Higher requirements on the quality of castings
Modern foundry industry puts forward higher requirements on the quality of castings．At present，the production of small and medium—sized high—precision castings are often used precision casting process，but it has complex process，high standards of materials and equipment investment．Coated sand shell casting process not only can ensure the quality of castings also greatly reduce the cost of production，which has drawn more and more attention．However，there are limitations of traditional original coated sand．For silica sand，it has large angular coefficient and thermal expansion rate，which making the casting surface finish decreased．The new type artificial spherical sand— ceramic sand has excellent comprehensive performance，gradually being used as the original sand in casting production．At a low resin addition amount，fine—grained Fused Ceramic Sand can reach high strength．The surface precision of the shell castings can be comparable to precision castings．However，the price of pearl sand is higher than silica sand，there are few research works on the Fused Ceramic Sand related process at present．Therefore，the outstanding performance characteristics and advantages compared with other casting sand，Fused Ceramic Sand are not fully utilized．
In this article, Fused Ceramic Sand preparation process，curing process and regeneration process are studied，which in order to obtain high quality coated sand and achieve zero emissions of casting production and efficient recycle of resources．
By means of OM，SEM，molding sand strength testing machine，molding material gas generation tester and thermal analysis，the Fused Ceramic Sand performance and quality of recycled sand were evaluated．Orthogonal experiment method was used to optimize the coating process of 100-200 mesh pearl sand．Determining the reasonable process parameters of pear coated sand curing process and regeneration process，and analyzing the used sand regeneration mechanism．
The following conclusions were obtained：
(1)Through orthogonal test，the optimal coating parameters of 100-200 mesh pearl sand are as follows：the resin adding temperature is 150℃，the mixing time is 80s，the curing agent adding temperature is 120℃ and the mixing time is 60s．The lubricant adding temperature is about 85℃ and mixing time is about 45s．At this point，Fused Ceramic Sand tensile strength reached 2．62MPa and flexural strength reached 6.21MPa．
(2)The maximum tensile strength and flexural strength of 1 00-200 mesh Fused Ceramic Sand Can be obtained under curing conditions of curing temperature of 230℃ and curing time of 120s，respectively 1.64MPa and 4.78MPa．At this time，the main fracture mode between sands is cohesive fracture，which can realize the maximum bonding efficiency．
(3)100-200 mesh used Fused Ceramic Sand thermal regeneration process parameters：heating temperature is about 680℃～700℃，holding time is 20min；the heating temperature of thermal-mechanical regeneration process is 600℃．The tensile
strength and flexural strength of Fused Ceramic Sand that prepared by recycled sand were close to or even better than the new coated sand with the same coating pattern，and the gas production decreased．
(4)Thermal regeneration provides thermal energy for pearl sand during thermal regeneration．The residual resin on the surface of sand was decomposed and the surface quality of the sand has improved；The thermal-mechanical regeneration method make the brittle inert membrane rupture and fall off by the external force of mutual collision and friction，which achieving the better regeneration effect．