July 27, 2021: Pharmaceutical Interview Questions and Answers
#ParticleSizeReductionMechanisms #ParticleSizeReductionOperatingPrinciples #EquipmentClassificationsForParticleSizeReduction
1. What are the different particle size reduction mechanisms?
| Particle size reduction mechanisms | Description |
| Impact | Particle size reduction by applying an instantaneous force perpendicular to the particle/ agglomerate surface. The force can result from particle-to-particle or particle-to-mill surface collision. |
| Attrition | Particle size reduction by applying a force in a direction parallel to the particle surface. |
| Compression | Particle size reduction by applying a force slowly (as compared to Impact) to the particle surface in a direction toward the center of the particle. |
| Cutting | Particle size reduction by applying a shearing force to a material. |
2. What are the types of Equipment used for Particle Size Reduction/ Separation. Explain its Operating Principles.
| Types of Equipment | Operating Principles |
| Fluid Energy Milling | Particles are reduced in size as a result of high-speed particle-to-particle impact and/or attrition; also known as micronizing. |
| Impact Milling | Particles are reduced in size by high-speed mechanical impact or impact with other particles; also known as milling, pulverizing, or comminuting. |
| Cutting | Particles are reduced in size by mechanical shearing. |
| Compression Milling | Particles are reduced in size by compression stress and shear between two surfaces. |
| Screening | Particles are reduced in size by mechanically induced attrition through a screen. This process commonly is referred to as milling or deagglomeration. |
| Tumble Milling | Particles are reduced in size by attrition utilizing grinding media. |
| Separating | Particles are segregated based upon particle size alone and without any significant particle size reduction. This process commonly is referred to as screening or bolting. |
3. Explain Equipment Classifications for Particle Size Reduction/ Separation. Give example of Equipment for each classification.
| Equipment type | Sub classification description | Sub classification |
| Fluid Energy Mills | Fluid energy mill subclasses have no moving parts and primarily are distinguished from one another by the configuration and/ or shape of their chambers, nozzles, and classifiers. | Tangential Jet Loop/ Oval Opposed Jet Opposed Jet with Dynamic Classifier Fluidized Bed Fixed Target Moving Target High Pressure Homogenizer E.g. Jet mill |
| Impact Mills | Impact mill subclasses primarily are distinguished from one another by the configuration of the grinding heads, chamber grinding liners (if any), and classifiers. | Hammer Air Swept Hammer Conventional Pin/ Disc Cage E.g. Hammer mill Pin mill Impact mill Cage mill Disk mill Ball mill |
| Cutting Mills | Although cutting mills may differ from one another in whether the knives are movable or fixed and in the classifier configuration, no cutting mill subclasses have been identified. | No sub class E.g. Multimill Comill |
| Compression Mills | Although compression mills may differ from one another in whether one or both surfaces are moving, no compression mill subclasses have been identified. | No sub class E.g. Roller mill |
| Screening Mills | Screening mill subclasses primarily are distinguished from one another by the rotating element. | Rotating Impeller Rotating Screen Oscillating Bar E.g. Multimill Comill |
| Tumbling Mills | Tumbling mill subclasses primarily are distinguished from one another by the grinding media used and by whether the mill is vibrated. | Ball Media Rod Media Vibrating E.g. Ball mill Tubular Rod Mills |
| Separators | Separator subclasses primarily are distinguished from one another by the mechanical means used to induce particle movement. | Vibratory/ Shaker Centrifugal E.g. Vibro sifter Ultra Centrifugal Mill |
Source: fda.gov
