Simple Solutions That Work! Issue 15

20 Here’s how to adjust setups for each of the three main casting processes. 1. Sand Casting Sand casting is the easiest setup, since the sand mold is insulating and the external mold faces are generally cool. This allows us to neglect internal interfaces and use low cooling conditions into the foundry air. The basic setup is shown in Figure 2 . External cooling is represented by a low external heat transfer coefficient of 1.5, and the use of internal HTCs is turned off. 2. Investment Casting Setup for investment casting is more complex than sand casting because the investment shell is normally preheated to a high temperature. The ceramic shell is insulating (like sand), so we can ignore Internal HTCs. The high shell temperature requires a larger external HTC, along with radiation view factor calculations, which adjust the external HTC based on what each area of the shell sees in terms of other hot or cold areas on the shell. The setup details are shown in Figures 3 and 4 . 3. Permanent Mold Casting Permanent mold casting has the most complex setup. Since a metal die is conductive (like the metal that’s poured into it), die coatings significantly affect heat transfer. This is taken into account with a table of HTCs, which measure the resistance to heat flow at any surface between two materials, such as casting/die, die/air, and gating/die. Insulating sprays on the gating/risering can easily be handled using HTCs. You can also configure the system to lower the HTC on a casting surface when it solidifies. This is used to simulate the air gap that forms as the Figure 2. Setup Considerations for Sand Casting. Figure 3. Setup Considerations for Investment Casting. Figure 4. Graphic Depiction of Radiation View Factor Analysis.