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6. 1. 2. Dispersed solid waste processing
Most stages of technological processes in the metallurgy of ferrous metals are accompanied by the formation of solid dispersed waste, which is mainly the remains of ore and non-metallic mineral raw materials and products of its processing. By chemical composition, they are divided into metallic and nonmetallic (mainly represented by silica, alumina, calcite, dolomite, with an iron content of not more than 10 - 15% of the mass). These wastes belong to the least utilized group of solid wastes and are often stored in dumps and sludge storages.
The localization of particulate solid waste, especially metal-containing waste, at storage facilities causes complex pollution of the environment in all its components due to dispersion of fine particles by the winds, migration of heavy metal compounds in the soil layer and groundwater.
At the same time, these wastes belong to secondary material resources and in their chemical composition can be used both in the metallurgical industry itself and in other sectors of the economy.
As a result of analysis of the dispersed waste management system at the Severstal base metallurgical plant, it was found that the main accumulations of metal-containing sludge are observed in the gas treatment system of the converter, blast furnace, production and heat power facilities, pickling compartments of rolling production, flotation of coal from coke production and slag removal.
A typical scheme of flows of solid dispersed waste of closed production in a general form is presented in Fig. 3.
Of practical interest are sludge from gas cleaning systems, sludge from iron sulfate from pickling compartments of rolling production, sludge from blasting machines from blast furnaces, waste from flotation enrichment proposed by Severstal OJSC (Cherepovets), involves the use of all components and is not accompanied by the formation of secondary resources.
The stored metal-containing dispersed wastes of metallurgical production, which are the source of ingredient and parametric pollution of natural systems, represent unclaimed material resources and can be considered as technogenic raw materials. Such technologies can reduce the accumulation of waste by utilizing converter sludge, producing a metallized product, the production of iron oxide pigments based on industrial sludge, and the integrated use of waste to produce Portland cement.
6. 1. 3. Disposal of sludge from iron sulfate
Among hazardous metal-containing wastes, there are sludges containing valuable, scarce and expensive components of non-renewable ore raw materials. In this regard, the development and practical implementation of resource-saving technologies aimed at the disposal of waste from these industries is a priority in domestic and world practice. However, in some cases, the introduction of technologies effective from the point of view of resource conservation causes a more intense pollution of natural systems than the disposal of these wastes by storage.
In view of this circumstance, an analysis is needed of the methods widely used in industrial practice for utilization of technogenic sludge of iron sulfate extracted during regeneration of spent pickling solutions formed in the crystallization devices of flotation sulfuric acid baths after sheet steel decapitation.
Anhydrous sulfates are used in various sectors of the economy, however, the practical implementation of methods for the disposal of industrial sludge from iron sulfate is limited by its composition and volume. The sludge resulting from this process contains sulfuric acid, impurities of zinc, manganese, nickel, titanium, and others. The specific rate of sludge formation is over 20 kg / t of rolled metal.
It is not advisable to use technogenic sludge of iron sulfate in agriculture and in the textile industry. It is more advisable to use it in the production of sulfuric acid and as a coagulant for cleaning wastewater, in addition to purification from cyanides, because complexes are formed that are not oxidized even by chlorine or ozone.
One of the most promising areas for processing technogenic sludge from iron sulfate, which is formed during the regeneration of spent pickling solutions, is its use as a feedstock for the production of various iron oxide pigments. Synthetic iron oxide pigments have a wide range of applications.
The utilization of the sulfur dioxide contained in the flue gases of the calcining furnace formed upon receipt of the Kaput-Mortum pigment is carried out according to the known technology using the ammonia method to form an ammonium solution used in the production of mineral fertilizers. The technological process for producing the Venetian Red pigment includes the operations of mixing the initial components, calcining the initial mixture, grinding and packaging, and excludes the operation of dewatering the initial charge, washing, drying the pigment and utilizing the exhaust gases.
When using technogenic sludge of iron sulfate as the feedstock, the physicochemical characteristics of the product do not decrease and meet the requirements for pigments.
The technical and environmental effectiveness of the use of technogenic sludge of iron sulfate to obtain iron oxide pigments is due to the following:
No stringent sludge composition requirements;
No preliminary preparation of sludge is required, as, for example, when used as flocculants;
It is possible to process both freshly formed and sludge accumulated in dumps;
Volumes of consumption are not limited, but determined by the sales program;
It is possible to use the equipment available at the enterprise;
Processing technology involves the use of all components of the sludge, the process is not accompanied by the formation of secondary waste.
6. 2. Non-ferrous metallurgy
In the production of non-ferrous metals, a lot of waste is also generated. The enrichment of non-ferrous metal ores expands the application of preconcentration in heavy media, and different kinds separation. The enrichment process in heavy media allows the comprehensive use of relatively poor ore in processing plants that process nickel, lead-zinc ore and other metal ores. The light fraction obtained in this case is used as filling material in mines and in the construction industry. In European countries, waste generated during the extraction and enrichment of copper ore is used to lay the worked out space and again in the production of building materials, in road construction.
Subject to the processing of poor low-grade ores, hydrometallurgical processes that use sorption, extraction and autoclave devices are widespread. For the processing of previously thrown hard-to-recycle pyrrhotite concentrates, which are raw materials for the production of nickel, copper, sulfur, and precious metals, there is a waste-free oxidation technology carried out in an autoclave apparatus and representing the extraction of all the main components mentioned above. This technology is used at the Norilsk Mining and Processing Plant.
Valuable components are also extracted from the sharpening waste of carbide tools and slags in the production of aluminum alloys.
Nepheline sludges in cement production are also used and can increase the productivity of cement kilns by 30% while reducing fuel consumption.
Almost all TPO of non-ferrous metallurgy can be used for the production of building materials. Unfortunately, not all TPOs of non-ferrous metallurgy are still used in the construction industry.
6. 2. 1. Chloride and regenerative processing of non-ferrous metallurgy waste
Theoretical and technological foundations of the chlorine-plasma technology for processing secondary metal raw materials were developed at IMET RAS. The technology has been developed on an enlarged laboratory scale. It includes the chlorination of metal wastes with gaseous chlorine and the subsequent reduction of chlorides with hydrogen in an RFI-plasma discharge. In the case of processing of monometallic waste or in cases where separation of the extracted metals is not required, both processes are combined in one unit without condensation of chlorides. This was the case with the processing of tungsten waste.
The solid alloy waste after sorting, crushing and cleaning from external contaminants before chlorination is oxidized with oxygen or oxygen-containing gases (air, CO 2, water vapor), as a result of which carbon burns out, and turns tungsten and cobalt into oxides with the formation of a loose, easily milled mass, which is reduced by hydrogen or ammonia, and then actively chlorinated by gaseous chlorine. The extraction of tungsten and cobalt is 97% or more.
In the development of research on the processing of waste products and outdated products from them, an alternative technology for the regeneration of carbide-containing solid alloy waste has been developed. The essence of the technology lies in the fact that the starting material is oxidized with an oxygen-containing gas at 500 - 100 ºС, and then is subjected to reduction with hydrogen or ammonia at 600 - 900 ºС. Sooty carbon is introduced into the formed loose mass and after grinding a homogeneous mixture is obtained for carbidization, carried out at 850 - 1395 ºС, and with the addition of one or more metal powders (W, Mo, Ti, Nb, Ta, Ni, Co, Fe), which allows you to get valuable alloys.
The method solves priority resource-saving tasks, ensures the implementation of technologies for the rational use of secondary material resources.
6. 2. 2. Disposal of foundry waste
Utilization of foundry waste is an urgent problem of metal production and rational resource use. When smelting, a large amount of waste is generated (40 - 100 kg per 1 ton), a certain part of which is bottom slag and bottom discharge, containing chlorides, fluorides and other metal compounds, which are not currently used as secondary raw materials, but are disposed of in dumps. The metal content in such dumps is 15–45%. Thus, tons of valuable metals are lost, which must be returned to production. In addition, there is pollution and salinization of soils.
In Russia and abroad, various methods for processing metal-containing waste are known, but only some of them are widely used in industry. The difficulty lies in the instability of the processes, their duration, low metal yield. The most promising are:
Melting metal-rich waste with a protective flux, mixing the resulting mass for dispersion into small, uniform in size and uniformly distributed over the melt drops of metal with subsequent co-precipitation;
Dilution of the residues with a protective flux and pouring through a sieve of molten mass at a temperature below the temperature of this melt;
Mechanical disintegration with sorting waste rock;
Wet disintegration by dissolution or flux and metal separation;
Centrifugation of liquid smelting residues.
The experiment was carried out at a magnesium production enterprise.
When disposing of waste, it is proposed to use existing foundry equipment.
The essence of the wet disintegration method is to dissolve the waste in water, clean or with catalysts. In the processing mechanism, soluble salts are re-added to the solution, and insoluble salts and oxides lose their strength and crumble, the metal part of the bottom discharge is released and easily separated from non-metallic. This process is exothermic, proceeds with the release of a large amount of heat, accompanied by drilling and gas evolution. The yield of metal in laboratory conditions is 18 - 21.5%.
More promising is the method of melting waste. To dispose of waste with a metal content of at least 10%, it is first necessary to enrich the waste with magnesium with a partial separation of the salt portion. Waste is loaded into the preparatory steel crucible, flux (2 - 4% of the mass of the charge) is added and melted. After the waste is melted, the liquid melt is refined with a special flux, the consumption of which is 0.5 - 0.7% of the charge mass. After settling, the yield of metal is 75 - 80% of its content in slags.
After draining the metal, a thick residue remains, consisting of salts and oxides. The content of magnesium metal in it is not more than 3-5%. The purpose of further waste processing was to extract magnesium oxide from the nonmetallic part by treating them with aqueous solutions of acids and alkalis.
Since the conglomerate decomposes as a result of the process, after drying and calcining it is possible to obtain magnesium oxide with up to 10% impurities. Part of the remaining non-metallic part can be used in the production of ceramics and building materials.
This pilot technology allows you to dispose of over 70% of the mass of waste previously dumped in dumps.
Foundry is characterized by toxic air emissions, wastewater and solid waste.
An acute problem in the foundry is the unsatisfactory state of the air. Chemicalization of foundry, contributing to the creation of advanced technology, at the same time poses the task of improving the air environment. Largest amount dust is emitted from equipment for embossing molds and rods. Various types of cyclones, hollow scrubbers and washing cyclones 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 the foundry poses a particularly acute problem of purifying air emissions from toxic substances, mainly from organic compounds of phenol, formaldehyde, carbon oxides, benzene, and others. To neutralize the organic vapors of the foundry, various methods are used: thermal combustion, catalytic afterburning, adsorption activated carbon, ozone oxidation, bio-treatment, etc.
The sources of wastewater in foundries are mainly installations for hydraulic and electro-hydraulic cleaning of castings, wet cleaning of air, and hydro-generation of used molding sand. Huge economic importance for the national economy has the disposal of wastewater and sludge. The amount of wastewater can be significantly reduced through the use of recycled water supply.
Solid foundry waste entering dumps is mainly spent foundry sands. A small 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. Using a regenerator reduces the consumption of fresh sand, as well as binders and catalysts. The developed technological processes of regeneration allow sand to be regenerated with good quality and high yield of the target product.
In the absence of regeneration, spent molding sand, as well as slag, must be used in other industries: waste sand - in road construction as a ballast material for leveling the relief and building embankments; waste sand and tar mixtures - for the manufacture of cold and hot asphalt concrete; a small fraction of the used molding sand - for the production of building materials: cement, brick, tiles; waste liquid-glass mixtures - raw materials for building cement mortars and concrete; foundry slag - for road construction as crushed stone; fine fraction - as a fertilizer.
Solid foundry waste should be disposed of in ravines, spent quarries and mines.
CASTING ALLOYS
IN modern technology cast parts from very many alloys are used. At present, in the USSR, the share of steel casting in the overall balance of castings is approximately 23%, of cast iron - 72%. Castings from non-ferrous metal alloys about 5%.
Cast iron and cast bronzes are the “traditional” cast alloys used since ancient times. They do not have sufficient ductility for processing by pressure, products from them are obtained by casting. At the same time, wrought alloys, for example, steel, are widely used to produce castings. The possibility of using the alloy to produce castings is determined by its casting properties.
3 / 2011_ MGSu TNIK
DISPOSAL OF WASTE LITHIUM PRODUCTION IN THE MANUFACTURE OF CONSTRUCTION PRODUCTS
RECYCLING OF THE WASTE OF FOUNDRY MANUFACTURE AT MANUFACTURING OF BUILDING PRODUCTS
B.B. Zharikov, B.A. Jezerski, H.B. Kuznetsova, I.I. Sterkhov V. V. Zharikov, V.A. Yezersky, N.V. Kuznetsova, I.I. Sterhov
In these studies, the possibility of disposal of the used molding sand when using it in the production of composite building materials and products is considered. Formulations of building materials recommended for 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
During the process foundry accompanied by the formation of waste, the bulk of which is spent molding (OFS) and core mixtures and slag. Currently, up to 70% of this waste is disposed of annually. Warehousing of industrial waste also becomes economically inexpedient for the enterprises themselves, since due to the tightening of environmental laws, an environmental tax has to be paid for 1 ton of waste, the amount of which depends on the type of stored waste. In this regard, there is a problem of disposal of accumulated waste. One of the solutions to 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 burden in landfills and eliminate direct contact of waste with the environment, as well as increase the efficiency of use of material resources (electricity, fuel, raw materials). In addition, the materials and products manufactured using waste products comply with environmental and hygienic safety requirements, since cement stone and concrete are detoxicants for many harmful ingredients, including even waste ash containing dioxins.
The aim of this work is to select the compositions of multicomponent composite building materials with physical and technical parameters -
NEWSLETTER 3/2011
comparable to materials produced using natural raw materials.
An experimental study of the physicomechanical characteristics of composite building materials.
The components of composite building materials are: spent molding mixture (particle size module MK \u003d 1.88), which is a mixture of binder (Ethylsilicate-40) and aggregate (silica sand of various fractions), used to completely or partially replace fine aggregate in a composite mixture material; Portland cement M400 (GOST 10178-85); quartz sand with MK \u003d 1.77; water; S-3 superplasticizer, which helps to reduce the water demand of the concrete mixture and improve the structure of the material.
Experimental studies of the physicomechanical characteristics of the cement composite material using OFS were carried out using the experimental design method.
The following indicators were chosen as response functions: compressive strength (U), water absorption (U2), frost resistance (! H), which were determined by 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 area of \u200b\u200bits application and the appropriateness of use.
The following factors were considered as influencing factors: the fraction of the content of ground DFS in the aggregate (x1); water / binder ratio (x2); aggregate / binder ratio (x3); the amount of additive plasticizer C-3 (x4).
When planning the experiment, the ranges of changes in the factors were taken based on the maximum and minimum possible values \u200b\u200bof the corresponding parameters (Table 1).
Table 1. - Intervals of variation of factors
Factors Range of factors
x, 100% sand 50% sand + 50% ground OFS 100% ground OFS
x4,% of the mass. binder 0 1.5 3
Changing the mixed factors will allow 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 \u200b\u200bof the levels of mixed factors (x1, x2, x3, x4) and are described, in turn, by a second-order polynomial.
As a result of the experiments, matrices of values \u200b\u200bof the response functions V1, V2, V3 were formed. Taking into account the values \u200b\u200bof repeated experiments for each function, 24 * 3 \u003d 72 values \u200b\u200bwere obtained.
Estimates of unknown model parameters were found using the method least squares, that is, minimizing the sum of the squared deviations of the values \u200b\u200bof Y from the calculated model. To describe the dependences V \u003d Dx, x2, x3, x4), the normal equations of the least squares method were used:
) \u003d Xm ■ Y, whence:<0 = [хт X ХтУ,
where 0 is the matrix of estimates of unknown parameters of the model; X is the matrix of coefficients; X is the transposed matrix of coefficients; Y is the vector of observation results.
To calculate the parameters of the dependences V \u003d Dxl x2, x3, x4), the formulas given in for plans of type N.
In the models with a significance level of a \u003d 0.05, the significance of the regression coefficients was checked using the Student's t-criterion. With the exception of insignificant coefficients, the final form of mathematical models was determined.
Analysis of 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 of 0.6 (x2 \u003d 1) and the amount of aggregate relative to the binder is 3: 1 (x3 \u003d -1) . The models of the studied dependencies have the form: compressive strength
y1 \u003d 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 \u003d 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 \u003d 25.93 + 4.83 x1 + 2.28 x4 +1.06 x1 +1.56 x1 + 4.44 x1 x4 - 2.94 x4 +1.56 x4 + + 1.56 x2 + 3, 56 x42
To interpret the obtained mathematical models, graphical dependences of the objective functions on two factors were constructed, with the fixed values \u200b\u200bof two other factors.
"2L-40 PL-M
Figure - 1 Isolines of compressive strength of composite building material, kgf / cm2, depending on the proportion of OFS (X1) in the aggregate and the amount of superplasticizer (x4).
I C | 1u | Mk1 ^ | b1 || mi. 1 ||| (| 9 ^ ______ 1 |<1ФС
Figure - 2 Isolines of water absorption of 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 ■ UN) B 0-5
Figure - 3 Isolines of frost resistance of a composite building material, cycles, depending on the proportion of OFS (xx) in the aggregate and the amount of superplasticizer (x4).
An analysis of the surfaces showed that with a change in the OFS content in the aggregate from 0 to 100%, 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 are observed. With a change in the amount of S-3 superplasticizer from 0 to 3 (wt%), an average increase in strength by 12% is observed; water absorption by weight varies from 10.38% to 16.46%; with a filler consisting of 100% OFS, frost resistance increases by 30%, but with a filler consisting of 100% quartz sand, frost resistance decreases by 35%.
Practical implementation of experimental results.
By analyzing the obtained mathematical models, it is possible to identify not only the compositions of materials with increased strength characteristics (table 2), but also to determine the compositions of composite materials with predetermined physical and mechanical characteristics with a decrease in the proportion of binder (table 3).
After the analysis of the physicomechanical characteristics of the main building products, it was revealed that the formulations of the obtained compositions of composite materials using foundry industry waste are suitable for the production of wall blocks. These requirements correspond to the composition of the composite materials, which are shown in table 4.
X1 (filler composition,%) x2 (W / C) X3 (filler / binder) x4 (super plasti fixative,%) ^ compress, 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_
x! (filler composition,%) x2 (W / C) x3 (filler / binder) x4 (superplasticizer,%) Ls, 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 Physico-mechanical characteristics of building composite
foundry waste materials
x1 (composition of aggregate,%) x2 (W / C) x3 (aggregate / binder) x4 (super-plastic fixative,%) ^ compress, kgf / cm2 w,% P, gr / 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
Building products Technical requirements for wall blocks according to GOST 19010-82 Price, rub / pc
Compressive strength, kgf / cm2 Thermal conductivity coefficient, X, W / m 0 С Average density, kg / m3 Water absorption,% by weight Frost resistance, brand
100 according to manufacturer's specifications\u003e 1300 according to manufacturer's specifications according to manufacturer's specifications
Sand concrete block LLC Tam-bovBusinessStroy 100 0.76 1840 4.3 I00 35
Block 1 using OFS 100 0.627 1520 4.45 B200 25
Block 2 using OFS 110 0.829 1500 2.8 B200 27
NEWSLETTER 3/2011
A method is proposed for involving technogenic wastes instead of natural raw materials in the production of composite building materials;
The basic physical and mechanical characteristics of composite building materials using foundry waste have been investigated;
Compositions of equal strength composite construction products with a reduced cement consumption of 20% have been developed;
The compositions of mixtures for the manufacture of building products, for example, wall blocks, are determined.
Literature
1. GOST 10060.0-95 Concrete. Methods for determining frost resistance.
2. GOST 10180-90 Concrete. Methods for determining the strength of the control samples.
3. GOST 12730.3-78 Concrete. Method for determining water absorption.
4. Zazhigaev L.S., Kishyan A.A., Romanikov Yu.I. Methods of planning and processing the results of a physical experiment.- M.: Atomizdat, 1978.- 232 p.
5. Krasovsky G.I., Filaretov G.F. Planning an experiment. - Мn .: Publishing house of BSU, 1982. -302 p.
6. Malkova M.Yu., Ivanov A.S. Ecological problems of foundry 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.
Keywords: ecology in construction, resource saving, spent 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.
Liteproductionaboutdstvo, one of the industries whose products are castings obtained in foundry molds when filled with liquid alloy. On average, about 40% (by weight) of blanks for machine parts is manufactured by casting methods, and in some engineering industries, such as machine tools, the proportion of cast products is 80%. Of all the cast billets produced, engineering consumes about 70%, the metallurgical industry - 20%, and the production of sanitary equipment - 10%. Cast parts are used in metalworking machines, internal combustion engines, compressors, pumps, electric motors, steam and hydraulic turbines, rolling mills, agricultural machinery. cars, cars, 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, for example forging. By casting, it is possible to obtain billets of varying complexity with small allowances, which reduces metal consumption, reduces the cost of machining and, ultimately, reduces the cost of products. By casting can be made products of almost any mass - from several g up to hundreds t with walls with a thickness of tenths mm up to a few m The main alloys from which castings are made: 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.
The classification of production waste is possible according to various criteria, among which the following can be considered the main ones:
by industries - 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 compound, etc.)
in production cycles - in the extraction of raw materials (overburden and oval rocks), in enrichment (tails, sludge, plums), in pyrometallurgy (slag, sludge, dust, gases), in hydrometallurgy (solutions, precipitation, gases).
At a closed-cycle metallurgical plant (cast iron - steel - rolled), solid waste can be of two types - dust and slag. Quite often, wet gas cleaning is used, then instead of dust, sludge is a waste. The most valuable for ferrous metallurgy are iron-containing waste (dust, sludge, scale), while slag is mainly used in other industries.
During the operation of the main metallurgical units, a greater amount of fine 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 sinter charge).
Examples of foundry waste:
Foundry Burnt Sand
Arc furnace slag
Non-ferrous and ferrous metal scrap
Oil waste (waste oils, greases)
Molded burned sand (molding sand) - foundry waste, physically-mechanical properties approaching sandy loam. It is formed as a result of applying the sand casting method. It consists mainly of quartz sand, bentonite (10%), carbonate additives (up to 5%).
I chose this type of waste because the issue of disposal of the used molding sand is one of the important issues of foundry from an environmental point of view.
Molding materials should exhibit mainly refractoriness, gas permeability and ductility.
The refractoriness of the molding material is its ability not to melt and sinter when it comes into contact with molten metal. The most affordable and cheapest molding material is quartz sand (SiO2), which is sufficiently refractory for casting the most refractory metals and alloys. Of the impurities accompanying SiO2, 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 smelting cast iron and bronze, harmful impurities 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 gas permeability. With poor gas permeability of the molding earth, gas shells (usually spherical in shape) can form in the cast and cause casting to be rejected. Shells are detected during subsequent machining of the casting when removing the upper layer of metal. The gas permeability of the molding earth depends on its porosity between the 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 greater gas permeability than sand with rounded grains. Small grains, located between large ones, also reduce the gas permeability of the mixture, reducing porosity and creating small winding channels that impede the exit of gases. Clay, having extremely fine grains, clogs the pores. Excess water also clogs the pores and, in addition, evaporating in 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 its shape, resisting external forces (shock, impact of a jet of liquid metal, static pressure of the metal cast into the mold, pressure of the gases released from the mold and the metal when casting, pressure from metal shrinkage, etc. .).
The strength of the moldable mixture increases with increasing moisture content to a certain limit. With a further increase in the amount of moisture, strength decreases. If there is clay impurity in the foundry sand (“liquid sand”), the strength increases. Greasy 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 binder layer between the individual grains of sand is achieved by thorough and continuous mixing of sand with clay.
The plasticity of the molding sand is called 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 filling of the mold with metal. The finer the grains of sand and the more evenly 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 ductility decreases dramatically.
When storing spent molding sand in a landfill, dusting and environmental pollution occur.
To solve this problem, it is proposed to carry out the regeneration of spent molding sand.
Special additives. One of the most common types of castings marriage is the burning of the molding and core mixture to the casting. The causes of burning are varied: insufficient refractoriness 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 forms, etc. Three types of burn are distinguished: thermal, mechanical and chemical.
Thermal burn is relatively easy to remove when cleaning castings.
A mechanical burn is formed as a result of penetration of the melt into the pores of the molding 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 by fusible compounds of the type of slag that occur during the interaction of molding materials with the melt or its oxides.
Mechanical and chemical sticks are either removed from the surface of the castings (a large expenditure of energy is required), or the castings are finally rejected. Prevention of burning is based on the introduction of special additives into the molding or core mixture: ground coal, asbestos chips, fuel oil, etc., as well as coating the working surfaces of molds and cores with non-stick paints, sprays, rubbers or pastes containing highly refractory materials (graphite, talc), which do not interact at high temperatures with oxides of melts, or materials that create a reducing medium (ground coal, fuel oil) in the mold when it is poured.
Preparation of molding sand.The quality of the artistic casting largely depends on the quality of the molding mixture from which its mold is prepared. Therefore, the selection of molding materials for the mixture and its preparation in the manufacturing process of casting is important. The molding mixture can be prepared with fresh molding materials and spent mixture with a small addition of fresh materials.
The process of preparing molding mixtures from fresh molding materials consists of the following operations: making a mixture (selection of molding materials), mixing the components of the mixture in dry form, moistening, mixing after wetting, aging, loosening.
Compilation. It is known that molding sands that meet all the technological properties of the molding sand are rare in nature. Therefore, mixtures are usually prepared by selecting sands with different clay contents, so that the resulting mixture contains the right amount of clay and possesses the necessary technological properties. This selection of materials for preparing the mixture is called composing the mixture.
Mixing and moisturizing. The components of the molding sand are thoroughly mixed in dry form in order to evenly distribute clay particles over the entire mass of sand. The mixture is then moistened by adding the right amount of water, and again mixed so that each of the sand particles is covered with a film of clay or another 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 a large amount of materials by hand is a big and time-consuming job. In modern foundries, the components of the mixture during its preparation are mixed in screw mixers or mixing runners.
Mixing runners have a fixed bowl and two smooth rollers sitting on the horizontal axis of a vertical shaft connected by a bevel gear to an electric motor gearbox. An adjustable gap is made between the rollers and the bottom of the bowl, which prevents plasticity, gas permeability, and fire resistance from crushing the mixture of grain grains. To restore the lost properties, 5-35% of fresh molding materials are added to the mixture. This operation in the preparation of the molding mixture is called refreshment of the mixture.
Special additives in molding sand. Special additives are introduced into the molding and core mixtures 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 loosening in massive knots of castings when they solidify. Sawdust and peat are introduced into mixtures intended for the manufacture of molds and rods to be dried. After drying, these additives, decreasing in volume, increase the gas permeability and ductility of the molds and cores. Caustic soda is introduced into the molding quick-hardening mixtures on liquid glass to increase the durability of the mixture (clumping of the mixture is eliminated).
The process of preparing the molding mixture using the used mixture consists of the following operations: preparing the used mixture, adding fresh molding materials to the used mixture, mixing in the dry state, moistening, mixing the components after wetting, aging, loosening.
Sinto's existing Heinrich Wagner Sinto company mass-produces the new generation of FBO molding lines. On the new machines, non-flask molds with a horizontal plane of the connector are manufactured. More than 200 such machines successfully operate 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 spills of sand and provides comfortable conditions and cleanliness in the workplace. In developing the sealing system and transport devices, great attention was paid to minimizing noise levels. FBO units meet all environmental requirements for new equipment.
The mixture filling system allows precise molds to be produced using a bentonite binder sand. An automatic mechanism for controlling the pressure 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 a small wall thickness. This compaction process allows you to vary the height of the upper and lower half molds 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 their composition and the degree of environmental impact, the used molding and core mixtures are divided into three hazard categories:
I - almost inert. Mixtures containing clay, bentonite, cement as a binder;
II - waste containing biochemically oxidized substances. This is a mixture after pouring, the binder in which are synthetic and natural compositions;
III - waste containing low toxic, slightly soluble in water substances. These are liquid glass mixtures, unannealed sand - resin mixtures, mixtures cured by compounds of non-ferrous and heavy metals.
In case of separate storage or burial, the landfills of spent mixtures should be located in separate places free from development, which allow the implementation of measures that exclude the possibility of pollution of settlements. Landfills should be placed in areas with poorly filtering soils (clay, sandstone, shale).
Spent molding sand, knocked out of the flask, must be recycled before reuse. In non-mechanized foundries, it is sifted on a regular sieve or on a mobile mixing and preparation plant, where metal particles and other impurities are separated. In mechanized workshops, the spent mixture is fed from under the knocked out lattice by a conveyor belt to the mixture preparation department. Large lumps of the mixture formed after knocking out forms are usually kneaded with smooth or grooved rollers. Metal particles are separated by magnetic separators installed in areas of the transfer of the spent mixture from one conveyor to another.
Burning land regeneration
Ecology remains a serious problem in foundry, since about 50 kg of dust, 250 kg of carbon monoxide, 1.5-2.0 kg of sulfur oxide, 1 kg of hydrocarbons are released during the production of one ton of casting from ferrous and non-ferrous alloys.
With the advent of forming 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. Improvement of foundry should be directed not only at solving economic problems, but 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 is manifested, in which the harmful effect of each individual ingredient (dust, gases, temperature, vibration, noise) increases sharply.
Upgrading measures in the foundry distinguish the following:
replacement of cupolas with low frequency induction furnaces (the size of harmful emissions decreases: 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 the capture and neutralization of hazardous 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 thermal degradation of molding and core mixtures, in which synthetic resins are a binder. These substances are highly soluble in water, which creates the danger of them getting into water bodies when washed out by surface (rain) or groundwater.
It is economically and environmentally unprofitable to discard the used molding sand after being knocked out into dumps. The most rational solution is the regeneration of cold-hardening mixtures. The main purpose of regeneration is the removal of binder films from silica sand grains.
The most common is the mechanical method of regeneration, in which the binder films are separated from quartz sand grains due to mechanical grinding of the mixture. Binder films are destroyed, converted to dust and removed. Regenerated sand is supplied for further use.
The technological scheme of the mechanical regeneration process:
embossing of the mold (the cast mold is fed to the canvas of the embossed grating, where it is destroyed due to vibration shocks.);
fragmentation of pieces of the molding mixture and mechanical grinding of the mixture (The mixture passing through the knockout grill enters the system of scrubbing sieves: a steel screen for large lumps, a sieve with wedge-shaped openings and a small grinding screen classifier. The built-in sieve system grinds the molding mixture to the required size and filters out metal particles and other large inclusions.);
cooling of the regenerate (the Vibratory elevator provides the transportation of hot sand to the cooler / dust collector.);
pneumatic transfer of regenerated sand to the molding section.
The technology of mechanical regeneration provides the possibility of reuse from 60-70% (Alpha-set process) to 90-95% (Furan-process) of regenerated sand. If for Furan-process these indicators are optimal, then for the Alpha-set of the process the reuse of regenerate only at the level of 60-70% is insufficient and does not solve the environmental and economic issues. To increase the percentage of use of regenerated sand, it is possible to use thermal regeneration of mixtures. The quality of the regenerated sand is not inferior to the fresh sand and even surpasses it due to the activation of the grain surface and the blowing of dust fractions. Thermal regeneration furnaces operate on the principle of a fluidized bed. The regenerated material is heated by side burners. The heat of the flue gas is used to heat the air supplied to the formation of a fluidized bed and to burn gas to heat the regenerated 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 medium 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% regenerated mixture), it has the following disadvantages: equipment complexity, high energy consumption, low productivity, high cost.
All mixtures undergo preliminary preparation before regeneration: magnetic separation (other types of cleaning from non-magnetic scrap), crushing (if necessary), sifting.
With the introduction of the regeneration process, the amount of solid waste discharged into the dump decreases 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 sufficiently 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, using molding earth for the manufacture of foundry molds and cores in the manufacture of molded cast metal parts. After using the molds, burned earth forms, the utilization of which is of great economic importance. Molding soil consists of 90-95% of high-quality quartz sand and small amounts of various additives: bentonite, ground coal, caustic soda, water glass, asbestos, etc.
The regeneration of burnt earth formed after casting of products consists in the removal of dust, fine fractions and clay, which lost its binding properties under the influence of high temperature when filling the mold with metal. There are three ways to regenerate burnt earth:
electrocrown.
Wet way.
With the wet regeneration method, the burnt earth enters the system of successive settling tanks with running water. During the passage of sedimentation tanks, sand settles at the bottom of the pool, and small fractions are carried away by water. The sand is then dried and returned to production for the manufacture of foundry molds. Water is supplied for filtration and purification and is also returned to production.
Dry way.
The dry method of regeneration of burnt earth consists of two sequential operations: separation of sand from binders, which is achieved by blowing air into the drum with the ground, and removing dust and small particles by suctioning them from the drum together with air. Air coming out of the drum containing dust particles is cleaned with filters.
Electrocoronous method.
During electrocorne regeneration, the spent mixture is divided 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 precipitating electrode are greater than gravity, then the grains of sand settle on the surface of the electrode. By changing the voltage at the electrodes, it is possible to separate the sand passing between them into fractions.
The regeneration of molding mixtures with liquid glass is carried out in a special way, since with repeated use of the mixture more than 1-1.3% of alkali is accumulated in it, which increases the burn-in, especially on cast iron castings. A mixture and pebbles are fed into the rotating drum of the regeneration unit at the same time, which, pouring from the blades onto the walls of the drum, mechanically destroy the liquid glass film on the grains of sand. Through adjustable louvers, air enters the drum, which is sucked out with the dust into a wet dust collector. Then the sand together with pebbles is fed into a drum sieve for screening 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. To this end, the forming elements are previously 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, because it contains liquid glass and alkali.
The basis of the magnetic separator is 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 released from the flow of a common moving mixture, which change their path in the direction of action 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 the system of electronic scales and optical dispensers
Also, the used molding mixture is used in the production of cinder block.
Cinder blocks are made from a molding mixture with a moisture content of up to 18%, with the addition of anhydrites, limestone and accelerators for setting the mixture.
Technology for the production of cinder blocks.
A concrete mixture is prepared from the used molding sand, slag, water and cement. Mix 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 into the matrix, it shrinks by pressing and vibration, then the matrix rises, and the cinder block remains in the pan. The resulting drying product keeps its shape due to the stiffness of the solution.
The process of curing. Finally, the cinder block solidifies within a month. After final hardening, the finished product is stored for a further set of strength, which, according to GOST, should be at least 50% of the design. Next, the cinder block is shipped to the consumer or used on its own site.
Germany.
KGT brand regeneration plants. They provide the foundry industry with an environmentally and economically viable recycling technology for foundry mixtures. The reverse cycle reduces the consumption of fresh sand, auxiliary materials and the area for storage of the spent mixture.