The first step in the production process of graphite electrode is the calcination of raw materials

Calcination is the production of carbon graphite products of various coke, anthracite in basically isolated air conditions for high temperature distillation. A series of profound changes have taken place in various carbon raw materials from elemental composition to organizational structure during calcination.

The purpose of calcination has the following four points

(1) Remove volatiles from raw materials.

In addition to asphalt coke and metallurgical coke, other carbon raw materials (petroleum coke, anthracite, etc.) contain a considerable amount of volatiles, and the mass fraction of delayed petroleum coke volatiles is as high as 12%~16%. The more volatile materials the raw material contains, the lower the degree of carbonization or coking of the raw material. Since the existence of a large number of volatiles has a great impact on a series of physical and chemical properties of raw materials, eliminating volatiles in raw materials and improving carbon content is one of the purposes of calcination, and it is also the premise of improving the physical and chemical properties of raw materials.

(2) Improve the density and strength of raw materials.

At the high temperature of calcination, when the volatiles are discharged, the complex decomposition and polycondensation of the polymer hydrocarbons occur, the molecular structure is constantly changing, and the volume of the raw material itself gradually shrinks, and the result of the volume contraction improves the density and strength of the raw material. For the raw material after combustion, whether it is true density, false density and mechanical strength, there is a considerable degree of improvement. If a variety of carbon graphite products are produced with raw materials that are not burned or have insufficient combustion degree, the raw products after forming will produce a large volume shrinkage during the roasting process, which will destroy the complete structure of the product and cause cracks.

(3) Improve the electrical conductivity of raw materials.

The improvement of the electrical conductivity of raw materials is the comprehensive result of the volatiles removed from raw materials after calcination and the change of molecular structure. Most carbon graphite products are used as conductive materials, and the electrical conductivity of products depends to a large extent on the degree of heat treatment of several heat treatment processes (calcination, roasting and graphitization), how to determine the electrical conductivity of raw materials after calcination (that is, to determine the size of the powder resistivity) can directly judge the quality of raw materials.

(4) Remove water from raw materials.

If the raw material contains more water, it is not conducive to the crushing, screening, grinding and other operations, and will affect the adsorption of the raw material particles to the binder. Therefore, although some raw materials (such as metallurgical coke and asphalt coke) have been coked at high temperature in the coke oven, they can be calcined without calcination, but because of the watering of coke after pushing coke, and the addition of some moisture during transportation and storage, they must be dried before use.