Hardware knowledge: spring surface treatment

In recent years, spring designers have known about the surface finishing of spring. Finishing (finishing) process is to put the spring directly into a series of finishing machines such as inclined centrifugal type, spiral vibration type and eddy current type, and add appropriate amount of abrasive, abrasive and water for finishing. Generally, the finishing time is about 20 ~ 30min. The specific finishing time depends on the shape of spring and the amount of device. After finishing, take out the spring and rinse it with tap water, then immerse it in SM series water film to replace antirust oil for a few minutes and then take it out. At this time, a layer of 5 μ m antirust oil film is attached to the spring surface, which protects the spring from corrosion.


This method greatly supports the traditional propagation process, such as degreasing, cleaning, pickling and dehydrogenation. At present, the spring used in finishing process includes plunger spring for oil pump and nozzle and pressure regulating spring for injector, and support spring for refrigerator compressor. The performance (service life) and corrosion resistance of the spring treated by smooth finishing and conventional oxidation or coating treatment are compared without further test and practice.

The corrosion of spring can be divided into chemical corrosion and electrochemical corrosion according to the type of reaction. They are the result of the change of metal atoms on the spring surface or the change of electron gain and loss into ionic state.
If the metal on the spring surface only reacts with the surrounding medium, and the spring causes corrosion, it is called chemical corrosion. For example, the spring oxidizes to form an oxide film in a particularly dry atmosphere, and the spring changes chemically with the liquid or impurities in the non electrolyte liquid, which belongs to chemical corrosion.

If the spring is in contact with electrolyte solution, the corrosion caused by the action of micro cell is called electrochemical corrosion. For example, the spring is in contact with acid or salt solution, which is electrolyte. The electrode with different potential difference is formed due to defects or impurities on the surface of spring, so that the spring is continuously subjected to electrolytic corrosion; Another example is that the spring is in a humid atmosphere, because the water vapor in the atmosphere condenses into water film or water droplets on the spring surface, and the corrosive gases in the atmosphere (such as sulfur dioxide and hydrogen sulfide in industrial waste gas or salt fog in the marine atmosphere) dissolve in the water film or water droplets to form electrolyte. In addition, the impurities or defects of spring metal can form electrodes with different potential difference, and the spring also produces electrolytic corrosion. These are electrochemical corrosion.

Chemical corrosion of spring is small and slow, while electrochemical corrosion is main and common. But generally speaking, chemical corrosion and electrochemical corrosion exist at the same time.
In the process of manufacture, storage and use, springs often suffer from the corrosion of surrounding media. Because the spring works by elastic force, the spring will change after corrosion and lose its function. Therefore, to prevent the corrosion of the spring can ensure the stability of the spring and prolong its service life.

According to the nature of the protective layer, it can be divided into metal protective layer, chemical protective layer, non-metallic protective layer and temporary protective layer. The first three methods are introduced in this paper.
Stainless steel spring and copper wire spring have certain anti-corrosion ability, so they are generally not treated with anti-corrosion.