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Hard Chrome Misting and How to Improve the Plating Operation

Chromic acid solutions generate considerable chromic acid misting when electrified, sometimes called fuming.

Eric Svenson Sr.Eric Svenson Sr.This is caused by the DC reducing the chromic acid in the solution to a chromium metal deposit. Several preceding reactions are involved, including the breakdown of water, which generates significant amounts of hydrogen and oxygen gassing. These gasses form bubbles that burst at the solution level, propelling chromic acid mist into the surrounding environment.

Chrome misting creates several problems for the chrome plating shop:

  1. It’s a health hazard for the employees.
  2. It causes a hex-chrome discharge into the atmosphere.
  3. It results in a messy workplace.
  4. It often increases copper impurities in the plating bath.

Ideally, there wouldn’t be any chrome mist build-up on the bus bars, fixtures, tank rims, nearby equipment, or even the shop floor. This misting on the bus bars is one cause of increasing copper impurities. Keeping the anode and fixture contacts free of chrome mist build-up also ensures better DC connections and improved plating results. This is difficult with older system designs but entirely possible using today’s innovations; more on later.

Regulations

The EPA and OSHA identified chromic acid misting issues and implemented regulations limiting the maximum employee exposure and the air discharged from the ventilation system. According to our data, the current federal limits are shown below. Some states follow these limits, while others are more restrictive.

  • Employee Exposure: 5.0 µg/cubic meter of air
  • Air Discharge: 0.006 mg/dscm (dry standard cubic meter of air)

Many hard chrome operations have difficulty meeting these regulations, to say nothing about the expense involved and its impact on their profitability. This becomes even more difficult with the constant tightening of the regulations.

Mist Control

Several methods have been used to control chromic acid misting. Some operations rely on stand-alone methods, while others combine several to achieve compliance and a clean workplace.

These include floating polypropylene balls, tank covers, fume suppressants, and ventilation systems. The pros and cons of each approach follow:

Floating Polypropylene Balls

Floating polypropylene balls (typically 1-2” in diameter) had seen rather widespread use in earlier years. To be effective, though, these needed to be 3-4 balls deep; otherwise, the chrome misting escape around them. However, floating PP balls have several application problems, and many operations have been replaced with better options; some of their issues include the following:

  1. They tend to get caught between the anodes and the fixtures.
  2. These frequently end up in the rinse tanks and on the shop floor.
  3. Over time they form an oily scum on the bath surface that coats the parts entering the tank, which causes several plating problems.

Tank Covers

Various designs and materials have covered the chrome tanks during plating.

Generally, these have not proven overly successful or very work-efficient. For one, they greatly slow production because of the time lost in placing and removing or opening and closing them. Another issue is the considerable amount of chrome mist build-up on their underside, which creates a mess that constantly needs rinsing.

Some lid designs leak fumes around their ends, posing safety concerns for workers, environmental problems, and a filthy shop.

Fume Suppressants

Fume suppressants are chemical additives for chrome baths that suppress the misting by creating a thick foam blanket or lowering the bath’s surface tension.

Foam blankets were the initial approach but have lost favor because of 1) the extremely loud and sometimes dangerous hydrogen explosions caused by contact arching and 2) the foam frequently gets drawn into the exhaust hoods.

An improvement was the development of fluorinated surfactants. These reduced the fuming by lowering the bath’s surface tension rather than creating a foam blanket. They were available in low-foam and non-foaming types based on semi-permanent or permanent surfactants. Permanent surfactants were preferred because they didn’t break down due to the oxidizing nature of a hot chromic acid solution, which caused excessive trivalent build-up and other plating issues.

Fume Suppressant in Hard Chrome BathFume Suppressant in Hard Chrome BathWhile workable, fume suppressants became excessively expensive while also causing monitoring and recording headaches for the operation, factors that greatly increased the operational costs.

The majority of these permanent fume suppressants were based on PFOS chemistry. However, the recent EPA ban on PFOS chemicals raised havoc with the hard chrome industry and created a mandated shortage of suitable fume suppressants. This left many shops scrambling for a replacement where the only alternative was using a PFAS-based fume suppressant, a similar polyfluorinated chemical. The EPA is looking into banning all polyfluorinated chemicals shortly, including PFAS, PFOA, and other related ‘forever chemicals’. History tells us that anytime the EPA ‘looks into something,’ it’s typically just a matter of time before it’s implemented.

Therefore, the fume suppressant replacements will likely be short-lived, leaving many shops with a serious dilemma about controlling their chrome misting.

Ironically, the EPA first regulated chrome discharges, then somewhat forced platers into using a fume suppressant, and finally banned the most effective chemical used in those suppressants.

Ventilation Systems

The original chrome bath ventilation system was a simple wall fan behind the tank. This forced large quantities of chrome mist outside and made a mess of the building, property, and the environment. For obvious reasons, this approach is no longer being used. Wet scrubbers were then employed as a stand-alone device. This was an improvement but did not meet the updated chrome emission standards. The next evolution was the development of mesh pad devices, some of which also included a HEPA filter.

With the proper design, the mesh pad/HEPA filter system can meet today’s stringent emission standards. However, these systems require a frequent wash-down schedule and replacement of the HEPA filter, which tends to plug with particulate matter.

Several new developments using the mesh pad approach are available for operations looking to update their system for true Zero Discharge and environmental compliance assurance.

Mist Reduction

Reduced Misting from a Triple Catalyst Bath.Reduced Misting from a Triple Catalyst Bath.Eliminating the misting in hex-chrome plating is impossible, but there is hope. The answer to this dilemma is twofold:

  1. Reducing the amount of misting generated and
  2. Sufficiently controlling it to eliminate the problem

A higher-efficiency plating bath, such as the Triple Catalyst Bath, can reduce mist generation. A typical hard chrome process may operate at only 18% efficiency, meaning that 82% of the DC is used to generate the misting.

With the proper bath controls, this efficiency can be increased to around 30%, so more of the DC is used to plate chrome and less to create misting. In addition to reducing misting, these high-efficiency baths also offer increased plating speeds and improved metallurgical properties of the chrome deposit.

Improving Mist Control

Several methods are now available to control chrome misting. The goal is to prevent its escape from the tank and keep most of it from entering the ventilation hood. As much as 85% of the misting can be returned directly to the bath, reducing the ventilation system's load. Details on how this is accomplished vary with the particular application and are part of the Sustainable Hard Chrome approach.

Sustainable Hard Chrome

Sustainable should not be confused with the Green New Deal or climate change concerns. Instead, sustainability in our industry simply refers to a new method of hard chrome plating where:

  1. The chemistry is captured for reuse.
  2. There are no processed chemicals for waste treatment.
  3. Any minute traces of chrome released are below detectable limits (essentially zero).
  4. The workers are significantly below the PEL limits for chrome.
  5. The shop stays clean.

This approach keeps the regulators at bay and significantly lowers operational costs. In addition, the operation stays compliant regardless of how stringent the discharge limits become in future years. Why? Because they can’t regulate below Zero.

The Sustainable Approach has been confirmed by an EPA-approved laboratory as follows:

  • The EPA stack discharge was essentially Zero (below detectable limits).
  • The employees tested between 55 - 156 times below the OSHA PEL limit.

As unbelievable as those results are, what’s even more amazing is that they were accomplished while operating at 20,000 DC amperes over a full eight-hour day—and without using a fume suppressant. Most hard chrome operations operate well below that ampacity, so their results are expected to be even better. The savings gained by eliminating a fume suppressant are the icing on the cake.

Adopting Sustainable Technology

Typical Old School Hard Chrome Plating Tank.Typical Old School Hard Chrome Plating Tank.Many hard chromes operating today were designed years ago before this technology was available. They suffer from higher operating costs and constant aggravation from regulators. Many have upgraded their equipment, perhaps several times, to meet the ever-increasing regulation limits, yet their future remains uncertain.

Most hard chrome operations can be upgraded to adopt this sustainable technology. This involves renovating the operation using innovative equipment designs and a high-efficiency plating process. This combination has proven to considerably exceed all EPA and OSHA standards.

Applying the sustainable concept to an existing plating line typically involves:

  1. An on-site review of the existing installation.
  2. Considerations for the plating bath, the anodizing, fixturing, and related items used.
  3. An engineering period to determine what modifications are needed and to provide
  4. the various specifications and costs.
  5. Procuring and installing the needed modifications.
  6. A brief training program for maintenance and operation.

The sustainable approach is a technological breakthrough that allows continued hard chrome plating in an environmentally safe manner. This extends well into the future without concerns over additional regulatory encroachments. Hex-hard chrome has proven to be the absolute best wear surface available; there’s no need to replace it with more costly processes or dubious ones like trivalent hard chrome, which produces excessive waste products.

Forward Planning

The hard chrome industry is still in regulatory flux, with uncertainties about its future. This has caused a significant reduction in the number of hard chrome operations in recent years, as many shops have gone out of business.

Some feel the market was overly saturated, and the reduction resulted from natural consolidation. However, this allowed those operations to continue because they were able to increase prices to reflect actual market conditions. This trend is expected to continue for many years to come.

The takeaway is that operations that upgrade to the Sustainable Approach will survive and thrive with further market reductions, less competition, and lower production costs. For OEMs, their operations will continue unencumbered by future discharge regulations and avoid threats to their production capability.

Now is the time to develop a sustainable hard chrome strategy. Consider the extreme loss if your operation were closed due to future non-compliance issues.

Eric Svenson Sr. is CEO of Plating Resources and a Master CEF and IUSF member. Visit www.Plating.com. If you have any questions or wish to explore this topic further, please contact Vicky at Vicky@Plating.com.