In reconditioning components in agricultural machines, wear-resistant coatings are deposited on components by the sintering of metallic powders. The process is based on the formation of a wear-resistant coating from a powder subjected to the pressure p within the roller-electrode and the component through which electric current is passed ( Fig. 1 a). The layer of the powder, trapped in the zone of engagement, changes its specific electrical resistance as a result of compacting of the powder during rotation of the component to the angle (p and is heated with electric current passing through it. The generated heat is accumulated in the sintered layer of the powder and as a result of heat conductivity it is transferred into the rollerelectrode and the component (Fig. lb).The wide range of the reduced components and also the scatter of the parameters of the powders result in the need to carry out a large volume of experimental investigations.In this work, the authors developed a mathematical model which takes into account the main technological factors and makes it possible to predict the initial parameters of the process ensuring the required quality of the wear-resistant coating and the maximum productivity and minimum energy expenditure.Analysis of Ref. 1 and 2 shows that the quality of the coating depends mainly on the maximum temperature on the powder, reached at the moment of sintering.The equation of the heat balance in accordance with the thermal schema of the examined process of heat transfer (Fig. lb) has the following form [1] where q t is the heat flow, determined by Joule heat sources; q el , q c are the heat sources in the roller-electrode and component, respectively.Assuming that the distribution of heat sources in the thickness of the layer of the powder is uniform at every fixed moment of time and using the method of the thermally thin layer, 3 equation [1] can be written in the following form:1 Principa] diagram of production equipment (PE) and the diagram of heat transfer in the electrode-powder-componentwhere h is the thickness of the powder layer; c sc , X sc is the specific heat capacity; \ t , X c is the heat conductivity of the material of the roller-electrode and the component, respectively; p is the polar coordinate.From the moment of engagement of the powder particles up to complete sintering of the powder at T= T max the time is t s = cp 2 /co (cp 2 is the angle of engagement; to is the angular velocity), and this time is considerably shorter than the total duration of the process t ßn = 2jt/co. During the period t sc the heat effect propagates into the thickness of the roller-electrode and the component to a small depth d d and d c , respectively. Therefore, to determine the heat flows q el and q c in equation [2] in accordance with the required law of variation of temperature T(t) -T(R c , t) = T(R el , t) it is possible to use the solution of the following boundary conditions of heat conductivity: ar dT p=R c [3]
We have obtained a modified function of transforming intelligent sensor of contact surface temperature (IS CST) of electric contact “forming the electrode-part” and having a significant influence on quality of restoring the cutting edge of discs of tillage machinery which may only slightly exceed recrystallization temperature of the material of the part. Setting the sensor to restore a specific part is achieved by developing and programming on the microcontroller the function of converting and storing the intelligent system of standard parameters in the non-volatile memory. The re-search goal is to clarify the function of transforming IS CST and to substantiate the opportunity of its application for solution of the set task of control and monitoring. We have provided a schematic diagram of a plant for electrocontact restoration of the cutting capacity of disk tillage tools. The entire restoration process is divided into two stages: static one (without rotating the part) with duration of 1-2 seconds when temperature is monitored in the dynamic mode; and dynamic one, with the set rotation speed of the disc. As a physical analogue of the process, we have considered an “electrode-part” flat contact with a center-located thin com-pound bar thermally insulated at the ends and on the side surface. In addition, a numerical experiment is used to show that introduction to the original polynomial transfor-mation function with three correction indexes enables to reduce the methodological error of measurementsof the contact surface temperature to 0.5°C in the time interval from 1.2 seconds to 1.9 seconds (the electrode material is electro-ceramics).
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