MANUFACTURE OF FABRICATED METAL PRODUCTS # 1

This facility is an electroplating unit that performs zinc, nickel, brass, and chrome plating. Seventy percent of production is comprised of brass articles. The facility operates with 23 workers who work in a single 8-hour shift, 300 days a year. Approximately 15 m² of metal surface is finished per day.

Facility operations can be divided into five main steps:

Polishing paste is applied to stationary belt sanders to provide the necessary abrasion. The parts are then polished with the sanders. Dust generated by the polishing process is collected by vacuums connected to each machine.

Prior to metal finishing, many parts are cleaned in a vapor degreaser that uses trichloroethylene (TCE) to remove grease and other impurities. Parts removed from the degreaser are dried with paper towels.

The facility electroplates many different kinds of parts. Several parts are hung on special racks that are constructed specifically to handle the part. Other pieces are plated in baskets that are placed directly in the solutions.

The metal finishing line consists of washing tanks, rising tanks, and nickel and chrome plating and recuperation baths. A copper cyanide bath is located across from the line and is used to plate zamak before it is plated to nickel and chrome. All plating is manual. Times are not exact, and there considerable variation in soaking times among different parts and different workers.

Before gilding, parts are rinsed in special rinse baths. They are then immersed in gilding solution for less than a minute.

At the time of the assessment, there were a number of pollution problems including,

The objective of cleaner production assessment was to propose a program of pollution prevention that would:

The assessment was performed by an EP3 team comprised of an expert in metal finishing and a pollution prevention specialist.

Process / product modification; Housekeeping; New technology; Recovery, Reuse and Recycle; Material substitution

Cleaner Production Application

Overall, the assessment identified 18 pollution prevention opportunities at this facility. Recommendations for pollution prevention include,

Recommended Pollution Prevention Opportunities:

Polishing:

1. Reduce time between buffing and cleaning.
2. Replace polishing compound with one compatible with aqueous alkaline cleaners.
3. Improve operator performance by purchasing fixtures and jigs provide training.
4. Reduce compound and heel use through proper operating practice.

Solvent degreasing:

1. Replace this process step with aqueous alkaline cleaner

Alkaline cleaning:

1. Eliminate cyanide use in cleaning
2. Improved process control and solution monitoring.

Acid dip (10% sulfuric):

1. Isolate acids for steel and brass.
2. Improved process control and solution monitoring.

Acid dip depassivation of nickel:

Eliminate this process step, since cleaner is adequate.

Acid dip mixed acid stripper:

Replace with solutions in smaller tanks, and practice segregation and recovery.

Copper cyanide:

Improved process control and solution monitoring

Cyanide brass metal finishing:

Improved process control and solution monitoring

1. Improved process control and solution monitoring. Improved product quality with less solution loss.
2. Less frequent purification.

Chrome metal finishing:

1. Capture and return 100% of dragout to the process solution.
2. Improved process control and solution monitoring porous pot.

Rinsing effectiveness:

Add agitation and sprays; control water use and reduce water use.

Polishing debris:

As currently performed, the polishing process leaves considerable debris (consisting of a mixture of polishing compound and solids from the polishing wheel) inside the pieces. These deposits cannot be removed by scraping or wiping.

To alleviate this problem, the facility can take following steps.

Degreasing:

The facility currently employs the chlorinated solvent TCE to degrease parts. TCE is highly toxic and chemically reactive, and has been linked to liver cancer and ozone depletion. Parts can be cleaned equally well, or better, through the use of aqueous alkaline cleaners. Thus, the facility can greatly reduce its environmental impact and improve product quality by implementing an alkaline cleaning system. Further, the alkaline system cost effective than the TCE system.

Acid Dips:

In this facility's plating process, an acid dip (usually 10 percent sulfuric acid) is used to remove any oxides that may have developed on the brass or steel surface. With time, copper and organic contamination accumulates in the acid bath. If more than 300 mg/l of copper is present in the acid dip, the bath can cause adhesion problems for the steel substrate. Further, copper contamination also impacts the nickel metal finishing solution. While the facility utilises nickel depassivation to remove the copper contamination, it is not efficient, wasting nickel, brightener, and energy.

Separate acid dips for steel and brass substrates will improve the quality of both the steel substrate cleaning, and the nickel metal finishing solution, and, hence, reduce the number of rejects the facility produces.

Cyanide Metal finishing:

Cyanide metal finishing cannot be eliminated at this facility because the known non-cyanide alkaline alternatives do not function well in this application. However, improved process control and solution monitoring could enhance product quality, and, hence, reduce the number of rejects the facility produces.

Nickel and Chrome Waste:

Currently, the facility purifies the nickel bath six times per year.

Water Use:

Wastewater is generated in significant volumes from the facility's rinse steps. Some fairly simple changes can be made that will reduce water use by 25 percent. The use of air or solution agitation would increase the efficiency of the rinses, and reduce the frequency of changes. Spray rinses would also be more efficient than the current practice. Lastly, water inputs should be installed with switches that turn off the inputs after a set period of inactivity.

None reported.

EP3 Clearinghouse (United States)

Tel : 1 (703) 351-4004

Fax : 1 (703) 351 6166

Internet: apenderg@habaco.com

This case study was carried out in a developing country in which EP3 has an established Program. It was submitted to UNEP IE and edited for the ICPIC diskette in August 1995.

Subsequently the case study has undergone a technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.