SIZE ALTERATION Flashcards
Size Alteration of AB Materials
Size Reduction
Size Enlargement
includes cutting, crushing and grinding, and milling
size reduction
The performance of a machine for reducing the size of material is
characterized by the capacity, the power required per unit of material
reduced, the size and shape of the product before and after reduction,
and the range in size and shape of the resultant product.
Size Characteristics
particles or units which can be accurately measured and easily seen with
minimum measurement approximately 1/8 & in. or more.
dimension range
example for dimension range
Diced fruit and vegetables and chopped
forage
particles with minimum dimension range of 0.125 to 0.0029 in. approximately.
sieve range
examples of sieve range
ground feed and commercial fertilizers
particles with minimum dimension less than 0.0029 in.
microscopic range
Examples of microscopic range
chemical powders, dusts, and Portland cement
Reduced materials may be placed in three groups or classes based upon
size.
dimension range
sieve range
microscopic range
The simplest method and the one
most frequently used for placing granular
materials in class 2
Tyler Sieves
has a
definite shaking motion and can be adjusted for
time of operation, can be used for carefully
controlled studies.
Ro-Tap
A classification system devised by D. A. Abrams for concrete work is used
by the American Society of Agricultural Engineers for determining the performance of feed
grinders.
Fineness Modulus
Although the fineness modulus gives an average size, it does not indicate
the distribution of the fines and coarses in any sample, and the average grain size is not
proportional to the modulus index. These objections can be overcome by using the
uniformity index which is demonstrated on the basis of the tabulated analysis.
Uniformity Index
SZE CHARACTERISTICS
Tyler Sieves
Fineness Modulus
Uniformity Index
Energy Requirements
The size of agricultural products is reduced by:
cutting
crushing
shearing
It is separation or reduction which is produced by pushing or forcing
a thin, sharp knife through the material to be reduced.
cutting
It is the reduction by applying a force to the unit to be reduced in
excess of its strength.
crushing
is a combination of cutting and crushing.
shearing
reducing devices
Hammer Mills Burr Mills Crushers Roll Crushers Jaw Crusher
are processes that
purposely combine small particles into large permanent
masses in which the initial primary units are still identifiable.
size enlargement operations
These processes are considered on the basis of the
principal mechanism used to bring the particles
together into agglomerates.
- Compaction
- Granulation
- Encapsulation
- Pelletizing or Tableting
- Sintering or Heat Hardening
- Agglomeration
Two main categories of size enlargement
intantizing
extrusion
Processes that aim to control the functional properties(Density
and Porosity) of the materials in order to to influence properties such as
reconstitutability, dispersibility, and solubility.
intantizing
Processes with an objective of obtaining definite shapes or
defined forms.
extrusion
Transforms a powder material into larger entities, to end up with an aggregate considerably
larger in size and with a porous structure.
granulation/tumbling agglomeration
Powders are densified and compacted by the application of External Force in a confined space.
With most materials, the necessary condition to produce a strong compact is to reduce the
porosity to a minimum and increase the density at the maximum.
compaction/pressure method
Bonding by treatment at high temperature
sintering/heat method
Bonding by treatment at high temperature
sintering/heat method
involves the incorporation of food ingredients, enzymes, cells or other materials in small
capsules.
encapsulation
a method of agglomeration, or particle size enlargement, in which material fines are
processed into pellets or granules
pelletizing
a method of agglomeration, or particle size enlargement, in which material fines are
processed into a tablet.
tableting
Forces involve in Agglomeration and
Granulation
- Solid and Liquid Bridges, Capillary Forces
- Van der Waals’ forces
- Electrostatic forces
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