60 Questions
Which method of size reduction involves the material being gripped between two surfaces and crushed by the application of pressure?
Compression
What is the main mechanism involved in cutting for size reduction?
Using a sharp edge
In which method of size reduction do the surfaces move relative to each other, resulting in shear forces breaking the particles?
Attrition
What are the basic parts that make up a mill according to the text?
Feed chute, grinding mechanism, discharge chute
Which method of size reduction involves the material being reduced to the desired size by passing it once through the mill?
Open-circuit milling
What happens in the impact method of size reduction?
The material comes into contact with a fast-moving part that imparts kinetic energy.
What is the mechanism of size reduction in a roller mill?
Compression and shearing action
How are the rolls in a roller mill rotated?
One roll is driven directly, and the other is rotated by friction
What is the primary mechanism of size reduction in a hammer mill?
Centrifugal force and impact
What is the function of the screen in a hammer mill?
To allow particles fine enough to pass through and discharge them
Which processing variable is important for hammer mills?
Hammer tip speed
In a roller mill used for milling ointments, pastes, and suspensions, how are the rolls driven?
Both rolls are driven directly but at different speeds
What is the primary mechanism by which the particle size is reduced in fluid-energy mills?
Inter particular attrition
Why is air commonly used in fluid-energy mills?
To lower the temperature during milling
What are two important machine-related factors mentioned for fluid energy mills?
Grinding chamber geometry and nozzle characteristics
In addition to the cost of the mill, what other factors should be considered when selecting fluid energy mills for production?
Cost of fluid-energy source and dust collection equipment
What drawback is associated with the potential build-up of compressed product in fluid-energy mills?
Decreased milling efficiency
What justifies the high capital and running costs in the pharmaceutical industry related to fluid-energy mills?
High value materials processed
What is the key factor in the operation of a ball mill?
The speed of rotation
What type of action is responsible for most size reduction in a ball mill at higher speeds?
Impact
What is the purpose of the coarse screen at the outlet of a ball mill?
To prevent the loss of the grinding balls
Which of the following statements about hammer mills is true?
The speed and screen can be rapidly changed
What is the advantage of a continuous ball mill over a batch-operated ball mill?
Continuous operation
What is the purpose of the balls or pebbles in a ball mill?
To act as the grinding medium
What is the primary reason for recycling larger particles during milling?
To achieve better control over particle size
Which factor determines the choice between wet and dry milling?
The potential for physical or chemical changes in water
What is the typical lower limit for particle size achievable by wet grinding?
10 μm
Which type of mill is typically used for wet grinding of pharmaceutical materials?
Low-speed mill
Which factor is NOT considered when selecting a mill for pharmaceutical materials?
Cost of the mill
What is the primary reason for considering dust control when selecting a mill?
All of the above
What is the primary mechanism of size reduction in a hammer mill?
Impact
Which processing variable is crucial for determining the particle size achieved in hammer mills?
Rotor speed
What type of mill uses a combination of compression and shearing action for size reduction?
Roller mill
What is the primary mechanism involved in size reduction by cutting?
Force applied over a narrow area using a cutting edge
In which method of size reduction does the material experience shear forces due to the relative movement of surfaces?
Attrition
In a roller mill used for milling ointments, pastes, and suspensions, what is the main method of size reduction?
Attrition
What is the principle of operation in most mills dependent on?
A combination of cutting, compression, impact, and attrition
Which factor plays a key role in determining the choice between wet and dry milling for pharmaceutical materials?
Processing temperature
In open-circuit milling, how is the material reduced to the desired size?
By passing it once through the mill
What contributes significantly to the size reduction in a ball mill at higher speeds?
Attrition
Which part of a mill delivers the material into the grinding mechanism?
Feed chute
What is the main action involved in the impact method of size reduction?
Imparting kinetic energy to the material
Which of the following is NOT a benefit of increasing the surface area of a material through milling?
Decreased flowability of powders and granules in high-speed equipment
Which of the following statements is TRUE regarding the mixing or blending of solid ingredients in pharmaceutical manufacturing?
Blending is more uniform when the ingredients have similar particle sizes
Which of the following statements about the mechanism of size reduction in a ball mill is INCORRECT?
The size reduction is achieved by compressing the material between the balls
In the context of milling pharmaceutical materials, what is the primary reason for recycling larger particles?
To ensure uniform particle size distribution in the final product
Which of the following statements regarding the selection of a mill for pharmaceutical materials is INCORRECT?
The cost of the mill is the only factor to be considered
What is the primary mechanism of size reduction in a roller mill?
Compression forces applied by the rolls gripping the material
What is the main factor that contributes to reducing the particle size in fluid-energy mills?
Impact from the air and steam
Why is air commonly used in fluid-energy mills for milling pharmaceuticals?
To cool the system and counteract heat generated
What is a significant drawback associated with the build-up of compressed product in fluid-energy mills?
Changes in milled particle size due to blockages
Why might high capital and running costs be less of a concern in the pharmaceutical industry when using fluid-energy mills?
Pharmaceutical materials are of higher value
What plays a crucial role in selecting fluid energy mills for production, apart from the cost of the mill itself?
Number and angle of nozzles
In fluid-energy mills, what is primarily responsible for reducing particle size apart from interparticular attrition?
Shear forces between particles
What is the primary advantage of using a hammer mill for size reduction in the pharmaceutical industry?
Versatility in milling dry materials, wet filter-press cakes, ointments, and slurries
Which statement best describes the relationship between hammer tip speed and particle size reduction in a hammer mill?
Higher hammer tip speeds contribute to finer particle sizes as particles follow a pathway closer to the screen
What is the primary reason for using a thicker screen in a hammer mill?
To produce a relatively finer mash by limiting the angles at which coarser particles can pass through
Which statement best describes the relationship between particle size and impact energy during milling?
Larger particles impact with higher kinetic energy than smaller particles at constant velocity
Which of the following statements regarding the use of fluid-energy mills in the pharmaceutical industry is true?
The high capital and operating costs of fluid-energy mills are justified by the need for precise particle size control
Which factor is NOT mentioned in the text as important for selecting a mill for pharmaceutical materials?
Compatibility with the specific chemical properties of the material being milled
Explore different methods of size reduction including cutting, compression, impact, and attrition. Learn about how each mechanism works to reduce material size effectively. This quiz covers key concepts related to Chapter 2 on Milling.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
