After fluid of metal of 1) permeability high temperature irrigates casting mould, model inside be full of a large number of gas, these gas must by successful eduction goes inside casting mould, molding sand can let the function that gas passes through this kind call permeability. Will make cast produces air hole otherwise, irrigate the blemish such as inadequacy. The permeability of casting mould suffers close fact of content of arenaceous granuality, clay, moisture content and sand mold to spend the influence that waits for an element. Finer, clay and moisture content exceed arenaceous size close fact of tall, sand mold is spent taller, permeability differs the ability that 2) intensity molding sand resists outside force is destroyed to call strength more. Molding sand must be had enough high intensity talent is in modelling, carry, dent is not caused in process closing case, pouring when also won't destroy casting mould surface. The intensity of molding sand is unfavorable also and exorbitant, because of,meet otherwise the fall of sex of permeability, concede, make cast produces limitation. The metallic liquid of high temperature of 3) fireproof sex irrigates the strong to casting mould generation hot action after entering, because this molding sand should have counteractive high temperature,the ability of hot action is able to bear or endure namely bad temper. If build the fireproof sex that profile expects to differ, cast easy generation is stuck arenaceous. Content of the SiO2 in molding sand is more, molding sand grain is bigger, fireproof sex is better. 4) plasticity points to molding sand to be out of shape below outside force action, can complete ground retains the ability of visible already form after purify outside force. The plasticity of modelling material is good, modelling operation is convenient, the sand mold appearance that makes is accurate, clear-cut. Cast of 5) concede sex is when condensation, bulk happening is contractive, molding sand should have certain compressed8 capacity, call concede sex. The concede sex of molding sand is bad, internal stress of cast easy generation or craze. Molding sand jumps over close fact, concede sex is poorer. The content such as wood chip is joined to be able to raise concede sex in molding sand. CNC Milling