At present, the new technologies and methods to reduce the carburization of steel castings mainly include negative pressure combustion empty shell casting technology, oxygen enriched combustion technology, carbon removal method, decarbonization factor method, lost foam casting process without film seal and so on. The negative pressure combustion empty shell casting technology and the oxygen enriched combustion technology both burn out the foam pattern before pouring, so as to prevent the carburization of lost foam casting steel castings; The carbon emission method, decarbonization factor method and the lost foam process without film seal can provide oxygen more fully during the pouring process, so that the foam can burn more fully, and the combustion products are discharged through the vacuum system, so that the carburization defects of lost foam steel castings can be controlled.
1. Lost foam casting EPS negative pressure combustion empty shell casting method
Lost foam casting EPS negative pressure combustion empty shell casting method is a casting method that makes EPS quickly burn into empty shell or close to empty shell under the condition of dry sand negative pressure, so as to post cast and inject excellent lost foam casting steel castings without carburizing defects or slight carburizing defects. This method aims to reduce the influence of hydrocarbon foam on the quality of lost foam casting steel castings. At present, this technology is only limited to the production of simple thick and large parts, the effect on other types of parts is not obvious, and other auxiliary process conditions need to be added.
2. Oxygen enriched combustion technology
Oxygen enriched combustion technology refers to the technology that ignites the foam pattern before pouring and supplies high-pressure oxygen to it at the same time, so as to make the foam pattern burn quickly and fully, and pour after the foam pattern burns clean.
3. Production method of “carbon emission method”
The carbon removal method uses the large riser as the pouring system directly, adopts the pouring mode of top injection, and cooperates with the method of high vacuum and negative pressure. During pouring, air smoothly enters the mold cavity through the large riser under the action of negative pressure, providing sufficient oxygen for foam combustion and accelerating the combustion of the pattern; At the same time, the combustion products can also be discharged from the cavity through the riser. A large amount of black smoke can be seen escaping from the riser during the whole pouring process. In the whole process, the foam “disappears” through combustion, and the combustion products can be effectively discharged from the mold, which can effectively reduce the carburization defects.
4. Decarbonization factor method
Decarburization factor method is a method to make the pattern by adding a certain amount of substances that decompose a large amount of oxygen at high temperature to EPS during the pre foaming of white mold, so as to realize the non carburization of lost foam casting steel castings. The actual production has proved that adding oxygen increasing substances into gun foam beads can control the carburization of small low carbon steel parts; When the addition amount is 21%, the foaming density is 20 ~ 22 g / L, and the effect is the best.
5. Lost foam casting process without film seal
The lost foam casting process without film seal mainly removes the upper film, which aims to provide sufficient oxygen for white mold pyrolysis during pouring, plays a certain role in reducing residual ash and easily adsorbed medium and high molecular weight products, reduces carburizing sources, and is feasible in production practice with appropriate compaction cycle, pressure head and negative pressure.