Grinding (sa book) Flashcards
is the last stage of the comminution process.
Grinding
A ____ consists of a horizontal rotating steel shell supported by end bearings on which hallow trunnions revolve. Loose crushing bodies, known as ____, are placed inside the shell.
Grinding Mills
Grinding Medium
Either ____ or ____ are used as grinding medium
Steel Balls/ROds or pebbles
____, forces which result from the application of forces by rolling and sliding bodies tend to produce more fine particles than impact forces applied on particles by repetitive blows.
Attrition or Shearing
____ are relatively high in power consumption and require expensive foundations. ____ are normally loaded to approximately 50 percent of its volume with grinding medium.
Grinding Mills
The interior of tumbling mill is lined by replaceable liners usually made of ____ but sometimes of ____.
alloy steel
rubber
____ favor abrasion resulting in fine grinding but high metal wear.
Smooth Liners
In a ____, the material is fed by gravity through the spout.
Spout Feeder
In ____, the entire mill feed enters the drum and an internal spiral carries it and fed to the mill. Grinding balls are conveniently added through this feeder during operation.
Drum Feeder
In case of ____, material is fed to the drum and the scoop picks it up and fed to the mill.
Scoop Feeder
In ball mills, the grinding medium is ____; in rod mills, ____; in tube or pebble mills , ____ of hard rock or other nonmetallic material; in autogenous mills, ____ particles
steel balls
steel rods
pebbles
coarse ore particles
____ usually have a length to diameter ratio of 1.5 to 1.0. According to the shape of the mill, the ____ are classified as cylindroconical and cylindrical mills
Ball Mills
Grinding of ore particles takes place due to simple rolling of one ball over the other ( ____ ) and by the free fall of balls ( ____ ).
cascading
cataracting
____ leads to fine grinding whereas ____ leads to coarse grinding.
Cascading
Cataracting
As the speed of the mill increases, the balls are lifted higher and a stage is reached where the balls are carried around the shell and never allowed to fall. That means ____ occurs. The balls will rotate as if they are part of the shell.
Centrifuging
The speed at which centrifuging occurs is known as ____.
Critical Speed
An ____ where no balls occupy this zone during operation.
Empty Zone
A ____ zone where no grinding takes place
Dead zone
When the speed of the mill exceeds the critical speed, all these zones ____, the balls will centrifuge and no grinding takes place anywhere inside the mill. Hence the mill should be operated at a speed below the critical speed. The usual range is _____% of critical speed.
dissapear
60-80%
Balls vary in size from 1 to 6 inches. The largest balls are used for coarser grinding. Initially, at the start of a ball mill, balls of various sizes, known as ____, are introduced. As the balls wear out gradually, only the largest balls are added as make up media
seasoned charge
A ____ uses rods as a grinding medium. Length to diameter ratio is between 1.5 and 2.5. Rods are a few centimeters shorter than the length of the mill to avoid any jamming of rods in the mill. The rods are kept apart by the coarsest particles. The grinding action results from line contact of the rods on the ore particles and is exerted preferentially on the coarsest particles. Smaller and fine particles do not grind till the coarsest particle is reduced in size.
Rod Mill
This can clearly be observed in Figure 9.4. Thus the rod mill produces a more closely sized product with little oversize or slimes. Hence the rod mills may be considered as ____.
Coarse Grinding Machines
Two types in peripheral discharge mill
In the ____ mills, the material is fed at one end of the mill and the ground product is discharged from the other end by means of several peripheral apertures into a close-fitting circumferential chute.
End Peripheral Discharge Mills
Two types of peripheral discharge mill
In ____, the material is fed at both ends of the mill and the ground product is discharged through a circumferential port at the centre of the shell.
Centre Peripheral Discharge Mill