Introduction to the common process of fastener surface treatment---phosphating/oxidation
Phosphating
Definition: The metal is chemically treated in a phosphate solution containing manganese, iron, and zinc to form a phosphate-protective film that is poorly soluble in water.
Phosphating, chemical conversion film treatment (chromate passivation of zinc, phosphating, oxidation of steel)
Phosphating is cheaper than galvanizing, and corrosion resistance is worse than galvanizing.
Two types of fastener phosphating are commonly used, zinc phosphating and manganese phosphating. Zinc phosphating lubrication performance is better than manganese phosphating, manganese phosphating corrosion resistance, wear resistance is better than galvanizing. It can be used at temperatures ranging from 225 to 400 degrees Fahrenheit (107 to 204 ° C).
High-strength bolts are phosphated to avoid hydrogen embrittlement problems. Therefore, bolts of grade 10.9 or higher in the industrial field are generally treated with a phosphating surface. Especially the connection of some important parts. For example, engine connecting rod bolts, nuts, cylinder heads, main bearings, flywheel bolts, wheel bolt nuts, etc.
1. Classification and application of phosphating
According to the phosphating film forming system: zinc system, zinc calcium system, zinc manganese system, manganese system, iron system, amorphous phase iron system.
According to phosphating film thickness (film weight) classification (GB/T6807-2001): sub-lightweight (0.1-1.0g/m2); lightweight (1.1-1.4) times weight (4.6-7.5) heavyweight (>7.5 Generally, as the basis for coating the bottom layer, the thicker it is, the less applicable.
Processing temperature: room temperature or room temperature; low temperature: 25-45 ° C; medium temperature: 60-76 ° C; high temperature: greater than 80 ° C.
Classification of phosphating treatment methods: brushing method, full immersion method, full spray method, spray-soak combination method.
Also according to the classification of accelerators........
Phosphating membrane function classification: coating base, anti-corrosion phosphating, cold processing lubrication, wear-resistant phosphating.
2. Standard parts commonly used phosphating solution formula and process (reference)
Phosphating simplified process: degreasing---pickling---(blackening)---phosphating---blocking---aging---drying oil
Oxidation
Definition: Blue or black, the process of steel in a solution containing an oxidizing agent to form a uniform blue-black to black film on its surface
classification:
a. High temperature chemical oxidation (alkaline chemical oxidation)
b. Normal temperature chemical oxidation (acid chemical oxidation)Process
a. Add oxidant (sodium nitrite) to the strong alkali (sodium hydroxide) solution at 135 ~ 145 ° C, 60 ~ 90min → soap liquid, 3 ~ 5min → wash, dry and oil.
b. An oxide film with a very thin Fe3O4 as the main component, 0.5~1.5μm.
Function: Improve the corrosion resistance, lubricity and appearance of the parts.
Applicable to agricultural machinery products with poor quality appearance requirements.
Related information recommended:
Selection and Introduction of Surface Treatment Process for Fasteners (I)—Electroplating
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