In order to solve the internal shrinkage defects of small-modulus ductile iron mandrel castings and to change the traditional process design idea of artificially increasing the casting quality perimeter quotient, xinyuanzhu Group successfully determined the no-colonel casting process scheme through actual production tests. The process solution has greatly increased the output rate, reduced the production cost, and dissected the casting without any internal shrinkage defects, thus proving that the small modulus ductile iron parts can also be cast without risers. The weight of the casting is a small casting, and traditional casting theory and experience suggests that small castings must focus on riser shrinkage. The geometric modulus of the casting does not satisfy the ductile iron casting conditions required by the data, and the mass perimeter quotient does not satisfy the ductile iron casting conditions required by the data, and according to these traditional theories, the casting must be set up to fill the shrinkage riser in order to obtain a qualified product without internal shrinkage defects. However, due to the wide solidification range of ductile iron parts, paste-like solidification, no crusting on the surface before the internal solidification, and the expansion of the graphite expansion to enlarge the movement of the shape wall, it is difficult to eliminate the internal shrinkage defects of the riser. xinyuanzhu Group, in order to reduce the production cost and produce qualified products, researched the production process of the mandrel casting and found a method of casting without riser, which was applied to the production. In order to reduce the production cost and produce qualified products, Xinyuanzhu Group researched the production process of the mandrel casting and found a casting process method without riser, which was applied to the production.
Considering that there is a slender hole of φ40 mm×480 mm inside the core casting, the sand core of the hole will be bent by the buoyancy of the high temperature iron liquid when casting horizontally, and other measures will increase the difficulty of operation, the initial process plan is to choose horizontal molding, flange facing upward and vertical pouring, as shown in Figure 2. The initial process plan is to set two φ85 mm×120 mm filler holes on the top surface of casting location (flange) and bottom injection pouring system.
Trial results: process output rate of 73%, castings dissected with internal shrinkage, not up to the technical requirements.
Improve the process
Improvement on the basis of the initial process, according to the solidification characteristics of ductile iron, it is difficult to eliminate shrinkage defects by setting the riser. However, there is also information that whether the ductile iron parts can realize the casting without collets requires a comprehensive analysis of various factors, which cannot only meet the theoretical conditions, whether the superposition of expansion and shrinkage can be realized, and whether the expansion force of precipitated graphite can be effectively used to compensate for the shrinkage of the casting, which is the essential condition of whether the casting without collets can be realized. Moreover, even if the geometric conditions of the ductile iron parts themselves do not meet the conditions of no-collet casting, the conditions can be artificially created, such as the reasonable setting of external chilled iron and exhaust piece (chilled riser), which is equivalent to the cross existence of thick wall and thin wall in the casting structure, so that balanced solidification can be realized and no-collet casting can be achieved. According to this viewpoint, the majority of ductile iron parts are favorable conditions for achieving riserless casting, but not necessary conditions for achieving riserless casting in ductile iron parts. The inherent mass perimeter of the casting is determined by the shape structure and size of the casting itself, but the shape and mass perimeter of the casting can be changed artificially, such as adding heat dissipation bars to the outer wall of the casting. The mandrel mass perimeter quotient is small, and the improved process solution is to add some tendons to its outer wall.
Trial production results: process yield 82%, still using horizontal molding, vertical pouring, bottom injection type pouring system process, quality perimeter quotient reached 37 kg/cm³.
The trial production verified that the same furnace molten iron simultaneously poured two pieces each of sand moulds made by the initial process and the improved process, and the castings were dissected with shrinkage defects inside the initial process scheme and without any shrinkage defects inside the castings of the improved process scheme. This shows that, although the casting geometry modulus is small, can not reach the conditions of the riserless casting, but by artificially increasing the mass perimeter quotient, you can achieve riserless casting.
Process principle: the casting has both relatively thick-walled part and relatively thin-walled part, after pouring the metal liquid solidification, the thin-walled part of the heat is small, fast solidification, thick-walled part of the heat, slow solidification, the whole cooling and solidification cycle in the casting so that the expansion comes early, you can achieve the mutual superposition of shrinkage and expansion, that is, balanced solidification. The thin-walled part of the solidification shrinkage can be compensated by the thick-walled part of the complementary shrinkage, the thick-walled part of the solidification shrinkage can be compensated by the graphite expansion of the thin-walled part of the crystallization precipitation, and then, the graphite expansion of the thick-walled part of the crystallization precipitation further compensate for the microscopic shrinkage of the thick-walled part, so that the internal organization of the whole casting is dense.
According to the above process principle, the expansion of the casting solidification comes early to realize the mutual superposition of shrinkage and expansion to achieve balanced solidification. Then, adding cold iron to the outer wall of the casting can also play the same role as cold reinforcement. Cold iron area of action, equivalent to cold bars to increase the area of heat dissipation, the effect is better than cold bars, the result is equivalent to increase the mass of the casting perimeter quotient. and cold iron can not be covered with the outer surface, should be intermittent, so that it is equivalent to a thin wall adjacent to a thick wall, thin wall and thick wall parts cross each other to facilitate the mutual superposition of shrinkage and expansion. So on the basis of the above process and then improved, to the outer wall of the casting with cold iron
Trial results: the process yield of 90%. Actual production test, castings after dissection without any internal shrinkage defects
Xinyuanzhu Group specializes in the production of Ductile iron castings, Pig iron gray iron casting, Steel casting, Brass Casting, Malleable Iron Casting, and undertakes batch casting processing of castings. Welcome guests to cooperate with pictures or samples.