Appearance quality: the surface is not allowed to have not blackened spots, deposits, colour should be uniform, blue-black should be dense, and no mechanical damage and other defects. Due to the different materials or processing technology of the parts, parts blackening allows the existence of differences in colour.
Standards for Blackening Finishes
Author: Robby
The standard of blackening surface treatment mainly includes the following aspects:
Appearance quality: the surface is not allowed to have not blackened spots, deposits, colour should be uniform, blue-black should be dense, and no mechanical damage and other defects. Due to the different materials or processing technology of the parts, parts blackening allows the existence of differences in colour.
Blackening performance: the surface should have good densification, after the densification test, there shall be no red replacement of copper phenomenon; the surface should have good abrasion resistance, after the friction resistance test, there shall be no discolouration or bottom phenomenon; the surface should have a certain degree of corrosion resistance, after the anticorrosion test, there shall be no corrosion spots or corrosion The surface should have certain anti-corrosion property, after anti-corrosion test, no corrosion spot or rust spot phenomenon.
Subsequent performance: the deformation of the parts generated by the blackening treatment of the parts shall not affect the subsequent processing performance and the use of the performance of the parts.
Quality control:
Appearance inspection: the blackened parts wiped clean and placed under the illumination of 400 ± 100lx (equivalent to 40W fluorescent lamp illumination), a distance of 300mm ~ 350mm, normal visual inspection. Appearance of blue-black or deep black, dense, uniform film crystallisation, no bottoming out of the product, no obvious colour difference, no whitening and other abnormal phenomena.
Density test: the blackened parts wiped clean, at room temperature in a flat part covering the surface of the oxide film drop 3 drops of 30g / L of copper sulfate solution, 30s after the surface cleaning, drying, the surface should be no discolouration, replacement of copper and other phenomena.
Friction resistance test: wipe the blackened parts clean, with the appropriate amount of cotton cloth or cotton yarn, with a hand of 5N pressure to repeatedly wipe 0.5min, normal visual inspection, the surface of the parts should be in line with the requirements of wear-resistant rubbing performance.
Corrosion resistance test: the blackened parts to oil cleaning and wipe clean, suspended in a salt spray test chamber, according to GB/T 10125-1997 neutral salt spray test requirements for testing, the surface of the parts should meet the corrosion resistance requirements.
Common blackening treatment methods include:
Oxidation blackening: Using sodium hydroxide, ferric chloride and other compound solutions for treatment to form a dense oxide layer with good corrosion resistance and decorative properties. The main parameters include immersion temperature (60-90℃), immersion time (30-60 minutes), sodium hydroxide concentration (5-10%), ferric chloride concentration (5-20%) and so on.
Chemical black: Using the solution containing ferric chloride to form a dense oxide layer on the surface of the material through chemical reaction. The main parameters include immersion temperature (20-30℃), immersion time (5-10 minutes), ferric chloride concentration (5-10%) and so on.
Black plating: using electrochemical methods to coat the surface of the material with a layer of black metal oxide.