Separating Different Materials

Separating Different Materials - Horizontal vs. Incline Vibrating Screens

The specific application often determines whether horizontal screens or incline screens should be used at an aggregates plant. Following is a look at the advantages and disadvantages of each.

The major benefits to using horizontal (flat) vibrating screens compared to incline screens: The major benefits of horizontal screens include lower overall height and more-efficient fine wet processing. The improvement in fine wet screening is attributed to forcing near-size material through the openings with a water spray. The efficiency improvements are mainly due to a lower travel rate of the material.

Typical installations/applications for horizontal screens in the aggregates industry: Horizontal screens are selected primarily because of their low profile. Therefore, the most typical installation would be on a portable plant. Correspondingly, the typical applications of those units become anything within a portable-plant circuit. Although the horizontal screens can be set up to "scalp" material, they are more often found in sizing applications. When horizontal screens are selected for stationary plants, they are normally found as tertiary or "finishing" screens.

Major drawbacks to using horizontal vibrating screens compared to incline screens: The major drawback of a traditional horizontal screen is the inability to use gravity to assist with material movement. Without gravity, users are forced to increase speed and/or stroke to achieve a higher acceleration and an acceptable travel rate. Although increasing the acceleration compensates for not having the benefit of gravity, horizontal screens will typically weigh more and cost more to purchase than incline screens. The large stroke (large mechanism) and heavy component design, in turn, require a higher horsepower motor. Also, an incline screen tends to "tumble" the material better. This benefit comes from the slope and the circular-stroke pattern. An elliptical motion horizontal helps to compensate for this effect.

How the design and construction of a horizontal screen, deck frames and supporting structure differ compared to inclined screens:

- Design: Virtually all horizontal screens without self-synchronization have timing gears. Most incline screens are single-mechanism screens and do not require a timing device. When an incline screen requires dual mechanisms to achieve the performance requirement, circular motion allows for use of a timing belt instead of gears.

- Frames: Owing to the increased acceleration applied to horizontals, the structural design of screen components and deck frames must be more robust. A horizontal screen of the same size will normally weigh more than that of an incline.

- Structure: Since the support structures for screen towers are sized based on the loading and speed of the unit, the same size horizontal screen could require larger beams to adequately transfer the loads. However, there is also less steel required to support horizontal screens owing to the decreased height. The peripheral components of the installation are also affected. The lower horizontal screen requires a smaller conveyor in length and horsepower.

The most important features and components to consider when evaluating horizontal screens:

- Features: Deck clearance, stroke adjustments (amount and angle), and shapes of the stroke are the most important features of typical horizontal screens in aggregate applications. If the screen does not have deck clearance in concordance with all of the applications for which it will be used, the result will be premature wear on components (this issue becomes more important when the screens are exposed to several different quarries and applications). By having an adjustable stroke, the user is able to optimize the performance of a machine when changing products or materials. Note: An oval stroke on a horizontal screen is typically preferred to straight-line motion, because of the "tumbling" effect that it can provide.

- Components: The deck frame and mechanism are two of the big components to evaluate as these items have a big impact on overall performance and reliability.