The quality of graphite electrode is affected by particle diameter, flexural strength, resistivity and so on. Let DanCarbon talk about How to choose high quality graphite electrode?
There are many bases for graphite electrode selection, but there are four main criteria:
1. Average particle diameter of graphite electrode
The average particle diameter of the material directly affects the discharge condition of the material. The smaller the average particle, the more uniform the discharge, the more stable the discharge condition and the better the surface quality. For forging and die-casting molds with low surface and precision requirements, it is usually recommended to use materials with coarser particles, such as ISEM-3. For electronic molds with high surface and precision requirements, materials with average particle size below 4 m are recommended to ensure the precision and surface finish of the molds to be processed. The smaller the average particle is, the smaller the loss will be and the greater the force between the ion groups will be. At the same time, the larger the particle, the faster the discharge rate, the less the rough machining loss. The main reason is that the current intensity of the discharge process is different, which leads to different discharge energy. However, the surface finish after discharge changes with the change of particles.
2. Flexural strength
Flexural strength is a direct reflection of the strength of the material, indicating the tightness of the internal structure. The material with high strength has better discharge resistance. For the electrode with high precision, the material with better strength should be selected as far as possible.
3. Shore hardness
In the subconscious understanding of graphite, graphite is generally considered as a relatively soft material. However, the actual test data and application show that the hardness of graphite is higher than that of metal materials. In the special graphite industry, the general hardness test standard is the Shaw hardness test method, the test principle is different from the metal test principle. Due to the layered structure of graphite, it has a very superior 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 be treated.
But because of its high hardness, in cutting, the loss of the tool will be slightly greater than the cutting tool of the metal. At the same time, the high hardness of the material in the discharge loss control is better. In the EDM material system, there are two kinds of materials with the same particle size that are widely used, one with slightly higher hardness and the other with slightly lower hardness, to meet the needs of customers with different requirements. Mainly considering the various types of customers to discharge and machining bias direction.
4. Inherent resistivity
According to characteristic statistics, if the average particles are the same, the discharge rate 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 will be correspondingly slightly lower than those with high resistivity. That is, the discharge speed, loss will be different. Therefore, it is very important to select materials according to the needs of practical application. Due to the particularity of powder metallurgy, each parameter of each batch of material has its representative value and has a certain range of fluctuation. However, the discharge effect of graphite electrode of the same grade is very similar, and the difference of application effect caused by various parameters is very small. The selection of electrode materials is directly related to the discharge effect, and to a large extent, the selection of materials determines the discharge speed, machining precision and surface roughness.