Due to the liquid shrinkage and solid shrinkage of liquid metal during solidification, the holes formed at the last solidification part of the casting can not be supplemented by external liquid metal in time, so shrinkage cavity and shrinkage porosity casting defects are formed. Among them, those with concentrated distribution and large volume are called shrinkage cavities, and those with small and scattered distribution are called shrinkage porosity.
There are two main ideas to prevent casting defects from shrinkage porosity and shrinkage cavity. One is to control the solidification mode of castings, and the other is to adopt more reasonable casting process. Control the solidification mode of castings, that is, adopt various measures to make the castings solidify in sequence according to the distance between the parts and the riser, or gradually ensure that the temperature difference between the structures of each part is small, so that all parts solidify at the same time. In order to realize simultaneous solidification, the common concrete measures are: setting the ingate at the thin wall of the casting; Add overflow trough or overflow riser at the thin-walled parts to slow down the cooling speed of these parts; Chill iron or high heat storage molding sand shall be set at the bulge and wall junction where shrinkage porosity and shrinkage cavity are easy to occur.
By improving the casting process to prevent shrinkage porosity and shrinkage cavity, it is necessary to adjust the pouring temperature and pouring speed, and use riser and cold iron when necessary. Generally, the top pouring system uses high-temperature slow pouring, while the bottom pouring system uses low-temperature slow pouring combined with supplementary pouring riser to strengthen sequential solidification. Riser and cold iron are also the most effective process means to prevent shrinkage cavity casting defects. Generally, the riser is set at the thick part or hot joint of the casting, and its size shall ensure that enough liquid metal can be provided for the position of shrinkage hole. At the same time, the feeding channel between the riser and the feeding part shall be kept unblocked during the whole feeding process. The cold iron is usually used with the riser to form an artificial feeding channel and end area, so that the riser can obtain a longer effective feeding distance.
ABOUT KEVA
Keva Casting is a professional casting company that focuses on Construction, Machinery, Automobile, Hardware, Pipeline and many other industries.
We provide top quality products with the best service based on our complete production chain including our own mold design, advanced production techniques, and full management of the supply chain. Keva Casting has two factories located in Zhucheng, China's Shandong province.
We use "shell molding", which is a new technique that has been developed in recent years.This new technique has simplified production procedures and reduced air pollution compared with traditional sand casting and investment casting. Shell making and core making are faster to ensure production in enormous quantities. The dimensions and surface finishing are satisfactory for all kinds of industrial requirements. Besides supplying our own formwork & scaffolding systems, our casting products also supply OEM services in various industries.