Metering nozzle is functional refractory material for controlling steel liquid flow rate during the process of continuous casting billet making. Through fixed caliber of metering nozzle, steel liquid can flow from tundish to casting mold with a constant speed. The size of nozzle hole depends on billet dimension and drawing speed of continuous casting machine, usually between 12~20mm. During the whole continuous casting process, nozzle hole’s diameter should be constant to ensure stable steel liquid flow rate, thus metering nozzle is key functional refractory component for continuous casting billets making, its quality will affect the whole continuous casting process. Metering nozzle should not only be safe and stable, but also should have characteristics such as no blockage, no spalling, no cracking and small diameter enlarging speed. To meet these requirements, nozzle materials should have excellent scouring resistance, corrosion resistance, erosion resistance and thermal shock resistance.
Metering Nozzle Types
Currently, universally used metering nozzle material is zirconia containing refractory. The content and grade of zirconia can directly affect nozzle hole enlarging speed and service life. The enlargement rate of 95% zirconia nozzle hole is about 0.03mm/h. According to structure, there are 3 types of metering nozzles, homogeneous nozzle, direct compound nozzle and inserting nozzle. Homogeneous metering nozzle are those which’s main composition is zircon or those contain relatively low ratio of zirconia. It is suitable for applications which have shorter continuous casting time. Direct compound metering nozzle main body is zircon based, only nozzle hole part is compounded with high zirconia containing layer. Direct compound metering nozzle has advantages such as longer service life than zircon based nozzle, low production cost. But due to different expansion coefficient , compound nozzle has large cracking possibility during using, composite layer’s zirconia content should not be much high, generally between 70%~80%. Inserting type metering nozzle is divided into outer coating and inner core, they are produced separately and then are bound together by refractory chamotte. Outer coating is sintered high alumina refractory, inserted inner core is zirconia refractory. Inserting metering nozzles have low production cost, good thermal shock resistance and various ZrO2 content, are the main structure adopted in production.
The inner core materials of zirconia metering nozzle are partial stable fused zirconia and zircon. Sintering temperature correlates with zirconia content, the sintering temperature of zircon nozzle is between 1630℃~170℃. Stable fused zirconia nozzle inner core’s sintering temperature is between 1750℃~1800℃.
Zirconia Metering Nozzle Core Refractory Physiochemical Index
Item
X-75
X-80
X-85
X-93
X-95
Z-65
Z-75
Z-95
ZrO2%
75
80
85
93
95
67.3
76.2
95.6
SiO2%
31.1
21.5
CaO%
3.0
3.0
3.0
MgO%
2.4
Apparent porosity%
22
21
22
24
18
20
20.5
12.5
Bulk density g/cm3
3.9
4.0
4.1
4.3
4.7
3.75
3.94
4.95
Compression strength MPa
60
95
60
Thermal shock resistance times
>5
>5
Continuous casting time/h
5
7
8
8
15
/
/
20
Quick Changing Nozzle
Metering nozzle may happen cracking accident or nozzle core enlargement during production. To solve these problems and prolong metering nozzles’ service life, non stop quick changing technique is developed. Through online quick changing of metering nozzle, unit ladle continuous casting time is large scale increased, max. time can reach to 70h.
Quick Changing Nozzle Refractory Physiochemical Index
