Factors Affecting Size Reduction: It includes
6. Softening temperature
7. Moisture content
It is a surface property of the material. The hardness of the material is measured by a devised known as Moh’s Scale, The Moh scale is from 1 to 10. Material of hardness 1 to 3 are classified as soft (eg talc, waxes), 4 to 7 intermediate (Limestone and bauxite), and 8 to 10 hard (Quartz and diamond). The harder the material the more difficult it is to reduce in size.
The Toughness of the material is sometimes more important than the hardness. Soft but tough material may present more problems in reducing size than a hard but brittle substance. For example, it is difficult to break the rubber than a blackboard chalk stick.
Abrasiveness is a property of hard materials. The final powder may be contaminated with more than 0.1 percent of the grinding mill’s worn metal during the grinding of abrasive substances.
Stickiness is a property that causes considerable difficulty in reducing the size because the material gets to adhere to the grinding surfaces or the screen meshes may be blogged.
It is the opposite of stickiness. It can also lead to size reduction difficulties as the material acts as a lubricant and decreases the efficiency of grinding surfaces.
6. Softening Temperature
During the size reduction process, sometimes heat is generated which can cause some substances to soften, and the temperature at which this occurs may be important. Waxy substances, such as stearic acid, or drugs containing oils or fats are examples that may be affected. Some methods can be used to overcome this like cooling the mill, either by a water jacket or by passing a stream of air through the equipment.
7. Moisture Content
The moisture content influences several properties that may affect size reduction, For example, hardness, toughness, or viscosity. In general, the materials must be dry or moist and not merely moist. Usually, less than 5 percent moisture is adequate if the substance is to be ground dry or more than 50 if it is being subjected to wet milling.
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