1, to the complex thin wall castings, in order to improve the precision cast molding shell permeability, where possible, at the top. To vent.Setting up reasonable pouring system and prevent casting gas volume, and is advantageous to the discharge gas in the cavity.2, properly increasing pouring temperature, try to reduce the ladle nozzle distance to the sprue cup, reduce the pouring speed, make the liquid metal filling smooth, prevent into gas, and liquid metal in the cavity gas energy discharge smoothly.3, lost wax pattern material should be ruled out clean, residual modulus material should be as little as possible.4, shell roasting to fully, should have a high enough temperature;Silica sol and ethyl silicate shell from 950 to 1100 degrees Celsius, sodium silicate shell from 850 to 900 degrees Celsius;Holding time is greater than the &, to ensure precision cast molding shell roasting, gas forming material fully ruled out.Roasting completely shell is white or light gray, should not have black patches.