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Apron Feeder
A feeder is a piece of material handling equipment used to regulate the flow of a bulk material from a bin or hopper[1].  A feeder is essentially a conveyor used for short distances where a constant rate of dispersal is required.[2]  There are many types of feeders to suit many different industries; ranging from mining, to pharmaceuticals, to agriculture. Feeders are often used in conjunction with other types of material handling equipment, like conveyors, crushers, dryers, grinders, blenders, and mixers.[3]

Contents

[edit] How it Works

Feeders can be loosely classified as either volumetric or gravimetric:[4]

[edit] Volumetric Feeder

Volumetric feeders achieve precise outputs through a process similar to using a measuring cup. First, fill the cup past the brim, then shake it to settle the contents, level-off any excess above the brim, and tap on the bottom to dislodge anything stuck to the sides of the cup.[5]

In a volumetric feeder, material is first fed into a hopper. Next, vibrations encourage the material to form a consistent density. Then, material is levelled off as it is forced through an adjustable gate at a constant speed. Lastly, the material is exposed to more vibrations as it exits the feeder, which dislodges any stuck material.  By maintaining a constant density, a constant speed, and a constant opening size, volumetric feeders are able to achieve a near constant output.[6]

[edit] Gravimetric Feeder

Gravimetric feeders, also known as loss-in-weight feeders, are used for applications which require extremely precise output, even more than a volumetric feeder. In a gravimetric feeder, the weight of the material being processed within the feeder is constantly monitored with the goal of keeping a steady weight. If there is too little material in the feeder, then the rate of supply is increased. If there is too much material, then the rate is decreased.[7][8][9]

[edit] Types

Feeders are further segmented according to their method of conveying: [10]

[edit] Apron Feeder

Apron feeders are typically used in the mining industry to handle bulky material coming directly from a jaw crusher. The “apron” is a conveyor made up of a series of steel pans fit snugly together. The apron is propelled by steel chains rotating around metal sprockets. The rate of discharge is controlled by adjusting the height of the gate or adjusting the speed at which the apron rotates.[11]

[edit] Belt Feeder

Belt feeders are used in lieu of apron feeders when material is of a fine composition. A belt feeder is simply a conveyor with a short belt. Typically belt feeders are less expensive than apron feeders, and operate at higher speeds. However, they not suited for heavy-duty applications.[12]

[edit] Chain Feeder

Chain feeders are used to control the release of a bulky material within a bin. Their design consists of several heavy chains, which drape over top of the bulky material on an incline. While resting, the chains hold the material in place. When the chains are moved, material slides down the incline.[13]

[edit] Roller Feeder

Roller feeders are used to handle dry granules and powders. Material is fed into a hopper at an uncontrolled rate where it is agitated by guiding vanes so it keeps a consistent density. These guiding vanes then direct the material towards the hopper’s outlet. The material passes between two steel rollers, which compresses the material into a thin uniform ribbon.[14]

[edit] Rotary-Vane Feeder

Rotary-vane feeders are used for low density powdered material. These units feature a rotating vane (a rotating cross with four separate quadrants). At the top of the vane rotation, each quadrant scoops up a load of material. At the bottom of the rotation, the load of material is discharge by gravity. The rate of discharge is determined by the speed at which the vane rotates.[15]

[edit] Revolving Disc Feeder

Revolving disc feeders, also known as a rotating table feeders, are able to process many types of material, including fine, bulky, and sticky. These units feature a hopper above a rotating table. As the table rotates, material falls from the hopper onto the table’s face at a constant rate by gravity. Then, the material is directed off of the table by stationary arms called skirt boards. The rate of discharge is controlled by changing the speed at which the table rotates, or by adjusting the size of the opening where material exits the hopper.[16]

[edit] Screw Feeder

See also: Screw Conveyor

Screw feeders are used to transport fluids and fine granular materials. A rotating auger within a cylindrical encasing propels material. The rate of discharge is controlled by the speed of rotation.

[edit] Vibrating Grizzly Feeder (VGF)

Vibrating Grizzly Feeders are used in the mining and construction industries to separate large rocks from fine material.[17] Grizzly feeders are powered by an off-balance electric motor, which causes the unit’s vibrations.[18] They operate by conveying ore over a series of steel beams, which prevents large rocks from passing. The mixture that falls through is entirely fine.

[edit] Vibratory Feeder

Vibratory feeders are used for a wide variety of materials, including aggregate, coal, and chemicals.[19]  Essentially, a vibrating feeder is a ramp which vibrates to agitate material into falling down an incline. The vibrations spread the material evenly along the ramp, which results in a smooth discharge. [20]

[edit] Common Manufacturers

[edit] References

  1. Fayed, Muhammad E. and Skocir, Thomas S. Mechanical Conveyors: Selection and Operation. Technomic Publishing Company, Inc: 1997.
  2. Kulwiec, Raymond A. Materials Handling Handbook. John Wiley & Sons, Inc: 1985.
  3. Kulwiec, Raymond A. Materials Handling Handbook. John Wiley & Sons, Inc: 1985.
  4. Kulwiec, Raymond A. Materials Handling Handbook. John Wiley & Sons, Inc: 1985.
  5. Rugged Construction and High Accuracy. Vibra Screw Inc. [October 5, 2009].
  6. The Versifeeder. Vibra Screw Inc. [October 5, 2009].
  7. Application Overview: Screw Feeder. Yaskawa [October 5, 2009].
  8. Gravimetric Feeders. Olds Elevator [October 5, 2009].
  9. Giles, Jr., Harold F., Wagner, Jr., John R., and Mount, III, Eldrisge M. Extrusion: The Definitive Processing Guide and Handbook. William Andrew, Inc.: 2005.
  10. Kulwiec, Raymond A. Materials Handling Handbook. John Wiley & Sons, Inc: 1985.
  11. Willis, B.A. and Napier-Munn, T.J. Wills' Mineral Processing Technology. Elsevier Ltd: 2006.
  12. Willis, B.A. and Napier-Munn, T.J. Wills' Mineral Processing Technology. Elsevier Ltd: 2006.
  13. Willis, B.A. and Napier-Munn, T.J. Wills' Mineral Processing Technology. Elsevier Ltd: 2006.
  14. Liptak, Bela G. Process Measurement and Analysis. CRC Press LLC: 2003.
  15. Liptak, Bela G. Process Measurement and Analysis. CRC Press LLC: 2003.
  16. Liptak, Bela G. Flow Measurement. Chilton Book Company: 1993.
  17. Syntron® Grizzly Bar Screens. FMC Technologies [October 8, 2009].
  18. Vibrating Grizzly Feeders. CrusherManufacturers.com [October 8, 2009].
  19. Vibrating (Vibratory) Feeders and Conveyors for mining and quarry operations, aggregate, chemical and industrial processes. JeffreyRader.com [October 8, 2009].
  20. What is a Vibratory Feeder?. Wise Geek [October 8, 2009].