GALVANIZING STEEL SPRINGS
Description
Galvanic zinc plating of springs is designed to protect them from corrosion. The requirements for coating are higher than when processing other products - galvanizing can cause hydrogenation of high-strength steel and, as a consequence, its “hydrogen embrittlement”. This, in turn, will lead to a decrease in the service life of the springs during further work in tension and compression. To remove hydrogenation, the springs are heat treated and only then passivated. The thickness of the iridescent zinc coating on the springs can range from 6 to 50 microns. It depends on the required degree of protection of the surface to be coated. The use of a thin coating (less than 6 microns) is impractical, because in this case, the protective characteristics of zinc will be unacceptably low. With thick-layer galvanizing (more than 50 microns), internal stresses in the coating increase. The thickness of the rainbow chromate film on galvanized springs is usually 0.25-0.5 microns and does not affect the mechanical characteristics of the products. The content of hexavalent chromium in the chromate film varies from 80 to 220 mg/m2. The durability of yellow zinc in 5% salt spray is 200-300 hours. The corrosion rate of non-passivated zinc depends on pH:
Zinc plating of springs can be carried out using different technologies. Shiny coatings are more hard and less flexible than semi-shiny ones. The type of passivation has virtually no effect on microhardness.
You can order galvanizing of steel springs in accordance with GOST 9.305-84 by phone and email specified in the section "CONTACTS".
Characteristics
|
Designation (example) |
Zn |
|
Thickness |
6-50 microns (optimal, greater thickness is possible) |
|
Microhardness |
490-1180 MPa |
|
Electrical resistivity at 18° C |
5.75×10-8 Ohm⋅m |
|
Permissible operating temperature |
300° C |
Advantages galvanizing:
- With a thickness of 24 microns, the use of this coating is possible in difficult operating conditions.
- The zinc coating produced at our enterprise is ductile, thanks to the use of unique shine-forming additives in the electrolyte, which is especially important for springs. It also has a high uniformity in thickness, which is confirmed by metallographic studies:
A microphotograph of a cross-section of the coating is shown below:
Disadvantages galvanizing:
- Yellow chromate film on zinc is mechanically relatively weak. With constant mechanical impact (touch of a tool, hands), the zinc coating loses its decorative appearance.
- Steels with a tensile strength higher than 1380 MPa cannot be galvanized without heat treatment, since due to hydrogenation they lose the necessary ductility.
- At temperatures above 250°C and below -70°C, the coating has increased brittleness.
- Zinc coating has low chemical resistance to the effects of products released during the aging of organic materials.
Read also articles
Galvanizing mechanism
Description of the galvanic galvanizing process. Electrolytes.
Hydrogenation and removal of hydrogenation of steel after galvanizing
The problem of hydrogenation during galvanizing. How to dehydrate?
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