Thermal parameters of centrifugal induction deposition of powder coatings

Abstract

An engineering method of calculation of the thermal parameters of centrifugal induction sintering of a powder onto the surface of a workpiece with allowance for the geometric, thermophysical, and electrophysical parameters of the workpiece and the powder layer and for the convective and radiative heating of the exterior surface of the workpiece has been developed. A system for control of the temperature of the workpiece in the process of centrifugal induction sintering of the powder coating onto it has been developed.Introduction. One of the most efficient methods of deposition of powder coatings on workpieces is centrifugal induction sintering (CIS) of a powder onto their surface [1]. This method makes it possible to deposit coatings onto interior, exterior, and end surfaces of the workpiece.A schematic diagram of a device for deposition of a powder coating on an interior surface of the workpiece by the CIS method is given in Fig. 1. In accordance with this method, a dose of powder material is placed into the internal cavity of the workpiece, which is covered with lids on the ends through nonstick gaskets. The workpiece is fixed on a centrifugal unit, is positioned in relation to the inductor, is brought into rotation around its own axis, and is heated by the inductor of the high-frequency-current generator (HFCG). As the workpiece reaches a temperature of 0.7-0.95 T melt controlled by an optical pyrometer, its isothermal heating stops and it cools down to 700-900 K. Thereafer the rotation of the workpiece stops; it is removed from the centrifugal unit and cools down to room temperature in a static condition. The coating deposited on the workpiece in this way is treated with the aim of giving it a certain size.The existing methods of solving thermal problems in induction sintering of powder coatings onto workpieces' surfaces [2-4] do not take into account the presence of radiative heat transfer between these surfaces, which substantially reduces the accuracy of calculations. Operational methods and the finite-interval method used for solving such problems are not suitable for engineering practice, since they include extremely cumbersome mathematical calculations that require the use of computer facilities.The purpose of this investigation is to develop methods for determination of thermal parameters of CIS of powder coatings onto workpieces' surfaces, and also means of control over the temperature of this process.Main Assumptions. The most important stage of the CIS process, which determines the physicomechanical and operational characteristics of obtained two-layer coatings of hollow products, is isothermal seasoning of these coatings at the temperature of powder-material sintering. The main technical problem at this stage is to maintain an assigned average temperature of the powder layer (sintering temperature) during a certain time interval (sintering time). At the same time, the thermal conditions at the previous stages of heating do not have a significant effect on the kinetics of the process of sintering o...

Creation of AlSi12 Alloy Coating by Centrifugal Induction Surfacing with the Addition of Low-Melting Metals

“…Pavan [5] shows that when pouring an aluminum bronze melt into the inner cavity of a steel billet rotating around its own axis, a uniform distribution of the melt around the perimeter is achieved, and the resulting coating has satisfactory tribotechnical properties. Gafo & Sosnovskii [6,7] provide data on the process modeling of applying bimetallic coatings based on powder materials by centrifugal surfacing technology combined with induction heating. According to these data, the use of induction heating by high-frequency currents ensures uniform heating of the sleeve, while the temperature difference on the inner and outer sides of the sleeve does not exceed 11 • C. Sosnovskii [8] provides data on the modification of a CuSn (10%) P (1%) coating on a steel sleeve with ultrafine boehmite particles, according to which the alloy reinforcement ensures an increase in both the tribological properties and the coating hardness.…”