in open casting, top nozzle fixed at the tundish wellblock has 22mm dia, while the bottom nozzles can be changed to get desired speed.
bottom nozzles have varying dias like 15.5mm, 17mm, 18mm, 19mm, 20mm and 22mm. first one is always used at the start of casting so that the start of casting is slower, while the largest dia nozzle is used to get the maximum flowrate and hence the maximum casting speed.
pic shows a bottom nozzle that has a dia of 17mm.
bottom nozzles have varying dias like 15.5mm, 17mm, 18mm, 19mm, 20mm and 22mm. first one is always used at the start of casting so that the start of casting is slower, while the largest dia nozzle is used to get the maximum flowrate and hence the maximum casting speed.
pic shows a bottom nozzle that has a dia of 17mm.
we can see the number 7 embosed on the nozzle itself so as to identify the dia of 17mm. 15.5mm dia nozzles will have 5 imprinted while 21mm dia nozzle will have 1 embosed and 19mm dia nozzle will have 9 imprinted.
in the above pic the cream-coloured part at the center that has the bore of 17mm dia is zirconia insert which has a very very good oxidation resistance at high temperatures, strength and erosion resistance. and the gray colored granules that surround the zirconia insert are made of alumina which also has good thermal properties but not as stable as zirconia against erosion.
the pic below shows the surface that will mate with similar surface of top nozzle. this is the surface that normally lies facing upwards while the side shown above normally stays facing mould.
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