| The main work in this paper is to study the secondary cooling system and solve the serious problems like internal cracks etc. at high casting speed for No.l ROKOP continuous caster of Chuanwei Iron and Steel Group Company, which results in increment of productivity. In addition, the work that the author has done to increasing the productivity is alsoset forth in this paper.The paper begins with the reviews of development situation of high efficiency continuous casting technique all over the world. In this paper, characters of the applied nozzles both in normal temperature and high temperature have been tested, the finite difference method is used to discretize the differential equations, the mathematical model of heat transfer for high speed ROKOP continuous caster is established. In the model, the varied time steps is adopted, the characters of heat transfer and nozzles'layout are taken into account adequately, the effective specific flowrate and effective spraying coefficient are adopted. So the model is more accurate, and base on it, the general software of secondary cooling with multi-purposes is compiled.According to the demands of metallurgical rules and with help of the heat transfer model, the simulation caculation has been done. The results show that the original structures of two segments of secondary cooling zone with length of 1.647m are not adapted to high speed casting, and the secondary cooling zone prolonged with 5 segments of 3.500m is put forward. By calculation, the new secondary cooling systems adapted to high casting speed of No.l ROKOP continuous caster of Chuanwei Iron and Steel Group Company are obtained, and the temperature fields of billet, the parameters of solidification, the relations between casting temperature and maximum casting speed etc. are also achieved.According to the mathematical madel, the secondary cooling systems of the original structures are simulated according to equivelent specific cooling water. By calculation, the billet surface temperature is about 600℃ to 700℃ in the secondary cooling zone, and reascends about 500℃ to 600℃ beyond the secondary cooling zone at higher casting speed, which is the direct reason for the internal cracks. While for the structures of 5 segments, the billet surface temperature is about 800℃ to 900℃ in the secondary cooling zone and reascends about 200℃ beyond the secondary cooling zone. So the secondary cooling system with structures of 5 segments enable the billet have good qulity at high casting speed.On the mean time, in order to gain usual producing of No. 1 ROKOP continuous casting machine of Chuanwei Iron and Steel Group Company at high casting speed, the necessary technique rebuilding practics on some technics and equipment of the continous casting machine has also been done. They includes: improving the water quality of mould and secondary cooling; adopting the ion-stick; strengthen the cooling of mould;adopting narron-slot flame billet cutting spray lance;improving the purity of the molten steel and reducing the molding tempreture properly;acquiring the technique of long life tundish.The innovation of the structures of secondary cooling zone and the establishment of the new secondary cooling system is crucial to the realization of high-efficiency producing among them.The result has been used at No. 1 continuous casting machine of Chuanwei Iron andSteel Group Company for more than one year. The steady casting speed is 3.0m to 3.2m per minute and maximal casting speed can reach 3.4m to 3.6m per minute, the internal cracks of the billet disappear, the production increases greatly and the high efficient of the continuous machine is realized. The results of the studies also give direction for high efficient reformation of so many ROKOP continuous casting machine in nation.
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