Peculiarities of heavy electro-mechanical plating on medium carbon steel 30 and 38 ChN3MA

Abstract

Abstract.One of the urgent problems in mechanical engineering is development of efficient inexpensive thick-layered coatings for repair worn-out large-sized parts. To solve these problems a comparatively new method of electro-plating with simultaneous mechanical impact of a tool upon coating under formation is promising enough. In this paper there are considered the peculiarities of plating through this method of thick-layer electro-mechanical iron plating on medium carbon steel 30 and 38 ChN3MA, and the composition, structure and properties of coatings obtained are analyzed. Coatings were applied upon crank main journals made of steel 38ChN3MA and upon models imitating crank main journals made of steel 30. Micro-hardness of the coating obtained, roughness, a chemical composition and a structure were analyzed. The results of the investigations have shown that a more significant role in hardness increase is played not by a chemical composition of medium carbon steel upon which it is applied, but a preparation of the surface and the technology of coating and also an electrolyte composition. The structure of electro-mechanical plating is less defective, contains a value of detrimental impurities considerably lower of allowable values and has a satisfactory adhesion strength with a substrate. Problem definitionAt present one of the urgent problems in mechanical engineering is development of efficient and inexpensive heavy coatings for repair of worn large-sized parts [9,10,11]. Such coatings must have an increased thickness, good durability of adhesion with a basis, sufficient hardness and wear-resistance. In world practice the reduction of worn-out large-sized parts is carried out by retailoring [12,13,14], sputtering [15,16,17], cladding [18,19,20] and so on. But all these methods suppose an intensive thermal impact upon a part under reduction that results in hard-removable buckling and shrinkage.Therefore, more and more attention is paid to the process of galvano-mechanical metal deposition without temperature increase -flow-contact deposition of galvanoplatings with the mechanical activation of a cathode surface [5,6,7,8]. It is well-known that the mechanical effect upon a part in the course of galvanic deposition allows increasing the allowable current density, a deposition rate, micro-hardness, coating thickness and also improving the adhesion with a basis and decreasing residual stresses. Investigation procedure and equipmentThe considered in this paper off-bath method of the restoration through an electro-galvanic dry topping in a flowing electrolyte with the mechanical effect by a smoothing tool in the course of deposition is realized at small temperatures (40 -50 0 С). It prevents buckling and shrinkage in parts and ensures the required thickness (1.5 -1.8 mm), micro-hardness (600 -650 HV) and low roughness (Rа 1.25 -2.5 µm) stipulating for a small allowance for the further grinding of a layer restored. The method has small material and power expenses and a quick recoupment at the espense of the applicatio...

Theoretical basis of justification of electromechanical hardening modes of machine parts

“…Analysis of the thermal processes of the high-temperature contact zone of the tool and part shows that the thermal balance, taking into account the thermophysical properties of the material and the temperature values of the critical points of phase transformations, is expressed by the equation (7).…”

“…The world trend of innovative development of repair and maintenance of power, transport and technological machines is characterized by development and implementation of technological solutions in agricultural machine building with regard to restoration of machine part operability with application of combined methods of combination of temperature, power and time effects in various manifestations, for example, laser, electromechanical and other types of treatment [4; 5]. As the cost of the electromechanical processing equipment is considerably lower, the electromechanical processing method is the most preferable, but the methods of implementing hardening for different machine parts are varied due to different technical requirements, besides, the issues of theoretical justification and coordination of processing modes and process parameters are not deeply disclosed [2][3][4][5][6][7].…”

Features of Iron Coating Electro-Galvanic Method

“…Очень важным моментом является подготовка поверхности детали к осаждению, а именно -электрохимическое декапирование. Как правило, декапирование проводят в отдельной ванне, и при переносе подготовленной детали из ванны декапирования в ванну осаждения на ее поверхности появляется тонкий слой окислов, что значительно уменьшает прочность сцепления покрытия с основным металлом [1].…”

“…При механическом активировании катодной поверхности, как правило, используется инструмент в виде бруска из минералокерамики с полированной поверхностью. Этот процесс получил название «гальваномеханическое осаждение металла» [1][2][3][4][5][6] (в нашем случае электро-гальваномеханическое железнение (ЭГМЖ).…”

Method of justification of machine parts hardening modes

“…An overview of research in the field of electromechanical processing of machine parts from medium and high-carbon steels showed that that as a result of electromechanical hardening, a white layer is formed on the surface; having non-uniform properties due to alternation of hardened and non-hardened structures [10], and during application of electromechanical coatings on the example of crankshaft main journals influence of preliminary and main processing modes is established [11], issues of improvement of quality of reducing coatings are proposed to be solved on the basis of subsequent electromechanical processing [12]. It should be noted that the mentioned studies did not carry out optimization of processing modes, which does not allow to realize potential level of mechanical properties of materials of parts taking into account their chemical composition.…”