Macropores formed in hot spot or solidification part of Dalian castings due to poor feeding during solidification The distribution characteristic is concentrated shrinkage; When the crystallization temperature range of the alloy is wide, there is a wide solidification region of liquid and solid phases after the crust on the surface of the casting. Continue to solidify, and the solid phase continues to increase. At the later stage of solidification, the dendrites formed by Mr contact with each other, dividing the alloy liquid into many small closed areas. When the solidification shrinkage of the alloy liquid in the closed area is not supplemented, shrinkage porosity is formed. Shrinkage porosity can be seen as many dispersed small shrinkage cavities. The wider the crystallization temperature range of the alloy, the easier it is to form shrinkage porosity.

E-commerce will become a sharp weapon to occupy the spare parts market. Looking back on the performance of the past year, many people find that in fact, few companies have become beneficiaries in the "intrigue" competition. This kind of almost malicious competition has greatly damaged the vitality of many large companies, and it is even harder for small and medium-sized enterprises to taste the sweetness in it. Therefore, under the warning of industry experts, people realize that such competition can only kill each other. When we suddenly woke up, we found that the appetite of the market had been basically fed. This led to the "ice age" of construction machinery at the end of the year.

After finishing the outer contour of the casting, there shall be no casting defects such as air holes. The sand (slag) holes are unevenly distributed small cavities on the casting surface, which are usually irregular, of different depths, and the interior is not bright and clean, without cold mouth. It is mainly because the molten iron is not clean, the slag is mixed during pouring, and the sand is shoveled when the slag filter is lowered. Small residual sand particles in the mold rush into the mold cavity with molten iron. During mold closing, sand particles fall off due to extrusion between molds or between molds and sand cores.

Influence of mold making on linear shrinkage of castings: a. the influence of wax injection temperature, pressure and holding time on investment mold size is obvious in wax injection temperature, followed by wax injection pressure. The holding time has little effect on investment mold size after ensuring investment molding. Influence of shell making materials: Zircon sand, zircon powder, Shangdian sand and Shangdian powder are used. Because their expansion coefficient is small, it is only 4.6 × 10-6/ ℃, so it can be ignored. After processing, the surface of the casting appears micro concave convex, and there are "shiny" hard spots in some parts. The surface hardness of the casting varies greatly, up to 30~50hb, and the hardness of the hard spots may exceed the standard. The large hardness difference of castings is easy to cause uneven wear of the working surface, resulting in poor machining accuracy of the airport and high noise of the diesel engine.

There shall be no casting defects such as air holes after finishing the outer contour of castings. Small unevenly distributed cavities appear on the surface of the casting, which are usually irregular, of different depths, and the interior is not bright and clean, without cold mouth. It is mainly because the molten iron is not clean, the slag is mixed during pouring, and the sand is shoveled when the slag filter is lowered.