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December 2009 |
In the Line of Fire |
 SWECO Round Separator Many indoor shooting ranges use recycled rubber chunks at the back wall for bullet catch. Traditionally, the rubber would have to be replaced with new material and the old material would have to be sent to hazardous waste due to lead powder that builds up. Though some of the rubber would still be in good condition, the entire pile would have to be replaced as the lead content, degraded rubber bits, and casings increased. A customer in California contacted SWECO after pressure from the EPA. |
They wanted to safely remove the casings and lead powder from the rubber pile and reuse as much of the rubber as possible. SWECO provided a ZS30 Round Separator with a rather course screen. After hours, the operator shovels the rubber into the SWECO Separator. What comes off the top of the screen is sent back to the pile. The fines are degraded rubber powder, lead powder, and smaller or broken casings. The backstop pile is then refreshed with virgin rubber rather than replaced. The unit had to be fully portable because anything left in sight becomes a target. The customer needed to wheel the SWECO Separator into a closet and out of sight when not in use. The 30-inch machine was put on casters, and SWECO provided a Basic Vibe Electrical System with a 10-foot cord. The customer sent SWECO a distinctive 230V plug to be installed on the separator to assure proper electrical continuity. |
At the end of the day, the customer is saving money on replacement backstop rubber by being able to decontaminate the pile and continue to reuse rubber until is wears out. The customer is also saving money in hazardous waste expenses since they are no longer disposing of the entire backstop every time. Recycled rubber mainly comes from the reclycling of rubber tires
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 Introduction to Air Classification Air classifiers are preferred over fine screening in one or both of the following situations: 1) the rate is too high for fine screening, and 2) the cut point is too fine for screening. Take for example an application in which calcium carbonate must be separated at 75 microns. A common round vibrating separator with a 200 mesh screen can make a very sharp separation in such an application at about 1 t/h. But what if the desired processing rate is 30 t/h? Sure, you could install 30 vibrating screens, but that’s not really practical. A single air classifier could handle the entire 30 t/h. As another example, let’s say we have a toner powder that we want to separate at 5 microns. It is not possible to accomplish this with a screen for the simple reason that it is not physically possible to weave a screen with openings as small as 5 microns. But a high performance turbo classifier can easily make such a separation. There are several types of air classifiers available. Perhaps the simplest is the "falling bed aspirator". This is a static device in which the material to be classified falls by gravity through an upwardly moving air stream. The lighter, finer material is carried off by the air and the heavier, coarser particles fall out the bottom. This extremely simple device can be used when the difference in particle size is huge, such as de-dusting a granular or pelletized material. |
For more accurate and finer separations, one can use a rotary air classifier. Sometimes these are referred to as "dynamic" or "whizzer" classifiers. In these devices the material to be classified is dropped onto a rotating circular disk that flings the material out to its edges. Below the disk is a fan generating an air stream such that flows upwards all around the periphery of the disk. Coarser, heavier particles fall off the disk into a hopper. Finer, lighter particles are lifted by the air and flow up and over a wall into a separate hopper. The cut point can be changed by varying fan speed and adjusting directional vanes. While these types of classifiers are relatively inexpensive they cannot make very sharp cuts and are generally limited to finenesses in the range of 300 microns down to 45 microns. Turbo Air Classifier For applications that require very sharp cuts or very fine cut points, a turbo classifier is the way to go. The turbo classifier is not a standalone unit. It requires a separate air moving system to pull air through the classifier. The turbo classifier itself resembles a squirrel cage blower, but in this case the spinning rotor is not there to generate an air flow, rather, it is there to make a separation |
 Ultrafine Turbo Air Classifier based on particle size. The external air moving system is configured to suck air "backwards" through the rotor, that is, air is drawn through to the inside of the rotor. The material to be classified is introduced to the air flow upstream of the classifier. As the material enters the classifier it encounters the spinning rotor where a "tug-of-war" is played out on each particle. Aerodynamic forces from the flowing air try to pull the particle into the rotor. Simultaneously centrifugal forces from the spinning rotor try to push the particle out away from the rotor. Which force wins depends on the particle’s size. For coarse particles, centrifugal force wins. These particles are flung out away from the rotor and fall into a collection hopper. For smaller particles, aerodynamic force wins. These fine particles are drawn through the rotor and conveyed to a dust collector where they are dropped out of the air flow. Most turbo classifiers operate in the range of around 150 microns down to 5 or 10 microns. But highly advanced turbo classifiers can achieve cut points as fine as 1 micron, making them suitable for nanotechnology applications. A variety of manufacturers offer various types of air classifiers for a wide range of applications. As with other process equipment, selecting the right manufacturer requires thorough research and often involves laboratory testing. |
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Low Profile Flow-Thru Separator The SWECO Low Profile Flow-Thru Separator offers high capacity wet or dry scalping in a compact, low headroom design. Dual motors mounted on opposite sides of the Low Profile create the 3-D motion that allows maximum flow-thru of material. Because of its headroom requirements (as little as 15 inches) and straight, flow-thru design, the Low Profile fits easily into existing product lines without reworking the entire system. Inlets and outlets can be custom |
designed to mate with existing equipment and piping. The Low Profile is ideally suited for prepackaging screening in many food and pharmaceutical applications, as well as for bulk bag unloading and screening of raw ingredients. SWECO Low Profile |
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