Development and application of the hottest low tem

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The development and application of low-temperature iron plating technology. Its principle is to make the two half waves of alternating current unequal through certain means, and the larger half wave after being energized makes the workpiece cathode polarity and plated with a layer of coating; Another smaller half wave makes the workpiece have anode polarity, and part of the coating is electrolyzed off, which gradually thickens the coating. Low temperature iron plating equipment is simple, the obtained coating is uniform, the surface is smooth, and the bonding strength is high

1 characteristics of low-temperature iron plating

(1) the hardness of low-temperature iron plating layer is high. The hardness range can be adjusted through process control. The Rockwell hardness can reach 63 ~ 65 at most

(2) the iron plating layer is integrated with the substrate, and the bonding strength between the coating and the substrate is high. Microscopically, the ferrite in the iron plating layer and the ferrite in the matrix are continuously distributed

(3) there are micro cracks on the surface of the coating. It has good oil storage performance and good wear resistance

(4) the deposition rate of low-temperature iron plating is fast, about 0.6 ~ 1.0mm/h, and the coating thickness can reach 2mm at a time. In addition, iron plating is low-cost and non-toxic, so it can be widely used

2 development of low-temperature iron plating technology

there were research reports on iron plating abroad as early as 1846, which was initially applied to iron plating on the surface of printed lead plates [2]. A thin layer of iron is plated on the lead and copper plates used in the printing industry, which can improve their wear resistance, prolong their service life, and prevent the effect of some printing pigments. At that time, the sulfate iron plating method was adopted. The deposition rate of this iron plating solution was very slow and the application area was narrow. In 1908, some scholars began to study the chloride iron plating process. The results showed that the coating obtained at room temperature was hard and brittle, high internal stress, poor adhesion and easy to fall off, so it was only suitable for high-temperature electroplating. After the improvement of this plating solution system, a high-temperature chloride direct current iron plating process has been formed, and it has been widely used in the universal testing machine for wearing parts repair of wood-based panels for mechanical testing of various wood-based panels, plywood, fiberboard, particleboard, etc., which meets the requirements of gb/t17657 ⑵ 013 wood-based panel performance test method; However, high-temperature iron plating requires complex heating and insulation equipment. The plating solution is volatile, and because it is an acid solution, it has serious environmental pollution, and the hardness and wear resistance of the coating are poor [1]. At the end of 1960s, due to the development of electronic technology, some countries adopted asymmetric electroplating power supply [2] in iron plating technology, so that the chloride iron plating technology has been developed, and the hardness and wear resistance of the coating have also been significantly improved. In recent years, most countries have shifted the research of iron plating to amorphous coatings, corrosion-resistant coatings and magnetic coatings

China introduced DC iron plating technology from the Soviet Union in the 1960s to repair mechanical parts with out of tolerance due to wear [3]. At that time, because the temperature of the plating solution was generally above 80 ℃, the composition of the plating solution was difficult to control. The acid mist generated during the anodic etching and electroplating process before plating had a serious impact on personnel and the environment. In addition, the hardness of the coating was low (Brinell hardness was 200 ~ 400), the wear resistance was poor, and the scope of application was greatly limited

1975, an asymmetric AC continuous flow iron plating process was first developed in China. At the same time, in order to firmly combine the coating with the substrate, 30% sulfuric acid was used for anodic etching activation before plating. Because the plating temperature was only 25 ~ 50 ℃, it was called low-temperature iron plating process [4]. The process equipment is simple and conforms to China's national conditions. The Rockwell hardness of the coating can reach 50, with good wear resistance. The deposition rate can reach 0.15 ~ 0.30mm/h, the current efficiency can reach more than 90%, the one-time plating thickness can reach 2.0 ~ 3.5mm, and can be continuously plated; The raw materials of plating bath are cheap, easy to buy and low in cost, which have attracted extensive attention. The properties of plating bath and coating have been studied, and have been developed and applied in China. Since the treatment solution is easy to cause harm to operators and the environment when sulfuric acid is used for anodic etching and activation, the iron plating process of direct current small current starting after hydrochloric acid corrosion and the sulfur free acid anodic etching and iron plating process of symmetric AC activation + asymmetric AC starting in the plating bath soon appeared. However, some key technical problems, especially the poor process stability and the low bonding strength between the iron plating layer and the substrate, have not been well solved, resulting in the decline of the quality of iron plated workpiece. Therefore, in the late 1970s, the iron plating process was at a low tide, and many manufacturers were forced to stop production and change production

after entering the 1980s, dongwensheng et al. [] developed an iron plating process without anode etching, It has been successfully applied to the repair of mechanical parts (such as crankshaft and shaft "new chemical materials are an important direction for the transfer and upgrading of the chemical industry) and plane parts. The coating is firmly bonded to the substrate. The bonding strength of the iron coating measured by the pin pulling method can reach 360MPa. In various iron-based materials (including carbon steel, cast iron, cast steel, alloy steel) A stable and reliable coating can be obtained by plating. The cancellation of the anodic etching process before plating not only greatly reduces the environmental pollution, but also reduces the labor intensity, and the yield reaches more than 99%, which indicates that the domestic iron plating technology has developed to a stable and reliable practical stage

3 research status of low-temperature iron plating

in recent years, with the increasing needs of the society, and with the in-depth study of iron plating theory, low-temperature iron plating technology is also developing, and its application field is expanding. The early iron plating repair in China mostly focused on the crankshaft and other shaft parts used in agricultural machinery, automobiles and other transportation tools. At present, it has entered the stage of repairing large parts such as diesel engine crankshaft, steam turbine rotor, cylinder liner and cross head in ships, diesel locomotives, oil fields, mines and metallurgical machinery

at present, the main research direction of low-temperature iron plating technology in China is to strengthen the coating and improve its thermal stability. Songxiufu [7] obtained a superior composite coating by adding serpentine nanoparticles to the plating solution, and the microhardness of the coating reached about 6000mpa. Yang Sen, Liu Yi and others [] obtained a composite coating with a microhardness of 8340mpa by adding rare earth cerium to the plating solution, and studied in detail the effects of pH value, current density, temperature and the mass concentration of iron in the plating solution on the low-temperature iron plating process and performance

songbangcai et al. [12] studied the brush iron plating process. Under the optimized bath formula and process conditions, a good iron plating layer can be obtained. Using iron filings and ferric chloride to prepare the plating solution has the advantages of low cost, fast preparation rate, high hardness and good adhesion. Huangxiaoting et al. [13] developed a formula for brush iron plating solution. The maximum thickness of the coating obtained in the optimized solution is 1mm, and the Rockwell hardness is between 40 and 50. It is a manufacturer of food contact materials with good adhesion and oxidation resistance. Zhang Hao et al. [14] studied the effect of periodic reverse pulse electroplating on the performance of iron plating layer. The results show that under the same current density, the periodic reverse pulse iron plating layer can penetrate 1.6cm into the copper ring, the coating strength is up to 38kn, the hardness is high, the toughness is good, and the elongation is up to 3%; High current efficiency, deposition efficiency up to 86%, strong deep plating ability

4 development prospect of low temperature iron plating

at present, iron plating technology still has a great potential market. In general, most of the parts to be plated are the outer surface of the parts; However, the internal surfaces of components such as automobile, marine cylinder liners, crankshafts and so on are often severely worn, and the number is huge. Domestic enterprises that use iron plating to repair important parts and components have a considerable scale

it can be predicted that the main development trend of low temperature iron plating technology is to further improve the corrosion resistance, heat resistance and wear resistance of iron plating layer. It is one of the effective ways to add an appropriate amount of alloy elements to the plating solution. In addition, non etching low-temperature iron plating technology has many advantages, so there is a lot of room for development in both theoretical research and practical application. As long as the relevant technical problems are solved, iron plating technology will have a wider application prospect in injection molding industry

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