Revestimento de óxido preto: O que é óxido preto?

Black Oxide Coating: What is Black Oxide?

Black oxide, sometimes called blackening, is the act of converting the top layer of a ferrous material with a chemical treatment. Treating fasteners with a black oxide coating not only adds a nice clean black appearance, but can also add a slight layer of corrosion and abrasion resistance. To achieve maximum corrosion resistance, black oxide can be waxed or oiled to add an extra layer of protection. The wax coating may fade the color of the treatment, but it offers better durability. Black oxide treatment is also known as gun blueing.

When fasteners are immersed in black oxide bath materials (hot and hot processes), the aggressive chemical components convert the top layer to magnetite. Black oxide stainless steel nuts bolts and washers are the most common form of black oxide fasteners available. Valued both for the corrosion resistance of stainless steel and the additional benefits of black oxide treatment.

Materials that can obtain black oxide treatment

blackened finish washers

  • Stainless steel
  • Copper
  • Copper-based alloys
  • Zinc
  • Powdered metals
  • silver solder

Black Oxide Processes

Darkening can be achieved in several ways. There are three main ways to do this. If you're interested in the specifics of each type, check out this Wikipedia article.

Hot shower

The process of treating fasteners with different chemicals to convert the surface material into magnetite. The process is completed by submerging the fasteners in several tanks and occasionally placing them in water. Once the soaking process is complete, the top layer of fixative becomes porous and a layer of oil is applied. The oil penetrates the material adding extra resistance to corrosion and rust. This process creates a black oxide bath that meets MIL-DTL-13924, AMS 2485, ASTM D769, and ISO 11408 standards.

Cold coating

The cold process applies a compound (copper selenium) to the fasteners at room temperature. This process is more convenient to work at home as it does not require many chemicals at high temperatures to apply. Once applied, it is considered weaker than other forms of oxidation until a layer of oil or wax is applied to the surface.

Medium temperature bath

Similar to the hot bath treatment method, but does not produce the same toxic fumes as the hot bath and the surface is converted to magnetite at a much lower temperature. This method can also meet the same military standards produced by the hot bath version.

Benefits of Black Oxide Fixatives black stainless steel Allen screws

  • It does not significantly alter the dimensions of the fasteners as with hot-dip galvanizing.
  • A cheaper alternative to other corrosion resistance methods such as electroplating.
  • An attractive look when you don't want a shiny shine.
  • The process can typically be done in large quantities, making it faster and cheaper for smaller sizes.
  • Reduces the risk of wear by adding an oil finish
  • Decorative finish
  • Adds a layer of light corrosion and abrasion resistance
  • Paint adheres well to black siding if painting is required

Black oxide screws will rust

Black oxide adds a light layer of corrosion and abrasion resistance to fasteners. Like any material, black oxide treated fasteners can rust in the right environments. It will depend on whether the fastener is damaged or damaged, the type of metal with black oxide treatment and the environmental conditions.

Disadvantages of black oxide

Black oxide is not as corrosion resistant as some of the other options available for improving corrosion resistance.

The black oxide finish can be easily erased. To prevent this, tape the tip to create a tighter fit and prevent scratches if it slips off the unit.

Black residue from fasteners may come off, so for some applications it is recommended to dry them before use. This extra step can be labor-intensive if many fasteners are needed.

Black oxide fasteners are widely used in the automotive industry due to their glossy black appearance. This appearance can deteriorate very quickly even in hot environments. Often, after a coat of black oxide is applied to a fixative, they are placed in an oil bath for an additional layer of protection. The oil residue that remains on fasteners will begin to turn brown when in high temperature environments. Many users find that the screws seem to rust prematurely. It is not recommended to place black oxide screws on or near engines.

Custom coating for fasteners

locknuts with black nylon insert

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