Surface coatings for screws
– For extra performance
High-quality stainless steel screws deliver even better performance when they are coated. Surface coatings furnish screws with a thin layer that is a few microns thick
that effectively modifies the surface of the screws adding new or improved properties.
1. Less friction
2. Prevention of cold welding
3. A more decorative appearance
4. Even better protection against corrosion
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.
- Lubricant: A lubricious coating is applied to the entire screw in a dip or with a drum coating.
This lies against the surface of the screw as a dry and transparent film.
- Galvanizing: A risk of contact corrosion exists when contact between stainless steel and a less noble metal takes place.
This can be prevented by a zinc coating.
- Teflon: The PTFE plastic, better known under the brand name Teflon, is a proven form of corrosion protection and friction
reduction method. This very durable plastic is equally resistant to UV radiation, chemicals and high temperatures.
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.