Let’s begin by defining “blinding of a screen”. Blinding is when there is a decrease in the open area of a screen due to coating or plugging. We are going to focus on plug blinding as it has become more prevalent due to the increase in recycling. Plug blinding occurs when you are screening material that contains particles with irregular shapes similar to candy corn where the point can fall into a screen opening and then gets stuck or plugs the opening which prevents fine material from passing. Eventually the screen section can lose its screening effectiveness as more of these particles plug into screen openings. Since this material wedges into the screen opening, the vibration energy used to screen the material isn’t always sufficient to knock them out of the opening. The recycling of plastics for one creates irregularly shaped materials that can plug openings thereby adversely affecting screening. Our challenge is to find a way to reduce plug blinding to keep our screening efficient and to reduce the cost of downtime to manually clean the screen deck.
The most efficient means I’ve found to reduce plug blinding is installation of a ball tray deck beneath the screen section. The ball tray consists of compartments with perforated plate at the bottom. Balls are placed in each compartment that freely bounce during the operation of the screener so they strike the underside of the screen surface and therefore randomly knock out the clogged material. The fine material that passes through the screen then passes through the perforated plate at the bottom of the ball tray where it can then be collected.
Ball trays are most effective when the vibration energy produced makes the balls more active. Vibratory Screeners that produce linear force like our model EMS electromechanical screeners are ideal for making the balls more active and therefore more effective in reducing plug blinding. Screeners that use an electric motor to rotate a shaft with counter weights on both ends to produce a circle throw motion can also be effective.
See below a drawing of a specific application for screening plastic regrind where a ball tray deck was utilized. The cutaway provides an illustration of the ball tray deck. The requirement for this application was two screen decks with different openings to create three separate product streams. In this case, we were able to use a single deck profile by inserting a fine screen at the feed end and the coarse screen at the discharge end. The ball tray deck effectively reduced plug blinding of both screens.
We therefore recommend considering ball tray decks if you are experiencing plug blinding. The savings in valuable man hours to keep your screen openings clear should ultimately offset the additional expense.
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Featured Image: Cleveland Vibrator Co.’s Ball Tray Deck Illustration
Featured Image: Cleveland Vibrator Co.’s Ball Tray Deck Spec Sheet