Why hard chrome?
Hard chrome can be applied in a wide range of industrial sectors. Surface coating with hard chrome provides resistance to corrosion and wear, without compromising the characteristics of the base metal. Hard chrome also has a wide variety of desirable properties and characteristics.
What is hard chrome?
Hard chrome plating is an electrolytic process using a chromic acid based electrolyte. The part is made the cathode and, with the passage of a direct current via lead anodes, chromium metal builds on the component surface.
A wide variety of parts can be coated; it requires only the proper fixturing, a large enough bath, sufficient lifting capacity and adequate power sources.
What are the benefits?
It is very hard
850 – 1000 HV (65 – 70 RC), harder than most industrial abrasives, combined with a low coefficient of friction.
Excellent adhesion to the substrate
Before plating, substrates are thoroughly cleaned so that the surface to be coated is completely free of contaminants. The final adhesion is achieved in the plating bath itself, where an initial reverse voltage removes any residual surface contamination.
Applicable to a variety of substrates
Steels, stainless steels, copper and brass are the most receptive metals for an adherent deposit. Aluminum and more exotic metals, such as Inconel, Hastelloy and titanium, are more difficult to plate, but with the proper pretreatment methods an adherent deposit can be achieved.
Excellent resistance to abrasion
Even under high contact stress it provides a very low wear rate with abrasive products such as textiles, paper and foodstuffs. With thick deposits, it gives excellent wear resistance against sand, coal, cement, limestone, glass fibers, etc.
Abrasion being the most common and destructive wear process in industry, hard chrome has the potential to solve many problems in pumps, valves, bearings, etc., across a wide range of industries, including pharmaceuticals, chemicals, oil and gas, textiles, printing, food, mining, aerospace and many others.
Low application temperature
The process temperature has no effect on the properties of the substrate, since it does not exceed 60 °C.
A wide range of geometries
With careful attention to anode design and fixturing, chrome plating can be applied evenly to flat surfaces, fine bores (even with large aspect ratios), cylindrical shafts or rollers, holes and close-tolerance areas.
A glossy and attractive finish
It responds well to grinding and polishing (not machining), providing ideal surfaces for sensitive products such as textiles and paper.
A stable, corrosion-resistant coating
Suitable for most organic acids and gases (not chlorine), excellent in hot oxidizing or reducing air, and with commodities such as beer, sugar, brine, coal gas, cyanides, fruit acids, molten glass, glue, milk, oils and fuels.
Frequently asked questions
On what materials can hard chrome be applied?
Hard chrome may be deposited on a wide variety of metals. Steel, stainless steel, copper and brass are the most receptive to an adherent deposit. Exotic metals, such as aluminum, nickel-based alloys (Inconel, Hastelloy) and nitrided steels, are more difficult to chrome, but with proper pretreatment methods it can be achieved.
What deposit thickness of hard chrome can be applied?
Deposit thicknesses range from “flash” (very thin deposits, 0.0005” to 0.001”) to “heavy build” (in some cases up to 0.040”). The final application of the part generally determines the thickness required.
As the thickness of hard chrome increases, surface defects and roughness are amplified, because hard chrome has no leveling effect. Usually a greater thickness than required is applied, and the part is then ground to the desired dimensions.
What is the hardness of the chrome deposit?
The hard chrome deposit has a hardness of about 900 HV (66 Rc). Hardness testing should be done in accordance with ASTM B-578, except that a Vickers indenter and a 100 g load must be used (QQ-C-320); higher loads would perforate the chrome layer and give erroneous results.
What chrome thickness should you specify?
If you do not have a thickness requirement, drawing or specification, please contact us. We can help you discuss your application and determine the required thickness.
Does Agro Crom perform decorative chrome?
Agro Crom does not perform “decorative chrome”, such as that used on car bumpers, motorcycle fenders, tables, chairs, etc.
Can hard chrome be removed from a part once it is applied?
In most cases the existing chrome, whatever its thickness, can be removed by chemical stripping or grinding. In many cases chemical removal is recommended.
Does hard chrome plating embrittle the part?
Yes, as in all electrochemical processes, hydrogen embrittlement occurs. This applies to steel parts with a hardness above 40 Rc, for which a de-embrittlement treatment is recommended.