Good Vibrations - Part 2
March 30, 2004 By: Leon Luadzers Pit & QuarryThe vibrating scalper plays a key role in the success of most material processing plants.
 |
This is the second in a two-part article on vibrating scalpers. It is an update of an article that originally appeared in Pit & Quarry 16 years ago. – Ed.
Grizzly bars are popular for use in extra-heavy-duty, high-capacity applications. They are very sturdy and can withstand large feed size. Grizzly bars also provide the highest capacity owing to the long spacing between the bars.
It is advisable, however, to design in a thick, solid plate impact area ahead of the bars rather than dump directly onto the bars. The impact section will help prevent grizzly bar breakage and abnormal wear as well as help spread out the material for better separation.
Heavy-duty, tapered bars are used for most applications, however, special fabricated bars are sometimes used when special lengths, heights and configurations are required. The spacing between grizzly bars can typically be adjusted in order to provide different openings.
Special attention must be given to the relationship between the heights and spacing of grizzly bars. Large openings require taller grizzly bars to help prevent materials from bridging between the bars and support beams. This is especially important when slabby, elongated material or rip-rap is being processed. It is typically recommended that the grizzly bars be provided in two or three sections with a step between to help prevent plugging and to help tumble and segregate the material in order to improve separation.
Perforated plate
Product specifications may require a more precise separation, thus requiring the use of a perforated plate deck. The plate can be designed with square, slotted or round holes with various patterns. Heavy-duty, flat, perforated plate decks are normally provided with up to 8-in. deck openings and smaller. A solid impact area is often included at the feed end. Perforated plate decks typically have less capacity than grizzly bars as they have less open area.
Flat, perforated plate, which can be constructed of abrasion-resistant steel, has traditionally been bolted in place and supported by several heavy cross beam members. Perforated plate decks are typically constructed from 1/2-in. to 1-in.-thick plate and are normally designed in sections so high wear areas can be replaced separately.
 Two kinds of scalping |
Perforated plate can also be provided with skid bars, which help prevent plugging and also protect the plate. Skid bars are usually constructed of abrasion-resistant steel bars, which are typically 2 in. to 4 in. tall and welded to the plate between the rows of holes.
Other decking materials such as heavy wire cloth, rod decks, rubber and urethane are also used on scalper units. Each application dictates the type of decking that best meets the requirements of the application.
Rubber and urethane may provide good wear life and reduce the noise of material cascading over the deck. These are typically thick panels, 1 in. to 3 in., and typically reduce the capacity of the scalper owing to less open area. Feed material tends to bounce more on these decks and this may affect screening negatively, and the feed rate of the oversize material typically increases, which may require the scalper unit be slowed down or the slope reduced.
Heavy-duty wire cloth will typically increase the open screen area, which increases the capacity of the scalper. Wire cloth typically has shorter service life and cannot accept the impact that grizzly bars and perforated plate can handle.
Rod decks may work well in limited applications with sticky materials. They are normally used for smaller openings with smaller feed size.
Installations
Inclined scalpers are normally installed at slopes from 15 to 20 degrees and thus the large oversize material can discharge off the deck at a high rate of speed making it difficult to control. Sometimes, chain curtains or rubber belting is mounted above the scalper and draped down on the deck in order to reduce oversize material bounce and discharge speed.
It is important to feed the scalper properly in order to take advantage of the deck area and to help provide a uniform bed of material. Material fed from a conveyor, chute or feeder should be fed onto the scalper impact area. Material feed drop should be minimal to prevent frame and deck damage and to help prevent material bounce. Its advisable to feed the scalper near the center of the impact area so material spreads out evenly across the deck.
The inclined scalper requires more head room than the horizontal scalper, which may be important in some applications where there are height limitations.
As with any vibrating unit, it is important to make sure the unit is mounted level so the feed distributes evenly over the deck. It is also important to make sure there is adequate operating clearance between the structure and the live frame and springs.
The vibrating scalper plays a key role in the success of most material processing plants, so it is important to carefully size and select the unit. Scalpers are usually involved in the toughest duty in any plant - handling the largest feed material.
It is critical, therefore, that each unit be designed with the correct decking and extra-heavy-duty features. It is equally important that the vibrating scalper be built and designed by a quality manufacturer and supported by an experienced group of application and product experts.
;
Please send any technical comments or questions to our webmaster.