Hexavalent chrome plating, or simply chrome plating, is the electrical application of a coating of chrome onto a surface for decoration, corrosion protection, and durability. An electrical charge is applied to a tank containing a chrome solution. The electrical charge causes the chrome metal particles in the tank to fall out of solution and deposit onto objects placed in the plating solution.
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A thick layer of chrome (10 to 500 μm or 0.01 to 0.5 mm, up to the thickness of a dollar bill) is deposited directly on the base metal (usually steel) to provide a smooth surface that is resistance to wear under extreme conditions. Tanks used in hard chrome plating operations contain chromic acid (containing hexavalent chrome), sulfuric acid, and water. Chrome electroplating requires constant control of the plating bath temperature, electrical power, plating time, and bath composition. Example parts include hydraulic cylinders, rotors, bearings, and agricultural equipment.
A thinner layer of chrome (0.003-10 μm or 0. -0.01mm, up to the thickness of fine particulate matter) is deposited usually over a layer of nickel previously placed on the base material (e.g., brass, steel, aluminum, or plastic) for looks and basic wear protection. Decorative electroplating baths operate on the same principle as the hard chrome plating process, but requires shorter plating times and operates at lower electrical power. Example parts include car parts, musical instruments, tools, and furniture.
Chromic acid anodizing is used primarily on aircraft parts and architectural structures that are subject to high stress and corrosion. Chromic acid anodizing is done via a different electrical process than hard or decorative plating and is used to provide a thin oxide layer (around 0.03 μm or 0. mm, about 1/th the size of a human hair) on aluminum that imparts the following properties: corrosion protection, electrical insulation, and ease of coloring. Example parts include aerospace components and precision machined parts.
Inhalation of hexavalent chrome over time may cause:
Workers who breathe in hexavalent chrome may experience irritation of the nose and throat. They may also show symptoms including sneezing, coughing, running noses, itching and burning. Repeated or lengthy exposures may cause sores in the nose, resulting in nosebleeds. Over time, some workers develop allergies to hexavalent chrome. For them, inhaling the particles may cause asthma symptoms.
Many chrome plating facilities are located in urban, low-income areas. They can expose nearby residents to hexavalent chrome and other dangerous byproducts that can lead to increased cancer rates in the surrounding populations. Because of the potential damage to the environment that metal finishing can cause, chrome plating facilities must treat their wastewater before releasing it. The byproducts also must go through a rigorous disposal protocol because of the dangers they pose.
From decorative etching to industrial and commercial applications, hard chrome coating is highly sought after due to its durability, versatility, and highly protective benefits. In this overview, we’ll dissect the two prevalent hard chrome plating processes, explain the benefits of thin dense chrome over other hard chrome plating applications, and discuss the required controls, industry specifications, and critical expertise that made Armoloy the gold standard in thin dense chrome coatings.
Chrome plating creates a thin layer of chromium on metal tools, equipment, and parts, with the goal of minimizing damage and extending their life.
The two main hard chrome plating processes are Hexavalent chromium plating and Trivalent chromium plating. Both processes involve placing a base metal into an electrolyte salt bath vat that contains different chemicals (chromium trioxide and sulfuric acid for Hexavalent chrome) where it warms to solution temperature. The plating is then applied for a period of time, so it attains the right amount of thickness required. For example, Armoloy’s thin dense chrome plating is applied much more slowly than traditional hard chrome plating, resulting in greater density and hardness exceeding 70 HRC vs. 65 HRC.
While it is the less toxic and more environmentally of the two, Trivalent chrome has seen more success in decorative vs. industrial purposes. An article in Finishing and Coating (November ) provides a comprehensive comparison of both processes, with Hexavalent chrome outperforming Trivalent chrome across a variety of factors.
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Looking at deposit properties specifically, Hexavalent chrome has an excellent track record for hardness, ductility, adhesion, lubricity, wear resistance, and corrosion resistance.
In contrast, little is known about how Trivalent chrome performs across most of these parameters and has yet to see improvements in the functional chrome coating applications. In terms of hardness and adhesion, we do know that Trivalent chrome deposits are softer and weaker, impacting wearability. Macro cracking is also common. Wear resistance and corrosion resistance are also poor. In fact, for many applications, Trivalent chrome shouldn’t be placed directly on stainless steel; rather, it requires a nickel underlayer. As a result of these factors, Trivalent chrome is less than ideal for most industrial applications.
For OEM engineering and design purposes, thin dense chrome has all of the high-performance benefits of hard Hexavalent chrome—harness, wear prevention, low coefficient of friction—but with additional anti-corrosive properties.
Why? Hard chrome is thicker (from 0. to 0. in.) than thin dense chrome (0. to 0. in.). Therefore, large cracks and porosity are common on surfaces coated with hard chrome; large, exterior, easy-to-access surfaces are best suited for hard chrome applications.
In contrast, thin dense chrome is not a micro cracked deposit, and therefore, doesn’t have the porosity and cracks found in conventional hard chrome plating. The high degree of uniformity and versatility that thin dense chrome provides reduces the post grinding and honing common in sizing processes. Finally, the lower deposit thickness also minimizes buildup and dimensional changes, making it ideal for interior, hard-to-reach areas where precise tolerances are paramount and part balance is necessary.
As a result, thin dense chrome is the top choice for mitigating metal failure problems and improving repair and maintenance outcomes. Armoloy offers an engineered thin dense chrome coating technology rather than simply a plating, and we’re able to customize our coatings to our clients’ exact specifications.
Armoloy has spent decades innovating and refining our thin dense chrome plating process. Our ISO : certification verifies our compliance, and various sensitive industries, including medical and food processing and packaging, approve our thin dense chrome plating. Our Innovation and Process Development Center’s subject matter experts work with new application inquiries to ensure proper documentation and certification.
Plating specifications:
Measuring and testing specifications:
Over the years, we have developed and refined our coating technology, giving Armoloy a distinct advantage in the marketplace—few conventional plating products can compare. Armoloy provides a full range of thin dense chrome surface coatings, including:
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