　　Clay brick is made by hard clay, calcined clay and bonding agent through pelletizing and milling, mixing as per certain ratio, pressing molding and burning under high-temperature. Fire-resistant clay bricks can be divided into special clay bricks (including clay bricks for blast furnaces, clay bricks for glass kilns and clay bricks for hot-blast furnaces) and general clay bricks.

　　General clay bricks can be divided into such three grades as PN-1, PN-2 and PN-3 as per physical and chemical indexes.

　　Special clay bricks can be divided into such three grades as ZN-45, ZN-40 and ZN-36 as per physical and chemical indexes.

Physical and chemical indexes of general clay bricks：

Item	Indexes
Item	PN-1	PN-2	PN-3
0.2MPa load softening starting temperature ℃ ≥	1300	1250	1200
Changes in heating permanent line (1350°C×2h) %	-0.2～+0.1	-0.3～+0.1	-0.4～+0.1
Apparent porosity % ≤	24	26	28
Ambient compression strength Mpa ≥	30	25	20

Physical and chemical indexes of special clay bricks：

Item	Indexes
Item	ZN-45	ZN-40	ZN-36
Al2O3 % ≥	45	40	36
0.2MPa load softening starting temperature ℃ ≥	1430	1380	1350
Changes in heating permanent line (1350°C×2h) %	-0.2～+0.1	-0.3～+0.1	-0.4～+0.1
Volume density g/cm³	2.0～2.3
Apparent porosity % ≤	16	19(22)	22(24)
Ambient compression strength Mpa ≥	60	40(35)	35(30)

Clay 2 piece brick

Universal arc brick

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