Industry News

- January 15, 2021

Carbon product formula

The formulation of carbon products is mainly determined through experiments due to the variety of technical requirements. In general, follow the following principles:

(1) Petroleum coke and pitch coke have low ash content, and the finished product has high mechanical strength and medium conductivity. The mechanical strength of pitch coke products is higher than that of petroleum coke, but its resistivity is higher than that of petroleum coke. The graphitization of pitch coke is worse than that of petroleum coke, so the electrical conductivity and thermal conductivity are slightly worse. General small carbon products, such as carbon parts for communication, carbon resistors, various carbon rods, etc., require higher mechanical strength. Use finely ground pitch coke as the main material, and carbon black or graphite to adjust the resistance.

(2) Carbon black has the smallest particles, so it has a large specific surface and can absorb a large amount of binder. When the product is roasted, the binder is coked with carbon black particles as the center. Due to the large surface activity of carbon black, the coking value of the binder is high. Therefore, adding carbon black to the formulation can significantly improve the mechanical strength of the product. But its side effect is that the shrinkage rate of the product is also very large, it is easy to deform or crack the product, and it is difficult to grasp the shape and size. At the same time, the product has extremely high hardness and is difficult to process (the hardness decreases after graphitization). On the other hand, because carbon black particles are small and can fill the gaps between other carbon powders, adding part of carbon black to the formula can increase the volume density of the product and reduce the porosity. But for large products, it should not be added. Carbon black particles are highly dispersible and increase the contact points between particles, thus increasing the electrical resistivity of the product. Carbon black can be added to increase the electrical resistivity of the product. The amount of addition depends on the technical requirements of the product. The addition of carbon black will increase the friction coefficient of the product. For small sliding contact materials that are not graphitized, too much carbon black is detrimental to the service life of the product. The burning rate of carbon black products is relatively high. Using this feature, carbon black can be used as the outer shell of the arc carbon rod. Although the burning speed is too large for strong arc rods, it is also a disadvantage. However, the slow burning speed reduces the arc intensity, and the arc intensity is the main indicator. If the burning speed is not too high, then his influence will take a back seat.

(3) Flake graphite can significantly improve the conductivity and lubricity of the product, and reduce the hardness of the product. It is commonly used in pure carbon products to reduce the electrical resistivity and wear of the products. However, adding flake graphite will significantly reduce the mechanical strength of the product. Therefore, it is not advisable to add too much flake graphite (except some soft electrochemical graphite brushes) for all products that are to be graphitized.

(4) The particle size of earthy graphite is very fine, which can absorb more binder, and the finished product has higher mechanical strength. But the earthy graphite itself is very soft. Although the finished product has higher mechanical strength, it is not brittle and hard like pitch coke, but has a higher resistance to impact load. It is generally used to adjust the hardness of products as a component of carbon products subject to mechanical impact, such as piston rings, seal rings, bushings, electric brushes for electric cars, etc. Because of its high ash content, it is rarely used alone except for battery carbon rods.