July 27, 2021: Pharmaceutical Interview Questions and Answers

#ParticleSizeReductionMechanisms #ParticleSizeReductionOperatingPrinciples #EquipmentClassificationsForParticleSizeReduction

1. What are the different particle size reduction mechanisms?

Particle size reduction mechanismsDescription
ImpactParticle 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.
AttritionParticle size reduction by applying a force in a direction parallel to the particle surface.
CompressionParticle size reduction by applying a force slowly (as compared to Impact) to the particle surface in a direction toward the center of the particle.
CuttingParticle 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 EquipmentOperating Principles
Fluid Energy MillingParticles are reduced in size as a result of high-speed particle-to-particle impact and/or attrition; also known as micronizing.
Impact MillingParticles are reduced in size by high-speed mechanical impact or impact with other particles; also known as milling, pulverizing, or comminuting.
CuttingParticles are reduced in size by mechanical shearing.
Compression MillingParticles are reduced in size by compression stress and shear between two surfaces.
ScreeningParticles are reduced in size by mechanically induced attrition through a screen. This process commonly is referred to as milling or deagglomeration.
Tumble MillingParticles are reduced in size by attrition utilizing grinding media.
SeparatingParticles 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 typeSub classification descriptionSub classification
Fluid Energy MillsFluid 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 MillsImpact 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 MillsAlthough 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 MillsAlthough 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 MillsScreening mill subclasses primarily are distinguished from one another by the rotating element.Rotating Impeller Rotating Screen Oscillating Bar  
E.g. Multimill
Comill
Tumbling MillsTumbling 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
SeparatorsSeparator 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

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