Most springs are used in different types of corrosive environments. Due to the effects of chemical corrosion and electrochemical corrosion, the surface of the spring will be corroded to different degrees, resulting in premature damage of the spring. Therefore, anti-corrosion treatment must be carried out. The anti-corrosion treatment of the spring is to cover the spring surface with anti-corrosion materials to form a protective layer, which separates the spring from the corrosive medium to achieve the purpose of anti-corrosion.
There are three common methods for spring corrosion prevention: electroplating, oxidation and painting. Electroplating is an effective method to obtain metal surface protective layer, and is also the main method of spring anti-corrosion treatment. It is characterized by good adhesion, fine and compact crystallization, small porosity, uniform thickness and good physical, chemical and mechanical functions. Electroplating includes zinc plating, chromium plating, copper plating, tin plating and nickel plating, and the common application is zinc plating.
The galvanized surface of the spring is generally white or colored. Zinc hardly changes in dry air. In humid air or water containing carbon dioxide, white zinc oxide film will be produced, which can play a role of corrosion inhibition. The zinc coating is suitable for use under various atmospheric conditions, but the corrosion resistance of zinc is poor in aqueous solutions containing acid, alkali and salt and in pure marine atmospheric conditions.
Zinc plating is characterized by low cost, simple process and good effect, so it is widely used in the corrosion prevention of medium and small springs used in the atmosphere. After galvanizing, the spring shall undergo passivation and dehydrogenation treatment to improve the corrosion resistance of the spring and avoid hydrogen embrittlement. In particular, small springs are more prone to hydrogen embrittlement. Special attention must be paid to pickling and electroplating. Oxidation treatment the oxidation treatment of the spring is also called bluing or blackening. After oxidation treatment, the spring surface produces protective magnetic iron oxide with a thickness of about 0.6 ~ 2um. Because the film is thin and has many voids, the protection ability is poor. Therefore, oxidation treatment can only be used to prevent corrosion of springs working in non corrosive media.
Due to the low cost of oxidation treatment, simple process formula, high production efficiency and no influence on the characteristics of springs, it is widely used for surface corrosion prevention of cold formed small springs. In addition to oxidation treatment, there is also phosphating treatment. The phosphating film is relatively stable under atmospheric conditions. Its corrosion resistance is 2-10 times higher than that of oxidation treatment. Painting is also one of the main methods for spring corrosion prevention. Most of them are used in large and medium-sized springs. In particular thermoformed springs and leaf springs. The paints used for springs mainly include asphalt paint, phenolic acid paint and epoxy paint. For some important springs, in order to improve the adhesion and corrosion resistance of the paint, the process of phosphating before painting is also adopted. The commonly used painting methods are painting and dipping. With the development of process technology, in order to improve work efficiency, paint utilization rate and paint quality, new processes such as electrostatic spraying will be promoted.
