Planetary mixer – principle, construction, working, uses, merits, demerits MCQs With Answer

Planetary mixer – principle, construction, working, uses, merits, demerits MCQs With Answer

The planetary mixer is a versatile high-viscosity mixing device used widely in pharmaceutical formulation and compounding. This introduction outlines its mixing principle (simultaneous rotation and revolution), key construction elements (mixing pan, planetary agitator, drive, scrapers, jacket), working features (vacuum capability, temperature control, variable speed), common pharmaceutical uses (ointments, creams, suspensions, pastes), and practical merits and demerits for B. Pharm students. Understanding these aspects helps with equipment selection, process validation, cleaning, and scale-up. Emphasis on GMP, material selection, and maintenance is crucial for safe, reproducible formulations. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the basic mixing principle of a planetary mixer?

• Only the vessel rotates while the tool is stationary
• The tool rotates on its axis and simultaneously revolves around the vessel axis
• The tool oscillates back and forth in a linear motion
• Only the tool rotates without revolution

Correct Answer: The tool rotates on its axis and simultaneously revolves around the vessel axis

Q2. Which component in a planetary mixer prevents product from sticking to the vessel wall?

• Anchor
• Scraper
• Turbine
• Gearbox

Correct Answer: Scraper

Q3. Which material is preferred for construction of pharmaceutical planetary mixers?

• Cast iron
• Stainless steel 316L
• Aluminum alloy
• Plastic-lined steel

Correct Answer: Stainless steel 316L

Q4. How does a jacketed vessel in a planetary mixer aid processing?

• Provides electrical insulation
• Controls temperature by circulating heating or cooling fluid
• Prevents rotation of the vessel
• Reduces the need for scrapers

Correct Answer: Controls temperature by circulating heating or cooling fluid

Q5. What is a primary advantage of planetary mixers for pharmaceutical ointments?

• Low volumetric throughput for liquids only
• Effective mixing of high-viscosity and sticky formulations
• High centrifugal separation of solids
• They use negligible power

Correct Answer: Effective mixing of high-viscosity and sticky formulations

Q6. Which of the following is a major limitation (demerit) of planetary mixers?

• Inability to mix viscous products
• Complex cleaning and potential validation challenges
• They cannot be jacketed for temperature control
• They are only suitable for continuous processing

Correct Answer: Complex cleaning and potential validation challenges

Q7. What is the purpose of vacuum capability in many planetary mixers?

• To pressurize the vessel for reactions
• To degas the product and remove entrapped air or solvents
• To cool the product rapidly
• To increase rotational speed

Correct Answer: To degas the product and remove entrapped air or solvents

Q8. Which agitator type is commonly used in planetary mixers for scraping and heat transfer?

• Propeller
• Anchor or scraper
• Tangential blade
• Static baffle

Correct Answer: Anchor or scraper

Q9. Compared to a ribbon blender, planetary mixers are better suited for:

• Large, free-flowing powders only
• Low-viscosity liquids requiring minimal shear
• Small-to-medium batches of high-viscosity pastes and creams
• Continuous high-throughput blending of dry powders

Correct Answer: Small-to-medium batches of high-viscosity pastes and creams

Q10. Which feature improves heat transfer in a planetary mixer?

• Absence of scrapers
• Jacketed vessel with close scraper clearance
• Using a plastic vessel
• High headspace volume

Correct Answer: Jacketed vessel with close scraper clearance

Q11. What is a ‘double planetary’ mixer?

• A mixer with two vessels stacked vertically
• A mixer with two planetary agitators rotating and revolving for larger volumes
• A mixer that only rotates the vessel twice per minute
• A mixer with a single agitator but two scrapers

Correct Answer: A mixer with two planetary agitators rotating and revolving for larger volumes

Q12. Which validation documents are typically required for pharmaceutical planetary mixer installation and qualification?

• Only routine maintenance log
• IQ, OQ, PQ (Installation, Operational, Performance Qualification)
• Only a user manual
• No documentation is needed

Correct Answer: IQ, OQ, PQ (Installation, Operational, Performance Qualification)

Q13. Which cleaning method is often challenging for planetary mixers due to complex geometry?

• Manual disassembly and cleaning
• CIP (Clean-in-Place)
• Solvent immersion of individual parts
• Steam sterilization only for non-sterile products

Correct Answer: CIP (Clean-in-Place)

Q14. Why are scrapers important in planetary mixers when processing viscous materials?

• They increase vessel pressure
• They continuously remove product from the vessel wall to prevent dead zones
• They reduce mixing speed significantly
• They act as heating elements

Correct Answer: They continuously remove product from the vessel wall to prevent dead zones

Q15. For which pharmaceutical operation is a planetary mixer especially suitable?

• Sterile aseptic filling of vials
• Preparation of semi-solid dosage forms like creams and ointments
• Large-scale granulation of dry powders in a continuous line
• High-throughput capsule filling

Correct Answer: Preparation of semi-solid dosage forms like creams and ointments

Q16. Which operational parameter most directly affects shear generation in a planetary mixer?

• Room humidity
• Agitator speed and tool geometry
• Colour of the vessel
• Type of lighting in the room

Correct Answer: Agitator speed and tool geometry

Q17. Which cleaning validation parameter is crucial after preparing different batches in the same planetary mixer?

• Cross-contamination limits and rinsate assay
• Only visual inspection
• Temperature mapping of the jacket
• Verification of gear oil level

Correct Answer: Cross-contamination limits and rinsate assay

Q18. What is a common maintenance issue in planetary mixers?

• Frequent replacement of vessel insulation
• Wear of scraper seals and bearings due to abrasive products
• Rusting of internal painted surfaces only
• Motor always running without load

Correct Answer: Wear of scraper seals and bearings due to abrasive products

Q19. Which of the following best describes scale-up challenges for planetary mixers?

• Scale-up is straightforward by increasing speed only
• Geometric similarity and power/volume changes complicate direct scale-up
• Scale-up reduces cleaning needs
• Scale-up is irrelevant for semi-solids

Correct Answer: Geometric similarity and power/volume changes complicate direct scale-up

Q20. Which safety feature is essential for planetary mixers used in solvent-containing formulations?

• Non-explosion-proof motor in a ventilated room
• Explosion-proof electrical fittings and vapor handling
• Open flame nearby for drying
• Plastic scrapers for solvent resistance only

Correct Answer: Explosion-proof electrical fittings and vapor handling

Q21. Why might a planetary mixer be preferred over a rotor-stator high-shear mixer for certain products?

• For highly aqueous low-viscosity emulsions only
• For very high-viscosity, shear-sensitive pastes requiring surface scraping and heating
• For continuous high-throughput milling
• For sterile filtration of liquids

Correct Answer: For very high-viscosity, shear-sensitive pastes requiring surface scraping and heating

Q22. Which test is commonly used to evaluate blend homogeneity after mixing in a planetary mixer?

• Visual colour only
• Assay of active ingredient at multiple sampling points
• Measuring vessel weight only
• Checking motor amperage

Correct Answer: Assay of active ingredient at multiple sampling points

Q23. Which design choice reduces the formation of dead zones in a planetary mixer?

• Large clearance between scraper and vessel wall
• Close scraper clearance and multiple agitator paths
• Using no scraper at all
• Decreasing agitator eccentricity to zero

Correct Answer: Close scraper clearance and multiple agitator paths

Q24. What advantage do multiple planetary agitators provide in larger mixers?

• They increase dead zones
• They improve uniformity and reduce mixing time for larger batches
• They decrease heat transfer efficiency
• They prevent vacuum application

Correct Answer: They improve uniformity and reduce mixing time for larger batches

Q25. Which statement about planetary centrifugal mixers is true?

• They only rotate the vessel
• They combine planetary motion with centrifugal action to improve deairing and wetting
• They are unsuitable for degassing
• They use no scrapers

Correct Answer: They combine planetary motion with centrifugal action to improve deairing and wetting

Q26. In pharmaceutical use, why is stainless steel 316L preferred over 304 for certain planetary mixer components?

• 316L is less corrosion resistant than 304
• 316L has better corrosion resistance and lower carbon for welding, important for CIP and solvents
• 304 is always superior to 316L
• 316L is magnetic whereas 304 is not

Correct Answer: 316L has better corrosion resistance and lower carbon for welding, important for CIP and solvents

Q27. Which parameter most affects power consumption in a planetary mixer?

• Colour of the product
• Viscosity of the load and filler level
• Ambient lighting
• Length of the power cable

Correct Answer: Viscosity of the load and filler level

Q28. What is the effect of operating a planetary mixer under vacuum during mixing?

• Increases air entrainment
• Reduces boiling point but helps remove entrapped air and volatile solvents
• Prevents heating of the jacket
• Stops rotation of the agitators

Correct Answer: Reduces boiling point but helps remove entrapped air and volatile solvents

Q29. Which accessory improves deagglomeration when attached to a planetary mixer?

• Static baffle
• High-shear rotor-stator insert or disperser attachment
• Solid lid only
• Insulating cover

Correct Answer: High-shear rotor-stator insert or disperser attachment

Q30. For aseptic or sterile product manufacture, planetary mixers are generally:

• Ready for sterile use without modification
• Not normally designed for aseptic processing without special containment and validation
• Always used inside isolators as standard
• Only used for liquid sterile filtration

Correct Answer: Not normally designed for aseptic processing without special containment and validation

Q31. Why is clearance between scraper and vessel wall critical?

• Large clearance increases scraping efficiency
• Too large clearance creates dead zones; too small increases wear and motor load
• Clearance has no effect on mixing
• More clearance always reduces cleaning needs

Correct Answer: Too large clearance creates dead zones; too small increases wear and motor load

Q32. Which of the following is NOT typically a use of planetary mixers in pharmacy?

• Preparation of topical creams and ointments
• Dispersion of powders into viscous bases
• High-volume aseptic fill of sterile injections on a continuous line
• Production of cosmetic semi-solids and suspensions

Correct Answer: High-volume aseptic fill of sterile injections on a continuous line

Q33. Which operational control is essential for reproducible batches in a planetary mixer?

• Time, speed, temperature, and vacuum control
• Only visual check of viscosity
• Colour of the agitator
• Ambient room smell

Correct Answer: Time, speed, temperature, and vacuum control

Q34. What role does the gearbox play in a planetary mixer?

• It heats the product
• It transmits and modifies motor speed/torque to the planetary heads
• It provides scrapers
• It acts as a vacuum pump

Correct Answer: It transmits and modifies motor speed/torque to the planetary heads

Q35. How does fill level affect mixing performance in a planetary mixer?

• Fill level has no effect on mixing
• Very low or very high fill levels can reduce mixing efficiency; an optimum fill is recommended
• Lower fill always speeds mixing
• Higher fill always improves mixing uniformity

Correct Answer: Very low or very high fill levels can reduce mixing efficiency; an optimum fill is recommended

Q36. Which of the following maintenance tasks is commonly required for planetary mixers?

• Never checking seals
• Regular inspection and replacement of scraper seals, bearings, and gearbox lubrication
• Painting the interior between batches
• Removing the jacket permanently

Correct Answer: Regular inspection and replacement of scraper seals, bearings, and gearbox lubrication

Q37. For degassing viscous formulations, a planetary mixer with which feature is most useful?

• Open vessel with no lid
• Vacuum capability combined with planetary motion
• Only a heating jacket without vacuum
• No scrapers and low speed

Correct Answer: Vacuum capability combined with planetary motion

Q38. What is the likely effect of excessive mixer speed on shear-sensitive biological excipients?

• Improves biological activity
• May denature or damage shear-sensitive molecules
• Has no effect whatsoever
• Automatically sterilizes the product

Correct Answer: May denature or damage shear-sensitive molecules

Q39. Which cleaning approach is preferred to minimize cross-contamination in pharmaceutical planetary mixers?

• Validated cleaning procedure with analytical rinsate testing
• Wiping with a dry cloth only
• Relying on occasional visual checks
• Neutral pH water only with no validation

Correct Answer: Validated cleaning procedure with analytical rinsate testing

Q40. Which structural design helps prevent solvent vapor escape during solvent-containing processes?

• Open top vessel
• Sealed lid with proper vapor handling and explosion-proof design
• Porous cover
• Large vents without control

Correct Answer: Sealed lid with proper vapor handling and explosion-proof design

Q41. Which quality attribute is typically measured to confirm uniform mixing of a topical formulation?

• pH of the jacket fluid
• Content uniformity of active ingredient across samples
• Colour of the mixer exterior
• Length of the power cable

Correct Answer: Content uniformity of active ingredient across samples

Q42. What is an advantage of a tilting vessel feature on some planetary mixers?

• Increases scraping clearance permanently
• Makes discharge and cleaning easier by tilting out the product
• Prevents use of vacuum
• Reduces jacket efficiency

Correct Answer: Makes discharge and cleaning easier by tilting out the product

Q43. Which of the following is true regarding energy input in planetary mixing of viscous systems?

• Energy input is negligible regardless of viscosity
• Higher viscosity demands greater specific energy (power) for mixing
• Energy decreases with increasing viscosity always
• Mixing energy is independent of tool geometry

Correct Answer: Higher viscosity demands greater specific energy (power) for mixing

Q44. For preventing cross-contamination between batches, which practice is recommended?

• Change only the scrapers between batches
• Follow a validated cleaning and changeover procedure including analytical checks
• Mix two products consecutively to clean the vessel
• Rely on operator smell test

Correct Answer: Follow a validated cleaning and changeover procedure including analytical checks

Q45. Which seal type is commonly used in planetary mixers to prevent leaks around rotating shafts?

• Cloth packing only
• Mechanical seals or hygienic lip seals designed for rotating shafts
• No seals at all
• Cardboard gaskets

Correct Answer: Mechanical seals or hygienic lip seals designed for rotating shafts

Q46. How does scraper design influence heat transfer efficiency?

• Well-designed scrapers ensure frequent contact with the jacketed wall, improving heat transfer
• Scrapers reduce heat transfer always
• Scrapers only affect aesthetics
• Scrappers are unrelated to heat transfer

Correct Answer: Well-designed scrapers ensure frequent contact with the jacketed wall, improving heat transfer

Q47. Which precaution is necessary when using planetary mixers with organic solvents?

• Use non-certified electrical components near flammable vapors
• Ensure explosion-proof design, proper ventilation, and solvent recovery measures
• Do nothing special; standard mixers are sufficient
• Only use plastic vessels

Correct Answer: Ensure explosion-proof design, proper ventilation, and solvent recovery measures

Q48. Why might a planetary mixer have multiple tool geometries available?

• To match mixing tool shape with formulation needs (scraping, folding, dispersing)
• To increase motor noise
• To prevent use of jackets
• To reduce safety features

Correct Answer: To match mixing tool shape with formulation needs (scraping, folding, dispersing)

Q49. Which testing method can be used to demonstrate reproducible mixing performance during PQ?

• Measuring motor oil temperature only
• Batch-to-batch content uniformity assays and rheological testing
• Counting the number of revolutions only
• Checking the external paint finish

Correct Answer: Batch-to-batch content uniformity assays and rheological testing

Q50. In formulating a cream that traps air, what combination will best reduce bubbles and ensure quality?

• High speed with no vacuum and no scrapers
• Planetary motion with vacuum degassing and efficient scrapers/jacket control
• Only heating the vessel and no mixing
• Filling the vessel to overflow for agitation

Correct Answer: Planetary motion with vacuum degassing and efficient scrapers/jacket 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