Hammer Mill and Cyclone Separator Overview
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Questions and Answers

Which mill type predominantly uses impact and shear stress for size reduction?

  • Rotor Mill.
  • Ball Mill.
  • Conical Ball Mill.
  • Pin Mill. (correct)

What is the primary factor that distinguishes between 'cascading' and 'cataracting' modes in a ball mill?

  • The material of the balls.
  • The speed of rotation. (correct)
  • The size of the product discharged.
  • The cylinder diameter.

Which mill is best suited for processing thermolabile materials due to its low operating temperatures?

  • Conical Ball Mill
  • Rotor Mill
  • Pin Mill (correct)
  • Ball Mill

What adjustments can be made to the ball mill to alter the final product size?

<p>Changing ball size, mill speed and mill diameter. (C)</p> Signup and view all the answers

Which mill type is most suitable for achieving sterile/aseptic grinding conditions?

<p>Ball Mill. (C)</p> Signup and view all the answers

What is the primary force that causes particle separation in a cyclone separator?

<p>Centrifugal force from a vortex (C)</p> Signup and view all the answers

Approximately what percentage of energy input in a hammer mill is typically converted into new surface area?

<p>40% (D)</p> Signup and view all the answers

Which component within a hammer mill directly facilitates particle size reduction via impact?

<p>Rotating disc with hammers (B)</p> Signup and view all the answers

In a cyclone separator, where do the coarser particles typically exit?

<p>Through the underflow outlet (B)</p> Signup and view all the answers

What is the typical size of powder produced by hammer mills?

<p>Around 100 micron (C)</p> Signup and view all the answers

Which term best describes the flow pattern imparted to material inside a 'Comil'?

<p>Vortex flow (C)</p> Signup and view all the answers

What is the purpose of the screen in both the hammer mill and the 'Comil'?

<p>To control the size of the output particles (C)</p> Signup and view all the answers

Which process is NOT typically performed by a hammer mill?

<p>Filtration (C)</p> Signup and view all the answers

Which mechanism primarily achieves particle size reduction in a fluid energy mill?

<p>Attrition between particles (A)</p> Signup and view all the answers

What is a key advantage of using a fluid energy mill for heat-sensitive materials?

<p>Cooling effect due to expanding gas (B)</p> Signup and view all the answers

Which factor is NOT a primary determinant of particle size in a fluid energy mill?

<p>Feed material's shape (C)</p> Signup and view all the answers

Why are fluid energy mills suitable for processing oxidizable materials?

<p>They use inert gases, which prevent unwanted oxidation. (D)</p> Signup and view all the answers

A disadvantage to using a fluid energy mill is:

<p>High running costs (D)</p> Signup and view all the answers

Apart from material stability, which factor is NOT considered when selecting grinding machinery?

<p>Surrounding air humidity (C)</p> Signup and view all the answers

Which parameter, specific to fluid energy mills, helps achieve a narrow particle size distribution?

<p>Precise control of fluid pressure and feed rate (D)</p> Signup and view all the answers

In the fluid energy mill process, where does the venturi feeder direct the material?

<p>Into a milling chamber (A)</p> Signup and view all the answers

Flashcards

Hammer Mill

A type of mill that uses hammers attached to a rotating disc to break down material into smaller particles.

Sieve Mesh

A component of a hammer mill that controls the size of the particles produced by the mill.

Cyclone Separator

A type of separator that uses centrifugal force to separate particles based on their size and density.

Comminution

The process of reducing the size of particles by impact or attrition.

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Particle Size Control

The ability of a hammer mill to produce a wide range of particle sizes, from coarse to very fine.

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Wet Grinding

The process of grinding material in the presence of liquid.

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Cutting Mill

A type of mill that uses a rotating impeller to create a vortex flow pattern, forcing material through a screen to reduce its size.

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Comil

A type of cutting mill with a conical screen chamber and rotating impeller, used for size reduction and particle separation.

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Rotor Mill

A milling technique where particles are reduced by the impact of rotating blades against a sieve ring. This method works particularly well for materials that need to be reduced to a fine size (less than 100 microns).

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Pin Mill

A type of mill that uses two horizontal steel plates with pins to grind materials. It's effective for non-abrasive materials and causes less heat buildup, making it ideal for heat-sensitive materials.

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Ball Mill

This mill uses a rotating cylinder filled with balls (e.g., stainless steel, porcelain) to grind materials. The grinding action is a combination of impact (the balls hitting the material) and attrition (the balls rubbing against each other and the material).

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Cascading vs Cataracting

The movement of balls inside the mill can be categorized as either 'cascading' or 'cataracting'. Cascading happens at low speeds and involves mainly attrition (rubbing), while Cataracting occurs at higher speeds and involves more impact.

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Conical Ball Mill

A conical ball mill is a modified type of ball mill where the cylinder is shaped like a cone. This design helps to improve the grinding efficiency and can be used for grinding a wider range of materials.

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Fluid Energy Mill

A type of mill that uses high-speed fluid jets to break down material into smaller particles. This is ideal for sensitive materials and produces consistently fine powder.

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Fluid Energy Mill : Type 1

A specific type of fluid energy mill where the fluid (usually air) is injected into a chamber through a venturi, creating a high-velocity stream that grinds the material.

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Fluid Energy Mill : Type 2

Another type of fluid energy mill where the fluid is injected into a chamber through a venturi, carrying the material through a cyclone separator for fine particle separation.

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TCD Microniser

A special type of fluid energy mill designed for very fine grinding (micron-level). It combines a high-velocity fluid stream and a milling chamber for precise particle size control.

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Factors affecting particle size in a Fluid Energy Mill

The size of the particles produced in a fluid energy mill is influenced by several factors like the feed material's initial size, the rate at which it enters the chamber, and the fluid's pressure. This offers flexibility in controlling particle size.

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Heat Sensitivity

A major advantage of fluid energy mills is the minimal heat generated due to the cooling effect of the expanding fluid. This makes it suitable for temperature-sensitive materials.

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Choosing a Grinding Machine

Some factors to consider when choosing a grinding machine include the purpose of the powder, the material's properties (like crystal form, moisture, and stability), and the potential health hazards involved.

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Study Notes

Hammer Mill

  • Also known as a comminuting or impact mill
  • Disc rotates at high speeds (up to 8000 rpm) with hammers
  • Direct impact crushing
  • Sieve mesh used
  • Cooling jacket to manage heat produced (approximately 40% of input energy becomes heat)
  • Cyclone separator used for particle separation

Cyclone Separator

  • Reverse-flow cyclone
  • Particles (in air or liquid suspension) are introduced tangentially
  • High fluid velocity creates a vortex, throwing particles onto the walls
  • Particles fall down the conical section due to fluid flow
  • Coarser particles separate from the fluid stream and are discharged
  • Fines (smaller particles) remain in the fluid and leave through the vortex finder
  • Can use multiple cyclones for different flow rates/dimensions

Hammer Mill (Further Details)

  • Hammer heads: flat, knife, or file-edged
  • Can produce very fine powder (approximately 100 microns)
  • High control over particle size
  • Very rapid process
  • Also used for mixing, wet-grinding, and ointment milling

Cutting Mill

  • Continuous process

Swing Hammer Mill

  • Not further described in detail

"Comil"

  • Feed material introduced into a conical screen chamber
  • Rotating impeller creates a vortex flow
  • Material moved to screen surface via centrifugal acceleration
  • Size reduction and discharge through screen openings
  • Impact and shear stress
  • Product discharged at the bottom of the milling chamber
  • Particle size can be optimized by screen, impeller, or speed selection

Rotor Mill

  • Rotor with hardened steel blades
  • High rotation speeds (>15,000 rpm) within a circumferential sieve ring
  • Size reduction to <100 microns

Pin Mill

  • Two horizontal steel plates with concentric rings of pins
  • Stress: impact and attrition
  • Pin arrangements can alter particle size
  • Low milling temperatures are good for thermolabile materials
  • Suitable for soft, non-abrasive powders

Ball Mill

  • Rotating hollow cylinder half-filled with balls (stainless steel, porcelain, flint)
  • Cylinder material: stainless steel, chrome, or porcelain
  • Stress: impact and attrition

Ball Mill Operation Considerations

  • Low speeds: cascading (attrition-dominant)
  • Higher speeds: cataracting (impact-dominant)
  • Size of product altered by changing ball size, mill speed, and diameter
  • Wet grinding possible
  • Can be enclosed for sterile/aseptic grinding
  • Can use inert gases for oxidizable materials
  • Milling time can be long

Modifications to Ball Mills

  • Conical ball mill
  • Planetary ball mill

Fluid Energy Mill/Microniser/Jet Mill (Type 1)

  • Fluid energy supply manifold
  • Creates tangential and rotational forces for particle size reduction
  • Used for high-micron (e.g., < 5µm) size reduction

Fluid Energy Mill/Type 2

  • Similar to Type 1, though not as detailed in the provided materials

TCD Microniser

  • More detailed diagrams, but fewer description details available.

Factors Influencing Grinding Machinery Selection

  • Consider physical properties of feed and product
  • Required purpose of the powder
  • Properties of the material to be ground (physical form, crystal type, moisture content, etc.)
  • Material stability (oxygen, heat, metals), aseptic conditions
  • Health hazards (dust)

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Description

Explore the essential functions and operations of the hammer mill and cyclone separator. This quiz covers the mechanics of impact crushing, particle separation, and the efficiency of different designs. Understand the applications and benefits of each component in industrial processes.

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