Non metallic protective layer of spring
The non-metallic protective layer is to dip or spray a layer of organic substances, such as paint, asphalt and plastic, on the spring surface to protect the spring from corrosion.
The non-metallic protective layer has thick film, good chemical stability and good mechanical anti-corrosion effect, but it has low hardness and is easy to be scratched and damaged. At the same time, the film has aging phenomenon.
The following types of paints are usually used for the spring paint layer:
a. Asphalt paint asphalt paint has good water resistance, moisture resistance and corrosion resistance, especially excellent acid resistance and good alkali resistance. But the adhesion, mechanical strength and decorative performance are poor.
b. Phenolic paint phenolic paint is divided into primer and finish. Phenolic primer has strong adhesion and good rust prevention performance, but the mechanical strength and gloss of paint film are poor. Phenolic topcoat has hard film and good gloss, but poor weather resistance and easy to turn yellow.
c. Alkyd paint alkyd paint has tough film, strong adhesion, good mechanical properties, excellent gloss, good durability and certain oil resistance and insulation properties. Its disadvantage is that the surface dries quickly and sticks to the hand for a long time, easy to wrinkle, water and alkali resistance.
d. Epoxy paint epoxy paint has strong adhesion, high hardness, good toughness, flexion resistance, impact resistance, hard but not brittle. It has excellent resistance to water, acid, alkali and many organic solvents, especially alkali resistance. Its disadvantages are fast surface pulverization and high solvent selectivity. Water soluble epoxy paint is used for electrophoretic painting.
In general, the paint layer can be used alone or as a colorant after phosphating. Sometimes, some springs are painted with different colors to distinguish them in order to divide them into grades according to load. The specific type and brand of paint shall be determined according to the working environment. If necessary, it shall be indicated in the spring drawing.
There are many construction methods for paint, and the following methods are mostly used for spring
a. Dip coating method dip coating method is to immerse the spring in the paint tank, and then take it out to let the excess paint liquid on the surface drip naturally. After drying, it is covered with a layer of paint film on the spring surface.
Dip coating method has high production efficiency and can be applied to mechanized and automatic production. Moreover, the technology is simple and the operation is convenient. However, the paint volatilizes rapidly, and the paint containing heavy pigment and two-component paint (amine cured epoxy paint, polyurethane paint, etc.) should not be used. The paint film of dip coating method is not flat enough, which is easy to produce the phenomenon of thin at the top and thick at the bottom and sagging at the edge.
b. Spraying method spraying is to spray the paint into mist like small particles by using a spray gun, and evenly deposit a layer of paint film on the spring surface.
The spraying method has the advantages of high work efficiency, convenient construction and strong adaptability, and the thickness of the paint film is relatively uniform, flat and smooth. However, the effective utilization rate of paint by spraying method is only 70% and about 80% a day. At the same time, more solvents are required than other methods. These solvents will volatilize completely and the loss is too large. In addition, due to the diffusion of paint mist particles and the volatilization of solvents, environmental pollution is caused and workers’ health is affected.
c. In the electrostatic spraying method, the negative charge is induced at the moment when the thermosetting powder passes through the nozzle. Under the action of the warehouse and compressed air, the plastic powder is evenly coated on the surface of the spring. Then, the sprayed spring is heated and insulated (plasticized) in the oven at the temperature of 150 ~ 180 ℃ to form a smooth and firm surface protective layer. The general insulation time is 40 ~ 60min.
This process has the advantages of high production efficiency, suitable for flow production, good product quality, uniform film thickness and good adhesion. At present, this method is widely used in spring manufacturing industry.
d. With the change of the main engine structure and the increasingly harsh working conditions of the spring during operation, in order to improve the service life of the spring, the surface anti-corrosion treatment of valve spring is changed to apply special anti-corrosion oil (grease) after spring cleaning to replace the traditional oxidation or coating treatment.
In recent years, the spring surface finishing (finishing) treatment has also been recognized by spring designers. The finishing (finishing) process is to put the spring directly into the inclined centrifugal or spiral vibration, eddy current and other series of finishing machines, and add an appropriate amount of abrasive, abrasive and water for finishing. Generally, the finishing is about 20 ~ 30min, and the specific finishing time depends on the shape of the spring and the amount of the device. After finishing, take out the spring, wash it with tap water, immerse it in SM series water film replacement antirust oil for several minutes, and then take it out.
At this time, a layer of 5 is attached to the spring surface μ M anti rust oil film, which protects the spring from corrosion. This treatment method greatly reduces the traditional cumbersome processes, such as degreasing, cleaning, pickling, dehydrogenation and so on. At present, the springs using polishing (finishing) technology include: plunger spring for oil pump nozzle and pressure regulating spring for fuel injector; Support spring for refrigerator compressor, etc. The comparison of performance (service life) and corrosion resistance between the spring treated by finishing (finishing) and the spring treated by conventional oxidation or coating needs to be further tested and practiced to make a more reliable conclusion.
