Defect name: shrinkage. Definition and Characteristics: The upper plane collapses in the thick section of the casting or at the junction of the sections. Most of the shrinkage occurs at the thick section of the castings, and sometimes it also appears on the surface near the inner shrinkage cavity or shrinkage zone. There are often shrinkage cavities and porosity under the depression, and there is no obvious difference between the depression surface and the surrounding surface.Identification method Visual inspection with the naked eye. Note the difference between surface pores and open shrinkage cavities. The exposed shrinkage cavity is mostly funnel-shaped, with a rough surface, often accompanied by thick dendrites; when the surface pores occur at the thick section, the appearance is similar to the depression, and it is caused by the cavity gas of the low-permeability mold floating to the upper surface of the casting, or the gas and paint in the sand mold invade the surface of the casting to form. To distinguish with these two defects, it is often necessary to check whether the air permeability and ventilation of the sand mold are good, and sometimes the casting must be dissected to see whether the interior is subcutaneous pores, shrinkage cavities, or shrinkage porosity. Cause: During the casting solidification and shrinkage process, the molten metal solidifies slowly at the thick section or hot joint, and the atmospheric pressure will sink the solidified shell on the surface of the casting with a certain degree of plasticity.Prevention method:1. Modify the casting design to avoid sudden changes in section thickness, increase the fillet at the junction of thick and thin sections, and set process subsidies to improve sequential solidification conditions.2. If possible, risers should be added, and cold iron or auxiliary runners should be set to ensure the correct solidification sequence and feeding.3. Take measures related to the prevention of shrinkage cavities.remedy1. If it does not affect the performance, it can be filled with putty.2. Parts that need to withstand gas or liquid pressure should be impregnated. After passing the sealing test, the surface should be filled with putty3. The depression on the processing surface or working surface can be repaired by welding if the technical conditions permit.2. Defect name: wrinkled skin. Definition and Characteristics: Irregular coarse-grained or wrinkled scars on the surface of the casting, and a shell with deep reticular grooves (elephant-like wrinkled skin). Usually appear on the upper surface and elevation of alloy steel thin-walled castings rich in chromium, silicon, manganese, and other easily oxidizable elements, thick-walled ductile cast; on the upper surface of iron parts, the inner wall of ductile iron centrifugal cast pipe, the cross-section changes greatly The upper surface of the magnesium alloy casting. Identification method: Visual inspection with the naked eye. Easy to distinguish from other surface defects. Elephant-like wrinkled skin has deep reticular grooves, which is a unique defect of ductile iron castings and magnesium alloy castings. It is easy to distinguish from general wrinkled skins according to the type of alloy. Cause: 1. The compounds (oxides, sulfides, silicates, etc.) formed when magnesium ductile iron is treated with magnesium are usually dispersed in the molten metal in the form of thin films, float slowly in the ladle, and enter the casting with the molten metal during pouring. type, float to the upper surface of the casting, and gather on the inner wall of the casting during centrifugal casting, 2. Magnesium alloy is very easy to oxidize. If there is no protection during smelting and pouring, a thicker oxide film will be formed on the surface of the molten metal, which will be injected into the cavity along with the molten metal. When the liquid flow narrows from wide to narrow in the cavity, the oxide film gathers on the upper surface of the casting to form elephant-like wrinkled skin.3. The easily oxidizable elements in the alloy steel are oxidized during the pouring and filling process. 4. Generally, wrinkled skin is caused by the high viscosity of liquid metal, low pouring temperature or too slow pouring speed, gas generated by the reaction of metal oxide metal liquid and mold wall during pouring, and low temperature of the metal mold. Prevention method: 1. Use high-quality furnace materials to smelt nodular cast iron to reduce the sulfur content, gas, and inclusion content of the original molten iron; reduce the amount of magnesium added to reduce the residual magnesium of nodular cast iron under the premise of ensuring spheroidization; adjust the carbon content and carbon equivalent of molten iron Properly increase the spheroidizing temperature and strengthen the inoculation treatment to reduce the viscosity of molten iron and improve the fluidity of molten iron; use a ladle with good slag blocking effect, and the molten iron stays in the ladle for a sufficient time before pouring to make the slag and inclusions fully float up. 2. Use a protective atmosphere to smelt and cast magnesium alloys to prevent the oxidation of molten metal; the pouring position and pouring system settings should ensure that the molten metal fills the cavity quickly and stably, shortening the filling process; vacuum suction casting is used.3. The easy-to-oxidize alloy steel is poured in a reducing or neutral atmosphere.4. Adjust the composition of the alloy to improve its fluidity, appropriately increase the pouring temperature and pouring speed, prevent the molten metal from oxidizing during the pouring process, improve the composition of the molding sand and coating to prevent the chemical reaction between the mold wall and the molten metal, and let it stand in the ladle enough Time and strengthen slag blocking, properly increase mold temperature during metal mold casting 5. Set filter screen and slag collection bag in the gating system Remedy Castings with wrinkled skin defects are usually not scrapped. The wrinkled skin on the unprocessed surface can be polished off with a grinding wheel, and the wrinkled skin on the processed surface can generally be machined off.