Study Of Technology And Mechanics On Steel Electrochemical Texturing

With the rapid development of the auto appliance industry and electrical household appliances industry, the quantity demand of the high quality of cold rolled sheet is increasing with each passing year. The operational performances, molding and painting, are the most important targets for cold rolling plate. The operational performances are closely connected with the characteristic parameters of steel strip surface topography. The uniform distribution of the roughness and the irregular distribution of the morphology can reduce optical interference fringes and avoid the orange peel effect to improve the optical properties of the coated strip.Roller plays a critical role in iron and steel industry. Any kind of plates and profiles are produced roll forming process. The service condition of the roller affects not only the steel consumption in the process of production and the production cost, but also the stability of production and product quality. Now the manufacturing quality and level of the roller is becoming the vital signs for national metallurgy technology.There are three textured technologies in common industry use, Shot Blast Texturing (SBT)、 Electrical Discharge Texturing (EDT) and Laser Beam Texturing (LBT). All of the three textured technologies can make roller surface materials fall off or overfire to form aculeate and concave surface. The roughness of the manufactured texturing rollers attenuated rapidly inducing lower using life because of the effect of cold roller’s material. If the amounts of the concaves on the surface of cold roller are higher than that of heaves, it makes against for steel strip to copy the roughness of the roller.In this thesis, the surface treatment, central layer and additive agents were induced the controlled chromium deposition to achieve the surface conFig.uration and to obtain the controlled surface morphology, roughness and hardness. Through the controlled process, the bonding strength of the substrate and central layer, the chromium layer and the central layer can be improved to reduce the risk of the electroplating sloughing.In this thesis, a series of chromium plating experiments were designed to perform the particle-doped and pulse chromium electroplating texture experiments on steel. Pulse power source and DC electrical source were used in these experiments. For the particle-doped chromium electroplating texture experiments, the Al2O3and the WC particle-doped nickel electroplating were prepared as the central layer, followed the top chromium coating was obtained by DC electroplating. For the pulse chromium electroplating texture experiments, the nickel electroplating was prepared as the central layer and followed top chromium layer was obtained by pulse electroplating with different parameters. The certain extent of roughness and hemispherical crystal coatings, which there were more bulging on the surface, were obtained by both the methods mentioned above. This kind of morphology can be beneficial for copying the surface topography of cold rolls.From the results of particle-doped electroplating experiments, it was shown that the temperature of the electroplating bath was the greatest impact factor, the pH value of the electroplating bath was the second greatest impact factor and the current density had less effecting in all effecting parameters. To obtain the highest roughness of the central layer, the optimal technological conditions were as following:temperature50℃, current density5A/dm2, and pH4.8. The surface roughness of the central electroplating layer was in the range of2-5μm. When deposited by chromium coating, the hardness of the coatings was about1031.8HV, and the roughness of the coatings was in the range of2-4μm. The coatings deposited on steel sheet showed better roughness and rigidity.From the results of pulse electroplating experiments, it was shown that the pulse technological parameters affected the roughness (Ra) very distinctly from0.966to3.788. The three parameters, which consisted of pulse current density Jp, turn-off time toff and electroplating time t, were the evident facters to affect the roughness. The duty cycle y, which was determined by turn-on time ton and turn-off time toff, also affected the roughness. With the increasing of electroplating time, the roughness increased to a certain degree until the electroplating time reached to100min. The appropriate temperature of the electroplating bath was about50℃.The tests of pulse texturing showed that the binding force between the coating and the substrate are qualified. The nickel electroplating layer, which was as the intermediate layer between the metal substrate and chromium deposition, showed a well role transition. This intermediate layer can not only increase the binding force between the coatings, but also can reduce the internal stress of the chromium electroplating to lessen the surface cracks of the chromium deposition. From the analysis of compositions, it was shown that the main component chromium can obtain better hardness and wear resistance.The experiments showed that texturing on the surface of steel sheet was feasible under certain conditions by particle-doped and pulse electroplating. The textural coatings showed hemispherical crystals and high peak density.The model of pulse electroplating diffusion double electric layer was established. The concentration metal ions located in the pulse diffusion layers near the electrode presented undulate constantly with the switching of pulse current. The movement velocity of metal ions was critical relatively with the current intensity. When using pulse electroplating, the larger concentration of metal ions in the diffusion layer can be obtained on account of higher peak value of pulse current. The larger roughness and perfect surface morphology can be obtained when the growing-up velocity of grains was greater.