Edge runner mill – principle, construction, working, uses, merits, demerits MCQs With Answer

Edge runner mill – principle, construction, working, uses, merits, demerits MCQs With Answer

The edge runner mill is a traditional pharmaceutical size reduction and mixing equipment used for wet and dry grinding of herbs, granules and excipients. B. Pharm students must understand the mill’s principle of compression and shear between heavy rotating wheels and a grinding pan, its constructional parts such as runners, pan, bevel gears and scrapers, and operational factors influencing particle size distribution, heat generation and throughput. This guide covers working, cleaning, maintenance, applications, merits and demerits with emphasis on pharmaceutical processing, cGMP considerations and safety. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary size reduction mechanism in an edge runner mill?

• Impact by rapid collisions
• Compression and shear between runners and pan
• Centrifugal milling by high-speed rotors
• Ultrasonic cavitation

Correct Answer: Compression and shear between runners and pan

Q2. Which component directly contacts the material to grind in an edge runner mill?

• Bevel gear
• Grinding pan and heavy runners (wheels)
• Motor shaft bearing
• Feed hopper

Correct Answer: Grinding pan and heavy runners (wheels)

Q3. Edge runner mills are best suited for which type of pharmaceutical processing?

• High-speed micronization of APIs
• Coarse wet grinding, crushing and mixing of herbs or granules
• Sterile aseptic fill-finish operations
• Emulsification of parenteral formulations

Correct Answer: Coarse wet grinding, crushing and mixing of herbs or granules

Q4. What factor most influences the fineness of material produced by an edge runner mill?

• Ambient humidity only
• Wheel weight, clearance and residence time
• Color of the grinding pan
• Motor brand

Correct Answer: Wheel weight, clearance and residence time

Q5. Which material of construction is commonly used for pharmaceutical-grade edge runner mill pans?

• Plain carbon steel without coating
• Stainless steel (SS 316/304)
• Cast iron with lead lining
• Uncoated aluminum

Correct Answer: Stainless steel (SS 316/304)

Q6. Which drive arrangement is typical for an edge runner mill?

• Direct high-speed electric spindle at 10,000 rpm
• Low-speed heavy torque drive through gears
• Hydraulic hammer drive
• Pneumatic impact drive

Correct Answer: Low-speed heavy torque drive through gears

Q7. A major advantage (merit) of edge runner mills in pharmaceutical processing is:

• They provide sterile, closed-system milling by default
• Simple construction, easy operation and ability to handle wet masses
• Ultra-fine particle production to nanometer range
• Zero heat generation during milling

Correct Answer: Simple construction, easy operation and ability to handle wet masses

Q8. A common demerit of edge runner mills is:

• Extremely high throughput unsuitable for lab scale
• Poor control over particle size distribution and potential contamination
• Ability to process sterile APIs without validation
• Low maintenance requirements

Correct Answer: Poor control over particle size distribution and potential contamination

Q9. What is the role of scrapers or paddles in an edge runner mill?

• To increase motor speed
• To prevent material buildup on the pan and promote uniform grinding
• To cool the product by evaporation
• To measure particle size online

Correct Answer: To prevent material buildup on the pan and promote uniform grinding

Q10. Which parameter should be monitored to avoid excessive heating during milling?

• Pan color
• Temperature of the material and milling time
• Sound frequency only
• Voltage supply fluctuations only

Correct Answer: Temperature of the material and milling time

Q11. Why is stainless steel preferred over cast iron for pharmaceutical edge runner mills?

• Higher electrical conductivity
• Corrosion resistance, ease of cleaning and compliance with cGMP
• It is lighter and less durable
• Better magnetic properties

Correct Answer: Corrosion resistance, ease of cleaning and compliance with cGMP

Q12. Which operational change increases shear forces in an edge runner mill?

• Reducing wheel weight
• Increasing wheel-to-pan clearance
• Increasing wheel load and reducing clearance
• Decreasing residence time

Correct Answer: Increasing wheel load and reducing clearance

Q13. For wet milling in an edge runner mill, which aspect is critical?

• Use of organic solvent without safety precautions
• Controlled liquid-to-solid ratio and effective drainage/collection
• Completely drying the pan before every batch
• Maintaining zero humidity in the room

Correct Answer: Controlled liquid-to-solid ratio and effective drainage/collection

Q14. Which safety or hygiene practice is essential for pharmaceutical edge runner mills?

• Skipping record-keeping for each batch
• Regular cleaning, validation, and avoiding cross-contamination
• Using untested lubricants inside the product contact area
• Operating at maximum speed at all times

Correct Answer: Regular cleaning, validation, and avoiding cross-contamination

Q15. How does particle hardness affect the performance of an edge runner mill?

• Harder particles require less energy to break
• Harder particles increase wear and require more energy for size reduction
• Hardness has no effect
• Softer particles always clog the mill

Correct Answer: Harder particles increase wear and require more energy for size reduction

Q16. Which maintenance task helps prolong the life of the edge runner mill?

• Ignoring gear lubrication
• Regular inspection and lubrication of bearings and gears
• Running the machine dry at high load permanently
• Using any abrasive to clean the pan frequently

Correct Answer: Regular inspection and lubrication of bearings and gears

Q17. In pharmaceutical use, edge runner mills are often used to prepare:

• Sterile injectable concentrates
• Herbal decoctions, coarse suspensions, and triturations
• Lyophilized powders under vacuum
• High-shear emulsions for parenterals

Correct Answer: Herbal decoctions, coarse suspensions, and triturations

Q18. The clearance between wheel and pan influences:

• Only the color of the final product
• The extent of compression and resultant particle size
• Only the electrical consumption
• The motor brand compatibility

Correct Answer: The extent of compression and resultant particle size

Q19. Which inspection is important after milling pharmaceutical materials to ensure quality?

• Particle size distribution and moisture content
• Only visual color check
• Only motor vibration check
• Only pan surface roughness

Correct Answer: Particle size distribution and moisture content

Q20. Edge runner mills typically operate at:

• Very high speeds (>10,000 rpm)
• Low speeds with high torque (tens of rpm to a few hundred rpm)
• Ultrasonic frequencies
• Vacuum-sealed zero rpm

Correct Answer: Low speeds with high torque (tens of rpm to a few hundred rpm)

Q21. Which application is NOT appropriate for an edge runner mill?

• Coarse grinding of plant material
• Fine micronization to sub-micron range
• Preparation of wet masses for granulation
• Crushing tablets into powders

Correct Answer: Fine micronization to sub-micron range

Q22. What is a common sign of excessive wear in the runners?

• Decreased power consumption
• Uneven grinding and increased particle size with longer milling time
• Improved fineness without changes
• Silencing of the machine

Correct Answer: Uneven grinding and increased particle size with longer milling time

Q23. Which cleaning method aligns with cGMP for product contact surfaces?

• Wiping with unvalidated solvent
• Validated cleaning procedures using appropriate detergents and rinsing
• Leaving residues to dry for next batch
• Using industrial paint to seal residues

Correct Answer: Validated cleaning procedures using appropriate detergents and rinsing

Q24. Which factor reduces contamination risk during milling?

• Use of porous pan materials
• Closed feed systems, stainless steel contact parts and dedicated equipment per product family
• Operating at very high temperatures
• Mixing multiple products in one batch intentionally

Correct Answer: Closed feed systems, stainless steel contact parts and dedicated equipment per product family

Q25. Which parameter is least likely to be controlled in an edge runner milling process?

• Residence time
• Wheel loading and clearance
• Exact micron-level particle size for sub-micron targets
• Moisture content of feed

Correct Answer: Exact micron-level particle size for sub-micron targets

Q26. What is the typical effect of increasing feed rate into an edge runner mill?

• Always increases fineness
• May reduce residence time, leading to coarser product if overloaded
• Reduces wear on the wheels
• Completely stops the mill

Correct Answer: May reduce residence time, leading to coarser product if overloaded

Q27. Which lubrication practice is appropriate for the drive gears of a pharmaceutical edge runner mill?

• Using food-grade or pharmaceutical-grade grease away from product contact zones
• Applying raw engine oil inside the pan
• Never lubricating gears to avoid contamination
• Using adhesives instead of grease

Correct Answer: Using food-grade or pharmaceutical-grade grease away from product contact zones

Q28. What is a design feature that facilitates cleaning of an edge runner mill?

• Fixed, non-removable runners
• Removable pan and runners with smooth polished surfaces
• Rough cast surfaces to trap residues
• Hidden fasteners preventing disassembly

Correct Answer: Removable pan and runners with smooth polished surfaces

Q29. Which monitoring helps optimize energy efficiency during milling?

• Ignoring motor load
• Monitoring power consumption vs throughput and adjusting feed and clearance
• Maximizing motor speed irrespective of load
• Using the heaviest possible wheels always

Correct Answer: Monitoring power consumption vs throughput and adjusting feed and clearance

Q30. When validating an edge runner mill process, which attribute is commonly assessed?

• Particle size distribution, weight uniformity and microbial limits (if applicable)
• Only color matching
• Only motor brand authenticity
• Only electrical wiring color

Correct Answer: Particle size distribution, weight uniformity and microbial limits (if applicable)

Q31. Which operational change can decrease heat generation during milling?

• Increasing milling time indefinitely
• Reducing speed, intermittent operation or adding cooling liquid
• Adding abrasive grit to speed up grinding
• Using smaller wheels with same load

Correct Answer: Reducing speed, intermittent operation or adding cooling liquid

Q32. What is a common use of edge runner mills in herbal medicine preparation?

• Sterile packing of tinctures
• Pulverizing roots and barks to produce coarse herbal powders and pastes
• High-pressure homogenization of extracts
• Lyophilization of decoctions

Correct Answer: Pulverizing roots and barks to produce coarse herbal powders and pastes

Q33. What maintenance action should be taken if abnormal vibration is detected?

• Ignore and continue running
• Stop the machine, inspect bearings, alignment and wheel balance
• Increase feed rate to balance vibrations
• Add more product to the pan

Correct Answer: Stop the machine, inspect bearings, alignment and wheel balance

Q34. Which measure improves reproducibility of batches in an edge runner mill?

• Random changes to feed and speed for each batch
• Standardized operating procedures specifying feed rate, wheel loading, speed and time
• Using different pans each batch without documentation
• Varying clearance unpredictably

Correct Answer: Standardized operating procedures specifying feed rate, wheel loading, speed and time

Q35. In terms of scale-up, edge runner mills are generally:

• Highly linear and easy to scale to any size without changes
• Challenging to scale linearly due to changes in energy distribution and residence time
• Only available in one size worldwide
• Impossible to use for any scale-up

Correct Answer: Challenging to scale linearly due to changes in energy distribution and residence time

Q36. What inspection should be performed on product contact surfaces periodically?

• Visual inspection, surface finish measurement and microbiological monitoring when applicable
• Only color matching
• Only checking for magnetism
• Only weighing the pan

Correct Answer: Visual inspection, surface finish measurement and microbiological monitoring when applicable

Q37. Which grinding media are used in edge runner mills?

• High-speed rotating beads
• The heavy integral wheels or rollers themselves (no separate beads)
• Ceramic beads are always added
• Liquid nitrogen as grinding media

Correct Answer: The heavy integral wheels or rollers themselves (no separate beads)

Q38. For controlling cross-contamination, what is a recommended practice?

• Use shared equipment for all potent APIs without cleaning
• Dedicated equipment or validated cleaning between product families
• Deliberately leaving residues to dilute next batch
• Only cleaning by dry brushing

Correct Answer: Dedicated equipment or validated cleaning between product families

Q39. Edge runner mill noise is primarily caused by:

• Electrical supply only
• Mechanical contact between runners and pan, bearing wear and imbalance
• The color of material being milled
• Humidity in the room only

Correct Answer: Mechanical contact between runners and pan, bearing wear and imbalance

Q40. Which troubleshooting step is correct for inconsistent product fineness?

• Change pan color
• Check feed rate, wheel condition, clearance and operating time
• Replace motor with a smaller one
• Stop monitoring parameters

Correct Answer: Check feed rate, wheel condition, clearance and operating time

Q41. What advantage does polished surface finish provide on product contact parts?

• Increases particle size
• Facilitates cleaning and reduces microbial harborage
• Encourages adhesion of residues
• Promotes rust formation

Correct Answer: Facilitates cleaning and reduces microbial harborage

Q42. Which documentation is essential for each batch processed in an edge runner mill?

• Batch record including operating parameters, cleaning and inspection results
• Only the operator’s signature without details
• No records are necessary
• Only a photograph of the machinery

Correct Answer: Batch record including operating parameters, cleaning and inspection results

Q43. What is a consequence of excessive moisture in feed material?

• Improved free-flowing powder formation
• Formation of sticky masses, clogging and reduced milling efficiency
• Increased motor efficiency
• No change in mill performance

Correct Answer: Formation of sticky masses, clogging and reduced milling efficiency

Q44. Edge runner mills are classified under which category of equipment?

• High-pressure homogenizers
• Low-speed, high-torque size reduction and mixing equipment
• Sterilizers
• Freeze dryers

Correct Answer: Low-speed, high-torque size reduction and mixing equipment

Q45. Which parameter is most directly related to mill throughput?

• Ambient light intensity
• Feed rate and wheel contact area
• Color of the feed
• Operator’s height

Correct Answer: Feed rate and wheel contact area

Q46. Which is a suitable troubleshooting action for high power draw with low throughput?

• Increase wheel clearance without inspection
• Inspect for overloading, worn bearings, or jammed pan and adjust operating conditions
• Decrease feed size to larger chunks purposely
• Remove lubrication entirely

Correct Answer: Inspect for overloading, worn bearings, or jammed pan and adjust operating conditions

Q47. Which mill alternative is better suited for achieving narrow particle size distribution and fine milling?

• Edge runner mill
• Ball mill, jet mill or colloid mill depending on target size
• Hand grinding with mortar and pestle only
• Using a spoon to crush manually

Correct Answer: Ball mill, jet mill or colloid mill depending on target size

Q48. Which environmental control is beneficial during milling of hygroscopic materials?

• High room humidity
• Controlled low humidity and temperature to prevent caking
• Open windows with outdoor air
• Direct sun exposure on the product

Correct Answer: Controlled low humidity and temperature to prevent caking

Q49. Why might an edge runner mill be chosen over a high-speed rotor mill for some applications?

• To achieve sub-micron particles economically
• To gently process wet masses and coarse material with low heat generation
• Because it is the only available option
• To produce sterile injectable products directly

Correct Answer: To gently process wet masses and coarse material with low heat generation

Q50. Which regulatory concern must be addressed when using edge runner mills for pharmaceutical production?

• No documentation is required for milling operations
• Cleaning validation, traceability, equipment qualification and contamination control
• Only color of machine needs approval
• Only electrical inspection is necessary

Correct Answer: Cleaning validation, traceability, equipment qualification and contamination control

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com