Abrasion

Attrition, wear are important terms when bulk solids are mixed or conveyed. Abrasion always occurs in the contact area when two bodies move relative to each other. In this process, the harder of the two bodies damages the surface of the softer solid. This form of abrasion is referred to as abrasion.

Abrasion increases

• if the coefficient of friction between the bodies is high
• when the pressure between the bodies increases
• when the surface of the moving body is rough
• when the speed difference between the bodies increases
• when the friction between the moving bodies increases (this can be the case when they heat up)
• when there is a viscous liquid between the bodies
• when there is an abrasive powder between the bodies.

Particles of bulk material are also considered to be bodies. These generally have an irregular shape. They have a minimum and maximum diameter. Bulk materials can be classified according to their particle size as follows:

• micro-structured: 10-6 metres (designation µm)
• nano-structured: 10-9 metres (designation (nm)

When mixing a bulk material with a rotating agitator, the drive torque is a measure of the ‘internal friction’ of the bulk material. During mixing or conveying, the particles rub against each other. But they also rub against the mixing tool and the wall of the mixing chamber.

Wear on the mixing tool and the mixing container is undesirable. On the one hand, they contaminate the mixture, and on the other, they destroy the mixer.

Countermeasures are:

1. Reducing the speed of the mixing tool.
2. Reducing the mixing time; however, points 1) and 2) only work if the mixing system has a high mixing efficiency.
3. Reducing the conveying speed.
4. Selecting a particularly hard mixing material for the mixer/conveyor.
5. Hardfacing the tool parts by welding hard metal.
6. Selecting a suitable coating (oxide ceramic).