Simple Solutions That Work! Issue 13

the airflow and the castings enter the cooling tunnel at opposite points and flow in opposite directions. The temperature gradient at the inlet of the cooling tunnel is smaller, thus reducing thermal stress of the castings, while the overall efficiency of the cooling process is maximized. According to layout and space constraints, it is possible to adopt a combination of both heat exchange arrangements: parallel- flow and counter-flow. In addition to the co-current and counter-current air flows, a further cooling air flow, also referred to as “cross flow”, enters the system through some slots on the belt pans. Thus, the cooling rate performance is enhanced. In this way, cooling air not only flows around the castings, but also passes through them, resulting in a more effective cooling. Figure 3 shows a typical configuration of the cooling tunnel held under negative pressure. A stream of cooling air flows at controlled speed to avoid thermal shocks to the castings. Ambient air is forced to enter the extremities of the cooling tunnel and then it is sucked from the central hood. CFD MODEL In order to perform an efficient casting cooling process, the thermal properties both of air and of castings have to be thoroughly investigated. Thus, a CFD (Computational Fluid Dynamics) approach is required to implement the casting cooling simulation model. Starting from the casting 3D model, a calculation grid (mesh) is generated. Then, both the thermal properties and the boundary conditions are set in the pre-process ambient of a dedicated CFD software. As a result, the cooling curve is finally obtained through the post- process along with further process parameters: e.g. air speed and pressure drop in the cooling tunnel, castings and air temperature. In order to validate the above CFD analysis, an experimental test campaign can be carried out if the reference castings are available. EXPERIMENTAL TESTS Thanks to a specific test-rig equipped with a cooling tunnel prototype, it is possible to validate and adjust the theoretical curve obtained from the CFD analysis. A set of thermocouples welded on the tested casting is connected to a data acquisition system. 54 It is possible to monitor the temperature trend of that casting during the heating stage in the oven, until the end of the cooling process. The thermocouples positions are defined according both to clients input and to critical cooling areas highlighted by the CFD analysis. Figure 4 shows a comparison between the experimental results and the analytical once obtained through the CFD analysis. Figure 4: Experimental and Analytical results Contact: GAETANO CORAGGIO [email protected]