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

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

End runner mill is an essential pharmaceutical size‑reduction device used in powder processing for B. Pharm students preparing for practicals and exams. This SEO‑friendly introduction explains the principle (compression and attrition between a rotating runner and stationary bed), basic construction (runner wheel, bed ring, feed chute, and drive), working features (feed control, gap adjustment, and discharge), primary uses in pharmaceutical powder milling, and common merits and demerits including heat generation, contamination risk, and maintenance. Keywords: End runner mill, principle, construction, working, uses, merits, demerits, MCQs, B. Pharm students, pharmaceutical milling, powder processing. Now let’s test your knowledge with 50 MCQs on this topic.

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

• Impact between hammer and plate
• Compression and attrition between a rotating runner and stationary bed
• Centrifugal force causing particle fracture
• Ball collision in a rotating drum

Correct Answer: Compression and attrition between a rotating runner and stationary bed

Q2. Which component of an end runner mill directly contacts and grinds the material?

• Feed hopper
• Runner wheel
• Drive motor
• Collection cyclone

Correct Answer: Runner wheel

Q3. How is particle size commonly controlled in an end runner mill?

• By changing the rotor speed only
• By adjusting the gap between runner and bed
• By altering feed humidity exclusively
• By changing grinding media sizes

Correct Answer: By adjusting the gap between runner and bed

Q4. End runner mills are best suited for which type of materials?

• Highly elastic materials like rubber
• Brittle and friable solids
• Wet slurries
• Long fibrous materials like cotton

Correct Answer: Brittle and friable solids

Q5. Which advantage is typically associated with end runner mills in pharmaceutical use?

• Producing extremely fine nanoscale particles without equipment change
• Low heat generation compared with high‑speed impact mills
• Suitable for very high throughput continuous wet milling
• No need for routine maintenance

Correct Answer: Low heat generation compared with high‑speed impact mills

Q6. A common disadvantage of end runner mills is:

• High contamination from metal wear if not monitored
• They eliminate all static charge in powders
• They are fully self-cleaning
• They work best with liquid feeds

Correct Answer: High contamination from metal wear if not monitored

Q7. Which operational parameter most directly affects throughput in an end runner mill?

• Ambient humidity only
• Feed rate into the grinding zone
• Color of the material
• Length of the electrical cable

Correct Answer: Feed rate into the grinding zone

Q8. In terms of GMP, which consideration is crucial for end runner mill operation in pharmaceutical manufacturing?

• Random sampling of electrical supply
• Cleaning and cross‑contamination control
• Using only wooden grinding parts
• Operating only at night

Correct Answer: Cleaning and cross‑contamination control

Q9. Which maintenance activity is common for end runner mills?

• Replacing grinding media daily
• Periodic inspection and dressing of grinding surfaces
• Wetting the feed to reduce dust every hour
• Changing the motor oil weekly regardless of runtime

Correct Answer: Periodic inspection and dressing of grinding surfaces

Q10. Which of the following is a typical use of an end runner mill in pharmacy?

• Dry size reduction of active pharmaceutical ingredients (APIs)
• Sterilizing injectable solutions
• Tablet coating application
• Lyophilization of probiotics

Correct Answer: Dry size reduction of active pharmaceutical ingredients (APIs)

Q11. The principle of attrition in an end runner mill refers to:

• Chemical degradation of the material
• Gradual wearing and fracturing through rubbing action
• Electrostatic attraction of particles
• Melting and resolidification of particles

Correct Answer: Gradual wearing and fracturing through rubbing action

Q12. Which parameter should be minimized to reduce thermal degradation of heat‑sensitive APIs during milling?

• Residence time and excessive frictional heat
• Feed particle brittleness
• Surface hardness of the bed
• Ambient lighting

Correct Answer: Residence time and excessive frictional heat

Q13. How does feed particle size influence milling in an end runner mill?

• Smaller feed particles always reduce throughput
• Larger feed particles may require more energy and time to reduce
• Feed size has no impact on milling efficiency
• Only color affects milling, not size

Correct Answer: Larger feed particles may require more energy and time to reduce

Q14. Which material of construction is preferred for pharmaceutical end runner mill parts contacting product?

• Uncoated iron with visible rust
• Food‑grade stainless steel to minimize contamination
• Polished copper for aesthetics
• Porous wood for absorption

Correct Answer: Food‑grade stainless steel to minimize contamination

Q15. End runner mills are compared to hammer mills; a key difference is:

• End runner mills use impact, while hammer mills use attrition
• Hammer mills typically produce more fines due to higher impact energy
• End runner mills are exclusively used for liquids
• Hammer mills require no maintenance

Correct Answer: Hammer mills typically produce more fines due to higher impact energy

Q16. Which design feature helps control dust generation in an end runner mill?

• Open grinding area with no hood
• Enclosed housing with dust extraction or collection
• Using only coarse feed
• Placing the mill outdoors

Correct Answer: Enclosed housing with dust extraction or collection

Q17. What is the role of the feed chute in an end runner mill?

• To cool the motor
• To direct and meter material into the grinding zone
• To apply coating to the particles
• To generate electric current

Correct Answer: To direct and meter material into the grinding zone

Q18. Which factor most affects the wear rate of grinding surfaces in an end runner mill?

• Hardness and abrasiveness of the feed material
• Color of the feed
• Ambient humidity only
• Time of day

Correct Answer: Hardness and abrasiveness of the feed material

Q19. In process validation, why is particle size distribution from an end runner mill important?

• It determines tablet color exclusively
• It affects dissolution, content uniformity, and downstream processing
• It has no regulatory significance
• It only matters for packaging aesthetics

Correct Answer: It affects dissolution, content uniformity, and downstream processing

Q20. Which operational change can reduce generation of fines in an end runner mill?

• Increase feed rate excessively
• Increase gap slightly to produce coarser particles
• Decrease bed hardness
• Operate at maximum speed always

Correct Answer: Increase gap slightly to produce coarser particles

Q21. Why is cooling sometimes necessary when milling heat‑sensitive APIs?

• To increase residence time
• To prevent thermal decomposition and preserve potency
• To reduce particle size further
• To make the product sticky

Correct Answer: To prevent thermal decomposition and preserve potency

Q22. Which monitoring parameter helps ensure consistent mill performance?

• Electrical cable length
• Power consumption and motor load
• Operator shoe size
• Color of the control panel

Correct Answer: Power consumption and motor load

Q23. Which safety feature is important for end runner mills in pharma labs?

• Absence of emergency stop
• Interlocked guards and emergency stop switch
• Exposed rotating parts for cooling
• Removal of all labels

Correct Answer: Interlocked guards and emergency stop switch

Q24. How does humidity of the feed affect milling in an end runner mill?

• High humidity can cause agglomeration and clogging
• Humidity has no effect
• Low humidity always causes corrosion
• Higher humidity increases motor RPM

Correct Answer: High humidity can cause agglomeration and clogging

Q25. Which cleaning validation concern is specific to end runner mills?

• Verifying removal of product residues from grinding surfaces and crevices
• Ensuring motor bearings are oily
• Documenting electrical wiring color
• Validating paint finish durability

Correct Answer: Verifying removal of product residues from grinding surfaces and crevices

Q26. Which outcome indicates overmilling in an end runner mill?

• Narrow particle size distribution centered at target
• Excessive fines and possible amorphization of API
• Reduced surface area
• Decreased dissolution rate always

Correct Answer: Excessive fines and possible amorphization of API

Q27. What is a practical step to minimize cross‑contamination when using the same mill for different products?

• Skipping cleaning between batches
• Implementing validated cleaning and using dedicated liners if needed
• Changing product color only
• Mixing products intentionally

Correct Answer: Implementing validated cleaning and using dedicated liners if needed

Q28. Which inspection before milling helps prevent equipment damage?

• Checking for metal or large foreign objects in feed
• Ensuring feed is wet
• Confirming operator preference
• Measuring building height

Correct Answer: Checking for metal or large foreign objects in feed

Q29. Which mill parameter is adjusted to change the degree of attrition?

• Gap between runner and bed
• Ambient lighting
• Color of the hopper
• Operator’s voice volume

Correct Answer: Gap between runner and bed

Q30. In scale‑up from lab to pilot scale, which factor must be considered for end runner mills?

• Geometric similarity and energy input per unit mass
• Using different active ingredients only
• Changing regulatory requirements arbitrarily
• Replacing stainless steel with plastic always

Correct Answer: Geometric similarity and energy input per unit mass

Q31. Which test is commonly used to assess particle size after milling?

• pH testing
• Laser diffraction or sieve analysis
• Thermogravimetric analysis only
• UV‑Vis at 800 nm

Correct Answer: Laser diffraction or sieve analysis

Q32. Which operational change can increase milling efficiency without changing gap?

• Optimizing feed rate and feed distribution
• Painting the mill a different color
• Removing the feed chute
• Operating without motor lubrication

Correct Answer: Optimizing feed rate and feed distribution

Q33. Which material property makes a substance difficult to mill in an end runner mill?

• High brittleness
• High elasticity and toughness
• Low melting point only
• Being a crystalline solid

Correct Answer: High elasticity and toughness

Q34. Why might a classifier be integrated after an end runner mill in a process line?

• To cool the air only
• To separate oversize and fine fractions for better control
• To add moisture to the powder
• To act as a redundant hopper

Correct Answer: To separate oversize and fine fractions for better control

Q35. Which routine record is important for regulatory compliance when using an end runner mill?

• Batch log with process parameters, cleaning and maintenance records
• Personal phone numbers of operators only
• Color preference of the supervisor
• Weather forecast for the day

Correct Answer: Batch log with process parameters, cleaning and maintenance records

Q36. What is the likely effect of increasing rotor speed in an end runner mill while keeping gap constant?

• Reduced attrition and coarser product
• Increased energy input leading to finer particles and more heat
• No change at all
• The mill will automatically switch off

Correct Answer: Increased energy input leading to finer particles and more heat

Q37. Which powder characteristic improves flow through an end runner mill feed chute?

• High cohesiveness
• Good flowability (low cohesiveness)
• Large static charge
• Sticky surface due to moisture

Correct Answer: Good flowability (low cohesiveness)

Q38. For highly potent APIs, which practice reduces operator exposure during milling?

• Open‑bench milling with no containment
• Using closed, contained milling with local exhaust and PPE
• Increasing manual handling steps
• Removing all protective equipment

Correct Answer: Using closed, contained milling with local exhaust and PPE

Q39. Which testing after milling helps detect contamination from wear?

• Assay for heavy metals and particle morphology checks
• Only checking smell
• Measuring humidity exclusively
• Color assessment under visible light

Correct Answer: Assay for heavy metals and particle morphology checks

Q40. Which adjustment would you try first if the mill is producing too many oversized particles?

• Decrease feed rate and/or reduce the gap
• Increase hopper capacity
• Stop cleaning the mill
• Change lighting in the room

Correct Answer: Decrease feed rate and/or reduce the gap

Q41. What is a benefit of using end runner mills for granule reduction prior to tablet compression?

• They uniformly reduce granule size to improve blend homogeneity and compression
• They add moisture to granules
• They sterilize granules
• They remove active ingredient intentionally

Correct Answer: They uniformly reduce granule size to improve blend homogeneity and compression

Q42. Which environmental control is relevant during milling of hygroscopic powders?

• Temperature and relative humidity control to prevent caking
• Music selection for operators
• Wall color to improve aesthetics
• Removing air conditioning always

Correct Answer: Temperature and relative humidity control to prevent caking

Q43. When troubleshooting noise or vibration in an end runner mill, the first check should be:

• Inspecting for imbalance or foreign objects and checking bearing condition
• Changing the product color
• Increasing the motor voltage arbitrarily
• Closing the doors to muffle sound

Correct Answer: Inspecting for imbalance or foreign objects and checking bearing condition

Q44. Which regulation or guidance is most directly applicable to milling operations in pharma?

• GMP (Good Manufacturing Practice) and relevant pharmacopeial standards
• Traffic laws
• Maritime navigation rules
• Building fire codes exclusively

Correct Answer: GMP (Good Manufacturing Practice) and relevant pharmacopeial standards

Q45. Why might liners or coatings be used on grinding surfaces?

• To reduce contamination and wear and to provide easier cleaning
• To increase electrical conductivity
• To make the mill heavier
• To absorb moisture intentionally

Correct Answer: To reduce contamination and wear and to provide easier cleaning

Q46. Which milling outcome would suggest the need to change to a different milling technology?

• Desired particle size is achievable with minor adjustments
• Material is highly elastic and resists comminution in end runner mill
• Mill operates within normal parameters
• Cleaning validation passes consistently

Correct Answer: Material is highly elastic and resists comminution in end runner mill

Q47. What is a sign that the grinding surface requires dressing or replacement?

• Stable product quality over many batches
• Degraded particle size control and increased energy consumption
• Reduced noise and vibration
• Lower motor load than usual

Correct Answer: Degraded particle size control and increased energy consumption

Q48. Which practice improves reproducibility of milling results batch to batch?

• Recording and controlling process parameters like gap, speed, and feed rate
• Changing parameters randomly each run
• Using different operators without training
• Skipping calibration of instruments

Correct Answer: Recording and controlling process parameters like gap, speed, and feed rate

Q49. What is an appropriate way to handle sticky or agglomerating powders in an end runner mill?

• Use pre‑drying, anti‑caking agents or choose alternative milling techniques
• Increase humidity to promote sticking
• Run the mill with no feed
• Abruptly shut off the motor when fed

Correct Answer: Use pre‑drying, anti‑caking agents or choose alternative milling techniques

Q50. Which documentation is essential after changing mill settings for a production batch?

• Updated batch record with reasons for change and monitoring results
• Only a verbal note to a colleague
• Removing historical records
• Recording the change in a personal diary

Correct Answer: Updated batch record with reasons for change and monitoring results

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