The riser is a structure for storing molten metal in the mold, which is used to compensate for the possible shrinkage during the formation of sand castings, prevent shrinkage cavities and porosity of sand castings, and also play the role of exhaust, slag collection and guiding mold filling.
In the design of riser process scheme of steel castings, the following principles shall be met:
(1) The solidification time of the feeding area of the sand casting shall be less than or equal to the solidification time of the riser to ensure that the sand casting solidifies before the riser.
(2) There should be enough liquid metal in the riser to supplement the liquid shrinkage, solidification shrinkage and the expanded volume of the mold cavity after pouring.
(3) During the solidification of liquid metal, there should always be a feeding channel between the riser and the Fed area, and keep the expansion angle towards the riser, so that the liquid metal can flow smoothly into the sand casting under the action of gravity.
(4) In order to make the liquid metal flow smoothly into the feeding area of sand castings, there should be sufficient positive pressure inside the riser. At the same time, in order to avoid prolonging the solidification time of sand castings due to the setting of risers, the geometric hot spot of sand castings should be greater than or equal to the contact hot spot between risers and sand castings.