Chapter 2 |Milling

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Which method of size reduction involves the material being gripped between two surfaces and crushed by the application of pressure?

Cutting

Impact

Compression (correct)

Attrition

What is the main mechanism involved in cutting for size reduction?

Imparting kinetic energy

Using a sharp edge (correct)

Application of pressure

Subjecting material to shear forces

In which method of size reduction do the surfaces move relative to each other, resulting in shear forces breaking the particles?

Attrition (correct)

Cutting

Impact

Compression

What are the basic parts that make up a mill according to the text?

Feed chute, grinding mechanism, discharge chute Signup and view all the answers

Which method of size reduction involves the material being reduced to the desired size by passing it once through the mill?

Open-circuit milling Signup and view all the answers

What happens in the impact method of size reduction?

The material comes into contact with a fast-moving part that imparts kinetic energy. Signup and view all the answers

What is the mechanism of size reduction in a roller mill?

Compression and shearing action Signup and view all the answers

How are the rolls in a roller mill rotated?

One roll is driven directly, and the other is rotated by friction Signup and view all the answers

What is the primary mechanism of size reduction in a hammer mill?

Centrifugal force and impact Signup and view all the answers

What is the function of the screen in a hammer mill?

To allow particles fine enough to pass through and discharge them Signup and view all the answers

Which processing variable is important for hammer mills?

Hammer tip speed Signup and view all the answers

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 Signup and view all the answers

What is the primary mechanism by which the particle size is reduced in fluid-energy mills?

Inter particular attrition Signup and view all the answers

Why is air commonly used in fluid-energy mills?

To lower the temperature during milling Signup and view all the answers

What are two important machine-related factors mentioned for fluid energy mills?

Grinding chamber geometry and nozzle characteristics Signup and view all the answers

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 Signup and view all the answers

What drawback is associated with the potential build-up of compressed product in fluid-energy mills?

Decreased milling efficiency Signup and view all the answers

What justifies the high capital and running costs in the pharmaceutical industry related to fluid-energy mills?

High value materials processed Signup and view all the answers

What is the key factor in the operation of a ball mill?

The speed of rotation Signup and view all the answers

What type of action is responsible for most size reduction in a ball mill at higher speeds?

Impact Signup and view all the answers

What is the purpose of the coarse screen at the outlet of a ball mill?

To prevent the loss of the grinding balls Signup and view all the answers

Which of the following statements about hammer mills is true?

The speed and screen can be rapidly changed Signup and view all the answers

What is the advantage of a continuous ball mill over a batch-operated ball mill?

Continuous operation Signup and view all the answers

What is the purpose of the balls or pebbles in a ball mill?

To act as the grinding medium Signup and view all the answers

What is the primary reason for recycling larger particles during milling?

To achieve better control over particle size Signup and view all the answers

Which factor determines the choice between wet and dry milling?

The potential for physical or chemical changes in water Signup and view all the answers

What is the typical lower limit for particle size achievable by wet grinding?

10 μm Signup and view all the answers

Which type of mill is typically used for wet grinding of pharmaceutical materials?

Low-speed mill Signup and view all the answers

Which factor is NOT considered when selecting a mill for pharmaceutical materials?

Cost of the mill Signup and view all the answers

What is the primary reason for considering dust control when selecting a mill?

All of the above Signup and view all the answers

What is the primary mechanism of size reduction in a hammer mill?

Impact Signup and view all the answers

Which processing variable is crucial for determining the particle size achieved in hammer mills?

Rotor speed Signup and view all the answers

What type of mill uses a combination of compression and shearing action for size reduction?

Roller mill Signup and view all the answers

What is the primary mechanism involved in size reduction by cutting?

Force applied over a narrow area using a cutting edge Signup and view all the answers

In which method of size reduction does the material experience shear forces due to the relative movement of surfaces?

Attrition Signup and view all the answers

In a roller mill used for milling ointments, pastes, and suspensions, what is the main method of size reduction?

Attrition Signup and view all the answers

What is the principle of operation in most mills dependent on?

A combination of cutting, compression, impact, and attrition Signup and view all the answers

Which factor plays a key role in determining the choice between wet and dry milling for pharmaceutical materials?

Processing temperature Signup and view all the answers

In open-circuit milling, how is the material reduced to the desired size?

By passing it once through the mill Signup and view all the answers

What contributes significantly to the size reduction in a ball mill at higher speeds?

Attrition Signup and view all the answers

Which part of a mill delivers the material into the grinding mechanism?

Feed chute Signup and view all the answers

What is the main action involved in the impact method of size reduction?

Imparting kinetic energy to the material Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

What is the primary mechanism of size reduction in a roller mill?

Compression forces applied by the rolls gripping the material Signup and view all the answers

What is the main factor that contributes to reducing the particle size in fluid-energy mills?

Impact from the air and steam Signup and view all the answers

Why is air commonly used in fluid-energy mills for milling pharmaceuticals?

To cool the system and counteract heat generated Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

In fluid-energy mills, what is primarily responsible for reducing particle size apart from interparticular attrition?

Shear forces between particles Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

Chapter 2 |Milling

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Questions and Answers

Which method of size reduction involves the material being gripped between two surfaces and crushed by the application of pressure?

What is the main mechanism involved in cutting for size reduction?

In which method of size reduction do the surfaces move relative to each other, resulting in shear forces breaking the particles?

What are the basic parts that make up a mill according to the text?

Which method of size reduction involves the material being reduced to the desired size by passing it once through the mill?

What happens in the impact method of size reduction?

What is the mechanism of size reduction in a roller mill?

How are the rolls in a roller mill rotated?

What is the primary mechanism of size reduction in a hammer mill?

What is the function of the screen in a hammer mill?

Which processing variable is important for hammer mills?

In a roller mill used for milling ointments, pastes, and suspensions, how are the rolls driven?

What is the primary mechanism by which the particle size is reduced in fluid-energy mills?

Why is air commonly used in fluid-energy mills?

What are two important machine-related factors mentioned for fluid energy mills?

In addition to the cost of the mill, what other factors should be considered when selecting fluid energy mills for production?

What drawback is associated with the potential build-up of compressed product in fluid-energy mills?

What justifies the high capital and running costs in the pharmaceutical industry related to fluid-energy mills?

What is the key factor in the operation of a ball mill?

What type of action is responsible for most size reduction in a ball mill at higher speeds?

What is the purpose of the coarse screen at the outlet of a ball mill?

Which of the following statements about hammer mills is true?

What is the advantage of a continuous ball mill over a batch-operated ball mill?

What is the purpose of the balls or pebbles in a ball mill?

What is the primary reason for recycling larger particles during milling?

Which factor determines the choice between wet and dry milling?

What is the typical lower limit for particle size achievable by wet grinding?

Which type of mill is typically used for wet grinding of pharmaceutical materials?

Which factor is NOT considered when selecting a mill for pharmaceutical materials?

What is the primary reason for considering dust control when selecting a mill?

What is the primary mechanism of size reduction in a hammer mill?

Which processing variable is crucial for determining the particle size achieved in hammer mills?

What type of mill uses a combination of compression and shearing action for size reduction?

What is the primary mechanism involved in size reduction by cutting?

In which method of size reduction does the material experience shear forces due to the relative movement of surfaces?

In a roller mill used for milling ointments, pastes, and suspensions, what is the main method of size reduction?

What is the principle of operation in most mills dependent on?

Which factor plays a key role in determining the choice between wet and dry milling for pharmaceutical materials?

In open-circuit milling, how is the material reduced to the desired size?

What contributes significantly to the size reduction in a ball mill at higher speeds?

Which part of a mill delivers the material into the grinding mechanism?

What is the main action involved in the impact method of size reduction?

Which of the following is NOT a benefit of increasing the surface area of a material through milling?

Which of the following statements is TRUE regarding the mixing or blending of solid ingredients in pharmaceutical manufacturing?

Which of the following statements about the mechanism of size reduction in a ball mill is INCORRECT?

In the context of milling pharmaceutical materials, what is the primary reason for recycling larger particles?

Which of the following statements regarding the selection of a mill for pharmaceutical materials is INCORRECT?

What is the primary mechanism of size reduction in a roller mill?

What is the main factor that contributes to reducing the particle size in fluid-energy mills?

Why is air commonly used in fluid-energy mills for milling pharmaceuticals?

What is a significant drawback associated with the build-up of compressed product in fluid-energy mills?

Why might high capital and running costs be less of a concern in the pharmaceutical industry when using fluid-energy mills?

What plays a crucial role in selecting fluid energy mills for production, apart from the cost of the mill itself?

In fluid-energy mills, what is primarily responsible for reducing particle size apart from interparticular attrition?

What is the primary advantage of using a hammer mill for size reduction in the pharmaceutical industry?

Which statement best describes the relationship between hammer tip speed and particle size reduction in a hammer mill?

What is the primary reason for using a thicker screen in a hammer mill?

Which statement best describes the relationship between particle size and impact energy during milling?

Which of the following statements regarding the use of fluid-energy mills in the pharmaceutical industry is true?

Which factor is NOT mentioned in the text as important for selecting a mill for pharmaceutical materials?

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