Underneath some of the rolls in a card, there are sheet metal screens , sometimes called pans. These screens are usually under the lickerin, lickerin transfer, breast, breast transfer, and main cylinder. The primary purpose of these screens is to control wind currents and thus prevent fiber blow out. A roll covered with teeth acts somewhat like a fan and can create wind cur-rents. On some cards these screens have openings or slits across them to allow trash to fall through. This is the case if the card is primarily running natural fiber. If the card is running synthetic fibers, the screens are usually solid. It is very important to maintain a proper setting of the screens, but once properly set, they need little adjustment. On newer cards there are better systems for opening the screens. The screens should be opened and cleaned frequently as fiber finish can build on the screens and cause the fiber to drag and distort the web.