Screening Demons Exorcised
- Published: Sunday, 01 July 2001 08:00
Blinded screens are a menace to production and profits. Diminished screen cloth opening area causes throughput to be limited, product gradations not to
Blinded screens are a menace to production and profits. Diminished screen cloth opening area causes throughput to be limited, product gradations not to be met and crushing circuits to be shut down for periodic screen cleaning. In fact, one limestone producer was shutting down for as many as three hours per day to clean its screens.
The West Fork Quarry operated by McClinton-Anchor, a division of APAC of Arkansas, produces more than 650,000 tpy of several products in northwest Arkansas. The limestone quarry encountered constant blinding problems when screening 3/16-in.-minus asphalt and 10 mesh aglime products. Most blinding occurred on the smaller-opening bottom screen decks.
ìWhenever we got into any type of wet material, our woven wire screens would blind over, sometimes two to three times a day,î says Walter Long, West Fork Quarry supervisor. And Arkansas' climate means the operation is dealing with wet material for about one-third of the year, he says. ìEven when it's not raining, we have extremely high humidity that makes the material wet.
ìWe would have to shut down production and beat the build-up off with a hammer.î That process usually involved two men working for as long as half an hour, he says. The downtime would reach 45 minutes when the shutdown and restart time was added.
Originally, the producer used oil-carbon and stainless steel woven wire in its asphalt and aglime circuits, but blinding forced the quarry to use #8 screen cloths to meet its 10 mesh aglime specs. Similarly, when the 3/16-in. screens blinded over, the company would struggle to make its asphalt spec product. Screen cloth service life averaging only three months compounded the quarry's burden. Sometimes, Long adds, the cloths would need changing every two months.
To improve both crushing circuits' efficiency, Long switched to Major Wire Industries' Flex-Mat Series T high-performance, self-cleaning screen cloth. The Series T design uses alternating straight and crimped wires to form triangular openings. Flex-Mat is manufactured with polyurethane strips bonded to the individual screen wires to eliminate the need for woven cross wires. The polyurethane strips allow wires to vibrate independently and at different frequencies to prevent material build-up and allow the screen to run cleanly, according to Major Wire.
In January 2001, West Fork Quarry switched to 3/16-in.-opening and 10 mesh Flex-Mat Series T on the bottom screen decks in its asphalt and aglime circuits ó five decks in all. The screen cloths virtually eliminated material blinding, even with wet material. ìI could probably count on one hand the number of times we've had to stop and clean since January,î Long says. Those cleanings, he says, have only occurred when the material is extremely wet.
The net result of this change, Long says, is that production has jumped about 4%. However, the biggest benefit has come from improved product consistency, which he reports is up 75%. ìWe are getting more consistent product sizing, and we have increased production of both products,î Long says.
West Fork Quarry also reports seeing longer wear life. With no cross wires, Flex-Mat has no high spots to prematurely wear, like traditional woven wire, the manufacturer says. Long purchased a replacement set of screens with his original set, but after almost a full year, he is still using the original set.
Long says that although the Flex-Mat cloths purchase cost is about three times more than what he previously used, the longevity and increased production more than off set the up-front costs. ìI'm well pleased with their performance,î he says.