When we make sand moulds, there are some paths for the entrance of aluminum into the mold cavity constitute the runner system and include the sprue, various feeders which maintain a good aluminum 'feed', and in-gates which attach the runner system to the casting cavity. Gas and steam generated during casting exit through the permeable sand or via risers, which are added either in the pattern itself, or as separate pieces. To be free of any porosity, we will place filter screens on the sprues.