this article focuses on the third production step for making graphite electrodes >>formulation<<. Small particles are combined with larger ones to form what we call the “bonestructure and binding material” of graphite electrodes. Our goal is to create a dense grain structure keeping the formation of pores to a minimum.

For each graphite electrode manufacturer this stage is a well kept trade secret. As explained in the raw material section, the most ideal raw material to produce graphite electrodes is needle coke. Therefore, electrodes of the highest quality contain as much of needle coke as possible – 100 %. However, as we will see later, there are also inferior qualities sold and so the formulation may contain petroleum coke as a substitute for needle coke.

There are three components to the structure (please also compare diagram below)

Screenshot (1)
particle structure of graphite electrodes. Source: GES Europe
  • aggregate material (= bone structure)
  • filling material
  • binding material (=pitch)

We call a grain size big with grain diameters is bigger than 1 mm. Medium in the range of 0,8 mm to 0,5 mm. Small grains have diameters of between 0,5 mm and 0,042 mm the last being the technical minimum at the moment.

Aggregate and filling material might be either petroleum or needle coke depending on the targeted quality. The three parameters to compose a recipe are thus: choice of raw material(s), grain sizes of aggregate and filling materials, ratio of aggreate, filling and binding materials.

As the name suggests, pitch is used to bind the different grains together and further increase density of the structure. It is also important for the later forming process. For the production fo graphite electrodes, this will be extrusion. Therefore, a higher content of pitch is desirable. Reason: for extrusion, bigger grain sizes are use for aggregate and filler; therefore more pitch is needed to fill up the pores.

Since the most important aspect about the composition is the different grain sizes to generate a high density, there is almost no limitation to the recipe. One formulation using four different grain sizes (petroleum coke alone, needle coke alone, or a mixture of both) might read as follows:

-> 0,8 mm – 40 %; 0,4 mm  – 20 %; 0,2 mm – 20 %; 0,1 mm – 20 %.

I hope you like this article. Please SHARE

 

 

 

2 thoughts on “ABC of graphite electrodes: how are graphite electrodes produced? (3b) – formulation

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.