Ball mill Grinding

Topics: Grinding mills, Particle size distribution, Abrasive machining Pages: 9 (1477 words) Published: October 28, 2013


TITLE: Ball mill grinding.

INTRODUCTION

Indeed the ball milling means, the reduction of particles to smaller sizes with the help of a ball mill. It can be done in two ways. They are,\ Dry milling
Wet milling
Generally, this has porcelain or steel ball as the grinding media. Commiution is occurred by several methods in the ball mill grinding. They are compression, impact and shear between the moving grinding media and the particles. The rate of this depends on some factors. These are mainly three categories.

1. Mill parameters (Diameter, speed and amount of media)
2. Properties of the grinding media (Shape, size and hardness) 3. Properties of the particles

MATERIALS AND APPARATES

Sand
Ball mill and pebbles
Set of sieves
Electronic balance

PROCEDURE

First of all, the ball mill was charge with pebbles to approximately 50% of the mill volume and with sand approximately 25% also. Then the ball mill was switch on and operation was done for one hour. Simultaneously the size distribution of the given sand was noted by using the set of sieves. After one hour later the size distribution was noted for the ground sample. Then ball mill was charged again with pebbles to approximately 25% of the mill volume and with sand approximately 25%. After that this sample was grounded for a one hour. After one hour later the size distribution was noted for this ground sample also. All readings were recorded.

CALCULATION

For sieve analysis of the first sample (without grindings)

Cumulative retain (sieve size 500)= 15.01+10.48

= 25.49

%Cumulative retain (sieve size 500)= 25.49/49.07x100%
= 15.67

Similarly other calculations can be evaluated. They can be tabulated as follows.

Sieve size
Before grinding
After grinding

Cumulative
Retain
%Cumulative
Retain
With 50% media
With 25% media

Cumulative
Retain
%Cumulative
Retain
Cumulative
Retain
%Cumulative
Retain
1000
7.69
15.67
20.66
43.76
0.85
1.8
710
15.01
30.58
26.2
55.49
2.37
5.0
500
25.49
51.94
31.58
66.89
5.59
11.85
355
31.39
63.96
36.56
77.44
10.78
22.86
250
39.64
80.78
39.3
83.24
20.36
43.19
180
42.85
87.32
41.97
88.90
23.61
50.08
150
46
93.74
42.78
90.61
27.54
58.42
105
49
99.85
44.6
94.47
32.26
68.43
75
49.06
99.97
46.09
97.62
37.08
78.65
pan
49.07
100
47.21
100
47.14
100

RESULTS

n value (dn,n=0-100)
Before grinding
(µm)
After grinding

With 50% media
(µm)
With 25% media
(µm)
25
770

357
50
425
810
197.5
75
275
305
82.5

DISCUSSIONS

Actually the efficiency of the ball mill is deepened on the angle of break when the process inside the ball mill is considered. It is measured up the periphery of the Mill from the horizontal. The most suitable angle of break ranges from 50 to 60 degrees from the horizontal. There are four factors affecting the angle of break:

Speed of Mill
Amount of grinding media
Amount of material
consistency or viscosity

Speed of mill
There is a specific operating speed for most efficient grinding. The smaller the Mill the faster in RPM it must run to attain critical speed The lower range is recommended for most wet grinding operations like paints and soft dry materials, and the higher break point (which provides a more severe grinding action) for most dry materials and wet grinding such hard products as enamel frit and glaze. It is also known that the grinding action in a larger Mill is more severe than in the smaller sizes the angle of break should be lower for the larger Mills than for the smaller 54.19 divided by the square root of the radius in feet. The rule of speed applies regardless of the type of grinding media

Amount of grinding media
For the most efficient results, the Mill should be at least half filled with grinding media. In steel ball grinding, many operators, especially in the paint industry, are satisfied to run with a...
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