Surface coatings for screws
– For extra performance

Against cold welding and for less friction

Cold welding, also known as “seizure” of the screw, severely hinders removal and maintenance for affected screw connections.
This is because the metallic work-pieces develop such a close connection with the molecular chains that they can only be loosened
by damaging the surfaces. Preventing against cold welding is fortunately not difficult. The countermeasure involves introducing a
lubricious coating into the screw connection. As corrosion protection, this reliably prevents against the screws seizing.

The decorative appearance of screws

High-quality products should also look high quality. Design-oriented screws can contribute to this aim with surface technology making
it possible. These following main methods of decorative surface treatment are possible:

• Chemical blackening: The screws are immersed in an acidic or alkaline solution during this process, which is also known as blackening. This forms a decorative black layer known as a patina.
• Electro-polishing: The screws are furnished shiny surfaces in this surface technology. For this purpose, a thin layer of material is removed using electrochemical means. Chemical treatment (passivation) furnishes the screw with a layer that protects it from oxidation. Owing to
  the hygienic and smooth surfaces it provides, this surface technology is used by companies in the pharmaceutical and food industry.
• Pickling and passivation: During pickling, the screws are dipped into an acid bath to clean off greases, oils and dirt. The treatment in the passivation bath allows the protective layer (passive layer) on the stainless steel to form faster again and thus protect the screws against environmental influences.

Improved corrosion protection for screws

If a screw requires increased corrosion protection, this can be provided by giving it a surface coating. Example: Hanger bolts are only available in the stainless-steel grade A2. If users require corrosion protection that corresponds to A4, this can be achieved with a coating.

The standard for this is zinc flake coating. The zinc flake applied in liquid form guarantees excellent corrosion protection. Screws protected with a zinc flake coating are also resistant to moisture and cleaning agents as well as fuel, engine oil, brake fluid and antifreeze. This makes zinc flake coating a preferred surface technology in the automotive industry. Coated screws like these are also excellent for use on outdoor applications, such as decks or facades.

Do you have any test certificate,
special packaging or special packing needs?

Our sales team will be more than
glad to help you and inform you
about the many options we have available for mechanical machining, thread locking and head painting.