The function of the riser: In the mold, the cavity of the riser is the cavity that stores the liquid metal. When the Casting Parts is formed, the metal is replenished to prevent shrinkage, shrinkage, exhaust, and collect slag.
The design of the riser: The riser with different functions has different form, size and opening position. Therefore, the design of the riser should consider the properties of the Casting Parts alloy and the characteristics of the Casting Parts.
1 For alloys with little volume shrinkage during solidification (such as gray cast iron), or alloys that do not produce concentrated shrinkage holes (such as tin bronze), the effect of the riser is mainly to mix the gas in the discharge cavity with the front of the collection flow. Inclusions or metal oxide film to reduce defects on Casting Partss. This type of riser is often placed opposite the inner gate, and its size does not have to be too large.
2 For Casting Partss that require controlled microstructures, the riser can collect the cooled metal liquid at the front of the flow to avoid overcooling of the Casting Parts. In a single-cast piston ring, a small riser is placed opposite the ingate to collect the cold metal, which will not cause white-colored tissue due to metal over-cooling, resulting in scrap Casting Parts. The size and location of such risers should be determined based on the microstructure of the Casting Parts.
3 For alloys with large volume shrinkage during solidification and tending to form concentrated shrinkage pores (such as cast steel, manganese brass, and aluminum bronze, etc.), the main role of the riser is to compensate for liquid shrinkage and solidification of the molten metal in the cavity. Shrinkage in the process to obtain a dense Casting Parts without craters. When the Casting Parts is cooled in the mold, the thinnest part solidifies first, and its shrinkage can be compensated by the thicker part in the vicinity; when the thick part solidifies, it can be compensated by the thickest part; when the thickest part is solidified, no foreign material can be obtained. The compensation will create a large shrinkage hole in the area. In this case, the role of the riser is to compensate for the final solidification of the Casting Parts, so it should be placed on the top or side of the thickest part of the Casting Parts, and its solidification requirements are later than the thickest part of the Casting Parts. Sleeve-shaped steel Casting Partss, with 3 risers above the thickest part, cut off the Casting Parts and its riser half in order to represent the dense Casting Partss and shrinkage holes in the riser. Local thickening added to the Casting Parts to improve the feeder's supply of Casting Partss. Due to the slowest cooling of the riser, shrinkage holes caused by feeding and shrinking will only occur in the feeder. The design of corrections for such risers and related processes is an important part of the design of the Casting Parts process. The size of the risers is generally determined by calculation methods, and important large Casting Partss can be designed with computer aided design. A variety of technical measures can be used to improve the feeding efficiency of the riser. For example, small and medium-sized Casting Partss can be equipped with a heat-insulating sleeve or a heat-generating sleeve around the feeder to slow down the solidification of the riser and reduce the size of the riser. In addition to the use of insulation or heat jackets, it is also possible to heat the top of the riser with an electric arc or flame to slow down its set. Another way to increase the efficiency of feeder feeding is to use different methods to increase the pressure in the feeder.