The corrosion of metal products is mainly due to electrochemical corrosion, and the metal surface is often attached to various impurities, such as human sweat, dust, rust, oil traces, etc. These are the factors that form micro-batteries and generate electrochemical corrosion. In order to ensure the quality of rust-proof packaging, metal products should be cleaned, rusted, and other pre-treatment before rust-proof packaging.

(1) Cleaning of metal products

The purpose of cleaning is to remove dirt, sweat, residual grease, organic matter, and other contaminants that remain on the surfaces of metal products. Cleaning is usually done with cleaning agents. Common cleaning methods are the following:

1 alkaline cleaning method. This is an older but still widely used cleaning method. The main purpose is to remove oil stains on metal surfaces. The cleaning agents used are sodium hydroxide, sodium carbonate, trisodium phosphate, water glass, and sodium pyrophosphate. Alkaline cleaners are obtained by dissolving these alkaline cleaners in water. The principle of cleaning is to use alkali and vegetable oil to generate saponification reaction to generate water-soluble substances to remove oil stains, but it is unsatisfactory for the saponification reaction of mineral oil, and a small amount of active agent can be added to the alkali liquor.

The lye cleaning method has good effect, wide application range, can be recycled, and the price is low, but it is corrosive and has corrosive effect on people, metals and other articles.

2 organic solvent cleaning method. This method is mainly used kerosene, gasoline, trichloroethylene, tetrachloroethylene. Ene, ethanol, acetone, etc. Organic solvent to oil. The dirt has a strong dissolving power, and no heating is required during the cleaning. It can be washed by immersing or scrubbing. The cleaning effect is good, and it is non-corrosive to metals and other objects, and has high volatility. However, kerosene, gasoline, ethanol and acetone are easily combustible; trichloroethylene and tetrachloroethylene are toxic and are easily decomposed. Their prices are high and they are mostly used for the cleaning of more sophisticated metal products.

3 surfactant cleaning method. Surfactants are formulated from a variety of non-ionic active agents. They have a hydrophilic structure and a hydrophobic group on the molecular structure. They can be adsorbed on the surface or interface of the solution in an aqueous solution and can be concentrated and oriented. Reduce the surface and interfacial tension, so strong decontamination ability, not only can clean grease, but also non-greasy grease, dirt, no obvious corrosion of metal products, low prices, is worth promoting the cleaning agent, suitable for precision Metal products cleaning. Commonly used surfactants are: 664,650l, 6503, fatty acid salts, sulfonates, alkyl trimethyl ammonium chloride and other cleaning agents.

The cleaning methods for metal products mainly include dipping, scrubbing, and spraying. Generally, the cleaning method should be selected according to the size, shape, material, batch, etc. of the object to be cleaned.

(2) Derusting of metal products

The rust on the surface of metal products will seriously affect the quality of rust-proof packaging. It is a major hidden danger and must be completely removed. Commonly used rust removal methods are as follows:
1 Artificial rust removal. Use abrasive cloth, sandpaper, steel brush, trowel and other tools to remove rust. This method is simple but inefficient.

2 mechanical derusting. Remove rust with wheels, cloth wheels, sprays, etc. The rust removal of the grinding wheel is only used on the non-working surface. The rust removal of the cloth wheel is mostly used on the surface where the surface finish requirements are relatively high, and their efficiency is low. The spray method is a harder material to hold particles such as steel, sand, etc. The particles are sprayed onto the metal surface by strong force, and the rust is removed by impact and friction. It has high efficiency, good effect and low cost, and is particularly suitable for special-shaped articles.

3 Chemical rust removal. There are two types of chemical rust removal, pickling and caustic washing, and pickling methods are widely used. Pickling involves impregnating metal products with various acids, such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Corrosion products chemically react with acids to remove water-soluble substances. The use of hydrochloric acid is more important. sulfuric acid. The pickling method is easy to operate, high in efficiency, and can be rust-removed where it can be impregnated. The cost is low. However, it is corrosive to metals and harmful to humans.
The alkali cleaning method is to immerse a metal product in a solution prepared from sodium hydroxide, glycolic acid, a complexing agent, a foaming agent, etc., and the rust and the alkaline solution react chemically to remove rust. It is less efficient than pickling but does not attack the base metal.