Understanding Dry Bulk Materials

Material Classifications  Code Chart  Material Characteristics  Mesh size equivalents Material Handling Terms    Pneumatic Conveying Terms

MATERIAL HANDLING BASIC TERMS
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Abrasiveness
The abrasiveness of a material is determined by its hardness factor and the shape of its particles.  For instance, a material which has a high Moh's hardness factor and has sharp, angular-shaped particles will be considered highly abrasive.

Adhesion
Adhering of the material to a surface or particle other than itself. (After material has been squeezed in your hand for one minute, observe the adhesive characteristic by noting particles sticking to your extended fingers.)

Adhesiveness
Adhesiveness can be described as "external cohesiveness" which is the ability of material to adhere to other surfaces.

Aeration
The action of introducing air (or gas) to a bulk material by any means.
Aeration may cause the material to become fluidized or agitated.

Air Retention
Air retention is the ability of a material to retain air (or other gas) in the void spaces of the material after the air (or gas) supply to it has been terminated. Air retention capability can vary between almost zero and several days, depending on the material's other physical characteristics.

Angle of Repose
The angle of repose of a bulk material is the angle formed between the horizontal and sloping surface of a piled material, which has been allowed to form naturally without any conditioning. 

Bulk Density (Fluidized)
Fluidized bulk density is the apparent bulk density of a material in its fluidized state. It is generally lower than either the packed or loose bulk density due to the air absorbed into the voids.

Bulk Density (Loose)
The loose bulk density (sometimes called the poured bulk density) o a bulk material is the weight per unit of volume (usually pounds per cubic foot) that has been measured when the sample is in a loose, non-compacted or poured condition. The loose bulk density may be close to the 'as conveyed" bulk density and is preferred for the purposes of pneumatic conveying system design.

Bulk Density (Packed)
The packed bulk density of a bulk material is the weight per unit volume (usually pounds per cubic foot) that has been measured when the sample has been packed or compacted in. For instance, a silo or bin or after containerized transportation. The packed bulk density does not compare to the conditions that the loose bulk density is preferred for the purposes of conveying system design.

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Bulk Material Composition
The following table describes the general compositions that may be found in a bulk material.

Term            Definition
Uniform         A single bulk material whose particles possess the same size and shape.
Non-Uniform   A single bulk material whose particle size and shape may vary.
Granular        A bulk material comprised of individual particles which can be visibly discerned.
Powder         A bulk material comprised of individual particles which cannot be visibly discerned.
Mixed           Two or more different bulk materials which have been combined.

Cohesiveness
Cohesiveness describes the tendency of a material to adhere to itself. The Cohesiveness of a bulk solid material can be caused by any and sometimes by all of several factors. These include electrostatic charging, surface tension effects, and interlocking of certain particle shapes, particularly fibrous types of materials. Cohesiveness in bulk solids causes erratic flow frombins. pipeline feeding problems, and adverse effects in certain kinds of valves.

Compressibility
Ability of a material to compress under head load (its own weight). Squeezing material in hand will reveal this characteristic.

Corrosiveness
Some materials have chemical properties which will, when combined with other materials such as moisture and air, cause chemical deterioration to materials of construction.

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Explosiveness
In certain conditions, some bulk materials can form potentially explosive mixtures when combined with air. These conditions depend on (a) the nature of the material itself, which would include its ignition temperature, its chemical reaction with oxygen, its particle size distribution, and so on; and (b) the nature of the operation involving the material.
Details of explosion risk, reactivity, and fire hazard are not required by law in most states in the U.S. to be listed on the Material Safety Data Sheet (MSDS). The MSDS must accompany any material which is transported, stored or tested.

In all cases involving explosive materials, reference should be made to NFPA classifications.

Floodability
Reflects a material's tendency to aerate and act as a fluid. (Squeeze material quickly in your fist. If it squirts through your fingers, then it is floodable.) Floodable materials are difficult to restrain in controlled feeding applications, and deserve conscientious sizing.

Flowability
Flowability is the ease with which a bulk material flows under the influence of gravity only.

Fluidized
Fluidized describes the state some bulk materials achieve when a gas has been entrained into the void spaces between the particles of the material. Material in a highly fluidized state tends to behave more like a fluid (as the term implies) than a solid bulk material.

Friability
Friability describes a bulk material where particles are easily crumbled or pulverized.

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