General Classification of Carbon Graphite Materials for Mechanical Seals

Graphite products

1. Baked graphite. In a sense, baked graphite is divided into hard carbon graphite and soft electrochemical graphite. They are made of petroleum carbon black, soot carbon black mixed with tar, asphalt, etc., crushed and pressed into blanks, and baked at high temperature. In addition to the different material components, the main difference between the two is that the latter needs to be graphitized at 2400-2800 degrees Celsius. When graphite is baked, pores (10%-30% pores) appear due to the volatilization of volatile substances in the binder and the polymerization, decomposition and carbonization of the binder. When used as a sealing ring, permeability leakage will occur, and the strength is low, so it is necessary to carry out impregnation treatment to fill the gap and strengthen it, that is, after impregnation treatment, it becomes an airtight product and the strength is also improved. However, the temperature resistance and corrosion resistance have decreased to varying degrees. There are three major types of impregnation materials used: organic resins, inorganic substances and metals.

2. Resin-bonded graphite, which is sintered graphite crushed, with phenolic resin or epoxy resin as a binder, mixed and pressed and sintered into products. The resin in the matrix becomes carbon particles after sintering, so it is an airtight graphite. It has poor thermal conductivity and large linear expansion coefficient; it is suitable for mass production and low cost; it is mainly used for low-load seals such as automotive cooling water pumps and household appliances.

3. Pyrolytic graphite, domestic pyrolytic graphite is pyrolyzed at high temperature by hydrocarbons such as propylene, so that carbon vapor penetrates into the pores of the carbon graphite blank, plays a role in plugging the pores, and forms a high-density, less porous, and low-permeability pure carbon graphite material. Its porosity is <1%, the compressive strength is 290mpa, the hardness is 70~75hs, and the linear expansion coefficient is 0.36×10-6 degrees Celsius. Pyrolytic graphite does not contain organic matter and metal, and is suitable for high temperature and strong corrosion conditions. Since it is not suitable for mass production, the cost is relatively high.