Graphite electrodes Raw materials and graphite electrode formulation
By:Yvonne Aug 21, 2020
The graphite electrode uses high-quality raw materials to change the molecular structure after calcination, which improves the conductivity of the raw materials, reduces the resistivity, and shrinks the volume, which plays a very important role in improving the quality of the graphite electrode.
► Raw materials for graphite electrodes
• Petroleum coke
It is a black or dark gray hard solid petroleum product with metallic luster and porosity. It is a carbon body made of tiny graphite crystals formed into granules, columns or needles. Petroleum coke component is hydrocarbon, containing 90-97% carbon, 1.5-8% hydrogen, and also contains nitrogen, chlorine, sulfur and heavy metal compounds.
• Needle coke
With obvious needle-like structure and fiber texture, it is mainly used as high-power and ultra-high-power graphite electrodes in steelmaking. Because needle coke has strict quality index requirements in terms of sulfur content, ash content, volatile content and true density, there are special requirements for the production process and raw materials of needle coke.
• Coal pitch
It is a pitch made from coal tar obtained from coal dry distillation and then processed by distillation. It is a black brittle block at room temperature, shiny; smelly, easy to burn when melted, and toxic. It is a secondary flammable solid. The softening point of pitch used for graphite electrodes is between 75-90℃. As a binder for the production of graphite electrodes.
► Calcination raw material quality index
► Graphite electrode formulation
The current production formulas are all based on specific conditions and gradually summarized and improved through long-term production practices.
When determining a formula, it should be noted that when different raw materials are used for each product, the particle composition of the aggregate and the amount of binder are adjusted accordingly. Theoretical analysis tells us that the same accumulation of balls of equal size is used. The maximum space filling rate is 74.05%, so two types of gaps are formed in the middle of the sphere, a tetrahedral gap and an octahedral gap. The diameter of the sphere filling the tetrahedral gap is 0.225 of the basic sphere, and the octahedral gap is filled The diameter of the sphere can be equal to 0.441 of the large particle sphere.
When choosing the ratio of various particle sizes with the experimental method, first use two kinds of particles to do the experiment, use one large particle and the other small particle, and use the large particle weight as 100 grams, and then compare it with 0-100 grams. Mix the second type of particles, and then take 100 grams of the mixture with the largest bulk density obtained, and then mix with the third particle of 0-100 grams, and then select the third mixture with the largest bulk density, mix with the fourth particle size, and do a series of experiments , Until you get the right mixture, the following figure shows the bulk density of the two mixtures with less ash coke 1.5-1.0 and 1.0-1.3 mm.
The bulk density of the mixture of two different particle size ratios
It can be seen from the above table that the volume proportion of the fifth experiment is the largest, and then the two sizes are grouped into 100
1.5 1.0 for 100 / (100 + 40) = 71.4%
1.0 0.3 for 100 / (100 + 40) = 28.6%
According to this ratio column, the mixture with the maximum bulk density can be obtained.
After the calcined raw materials are crushed, carbonaceous particulate materials of different sizes can be obtained. In order to obtain high-quality graphite products, we must appropriately mix carbonaceous materials of different particle sizes with different types of raw materials. Use appropriate weighing equipment to accurately weigh the weights of different particle sizes according to the requirements of the formula. In the production of carbon and graphite products, the correct formulation and accurate batching operations are very useful for the subsequent pressing and roasting graphitization processes. Big impact.