When a workpiece with oil stains is immersed in a solution rich in active substances, the originally disordered surfactant molecules have hydrophobic groups pointing towards the oil film and hydrophilic groups pointing towards the aqueous solution. They are arranged in an orderly manner on the surface of the workpiece, and each group has its own sound. In this way, the primary adsorption on the two interfaces constitutes a decrease in the tension of the watch decoration. Under the convection and mixing effect of the hot oil removal liquid, the oil film is pushed to tear, forming oil droplets that fall from the surface of the workpiece and gradually form extremely fine small balls. On the surface of the small balls, surface active agents are adsorbed, with hydrophilic groups facing outward and hydrophobic groups facing inward. Therefore, the mixture of two immiscible liquids becomes emulsion. The oil droplets gradually rise and accumulate on the surface of the oil removal to form an oil layer, which is then removed. Chemical degreasing is relative to electric degreasing. It uses the saponification effect of a hot alkali solution to remove saponified oil, and the emulsification effect to remove non saponified oil. The reaction of saponification is the alkaline effect of animal and vegetable oils with sodium hydroxide to generate water-soluble soap and glycerol. This is a method of removing oil by converting it into other substances through chemical reactions. Mineral oil is a non saponified oil that does not react with alkali, but can be dispersed through emulsification effect, breaking away from the surface of the titanium rod to remove oil.
From this, it can be concluded that the necessary conditions for chemical oil removal are as follows:
1. Rich in both alkalis and surfactants.
2. It has micro solution mixing (usually heated) or macro manual mixing. Room temperature oil removal mainly relies on the emulsification effect of external agents. When external mixing is not used, the oil removal power is not as good as that of heated chemical residual oil. The reaction speed of saponification also accelerates with the increase of temperature. Therefore, for room temperature or low-temperature oil agents, it is necessary to use them in mass production based on small experiments and consider them feasible. When planning the production line, this question should be carefully considered.
3. Metal ion impurities are inevitably rich in the degreasing solution, and they can also recover on the cathode workpiece, resulting in black or sponge like substances that affect the adhesion of the coating.
4. When the titanium component is on the cathode, the electrical oil removed is called the surface of the cathode degreasing titanium rod, while the electrical oil removed from the workpiece on the anode is called the anode degreasing.
Advantages of cathodic oil removal:
A. Electrolysis of 1 mole of water can produce 1 mole of hydrogen, while electrolysis of 2 moles of water can produce 1 mole of oxygen. When subjected to the same amount of electricity, the volume of gas produced on the cathode is twice that of the gas produced on the anode. The occurrence of gas is the main reason why electricity eliminates oil.
B. Basically does not corrode the workpiece. The hydrogen generated on the cathode has a recovery effect, which does not oxidize the metal atoms on the surface of the workpiece, nor does it lose electrons and dissolve from the workpiece in an ionic state. Therefore, copper and copper alloys, as well as zinc and zinc alloys (including die-castings), can only be degreased using a cathode. Otherwise, the surface will either oxidize and turn black, or suffer from severe corrosion.
