The analysis of effectiveness of methods of feed material (extrudate) preparation for feeding showed that the thermal method of its processing with the use of the KMZ-2 extruder is of most practical and academic interest. The studies carried out by V.V. Novikov showed that in the process of its formation the extrudate moves throughout the length of working chamber in the space between the screw flights and the inner surface of body, due to this the obtained mixture is heated and compacted. Based on the theoretical researches carried out by V.Yu. Frolov, it was found that the screw should have a variable pitch gradually decreasing with the movement of the processed feed material along its axis. During its movement the processed feed material is compacted and reaches the condition that allows to take the required shape in accordance with process requirements. Determination of rational parameters of variable pitch screw of extruder in areas for loading and pressing is a very important task on both practical and theoretical grounds. The aim of the article is to determine the rational design parameters of variable pitch screw of extruder in areas for loading and pressing of processed feed material on the basis of sunflower cake. At the initial stage, the design parameters of variable pitch screw of extruder in the area for loading of processed feed material were considered. At the next stage, the process of its compaction and compressing by means of screw was considered. As a result of theoretical researches of variable pitch screw of the KMZ-2 extruder, it was found that the density increasing of the processed feed material on the basis of sunflower cake is proportional to the decreasing of pitch of screw flight. The density of processed feed material depends on its physical and mechanical properties.

To ensure the operating efficiency of plowing unit it is required to comply with the specified speed regime of motion and optimal loading of tractor engine. Difference of tractive resistance of soil in different fields creates a situation where it is difficult to select the optimal loading of tractor engine providing constant speed. For example, for the fields with a specific resistance equal to 20 000 and 30 000 newton per square meter, tools with grasp width equal to 2.4 and 1.9 meters respectively are required. The aim of the paper is to find a design scheme of variable width tillage tool, which provides the necessary reliability and reduces the complexity of grasp width regulation. The main research method in achieving this goal is the rational use of condition of external force loading of working organs of tillage tool. The condition of external loading of working organs is investigated. The principal vector and principal moment are accepted as external load equivalents. The conditional center of external soil pressure on working organ is determined by finding the points of intersection of the axis of thrust-and-torque combination with the working surface of plow body. As a result of study, the design scheme of tillage tool that provides the necessary reliability and reduces the complexity of grasp width regulation is proposed. The value of external cutting forces in the obtained scheme is used as a sensor of specific resistance of soil in a specified field and provides the adjustment of grasp width of tool under optimal loading of tractor engine.

The article considers the applied methods for improving the thermal strength of pistons of internal combustion engines. Tractor diesels with combustion chamber in the piston have the greatest rate of temperature change at load rise and release, as well as the highest values of temperature gradients. The highest thermal loads occur in pistons with a semi-open combustion chamber. Periodic thermal loads with high value of temperature gradient lead to thermal fatigue fractures. Such fractures may begin with the appearance of cracks on the edge of combustion chamber. The presence even of a small crack on the edge of combustion chamber leads to its further growth, which can cause the destruction of piston. The main causes of cracks formation on the edge of combustion chamber are the alternating stresses induced from alternating gas pressure in cylinder during the working cycle; the low-frequency oscillations of the piston temperature arising from the changing of operation modes of engine; the high-frequency cyclical thermal oscillations caused by the temperature change of material in the surface layer of combustion chamber for each working cycle. The most common design and technology solutions improving the thermal strength of pistons are the following ones: the change of the edge radius of combustion chamber throat; the reinforcement of combustion chamber edge with more heat-resistant materials; the use of materials with high thermal stability for manufacture of pistons; the artificial heat insulation of piston or its cooling by oil. The disadvantage of use of cooling oil gallery is the acceleration of oil aging process. The alternative solution is to limit the heat supply to the walls of combustion chamber by means of heat protection coating applied by gas-flame, detonation or electric-arc way. The easiest way to improve the thermal strength of diesel piston with a semi-open combustion chamber is the design change.

Screen separators are widely used in grain-cleaning machines. The separation occurs in the process of movement of grain over the surface of screen. The relative movement of grain is provided by different devices with various modes of motion. The most common is a vibrating sieve pan (screener), in which the grain is moved over screen by inertia. Screener has a high efficiency, but the alternating dynamic loads cause the metal fatigue and reduce machine reliability. The grain-cleaning separators with cylindrical screens operate without dynamic loads and have a simple design. They are less sensitive to grain moisture and impurity. But the separation process uses only 1/4-1/6 of the cylindrical screen surface. This problem reduces the throughput and limits the scope of application of cylindrical screens. The proportion of useful surface area can be increased by simultaneous use of two cylindrical screens. They are located one inside the other and rotate in opposite directions. The grain enters on the inner surface of the inner screen and forms a movable layer that moves in the axial direction. During the movement process, the grain passes through perforations, while the large impurities fall down from the screen. The grain having passed through the perforations of the inner screen reaches the section of the outer screen that is clear of movable grain layer. The rational conditions of simultaneous operation of screens are determined, under them the separation process on the outer screen starts immediately after the grain had passed through the perforations of the inner screen. Due to that the separation area is increased by 34-57%.

The unified system of tolerances and fits is a very important system that provides internationally the interchangeability of products, and is widely used in machine-building and instrument-making industries, in repair and maintenance of machinery and in other fields. The new standard 286-1:2010 of International Organization for Standardization provides an improved international system of tolerances on linear dimensions containing series of tolerances and deviations. It contains the clear indication that the system refers to the two types of dimensional features, namely a cylinder and two parallel planes. In the older version of the standard 286-1:88, to interpret the part feature dimension the rule of outer limits was applied a priori, however, in the international standard 14405-1:2010, the interpretation of dimension on the double-point measurement was established. It means that the accuracy of form deviation no longer depends on the dimension accuracy and the requirements to the form should be established separately. Now, in many cases, normalization only of the diameter tolerance is not enough to control the design and performance characteristics of the joint. Theoretically, as provided by geometrical product specifications, it is necessary to establish the requirements and determine the outer limit; as well as in some cases, it is necessary to normalize the requirements for tolerances of form, waviness and surface roughness. The article describes the changes in the terminology from the perspective of the theory of precision and interchangeability. It is concluded that all minor changes in the terms, concepts and regulations do not affect the overall construction of the unified system of tolerances and fits, but clarification of a number of old terms and introduction of new concepts take place. Most significant is the arising of new link between the standards on geometric characteristics of products based on the principle of the general construction of models of precision and common terminology. Of particular note is a bad translation of English version into Russian language. The scientists working in the theory of precision and interchangeability were not involved in the translation. Most of the newly introduced terms could be interpreted more technically-oriented and more understandable.

Cultivation of crops is associated with multiple passes of machine units through the fields. The cumulative effect of soil compaction caused by repeated impacts of movers of machine units is considered as especially dangerous. The most intensive compaction process occurres in spring. The repeated passes of heavy machines and the compaction of surface and subsurface soil horizons lead to the decrease in yield potential of fields. The solving of compaction problem depends on the soil and climatic conditions, zonal cultivation technologies and crop harvesting, and on the machine system in operation. When forming the machine and tractor fleet of enterprises, the selection of general-purpose tractors serves as a basis. The least negative impact on the soil occurs when crawler tractors are used. The advantage of wheeled tractors is the possibility of their use for both field works and transport operations. But today the wheeled tractors are hardly used for transport operations because of their increased weight and power, which shows the necessity of use of such heavy crawler tractors as Ruslan and Challenger. Their use in combination with wheeled tractors of middle class allows to improve significantly the structure of machine and tractor fleet. The main power unit for farm enterprises with 1000 hectares of arable land is a general-purpose tractor of the 3rd traction class. The use of the HTZ-150K-09 tractor with 23.1R26 low-pressure tires with the air pressure of 80 kPa provides a permissible impact on the soil. The soil density in the surface layer reduces to 0.06 grams per cubic centimetre as compared to the use of 21.3R24 single wheels. This allows to put such tractor in operation for spring field works.