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Best Practices in Wood Waste Recycling Click here for printable PDF version Disk Scalping Screens Material: Wood Waste Issue: The wood waste delivered to a processing facility typically
contains a certain quantity of small-sized
wood (chips and chunks), fines, and small
contaminants mixed in with the larger pieces
of wood waste. This material can cause problems
for the processing facility. The small-sized
wood and fines complicates manual sorting
activities because they overwhelming sorters
with a many individual pieces that hide internal
contaminants, which appear upon the conveyor.
The wood fines are also typically mixed with
dirt and grit contaminants. The combination
of fines, dirt, and grit tend to cause excessive
wear on material-handling and size-reduction
equipment, thus creating excessive equipment
maintenance requirements. Finally, the small
contaminants can be easily missed by manual
and automated contaminant removal systems
before the size reducing process. Failure
to remove these small contaminants could lead
to excessive requirements on equipment maintenance
and degrade the quality of the end-product.
Best Practice: This Best Practice recommends the removal of small-sized wood, fines, and small contaminants from wood waste incoming into a processing facility. A disc scalping screen is one type of equipment that processors can use to perform this function. Following is a description of this equipment: Disc Scalping Screen: Disc
scalping screens are designed to align with
a chain or belt conveyor of the same width.
The disc scalping screen consists of a series
of driven shafts that turn in the direction
of material flow. The shafts are mounted with
discs, arranged in rows along the length of
the shaft. As the wood waste passes over the
turning discs, smaller material falls out
between the discs and the larger pieces are
carried across to the next conveyor or processing
equipment. Operators can control the size
of material that is allowed to fall through
the disc screen by varying the number of discs
and the distance between shafts. Some models
are available with adjustable discs that allow
better screening control. Disc scalping screens
are generally available in sections running
from about ten to fifteen feet in length. Implementation: Disc scalping screens should be installed in the initial stage of wood-waste processing to remove small materials and contaminants early in the process. Following is a description of the selection considerations for a disc scalping screen: Selection Considerations. The primary issues that an operator should consider when selecting equipment like a disc scalping screen include the following: operational issues (effectiveness, compatibility with other process equipment, capability to handle targeted production throughput, etc.), capital cost, maintenance issues, and safety issues. Operational: Through work with an equipment vendor, disc scalping screens can be sized to handle the types and volumes of wood waste processed at a given facility. Disc scalping screens function best when there is a large disparity between the size of the material passing through and that running over the top of the discs.
Cost: Disc screens are effective and relatively inexpensive compared to competing screen systems. Maintenance: Disc scalping screens usually require little maintenance. On occasion, particles that are under or on-size in only one dimension might attempt to pass through the openings and become trapped because of its irregular shape. This jamming, especially if caused by a stone or other hard material, is sometimes sufficient to jam the entire screen, which may result in mechanical damage to the drive and other components. The solutions to this problem include using spacers between the discs made from a softer, flexible material which allows the discs to deflect slightly and permit the trapped particle to drop free. Also, some hydraulic drives can sense pressure build-up and momentarily reverse rotation to clear the jam. Safety: The general operation of disc screens creates no unique safety issues so long as drive components are adequately guarded. Benefits: The removal of small wood, fines, and small contaminants during the initial stage of waste wood processing is an effective way to maximize contaminant removal and avoid excessive equipment wear. Disc scalping screens are an effective piece of equipment for removing small wood, fines, and small contaminants such as metal, rocks, glass, etc. from the larger pieces of wood waste. Application Site: This Best Practice applies to wood-waste processing facilities. Contact: For more information about this Best Practice, contact CWC (206) 443-7746, e-mail info@cwc.org. References:
1.
General Kinematics;
equipment brochure 2. Lyman, Mark. West Salem Machinery; Salem, OR. 3. Pneuco Sales and Engineering Ltd.; Richmond, BC, Canada. 4. Sherman, Raymond. General Kinematics; Barrington, IL.
5.
West Salem
Machinery; equipment brochure (See Appendix for an Equipment Manufacturers List)
Issue Date /
Update: March 1997
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