Partech Prelims LEC2

• may be used to create particles of a certain size and shape,

• to increase the surface area available for chemical reaction

• to liberate valuable minerals held within partiles

What are the importance of particle size reduction?

Yes, around 5% of all electricity generated is used in size reduction

Is Particle size reduction an energy intensive process?

It improves uniformity

How does size reduction affect mixing?

It rapids effective drying. If the size of granules is small, druing of granular mass becomes rapid.

How does size reduction affect the drying process?

In suspensions and emulsions, rate of sedimenration decreases if the particles are of small and uniform size.

How does size reduction affect physical stability?

It facilitates rate. When the surface area is larger, the dissolution of a substance increases.

How does size reduction affect dissolution?

The smaller the particle, the faster the absorption because of the increase in dissolution.

How does size reduction affect the absorption rate?

• compression

• impact

• attrition

• shear

• non-mechanical

What are the common mechanisms in size reduction?

Compression

particle disintegration by two rigid forces

Impact

particle breaks by a single rigid force

Attrition

breaking of particles by scraping between two surfaces

Shear

produced when the particle is compressed between two edges o the hard surfaces

Non-mechanical

size reduction mechanism that introduces energy such as thermal shock, explosive shattering, electrohydraulic

TRUE

TRUE OR FALSE: increasing the energy in a size reducing equipment leads to the increase of smaller and finer particles

kinetic energy

In case of impact comminution, _____ of the particles is used to generate the degree of deformation that is required for fracture.

brittle-elastic

A material is said to be _____ if the deformation of the product is initially proportional to the applied stress, and the fracture occurs suddenly

elastic and reversible

In linear range, the particle deformation is _______, but as soon as higher stresses are experienced, the material strength is exceeded locally, and cracks are triggered.

TRUE

TRUE OR FALSE: At lower values of F, elastic deformation occurs without fracture and the energy input is completely ineffective in achieving size reduction.

Stress field

It is directly proportional to the square root of crack length over distance from the crack tip

• Particle size, shape

• Flowability

• Stickiness

• Elasticity

• Dust explosion

• Morphology

• Hardness

• Reactivity

• Toxicity

• Corrosivity

• Moisture conent

• Composition

What are the key properties of solids to be known to designing a process or selecting an equipment?

• Type 1: Crushers

• Type 2: Grinders

• Type 3: Ultrafine Grinders

• Type 4: Cutting Machines

What are the four broad classifications of size reduction machines?

Crushers

It is the type 1 classification of size reduction machine that utilizes compression mechanism to produce coarse and fine particles.

Has two functions: primary which reduces to 6-10 in and secondary which reduces to ¼ in

Grinders

It is the type 2 classification of size reduction machine that utilizes impact mechanism to produce intermediate and fine particles

Its function is to reduce crushed feed to powders; intermediate products pass through 40 mesh and fine products pass through 200 mesh.

Ultrafine Grinders

It isthe type 3 classification of size reduction machines that utilizes shearing mechanism to produce fine particles

can be done on dry and wet basis

Cutting Machines

It is the type 4 classification of size reduction machine that utilizes shearing or laser mechanism ro produce fine particles

these are used to reduce particle to a fixed required size

Blake crusher

the swing jaw is fixd at the upper position

Dodge crusher

the swing jaw is fixed at the lower position

Universal crusher

the swing jaw is fixed at an intermediate position

Jaw and roll crushers (70-90) followed by impact crushers (30-40)

what size reducing equipment has the highest efficiency?

Impact mills and ball mills (1-10 and 5-10)

what size reducing equipment has the lowest efficiency?

Gyratory crusher

similar in basic concept to a jaw crusher, consisting of a concave surface and a conical head

Cone crusher

similar in operation to a gyratory cursher, with less steepness in the crushing chamber and more of a parallel zone between crushing zones

Smoother roll crusher

material is feeding from the feeding mouth above, through two opposite rotating grinding roler with the aid of friction and gravity

Toothed roll crusher

made up of a toothed roll assembly as shown in figure, which crushes the incoming feed material against a crushing plate

designed to reduce larger feed sizes to desired size at a 6:1 ratio

Tumbling mills

a cylindrical shell slowly turning about its horizontal axis and filled about half of its volume with grinding medium

Rod mill

high carbon steel rods about two and 4’’ in diameter is used instead of ball and extending the whole length of the mill

Hammer mill

a steel drum containing a vertical or horizontal rotating shaft or drum on which hammers are mounted

Attrition mill

grains are rubbed between the grooved flat faces of rotating circular roughened disks, axes of roughened disks may be horizontal or vertical, can be single runner or double runner

Fluidized energy mill

also known as micronizer, or jet mill, it consists of a hollow toroid that operates by particle impaction and attrition

jaw crusher > ball mill > fluid energy mill

What is the decreasing order of the average particle size produced by different size reduction equipments

• Rittinger’s Law

• Kick’s Law

• Bond’s Law

What are the three laws of energy utilization to reduce the size?

Rittinger’s Law

states that the energy required for reduction in particle size of a solid is directly proportional to the increase in surface area

applied where surface area created is significant - fine grinding

ignores deformation before fracture

applies to 100 micometers

Kick’s Law

states that the work required for crushing a given mass of material is constant for a given reduction ratio irrespective of the initial size

applied if plastic deformation within the elastic limit

applies to sizes greater than 10 mm

Reduction Ratio

the ratio of initial particle size to final particle size

Bond’s Law

states that the work required to form particles of size from a very large particle size is proportional to the square root of the surface to volume ratio of the product

used for generally hard materials, rough mill sizing

100 micrometers to 10 mm