GENERAL CONCEPTS OF GRINDING

Let’s remember a little bit of theory, and more specifically, what grinding is and by what methods it is carried out at the enterprises in industry.

The intensity of many technological processes depends on the value of the total surface area of processed solid materials. The higher this index is, the grinding is more effective. Increase in this indicator is achieved by reducing the size of pieces of material (grinding), which in turn ensures the quality of the finished product.

The process of reducing the size of material is called crushing or grinding.  Often crushing is defined as the reduction of only large pieces. This process is done in crushers.

The process of grinding smaller pieces is called milling. This process is mostly carried out with ball mills, which use grinding balls as the grinding media.

Fuel (coal), raw materials (rocks, ores), semi-finished and finished products are crushed.

Grinding is called coarse if pieces with cross-sectional size of 1000 to 200 mm, medium and intermediate – in the range of 250 to 50 mm, small in the range from 50 to 20 mm and fine (grinding) – in the range from 25 to 3 mm and less.

The overall degree of grinding characterizes the total result of grinding, carried out in several stages. For this purpose, cement plants use two-chamber ball mills. In the first chamber, grinding balls with a diameter of 100-50 mm are loaded. The second chamber is loaded with a assortment of grinding balls with a diameter of 25-40mm. At mining and processing plants single-chamber ball mills are used. I.e. steel balls with diameter of 120-100 mm are used in the first stage of grinding, 60-40 mm in the second stage, and 25-30 mm in the third stage.  The degree of grinding of pieces in one processing step is:

Grinding is done by crushing (1), impact (II), abrasion (III) and splitting (IV).

In most cases, there is a combined effect of grinding forces, for example, crushing with abrasion, impact with crushing and abrasion; sometimes the main forces are joined by side forces – bending and tearing.

The method of comminution is chosen taking into account the physical properties of the material to be comminuted, first of all, its hardness and the character of its fracture.

Impact and crushing are more effective for hard materials, abrasion is preferable for viscous materials, and splitting is preferable for brittle materials.

One of the most important factors characterizing the grinding process is the amount of energy required to grind one ton of material. The greater the strength of the material to be shredded, the more energy is required for shredding. We have already discussed the energy expenditure and how it is applied in practice in more detail in our publications:

https://energosteel.com/metod-smc/
https://energosteel.com/ispolzovanie-energeticheskih-indeksov-raschet-indeksa-bonda-dlya-sharovogo-izmelcheniya/
https://energosteel.com/test-padajushhego-gruza-po-metodike-jkmrc/
https://energosteel.com/ispolzovanie-energeticheskih-indeksov-raschet-indeksa-bonda-dlya-sterzhnevogo-izmelcheniya/
https://energosteel.com/metody-vybora-sag-melnic-iii-raschet-indeksa-bonda-drobleniya/
https://energosteel.com/metody-vybora-sag-melnic-ii-rabochij-indeks-f-bonda-v-izmelchenii/