Cast steels have high design and manufacturing flexibility and can find extensive applications. To get steel castings of good quality, the following cast steel defects can’t be ignored.
Sand hole
Sand holes are caused by the sand particles (blocks) washed down from the surface of the sand mold cavity by the liquid metal, or the sand particles (blocks) falling into the mold cavity during the molding and box closing operation do not have time to float into the pouring system and stay in the interior or surface of the casting. It is a common casting defect that there are small holes filled with mold (core) sand inside or on the surface of the sand hole defect.
Metal penetration
The surface of the casting is completely or partially covered with a layer of the mixture (chemical) of metal (or metal oxide) and sand (or coating) or a layer of molding sand with a burning structure, which makes the surface of the casting rough and difficult to clean. This defect mostly occurs at the parts with a strong heat effect on the surface of mold and core, which can be divided into metal penetration and sand burn-on. Metal penetration is formed by the penetration of liquid metal into the micropores on the mold surface. When the penetration depth is less than the sand radius, the casting does not form sand sticking, but the surface is rough. When the penetration depth is greater than the sand radius, metal penetration is formed. Sand burn-on is the product of the chemical interaction between metal oxides and molding materials, which is firmly combined with the casting.
Blowholes
Inside, on or near the surface of the casting, there are smooth holes of different sizes, round, long and irregular shapes, single or agglomerated. The color is white or with a layer of dark color, sometimes covered with a layer of oxide skin. Due to the different sources and causes of gas formation, the manifestations of pores are also different, including invasive pores, precipitation pores, and reactive pores.
Shrinkage
Irregular rough surface holes are formed in the thick section of the casting, at the hot spot or at the final solidification of the axis, where the grains are coarse and often contain dendrites The large and concentrated holes are called shrinkage holes, and the small and scattered holes are called shrinkage porosity. It is mainly due to the fact that the liquid shrinkage and solidification shrinkage produced by the casting during cooling solidification is much larger than the solid shrinkage, and there is no supplement of liquid metal at the last solidification place of the casting.
Sand inclusion
Sand inclusion refers to a layer of metal nodules or flakes on the surface of steel castings, and a layer of molding sand or coating is sandwiched between the metal nodules and castings. Scarring is due to a protruding scar where the metal liquid washes away a piece of sand locally on the mold surface or where stirring or boiling occurs, and the fallen sand is sandwiched in the scar or other parts of the casting. During pouring, the water on the surface of the wet mold cavity migrates to the interior of the sand mold due to the high-temperature baking of the liquid steel, forming a water condensation area with low strength, which is easy to delaminate the surface of the cavity and cause defects such as scab and sand inclusion of steel castings.
Cracks
Cracks can be divided into cold cracks and hot cracks. A cold crack refers to the crack caused by the local casting stress of the casting is greater than the ultimate strength of the alloy when the casting is cooled to the elastic state after solidification; Hot crack is a crack caused by the obstruction of solid shrinkage of castings when the strength and plasticity of castings are still very low at the end of solidification or shortly after final solidification.
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.