When the oily workpiece is immersed in a solution rich in active substances, the originally disordered surface active agent molecules, the hydrophobic groups of which point to the oil film, and the hydrophilic groups of which point to the aqueous solution, are arranged in order on the surface of the workpiece. In this way, it is mainly adsorbed on the two interfaces, which constitutes a decrease in the tension of the watch. Under the convection and mixing effect of the hot degreasing fluid, the oil film is torn to form oil droplets, which drop from the surface of the workpiece, and gradually fall into a very small ball. On the surface of the ball, the surface active agent is adsorbed, hydrophilic The base is outward, and the hydrophobic base is inward. Therefore, a mixture of two dissimilar liquids becomes an emulsion. The oil droplets gradually rise up, and the citrus auricum forms an oil layer and then is removed. Chemical degreasing is relative to electric degreasing. It removes saponified oil by means of the saponification effect of hot alkaline solution, and removes unsaponifiable oil by means of emulsification effect. The saponification reaction is the alkaline effect of animal and vegetable oils and sodium hydroxide to generate water-soluble fan and glycerin. This is a way to remove oil by converting fats and oils into other substances by chemical reaction. Mineral oil is unsaponifiable oil, which does not react with alkali, but can be dispersed by emulsifying effect, and it can be separated from the surface of the titanium rod of the workpiece to remove oil.
From this we can see that the conditions necessary for chemical degreasing are summarized as follows:
(1) It is rich in both alkalis and surface active agents.
(2) Mixing of microscopic solutions (usually heated) or macroscopic artificial mixing. Degreasing at room temperature mainly depends on the emulsifying effect of the surface active agent. When external force mixing is not used, the degreasing power is not as good as that of heated chemical residual oil. The saponification reaction speed also accelerates with increasing temperature. Therefore, for the room temperature or low temperature oil, it is necessary to use it in mass production based on small experiments and after thinking that it is feasible. In particular, this question should be carefully considered when planning the production line.
② In the degreasing fluid, it is inevitable that it is rich in metal ion impurities, they will also recover on the cathode workpiece, and black objects or sponges will occur, affecting the adhesion of the coating.
(3) When the titanium piece is on the cathode, the electric oil-free oil is called the cathode oil-removing titanium rod, and the electric oil-free oil on the anode is called the anode oil-free oil.
The advantages of cathode degreasing:
(A) 1 mol of hydrogen can be generated by electrolysis of 1 mol of water, and 1 mol of oxygen can be generated by electrolysis of 2 mol of water. When passing the same electricity, the volume of the gas produced on the cathode is twice that of the gas generated on the anode. The generation of gas is the main reason for oil-free electricity.
(B) Basically does not corrode the workpiece. Hydrogen generated on the cathode has a restorative effect, does not cause the metal atoms on the surface of the workpiece to oxidize or lose electrons, and dissolves from the workpiece in an ion state. Therefore, copper and copper alloys, zinc and zinc alloys (including die castings) can only be degreased by the cathode, otherwise, the appearance will be blackened or severely corroded.