contains a hermetic module communicated with the dusty fractions selection system, having a means for processing these fractions into a fine powder. 2 s. and 2 z. p. f-ly, 4 ill., 1 tab.
The invention relates to foundry production, and more specifically to a method for processing cast solid slags in the form of lumps with metal inclusions and a plant for the complete processing of these slags. These method and installation make it possible to almost completely utilize the processed slags, and the resulting end products - commercial slag and commercial dust - can be used in industrial and civil construction, for example, for the production building materials. Wastes generated during slag processing in the form of metal and crushed slag with metal inclusions are used as charge materials for melting units. Processing of cast solid slag lumps riddled with metal inclusions is a complex, labor-intensive operation that requires unique equipment, additional energy costs, therefore, slags are practically not used and are taken to landfills, deteriorating the environment and polluting the environment. Of particular importance is the development of methods and installations for the implementation of complete waste-free processing of slag. There are a number of methods and installations that partially solve the problem of slag processing. In particular, a method for processing metallurgical slags is known (SU, A, 806123), which consists in crushing and screening these slags to fine fractions within 0.4 mm, followed by separation into two products: metal concentrate and slag. This method of processing metallurgical slags solves the problem in a narrow range, since it is intended only for slags with non-magnetic inclusions. The closest in technical essence to the present invention is a method of mechanical separation of metals from metallurgical furnace slag (SU, A, 1776202), including crushing of metallurgical slag in a crusher and in mills, as well as separation by density difference in aquatic environment fractions of slag and recycled metal within 0.5-7.0 mm and 7-40 mm with iron content in metal fractions up to 98%
Waste of this method in the form of slag fractions after complete drying and sorting is used in construction. This method is more efficient in terms of the quantity and quality of the extracted metal, however, it does not solve the problem of preliminary crushing of the source material, as well as obtaining commercial slag of high quality in terms of fractional composition for manufacturing, for example, building products. For the implementation of such methods, in particular, a production line is known (SU, A, 759132) for separating and sorting waste metallurgical slags, including a loading device in the form of a feed hopper, vibrating screens above the receiving hoppers, electromagnetic separators, cooling chambers, drum screens and devices for moving the extracted metal objects. However, this production line also does not provide for preliminary crushing of slag in the form of slag lumps. Also known is a device for screening and crushing materials (SU, A, 1547864), including a vibrating screen and a frame with a crushing device installed above it, made with holes and mounted to move in a vertical plane, and the crushing device is made in the form of wedges with heads in their the upper part, which are installed with the possibility of movement in the frame holes, while the transverse dimension of the heads is greater than the transverse dimension of the frame holes. In a three-walled chamber, a frame moves along vertical guides, in which crushing devices are installed, freely hanging on the heads. The area occupied by the frame corresponds to the area of the vibrating screen, and the crushing devices cover the entire area of the vibrating screen grate. The movable frame, by means of an electric drive, rolls along the rails onto the vibrating screen, on which a block of slag is installed. Crushing devices at a guaranteed gap pass over the block. When the vibrating screen is turned on, the crushing devices, together with the frame, go down, without encountering an obstacle, for the entire sliding length up to 10 mm from the vibrating screen cloth, other parts (wedges) of the crushing device, having encountered an obstacle in the form of the surface of a slag block, remain at the height of the obstacle. Each crushing device (wedge), when it hits a slag lump, finds its point of contact with it. The vibration from the screen is transmitted through a block of slag lying on it at the points of contact of the wedges of the crushing devices, which also begin to oscillate in resonance in the frame guides. The destruction of the lump of slag does not occur, and there is only a partial abrasion of the slag on the wedges. Closer to the solution of the proposed method is the above device for separating and sorting dump and foundry slags (RU, A, 1547864), including a system for delivering the source material to the preliminary crushing zone, carried out by a device for screening and crushing materials, made in the form of a receiving hopper with an installed above it, a vibrating screen and devices for direct crushing of slag, vibro crushers for further grinding of material, electromagnetic separators, a vibrating screen, storage bins of sorted slag with dispensers and transport devices. In the slag supply system, a tilting mechanism is provided, which receives the slag with the cooled slag block in it and feeds it to the vibrating screen zone, knocking out the slag block onto the vibrating screen sheet and returning the empty slag to its original position. The above methods and devices for their implementation use crushing options and equipment for processing slag, during which non-utilizable dust fractions are released that pollute the soil and air, which significantly affects the ecological balance of the environment. The invention is based on the task of creating a method for processing slags, in which preliminary crushing of the source material, followed by its sorting into decreasing fraction sizes and the selection of the resulting dusty fractions, is carried out in such a way that it becomes possible to completely utilize the processed slags, and also to create an installation for implementing this method. This problem is solved in a method for processing foundry slags, including preliminary crushing of the source material and its subsequent sorting into decreasing fractions to obtain commercial slag with simultaneous selection of the resulting dusty fractions, in which, according to the invention, preliminary crushing is carried out selectively and oriented with a concentrated force of 900 to 1200 J, and the selected pulverized fractions are enclosed in a closed volume and have a mechanical effect on them until a fine powder with a specific surface area of at least 5000 cm 2 /g is obtained. It is advisable to use finely dispersed powder as an active performer for building mixtures. This embodiment of the method makes it possible to completely process foundry slags, resulting in two final products - commercial slag and commercial dust used for construction purposes. The problem is also solved by means of an installation for implementing the method, including a system for delivering the initial material to the pre-crushing zone, a device for crushing and screening, vibrating crushers with electromagnetic separators and transport devices that grind and sort the material into decreasing fractions, classifiers of coarse and fine fractions and a system selection of dusty fractions, in which, according to the invention, the device for crushing and screening is made in the form of a remote-controlled manipulator, on which a hydro-pneumatic impact mechanism is installed, and a sealed module is mounted in the installation, communicated with the dusty fractions selection system, having a means for processing these fractions into a fine powder . Preferably, a cascade of screw mills arranged in series is used as a means for processing pulverized fractions. One of the variants of the invention provides that the installation has a system for returning the processed material, installed near the coarse fraction classifier, for its additional grinding. Such an embodiment of the installation as a whole makes it possible to process foundry waste with a high degree of reliability and efficiency and without high energy costs. The essence of the invention is as follows. Cast foundry slags are characterized by strength, that is, resistance to destruction in the event of internal stresses that appear as a result of any loading (for example, during mechanical compression), and can be attributed in terms of compressive strength (compressive strength) to rocks of medium strength and strong . The presence of metal inclusions in the slag reinforces a monolithic block, strengthening it. The previously described destruction methods did not take into account the strength characteristics of the source material being destroyed. The fracture force is characterized by the value P = compressive F, where P is the fracture force in compression, F is the area of the applied force, was significantly lower than the strength characteristics of the slag. The proposed method is based on reducing the area of application of the force F to the dimensions determined by the strength characteristics of the material, the tool used and the choice of force P. Instead of the static forces used in the above technical solutions, the present invention uses dynamic forces in the form of a directed, oriented impact with a certain energy and frequency, which generally increases the efficiency of the method. Empirically selected parameters of the frequency and energy of strikes in the range of 900-1200 J with a frequency of 15-25 beats per minute. Such a crushing technique is carried out in the proposed installation using a hydro-pneumatic impact mechanism mounted on the manipulator of a device for crushing and screening slag. The manipulator provides pressure to the destruction object of the hydro-pneumatic impact mechanism during its operation. Regulation of the applied effort of crushing slag lumps is carried out remotely. At the same time, slag is a material with potential binding properties. The ability to harden them appears mainly under the action of activating additives. However, there is such a physical state of slags when potential binding properties appear after mechanical impacts on the fractions of the processed slag until certain sizes are obtained, characterized by the specific surface area. Obtaining a high specific surface area of crushed slags is an essential factor in their acquisition of chemical activity. Conducted laboratory studies confirm that a significant improvement in the quality of the slag used as a binder is achieved during grinding, when its specific surface area exceeds 5000 cm 2 /g. Such a specific surface area can be obtained by mechanical action on the selected dusty fractions enclosed in a closed volume (sealed module). This action is carried out using a cascade of screw mills arranged in series in a sealed module, gradually converting this material into a fine powder with a specific surface area of more than 5000 cm 2 /g. Thus, the proposed method and installation for processing slags make it possible to utilize them almost completely, as a result of which a commercial product is obtained, which is used in particular in construction. The integrated use of slag significantly improves the environment, and also frees up producing areas used for dumps. In connection with the increase in the degree of utilization of processed slags, the cost of manufactured products is reduced, which, accordingly, increases the efficiency of the invention used. In FIG. 1 schematically shows a plant for carrying out the slag processing method according to the invention, in plan; in fig. 2 section A-A in Fig. one;
In FIG. 3 view B in Fig. 2;
In FIG. 4 section B-B in fig. 3. The proposed method provides for complete non-waste processing of slag to obtain commercial crushed slag of the required fractions and pulverized fractions processed into a fine powder. In addition, a material with metallic inclusions is obtained, which is reused in melting units of linear and metallurgical production. To do this, a cast billet block with metal inclusions is preliminarily oriented crushed with a concentrated force from 900 to 1200 J over a vibrating screen with a failed grate. Metal and slag with metal inclusions, the dimensions of which are larger than the dimensions of the openings of the failure grate of the vibrating screen, are taken with a magnetic plate of the crane and stored in a container, and the pieces of slag remaining on the vibrating screen are sent for finer crushing to a vibrating jaw crusher located in the immediate vicinity of the vibrating screen. The crushed material that has fallen through the failed grate is transported through the system of vibratory jaw crushers with the selection of metal and slag with metal inclusions by electromagnetic separators for further grinding and sorting. The size of the pieces that have not passed through the failed grating ranges from 160 to 320 mm, and those that have passed from 0 to 160 mm. At subsequent stages, the slag is crushed to fractions with a size of 0-60 mm, 0-12 mm, and the slag with metal inclusions is taken. Then the crushed slag is fed to the coarse fraction classifier, where the selection of material with a size of 0-12 and more than 12 mm takes place. Larger material is sent to the return system for regrinding, and material with a size of 0-12 mm is sent along the main process stream to a fine fraction classifier, where a dusty fraction of 0-1 mm is selected, which is collected in a sealed module for subsequent exposure and obtaining a finely dispersed powder with a specific surface area of more than 5000 cm 2 /g, used as an active filler for building mixtures. The material with a size of 1-12 mm selected on the fine fraction classifier is commercial slag, which is sent to storage tanks for subsequent shipment to the customer. The composition of this commercial slag is shown in the table. Selected fractions of slag with metal inclusions are returned to the melting shop for remelting through an additional process flow. The metal content in crushed slags selected by magnetic separation is in the range of 60-65%
The fine powder used as an active filler is included in the composition of the binder, for example, to produce concrete, where the filler is crushed foundry slag with a fraction size of 1-12. The study of the qualitative characteristics of the obtained concrete indicates an increase in its strength when tested for frost resistance after 50 cycles. The method of slag processing described above can be successfully reproduced on a plant (Fig. 1-4) containing a system for delivering slag from the smelter to the pre-crushing zone, where a tilter 1, a vibrating screen 2 with a failed non-magnetic grate 3 and a remotely controlled manipulator 4 are located. from the remote control (C). The manipulator 4 is equipped with a hydro-pneumatic impact mechanism in the form of a cutter 5. To ensure more reliable crushing of the source material to the required size, a vibrating hopper 6 and a jaw crusher 7 are located near the vibrating screen 2. In addition, a crane 8 is mounted in the crushing zone to remove oversized metal pieces remaining on the failure grate 3. Crushed material using a system of transport devices, in particular belt conveyors 9, moves along the main process stream (shown in Fig. 1 with a contour arrow), on the path of which vibro-jaw crushers 10 and electromagnetic separators 11 are sequentially mounted, providing grinding and sorting of slag by decreasing fractions to the specified sizes. Classifiers 12 and 13 for coarse and fine fractions of crushed slag are mounted on the way of the main process flow. The installation also assumes the presence of an additional process stream (shown in Fig. 1 by a triangular arrow), including a system for returning material that is not crushed to the required size, located near the classifier 12 for a coarse fraction and consisting of conveyors and a jaw crusher 14 perpendicular to each other, and also a system 15 for removing magnetized materials. Accumulators 16 of the resulting commercial slag and a sealed module 17 are installed at the outlet of the main process stream, connected to the dust collection system, made in the form of a container 18. Inside the module 17, a cascade of screw mills 19 is sequentially located for processing pulverized fractions into a fine powder. The device works as follows. The slag tank 20 with cooled slag is fed, for example, by a loader (not shown) into the operating area of the installation and is placed on the trolley of the tilter 1, which overturns it onto the grate 3 of the vibrating screen 2, knocks out the slag block 21 and returns the slag to its original position. Next, the empty slag is removed from the tilter and another one with slag is installed in its place. Then the manipulator 4 is brought to the vibrating screen 2 for crushing the slag block 21. The manipulator 4 has an articulated arrow 22, on which a cutter 5 is hinged, crushing the slag block into pieces of different sizes. The body of the manipulator 4 is mounted on a movable carrier frame 23 and rotates around a vertical axis, ensuring the processing of the block over the entire area. The manipulator presses the pneumopercussion mechanism (dolbnyak) to the slag block at the selected point and inflicts a series of oriented and concentrated blows. Crushing is carried out to such a size that ensures the maximum passage of pieces through the holes in the failed grate 3 of the vibrating screen 2. After crushing is completed, the manipulator 4 returns to its original position and the vibrating screen 2 comes into operation. The waste remaining on the surface of the vibrating screen in the form of metal and slag with metal inclusions is taken magnetic plate of the crane 8, and the quality of the selection is ensured by installing a vibrating screen 2 failure grating 3 of non-magnetic material. The selected material is stored in containers. Other large pieces of slag with a low metal content collide with a failed grate into the jaw crusher 7, from where the crushed product enters the main process stream. The slag fractions that have passed through the holes of the failed grate 3 enter the vibrating bunker 6, from which the belt conveyor 9 is fed to the system of vibro-jaw crushers 10 with electromagnetic separators 11. itself in the specified stream. The material crushed in the main flow enters the classifier 12, where it is sorted into fractions of 0-12 mm in size. Larger fractions through the return system (additional process stream) enter the jaw crusher 14, are crushed and again returned to the main stream for re-sorting. The material passed through the 12 classifier is fed to the 13 classifier, in which dust-like fractions of 0-1 mm in size are selected, entering the hermetic module 17, and 1-12 mm, entering the accumulators 16. In the process of grinding the material in the main process flow, the resulting dust system of its selection (local suction) is collected in the tank 18, which communicates with the module 17. Further, all the dust collected in the module is processed into a fine powder with a specific surface area of more than 5000 cm 2 /g, using a cascade of sequentially installed screw mills 19. In order to streamline the cleaning of the main slag stream from metal inclusions along its entire path, they are selected using electromagnetic separators 11 and transfer to the system 15 for the removal of magnetized materials (additional process flow), subsequently transported for remelting.
CLAIM
1. A method for processing foundry slag, including preliminary crushing of the source material and its subsequent sorting into decreasing fractions to obtain commercial slag with simultaneous selection of the resulting dusty fractions, characterized in that preliminary crushing is carried out selectively and oriented with a concentrated force of 900 to 1200 J, and the selected pulverized fractions are enclosed in a closed volume and have a mechanical effect on them until a fine powder with a specific surface area of at least 5000 cm 2 is obtained. 2. Installation for processing foundry slag, including a system for delivering raw material to the pre-crushing zone, a device for crushing and screening, vibrating crushers with electromagnetic separators and transport devices that grind and sort the material into decreasing fractions, classifiers of coarse and fine fractions and a system selection of pulverized fractions, characterized in that the device for crushing and screening is made in the form of a remote-controlled manipulator, on which a hydropneumatic impact mechanism is installed, and a sealed module is mounted in the installation, communicated with the pulverized fractions selection system, having a means for processing these fractions into a fine powder . 3. Installation according to claim 2, characterized in that the means for processing pulverized fractions into fine powder is a cascade of successively arranged screw mills. 4. Installation according to claim. 2, characterized in that it is equipped with a system for returning the processed material, installed near the coarse fraction classifier, for its additional grinding.Foundry waste
foundry waste
English-Russian dictionary of technical terms. 2005 .
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Environmental problems foundry
and ways of their development
Environmental issues now come to the fore in the development of industry and society.
Technological processes for the manufacture of castings are characterized by a large number of operations, during which dust, aerosols and gases are released. Dust, the main component of which in foundries is silica, is formed during the preparation and regeneration of molding and core sands, the melting of foundry alloys in various melting units, the release of liquid metal from the furnace, its out-of-furnace processing and pouring into molds, at the casting knockout section, in the process stumps and cleaning of castings, in the preparation and transportation of raw bulk materials.
In the air of foundries, in addition to dust, there are large quantities of carbon oxides, carbon dioxide and sulfur dioxide, nitrogen and its oxides, hydrogen, aerosols saturated with iron and manganese oxides, hydrocarbon vapors, etc. Sources of pollution are melting units, heat treatment furnaces , dryer for molds, rods and ladles, etc.
One of the hazard criteria is the assessment of the level of odors. On the atmospheric air accounts for more than 70% of all harmful effects of foundry production. /1/
In the production of 1 ton of steel and cast iron castings, about 50 kg of dust, 250 kg of carbon oxides, 1.5-2 kg of sulfur and nitrogen oxides, and up to 1.5 kg of other harmful substances (phenol, formaldehyde, aromatic hydrocarbons, ammonia, cyanides) are released. ). Up to 3 cubic meters of waste water enters the water basin and up to 6 tons of waste molding sands are removed to dumps.
Intensive and dangerous emissions are formed in the process of melting metal. Emission of pollutants, chemical composition dust and exhaust gases is different and depends on the composition of the metal charge and the degree of its contamination, as well as on the condition of the furnace lining, the smelting technology, and the choice of energy carriers. Particularly harmful emissions during the smelting of non-ferrous metal alloys (vapours of zinc, cadmium, lead, beryllium, chlorine and chlorides, water-soluble fluorides).
The use of organic binders in the manufacture of cores and molds leads to a significant release of toxic gases during the drying process, and especially during metal pouring. Depending on the class of the binder, such harmful substances as ammonia, acetone, acrolein, phenol, formaldehyde, furfural, etc. can be released into the workshop atmosphere. stages of the technological process: in the manufacture of mixtures, curing of rods and molds, and cooling of the rods after removal from the tooling. /2/
Consider the toxic effects on humans of the main harmful emissions from foundry production:
- carbon monoxide(hazard class - IV) - displaces oxygen from blood oxyhemoglobin, which prevents the transfer of oxygen from the lungs to tissues; causes suffocation, has a toxic effect on cells, disrupting tissue respiration, and reduces oxygen consumption by tissues.
- nitrogen oxides(hazard class - II) - irritate the respiratory tract and blood vessels.
- Formaldehyde(hazard class - II) - a general toxic substance that causes irritation of the skin and mucous membranes.
- Benzene(hazard class - II) - has a narcotic, partly convulsive effect on the central nervous system; chronic poisoning can lead to death.
- Phenol(hazard class - II) - a strong poison, has a general toxic effect, can be absorbed into the human body through the skin.
- Benzopyrene C 2 0H 12(hazard class - IV) - a carcinogen that causes gene mutations and cancer. Formed during incomplete combustion of fuel. Benzopyrene has high chemical resistance and is highly soluble in water, from wastewater it spreads over long distances from sources of pollution and accumulates in bottom sediments, plankton, algae and aquatic organisms. /3/
Obviously, in the conditions of foundry production, an unfavorable cumulative effect of a complex factor is manifested, in which the harmful effect of each individual ingredient (dust, gases, temperature, vibration, noise) increases dramatically.
Solid waste from the foundry industry contains up to 90% of used molding and core sands, including reject molds and cores; they also contain spills and slags from the settling tanks of dust-cleaning equipment and mixture regeneration plants; foundry slag; abrasive and tumbling dust; refractory materials and ceramics.
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 sands, in which synthetic resins are the binder. These substances are highly soluble in water, which creates a risk of their getting into water bodies when washed out by surface (rain) or groundwater.
Waste waters come mainly from installations for hydraulic and electro-hydraulic cleaning of castings, hydroregeneration of waste mixtures and wet dust collectors. As a rule, wastewater from linear production is simultaneously contaminated with not one, but a number of harmful substances. Also, a harmful factor is the heating of water used in melting and pouring (water-cooled molds for chill casting, pressure casting, continuous casting of profile billets, cooling coils of induction crucible furnaces).
hit warm water into open reservoirs causes a decrease in the level of oxygen in the water, which adversely affects the flora and fauna, and also reduces the self-cleaning capacity of reservoirs. The wastewater temperature is calculated taking into account sanitary requirements so that the summer temperature of river water as a result of wastewater discharge does not rise by more than 30°C. /2/
A variety of assessments of the environmental situation at various stages of casting production does not make it possible to assess the environmental situation of the entire foundry, as well as the technical processes used in it.
It is proposed to introduce a single indicator of environmental assessment of the manufacture of castings - specific gas emissions of the 1st component to the given specific gas emissions in terms of carbon dioxide (greenhouse gas) /4/
Gas emissions at various stages are calculated:
- during melting- by multiplying the specific gas emissions (in terms of dioxide) by the mass of the smelted metal;
- in the manufacture of molds and cores- by multiplying the specific gas emissions (in terms of dioxide) by the mass of the rod (mould).
Abroad, it has long been customary to evaluate the environmental friendliness of the processes of pouring molds with metal and solidifying the casting with benzene. It was found that the conditional toxicity based on the benzene equivalent, taking into account the release of not only benzene, but also substances such as CO X, NO X, phenol and formaldehyde, in rods obtained by the “Hot-box” process is 40% higher than in rods obtained by the "Cold-box-amin" process. /5/
The problem of preventing the release of hazards, their localization and neutralization, waste disposal is especially acute. For these purposes, a complex environmental protection measures, including the use of:
- for dust cleaning– spark arresters, wet dust collectors, electrostatic dust collectors, scrubbers (cupola furnaces), fabric filters (cupola furnaces, arc and induction furnaces), crushed stone collectors (electric arc and induction furnaces);
- for afterburning cupola gases– recuperators, gas purification systems, installations for low-temperature CO oxidation;
- to reduce the release of harmful molding and core sands– reduction of binder consumption, oxidizing, binding and adsorbing additives;
- for disinfection of dumps– arrangement of landfills, biological reclamation, covering with an insulating layer, fixing soils, etc.;
- for wastewater treatment– mechanical, physico-chemical and biological cleaning methods.
Of the latest developments, attention is drawn to the absorption-biochemical installations created by Belarusian scientists for cleaning ventilation air from harmful substances. organic matter in foundries with a capacity of 5, 10, 20 and 30 thousand cubic meters / hour /8/. In terms of combined efficiency, environmental friendliness, economy and operational reliability, these plants are significantly superior to existing traditional gas cleaning plants.
All these activities are associated with significant costs. Obviously, it is necessary, first of all, to fight not with the consequences of damage by hazards, but with the causes of their occurrence. This should be the main argument when choosing priority directions for the development of certain technologies in foundry production. From this point of view, the use of electricity in the smelting of metal is most preferable, since the emissions of the smelting units themselves are minimal in this case... Continue the article>>
Article: Ecological problems foundry production and ways of their development
Article author: Krivitsky V.S.(ZAO TsNIIM-Invest)
