30 Questions
What is the recommended moisture content for materials to be ground dry?
5%
Why are enclosed mills necessary for certain substances?
To reduce dust and protect operators
What is the primary reason for carrying out size reduction in multiple stages?
To achieve a fine product size
Which method of size reduction involves the application of pressure?
Compression
What is the primary mechanism of the attrition method of size reduction?
Shear forces
What is the primary characteristic of materials that require enclosed mills?
High potency
What is the main purpose of incorporating a classifier in the system of a mill?
To retain particles until they are sufficiently fine
What is the benefit of using inert gases in certain cases of milling?
To protect sensitive materials from contamination
What is the result of the high degree of turbulence in the milling process?
Reduction of particle size through inter-particulate attrition
What is the typical particle size of the product produced by this method of milling?
5 um or less
What is the purpose of the motor-driven rollers in a ball mill?
To rotate the shell on its horizontal longitudinal axis
What is a key advantage of this method of milling compared to others?
The ability to produce particles with a smaller size than other methods
What occurs when the ball mill is operated at low speeds?
The mass of balls will slide or roll over each other
What is the purpose of pre-treating the feed to the mill?
To reduce the particle size to the order of 100 mesh
What is a characteristic of the ball mill that makes it suitable for use with toxic materials?
Its enclosed form
What is the primary mechanism of size reduction in a ball mill?
Impact of the particles between the balls
At what speed is the maximum size reduction achieved in a ball mill?
At about two-thirds of the speed at which centrifugation just occurs
What is a feature of the ball mill designed for batch milling?
A removable end plate or side entrance hatch cover
What is a major advantage of conical screening mills over oscillating granulators?
Reduced chance of screen breakage and metal contamination
What determines the size of the output in a conical screening mill?
The space between the rolls
Why is the conical screening mill effective for milling heat-sensitive materials?
It generates low heat
What is a disadvantage of oscillating granulators?
Wear on the screens
What is a characteristic of conical screening mills that makes them more desirable?
Their dual action of size reduction and mixing
What is the main purpose of size reduction in pharmaceutical technology?
To reduce larger size solid unit masses to smaller sizes
What is the general trend of the cost of size reduction as particle size decreases?
It increases
Which process requires the material to be crushed to expose cells for extraction?
None of the above
What does the Moh’s scale of hardness range between?
5 and 10
Why might a soft but tough material present more problems in size reduction than a hard but brittle substance?
Because it has a higher moisture content
Which material cannot be marked with a good penknife blade according to the text?
Rubber
Which comparison does the text make to illustrate the difference between tough and brittle materials?
Blackboard chalk and rubber
Test your knowledge on Size Reduction and Comminution in pharmaceutical technology with this quiz based on Lecture 7 by Omnia Sarhan. Learn about the process of reducing large solid masses to smaller ones, the reasons for size reduction, and its applications in pharmaceutical preparation.
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