Particle sizing (milling) Flashcards
What is crack propagation???
A process that takes place during size reduction.
The particles become strained by high localised stress which causes rupture and propagation of crack.
What are the different types of surface hardness?
Mohs scale:
Diamond at the top of the scale at 7
Talc at the bottom of the scale at 3
In terms of cutting methods, what is the cutting mill method???
A series of knives attached to a rotor and move against series of stationary knives attached to the casing.
What is the size reduction range of the cutting mill method???
(100- 50,000 μm)
In terms of impact methods, what is the hammer mill method???
Made of four or more hammers attached to a central shaft. All enclosed by a rigid metal case.
In terms of impact, what is the vibration mill method???
Around 80% of the mill is filled with porcelain or stainless steel balls.
What is the size reduction range of the hammer mill method???
(50-5,000 μm)
What is the size reduction range of the vibration mill method???
(1-1000μm)
In terms of attrition methods, what is the roller mill method???
Made of two or three porcelain/metal rollers mounted horizontally and separated by a gap.
When particles pass into the gaps, shearing takes
place.
What is the size reduction range of the roller mill method???
(1-200μm)
In terms of attrition methods, what is the ball mill method???
Consists of a hollow cylinder that can rotate around its horizontal longitudinal axis.
What is the size reduction range of the ball mill method???
30-50% of the cylinder is filled with balls.
What is a combined impact and attrition method???
A process where how fast they spin equals their rotational velocity.
If the velocity is too high the balls are thrown out of the mill by centrifugal force and no size reduction occurs
If it is too low then there is minimal size reduction and the balls will eventually fall to the base of the drum.
In terms of combined impact and attrition methods, what is the fluid energy mill method???
Made of hollow toroids of a diameter of 20-200 mm.
Air is injected as a high-pressure jet through nozzles resulting in forming zones of turbulence.
Coarse particles are retained in the toroid by means of a particle size classifier until sufficiently fine.
In terms of compression methods, what is the fluid roller mill method???
Two cylindrical rollers that rotate around their long axes.
One of the rollers is driven directly while introducing the particles between
the two rollers drive the rotation of the second rollers by friction.
