Effect of solidification process and mold vibration on wall thickness of furnace tube in centrifugal casting

In centrifugal casting of furnace tube, after pouring molten steel into the mold, on the one hand, the molten steel moves with the rotating mold; on the other hand, the molten steel exchanges heat with the surrounding environment through the mold, and the molten steel temperature will gradually drop. When the molten steel temperature drops below the solidus temperature, the molten steel will solidify into the casting furnace tube.

There are three basic ways of heat transfer: conduction, convection and radiation. Heat conduction, also known as heat conduction, refers to the heat transfer process that depends on the thermal motion of micro particles such as molecules, atoms and free electrons when there is no relative displacement between the parts of the object. Convection is the way of heat transfer caused by the relative displacement between different parts of the fluid and the mixing of cold and hot fluids. However, in engineering, when the fluid flows through another surface, convection and heat conduction work together, which is called convective heat transfer. The way that an object transmits energy through electromagnetic wave is called radiation. The object will emit radiation energy for various reasons, and the phenomenon that radiation energy is emitted due to heat is called thermal radiation. Fourier’s law, Newton’s cooling formula and Stefan Boltzmann’s law are used to calculate the heat transfer of heat conduction, convection and radiation.

Many people at home and abroad have carried out numerical simulation of solidification process of casting. Most of the research is based on commercial software of finite volume method, and some are based on finite difference method. The commonly used commercial softwares are ANSYS, fluent, FLOW3D, ProCAST, AnyCasting, etc. when using software simulation, the heat balance equation, Navier Stokes equation and continuity equation describing fluid motion are usually solved at the same time. The advantage of software simulation is that it is convenient and can be avoided There are many programming processes, but there are some special cases that can not be considered, such as mold vibration. For the finite difference method, if the solution domain or boundary conditions are not regular, the method is difficult to apply, which greatly limits the finite difference method in the numerical calculation of heat transfer, and the finite difference method also has the same problem as the software simulation, that is, it can not consider the special cases such as mold vibration.

The influence of mold vibration on molten steel flow in mold was studied. The cooling and solidification process of molten steel in mold was further considered. The coupling model of molten steel flow mold vibration cooling and solidification in horizontal centrifugal casting was established. The cooling and solidification process of molten steel and the influence of mold vibration on the wall thickness of casting furnace after solidification were analyzed by an example.

(1) Based on the coupled model of molten steel flow mold vibration, the solidification cooling process of casting furnace tube is added. Considering the influence of temperature change on material elastic modulus, the coupled model of molten steel flow mold vibration molten steel cooling for horizontal centrifugal casting is established. When solving the transient temperature field, the grid method is used to discretize the solution domain, and the heat balance equation is established for each grid, then the Euler method is used to solve the heat balance equation. The model can be used to solve the flow of molten steel in each section at any time, the vibration of the mold and the temperature of each point.

(2) Through the analysis of the roller supported horizontal centrifugal casting furnace tube and the calculation example, we can draw the following conclusions: the smaller the casting furnace tube mass is, the shorter the time to complete solidification is. When the casting tube mass is 309.6kg, the time to complete solidification is about 40s, and when the casting tube mass is 180.6kg, the time to complete solidification is only 40 s At the same time, the temperature of both ends is slightly lower than that of the middle.

(3) In a certain period of time, due to the gradual increase of mold temperature, the vibration of each node increases with the increase of time; the change of vibration with time will lead to the change of the wall thickness of the casting with time. In the same section, the maximum wall thickness of the cast pipe gradually increases with time, and the minimum wall thickness gradually decreases with time, that is, the wall thickness difference becomes more and more obvious with time The final wall thickness difference of each section of the casting furnace tube is in the order of micrometers, and the value of each wall thickness difference is determined by the mass eccentricity of the mold itself; the influence of the casting tube quality on the wall thickness difference is much smaller than that of the vibration.

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