Technological measures of controlling porosity defects in EPC

1. Choose suitable model material  use copolymerization foam as model material. Since the copolymer is zipper type decomposition, the gasification degree is high at one time  the liquid phase ratio is small. The small molecule gas is easy to overflow  the coating. The density of the white mold should be as small as possible on the premise of ensuring the strength  finish, reducing the total amount of gas generation. The pouring system adopts the hollow sprue  a filter to mechanically block the slag  absorb the comb flow for the liquid alloy, so as to make the filling more stable.

2. Application of pouring system  insulating riser The opening of the internal sprue should be conducive to the smooth, stable  rapid filling of the alloy, without the formation of dead angle area. The top of the casting is provided with an atmospheric pressure insulation riser, which integrates slag feeding into a whole. The relevant parts are provided with follow-up sand separation cold iron to realize the sequential solidification of the casting, float the gas, slag  gasification residues in the alloy to the riser,  reduce the probability of porosity, slag hole  shrinkage hole 。 Practice has proved that the feeding effect of riser  floating bead riser is better than that of foam spherical riser,  the riser covering agent can be used synthetically.

3. Improve the permeability of paint The particle size of refractory aggregate shall be suitable,  the sand like substance of 70-100 mesh in the aggregate shall contain 10-15%. The composite suspension agent binder shall be used,  the prepared coating shall have good strength at high  low temperature, wear resistance, easy brushing, no cracking, large exhaust capacity, good permeability, even sintering, easy peeling off  peeling after unpacking, no wetting with alloy  chemical reaction. Generally, the casting shall be brushed twice, with the coating thickness of 1-1.2mm 。  The quality management of EPC coating is very important. In mass production, the permeability of slag coating should be checked regularly,  the particle size of aggregate should be adjusted in time. Due to the organic matter contained in the binder  suspending agent of the coating, special attention should be paid to the fermentation  enzymatic change of the coating in summer  autumn. The qualified casting cannot be separated  the good coating,  the quality of the coating cannot be controlled lightly.

4. Pouring temperature should be suitable because the exothermic gasification foam should be exothermic in the mold filling process. It is suggested that the casting temperature of black alloy is 30-50 degrees higher than that of sand casting. The thermal effect of metal liquid  foam is restricted by pouring temperature. The pouring temperature is suitable for pyrolysis. The pyrolysis products of the mold are mainly small gas states, which are easily discharged  the cavity under the action of negative pressure field. When the pouring temperature is low, the pyrolysis of the mold is  enough, liquid residues will plug the coating layer, the pyrolysis gas will be blocked,  the pressure inside the cavity will form reverse pressure. In addition, the solidification speed is fast,  the gas slag in the alloy can  float to the riser, so the probability of forming porosity increases. The pouring temperature should match the alloy to avoid other casting defects caused by high temperature.

5. The deoxidation of molten steel  the killed EPC in ladle follow the principle of high temperature, low temperature  fast pouring. High temperature discharging is to leave a proper time for the cooling in the ladle. The deoxidization  slag removal of molten steel is the prerequisite to reduce the three hole defect. Before discharging, take samples to observe the shrinkage of molten steel. If the sample does  shrink, it is  allowed to discharge,  the furnace lining, ladle lining  furnace platform shall be kept clean  sanitary.