Blackening

 

 

 

 

 

​Why Blackening?

  • Corrosion ProtectionAdds years of service life to parts and extends the shelf life of stored parts.
  • Abrasion Resistance and Durability - The hard black chemical conversion finish does not chip, craze, peel or rub off.
  • Anti-Galling - When it is necessary to break in mating parts, the anti-galling surface sacrifices the lubricating layer of black during initial contact and abrasion, while a work-hardened surface is formed.
  • Lubricity - Oil-based, post treatments not only provide protection against corrosion, they also provide for smoother running of mating parts.
  • Dimensional Stability - The blackening process produces essentially no dimensional change (only 5 to 10 millionths of an inch added) which means the blackened parts retain their surface properties. Polished surfaces retain their gloss and heat-treated parts retain their Rockwell hardness. Tool integrity is preserved and critically sized parts can be finished.
  • Esthetic Appeal - The process produces a pleasing, decorative black finish which enhances the perceived quality of the part and improves the salability of the part.
  • Reduced Glare - There’s less eye fatigue with moving parts.
  • Productivity and Economy - A much faster process which saves time and money versus painting or plating processes. A simple, cost-effective means of providing corrosion protection to iron and steel parts.
  • Surface Preparation - For improving adhesion of subsequent paints and lacquers.
  • Environmentally Friendly - Usually there are no metallic ions in the rinse waters which would require treatment. However, the use of stainless steel baskets or barrels may require monitoring of the chrome concentration. The only by-product of the blackening reaction is harmless soda ash (Sodium Carbonate). Some Sodium Hydroxide will be dragged out of the cleaning tanks and the blackening tanks into the rinse tanks, but the resulting pH is usually within regulated limits. If not, the pH may be reduced economically with dilute acid.

 

Uses for Black Oxide:

  • Tools
  • Firearms
  • Automotive Parts (Spark Plugs)
  • Ball Screws
  • Gears
  • Fasteners
  • Wrenches

 

Industries Using Black Oxide:

  • Aerospace
  • Automotive
  • Defense
  • Architecture
  • Machining
  • Tooling

 

Three Types of Black Oxide:

Hot Black High Temperature 285º F - Sodium Hydroxide, Oxidizer Nitrite/Nitrate Bath

  • Requires ventilation for caustic fumes
  • Boiling solution care required - adding water and chemistry
  • 20 minutes blackening time
  • Fe2O3 convert in Fe3O4 (magnetic black rust)
  • Will not blacken cast iron or steel castings (parts turn red/mahogany color)
  • Powder metal parts blind holes
  • Offers abrasion resistance
  • Glossy blue-black color
  • High capital costs
  • pH adjust waste treatment system
  • Military Spec

Mid Temperature Blackening 220-245º F - Sodium Hydroxide, Nitrite/Nitrate Bath

  • Blackening time 30-45 minutes
  • Ventilation required for caustic fumes
  • No boiling - safer working environment for operator
  • Energy costs savings
  • High capital costs
  • pH adjust waste treatment system
  • Abrasion resistance - does not erase with pencil eraser
  • Passes oxalic acid military test
  • Meets Military Spec
  • Glossy blue-black color

Room Temperature Blackening 65-85º F - Phosphoric Acid, Selenium and Copper Bath

  • Blackening time 1-5 minutes
  • Deposit of Copper-Selenide
  • No ventilation required
  • No caustic fumes produced
  • Low capital costs
  • High energy cost savings
  • Ion Exchange Selenium and Copper rinse water
  • Does not meet military spec
  • Satin grey-black color