Milling Mechanisms in Industrial Pharmacy
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Questions and Answers

What is the factor of greatest importance in the operation of the ball mill?

  • The rotation speed (correct)
  • The size of the balls
  • The charge of the mill
  • The material of the balls

    • At low rotating speeds, what happens to the balls in the ball mill?

  • The balls are thrown out onto the mill wall by centrifugal force
  • The balls remain stationary
  • The balls produce a cascading action
  • The balls move with the drum until the force due to gravity exceeds the frictional force, and then slide back to the base (correct)

    • At high angular velocities, what happens in the ball mill?

  • The balls are thrown out onto the mill wall by centrifugal force (correct)
  • The balls remain stationary
  • The balls move with the drum until the force due to gravity exceeds the frictional force, and then slide back to the base
  • The balls produce a cascading action

    • At about two-thirds of the critical angular velocity, what action is produced in the ball mill?

    <p>The balls produce a cascading action</p> Signup and view all the answers

    Which of the following is a disadvantage of the ball mill?

    <p>It is difficult to clean and takes a long time for satisfactory milling</p> Signup and view all the answers

    Which of the following is an advantage of the ball mill?

    <p>All of the above</p> Signup and view all the answers

    What type of atmosphere is recommended for milling thermolabile, easily oxidizable, and combustible materials?

    <p>Inert atmosphere of carbon dioxide or nitrogen</p> Signup and view all the answers

    Why does the milling chamber need to be cooled during the milling process?

    <p>To prevent the solid material from melting</p> Signup and view all the answers

    What is the purpose of pretreatment for milling?

    <p>To ensure the feed is of proper size and enters uniformly</p> Signup and view all the answers

    What can happen if the heat generated during milling is not removed?

    <p>The material will undergo a phase change</p> Signup and view all the answers

    Which statement about milling in a closed system with dehumidified air is true?

    <p>It prevents explosive reactions in the mill</p> Signup and view all the answers

    Why is it crucial to cool the milling chamber during the milling process?

    <p>To prevent excessive heat buildup in the material</p> Signup and view all the answers

    What main method of size reduction involves the application of force over a very narrow area of material?

    <p>Cutting</p> Signup and view all the answers

    Which milling method results in the creation of internal stresses in the particle?

    <p>Impact</p> Signup and view all the answers

    What is the main factor that causes fracture or cracking of a particle during size reduction?

    <p>Energy exceeding the weakest flaw</p> Signup and view all the answers

    Which part of a mill imparts energy to the material for size reduction?

    <p>Cutting device</p> Signup and view all the answers

    In which method of size reduction are surfaces moving relative to each other, resulting in shear forces that break the particles?

    <p>Attrition</p> Signup and view all the answers

    What is the typical pressure range for the air or steam used in a fluid-energy mill?

    <p>100 to 150 pounds per square inch (psi)</p> Signup and view all the answers

    What is the role of residual strain energy in the process of fracture during size reduction?

    <p>Supply additional energy required for fracture</p> Signup and view all the answers

    What is the primary mechanism by which particle size reduction occurs in a fluid-energy mill?

    <p>Interparticular attrition</p> Signup and view all the answers

    Why is air typically used as the fluid in a fluid-energy mill rather than steam?

    <p>Most pharmaceuticals have a low melting point or are thermolabile.</p> Signup and view all the answers

    Which of the following is NOT an important machine-related factor in a fluid-energy mill?

    <p>The material of construction of the mill.</p> Signup and view all the answers

    What is a key disadvantage of using a fluid-energy mill?

    <p>High capital and running costs.</p> Signup and view all the answers

    What is a key advantage of using a fluid-energy mill?

    <p>Ability to produce powders with all particles below a few micrometers.</p> Signup and view all the answers

    What is the primary drawback associated with the type of mill described in the text?

    <p>The potential for the build-up of compressed product in the mill</p> Signup and view all the answers

    Which type of materials cannot be effectively milled by pressure or impact?

    <p>Fibrous materials</p> Signup and view all the answers

    Which statement best describes the effect of moisture content on the milling process?

    <p>Moisture content above 5% hinders comminution and may produce a sticky mass</p> Signup and view all the answers

    What is the primary factor that determines the choice of equipment for milling?

    <p>The physical properties of the material to be milled</p> Signup and view all the answers

    Which statement best describes the behavior of friable materials during milling?

    <p>Friable materials tend to fracture along well-defined planes and may be milled by attrition, impact, or compression</p> Signup and view all the answers

    What is the primary advantage of using a wet milling process for materials with high moisture content?

    <p>It allows for the milling of materials that cannot be effectively milled dry</p> Signup and view all the answers

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