Particle Size Reduction Flashcards
- info from table not included in the deck - no need to memorize size reduction range; focus on the method daw sabi ni maam
[TRUE OR FALSE] size reduction aids in efficient processing of solid particles by facilitating powder mixing or the production of suspension
TRUE
[true or false]
Some special functions of size reduction, such as exposing cells prior to extraction or reducing the bulk volume of a material to improve transportation efficiency
true
Influence of Material Properties on size reduction
- crack propagation and toughness
- surface hardness
- energy requirements of size reduction process
size reduction or comminution
crack propagation and toughness
[TRUE OR FALSE] Stress of material is concentrated at the middle of a crack
FALSE - tip of a crack
ease of comminution depends on _____________ or ____________ of the material and their relationship with crack initiation and propagation
brittleness or plasticity
crack is Propagated through regions of a material that possess the most ______ or ______, and is related to the strain energy in specific regions
flaws or discontinuities
German mineralogist
Mohs
Mohs scale
describe the hardness of a material
more quantitative measure of surface hardness was devised by
Brinell
[TRUE OR FALSE] Harder materials are more difficult to comminute and can lead to abrasive wear of metal mill parts, causing product contamination
TRUE
materials with large elastic components (e.g., rubber) are extremely soft which makes it (easy/difficult) to size reduce
difficult to size reduce
what is described by its position in a scale devised by a German mineralogist called Mohs
Surface Hardness
Materials such as rubber which are soft under ambient conditions, waxy substances such as stearic acid which soften when heated, and “sticky” materials such as gums are capable of _________ large amounts of energy through elastic and plastic deformation without _______ initiation and propagation.
absorbing; crack
polymeric material, which resists comminution at ambient or elevated temperatures, can be more easily size reduced by lowering the temperature below the __________ of material
glass transition point of the material
glass transition point of the material allows it to go from _______ to _______
plastic to brittle behavior
Moisture content of feed material below 5% is suitable for _______ and greater than 50% if _________ is to be carried out
dry grinding; wet grinding
Moisture content ______ is suitable for dry grinding and ________ if wet grinding is to be carried out
below 5%; greater than 50%
Table of materials
Mohs’ Scale
at the top of Mohs’ scale
diamond
diamond Mohs hardness
> 7
at the bottom of Mohs’ scale
talc
talc Mohs hardness
<3
[true or false]
diamond can scratch anything below it
true
[true or false]
talc is so soft it can be scratched by anything below it
false
it can be scratched by anything above it
a very ________ amount of the energy put into a comminution operation actually effects size reduction
small
___% of total energy is consumed; the remainder being lost in many ways, including elastic deformation of particles, plastic deformation of particles without fracture, deformation of metal machine parts, interparticle friction, particle machine wall friction, heat, sound and vibration
2%
Influence of Size Reduction and Size Distribution
- Uneven milling
- Particles agglomeration
consists of a series of knives attached to a horizontal rotor which act against a series of stationary knives attached to the mill casing.
Cutting Methods
During milling, size reduction occurs by fracture of particles between the 2 sets of knives, which have a clearance of a few mm.
Cutting Methods
Screen is fitted in the base of the mill casing and acts to retain material in the mill until sufficient degree of size reduction has been effected.
Cutting Methods
Useful in producing a coarse degree of size reduction of dried granulations prior to tableting and fibrous crude drugs such as roots, peels, or barks prior to extraction
Cutting Methods
can be carried out on a small scale using a mortar and pestle
Compression Methods
End runner and edge runner mills are mechanized forms of mortar and pestle
Compression Methods
Size reduction by compression can be carried out on a small scale using a ____________
mortar and pestle
mechanized forms of mortar and pestle type compression comminution
End runner and edge runner mills
a weighted pestle is turned by the friction of material passing beneath it as the mortar rotates under power
end runner mill
has the pestle equivalent mounted horizontally and rotating against a bed of powder, so that size reduction occurs by attrition as well as compression
Edge runner mill
size reduction in Edge runner mill occurs by attrition as well as compression (such techniques are (rarely/often) used in pharmaceutical production)
rarely
It uses 2 cylindrical rolls mounted horizontally and rotated about their long axis
roller mills
Hammer mills (50-8000 um); Vibration Mills (1- 1000 um) are under what method
Impact Methods
During milling the whole body of the milling is vibrated and size reduction occurs by repeated inpaction
vibration mills
in vibration mills, the body is filled to approximately ___% total volume with porcelain or steel balls
80%
balls used in vibration mills are made of _____ or ______
porcelain or steel
consist of a series of four or more hammers, hinged on a central shaft which enclosed within a rigid metal case
Hammer mills
in vibration mills, balls are of (different/same) sizes
same
Produce size reduction of solids in suspensions, pastes or ointments
Attrition Methods
what method:
2 or 3 porcelain or metal rolls are mounted horizontally with an adjustable gap, which can be as small as 20 um. The rollers rotate at different speeds so that the material is sheared as it passes through the gap and is transferred from the slower to the faster roll, from which it is removed by means of a scraper
Attrition Methods
in attrition method, how many porcelain or metal rolls are mounted horizontally with an adjustable gap
2 or 3
in attrition method, rolls are mounted horizontally with an adjustable gap, which can be as small as ______.
20 um
in attrition method, The rollers rotate at (same/different) speeds so that the material is sheared as it passes through the gap
different
in attrition method, The rollers rotate at different speeds so that the material is sheared as it passes through the gap and is transferred from the (slower to the faster roll/faster to slower roll), from which it is removed by means of a scraper
slower to the faster roll
what method:
Ball mills (1-200 um); pin mills (10-10,00 um); fluid energy mills (1-50,000 um)
Combined Impact and
Attrition Methods
consist of hollow cylinder mounted such that it can be rotated on its horizontal longitudinal axis. Mills usually contain balls with many different diameters owing to self attrition.
Ball mills
in ball mills, (small/large) balls tend to break down the coarse feed materials
large
in ball mills, (small/large) balls help to form the fine product by reducing void spaces between balls
small
acts by particle impaction and attrition. It is also known as jet mill
Fluid energy milling
fluid used in Fluid energy milling is usually _______
air
what technique
A fluid, usually air, is injected as high pressure jet through nozzles at the bottom of the loop.
Fluid energy milling
in fluid energy milling, high velocity of the air gives rise to _______ into which solid particles are fed. The high kinetic energy of the air causes the particles to impact with other particles with sufficient momentum for fracture to occur
zones of turbulence
(true/false)
Fluid energy milling involves low velocity fluid like air
false
high velocity
2 discs with closely spaced pins rotate against one another at high speeds.
Pin mills
pin mills technique is influence by _______
centrifugal force
(2) alternative techniques for combined impact and attrition method
Fluid energy milling and pin mills
alternative technique for impact method
vibration mills
alternative technique for compression method
roller mills
