Hard Chrome Plating: Extending the Life of Your Equipment
It is likely that when you hear the terms “chrome plating”, “chromium plating” or even just the term “chrome” you visualize a shiny metal surface. Pop culture has jumped all over the bandwagon as it looks cool and represents strength and durability. But aesthetics aside, chrome has a very unique set of characteristics that provide value in many industrial and commercial applications.
In this article we will dive into a brief history of chrome plating, what the chroming process is and how industry takes advantage of its many benefits. But before we go any further, lets address the most popular question about chrome…
Is Hard Chrome the same as Decorative Chrome?
The short answer is no. The biggest difference is the applied thickness. Although the process is similar, hard chrome plating and decorative chrome serve different functions:
- Hard chrome is used in industrial or commercial applications to improve the life span and performance of equipment, especially that which sees heavy, repeated use or is exposed to extreme temperatures or climate.
- Decorative chrome is primarily used for aesthetic appeal. Although it has similar benefits to hard chrome, it is applied much thinner and does not hold up against heavy industrial or commercial use. Think the automotive industry and the classic vehicles sporting chrome bumpers and mirrors, etc.
What is Hard Chrome Plating?
Hard chrome plating is a form of electroplating that is popular for its use as a surface coating. Long prized for its hardness, ability to minimize sliding wear, corrosion protection and for extending the life of metal parts, it can be found in many applications such as hydraulic and pneumatic cylinders, pump shafts and rotors, swivel posts and bodies, and downhole tools. In many cases it is used on components where there is metal-to-metal contact between moving parts due to its low coefficient of friction.
The terms “industrial chrome”, “engineered chrome” and even simply “hard chrome” are used interchangeably and all describe the same process.
Hard chrome can be applied from 0.0005” – 0.025” (0.012mm – 0.635mm) thick for a wide range of applications. Hard chrome is classified as a “cold” process where the operating temperature of 50 – 65 degrees Celsius ensures no damage to the physical or mechanical properties of the base material.
So, Why is Hard Chrome so Popular?
The success of hard chrome plating can be attributed to the many benefits and unique characteristics of the process. An increased hardness alone would be insufficient to secure widespread use due to the number of hard materials and hardening processes available. It is the combination of the improved qualities below that give chrome plating such remarkable results.
Electro-deposited chrome is extremely hard, typically 66-70 HRC. Through hard chrome plating, the surface hardness of your component is increased without modifying its properties.
Hard chrome has a very low coefficient of friction when compared to steel. This allows a component to operate at a lower temperature during operation, extending the life of your equipment.
The high hardness and low frictional properties of hard chrome, provide excellent resistance to abrasion and mechanical contact.
Hard chrome has a very high resistance to atmospheric oxidation and a good resistance to most oxidizing and reducing agents (with the exception to Chlorides and other Halides).
Sacrificial Wear Layer
Since hard chrome deposits can be removed with chemical strippers, without destructive effect to base material, the part can be stripped and re-plated repeatedly when worn.
Microcrack characteristics of hard chrome allows for oil retention which improves lubricity of plated parts.
A hydraulic cylinder stage is lowered into an electrolytic bath in preparation for hard chrome plating
The Electroplating Process
Electroplating is the process of applying a metal coating on another piece of metal (or conductive surface) through electro-deposition. Chromium plating, copper plating and silver plating are all specific types of electroplating.
Both an anode and a cathode (the part to be coated) are immersed in an electrolytic bath that is composed of a solution of salts, including the metal to be plated. An electrical (DC) direct current is passed through the solution, effecting the transfer of metal ions onto the cathodic surface.
The result is a completely adhered layer of chromium that will extend the life of your parts and components.
Prepping a Workpiece
Before chrome plating a workpiece, it needs to be prepped for ideal chrome adherence. All residual traces of dirt and surface impurities are removed manually and the piece is degreased to remove heavy soiling.
The next step is pre-polishing. The workpiece is brought to a consistent size and surface finish. This is done either by running a sanding belt over the turning piece or by grinding.
Then finally before plating, the workpiece is masked to ensure only the intended areas of the workpiece are chromed. This is achieved through the use of tapes, shields and special plating fixtures comprising the holding mechanism. Specialty fixtures are commonly produced for the countless shapes and sizes of components required to be chromed.
Coating thickness gage used for non-destructive measurement of non-magnetic coatings on steel, such as chrome plating
After plating, the workpiece is removed from the bath and polished or ground to a precise finish size. Almost any required finish can be achieved, but due to its extreme hardness proper stones, belts, wheels must be used.
A hollow workpiece, such as a hydraulic cylinder stage, is honed to remove residual chrome build up on the inside diameter. Most honing and grinding shops are qualified to hone or grind chromium. If required, consult your local chrome shop.
Due to its combination of multiple properties and benefits not possessed by any other process available, hard chrome plating provides value to almost every major industry, and has done so for almost a century.
Like any industrial process, strict health and safety procedures must be established when dealing with chrome and environmental standards must be stringently monitored and adhered to.
But with proper handling and care, the many benefits of hard chrome plating can go to work for you, extending the life of your equipment and reducing costly downtime.
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