The main components of the furnace waist and the upper part of the furnace body are: aluminum silicon series, aluminum silicon insulation series, silicon carbide series and carbon series. Furnace shaft is an important part of blast furnace smelting. The thickness of furnace shaft includes furnace shell, filler, cooling wall and furnace lining. In the process of blast furnace production, due to the physical and chemical factors such as rising gas flow and falling charge erosion and wear, high temperature and chemical reaction, the shaft erosion is serious, which destroys the operation furnace type, will affect the smooth smelting of blast furnace, as well as the service life and production of blast furnace *. The life of the furnace shaft is always a key problem for the long life of the blast furnace, which has attracted extensive attention.
Many foreign research units have done the method research of blast furnace body thickness detection, such as Japan, the United States and some countries in the Netherlands have used thermocouple method, electromagnetic pulse method, resistance method and capacitance method to detect furnace wall thickness.
The on-line monitoring technology of BF body thickness can monitor the change of BF body thickness in real time. It has been used in 11 blast furnaces such as Baotou Steel, Shougang, TISCO and Shuigang successively. It has been proved by the blast furnace production that this technology has a certain guiding role in mastering the thickness change of the furnace shaft, when the blast furnace should be supplemented and ensuring the production of the blast furnace. This technology won the third prize of science and technology progress of the Ministry of science and technology of the people's Republic of China in 1999, and won the national patent together with another technology in 2007. This technology has also been listed as the promotion project of scientific and technological achievements

Index item	High alumina			fireclay
	CS － A1	CS － A2	CS － A3	CS － N
AL2O3,%	＞ 80	＞ 79	＞ 80	＞ 40
SiO2,%	＜ 10	＜ 14	＜ 13	/
bulk density （ 110 ℃× 24h ） g/cm3	＞ 2.20	＞ 2.50	＞ 2.45	＞ 1.80
Flexural strength at room temperature CMOR ， MPa	＞ 8	＞ 14	＞ 11	＞ 4
Linear rate of change（ 110 ℃× 24h ），%	0～1.0	0～1.0	0～1.0	0～1.0
granularity， mm	＜ 1	＜ 3	＜ 3	＜ 1
Construction water addition，%	16～18	13～15	12～14	25～30
Characteristics and application parts	Air, heat, waist and upper part of furnace