Study on the composite casting process of vacuum lost mold Shell for nodular iron Pipe

Vacuumlost mold casting, also known as dry sand negative pressure lost mold casting process,  short for lost mold casting process, it is a new process based on the American solid mold casting technology patent in 1958, combined with the later vacuum seal molding technology research  development, has a strong production technology advantage.The ductile iron thin-walled pipe fittings produced by the lost mold process is prone to produce casting defects such as air insulation, cold insulation, carbon increase, foam residue, etc. These defects have a fatal impact on the quality of high-pressure pipe fittings, especially the exportation of UHV pipe fittings. At present, it has become the bottleneck of developing the high-end international pipe modern cast iron market.Investment casting, also known as investment casting, is a kind of advanced thin shell casting technology, which can produce precise  complex castings close to the final shape of the parts. The castings can be assembled directly without  with little processing, which can especially guarantee the inherent quality of thin-walled parts  reduce many casting defects.

Lost foam casting process  the investment casting process are advanced special casting process, two kinds of technological strengths, according to the situation of product quality  market demand, organic combination of the two kinds of technology will find a has both advantages of epc process, short production cycle, simple technological process, can produce larger casting),  have the characteristics of investment casting process (casting dimension stability, thin wall, within the cavity no carbon defects, high surface finish), thus to adapt to the new technology of mass production of high-performance export pipe fittings, to promote the development of the company certainly has the very vital significance.The experiment of the combination of the lost - mold production process  the investment - mold casting process has been successful.This process method is in the bubble model group system of coating a layer of 4 ~ 5 mm thick shell mold, then the overall baking, roasting  will thoroughly gasification bubble shape, make it hollow thin-walled shell mold, then simulate mold production process modelling, pouring, thoroughly solved the gas insulation, cold insulation, carburization, casting defects such as bubble residue, internal  surface quality  dimension precision castings increased significantly.

Model stiffness: There are two foams in the process of making  using the lost mold. The first raw material foams are pre-foams,  the raw materials for pre-foams are added to the mold cavity  then heated to form secondary foams.Casting system size: In order to make the casting system appearance has enough strength to facilitate the shell making,  to ensure that the casting cavity can be quickly  smoothly filled with liquid metal;Shell manufacturing: shell composition  structure, raw material selection  preparation of coatings, water glass shell manufacturing process (dipping  sanding, drying, chemical hardening, shell baking, foam model softening);Buried sand molding  pouring: In order to ensure the strength of shell molds, shell molds that have been roasted well  cooled to operating temperature are directly buried sand molding.