Size reduction Flashcards
reasons for size reduction (6)
increase SA for reaction improve extraction of active principles improve dispersibility in solution allow better mixing or blending enable rapid dissolution preliminary process in preparation of products
What are 3 modes of breakage
crack opening by tensile spreading at crack tip
crack sliding by shear deformation parallel to crack direction
crack tearing by shear deformation perpendicular to crack direction
Considerations in size reduction (3)
properties of material
fracture mechanics of particles
mechanical: type of equipment
properties of materials important in size reduction
thermolability
melting point
flammability
deformation characteristics
fracture mechanics of particles important in size reduction
hardness
tensile strength
mechanical considerations in size reduction
impact, shear on pressure
material in contact with product
temperature control
size reduction mechanisms (4)
impact, compression, shear, attrition
4 advantages of wet grinding
eliminate dust
easier to handle material
use less energy
increase ill capacity
3 disadvantages of wet grinding
increase wear of grinding medium
not applicable to soluble materials
may need to dry products
types of hammer mill
rotor type/rasping screen
knife edge rotor
impact edge
advantages of hammer mill
several models available, vertical and horizontal designs
medium to high shear applications
blades and screens are interchangeable
suitable for very hard materials
disadvantages of hammer mill
noisy& dusty
cannot plug feed
belt slip common due to load
high volume air generation, ventilation requirement
screen selection and installation complex, not scalable
sifting required after milling
temperature rise due to friction
How does cone mill work
particles in –> centrifugal force brings to screen –> size reduced and instantly ejected once of size
what is vibratory ball mill mostly used for
fine grinding
types of balls for vibratory ball milling
stainless steel
stoneware ceramic
