Carbon seal ring is installed in the annular groove of the sealing seat of the coal pulverizer, to isolate the hot air inside the coal pulverizer from the outside atmosphere. The inner circular surface of the ring is in contact with the drive shaft, and the outer circular surface is embedded in the groove of the transmission disk. In operation, no lubricant is required between the transmission shaft and the sealing ring, which requires that the self-lubricating property of the carbon ring must be very excellent. The internal hot air pressure of the coal mill is 10KPa and the temperature is ≤400°C. This requires that the carbon ring material must meet the temperature conditions of up to 400 °C and lower to -20 ° C, and have good mechanical strength in these conditions. Due to coal dust particles in operation environment, sometimes accompanied by water or water vapor, the reliability of the plant operation requires that the seal ring should have lifetime with more than 8,000 hours. This requires that the carbon ring material must have high strength and very good anti-wear properties, with certain mechanical strength, high processing accuracy and interchangeability.