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Collapse edit this section metal surface treatment agent
It mainly includes cleaning agent, antirust agent and phosphating solution. Metal surface treatment technology is divided into mechanical treatment (such as sandblasting, polishing, high-pressure water rinsing, etc.) and chemical treatment of two categories. As for coatings, electroplating and other technologies have been independently developed as a metal corrosion prevention technology, the chemicals used are usually not included in the scope of the metal surface treatment agent referred to here.
Metals and their products are often contaminated with various dirt and impurities on the surface during processing. Cleaning is an extremely important part of the metal surface treatment. In order to degrease the oil degreasing for the main goal of the common cleaning agent are petroleum-based cleaning agent, chlorinated hydrocarbon cleaning agent, alkaline cleaning agent and cleaning agent containing surfactants, etc..
Petroleum-based cleaning agents
The main ones are solvent gasoline, kerosene or light diesel. Its function principle is mainly to use its dissolving effect on the metal surface grease. Because this kind of solvent has strong penetration and good degreasing property, it is generally used for rough cleaning to remove a large number of grease dirt. But in actual use, often add some kind of synthetic surfactant, so that it has the ability to clean water-soluble dirt, and sometimes also add a small amount of antirust agent, so that after cleaning the surface has a short period of antirust ability. This kind of petroleum-based cleaning agent, especially gasoline, because of flammability, the use of fire safety measures must have adequate.
Chlorinated hydrocarbon detergent
Commonly used solvents are trichloroethylene and carbon tetrachloride. These solvents are characterized by their strong solubility for oils and fats, but have low boiling points and are generally non-flammable. Moreover, the specific heat is small and the latent heat of evaporation is small, so the temperature rise and condensation are fast. Its density is generally greater than air, and thus exists in the lower part of the air. Because of these characteristics, it can be used in vapor degreasing. As these solvents are expensive, they are usually recycled or recyclable. Some solvents, such as trichloroethylene, have certain toxicity. When light, air and moisture coexist, hydrogen chloride is produced by decomposition, which can easily cause metal corrosion; when co-heated with strong alkali, it can easily cause explosion, etc. Caution should be taken when using them.
Alkaline cleaning agent
Mainly sodium hydroxide, sodium carbonate, sodium silicate, sodium phosphate, etc., dissolved in water to become alkaline cleaning agent. Their principle of action is to be able to and oil in the fatty acid glycerol ester saponification occurs to form primary soap, so that the oil becomes water-soluble and be dissolved to remove. Among them, sodium hydroxide and sodium carbonate have the function of neutralizing acidic dirt. Sodium phosphate, sodium tripolyphosphate, sodium hexametaphosphate, etc. Both with the cleaning effect, but also to inhibit the role of corrosion. Sodium silicate has a gelling, dispersion, etc., cleaning effect is better. Alkaline detergent because of low price, non-toxic, non-flammable and other reasons, the use of more widely. But in the use of alkaline cleaning agent should pay attention to the material of the metal to be cleaned, choose the appropriate pH of the alkali solution. In addition, when using alkaline cleaners, surfactants are often added to form a compound formula to enhance the cleaning effect.
Folded antirust agent
It is a class of chemical agents added to various media such as water, oil or grease for the purpose of metal rust prevention. It can be divided into water-soluble antirust agent, oil-soluble antirust agent, emulsified antirust agent and gas phase antirust agent.
Water-soluble antirust agent
They can be dissolved in water to form an aqueous solution, and the metal is treated with this aqueous solution to prevent corrosion and rusting. Their anti-corrosion action can be divided into three categories. (1) The metal and the antirust agent form an insoluble and dense oxide film, thus preventing the anodic dissolution of the metal or promoting the passivation of the metal, thus inhibiting the corrosion of the metal. These rust inhibitors are also known as passivating agents, such as sodium nitrite and potassium dichromate. When using them, an adequate amount should be ensured. When the dosage is insufficient, a complete oxide film cannot be formed, and on the small uncovered metal surface, the density of corrosion current will increase, which will easily cause serious local corrosion. Metal and antirust agents generate insoluble salts, thus isolating the metal from the corrosive medium and preventing it from rusting. For example: some of the phosphate can function with iron to generate insoluble iron phosphate salt; some silicate can and iron, aluminum role to generate insoluble silicate and so on. (3) The metal and antirust agents generate insoluble complexes, which cover the metal surface and protect the metal from corrosion. For example, benzotriazole and copper can form chelate Cu(C6H4N3)2, which is neither soluble in water nor oil, thus it can protect the surface of copper.
Oil-soluble antirust agent
Also known as oil-soluble corrosion inhibitors. Most of them are long carbon chain organic compounds with polar groups. The polar groups in their molecules are closely adsorbed on the metal surface by charge; the non-polar groups of long carbon chain hydrocarbons are directed towards the outside of the metal surface, and can be mutually soluble with oil, so that the antirust agent molecules are arranged directionally on the metal surface, forming an adsorptive protective film to protect the metal from the erosion of water and oxygen. According to its polar group, it can be divided into five categories: ① sulfonate, chemical formula is (R-SO3. Generally used is the alkali metal or alkaline earth metal salts of petroleum sulfonic acid, such as barium petroleum sulfonate, sodium petroleum sulfonate, barium dinonylnaphthalene sulfonate and so on. Carboxylic acids and their soaps, chemical formula for R-COOH and (R-COO)nMm. as rust inhibitor carboxylic acids are animal and vegetable oils of fatty acids, such as stearic acid, oleic acid, etc., another oxyfuel, alkenesuccinic acid and other synthetic carboxylic acids, as well as petroleum products such as naphthenic acid. The polarity of the metal soap of the carboxylic acid is stronger than the corresponding carboxylic acid, so the antirust effect is better, but the oil solubility is smaller. And it will be hydrolyzed by water, and it is less stable when dispersed in oil, sometimes it is precipitated from oil. ③Ester, chemical general formula is RCOOR′. Lanolin and beeswax are natural ester compounds, and are also good metal antirust sealing materials. Esters of polyalcohols have good antirust effects, such as pentaerythrityl monooleate and sorbitan monooleate (Span-80), which are good metal antirust agents and are widely used. (4) Amines, the general formula is R-NH2, such as octadecylamine, etc. However, simple amines are widely used in mineral oil. However, simple amines are not good enough to prevent rust in mineral oil, but amine salts or other compounds produced by amines and organic acids, such as octadecylamine oleate, cyclohexylamine stearate, etc. are commonly used. (5) sulfur, nitrogen heterocyclic compounds, heterocyclic rings containing sulfur or nitrogen and some derivatives, are also better metal rust inhibitors, such as imidazoline alkyl phosphate salt, benzotriazole and α-mercaptobenzothiazole and so on. Imidazoline is used for ferrous and non-ferrous metal rust prevention, while benzotriazole is mainly used for copper and other non-ferrous metal rust prevention.
Emulsified antirust agent
There are two kinds of emulsified antirust agent: one is the suspension of oil particles in water, i.e. oil-in-water emulsion, which is usually milky white; the other is the suspension of water particles in oil, i.e. oil-in-water emulsion, which is usually transparent or translucent liquid. The emulsified antirust agent has not only antirust performance, but also lubrication and cooling performance, so it is often used as a lubricating coolant for metal cutting. In the past, the emulsifier in emulsified antirust agent is commonly used in vegetable oils and fats (such as vegetable oil, castor oil, etc.) through saponification process, and in the 21st century, triethanolamine oleate, sulfonated oil or non-ionic surfactant is used. In order to strengthen the rustproof performance, when mixing into emulsion with water, a certain amount of water-soluble antirust agent, such as sodium nitrite and sodium carbonate, sodium nitrite and triethanolamine can also be added. In addition, in order to prevent and slow down the deterioration of the emulsion, a small amount of antifungal agents, such as phenol, pentachlorophenol, sodium benzoate, etc., can be added.
Folded phosphate solution
Phosphate is an important method of corrosion prevention of metal materials, the purpose of which is to provide anti-corrosion protection to the base metal, for painting before priming, to improve the adhesion of the coating layer and corrosion resistance and in metal processing from friction reduction and lubrication. Phosphating is commonly used pretreatment technology, the principle should be a chemical conversion film treatment. Engineering applications are mainly steel parts on the surface phosphate, but non-ferrous metals such as aluminum, zinc parts can also be applied phosphate.