The vibrating scalper sizing formula determines the square footage required based on the specific application factors. A screen width is chosen which will result in acceptable material bed depth and a length is chosen which will provide the required screen efficiency rate. Today, scalpers are typically available in 4- by 8-foot to 8- by 20-foot size units.
Scalping screens can be single-deck units but many applications require them to size other products, therefore it is common to see double- and triple-deck scalpers. A flow program will individually size each deck. In some cases, the middle or bottom deck requires more screen area than the top deck.
A speed and stroke combination is selected based on the deck openings of the scalper screen. Generally speaking, a maximum stroke is required for the large deck openings to prevent material from plugging or sticking in the opening. It’s common for an inclined scalper to have a 1/2-inch stroke and to operate with a speed of 650 to 750 rpm, which typically results in a 3.2 to 3.5 G force.
Types of scalpers
Vibrating scalpers are available as inclined and horizontal-type units. Today, inclined scalpers are typically two-bearing, circle-motion units. Horizontal units are either linear motion (two-shaft) or triple-shaft (elliptical motion) units.
The inclined scalper is typically used in stationary plant applications and in some portable plants. The inclined scalper relies on gravity to move the material down the deck. This is a useful benefit when handling high tonnage rates and large feed sizes. It’s typically easier to prevent deck openings from plugging on an inclined scalper screen.
The horizontal scalper is often used on portable plants because it helps reduce travel heights. The linear or elliptical vibrator motion of the horizontal scalper performs the dual purpose of shaking the feed material and also conveys the feed down the deck. The material travel rate is lower on a horizontal screen, but one of the benefits is that this allows the operator to control the velocity of the material coming off the deck. The disadvantage of the horizontal screen is that the top deck opening must typically be limited to 4 inches or less to prevent plugging problems.
New vibrator development
One of the new developments in vibrating screens is the modular vibrator, which can create the necessary stroke and speed for scalper screens. The modular vibrator is durable and provides the highest bearing life at the lowest operating cost. The versatile unit may be used on both the inclined scalper screens and horizontal scalper screens.
The modular vibrator is a true cartridge-type vibrator that eliminates bearing replacements and dramatically reduces plant downtime. The modular design versus the traditional design eliminates oil leaks and shaft deflection. It also can be easily and safely maintained and replaced.
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