Metal casting is one of the most important production process of metal parts and components. Casting of metals is not an easy business and process, it has lots of parameters to be adjusted or designed to obtain succesful casting operations. One of these parameters is the fluidity. All the other parameters and design of metal casting process must done, by considering the fluidity of cast metal.
What Is Fluidity Of Cast Metals?
Fludity is very important parameter and this needed to be evaluated in very serious approach. Fluidity of liquids are generally defined as the inverse of viscosity. As you know that, the internal shear forces of fluids leads the situation of viscosity to withstand to the fluxing. The desire to flux of a fluid is defined as fluidity.
There are some factors that affect fludity of cas metals;
- Viscosity of liquid metal: As we stated above, when the viscosity of a liqud increases, fluidity decreases. There is a inverse relation with viscosity and fluidity of a liquid metal.
- Pouring temperature and melting temperature of metal: There is always a difference between the pouring temperature of metal and melting temperature of liquid metal. This difference guarantees the solidification of metal before reaching into the mold, inside gates. So melting temperature and the pouring temperature are the important parameters in terms of fluidty. Because, with the increasing temperature, fludity also increases.
- Heat transfer: If a metal is in the molten state, the temperature of this metal is very high. So, there is a great heat transfer between the molten metal and surrondings. When the molten metal advances in gates and channels to reach mold cavity, heat treanfer inside these gates is very important parameter to adjust the difference between pouring temperature and melting temperature. When the heat energy is given to surrounding by the metal fluid, temperature of metal fluid decreases. So, fludity decreases.
What Are The Effects Of Higher Temperatures On Metal Casting?
You may think that, we need to increase the pouring temperature of cast metal to the highest possible point, to increase the fludity. But there also another problems in the casting periods with very high pouring temperatures, these problems are;
- Penetration of metal liquid into sand: In sand casting operations, very hot liquid metal may penetrate on sand casting barriers, which will lead to the problem of surface defects and uneven cast metal geometries.
- Oxidizing of metal: Metal’s tend to oxidizing, increases exponentially with the increasing temperature. This means that, with very high pouring temperatures will lead the oxidizing of metal which is not desirable thing in metallurgy.
- Gas porosities: Boiling of metal liquid will lead trapped gas porosities inside the molten metal. After solidication, these voids that are originated from these gas porosities will lead the very serious mechanical property problems.
But freezing mechanisms of metal alloys and metals are quite different. Metal fluids freeze at constant temperature, which means much more easy manipulation of casting temperature. But in metal alloys, there is no exact freezing temperature. In a temperature range, two phases of fluid and solid occur. So, temperature manipulation of temperature is not easy. The solid phase can interfere the flux of fluid sides.
As you understand above, adjustment of proper temperature for pouring temperature of cast metal is not an easy business to achieve desirable fludity. You need to consider lots of kinds of parameters to specify a pouring temperature.
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