An alternative solution, which eliminates the need to store the middle fraction, is to run the middle fraction back into the processing line, and clean it during the regular separation process. Some operators merely connect an elevator from the middle discharge spout of the gravity and run the material back to the gravities’ feeder. For this reason the feeder on your Maxi-Cap is divided into two sections. The first, closest to the feed end, is the primary feeder and is intended to feed the incoming product at the desired rate. The second is located approximately3” closer to the discharge end of the machine, and is used to feed the middle product. Using the re-run chamber will place the middle product on the deck in the best area for proper separation. See Figure 23.
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An even better way of handling the middle fraction with the initial processing run is to
return the material to the feeder of the screen air machine. The screening action of the screen air machine will improve the condition of the middle fraction, before it is fed onto the gravity, by removing the larger light particles and the smaller heavy particles. The major advantage of this system is that all the material is cleaned in one processing operation, and no bin space is required for the middle product. The disadvantage is that the overall production of the plant is reduced by the amount that is fed back into the processing line.
A final alternative is to use a successive line to clean the middle product during the regular processing action. The should consist of a small screen machine to size the middling product and a Gravity Separator to finish the separation. This is probably the best solution for large processing plants. It allows for a high capacity primary processing line and a slower more precise secondary line to clean the middle fractions. It also eliminates the need for bin space to store the middle product foe later operation. The primary drawback of this system is the initial cost. However, the cost will be paid many times over in improved production and quality.
Stoners
Although Gravity Separators will remove stones and heavy material, they will not always do a complete job. The stoner will produce a clean product that is free of heavy contaminants. Stoners work on the same general principles as do Gravity Separators. However, they are designed to do a specific job, removing a small fraction of heavy material from a large fraction of light. Normally, Stoners cannot be used to grade materials on a Gravity Separator. Oliver Manufacturing offers a variety of Stoner sizes to meet specific needs.
Normally, two approaches are taken toward destining: Frist is the use of a Stoner before material is fed onto a Gravity Separator. By using this method, all of the material is fed onto the Stoner; and heavy contaminants are removed ahead of the Gravity Separator. In this approach, the Gravity Separator is used only to remove light material, producing a very good separation with minimum middle product. See Figure 24
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Figure 25
The second method is to send the product through the Stoner after the Gravity Separator. In this approach, all the material is fed onto to Gravity Separator before it is destoned. Then a small portion, 5% to 10% of the flow, is removed from the Gravity Separator at the rock trap and fed onto the Stoner. See Figure 25.
The major advantage in using the stoner after the Gravity Separator is that less space is required for a smaller Stoner.
A big disadvantage is that the Gravity Separator may not catch all the heavy contaminant at the rock trap. If the heavy trash misses the rock trap and the Stoner, it will not be removed and will be in the final product.
If you have stone, glass, metal or other heavy contaminants in your product, please contact us. We can discuss problems and arrange to have a test sample processed.
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Dust Control Accessories
The Gravity Separator is not intended to be a cleaning machine. With some commodities, dust is still present on the particles when they are introduced on the Gravity Separator. This can be both annoying and illegal.
Oliver has three systems to combat dust and get it away from the machine.
These are the Aspirating Feeder, supplied standard with your Maxi-Cap, an Oliver Mini-Hood or and Oliver Full-Hood.
Please see specifications section for air recommendations and requirements.
The Aspirating Feeder is ideal for controlling small amounts of dust generated in processing a product that is normally fairly clean. The Aspirating Feeder is designed to draw air through a curtain of feed as it falls onto the gravity deck. This will remove 70-90% of the fines, and other light trash which is present during the feeding operation.