Pulverization and its application to pigment

industry for size reduction

Prepared by

ABDUL VAHID M

SIZE REDUCTION

Reduction of particle size is an important operation in many chemical and other industries.

The important reasons for size reduction are:

• Easy handling

• Increase in surface area per unit volume

• Separation of entrapped components

laws governing size reduction

Rittinger’s law

The energy expended during comminution is proportional to the area of the new surface produced as a result of particle fragmentation.

Kick’s law

The energy is proportional to the size reduction ratio.

Bond’s law

The total work input represented by a given weight of crushed or ground product is inversely proportional to the square root of the diameter of the product particles.

MECHANISM OF PULVERIZATION

Pulverizer

A pulverizer or grinder is a mechanical device for the grinding of many different types of materials.

BASED ON PRINCIPLES OF PARTICLE SIZE REDUCTION

-IMPACT-ATTRITION-CRUSHING

PULVERISERS USE ONE, TWO OR ALL THE THREE PRINCIPLES.

TYPES OF PULVERIZERS

Speed Low

10 to 20 RPM

Medium

40 to 70 RPM

High

900 to 1000

RPM

Type Ball tube mills

(16 rpm in

Vindhyachal)

Bowl Mill,

MPS Mill,

Ball and Race

mill

Impact or

Hammer

Mill.

Beater Mill

or Fan Mill.

TYPES OF MILL

• Tube or ball mills: These are low-speed machines that grind the coal with steel balls in a rotating horizontal cylinder.

• Vertical spindle mill: These are medium-speed machines that include bowl mills, ring roll mills, and ring and ball mills. The bowl mills are further divided into deep bowl or shallow bowl mills.

• Impact mill: These are high-speed impact machines that use beater wheels to crush the coal.

Why we pulverizing pigments?

production of finely divided low pigments by an improved milling

process.

It has long been recognized in the art that pigments must be in a

relatively finely divided condition in order to' be useful in the

manufacture of such commodities as paints, paper, rubber, oilcloth

coatings, and the like.

It is necessary to reduce particle size in order to disperse the pigments

in different products.

DISPERSING PROCESS

High quality coatings of high brilliance and color strength are characterized by

a perfect pigment dispersion, optimal pigment particle size, and long-term

stabilization of the dispersed particle in the formulation.

The dispersion of a pigment in liquid coatings, paints or inks to produce stable

suspension, can be divided into the following three processes:

•Pigment wetting:

• All of the air and moisture is displaced from the surface and between the particles of the

pigment aggregates and agglomerates (clusters) and is replaced by the resin solution. The

solid/gaseous interface ( pigment/air) is transformed into a solid/liquid interface (pigment/resin

solution).

•Grinding stage:

•Through mechanical energy (impact and shear forces), the pigment agglomerates are broken

up and disrupted into smaller units and dispersed (uniformly distributed).

•Stabilization of pigment suspension:

•The pigment dispersion is stabilized by dispersing agents in order to prevent the formation of

uncontrolled flocculates. The resultant suspension is stabilized due to the adsorption of binder

species or molecules at the pigment surface.

Some Methods used for dispersing pigments are:

Ball milling

Ball mills are used for heavily agglomerated pigments

or for maximum dispersion.

A ball mill is essentially a large horizontal drum

suspended by axles at each end.

The pigments and resins or liquids are added to the

drum along with heavy round balls made of ceramic,

metal, or stone.

As the drum rotates, the pigment, liquid, and balls

cascade over each other, effectively mixing and

crushing the pigment agglomerates.

Stone Mill

The through-put speed is greater than the ball mill, but

it requires constant monitoring and adjustment from an

operator.

A mill base is fed by gravity or pump into an inlet at the

top of the mill.

The mill base is drawn down into a chamber where a

high speed motor is turning a dome-shaped stone

placed at a close range to a fixed stone.

The mill base is forced through the gap between the

two stones, which then grind the pigment.

Sand or Bead Mill

High speed media (sand or bead) mills became popular

around 1948 and are still widely used today for wet

grinding and dispersion of solids in liquids.

Bead mills operating with 250 micron grinding media

are effective for converting crude pigments to finished

pigment dispersions.

THANK YOU