this article focuses on the fourth production step for making graphite electrodes >>kneading<<. The small particles whose structure and composition was formulated in step 3, are now intermingled to a paste (remember – those components were the aggregate,- binding,- and filling materials).
There are different kinds of kneaders used
- Sigma double arms: one pair of blades, discountinuing working mode, blades rotate in different directions with different velocities.
- Eirich strong kneaders: two pairs of blades with different lengths and rotation directions, enables the material to rotate in four directions
- pressurized kneaders
- flaking kneaders for fine grains (up to 0.042 mm)
As heating media, graphite producers use the full range of either electricity, steam or hot oil with the later consisting of Diphenyl Oxide: 26.5% Biphenyl + 73.5% Biphenyl Ether. This is added in interlayer of kneader
Favorized by many graphite companies, Eirich kneaders allow for rotations in 4 directions and therefore homogeneous properties of the product. Each Eirich kneader has three characteristic components:
Eirich mixer model 1, Source: Eirich GmbH, website (2018)
Eirich mixer model 2, Source: sigmachina – eirichchina
- The rotating mixing pan, which delivers the mixture into the area of the mixing tools
- One or more mixing tools arranged eccentrically. The direction of rotation and the speed of the mixing tool(s) can be optimally adapted to the different applications.
- The bottom/wall scraper, providing additional agitation action. It prevents cakings on the wall and bottom of the pan and facilitates discharge when the mixing cycle is complete.
Graphite producers follow 3 principles when kneading
- When kneading temperature is below the standard, the process time should be longer
- When pitch’s melting point is below the standard, process time will be shorten
- Process time will be longer if material particles are relatively small.
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