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本文应用钢水凝固过程的偏析理论和热量传输原理推导了钢锭头部打水封顶的凝固模型,从理论上证明了打水封顶完全能够抑制气泡生成从而保证获得具有所希望厚度的无气孔的顶壳(或金属桥)。根据水封顶的传热特点,本文还推导了一个理论计算模型、各个厂家可依此确定适合于自己的生产条件的最佳打水封顶制度。应当指出,对于目前国内所用的8.55吨沸腾钢锭型,打水速度的理论计算值与日本专利所报道的实际值极为吻合。模铸法产生半镇静钢时,钢锭头部基本上不存在钢水静压力,表面上有一层凝壳后,由于钢液凝固收缩,在凝固壳下面的缩孔中甚至产生负压,这给放出气体创造了非常有利的条件。但是,如不采取措施,就不能保证头部有一定厚度的无气孔致密的顶壳,以防止钢锭在均热炉加热时钢锭头部气孔受到氧化,达到提高钢锭成材率的目的。实践证明,打水封顶是保证头部产生有一定厚度的无气泡致密层的一项有效措施。该措施在国外被广泛采用[1—5]。在日本,甚至有人把打水封顶的工艺参数作为申请专利的内容[6]。本文试图从理论上阐明打水封顶的作用原理,并给出打水速度和水量的的理论计算方法,以利指导生产实践。
In this paper, using the segregation theory and heat transfer principle of the solidification process of molten steel, the solidification model of the head of the ingot is deduced. It is theoretically proved that the water cap can completely suppress the generation of bubbles and thus ensure the obtaining of a non-porous top shell with the desired thickness (Or metal bridge). According to the heat transfer characteristics of water capped roof, this paper also deduced a theoretical calculation model, each manufacturer can determine the best watering cap system suitable for their own production conditions. It should be noted that for the current domestic use of 8.55 tons of boiling steel ingot type, the theoretically calculated value of the water drawing speed is in good agreement with the actual value reported in the Japanese patent. Casting method to produce semi-killed steel, the ingot head basically does not exist hydrostatic pressure, the surface has a layer of coagulation, due to solidification of molten steel shrinkage, shrinkage cavity below the solidification shell or even negative pressure, which gives release Gas creates very favorable conditions. However, if no measures are taken, there is no guarantee that the top of the head has a certain thickness of the top shell with no air holes to prevent the pores in the head of the ingot from being oxidized when the ingot is heated in the soaking furnace, so as to improve the ingot yield of the ingot. Practice has proved that the water cap is to ensure that the head to produce a certain thickness of the bubble-free compact layer of an effective measure. This measure is widely used abroad [1-5]. In Japan, some people even took the process parameters of watering and capping as the content of patent applications [6]. This paper attempts to clarify the principle of water-capping theoretically and give a theoretical calculation method of water-drawing speed and water volume to guide the production practice.