Function and design of Riser for foundry
Role of Risers
1. Take a pinch.
4.Logo for the metal filling cavity.
Casting riser is a part designed to supply the shrinkage of casting during solidification to prevent shrinkage cavity and shrinkage porosity.
Design of Risers
The type, size and location of risers with different function are different, so the design of risers should consider the properties of casting alloy and the characteristics of casting.
For Alloys (E. G. Grey cast iron) that do not contract very much in volume during solidification, or alloys (E. G. Tin Bronze) that do not produce concentrated shrinkage, the main function of the risers is to discharge the gas in the mold cavity and to collect the metal liquid mixed with inclusion or oxide film on the front of the liquid flow to reduce the defects on the casting. The riser is usually placed opposite the INGATE and its size need not be large.
For Castings requiring controlled microstructure, the risers can collect the cooled metal liquid at the front of the flow to avoid supercooling structure. Figure 2 shows a single cast piston ring with a small riser on the opposite side of the Ingate to collect the cold metal so that no white tissue will appear due to metal overcooling, resulting in casting obsolescence. The size and location of such risers shall be determined according to the microstructure requirements of the casting.
For alloys with large volume shrinkage during solidification and which tend to form concentrated shrinkage, such as cast steel, manganese brass, and aluminum bronze, the main function of the risers is to compensate the liquid shrinkage of the molten metal in the cavity and the shrinkage of the castings during solidification in order to obtain the compact castings without shrinkage. 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 There will be a large shrinkage cavity. In this case, the role of the riser is to compensate for the final solidification portion of the casting, so that it is placed above or on the side of the thickest part of the casting, and its solidification is required later than the thickest part of the casting. Fig. 3 shows a sleeve-shaped steel casting with three risers above the thickest part. The casting and one of the risers have been cut off in half to represent the compact casting and the shrinkage in the risers. The positive compensation is the local thickening of the castings added to improve the feeding of the risers. Since the risers are the slowest to cool, shrinkage due to feeding and self-shrinking occurs only in the risers. The design of such risers and their correction values is an important step in foundry technology design. The dimensions of risers are generally determined by calculation. Important large castings are available for computer-aided design. The feeding efficiency of the riser can be improved by various technical measures. For example, an insulating cover or heating cover can be added around the riser to reduce the size of the Riser Large castings can be used in addition to insulation or heating jacket, but also in the top riser with electric arc or flame heating to slow down its solidification. Another way to improve the feeding efficiency of the riser is to increase the pressure in the riser in different ways.