The terms “blinding” and “pegging” are often used interchangeably in describing material covering over screen surface area during any type of screening process, but there is a difference between the two. “Blinding” is typically caused by moisture or static energy in which a particle (or particles) adhere to the screen media. “Pegging” is caused when a particle (or particles) get stuck or wedged in between the wires of the screen media.
Preventing blinding and pegging
Because the McLanahan MD Vibratory Screen has screen decks at progressively steeper angles, we use screen opening sizes larger than the required actual size separation. This by itself reduces the potential for material to cause a pegging situation. However, screens having slotted openings are available to further reduce the potential for pegging. This is because a slotted screen offers 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.
Screens with slotted openings and screens with openings larger than the required actual size separation can reduce pegging situations.
We also offer ball decks, nylon chains, and a pneumatic screen tensioning system to assist with keeping the screen surfaces clear from a buildup of material.
1. Ball deck
A ball deck is simply a tray (or trays) installed underneath the screen media that contains balls (of various materials) that bounce up and into the bottom surface of the screen media. This rapid, continuous action of the balls beating against the underside of the screen media helps dislodge material that may be wedged.
Installing balls, like these, in a tray underneath the screen media can help dislodge material that may be wedged into the screen.
2. Nylon chains
Nylon chains are useful in potential 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 would have the opportunity to slowly build up and create a blinding situation.
Nylon chains draped along the screen panels create a "snaking" motion during normal operation that reduces the opportunity for material to build up.
3. Pneumatic tensioning system
What is the pneumatic screen tensioning system? Pneumatic tensioning is one of several methods used to protect against the blinding of a screen mesh, and it can be applied on all types of McLanahan MD Vibratory Screening products. The pneumatic tensioning system governs the tension of a screen cloth such that it is periodically slackened and then re-tensioned. This slackening will enable the screen cloth to rattle, thereby removing sticking or pegged particles. Both the slackening period and the tensioning period can be adjusted at the control panel.
Additionally, 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.
If you are interested in learning more about the pneumatic tensioning system for MD Vibratory Screens, click the button below to contact us for more information.
