Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/531447
AGGREGATES MANAGER July 2015 36 ensure both motors run together and in the proper direction. "Many of the dewatering screens manufactured use vibrat- ing motors, although some use exciter drives," Schott says. "If you have a dewatering screen that uses vibrating motors, you should verify the motors are turn- ing opposite of one another. The motor connections can easily be wired incorrectly, so customers should check to make sure the switchgear is installed to ensure both motors run together and in the proper directions to create the screen's linear motion." When conducting this visual inspection, producers should also take note of available clearance room, keeping all adja- cent equipment and structures a minimum of 3 inches away from the screen. When a screen starts up or shuts down, it hits a natural frequency and goes through an extra lung- ing motion, especially when powering down, Schott says. By maintaining the proper clearance, it ensures feed boxes, chutes, and other structures are kept far enough away to ensure the screen doesn't cause damage or become dam- aged itself. Producers should focus on how the material is being fed to the screen. Feed slurry should be centered and evenly distrib- uted across as much of the feed end of the screen as possible. Like other screens, the dewatering screens need to be fed evenly so it's not loaded to one side. If feeding evenly isn't possible, Schott says producers should at least try to have the material centered on the screen as much as possible. Next, producers should perform weekly checks to verify screen media, side wear liners, springs or buffers, and all bolts and fasteners are in proper operating condition, Schott says. "Producers should confirm the screen media is secure and not worn," Schott says. "At the same time, you should check the coil springs or rubber buffers and confirm they are not worn or damaged. If you notice excessive wear, it's time to order replacement parts as soon as possible. If the wear is isolated or on one side, troubleshoot the cause. Many times, it may be due to uneven feed or motor settings." Adjusting for optimal performance It's critical to first evaluate what type of material you are working with, the feed rate, and the feed percent solids to determine how you should initially start the dewatering screen, Schott says. Coarser material, such as concrete sand, is composed of bigger particles, which do not carry and hold as much water. Smaller particles, like those involved in fines recovery, have more surface area on which to hold water, which leads to a higher moisture content. Dewatering coarse material is easier, and the screen can handle more tonnage. As the feed becomes finer, the capacity of the dewatering screen is reduced. Although dewatering screens are designed with simplicity in mind and do not typically offer many options for adjust- ments, producers can not only adjust the stroke, but also manually adjust the discharge dam (or weir) to help control product moisture, bed depth, and rate of travel. It's a balancing act, Schott says, and one that often takes a couple of adjustments to obtain the "sweet spot" needed for a particular application to achieve the desired moisture content. "Raising the discharge dam will help build a bed of mate- rial on the media, which will naturally help squeeze that By fine-tuning variables such as raising the discharge dam or amount of feed material larger than the media opening, an operator can find the sweet spot for a particular application.