When choosing a corrosion protection for hardware one must be aware of the environment and any environmental restrictions the assembly may be subject to as well as the amount of corrosion the assembly will be exposed to.
In February 2003, the European Union adopted the “Restriction of Hazardous Substances Directive” or RoHS, as it is commonly referred to. The RoHS directive aims to restrict certain dangerous substances commonly used in electronic equipment. This practice has now been accepted worldwide by the medical, food, farm implement and auto industries, as well.
The following are the most common corrosion protections:
Hot Dip Galvanizing
Heavy zinc layer, usually 80-100 microns thick with the minimum practical thickness around 40 microns. Applied by dipping parts into molten zinc, this process is not recommended for higher strength grades. It is difficult to maintain thread tolerances and usually means over tapping the threads of the nut or female mating part. However, this is an excellent choice for outdoor use, such as highway construction.
Electrolytic Plating
The most common method for commercial hardware. Several different metals can be used with the most common being zinc. Other metals could be nickel, copper, etc. When used on fasteners with property class 10.9 (Grade 8) and case hardened fasteners such as tapping and thread forming screws, the risk for hydrogen embrittlement increases. The plating thickness may vary from 3-15 microns.
Mechanical Plating
An alternative to electro plating that can be used on materials sensitive to hydrogen embrittlement. It is simply a method of blasting the fasteners with very small pigments and a carrier, causing a fusing of plating metal (zinc, nickel, aluminum etc.) to the fastener surfaces. The thickness is about the same as for electro plating.
Coatings
The most common being manganese or zinc often used in high strength applications. Recent developments in engineering class coatings promises to solve hydrogen embrittlement but also improves the control of lubricity, which is very important in controlling torque tension relations.
Each type of corrosion has its own advantages and disadvantages. That’s why it is import to understand the environmental and mechanical requirements for each application before deciding on a finish. To learn more about how to determine the best plating for your environment, contact Bossard at ProvenProductivity@bossard.com.
Best Plating for Your Environment by Bossard
