Hexavalent hard chrome plating is under severe attack by environmental extremists.
Eric Svenson Sr.California is even considering banning the use of chromic acid completely. Some of us fear that California’s actions are a test balloon for adoption by the EPA. Having concern for the environment is admirable, but the regulators are ignoring the obvious.
Their recent actions are unjustified because these regulators make assumptions and use incorrect data regarding Hex-Cr’s actual harm to humans and the environment. There is also the issue of how critically important Hex-Hard Chrome is to America’s economy and defense. Eliminating or restraining it will have disastrous consequences.
The reality is that chromic acid is no more hazardous than a wide variety of other commonly used industrial chemicals.
The reality is that chromic acid is no more hazardous than a wide variety of other commonly used industrial chemicals. It has already been demonstrated that Hex-Cr can be used safely with no discharge to the environment (land, water, or air stream) and no harm to the employees. In fact, Hex-Cr has already been proven to be sustainable with literally zero emissions. But the ‘Green Movement’ still wants us to switch to the unproven, overly expensive, and ill-advised trivalent (Tri-Cr) hard chrome process.
This presents several enormous problems. Many of Tri-Cr’s metallurgical properties are unknown and could be dangerous where a part’s longevity is required because its mechanical properties are poorly understood. What is known, however, is that the Tri-Cr deposit falls short in several essential areas, particularly:
- Tri-Cr is less crystalline and contains carbon, thereby making it brittle.
- Its structure contains large macro-cracks that extend down to the substrate.
- The internal stress in the Tri-Cr deposit is much higher than Hex-Cr.
In short, Tri-Cr is not a viable replacement for the already proven and safe Hex-Cr process. Besides Tri-Cr’s questionable deposit properties, there are several other important issues to consider because of serious problems with the Tri-Cr process itself.
- Some Tri-Cr deposits are limited to less than 0.001” thickness.
- Tri-Cr cannot be Zero Discharged; it is a huge waste generator.
- The Tri-Cr bath uses complexing agents that make waste treatment very difficult and overly expensive.
- Tri-Cr requires a nickel underlayer for corrosion protection because of its wide and deep macro-crack structure that exposes the base metal. After-plate baking makes the Tri-Cr crack structure even worse.
- The throwing power and edge-burning problems with Tri-Cr are also an issue.
- The Tri-Cr process needs several additional tanks and support equipment, including waste treatment. It also requires considerably more floor space.
- The Tri-Cr process is much more expensive, including the bath chemistry, the equipment investment, and the operational costs.
- The Tri-Cr process is much harder to control and needs constant monitoring.
- The Tri-Cr bath is very sensitive to impurities, requiring frequent ‘bleeding.’ It also has a short lifetime requiring periodic bath dumps.
- With Tri-Cr, you become locked into a single supplier.
Industries choose Hex-Cr because of its outstanding metallurgical properties of hardness and wearability, along with its relatively low cost, ease of application, and zero discharge ability. That’s why it is the deposit of choice for a wide variety of critical components.
There is a reason that Hex-Cr was selected as the best wear surface almost a century ago.
Tri-Cr was tried and abandoned as problematic because Hex-Cr was so much better. The Tri-Cr vendors won’t tell you these things, nor will they disclose the extremely high installation and operating costs needed to apply it.
The above-mentioned deposit property issues of Tri-Cr are reported in a paper titled ‘Mechanical Behavior of Hard Chrome Deposited from a Trivalent Chromium Bath,’ published on 7 March 2022 by the Universite de Toulouse in Tarbes, France. This university boasts 4,500 doctoral students working in 145 research laboratories. It excels in the areas of science and technology. A copy of this paper, including references, is available from Plating Resources, Inc. Also available is a 14-page report with a more detailed comparison of the two processes.
Contact the author at PlatingResources@yahoo.com with any comments or questions or if you have any recent experience with the Tri-Cr process. Visit www.Plating.com
