CHARACTERISTIC AND PERFORMANCE PARAMETERS OF GRAPHITE MATERIAL

Characteristic: Graphite material is mainly composed of polycrystalline graphite, which belongs to inorganic non-metallic material, but it is called semi-metal because of its good thermal and electrical conductivity. Graphite has higher thermal and electrical conductivity than some metals, and has far lower thermal expansion coefficient, higher melting point and chemical stability than metals, which makes it of great value in engineering applications. It has good corrosion resistance, not reacting with any organic compounds.

Graphite is also a high temperature resistant material, which does not melt at high temperature. Graphite also has good thermal shock resistance and good self-lubricating properties.

The disadvantage of graphite is its poor seismic performance. With the increase of temperature, the oxidation rate increases.

Performance parameter

1. Average particle diameter of graphite materials

The average particle diameter of materials directly affects the discharge status of materials. The smaller the average particle size, the more uniform the discharge, the more stable the discharge condition and the better the surface quality.

For forging and die-casting dies with low surface and precision requirements, it is generally recommended to use materials with coarse particles, such as ISEM-3, etc. For electronic dies with high surface and accuracy requirements, it is recommended to use materials with average particle size less than 4 micron to ensure the accuracy and surface finish of the processed dies. The smaller the average particle size of the material, the smaller the loss of the material and the greater the interaction force between the ion groups. 

At the same time, the larger the particle size, the faster the discharge speed and the smaller the loss of roughing. The main reason is that the discharge energy varies with the current intensity during the discharge process. However, the surface finish after discharge varies with the change of particles.

2. Flexural strength of graphite materials

The flexural strength of the material is the direct reflection of the strength of graphite, showing the tightness of the graphite internal structure. The material with high strength has relatively good discharge wear resistance. For the graphite electrode with high precision, the material with better strength should be chosen as far as possible. 

3. Shore hardness of graphite materials

In the subconscious understanding of graphite, it is generally regarded as a soft material. But the actual test data and application show that the hardness of graphite is higher than that of metal materials. In the specialties graphite industry, the general hardness testing standard is the Shore hardness testing method, whose testing principle is different from that of metal. Because of the layered structure of graphite, it has excellent cutting performance in the cutting process. The cutting force is only about 1/3 of the copper material, and the machined surface is easy to handle. However, due to its high hardness, the tool wear will be slightly greater than that of metal cutting tools in cutting. At the same time, the material with high hardness has excellent control of discharge loss.

4. Inherent resistivity of graphite materials

According to the statistics on the characteristics of graphite materials, if the average particles of materials are the same, the discharge speed with high resistivity will be slower than that with low resistivity. For materials with the same average particle size, the strength and hardness of materials with low resistivity are also slightly lower than those with high resistivity. That is to say, the discharge speed and loss will be different. Therefore, it is very important to select materials according to the practical application. Due to the particularity of powder metallurgy, each parameter of each batch material has its own material representative value with a certain fluctuation range. But for the same grade of graphite material, its discharge effect is very close, because the difference of application effect caused by various parameters is very small. The selection of electrode materials is directly related to the effect of discharge. To a large extent, the selection of materials determines the final conditions of discharge speed, machining accuracy and surface roughness.