Causes of porosity in lost foam casting

1. The foam model vaporizes  decomposes to produce a large amount of vapor  residues that cannot be discharged in time,  the foam coating layer are filled with dry sand. Under the high temperature of the liquid alloy, a large amount of cracked The intrusion of hydrogen  oxygen into the casting is the key cause of porosity.

2. Poor deoxidation of molten steel, unclean slag removal in the furnace, furnace,  ladle, too short stabilization time, poor slag retention during the entire pouring process,  irregular pouring processing techniques that lead to slag holes.

3. Due to the improper design of the pouring system, the filling speed of the molten metal exceeds the speed of foam vaporization  vapor discharge, causing the filling front to entrap the vaporized residue in the molten metal  vaporize again, resulting in the decomposition of the black smoke on the inner wall Drop the air hole.

4. The pouring temperature is low, the molten metal at the front of the filling can  fully vaporize the foam,  the undecomposed residual material has  had time to float to the riser  is suspected of causing pores in the casting.

5. The specific location of the sprue is  standardized,  a dead corner area is generated during filling. Because of the effect of gas pressure in the cavity, vaporization residues accumulate in the blind spot to produce pores. The cross-sectional area of the sprue is too large, which makes the filling speed. Exceeding the speed of foam vaporization  retreat, it swallows the foam, decomposes the vaporization inside the alloy,  the vapor cannot be discharged to produce pores.

6. The air permeability of the coating is poor  the negative pressure is  enough,  the air permeability of the filled sand is poor,  the vapor  residue in the cavity cannot be discharged in time, resulting in pores under the filling pressure.

7. The pouring speed is very slow, unable to fill the sprue cup, exposing the sprue, entraining air, sucking in the slag,  producing entrapped air holes  slag holes.

8. The storage capacity of the sprue cup is too small, the molten metal will produce vortex,  the air will invade to produce pores.

9. The sealing performance of the junction between the sprue cup  the sprue  its pouring system is  very good, especially the connection between the sprue  the sprue cup is  very good, under the effect of negative pressure Sand inclusions  pores are very easy to produce. This kind of phenomenon can be calculated  expressed by Bernoulli equation.

10. The particle size of the molding sand is too fine, the dust content is high, the air permeability is poor, the negative pressure inside the pipeline is blocked,  the negative pressure is distorted. The negative pressure around the cavity is much smaller than the indicated negative pressure,  the vapor cannot be discharged in time. Layer to produce pores  wrinkled skin.