1. Field of the Invention
The present invention relates generally to mineral fiber production, and in particular to method and apparatus for extracting fiber product from a moving air stream.
2. Description of the Prior Art
In the art of producing mineral fiber, a spinning unit is utilized for fiberizing molten slag with air or steam. The fiber is conveyed through a flow chamber or collection chamber by down draft fans to a conveyor belt where it is removed by various methods and put into a conventional bagger. A limitation of this arrangement is that it is not a closed system, and the lint or airborn flywool by-product cannot be completely contained, thereby allowing a large quantity of fugitive airborne particles to be emitted into the atmosphere and contributing to pollution of the environment. Because of its damaging ecological effect, this airborne, fugitive fly by-product must be captured or recovered before the air stream, in which it is entrained, is discharged into the atmosphere.
Rotary filters have been developed for limiting such emissions to safe levels while allowing the mineral fiber process to be operated efficiently on a large scale. An example of a rotary filter assembly which is very effective in limiting emissions of airborne lint particles is illustrated and described in my co-pending application Ser. No. 273,360. In the operation of this type of rotary filter, high air stream flow rates are required because of the large mass of fiber product transported by the air stream. Most of the fiber product is agglomerated and is settled out in a settling chamber by gravity flow. However, a substantial amount of fiber product is airborne and accumulates in a blanket around the rotary screen. Because of the relatively high air stream flow rate, the fiber blanket which accumulates around the screen is maintained there by the pressure differential which arises as the air stream flows through the screen. This pressure differential, unless relieved, opposes gravity flow and the thickness of the fiber product blanket builds up until the flow of the moving air stream becomes choked off.
Various attempts have been made to clear the rotating screen, including directing a blast of air through the screen from an airblast tube located inside of the rotating drum. This approach has been somewhat successful for "wet" fiber product (i.e. fiber product produced by steam fiberizing). However, for "dry" fiber product produced by air fiberizing, it has been found that the dry air processed fiber product, because of its relatively low mass and dryness, tends to remain airborne within the settling chamber until the settling chamber fills, even though a portion of the rotary screen is being cleared continuously by the airblast tube. The turbulent movement of the dry fiber product within the settling chamber results in the settling chamber filling up faster than the dry product can be discharged, thus causing shut-down of the production line.