Metal processing, including metal cleaning, surface finishing and metal turning, milling, planing, cobalt, rolling, casting and other processes, in order to reduce labour intensity, improve product quality, energy saving, reduce costs, in a variety of processing processes often need to use a number of additives, which, surfactants play a very important role.
1. Principe
Surfactants are substances that can significantly reduce the surface tension of liquid or liquid-liquid interfacial tension, and their molecules are composed of polar hydrophilic group and non-polar hydrophobic group, and the common hydrophilic groups are carboxyl group, sulfate, sulfonate, amine group, quaternary amine group, hydroxyl group, etc; the hydrophobic group is the long-chain alkanes and hydrocarbons, represented by the group, due to the ‘two-philic’ properties of both hydrophilic and lipophilic, which can change the surface (or interfacial) properties of the cleaning solution to have lower surface tension during chemical cleaning. Because they have both hydrophilic and lipophilic ‘two pro’ nature, and thus in the chemical cleaning can make the cleaning solution surface (or interface) properties change, so that it has a lower surface tension. according to the surface active part of the different charges will be divided into anionic surfactants, cationic, non-ionic and amphoteric. surfactants have wetting, foaming, solubilisation, defoaming and other characteristics. 2, Anti-foaming properties.
2. Application in metal cleaning
Metal cleaning throughout the entire metal processing process, cleaning agent mainly by the cleaning agent, corrosion inhibitor, surfactant composition of the three components. surfactant in the chemical cleaning plays a role in adsorption, penetration, emulsification, dissolution, washing, etc., not only as an auxiliary agent in the chemical cleaning, but also as the main component has been widely attached importance to, especially in the pickling, alkali washing, corrosion inhibition, degreasing, killing, etc., has been playing an increasingly important role in the cleaning process. At present, surfactants as the main body of the water-based cleaning to overcome the chemical pickling, chemical alkaline cleaning and several other cleaning agent deficiencies, to become the main direction of development of metal cleaning.
Advantages of water-based metal cleaner: high cleaning efficiency, strong decontamination; good safety performance, no pollution of the environment; energy saving, low cost of washing; washing process of the washed parts without damage, after washing the parts do not corrode, etc. Water-based cleaners are mostly non-ionic surfactants and anionic surfactant complex as the main body, plus a variety of auxiliaries composed of a mixture of the former decontamination capacity, with good rust prevention, corrosion inhibition ability, the latter can improve and improve the comprehensive performance of the cleaner. The cleaning mechanism is with the help of surfactant wetting, penetration, emulsification, solubilisation, dispersion and other effects, so that the adhesion of oil on the metal surface weakened, and then applied to mechanical agitation, brushing, heating, ultrasonic and other physical methods, so that the oil off the metal surface, and into the wash solution was emulsified, dispersed. metal cleaning commonly used in surface Surface activators commonly used in metal cleaning are fatty alcohol polyethylene oxide ether, alkyl phenol polyethylene oxide ether, sodium dodecyl benzene sulfonate, dodecyl diol amide, sodium methoxy fatty amide benzene sulfonate and so on.
3. Application in metal phosphating treatment
Phosphate treatment is a dilute solution containing phosphoric acid, phosphate and other chemicals to deal with metal. metal surface in the above solution with phosphoric acid, phosphate medium chemical reaction, transformed into a complete layer of insoluble metal phosphate with medium corrosion protection. metal on this phosphate conversion film has a variety of uses, which can improve the combination of paint and metal and corrosion resistance; can also be used as a rust oil carrier, metal cold working process lubricant carrier, as well as lubricants for abrasive table. It can also be used as the carrier of antirust oil, the carrier of lubricant in the process of metal cold working and the lubricant of friction table.
In order to improve the structure of the phosphating film, improve the effect of phosphating, phosphating solution also contains other additives, which surfactants have the following roles: on the metal surface adherence of oil has emulsification solubilisation effect, and can prevent the re-precipitation of dirt; so that the solution produces wetting, penetration, and is conducive to the contact between the phosphating solution and the metal surface; to reduce the surface tension of the liquid, conducive to the phosphate reaction of the escape of hydrogen, to enhance the cathodic depolarization, thus accelerating the phosphating film process. Phosphate treatment commonly used surfactants are made of ethylene oxide and various hydrophobic hydrocarbon long chain condensation, that is, non-ionic surfactants.
4. Application in metal plating
In the electroplating process, in order to improve the performance of the electrolyte and improve the quality of the plating layer, often need to add some additives, of which surfactant is one of the main varieties, it has the role of levelling, bright, diffusion, change the physical properties of the plating layer, inhibition of the escape of acid mist, etc. Commonly used surfactants in electroplating are levelling, OP emulsifiers, sodium dodecyl sulphate, sodium methylene bis naphthalene sulfonate, fluorine surfactants, fatty acids, polyethylene oxide esters, polyethylene oxide castor oil, etc. Ethylene oxide ester of fatty acids, polyethylene oxide castor oil and so on.