This paper deals with service conditions of shaft equipment, in particular, inserts of sliding bearings for the purpose of increasing service life due to material substitution and wear resistance increase. As a new material high-chromium irons are offered. Studies are conducted on a microstructure and wear resistance of prototypes is measured. Experimental data are treated by methods of mathematical statistics which confirm reliability of results. The results obtained make it possible to suggest using high-chromium irons as the direct material to produce inserts of sliding bearings

A. E. Omarova

Sv. S. Kvon

T. S. Filippova

V. Y. Kulikov

English

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206  METALURGIJA 55 (2016) 2, 206-208SV. S. KVON, V. Y. KULIKOV, T. S. FILIPPOVA, А. Е. OMAROVA USING HIGH-CHROMIUM IRON AS MATERIAL FOR PRODUCTION OF THE EQUIPPING COMPONENTS OF MINE SHAFTSReceived – Primljeno: 2015-03-13Accepted – Prihvaćeno: 2015-09-15Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 55(2) 206-208 (2016)UDC – UDK 669.1.26:338:622:694.3:620.18:620.17=111Sv. S. Kvon, V. Y. Kulikov, T. S. Fillippova, А. Е. Omarova, Karaganda State Technical University, Karaganda, KazakhstanThis paper deals with service conditions of shaft equipment, in particular, inserts of sliding bearings for the purpose of increasing service life due to material substitution and wear resistance increase. As a new material high-chromium irons are offered. Studies are conducted on a microstructure and wear resistance of prototypes is measured. Experi-mental data are treated by methods of mathematical statistics which confirm reliability of results. The results obtained make it possible to suggest using high-chromium irons as the direct material to produce inserts of sliding bearings.Key words: chromium iron, mine shafts, sliding bearings, microstructure, mechanical propertiesINTRODUCTIONTo one of the critical elements of mine skip lifting, providing its high performance and trouble-free opera-tion, is reinforcement of mine shafts. The current trend of increasing depth development of mineral deposits, in-crease productivity rises vessels in vertical shafts. In this case, there is an increase of dynamic loads in the “vessel - reinforcement.” Therefore, in the complex issues relat-ed to the operation of the skip shaft rises, relevant and important is to increase the durability of reinforcement vertical shafts and vanes of skips, repair which is charac-terized by high metal content and significant costs.In the operation of lifting equipment is always mechan-ical and corrosive wear of conductors and  shootings.The service life of executions is determined mainly by corrosion wear. Unlike shootings conductors dura-bility mainly depends on the mechanical wear in con-tact with the guide devices of lifting vessels. In studies performed discusses mechanical wear.Mechanical wear of conductors is a consequence of the interaction, in particular, the friction between the guide device and skip the moving conductors. In this case, the wear rate is determined by the magnitude of the horizontal load on the system “conductor - lift ves-sel” and the coefficient of friction between the conduc-tor and the guide skip.Analysis of operating experience of existing shafts, as well as measurement data of actual loads on the rein-forcement it possible to identify the main causes of static and dynamic loads, and identify ways to reduce them.Horizontal loads on the conductors on the conductors are classified depending on the properties of structures of lifting vessels, piping and condition of the conductors.Based on the analysis and evaluation of the causes of the horizontal forces that cause wear reinforcement trunks, possible ways to reduce it and increase the dura-bility of reinforcement:-  the choice of rational structures, schemes and pa-rameters of reinforcement;-  increasing the degree of static equilibrium lifting vessels;- reducing the impact of torque rope;-  improvement of structures and materials vanes lift-ing vessels;-  increase the wear resistance of the conductors.Equipping of mine shafts has decisive impact on productivity and reliable service of a head frame. The sliding bearings are used as the guiding devices in mines. While in service they perceive different percus-sions, contact-cyclic stresses causing abrasive-mechan-ical wear. The rapid abrasion of inserts of sliding bear-ings leading to increase of clearance between directing ones and guide is the main reason for a short life of their service, on average about 14 days for skip winding.Therefore, the main reserve of increasing service life of bearings is wear resistance increase of inserts.As is known [1], increasing hardness of material leads to its wear resistance increase, in addition the fric-tion coefficient is decreased [2]. In other words, substi-tution of insert materials to harder ones will allow in-creasing service of their life as thus friction force the bearing-guide should be decreased and at the same time increase hardness of the bearing against wear. When choosing a material for the sliding bearings two circum-stances should be considered:first, the material hardness of bearings should be higher than  hardness of guides (250 HB) to pro-vide favorable conditions of friction, soft-hard steam;207SV. S. KVON et al.: USING HIGH-CHROMIUM IRON AS MATERIAL FOR PRODUCTION OF THE EQUIPPING...METALURGIJA 55 (2016) 2, 206-208secondly, material chosen should have a high red-hardness as the surface working temperature is considerably increased during the friction.Thus, considering loading and service conditions of the bearing-guide, requirements for insert materials can be formulated:1.  General surface material hardness should exceed hardness 250 HB.2.  Material red hardness shouldn’t be less than 600 0C.3.  Material should have good mechanical properties (sufficiently high values of strength σV and the impact hardness An). According to this principle, only a structure, where solid components lie as the separate fine ones evenly distributed inclusions in a ductile matrix, has high wear resistance.EXPERIMENTAL STADIESFor the purpose of developing measures to increase wear resistance of inserts detailed metallographic stud-ies of their structure were conducted.As a result of studies the direct material for produc-tion of inserts was established to be mild and medium carbon steel of group brands: St3...St5 depending on the party. The approximate chemical composition and some mechanical properties of these steel are given in Table 1.Table 1  Chemical composition and mechanical properties of steelNSteel grade Chemical composition / % Mechanical propertiesС Mn S P Re / MPa A / %1 St3 0,14 - 0,22 0,4 - 0,6 0,045 0,055 380 - 470 242 St4 0,18 - 0,27 0,4 - 0,7 - - 420 - 520 263 St5 0,28 - 0,37 0,5 - 0,8 - - 500 - 620 28All steel used is related to hypoeutectoid steel. The structure in an equilibrium state is presented by colo-nies of large-lamellar pearlite and inclusions of ferrite. Average hardness of similar structure fluctuates ranging from 160 to 190 HB, and the microhardness of a soft ferrite network makes about 125 - 150 kg/mm2. It is ob-vious that the similar microstructure has low wear re-sistance and relatively low mechanical properties.Application of carbon steel both in annealed, and in quenched conditions as material for production of in-serts is represented not exactly inexpedient. With an identical surface hardness after quenching the micro-structure of carbon steel has lower wear resistance, than for example, ledeburitic steel or white cast iron (Figure 1). It is explained by that the microstructure of the latter ones is presented by relatively soft matrix with hard ex-cess carbide inclusions, and the matrix acts as a lubri-cant, as reduces the surface wear degree.In addition red hardness of carbon steel makes only about 300 0C. As during the friction   hot   temperatures are developed  (to 600 0C), low red hardness causes pre-cipitate abating and material wear resistance on the one hand and, as a result, the friction coefficient increase on the other hand [2,3].The reasons stated (heat treatment inefficiency, un-satisfactory microstructure and low red hardness of car-bon steel) make inappropriate their application in the case under consideration and, accordingly, require se-lection of other measures to increase wear resistance of materials for production of inserts. Use of different surface methods of hardening is possible: thermochemical treatment, beading, spraying, etc. These techniques, however, require significant cap-ital investments that are justified only at large volumes of production.Thus, a likely way of wear resistance increase of in-serts is material substitution for more wear resistant, with the best mechanical properties. The analysis of properties and microstructure of dif-ferent materials taking into account the requirements stated above showed that the most acceptable material in this case are high-chromium irons. White cast iron is increasingly used as a material for tools and machine parts and mechanisms subjected to intense wear and oxidation. Traditionally it is attributed to fragile materi-als that significantly limits the scope of its use. Achieved advances in alloying and heat treatment white irons have changed the understanding of their properties and possible applications.Modern white cast irons - complexly multicompo-nent alloys, different in structure and special properties. a)b)Figure 1  The microstructure: a - hypoeutectoid steel; b -  white cast iron208SV. S. KVON et al.: USING HIGH-CHROMIUM IRON AS MATERIAL FOR PRODUCTION OF THE EQUIPPING... METALURGIJA 55 (2016) 2, 206-208When in operation [4] of similar materials the contour microgeometry change occurs which is followed by some hardening of surface layers.Thus, the inverted microstructure (hard component microhardness is about 1 500 kg/mm2), its stability, high hardness of a surface make it possible to assume the high resistance to wear during operation and, at the expense of high hardness, decrease of friction forces in couple the bearing-guide. Wear resistance tests were conducted parallelly in two ways: sample weight change and area change of a wear scar. Tests conducted not less than 5 times for each sample, results of tests were processed by methods of mathematical statistics. As results of conducted tests showed service life of the sliding bearings with wear resistant inserts due to reduction of wear is increased on average by 14 times.The obtained results of steel inserts substitution for castings from high-chromium iron makes it possible to recommend them for use in other components of the mining equipment where the impact wear takes place.AcknowledgmentThis publication has been produced within the sub-project “Establishment of the International Centre for Ma-terials Science”, funded under the project “Technology Commercialization”, supported by the World Bank and the Government of the Republic of Kazakhstan. Applications may not reflect the official position of the World Bank and the Government of the Republic of Kazakhstan. LITERATURE[1] Gulyaev A.P. Metallography. M. Metallurgy (2004). - 617 p.[2] Korshunova T.E. Structure, properties and applications of steels and cast irons. - Vladivostok: publ. VSUES. (2013). - 214p.[3] Bobro A.D. Alloy of cast iron. -M., Metallurgy (2009). – 312 p.[4] Panchenko V.V., Skakov Y.A., Popov K.V. and others. The laboratory metallography. M., Metallurgy. (2005). – 695 pNote:  The responsibile for English language is Nataliya Drak, Karaganda, KazakhstanThey are a separate group industrial iron that solidifies composite structure which is formed. It determines the specific properties of white irons in the cast state.The chemical composition of some most widespread grades is given in Table 2. High-chromium irons have good mechanical proper-ties, high hardness in a cast state, low fluctuation of hard-ness when properties change. High-chromium irons al-most don’t concede in fluidity to regular gray cast iron that allows using parts sufficiently difficult form directly after casting without the following machining. Table 2  Chemical composition of high-chromium wear resistant ironsGrade Content of elements / %С Mn Si Cr Ni1 2 3 4 5 6ICHH28I2 2,7 - 3,0 0,8 - 1,4 0,5 - 0,8 28 - 30 1,5 - 3,0ICHH15M3 3,0 - 3,5 0,3 - 0,6 0,5 - 0,9 12 - 18 -ICHH14G2N 2,0 - 2,4 0,5 - 0,7 1,8 - 3,2 13 - 15 1,2 - 2,0It should be noted that casting shrinkage of high-chromium irons is about 2 %, therefore when obtaining castings application of profits or shrinkage compensa-tion is required. In order to test wear resistant inserts of sliding bear-ings the pilot batch of inserts of bearings from IChH28N2 grade cast iron is molded. After cooling the detailed metallographic analysis of samples was made.Microstructural examination and mechanical prop-erties of pilot castings were made according to the pre-sent techniques.The casting microstructure (increase 400, Figure 2), as expected, is presented by a carbide austenitic eutec-tic. The high content of chrome (more than 10 %) in cast iron leads to formation of complex carbide of ce-mentitious type (Fe, Cr)3C which, in turn, has impact on a structure of the eutectic colonies.Crystallization begins with origin of an austenitic dendrite in which intercenter space the crystallization of complex carbide occurs. In a cast state the microstruc-ture of high-chromium cast iron represents a plastic austenitic matrix with separate inclusions of solid and brittle carbide. Microhardness testing of the studied phases validated their identifications: microhardness of carbides made 1 200 - 1 500 kg/mm2, and microhard-ness of an austenitic phase made about 650 kg/mm2 that is in good correspondence with data [3]. Value of aver-age hardness of a casting surface made 48 - 50 HRC. CONCLUSIONSThe obtained casting microstructure of high-chromi-um cast iron of the ICHH28N2 grade meets, thus, the Charpy principle on complete inversion of phases.The expected high wear resistant properties of cast-ings indicate by that fact that they are exploited directly in a cast state after annealing, i.e. with stable structure. Figure 2 The casting microstructure (х400)

Using high-chromium iron as material for production of the equipping components of mine shafts

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