Why chromium plating is extensively used in industries
Many industries have Plating lines and decorative chrome is almost always plated on top of nickel or copper or a nickel-plated layer because it creates a seal on the substrate to prevent corrosion problems. There are two main reasons why chromium is used in plating lines. First, it is either used for its decorative effect because the thin coating serves as a non-tarnishing, durable surface finish. Second, heavy coatings of hard chromium have special properties like resistance to heat, wear, corrosion, erosion and low coefficient of friction including anti-galling. Decorative chromium can be found in most automobile parts like bumpers and trims and household items where aesthetics is deemed important. Hard chromium differs from decorative chromium not only through the way it is used but the deposit thickness. A hard chrome deposit is usually within the range of 0.0005” to 0.0100” in thickness.
Advantages of hard chrome plating
The electro-deposition of hard chrome is carried out in most industries as a way to prolong the life of most metal parts that are subjected to wear, friction, abrasion and corrosion. These parts require protection when newly manufactured. Hard chrome has low surface energy and it is typically deposited on parts that slide or revolve or on machine parts, engines, compressors, pumps and pneumatic tools. Since a hard chromium deposit on a surface provides corrosion resistance, it has become a popular application. The process of chromium plating is also cold and it can impart a very hard surface on delicate parts without distorting or changing the physical properties of a substrate. This is more popularly referred to as surface hardening.
Hard chrome deposits have a hardness range of 56 to 74 R.C. respectively. Basically, hardness range is also dependent on the type of bath used. The higher the Rockwell C or R.C. number, the longer will be the expected service life of a component that has been subjected to chrome plating. If deposit hardness is the objective in the Plating lines, it is best to use the highest R.C. value. A component that has surface hardness exceeding 70 R.C. will provide the longest possible service life. In some cases, decorative chromium also has the same surface hardness range as hard chrome because of the greater thickness of deposit used on a component. With a chrome deposit of 0.002”, the surface will reflect the properties of chromium and not the substrate. The most expensive and durable process of chrome plating is achieved when a metal part if first coated with copper and then nickel before the application of chrome plating.