What's
A MRF--Analysis
Collecting and Analyzing Data
1.
Instruct students to sketch and label the improved mini-MRF in the chart
"Designing a Mini-MRF."
2.
Encourage students to make a log of the development of their stations
in the chart "Designing a Mini-MRF." Ask them to include a description
of the original design, rationale for the design, improvements made to
the design and suggestions for additional improvements. Allow groups to
discuss observations and outcomes with other groups.
Drawing
Conclusions
Q1: Which principles of physics apply in the operation of a MRF?
Cite examples.
A1: Students may refer to Example of Flow of Materials Through
a MRF or to their own mini-MRFs. Physics principles include work and motion
(conveyor carrying materials down the line), magnetism (sorting ferrous
metals), gravity (materials falling off the conveyor), density (flotation
and sorting of light fraction) and electricity (powering air classifiers
and conveyors).
Q2:
Your mini-MRF sorted a small volume of commingled materials. A large scale
MRF may sort tons of materials per hour. What problems do you think a
large scale MRF might have with sorting? (Consider such factors as materials
compaction and labor.) How might these problems be solved?
A2:
A large scale MRF dealing with tons of materials may have a problem with
compression. Compressed materials do not sort as easily as loose materials.
To overcome this problem, some MRFs utilize the "waterfall" effect. Materials
are moved on a series of conveyors positioned in such a way that materials
cascade over the edge of one belt onto another one underneath. The tumbling
motion loosens materials for easier sorting. Operation of a commercial
MRF can be labor intensive, which can contribute significantly to costs.
Some MRFs have mechanized portions of the sorting process, but still require
manual sorting of materials for which automated sorting is not available.
For instance, plastics as a whole may be removed from the commingled mix
mechanically, but different types of plastics must be separated from each
other by hand.
CYCLES
FOR SCIENCE RESOURCES
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