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that the size and has disorder in 55%, rigidity of samples offered almost identical.
For the description of processes contact interaction in cracks at shift has been used the imitating modelling based on the stereo-logic analysis of surfaces of cracks and structure of a material. As the initial the model of structure of concrete in which dense inclusions of a filler are dispersed in mortar to a matrix in a random way was considered. Development of deformations of shift is shown at the expense of plastic deformation of a material in zones of contact of ledges on all surface of a crack. Projections of the area of mutual contact in orthogonal directions for the given type and the volume maintenance of fillers is function Sere and а . By methods of the
сгс /
statistical analysis it was calculated probable number particles defined short of which were crossed by a crack on individual length. Possible distribution of the sizes of grains full out being continuous function, it was considered on the basis of an experimental curve рассева and for its description function of density of probability was used. The most probable general line of contact interaction received by integration on all interval of change of diameters distribution inclusions. The models of a drawing of dependence received at realisation т = f(S , а ) and о = f(S , а ) close enough approximated
crc 4 сгс сгс' сгс 4 сгс сгс' о г г
skilled curves. Integration of the received expressions was made for the area of mutual contact under the special program which easily unites with commercially accessible programs for calculations of ferroconcrete designs by method and others numerical methods.
Further models of development of critical inclined cracks in ferroconcrete beams, rectangular and T sections for experimental and estimations of the basic components of their resistance to a cut have been developed. Proceeding from conditions balance internal efforts analytical expressions, value shift rigidity in cracks ofbeams by use of skilled sizes dilatation displacement oftheir coast have been received.
For check of theoretical positions the program of tests ferroconcrete rectangular and T-beams from heavy and ceramic concrete by which results have been revealed is spent: levels of an ultimate load and character of destruction of beams; deformation in concrete on height of section and deflections of beams; comparative deformations in longitudinal and cross-section armature; dilatations and shift displacement of coast of cracks by specially developed technique; compression deformations in inclined concrete strips of edges T-beams. Calculations of bearing ability of beams at a cross-section bend have shown satisfactory conformity with the data of test of skilled beams.
References:
1. Ашрабов А. А. Лёгкий бетон и железобетон для индустриального строительства. - Ташкент. "Фан", 1988.
2. Ашрабов А. А. Оценка напряжений, передаваемых через трещины и стыки в железобетонных элементах. Научно-техн. журнал СамГАСИ «Проблемы архитектуры и строительства», - № 3, 2007.
3. Committee Euro-International du Beton. (1990). CEB - FIP Model Code 1990, CEB, Paris, Sept. - 1990. Bulletin d'Information 195.
Tilabov Bahodur Kurbonovich, Tashkent State Technical University named Abu Rayhan Beruni, city of Tashkent, Republic of Uzbekistan E-mail: [email protected]
Improving working efficiency and durability of cast parts of tilling machines
Abstract: chemical composition of hard alloy metal, microstructure of 35GL steel, phase composition, hardness, micro-hardness and depth of the hard-face coating were studied on the samples and part, resulting in casting on gasified styrofoam consumable pattern, on the work surface of which the powdered hard alloy metal is applied. There are given results of abrasive wear of cast hard-face coated samples before and after heat treatment with the double phase recrystallization. It is shown that the thermal processing with double phase recrystallization increases abrasive wear resistance in 3.0-3.5 times.
Keywords: cavityless casting, hard-coated, 35GL steel, coating thickness, thermal treatment with double phase recrystallization, microstructure, performance and durability of products.
Introduction. At present the recommendations for choosing of materials for manufacturing molded parts of machines and equipment subjected abrasive-corrosive wear usually do not consider the influence general corroding processes whose contribution to the overall wear of parts and equipment at relatively low external micro-wear is very substantial [1]. Therefore, study of peculiarities of abrasive-corrosive wear in corrosive environments is of great scientific and practical importance.
The most parts of machines and equipment operate under abrasive corrosive wear conditions when the material of details are required to be at the same time abrasive wear resistance and corrosion resistance. The life of these components is limited due to simultaneous exposure to abrasive and corrosive media. All this requires a constant renewal of technological equipment and spare parts.
The aim of this work is developing a production technology offoam model and producing of cast parts ofvarious machines and equipment with wear-resistant hard-alloy coating by casting on gasified models and their subsequent thermal treatment with double phase recrystallization [2]. The aim of the work was also to establish the possibility of effective surface hardening and improving wear resistance of 35GL steel by treating its working surface reliable and powerful hard-alloy coating.
It is known that many of the details of tillage and mining machines, working in direct contact with soil or rock, are exposed to hardfacing [3; 4]. This requires application of quite complex technological equipment associated with high consumption of scarce hard alloys and fluxes.
It is more rational to get these components by casting on gasified cellular polystyrene models with simultaneous applying a wear-
Improving working efficiency and durability of cast parts of tilling machines
resistant hard-alloy coating on the working surface of a foam model with dressing width of 2.0-3.0 mm [5].
Wear parts include tusks and paws cultivators tines, operating in the soil under the action of the abrasive medium. Therefore, the working surfaces of such parts are subjected to surface hardening by applying a hard-alloy cast of Sormayt PG-C27 type. Applying the hard-alloy coating is carried out by melting the metal coating on the working surface of the cast parts.
In this paper microstructure and abrasive wear of cast parts with hard-alloy coating obtained by casting on gasified models before and after treatment with double phase double recrystallization are investigated.
The methodology of the study. The chemical composition of the weld hard alloys such as sormayt PG-C27 (alloy composition: C 2,5-3,0; Si 0,8-1,2; Mn 0,7-1,0; Cr 27-29; Ni 0,6 -1,0; P 0,03; S 0,03). Cast specimens were made of 35GL steel so that 2.0-3.0 mm of a hard alloy layer occur on the working surface of items turned 2 (steel composition: C 0,3-0,4; Si 0,2-0,4; Mn 1,2-1,5; Cr to 0,3; Ni up to 0,3; Cu up to 0,3; P 0,03; S 0,03). Melted hard alloy metal of Sormayt PG-C27 type has a melting point of 1200-1280oC with relatively high wear resistance and toughness. Low melting temperature is 270-320 ° C lower than temperature of the cast metal promoting to full penetration and good contact with the base metal of 35GL steel. Choice of hard metals as objects of study is due to the need to study the effect additives of alloying elements inputting into the structure on the coating and abrasive wear resistance of steel castings [2; 3].
The technology of manufacturing products by casting based on gasified models includes manufacture of cellular polystyrene models. A liquid suspension is applied on the working surface of the model, consisting Sormayt PG-C27 powder. When manufacturing a suspension as a binder pulverbakelite and a 4% solution ofpolyvinyl alcohol were used. The layer thickness was 2.0, 2.5 and 3.0 mm. After drying of the coating model was moulded in quartz sand (simultaneous compacting by pneumatic vibration takes place) and filled with liquid metal, with the composition appropriate to the composition of 35GL steel at 1650 ° C through the gating system with siphon gating. When pouring there took place burning of a model and saturation of the cast surface by carbon up to 0.7% at the depth of 0.40-0.80 mm. In this way casting of a part with wear-resistant hard alloy coating is produced. Fill-out out with liquid metal is one of the main stages of moulding of casting, which determines many of its quality indicators.
Casting by gasified models polystyrene is increasingly used and recognized in many steel mills and machine shops of our country, intensive research and development of new innovative technologies, expanding the scope of its use for the different nomenclature of castings parts. It is possible to increase the efficiency of production by reducing the complexity of manufacturing penomodels and castings, as well as improve the quality of steel and cast iron castings: to increase their accuracy, to provide a smooth surface and reduce the machining allowance or do without it.
In case of contact of insert of Sormayt powder with liquid metal forming of solid crusted casting, melting of an insert, interaction of the liquid phase inserts with brown material of a crust occur and after crystallization there occurs forming of the structure of high-alloy white cast iron of eutectic or hypereutectic compositions on the surface. The transition from a wear-resistant coating to the base metal is sharp enough, although there are transition zones from hypereutectic of the eutectic, hypoeutectic zone to the zone of hyper-eutectoid steel. The presence and thickness of hypereutectic zone
depend on thickness of the coating on the model, hypereutectic zone is maximum at the coating thickness of 2.5 mm [5].
Macro and micro investigations were carried out by optical metallographic microscope MBS-1, MBS-9, MIM-8 and Neofot-21. Test specimens were round and consisted of four quadrants with dimensions of 12x12, 15x15, 15x20, 20x20 mm, and others.
The microstructure and micro-hardness of hard-alloy coatings after heat treatment vary considerably. If tempering is carried out with heating temperature 900 oC, then pearlite structure component undergoes martensitic transformation. Location of a carbide component is not changed. The coating depth does not change consisting both of hard-alloy layer and high-carbon sublayer. For example, after quenching samples at heating temperature 900 ° C and 920 ° C obtained by molding with 2.5 mm thick, the structure of eutectic component and arrangement of secondary carbides did not change. Only instead of pearlite component fine-needled martensite is observed.
When heated to the hardening temperature 1050-1100 ° C all secondary carbides are dissolved in austenite, only primary carbides remain in the eutectic composition. The samples, carbide coatings of which were obtained when casting on gasified models with 2.5 mm thick the structure consisting of eutectic carbides and martensite is formed on the surface. On the microstructure there can be easily seen martensitic needles, retained austenite, primary carbides and underlayer of high-carbon martensite (fig.1, a, b, c). A similar pattern is observed when considering the coatings microstructures in the samples obtained by lost foam casting with the thickness of 2.5 and 3.0 mm. In these cases, on the surface there are primary carbides and fine martensite observed (fig.1, c) [5].
Results and discussion. The hardness of the specimens was determined on Brinell TVB-4 and Rockwell TK-2 devices and micro-hardness was measured on a PMT-3 device at the load of 0.5 N. Abrasive wear of special samples and components were tested on PV-7 friction machine.
Microhardness within the limits of thickness ofhard alloy coating varies widely. The highest microhardness are in the samples obtained with dressing layer thickness of 2.5 mm on the model. At the surface hypereutectic structure with a large number of primary chromium carbides with a hardness of NV100 = 15300 MPa is formed. At the same time, microhardness of pearlite component of the eutectic is 7300 MPa. At the depth of 0.7-1.4 mm from the surface of coating depending on the dressing thickness the structure of the base metal hardness of 2600 MPa is already observed.
Specimens with chard-alloy coating for X-ray diffraction tests were round and with four quadrants with dimensions of20x20 and 22x22 mm. Phase composition of hard alloy was determined by X-ray analysis (DR0N-2.0), and phase analysis results give a better idea of the composition of the resulting coatings. The width of the X-ray lines was determined at half of a maximum height as the arithmetic mean of the four or five diffraction patterns or curves of distribution of X-ray radiation intensity [6]. Measurement errors calculations showed that they were within 5-10% depending on the study object. According to the research results it was found that on the specimen surface with wear-resistant coating special types of carbides Me23 C6, Me7 C3 and others are formed.
Comparative tests for abrasive wear resistance for a fixed abrasive were carried out in a laboratory unit as described in [7]. The specimens of70 mm long, 35 mm wide and 15 mm thick were tested on PV-7 machine, for sand were tested on quartz basis. The relative wear resistance was determined by the ratio of relative loss of the cast piece standard weight (steel 35GL) with wear-resistant carbide coating and weighed by the gravimetric method (VLA 200-M) after each test abrasion.
Figure 1. Microstructure of hard-alloy coating and high-carbon sublayer in the specimen obtained with coating thickness of 2.5 mm (a) X200 and 3.0 mm (b, c) X500 after tempering at heating temperature of 1100 ° C, drawback — 300 ° C. The structure of coarse and fine martensite, residual austenite at a depth of 0.6 mm from the surface of the carbide layer.
All specimens with hard coating before and after heat treatment with double phase recrystallization were tested for abrasion wear resistance. Tests for abrasive wear of had alloy coatings in time т were conducted on friction machine PV-7 using abrasive loose material. Hard-alloy coating dramatically increases durability: the thicker the
Table 1. - Abrasion wear of cast piece № 20 with coating thickness of 2.5 mm
coating, the smaller the amount of wear. The results of abrasion test of a case specimen № 20 and № 22 with 2.5-3.0 mm thick coating before and after heat treatment with a wear-resistant hard-alloy coating are shown in table 1 and 2 below.
Item № Steel grade Time of testing, min Wear before testing, mg Wear after testing, mg Wear difference before and after the test, mg
before heat treatment
1. 35GL 30 143,5598 143,5581 0,0017
2. 35GL 60 143,5581 143,5567 0,0014
3. 35GL 90 143,5567 143,5557 0,0010
4. 35GL 120 143,5557 143,5551 0,0006
5. 35GL 150 143,5551 143,5548 0,0003
6. 35GL 180 143,5548 143,5548 0,0000
after heat treatment
1. 35GL 30 139,6373 139,6367 0,0006
2. 35GL 60 139,6367 139,6364 0,0003
3. 35GL 90 139,6364 139,6362 0,0002
4. 35GL 120 139,6362 139,6362 0,0000
Table 2. - Abrasion wear of cast piece № 22 with coating thickness of 3.0 mm
Item № Steel grade Time of testing, min Wear before testing, mg Wear after testing, mg Wear difference before and after the test, mg
before heat treatment
1. 35GL 30 144,7689 144,7673 0,0016
2. 35GL 60 144,7673 144,7660 0,0013
3. 35GL 90 144,7660 144,7651 0,0009
4. 35GL 120 144,7651 144,7646 0,0005
5. 35GL 150 144,7646 144,7644 0,0002
6. 35GL 180 144,7644 144,7644 0,0000
after heat treatment
1. 35GL 30 140,2445 140,2440 0,0005
2. 35GL 60 140,2440 140,2437 0,0003
3. 35GL 90 140,2437 140,2436 0,0001
4. 35GL 120 140,2436 140,2436 0,0000
Results of the done theoretical research for choosing the type of hole of the corn sheller sieve and determining its useful.
As seen from tables 1 and 2, the tests carried out by us for abrasion wear with samples of coating thickness of 2.5-3.0 mm were completely consistent with the results of field trials, which do increase performance and durability ofmolded parts oftillers after heat treatment with dual phase recrystallization to two or three times.
Heat treatment affects not only wear resistance of surface, but the subsurface layers of hard-alloy coatings. This is important for a number of parts of tillers, where the wear limit can be about one millimeter. When comparing wear resistance of specimens with hard-alloy coatings before and after heat treatment it can be found that the effect of this treatment on the layer depth is increasing from 7% at the depth of 0.6 mm to 90% at the depth of 1.4 mm.
The technologies of application ofhard-alloy coatings in molding based on consumable patterns and subsequent thermal treatment with double phase recrystallization developed by us were used in production of an experimental batch of cast parts and tested under field conditions in different regions of the country. Field
test results have shown that the wear resistance of cast steel parts with hard-alloy coating without heat treatment, compaction stability and increase in wear resistance of 2.2-2.6 times, and after heat treatment with dual phase recrystallization are 3.0-3.5 times higher than that of commercially available products [8; 9].
Conclusions. Thus, it can be concluded that the effective way to increase the abrasive wear resistance is to apply wear-resistant hard-alloy coating with molding based on consumable patterns to operating surfaces of the products. Heat treatment hard-alloy coating of high-chromium alloy carried out with double phase recrystallization, is forming optimal structure of high-density dislocation, disperse and secondary coagulated primary carbides. The data submitted show that heat treatment ofhard alloy coating with a double phase recrystallization increases the efficiency and durability of finished castings in three or more times. The developed technology was implemented in production of «Metallmexqurilish» HK and «Uzmetkombinat» JSC with a good economic effect.
References:
1. Mavlyanov N. M. Improving reliability of the working bodies and quality ofpresowing and sowing machine-tools. - Tashkent: Mehnat, 2000. - 462 p.
2. Tilabov B. K., Mukhamedov A. A., Islamkulov K. M. Getting hard-alloy wear-resistant coatings on operating surfaces of machine parts//Bulletin (Khabarshysy) of the International Kazakh-Turkish University named after K. A. Yassavi. Turkestan. - Kazakhstan. -№ 3. 2004. 21-24 p.
3. Mukhamedov A. A. Effect of heat treatment on the wear parts with hard-alloy coatings. Monthly scientific-technical and industrial journal//Physical metallurgy and heat treatment of metals. MiTOM. - Russia. 2003. - № 3. 29-31 p.
4. Tkachev V. N. Depreciation and increase of durability of working organs of tillers. - M.: Engineering, 1996. - 293 p.
5. Tilabov B. K. The wear resistance of melted hard alloy of PG-C27 type with metastable austenite and martensite. Republican Inter-university collection of scientific papers. "Current issues in the field of technical and socio-economic sciences". - Tashkent: Issue 1, 2011. 359-362 p.
6. Skakov Y. A. Crystallography, X-ray and electron microscopy. - M: Metallurgy, 2010. - 632 p.
7. Tenenbaum M. M. Resistance to abrasion. - M.: Engineering, 1996. - 267 p.
8. Mukhamedov A. A. Heat treatment with double phase recrystallization for improving service properties of machine parts and tools//Heat treatment and technology of surface coating. Materials of the Congress. Vobume v. MOTO. December 11-14. - Moscov, 1998. P. 38-39.
9. Tilabov B. K. Increase the service life of cast parts tillihg machines. International Conference «Global Science and Innovation» March 23-24, 2016. USA. Chicago, 2016. С. 222-225.
Baymetov Rustam Isayevich, Scientific research Institute for mechanization and electrification of agriculture, Doctor of technical science, Professor, the chief of laboratory
Astanakulov Komil Dullievich, Scientific research Institute for mechanization and electrification of agriculture, Doctor of technical science, Senior scientific employee, the chief of laboratory
Fozilov Golibjon Gulomjonovich, Scientific research Institute for mechanization and electrification of agriculture, Scientific employee, laboratory of cereal harvesting machines, Uzbekistan,
E-mail: [email protected]
Results of the done theoretical research for choosing the type of hole of the corn sheller sieve and determining its useful area coefficient
Abstract: In the article results of the done theoretical research are illustrated which are about choosing the type of hole of the corn sheller machine sieve and determining its useful area coefficient. Keywords: corn, pith, husk, grain, corn sheller, sieve, types of the hole.
Nowadays, requirement is increasing for grain of the corn in Uz- to harvest the corn for grain. According to above written problem, a bekistan. However, farmers are coming face to different difficultness new type corn sheller machine was created at scientific research In-
