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Technical Articles
Home >> Technical Articles >>Screening Tests Making Good Results
Screening Tests Making Good Results
Time: 2009-02-10
Kason' s test center shows a brass recycler how a vibrating circular screener can help recover valuable brass from crushed slag
In late October 1988, Dale Knepp, vice president and plant manager for American Brass, Headland, Ala., saw an ad in a trade magazine for Kason's Vibroscreen® vibrating circular screener. American Brass recycles scrap brass into ingots, which are sold to manufacturers of plumbing fixtures and other hardware.
To make the ingots, the scrap brass is loaded into rotary furnaces and melted down. Borax is added to the molten brass, causing impurities to rise to the surface and form a slag that's skimmed off and cooled. The process generates about 40,000 pounds of slag per day.
When slag hardens, it traps small beads of pure brass, valued at approximately $.50 per pound. American Brass wanted to recover this brass by crushing the slag and separating the dust from the larger, brass-laden chunks. The company already had the necessary size reduction equipment, but needed a screener. Limited space and housekeeping concerns dictated that the new screener be compact and dust-tight.
Knepp thought the Vibroscreen might meet the plant's needs, so he called Kason and arranged a screening test. Henry Alamzad, a Kason test center engineer, asked Knepp to send two 55-gallon drums (about 300 pounds) of slag to the test center, along with a Material Safety Data Sheet (MSDS). Knepp then arranged to visit the test center to witness the screening tests.
When the test center received the slag, Alamzad analyzed its angle of repose, bulk density, particle size distribution, and particle shape to prepare for the test session.
Tests produce a clean separation
The tests were performed just 2 weeks after the initial contact. "It would've. been sooner," says Knepp, .'but Kason had to wait for me to find time to get there." For the tests, a screw feeder discharged slag into a 24-inch-diameter vibrating circular screener fitted with a 20-mesh screen.
Based on his experience with similar materials, Alamzad installed plough blades to catch material that collected along the edge of the screen and direct it out the discharge spout. This prevented oversize material from accumulating on the screen deck. He also installed reverse tie-downs to pull the center of the screen up. This created a sloped screening surface and prevented heavy material from collecting in the middle of the screen.
After the first separation test, Alamzad analyzed the particle size distribution of the overs and the fines and found that too much dust was being discharged with the overs. To remedy this, he replaced the 20 mesh screen with an 18-mesh screen. Further tests showed that this produced a cleaner separation.
Tests also showed that the screener operated more efficiently when a 10-mesh screen was placed above the 18-mesh screen. This reduced the load on the 18mesh screen and increased the available screening area.
After making these changes, Alamzad ran several more back-to-back tests to simulate production conditions and generate additional data. A total of eight test runs were made with good results.
The largest two fractions -- everything bigger than 18 mesh -- constituted 30 percent of the slag and contained about 30 percent brass. The fines constituted 70 percent of the slag and contained almost no brass.
The entire test procedure took 3 hours. "I was very impressed with the efficiency of the test center and with the way the vibrating circular screener worked," says Knepp. "After seeing the test results, I saw no reason to look any further -- the screener did exactly what we needed it to do." In December, American Brass purchased and installed a double-deck, 72-inch vibrating circular screener with 10-mesh and 18mesh stainless steel screens.
Screener helps reclaim brass beads from slag
The new screener handles as much as 12,000 pounds of slag per hour, with an average throughput of 40,000 pounds per day. Reducing and screening the slag allows American Brass to recover from 35,000 to 45,000 pounds of brass per month.
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