How to distinguish between riser and pouring riser?

riser

A supplementary part attached to the top or side of a casting to avoid defects. In the mold, the cavity of the riser is a container for storing liquid metal, which has many functions. Risers with different functions have different forms, sizes and opening positions, so the design of risers should consider the properties of casting alloys and the characteristics of castings.

(1) For alloys with small volume shrinkage during solidification (such as gray cast iron) or alloys without concentrated shrinkage cavities (such as tin bronze), risers are mainly used to exhaust the gas in the cavity and collect molten metal mixed with inclusions or oxide films at the front of the liquid flow to reduce defects on the castings. This kind of riser is mostly placed opposite to the inner gate, and the size does not need to be too large.

② For castings requiring microstructure control, the riser can collect the cooled molten metal at the front of the liquid flow to avoid supercooled structure on the castings. Fig. 2 is an integrally cast piston ring. A small riser is set opposite the inner gate to collect cold metal, so that the white structure will not appear there because of the undercooling of the metal, which will lead to the scrap of the casting. The size and position of this riser should be determined according to the microstructure requirements of the casting.

③ For alloys (such as cast steel, manganese brass, aluminum bronze, etc.). The volume shrinks greatly during solidification, and the main function of the riser is to compensate the liquid shrinkage of molten metal in the cavity and the shrinkage of the casting during solidification, so as to obtain a dense casting without shrinkage cavity. When the casting is cooled in the mold, the thinnest part solidifies first, and its shrinkage can be compensated by the thicker part nearby. When the thicker part solidifies, it can be compensated by the thickest part; When the thickest part solidifies, if there is no external compensation, a larger shrinkage cavity will be formed. In this case, the role of the riser is to compensate the last solidified part of the casting, so it should be placed above or on the side of the thickest part of the casting, and its solidification requirement is later than that of the thickest part of the casting. Fig. 3 is a sleeve-shaped steel casting with three risers above the thickest part. In order to show the dense castings and shrinkage cavities in the riser, the castings and a riser are cut in half. The modification in the figure is to locally thicken the casting to improve the supply of the riser to the casting. Because the cooling of the riser is the slowest, the shrinkage caused by feeding and self-shrinkage will only occur in the riser. The design of this riser and its related process modification are important links in casting process design. Riser size is generally determined by calculation method, and computer aided design can be used for important large castings. Various technical measures can be taken to improve the feeding efficiency of the riser. For example, for small and medium-sized castings, heat insulation jacket or heating jacket can be added around the riser to slow down the solidification of the riser and reduce the size of the riser. Large castings can be heated by arc or flame at the top of the riser to slow down their solidification speed, except for heat insulation or heating jacket. Another way to improve the feeding efficiency of the riser is to increase the pressure in the riser by different methods.