| Class |
Particle Distribution |
Particle Size |
L/D Ratio |
Bulk Density |
Compressibility |
Angle Of Repose |
Adhesive Cohesive Properties |
Class I
Granular, Free Flowing |
Uniform |
1/16 - 3/4" |
Small |
Uniform |
5% or less |
20° or less |
none |
Class II
Powders |
May or may not be Uniform |
20 - 200 mesh |
1-2 |
|
5-15% |
35° |
Slight Cohesive |
Class III
Powders |
Uniform |
200 - 400 mesh |
1-2 |
Slightly Permissible |
2-30% or more |
30 - 40° |
Moderate |
Class IV
Powders |
Uniform |
100 - 400 mesh ( 149 - 37 micron) |
Agglomerated "Chains" can be 4-5:1 |
|
20 - 30% or more |
40° or more |
Adhesive |
Class V
Fibrous, Flake Flocculent |
Non - Uniform |
1/2" X 1/8" |
3:1 or more |
Permeable |
Varies, from 2-10% |
Varies
upto 90° |
Interlocking Tendencies
|
Class I - Granular, Free Flowing :
These are the easiest materials to store,
discharge and convey. Very uniform particle size with consistent, low
length /
diameter L/D ratio. Most often " hard" granular shapes, from
1/16" - 3/4" ( 1.58 - 19mm) are not subject to degradation. They
exhibit no discernible adhesive or cohesive properties. Uniform Bulk Density,
Low Compressibility, ( less than 5%) and repose angle of 20° or less. Typical
examples are plastic pellets, coated prills, silica sand, and aggregates,
palletized /cured feed, ion exchange resin and dry salt.
Class II - Powder Sluggish :
These sluggish powders are comprised of
individual particles which cannot be readily discerned. Running in size from 20
-200 mesh ( 841-74microns). May or may not be uniformly distributed, L/D ratio
between 1-2. They posses sligh cohesive properties due to non - uniform
irregular particle configuration. Slightly compressible ( 5 -15%) and repose
angle upto 35°. Typical examples are baking flour, Limestone, Fluorspar,
pulverized mineral ore, soda ash, fine silica sand, ground coke and medium grade
sugar.
Class III - Powder Sluggish/ Fludizeable :
These powders ( 200 - 400 mesh /
74 - 37 micron ) are sluggish but fluidize able. Their slight permeability is
defined as the degree to which air, or another gas, may be passed through the
void spaces between the individual particulates of the material mass. Gas
entrained during conveying or processing does not readily "percolate
our" Gas retention capability can vary between zero to several hours,
depending upon other physical properties. The entrained gas gives the
powder a " liquid" or fluidized appearance. L/D ratios of 1-2. The
posses moderate cohesive properties which aid in gas retention, also possibly
due to large surface area. Compressibility varies from 5 - 15% a natural
repose angel of 30 - 40°. Typical examples : hydrated lime, cement, silica
gel, starch, fly ash, clay, polymers, carbon black.
Class IV - Powder, Sluggish , Adhesive
: These sluggish, adhesive, or
cohesive powders ( 100 - 400) mesh / 149-37micron) seldom exhibit particle
segregation. The particle shape may be agglomerated or dendritic ( having a
branched, crystalline shape with the " branches" extending from the
faces of the main body). This particle configuration may cause both internal and
external adhesion. L/D ratios of agglomerated " chains" can be 4-5:1.
Compressibility varies from 20 - 30% ( or more). Natural repose angle is excess
of 40°. Class IV is often associated with electro-static charge potential.
Typical examples are pigments (organic or inorganic) metallic oxides ( Ti02,
iron oxide, zinc oxide, lead oxide, chromium / nickel oxide), centrifuge
cake , fluorocarbons, sludges, vegetables products such as Soya bean meal,
cottonseed meal, high fat content bakery products, calcium carbonate and
dispersion resin.
Class V - Fibrous, Flake,
Flocculent
: These materials are generally the
toughest to handle due to their non-uniform particle size and shape, non -
uniform length to dismeter ratios (in excess of 3:1)and their mechanical
(physical) interlocking tendencies. These may be fibrous ( regular or irregular,
"thread like" with flexible structure), flakes( "plate like")
flocculent ( amorphous solids). Class V will interlock, mat or form large
agglomerates. Particle size and shape exceeds 1/2" X 1/8" ( 12.7-3mm).
Physical compressibility could vary from 2-10% highly permeable. The natural
repose angle can vary, upto 90°. Typical examples are wood chips, sawdust,
plastic regrind, asbestos fibers, fiberglass strand, chopped paper, steel/brass/aluminum
chips and e.g. residues such as bagasse.
