Electrochemical degreasing, also known as electrolytic degreasing, is a process in which oil stains on the surface of parts are removed under the action of direct current in an alkaline solution, with the parts as the anode or cathode and stainless steel plates, nickel plates, nickel-plated steel plates or titanium plates as the second electrode.
Author: Marisa
Electrochemical degreasing, also known as electrolytic degreasing, is a process of removing oil stains from the surface of parts under the action of direct current in an alkaline solution, with the parts as the anode or cathode and stainless steel plates, nickel plates, nickel-plated steel plates or titanium plates as the second electrode. Electrochemical degreasing liquid is similar to alkaline chemical degreasing liquid, but it mainly relies on electrolysis to enhance the degreasing effect. Generally, electrochemical degreasing is more effective, faster and more thorough than chemical degreasing.
In addition to the saponification and emulsification effects of chemical degreasing, electrochemical degreasing also has an electrochemical effect. Under electrolytic conditions, the polarization of the electrode reduces the interfacial tension between the oil and the solution, and the wettability of the solution to the surface of the part increases, which reduces the adhesion between the oil film and the metal, making it easy to peel off the oil stains and disperse them into the solution for emulsification and removal. During electrochemical degreasing, whether the part is the anode or the cathode, a large amount of gas is precipitated on its surface. When the part is the cathode (cathode degreasing), a reduction reaction occurs on its surface, and hydrogen is precipitated; when the part is the anode (anode degreasing), an oxidation reaction occurs on its surface, and oxygen is precipitated. The oxygen or hydrogen released at the interface between the metal and the solution during electrolysis plays an emulsifying role in the solution. Because small bubbles are easily adsorbed on the surface of the oil film, as the bubbles increase and grow, these bubbles tear the oil film into small oil droplets and bring them to the liquid surface, while stirring the solution, accelerating the removal of oil stains on the surface of the parts.
The electrochemical degreasing process conditions that have a greater impact on the degreasing quality are current density, temperature and degreasing time.
The selection of current density should ensure that a sufficient number of bubbles are precipitated, which can not only mechanically tear and peel off the electrode surface of the oil stains, but also stir the solution. Increasing the current density of electrochemical degreasing can speed up the degreasing speed, shorten the degreasing time, and improve production efficiency, but the increase in current density increases the cathode degreasing hydrogen permeation effect and aggravates the power consumption. In addition, the current density can be appropriately reduced during anode degreasing to prevent excessive metal corrosion, so the current density is generally controlled at 5-15A/dm2 during electrochemical degreasing.
The increase in temperature can enhance the emulsification effect, which is conducive to improving the degreasing effect. At the same time, it can increase the solution conductivity, reduce the cell voltage, and save electricity. However, if the solution temperature is too high, it will inevitably cause alkaline mist to diffuse indoors, deteriorate the environment, and accelerate the evaporation of the solution. When the solution contains a high content of chloride ions, it will also accelerate the corrosion of parts. When the temperature is too low, the degreasing effect is reduced, and sometimes rust may appear on the surface of the parts. The solution temperature of electrochemical degreasing is generally controlled at 60-80℃.
According to the conventional process, the degreasing time is usually set to first use the cathode degreasing for 3 to 7 minutes, and then use the anode degreasing for 0.5 to 2 minutes, so as to combine the advantages of the cathode and anode degreasing to achieve the complete removal of oil stains.
In addition, in the electrochemical degreasing tank, it should be noted that the cathode degreasing cannot use the iron plate as the anode, because the iron plate anode will dissolve and pollute the electrolyte.
Since the hydrogen and oxygen continuously generated on the electrode during electrochemical degreasing have an emulsifying effect, less or no emulsifier can be added to the electrochemical degreasing solution. The foam formed by too much emulsifier on the liquid surface is easy to adhere to the surface of the parts, which is not easy to clean and also affects the escape of gas on the electrode surface. When a large amount of precipitated hydrogen and oxygen are covered by the foam on the liquid surface, once the electrode and the hanger are in poor contact and cause electric sparks, it is very easy to cause an explosion and cause a safety accident.