SAND CASTING EQUIPMENT.

In the casting process of more than ten years, Xinyuanzhu Group summarized the reasons and appearances of casting defects in gray cast iron and ductile cast iron.
1. Stoma
Features: The pores in the casting refer to the smooth pores of different sizes that exist inside the casting, on or near the surface. The pore walls often have an oxidized color. Due to the different sources and formation reasons of the gas, the manifestations of the pores are also different, such as intrusive pores, precipitation pores, and subcutaneous pores.
2. Sand holes and slag holes
Feature: Small holes filled with core (sand) inside or on the surface of the defect are called blisters. If the shape of the defect is irregular with slag or inclusions inside, it is called a slag hole.
3. Shrinkage and porosity
Features: In the thick section of the casting, the hot joint or the shaft center and other places where the final solidification is formed, rough surfaces are formed, and there are more or less dendritic crystals. Large and concentrated pores are called shrinkage, and small and scattered ones are called shrinkage. Shrinkage cavity and shrinkage porosity are mainly caused by the liquid shrinkage and solidification shrinkage produced by the liquid metal during cooling and solidification much larger than the solid state shrinkage, and the molten metal cannot be supplemented at the place where the casting finally solidifies.
4. Sticky sand
Features: A layer of modeling material that is difficult to clean is adhered to the surface of the casting. There are two types of cemented sand: mechanical cemented sand and chemical cemented sand. The difference is that mechanical cemented sand is formed by the penetration of high-temperature molten metal into the pores between sand grains. Chemical cemented sand is a low melting point compound formed by metal oxidation and modeling materials. The castings are firmly bonded together to form.
5. Cracks
Features: There are straight or curved cracks on the surface of the poured castings. The cracks are divided into two types: hot cracking and cold cracking. The cracks of thermal cracking are mostly tortuous and irregular, and the surface of the fracture is light black with a darker oxidation color. The cracks of cold cracking are straighter, and the surface of the fractured part of the casting has a metallic luster and is relatively clean, sometimes with a slight oxidation color.
The main reason for cracks in castings is that the cooling and solidification shrinkage is hindered to produce internal stress. When the internal stress is greater than the strength of the metal material, the casting will crack and form cracks.
6.deformation
Features: Long castings are more prone to deformation, such as machine bed, diesel engine cylinder block, cylinder head, because the casting wall thickness varies too much, uneven cooling, easy to cause casting deformation. Some castings are deformed after being stored for a period of time after being processed.
7. Uneven hardness
Features: After processing, the surface of the casting appears microscopic unevenness, and there are "shiny" hard spots in some parts. The surface hardness of the casting varies greatly, reaching 30-50HB (foreign advanced level 5-10HB), hard The hardness of the spot may exceed the standard. The large difference in the hardness of the castings can easily cause uneven wear of the working surface, resulting in poor machining accuracy of the machine tool, and high working noise of the diesel engine.
8. No spheroidization or poor spheroidization of ductile iron parts
Features: The fracture of the casting is gray-black, and the mechanical properties are obviously low. The metallographic inspection can find that the graphite is in the form of flakes. The residual magnesium and rare earth content of the casting are too low. This situation is generally not spheroidization. The fracture of the casting is still silver gray, but there are scattered gray and black spots, and the mechanical properties are low. Metallographic examination can find that a small part of graphite is in the form of flakes or worms, and the residual magnesium and rare earth content of the casting are lower than the normal content. This condition is generally poor spheroidization.
9. Spheroidization decline
Features: Among the castings cast with molten iron in the same ladle, the spheroidization of the early pouring is good, and the castings of the late pouring are poor or not spheroidizing.
10. Graphite floating (including flowering graphite)
Features: A layer of clear and dense black spots can be seen on the upper surface of the fracture of the casting. Metallographic inspection can find that graphite balls are gathered at the top of the section, and there are sometimes continuous or individual flowering graphites in the lower part of the aggregation layer. Graphite floating seriously weakens the mechanical properties of ductile iron, and significantly reduces the strength, hardness, elongation and impact toughness.
11. Anti-white mouth
Features: White mouths (carbides) appear in the center of the casting section, while the structure of the outer layer where the cooling is relatively fast is normal. The main reason for this defect is that the gray cast iron has high sulfur content and too low manganese content, which does not meet the relationship of Mn=1.7S+0.3. In addition, the molten iron absorbs hydrogen or the graphite core in the molten iron is too small. Sulfur and hydrogen are easy to segregate to the center of the casting, and they are anti-graphitizing elements, which hinder the growth of graphite, so that the center of the casting is too cold to crystallize at the temperature of the white mouth, so that the center of the casting has a white mouth. The reason for the whiteness of small ductile iron parts is often due to the segregation of rare earth and magnesium in the hot joints, with high content. The appearance of carbides in the core of thick nodular iron parts is often due to the long solidification time of the core, and the graphite core is easily melted and disappeared.

Xinyuanzhu Group is a Casting Supplier, specializing in precision foundry, Ductile iron castings, and Pig iron gray iron casting. Guests are welcome to visit the factory.