More than once, we have mentioned that Energosteel specialists come into regular contact with various research organizations. These research institutions specifically specialize in grinding various materials.
Hence, while selecting valuable information for our readers, we came across a research report presented at the Belgorod cement conference in 2012.
The research was aimed at developing methods of mill loading with grinding balls that would provide the finest grinding without loss or increase in mill’s output while maintaining the grinding quality.
As is generally known, the effect of the grinding balls on the material to be ground is carried out via a shock compression impulse (SCI). The SCI value could be quantitatively expressed by means of the ratio between the mass of the grinding media in the mill and the mass of the concurrently ground material. This ratio can be determined by the following formula:
where: mg.b.– the mass of the grinding balls, kg;
mc.g.m. – the mass of the concurrently ground material, kg;
The picture shows the balls distribution in the mill under normal load.
With such laying out of the balls of the same diameter, the volume is distributed as follows: 52% goes to grinding balls, 48% is a void volume. That means, to achieve maximum grinding fineness, it is necessary to charge balls of different diameters. This will result in a decrease of dead volume between the grinding media.
The following distribution pattern was suggested for loading grinding balls without mixing balls of different diameters. This pattern allows reducing void volume by nearly half.
With such tight loading,the entire volume is distributed as follows: 74% goes to grinding balls, 26% is a void volume.
When using tight loading, the impulse of shock compression significantly increases and that directly influences the quality of grinding. The formula given above should be used for calculation of SCI. The results of the calculations are shown below.
SCI (under normal load) = 7.3 kg\kg.
SCI (under tight load) = 14.43 kg\kg.
The calculations clearly illustrate that the grinding balls mill load is twice efficient under the tight loading compared to the normal load.
Mill loads in question underwent lab comparative tests that proved the advantage of a tight mill load as opposed to a normal load. The research results are shown in the table below.
|Mill load||Grinding media mass in
|Grinding media volume in the mill load, m3||Voids volume in the mill load, m3||Grinding media density||Grinding fineness|
|Passed through the sieve 008, %||Specific surface area, m2/kg|
|Normal mill load||4.64||4.83||3.37||4.63||90.4-91.5||av. 290|
|Suggested tight load||5.90||4.83||1.61||6.10||97.3-97.6||av. 380|
The results of the lab tests were applied for performance assessment of a standard pipe mill, 3.2х15 m, under the normal and tight loads. The calculation results are provided below.
Output under a normal mill load = 54 t\hr.
Output under a tight mill load= 87.9 t\hr.
However, the question is, how is this tight load achieved? The answer is simple –through the application of lift-grooved armor plates in the grinding mill construction (see a picture below).
Our article hasn’t disclosed all the details of the calculations and the exact layout of the armor plates in the mill. This innovation was developed by specialists of the Belgorod State Technological University named on behalf of V.G.Shukhov. Studies were conducted under laboratory conditions for the cement industry. Nevertheless, Energosteel’s specialists are positive that this development can be applied to all types of ball mills and all industries, excluding semi-self-grinding mills.