BCR - The Finer Things

October 26, 2000
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As one Richtex plant recently discovered, the fines that don't go through your screens can make a big difference in grinding efficiency.

With the new screens, Plant 2 noticed an immediate improvement in operating efficiency.
Like many other U.S. brick manufacturers, Richtex Corp., a Division of Hanson Brick America, is experiencing a booming demand for its product. Business is good-and has been for at least the past decade. "I came to Plant 2 in 1985, and it's always just been wide-open, all you can make," says Jimmy Strunk, plant manager of Richtex's Plant 2 in Columbia, S.C.

But such success sometimes creates its own challenges. The plant produces about 100 million residential face brick per year-40 to 50 million more than it was designed for when it was first built in the early 1950s. Labor costs are high, and fuel prices, especially within the past several months, have soared to record levels. "In the past there were some things that you could keep doing the same way you'd always done them because it didn't cost much more, but things have changed. Now we've got to become more efficient and cut costs," says Strunk.

"If you were going to build a new plant today, you'd use a lot more automation and you would make sure everything you needed was in the right place. There are a lot of things that you would do differently. But when you're in an older plant, you have to deal with things the best you can," he adds.

Jimmy Strunk, plant manager of Richtex's Plant 2 in Columbia, S.C.

Retrofitting Old Machinery

The oldest of two Richtex plants in Columbia, Plant 2 houses two 384 American grinders, two brick machines, two kilns and two monorails to unload brick. Most of the equipment is by no means new, but it's been well taken care of, and modifications are made when necessary to improve production efficiency.

Such was the case with the plant's grinding systems. Each 1950s-vintage grinding system was originally equipped with four

4 x 7 ft screens. "For several decades, these grinders and screens sufficiently met the needs of the plant," Strunk says. "When the capacity of the plant increased, we purchased some used 5 x 7 ft screens and put in two more screens on each side for a total of six screens on each grinder."

Everything rolled along smoothly until the early 80s, when the plant changed mining operations and began mining a different shale. For a while, the new shale didn't seem much different from the old shale. But as Richtex continued digging in the new mine, the characteristics of the raw materials slowly began to change and soon affected the grinding operation. "The old screen banks had fairly large mesh screens that let large particles of material through. Because of the characteristics of the old material, those large particles were reduced down as they went through the pugging, prepugging and extrusion process. But this other shale did not break down that easily. We had to put on finer screens, which slowed the grinding process down," Strunk says.

As the plant's production capacity increased, more hours were required for the grinding operation-both because the material had to remain in the grinder longer to be reduced to a smaller particle size and because the finer screens prevented much of the material from flowing through. "We went from what we could get done in less than 40 hours to 45, and then 50, and then all day Saturday, and I hate to tell you how many Sundays have been worked. The old grinding circuit-which, again, in its time was fine, and the grinders still do a good job-just didn't have the capacity to keep up with our manufacturing needs," says Strunk.

The plant determined that it needed to get about 75 tons of material an hour per grinding machine to meet its manufacturing needs. To evaluate how much material was actually going through the grinding system, the plant weighed the material with a belt scale. On average, only about 60 tons of material per hour were going through each grinder. This meant that on a good day, the plant was running at least a 30 ton-per-hour deficit with both machines.

"We felt like the grinders could put out more, but we were getting an effect called 'piggybacking'-where a certain amount of fine ground material was going over our screen cloth but wasn't coming out. Sometimes it would take three or four passes to get it through the screen. We knew we could get more tonnage if we could just get it all through on the first pass," Strunk says.

Getting the Fines Out

While Plant 2 was evaluating its options, Richtex's Plant 9 in Ninety Six, S.C., was installing the solution to its own screening problem. Its new screens, supplied by Midwestern Industries in Massillon, Ohio, are designed for even material distribution without blinding or leakage-key factors in screening efficiency. A diverter plate is used to ensure an even distribution of material across the screen. A ball tray under the single-deck screen bounces, making the balls hit the screen to prevent blinding, and the screen is designed without skirt rubber to virtually eliminate leakage of oversized material. Additionally, the screen cloth can be changed out in a mere 15 or 20 minutes instead of the hour or hour and a half required with some screens.

"Plant 9 was thrilled with their results-everyone but the janitor ran up to take a look," says Strunk.

While Plant 9's grinding operation included a hammermill and a crusher, and a significantly greater amount of fines as a result, Strunk was still impressed with what he saw. "We decided that if Plant 9 had had such good luck with those screens, they might work for us as well," he says. The plant purchased two of the new screens immediately.

"We took out two 4 x 7 screens-56 square feet of screen coverage-and installed one 5 x 10 Midwestern screen-which gave us 50 square feet of coverage." Despite the smaller coverage area, Plant 2 noticed an immediate improvement in operating efficiency.

"On average, we've increased throughput about 18-20%," Strunk says. "We've had some days where we've hit 85 or 90 tons an hour, but on average we run 72 to 75 tons an hour, which is basically right where we need to be. And this reflects what our quality department had told us-we had about 20-25% more material that should have been going through on the first pass but wasn't."

Increased Production Efficiency

The first screen was installed in June 2000, and the second was completed the first week in August. Since that time, the company has once again been able to go back to meeting production demands in a five-day-per-week shift. "With these new screens, we feel like we have a fighting chance of getting the production we need out of the equipment that we have," says Strunk.

Strunk has asked company management to approve two more screens for his 2001 budget. "Even though there might not be a lot more fines to get out, when you look at the cost of changing the screens, and how much energy is involved in heating a typical screen, we can take out two units and replace it with one, and actually lower our energy and maintenance costs," he says.

Of course, new screens aren't the final frontier for Richtex-more upgrades will undoubtedly be part of Plant 2's future. But Strunk doesn't downplay the importance of such a small piece of equipment. "We still have more to do, but this was a big step for us-and by golly, it worked," he says.

For More Information

For more information about improving screening efficiency, contact Midwestern Industries Inc., P.O. Box 810, Massillon, OH 44648-0810; (330) 837-4203; fax (330) 837-4210; or e-mail info@midwesternind.com.


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