There are various types of equipment used in size reduction. The aim of this assignment is to
discuss and contrast any two of the equipment.
• Hammer Mill
“Size reduction takes place by impact force. It consists of high speed rotor rotating inside a
cylindrical casing. Shaft is usually kept horizontal, materials are fed into the mill from the top of
the casing and is broken by the rotating hammers and fall out through a screen at the bottom.
Feed is broken by the fixed or swinging hammers, pinned to a rotor. Hammers are rotated
between 1550 to 4000 rpm, strike and grind the material until it becomes small enough to pass
through the bottom screen. Fineness of grinding is controlled by the screen size. It can grind
tough fibrous solids, steel chips, food grains, hard rock etc.” (Size reduction – equipment for size
reduction, care and maintenance, n.d.).
Advantages
“It is rapid in action, and is capable of grinding many different types of materials. They are also
easy to install and operate, the operation is continuous. There is little contamination of the
product with metal abraded from the mill as no surface move against each other. The particle
size of the material to be reduced can be easily controlled by changing the speed of the rotor,
hammer type, shape and size of the screen.
Disadvantages
Heat buildup during milling is more, therefore, product degradation is possible. Hammer mills
cannot be employed to mill sticky, fibrous and hard materials. The screens may get clogged.
Wearing of mill and screen is more with abrasive materials”(Raval, 2016).
• Jaw Crusher
According to (Size reduction, n.d.)“In a jaw crusher, feed is admitted between two jaws, a
stationary jaw or anvil and a movable jaw, which reciprocates in a horizontal plane. It makes an
angle of 20 - 30o with the stationary jaw. It is driven by an eccentric so that it applies great
compressive force on the lumps caught between the jaws. Large lumps caught between the upper
parts of the jaws are broken, drop in the narrower space below and are re-crushed the next time
the jaws close. After sufficient reduction they drop out of the bottom of the machine. The jaws
open and close from 250 to 400 times per minute. Size reduction in jaw crushers occurs mainly
by a compression mechanism and to lower extent by impact.” (Maschinenfabrik, n.d.) states “Jaw
crushers are used for primary crushing of a wide variety of materials in the mining, iron and steel
and pit and quarry industries. Furthermore they are used in recycling processes. The feed
materials include, Rock ranging from medium-hard to extremely hard, as well as different kinds
of ore, building rubble, glass and other hard materials”.
Advantages
“Simple structure, low cost, maintenance are convenient, reliable work, small machine body,
easy to use.
Disadvantages
Lower productivity, lower power Consumption, bigger vibration, small crushing Ratio, uneven
particle size, can’t crowd feeding ore”(Jaw Crusher, 2015).
The major difference between the two equipment is that In Hammer Milling, size reduction takes
place by impact force and in Jaw Crushing, it takes place by the compression force. And the only
similarity is that both machines can grind hard rock.
References
•
Jaw Crusher. (2015). [ebook] pp. 9 .Available at:
https://www.slideshare.net/knowledge1995/jaw-crusher-55107659 [Accessed 16
Apr.2019]
•
Maschinenfabrik, A. (n.d.). Relaible Jaw Crusher Crushing. [ebook] pp. 2
.Available at: http://www.tlt.as/Undersider/documents/JawCrusher.pdf [Accessed
16 Apr.2019]
•
Raval, A. (2016) ‘Size Reduction Equipments’[PowerPoint presentation].
2210001: Size reduction. Available at:
https://www.slideshare.net/AmarRaval1/size-reduction-equipments (Accessed: 16
Apr 2019).
•
Size reduction – equipment for size reduction, care and maintenance.
(n.d.)[ebook] pp. 8,9.Available at:
http://eagri.org/eagri50/AENG252/pdf/lec09.pdf HYPERLINK
"http://shodhganga.inflibnet.ac.in/bitstream/10603/76528/6/06_chapter%201.pdf.
%20%5bAccessed"
•
[Accessed 16 Apr.2019].
Size reduction. (n.d.)[ebook] pp. 5.Available at:
https://scholar.cu.edu.eg/?q=magdi/files/chapter_4_updated.pdf HYPERLINK
"http://shodhganga.inflibnet.ac.in/bitstream/10603/76528/6/06_chapter%201.pdf.
%20%5bAccessed" [Accessed 16 Apr.2019].