A: Jeff Dierig, Sweco, says:
Paying close attention to how your screener is operating can help you stem larger problems from developing. For instance, a sudden drop in screener capacity could have several causes. The problem could be related to the material, such as an increase in moisture content, or a change in ambient conditions, such as higher temperatures or humidity. If screener throughput drops during the day shift but returns to normal during the night shift, higher daytime temperatures may be the culprit. To solve such problems, you may need to modify material storage and handling practices or improve temperatures and humidity control in your screener area.
Improper screen tension. A correctly tensioned screen is completely taut. This stretches out the mesh to the designated mesh opening size. An incorrectly tensioned screen will sag on the insert frame, causing the mesh openings to distort and restrict your material’s flow through the screen. Poor tension also can cause material to puddle on the screen rather than pass through the mesh openings. Establish a time interval for checking screen tension. The interval will depend on your screen type and manufacturer. For instance, you should typically tension a manually adjustable insert screen once a week. Also, check nonadjustable screens once a week to see if they’ve sagged or stretched and require replacement.
Screen deck wear. To prevent contamination, particularly if your screener uses stacked screen decks to process spices or other extremely pure products, you need to prevent screen deck abrasion. You can install screen decks with flaps on the edges that completely seal each screen from the others. You can also improve the screener’s longevity by installing a target plate across the inlet to disperse material so that it doesn’t crash down on the deck and abrade it. The target plate channels the material into the screener only as fast as the material can be processed, eliminating overloads.
Unsuitable or worn screen cleaners. Carefully choose screen cleaners for your screener. The cleaners can be balls, cubes, or other items that agitate, tap, or wipe the screen during sifting to prevent material from clogging or blinding the screen. You may need to run tests to find a screen cleaner that prevents blinding without wearing the screen. Whichever cleaners you choose will eventually wear. Check them periodically and replace them before they’re 20 percent reduced or small enough to pass through the retainer wire and end up in your material.
Whether the problem is large or small, address it immediately. The screener’s constant motion can very quickly turn a small problem into a big one.
Sweco supplies customized industrial separation equipment.