Merit Partnership Pollution Prevention Project for Metal Finishers


INNOVATIVE COOLING SYSTEMS FOR HARD CHROME ELECTROPLATING


INCREASED PRODUCTIVITY AND REGULATORY COMPLIANCE


The Merit Partnership is a joint venture between U.S. Environmental Protection Agency (EPA) Region 9, state and local regulatory agencies, private sector industries, and community representatives. This partnership was created to promote pollution prevention (P2), identify P2 technology needs, and accelerate P2 technology transfer within various industries in southern California. One of these industries is metal finishing, which is represented in the Merit Partnership by the Metal Finishing Association of Southern California (MFASC). Together, MFASC, EPA Region 9, and the California Manufacturing Technology Center (CMTC) established the Merit Partnership P2 Project for Metal Finishers. This project involves implementing P2 techniques and technologies at metal finishing facilities in southern California and documenting results. The project is funded by the Environmental Technology Initiative and EPA Region 9.

This fact sheet provides a summary of chrome emission regulations, information on external cooling systems for hard chrome electroplaters, and the benefits of implementing such systems, including reduced waste, decreased labor and material costs, and increased plating capacity. It also summarizes the results of an external cooling system case study conducted at a hard chrome electroplating facility in southern California.


THE DEVELOPMENT OF HARD CHROME AIR EMISSION REGULATIONS

Regulation of bath temperature and mixing of the plating solution are essential for successful hard chrome electroplating. The hard chrome electroplating process involves long plating times and intense heat generation. Failure to both dissipate the heat and maintain a uniform solution temperature impairs plating quality. In the past, hard chrome electroplaters maintained optimum plating temperatures (typically within 2 F of the target temperature of 135 F) by directing air bubbles upward through the plating solution. Turbulence created by the bubbles both mixed the plating solution and transferred heat from the solution to the air by evaporative cooling. Air bubblers were an easy and efficient means of maximizing production because they addressed the most problematic aspects of hard chrome electroplating: heat dissipation and solution mixing. As the bubbles reached the plating solution's surface and burst, air emissions containing chromium were created.

EPA introduced the National Emission Standards for Hazardous Air Pollutants (NESHAP), which became effective in January 1995, to regulate industrial air emissions. One part of NESHAP mandates that all hard chrome electroplating facilities meet several requirements established to minimize chrome emissions in plating operations involving chrome. Hard chrome electroplaters have been able to meet these requirements by discontinuing the use of air bubblers and implementing fume suppressant systems made up of plastic balls or foam that float on the surface of the plating solution.

COOLING HARD CHROME ELECTROPLATING SOLUTIONS

To maintain plating solutions that are well mixed and at the correct temperatures without the use of air bubblers, most facilities have opted to install cooling coils on the interior walls of their plating tanks. Figure 1 shows an internal cooling system of this type. However, internal cooling systems have drawbacks. For example, slower plating rates, increased downtime, and higher reject rates have been experienced after installing such systems. Parts are considered rejects by the electroplater if, after plating, they
A Rejected Part Creates Triple the Waste of a Successfully Plated Part

  • Raw materials used for initial plating
  • Initial plating stripped, neutralized and discarded
  • Raw materials used for replating

By reducing rejection rates, a facility can cut raw material usage, waste generation and labor costs.
do not meet specifications because of discoloration, poor adhesion, roughness, lack of hardness, or high porosity.

The rise in reject rates causes more waste generation (see Figure 2) and increases operation and maintenance (O&M) activities and repair costs. These increases hit hard at electroplaters' bottom lines.

The use of internal cooling systems decreases productivity for several reasons:


DEVELOPING A BETTER COOLING SYSTEM AT MICROPLATE

After NESHAP was enacted, internal cooling systems were the most commonly chosen alternative for cooling hard chrome electroplating solutions. External cooling systems were not generally considered an option until recently, when improvements in heat exchanger technology and refinements in their design made them a more attractive option. The primary improvements made in such systems involved both increasing the corrosion resistance of their components and overall system durability.

To assess the impact of an internal cooling system on the P2 and production aspects of a hard chrome electroplating facility, the Merit Partnership sponsored a P2 project involving evaluation of an external cooling system at the Microplate facility in Inglewood, California. Microplate is a relatively small facility covering about 10,000 square feet and employing seven people. There are nine hard chrome plating tanks at Microplate, three of which are currently used. Typically, one or two workers handle all the hard chrome electroplating duties. The facility specializes in thin, dense chrome electroplating for aerospace, vehicle, and various manufacturing customers.

Microplate found that the shortcomings of its internal cooling system were lowering productivity and creating a variety of operating problems. Reject rates increased because the poor mixing and uneven plating temperatures caused the chrome plating on some parts to fail hardness specifications, or experience poor adhesion, roughness, or porosity. This led to lower part loading rates (that is, fewer parts per plating run), and longer setup and plating times.

In an effort to improve production, Microplate installed an external cooling system at the facility in June 1995. Figure 3 shows the primary components of the external cooling system, including (1) a titanium, plate-type heat exchanger; (2) a 3/4 -horsepower, vertical discharge, centrifugal pump; (3) a cooling tower; and (4) a return header. Each component was designed to overcome the corrosion problems associated with exposure to chromic acid. The pump and all the piping that carries the plating solution are made entirely of corrosion-resistant chlorinated polyvinyl chloride (C-PVC). The seals and gaskets for the pump, for the piping, and between the plates in the treat exchanger are made of Viton@, a synthetic fluorinated material that is highly corrosion-resistant.

In the external cooling system, the plating solution is continuously circulated by the pump, which is submerged atone end of the tank, through the "hot" side of the heat exchanger. As seen in Figure 3, the solution returns to the plating tank via a submerged, horizontal header with exit holes along its entire width. The header lies at the opposite end of the tank. The flow of solution through the cool" side of the heat exchanger is controlled by a thermocouple with a set point 1 F above the ideal plating solution temperature. When the thermocouple is activated, the cooling water loop runs through the heat exchanger to a roof-mounted cooling tower.

IMPACT OF THE EXTERNAL COOLING SYSTEM

Microplate found that its application of an external cooling system solved many of the problems associated with internal cooling coils, thereby raising productivity and eliminating wastes associated with rejects. Most significantly, because of the higher cooling capacity of the plate-type heat exchanger used in the external cooling system, the number of parts Microplate could process is limited only by the size of the tank, and not by the capacity of the cooling system. By continuously circulating all the plating solution and returning the solution to the tank through a dispersion header, the system achieved complete solution mixing and maintained a uniform temperature throughout the solution. Also, with only a small, submersible pump at one end of the tank and a return header at the other end, nearly all the tank space became available for plating.

To calculate the impact of the external cooling system on its hard chrome electroplating process, Microplate first categorized parts according to plating difficulty (Types A, B, and C, with Type A being the easiest to plate and Type C being the most difficult; see Figure 4). Most parts with plating defects requiring work (that is, rejects) were Type Band C parts; Microplate chose to monitor the impact the external cooling system by tracking the number of rejects associated with these two types of parts. Microplate recorded and compared reject rates for two hard chrome electroplating tanks, one tank with an internal cooling system and one with an external cooling system, and found that the reject rate for the internal cooling system was reduced by over 90 percent. The reject rate for Type B parts decreased from 10.2 percent with the internal cooling system to 0.8 percent with the external cooling system. The contrast was most evident for Type C parts, as the reject rate decreased from 12.4 percent to 0.3 percent with an external cooling system (see Figure 5).

Microplate also found that the external cooling system significantly reduced waste associated with the electroplating process. Microplate calculates that production of sludge containing chrome generated during stripping decreased over 90 percent because of the installation of the external cooling system. Microplate also tracked the labor associated with replating rejects and found that the decrease in reject rates immediately reduced labor costs associated with rejects (that is, the labor costs for troubleshooting, stripping,
Calculating Costs

Guidance for Calculating Costs for Raw Materials and Waste Disposal from Rejects

  • 0.59 ounce of chromium per square foot of chrome plating per 0.001 inch of thickness
  • average cost of chromic acid is $3/pound
  • 3-5 pounds of sludge generated for each 1 pound of chrome plating stripped
  • cost of sludge disposal is $300/ton
  • fume-suppressing foam is $50/gallon
reracking, and replating) and by about $300 per month when combined with other savings (see Figure 6).

Long-term cost savings will result from Microplate's use of the external cooling system. Although Microplate estimates that the installation cost for an internal cooling system is less than that for an external cooling system, the company is most impressed with the increase in production capacity (at least 25 percent) resulting from its use of the external cooling system. Previously, Microplate had to limit the load (amperage) into the electroplating system because of the cooling system's limitations. With the installation of the external cooling system, cooling capacity and solution mixing are no longer limiting factors. Without these restrictions, Microplate is able to load the tanks with more parts and increase the amper age applied to the plating solution. Additional sources of increased productivity associated with the external cooling system include improved mixing, simplified racking, and diminished setup time.

Costs Category Due to RejectsMonthly Savings
Raw Materials
Sludge Disposal
Labor (14 hrs @ $18/hr)

Total
$ 5
$ 40
$252

$297
Figure 6: Savings due to Pollution Prevention


External cooling $8-$15/gallon of plating solution cooled
Internal cooling $6-$10/gallon of plating solution cooled
Figure 7: Comparing Capital Costs for Cooling


OTHER APPLICATIONS OF THE EXTERNAL COOLING SYSTEM

The external cooling system is potentially applicable to other electroplating processes, with different heat exchange materials being used:




ADDITIONAL SOURCES OF INFORMATION

For more information about the Merit Partnership, external cooling systems, or chrome emission regulations, you can contact any of the following individuals:

Laura Bloch (EPA Region 9) (415) 744-2279
John Siemak (CMTC) (310) 263-3097
Dan Cunningham (MFASC) (818) 445-3303
Steve Peterman (Microplate) (310) 478-0837
Ali Ghasemi (South CaliforniaAir Quality
Management Division)
(909) 396-2451


Assistance for this fact sheet was provided by PRC Environmental Management, Inc.