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22
UDK 621.78; 621.15
TECHNICAL AND TECHNOLOGICAL BASIS FOR PRODUCING CAST PARTS OF MACHINES WITH HARD COVERING
Tilabov Bahodir Kurbonovich, associate professor, Bahadirov Kudratkhon Gayratovich
Tashkent State Technical University named after Abu Rayhan Biruni,
Tashkent Uzbekistan
This article presents the technical and technological basis of manufacturing metal composite materials for cast parts of agricultural machinery by casting on gasified models. The technology of cellular polystyrene models of various types of cast machine parts with wear-resistant carbide coated type Sormayt PG-C27. Studied the macro - and microstructure of metals and alloys. Created as optimum modes of heat treatment with a double phase recrystallization for these parts and machinery. It is shown that the optimum heat treatment after double recrystallization phase of carbide wear resistance and durability of molded parts is increased 3-4 fold compared to series production.
Key words: polystyrene models, hardness, heat treatment, wear-resistant coated.
Tillage machines is an important means of agricultural production and play an important role in the development of the productive forces in our society. Development of tractor and agricultural machinery during the first ten-year, as well as special conditions of large agricultural enterprises of the Republic of Uzbekistan initiated the independent creative way in the creation of new designs of domestic high-performance cars and tractors, as the very first attempts to create designs tractor trucks for foreign models showed them disrepair in local conditions.
It is known that many of the agricultural machinery, tractors and cars on new designs and types, as well as spare parts are produced in our country. If you take agricultural machinery and tractors, namely, tillage machine parts and mechanisms, they are constantly working in direct contact with the ground in severe and harsh environments. These details are pointed feet universal cultivator tools sowing cultivators paws and teeth harrows.
Lancet paws tools and harrow teeth are made of medium-carbon steels 45, 50, or manganese steel 65G, 70G, and considered both imported and imported spare parts for machine parts and mechanisms. Parts manufactured from manganese steel 65G, 70G considered quality, but we did not make, and how we buy imported material for the currency. Parts manufactured from medium-carbon steels 45, 50, considered to be good, if we produce steel correspond to GOST 1050-98. All these parts work in the above heavy and hard soil conditions Abrasion. Therefore, many of the details and working bodies of agricultural, tillage, and other earth-moving machinery out of order as a result of abrasion. This leads to a decrease in performance cars, increased costs of spare parts, and to unjustifia-
bly large losses of material resources and the costs of repair and restoration work, as well as the increased cost of labor resources. [1]
Increased wear resistance and durability of cast steel or cast iron parts in agricultural engineering is a very urgent task. Department "Materials Science and Technology of Materials" Mechanics - Mechanical Engineering Faculty of the Tashkent State Technical University named Abu Rayhan Beruni and now HC «Metallmexqurilish» developed new manufacturing processes metallokompozit-sionnyh parts and machinery for various purposes by casting on gasified cellular polystyrene models [2].
This innovative technology has recently become increasingly common and application. It refers to the types of precision casting and has a number of advantages over the prior art methods of producing castings is reflected in increased accuracy and surface finish [3], reducing labor intensity and reduce process cycle, increasing the economic efficiency of production of castings and parts.
To ensure the necessary wear resistance of parts of agricultural machines, for example, of universal lancet paws tools ripper tines sowing cultivators and harrows the teeth are made of medium - and high carbon steels and sometimes iron. Workers and formative part of these components are subjected to a heat treatment or weld cast hard alloys. The disadvantages of the first embodiment are insufficient hardness and wear resistance, and the second - a large flow of scarce hard alloys.
A more rational to get these details by casting on gasified cellular polystyrene models while drawing on the work surface wear-resistant coating of carbide type Sormayt PG-C27. Therefore, for many agricultural tillage and details the method of casting on gasified models [2].
The essence of the method lies in the fact that a model of future castings made from pre-foamed polystyrene suspension PSV (TU 6-06-1690-99) with a grain size of 3-4 mm [4.5]. The molds are filled with polystyrene beads are inserted into the autoclave and the pressure of the supplied 2-2.5 kg / cm2 at sufficiently high temperatures to sinter the pellets in 100-1150C monolithic single mass of foam. After complete cooling under running water aluminum mold open and ready to benefit from it foam model. Finished models after drying coated carbide coating layer and then re-coated with nonstick drying paint (a mixture of asbestos powder with a binder).
In the paper paws cultivators, harrows naralnikov and teeth made by molding on gasified cellular polystyrene models with hard coating and subsequent thermal treatment with double phase recrystallization and presented two types of cultivators paws (Figure 1, A, A1, B, B1 in ,in 1).
Thus, all articles foam model arranged horizontally, and their working surface upward. For the formation of the carbide wear coating during casting paste was prepared consisting of carbide powders PG-C27 and an alcohol solution of po-lyvinyl butyral (a percentage by mass). These pastes were applied to the working surface foam model Fig.1, A, A1, B, B1) and subjected to thermal drying. After drying again fastened to the casting flask foam model container via the
riser elements of reservoir and the runner system. After assembly foam model made their forming dry quartz sand (1K016, 1K0315 GOST 2138-98) top to bottom flask and conducted simultaneously seal the pneumatic vibration. It then sets the flask to the main conveyor and filled with liquid metal through at 1539-16500C runner system when the cart siphon metal. Molten metal is fed directly to foam model. Under the influence of the polystyrene melt is gasified and forms a cavity filled with metal composition, the corresponding steel 35GL. In this way, casting parts with wear resistant carbide coating fig.1, c, c1) [2]. Filling the form of a liquid metal is one of the main stages of the formation of the casting, which determines many of the indicators of its quality.
According innovative technologies conducted a comprehensive study to determine the macro - and microstructure, hardness and microhardness specially prepared samples of natural and cast parts, X-ray analysis, chemical and spectral analysis, testing and other abrasive wear.
In accordance with the task objective of this work is to develop a technology of cellular polystyrene models and getting cast carbide parts with high abrasive wear resistance [2]. The object of research were cast parts of agricultural and tillers, cultivators such as the legs, and tooth harrowsS tools experiencing intense abrasion when sliding on the ground.
V
a)
b)
c)
fi
a')
bT
c1)
Fig.1. Foam models and castings cultivator tines with hard wear-resistant coating: a, a1-penomodelyam coated on the main wear surface; B, B1-penomodelyam around wears a surface coating; b, b1-alloy steel parts cultivators paws with carbide wear-resistant coating
and subsequent thermal hardening.
We study the structure of carbide type Sormayt PG-C27. Selection of the applied coating composition was made based on two criteria: 1 coverage must meet 3-4 fold increase in wear resistance as compared to the wear resistance of steel substrates; 2 coverage should include accessible and affordable ingredients and be simple technology of its application. Accordingly, as a coating on the working surface of items selected Sormayt PG-S27, and used as a binder of 4% solution of polyvinylbutyral in ethanol.
Results and discussion. All samples and castings after studies in order to increase the hardness of the surface and subsurface layers, necessarily subjected to various heat treatment regimes best dual phase recrystallization. Heat treatment was carried out at a heating temperature of 900 to 11500C [6,7]. After thermal processing, all samples were released from 200 to 6000C to give the required microstructure and durability.
Thus, the proposed technological modes has produced a pilot batch of three cast steel machine parts for field trials. Field trials were submitted to four games parts and determine their relative durability compared to the serial parts. Experimental details of steel coated shown 35GL processing stability and increased wear resistance to 2.4-2.8 times, and after heat treatment with the double phase recrystallization [7] to 3.5-4.0 times higher than the production details. Field tests were conducted in farms of different areas (districts) of the Republic of Uzbekistan and in different soil conditions and obtained positive test reports with the subsequent introduction into production. This manufacturing technique and getting foam model cast parts of agricultural and tillers with wear-resistant carbide coated type Sormayt PG-C27 is introduced with a good economic effect at the Tashkent factory HC «Metallmexqurilish».
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