Difference between revisions of "Sizing"

For chipping normally a chipper machine is used that consists of sharp cutting knives, that slice bigger parts into smaller chips. This is used e.g. for wood materials, straws, mixed garden residues and other feedstock that can be cut by a knife. Chippers are susceptible to knife wear from high soil content, metal contamination, rocks and stone, so the base feedstock normally needs to be cleaned before chipping. The size of the resulting materials is typically 10–30 mm after chipping.

Extrusion is a continuous process that can handle a wide range of feedstocks, including viscous and complex fluids and powders. The feedstock is heated and forced through an opening called 'die'. The feedstock is forced through the die by one or two screws in a heated barrel, the extruder.<ref>{{Cite book|author=Clive Maier|year=1998|book_title=Polypropylene : the definitive user's guide and databook|publisher=Plastics Design Library|place=Norwich, NY|ISBN=978-0-8155-1867-9}}</ref>

There are two types of grinding: coarse grinding, which can then be followed by fine grinding. Normally a grinder is used that cracks bigger parts into smaller particles. The size of the resulting materials is typically 0.2–2 mm. Grinding is achieved by shearing and/or friction and the grinding effect is achieved by multiple comminution in an increasingly narrowing grinding gap, which can usually be varied by axial displacement of a rotor or stator. The frequently tested process variables are screen size, angular velocity, time, feed rate, type, feed size, load, moisture content, and process.<ref>{{Cite journal|author=Tumuluru JS, Heikkila DJ|year=2019|title=Biomass Grinding Process Optimization Using Response Surface Methodology and a Hybrid Genetic Algorithm|journal=Bioengineering|volume=12|issue=6, no. 1|page=1-12|doi=10.3390/bioengineering6010012}}</ref>