The grinding process of the material directly depends on its hardness.
Earlier we considered the classification of rocks hardness according to the Protodyakonov scale, where the hardness coefficient bases on the degree of material resistance to compression.
There is also another method for determining material hardness – this is the Mohs scale of mineral hardness proposed by German mineralogist Friedrich Mohs in 1811. Many laboratories practice this method.
Mohs hardness is the scratch resistance of material surface through the scratching it with another material. A hardness depends on the connectivity degree of the material`s atomic structure.
A Mohs scale is a scale of reference minerals for assessing materials hardness by scratching. The scale is shown below.
|
Mohs Hardness Scale |
|
|
Standard mineral |
Hardness |
|
Talc |
1 |
|
Gypsum |
2 |
|
Calcite |
3 |
|
Fluorite |
4 |
|
Apatite |
5 |
|
Orthoclase |
6 |
|
Quartz |
7 |
|
Topaz |
8 |
|
Corundum |
9 |
|
Diamond |
10 |
There are ten minerals on the Mohs scale, each of which has a specific coefficient of hardness.
The hardness determination of other materials not represented on this scale is carried out using this set of reference materials by pressing them on the test material surface.
If the reference material leaves a scratch on the test material surface, then the reference material is harder.
It is important to remember that the range of standard minerals is not not linear. For example, diamond (measuring 10 on the scale) is not twice harder than apatite (measuring 5 on the scale). This scale places materials from a very soft mineral to a very hard mineral.
To determine the hardness of the test material any improvised means such as a fingernail (2.5), a knife (5.5) or glass (5.5) can be applied. It makes this method simple and affordable.
In most cases, the hardness coefficient of the material crushing in ball mills is in the range from 6 to 9 on the Mohs scale.
Steel grinding balls produced by Energoteel are suitable for grinding soft and hard materials.
In the production of grinding balls, the company’s specialists test not only the chemical composition of the raw materials, but also select the optimum technology of metal heat treatment, which provides not only a high hardness of the grinding steel balls, but also their resistance to abrasion and splitting.