67    AN ALUMINUM DIE CASTING WASTEWATER SYSTEM
John Ball, Professor
Department of Civil Engineering
The University of Alabama
Tuscaloosa, Alabama 35487
Jonathan R. Bonner, Engineer
Ball Engineering, Inc.
Tuscaloosa, Alabama 35486
INTRODUCTION
A study was conducted of the wastewater generation and treatability from an aluminum die casting
facility located in a small town in northwest Alabama. Initially, the effluent was being discharged
untreated. However, because of the new and very stringent EPA discharge limits for this industry, the
company was required to install a pretreatment system having an effluent quality that was essentially
below the detection limits for most of the parameters. This chapter presents a case history of the
design and operating experience of the new wastewater pretreatment system. The system includes oil-
water separation, chemical coagulation and settling followed by activated carbon adsorption. Because
of the strict permit requirements, the effluent did not easily meet the effluent limits. A number of
changes and field tests were made at the facility in an effort to reach compliance.
THE MANUFACTURING FACILITY
The Alabama facility, owned by a parent company having two other facilities in two other states,
was the first of the three to be subject to the new EPA regulations. The mill began operations with one
furnace and one die casting machine in December, 1977. The plant has expanded at a rate of about
two machines per year to a total of two furnaces and 15 die casting machines at the time of the study.
The facility uses only aluminum ingots in its casting process. The total work force is about 75
individuals with about 45,000 pounds of aluminum ingots used per operating day. The mill operates
on a three shift basis five days per week. All water discharges are ended Friday evening and do not
begin until Monday morning.
Figure 1 presents the die casting schematic for the facility showing the flow of aluminum using wide
cross-hatched lines. Water flow is shown with narrow, solid lines. Aluminum ingots are fed into one
of two melting furnaces along with return aluminum previously cast. The return aluminum includes
runners, flashings, and reject castings. The returned material averages about 20% of the total aluminum cast.
The melted aluminum is first transferred by a large traveling overhead ladle to a holding furnace
located at each machine. A small ladle then automatically dips a measured quantity of molten
aluminum from the holding furnace and pours it into a mold in the die casting machine. Next a
hydraulic ram brings half of the mold into position against the fixed mold half and casts the liquid
aluminum into the required shape. The ram is then retracted and the casting is removed from the fixed
mold half with a robot arm. The robot arm turns 90 degrees while a water spray cools the casting.
Finally the casting is stripped of all flashing and runners, then the arm drops the part onto a vibrating
conveyor. The casting moves to a dry shot blaster, is inspected, sorted, and packed for shipment.
Castings from this facility consist primarily of automobile alternator cases.
Water is introduced into the process from four sources. The first is non-contact mold cooling water
which continuously circulates between the cooling tower and cooling chambers of each die. The
second is as makeup dilution water in the die lube spray. The die lube spray is mixed as one part
concentrate to 25 parts water. City water is used to dilute the concentrate so as not to plug the small
nozzles in the blending device. The quantity of water from this source ranges between 1200 and 2000
gallons per day. This is the most contaminated source of wastewater with most of the water reaching
floor drains. Some of the die lube spray splashes on the casting and is then washed off and flows into
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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