Modelling and prediction of the conditions of the process of electric resistance sintering of metallic powder materials in reconditioning of components

Abstract

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]

Intellectualization of Control Processes and Monitoring of Electric Contact Heating During Restoration of Disc-Type Parts

“…Исследования, связанные с прогнозированием теплового состояния контактной системы и уточнением функции преобразования ИД ТКП, проводились с использованием экспериментальной установки, описанной в работе [6]. Данная установка позволяет осуществлять восстановление режущей способности (заострение) изношенной детали типа диск с помощью ЭМД, а её измерительная часть -фиксировать при электромеханическом деформировании темпе-ратурные изменения восстанавливаемой детали и параметры энерговвода.…”

Tribological Properties of Coatings Obtained with Electrocontact Welding of Metal Powder Materials

“…This is primarily caused by the presence of an extremely advanced internal phase interface between the solid body and pores [27][28][29][30][31]. Besides, the problems of wear resistance when using the fillers of powder compositions are underexplored, which allow to control the structure and physical mechanical properties of deposited reconditioning and / or hardening coating [24,[32][33][34][35].…”