RU2440866C1 - Moulding mix for production of steel and iron castings - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention relates to metallurgy. Proposed mix comprises the following components in wt %: used moulding mix making the base, bentonite clay - 5-10, ash of thermal electric power stations - 5-10. ^ EFFECT: improved surface quality of castings. ^ 1 cl, 2 tbl

Description

The invention relates to foundry and can be used in the preparation of raw sand and clay molding sand used in casting ferrous alloys. Composition, wt.%: Spent molding sand - base, bentonite 5-10%, ash and slag waste 5-10%. This ensures an improvement in the quality of the surface of the castings, eliminates burn-out, the formation of "bumps", improves knockability of castings.

The invention relates to the field of foundry, and in particular to the compositions of molding materials used in the manufacture of raw sand-clay molding sand with the addition of a cement binder.

It has been found that the closest analogue of the claimed invention is a molding mixture for castings from steel and cast iron, containing the spent molding mixture, bentonite clay (Molding materials and mold technology, under the editorship of S.S.Zhukovsky, M., Engineering, p.210 -213). In the foundry industry of the Krasnoyarsk Territory, molding clay based on kaolinite (K) and high-adhesive bentonite are used in the preparation of molding mixtures for the manufacture of castings from ferrous alloys.

Bentonite clays have a significantly higher ability to attach moisture than kaolinic. To obtain equal strength of the mixture in the wet state, the consumption of bentonite clays can be 2-3 times less than kaolinic. High stickiness of bentonites is obtained due to the extremely small size of their particles. Bentonites contain many colloidal particles smaller than 0.1 microns.

The Republic of Khakassia is located the clay deposit "Tenth Farm". The largest consumers of clay powders produced by Khakassky Bentonite OJSC are foundry and the drilling industry of the oil and gas complex. For the needs of the foundry industry, clay powders of the P1T1A and P2T1A brands are produced. The market for bentonite clay powders is the entire territory of the Russian Federation: in the west - these are large industrial enterprises, in the east - geological and oil and gas companies.

The mineral composition of clays is 7-8 horizons (vol.%): Montmorillonite - 70-72; hydromica - 1-2, kaolinite - 7-8, quartz - 7-8, alkaline feldspar - 6-7, mica - 4-5, calcite -1-2.

The chemical composition of bentonite, wt.%:

SiO ₂ - 60.5; TiO ₂ - 0.11; Al ₂ O ₃ - 16.25; Fe ₂ O ₃ - 1.70; FeO - 0.75; MgO - 2.38; MnO - 0.03; CaO - 1.75; Na ₂ O - 0.77; K ₂ O - 1.01; SO ₃ - 0.03.

To improve the quality of bentonite, it is activated. Activation is the replacement in the diffusion layer of the clay component of divalent calcium and magnesium ions with a monovalent sodium ion. At the same time, the amount of sodium ions increases and the molding mixture acquires some high mechanical characteristics of the mixtures obtained using sodium bentonites, such as survivability under thermal influences, dry strength and resistance to expansion defects. At the same time, they retain the good characteristics of Ca-bentonite mixtures, such as high compressive strength in bulk, good breakability during knockout, and good wettability. Activation is accompanied by an increase in the strength of the molding sand. The activating effect of additives depends on both the capacity and the composition of the exchange cations. Between the capacity of the exchange cations E (mEq) and the content of montmorillonite in bentonite Q _M (%), the following relation holds: E = 2.34 · Q _M -98, from which it can be seen that the content of montmorillonite determines the capacity of the exchange cations (Table. one). There is a direct relationship between these indicators.

Table 1 Comparative characteristics of the molding mixture using Na and Ca bentonite The properties Concrete Ca Concrete Na Compression Strength High Below Miscibility Above Low Dry compressive strength Low High Vitality vs. Firing Low High Thermal stability Bad Very good The fluidity of the forms of the mixture Good Worse Resistance to expansion defects of the mixture Low High Fragility of forms when knocking out High Low

The use of activated bentonite in the foundry of Khakassia causes a defect in the form of "bumps" of castings made of steel and cast iron.

An object of the invention is to reduce the amount of activated clay - a natural material - in the composition of the molding mixture and the use of ash and slag waste, the disposal of which is an important environmental problem.

The chemical composition of ash and slag waste can be characterized as follows: the elements should be divided into two groups - macro elements involved in the composition of individual mineral varieties of ash and slag (Al, Fe, Ca, Si, Mg, S, C), and micro elements that do not form independent minerals, but are present in ash and slag in the form of impurities to macroelements.

The technical result of solving the problem is:

- expansion of the range of materials used in the composition of the molding sand;

- improving knockability of the molding sand and improving the quality of the molding sand with the introduction of ash in its composition;

- receiving castings without "bumps" with a minimum surface roughness;

- obtaining an economic effect by reducing activated clay in the composition of the molding sand mixture and improving the quality of casting;

- a partial solution to the problem of disposal of ash and slag waste.

According to the proposed method, the ash of the thermal power station is introduced into the molding mixture. The chemical composition of ash and slag can be characterized as follows: the elements should be divided into two groups - macroelements participating in the composition of individual mineral varieties of ash and ash (Al, Fe, Ca, Si, Mg, S, C), and microelements that do not form independent minerals, and present in ash and slag in the form of impurities to macronutrients. Ash and slag waste is characterized by a decrease in the concentration of most trace elements during ash removal.

The mineral composition of sandstones and siltstones in the dumps of the sections is dominated by quartz (SiO ₂ ) up to 44%, potassium feldspars (KAlSi ₃ O ₈ ) - 25-46%, fragments of siliceous rocks - 17-30%. The main minerals of mudstones are kaolinite and hydromica. Re-excavation of overburden rocks during coal mining leads to aeration of the rocks and the occurrence of oxidative processes, the leading role among which is the oxidation of accessory sulfide minerals in the aerated layer during re-excavation.

Ash and slag waste from thermal power plants (TPPs) represent one of the global environmental problems. Thermal power enterprises in the south of the Krasnoyarsk Territory annually produce more than 1.2 million tons of ash and slag. On the territory of Siberia there are no ash dumps that fully meet the basic requirements for reliability and environmental safety imposed by current instructive and regulatory documents.

More than 1.2 million tons of ash and slag are generated annually at TPPs and state district power stations in the region. In ash dumps, which occupy 550 hectares, more than 24 million tons of this waste has been accumulated. In quarries, spaces are freed up annually, the volumes of which are estimated at 10-20 million m ³ .

The environmental impact of ash and slag disposal may include:

- local effects on the air;

- impact on surface water;

- impact on groundwater;

- effects on soils and vegetation;

- catastrophic breakthroughs of water and ash and slag.

The basis of the invention is the following technical problem - the use of ash TPP as a binder in the preparation of the molding mixture.

. Золошлаковые отходы имеют пылевидную фракцию с размерами частиц <0,01 мм. Исследовали водопоглощение образцов, изготовленных из песчано-глинистых смесей и смесей с добавлением золошлаковых отходов. Образцы массой 464 г пропитывали водой до разрушения. Водопоглощение исходного образца составило 10,7%, исследуемого образца - 12,6%.The process of preparing the proposed non-stick anti-shrink molding material is common in the technology of preparation of molding sand. Upon receipt of the test materials, their ingredients were mixed in the laboratory to obtain a homogeneous mass. Then the material was used further to carry out the necessary analyzes. Samples were made from the test mixture — size 68 mm, base diameter d = 86 mm. The composition of the mixture is 90% of the spent molding sand, 5% clay, 5% ash, sample weight 761 g. The sample was compacted with one blow of a standard copra. The density of the mixture was

. Ash and slag wastes have a dusty fraction with particle sizes <0.01 mm. We studied the water absorption of samples made from sand-clay mixtures and mixtures with the addition of ash and slag waste. Samples weighing 464 g were impregnated with water until failure. The water absorption of the initial sample was 10.7%, of the test sample - 12.6%.

The necessary technical result is achieved by the fact that the molding material contains the spent molding mixture, activated clay, ash and slag waste. The anti-contraction effect is due to the lower binding capacity of the ash. Improving the surface quality of the mold is provided by a smaller particle size of ash ≈ 2 times and, therefore, a higher density of the material (table 2).

table 2 No. of examples The composition of the molding material, wt.% Properties of molding compounds Surface Quality Assessment Spent mixture Clay bentonite Ash and slag waste The limit of compressive strength, MPa Compressive strength after heating 500 ° C, MPa Arithmetic mean deviation of the profile, microns one the basis 5 10 0.28 0.36 32 2 the basis 10 5 0.44 0.51 41 3 the basis 7 8 0.4 0.5 34 prototype the basis 10 0.18 0.28 26

The use of the proposed molding material allows to obtain a significant economic effect by reducing the consumption of clay, increasing the surface cleanliness of castings and partially solve the problem of disposal of ash and slag waste.

Claims (1)

The molding mixture for castings from steel and iron castings, containing the spent molding mixture, bentonite clay, characterized in that it additionally contains ash and slag waste from thermal power plants in the following ratio of elements, wt.%:
Spent sand the basis Clay bentonite 5-10 Ash and slag waste thermal power plants 5-10