“Blinding” is typically caused by moisture or static energy in which a particle (or particles) adheres to the screen media. “Pegging” is caused when particles are stuck or wedged in between the wires of the screen media.
The McLanahan MD vibratory screen has screen decks at progressively steeper angles, and employs larger screen opening sizes than the actual size separation. This by itself reduces the potential for material to cause pegging.
However, screens with slotted openings can further reduce the potential for pegging because they offer more screen surface area, and the shape of the opening reduces the potential for a particle to get “wedged” inside the opening created by the four wires.
Three ways to assist with clearing screen surfaces from a build-up of material include:
- A ball deck, a tray installed underneath the screen media that contains balls (of various materials) that bounce up and into the bottom surface of the screen media. The rapid, continuous action of the balls beating against the underside of the screen media helps dislodge material.
- Nylon chains, which are useful in blinding situations because of their motion on top of the screen surface during operation. Multiple strands of nylon chain (or rope) are draped along the length of the screen panel and, during normal operation, a “snaking” motion occurs, assisting with keeping the screens clear of material that otherwise could slowly build up and create a blinding situation.
- A pneumatic tensioning system that governs the tension of a screen cloth such that it is periodically slackened and then retensioned. This slackening will enable the screen cloth to rattle, thereby removing sticking or pegged particles. Both the slackening and tensioning periods can be adjusted at the control panel. Moreover, the pneumatic tensioning system is tied in with the machine’s control logic, such that the machine will shut down when the air pressure is insufficient to maintain proper tension on the screen cloth.
Source: McLanahan Corporation