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                                                                                  The main cause of angry holes in stainless steel casting









In the stainless steel casting process, the pore problem often occurs, which causes a lot of troubles for the casting processing. The pore is the bubble defect formed by the deposited gas in the ingot during the cooling and solidification of the metal liquid. Andrew will analyze the main causes of stomata below.
1. The permeability of the coating is poor or the negative pressure is insufficient. The gas permeability of the filling sand is poor, and the gas and residue in the cavity cannot be discharged in time, and the pores are formed under the filling pressure.
2, the pouring speed is too slow, can not fill the pouring cup, expose the sprue, entrapped in the air, inhaled the slag, forming the air hole and the slag hole.
3, the foam model gasification decomposition generates a large amount of gas and residues can not be discharged in time, the foam, the coating layer is filled with dry sand, the drying is poor, under the high temperature of the liquid alloy, cracking a large amount of hydrogen and oxygen into the casting is formed The main cause of stomata.
4. Due to the unreasonable design of the pouring system, the filling speed of the molten metal is greater than the foaming gasification and gas discharge speed, causing the filling front to enclose the gasification residue in the metal liquid and vaporize again to form the decomposition black hole of the inner wall smoke black. .
5. The joint between the sprue cup and the sprue and the pouring system is not well sealed, especially the connection between the sprue and the sprue cup is not good, and it is easy to form sand and pores under the action of negative pressure. This phenomenon can be calculated and explained by the Bernoulli equation.
6. The particle size of the molding sand is too fine, the dust content is high, the gas permeability is poor, and the internal pressure of the negative pressure pipe causes the negative pressure distortion, so that the negative pressure value around the cavity is far lower than the indicated negative pressure, and the vapor can not discharge the coating in time. Forming pores or wrinkles.
7. The pouring temperature is low, and the filling front metal liquid cannot fully vaporize the foam, and the undecomposed residual material can not be floated to the riser to solidify and form pores in the casting.
8. Poor deoxidation of molten steel, uncleaning of slag in the furnace, furnace and package, the sedation time is too short, the slag is not strong during the pouring process, and the pouring process is unreasonable to cause slag holes.
9. The opening position of the inner runner is unreasonable. When the filling is formed, a dead zone is formed. Due to the gas pressure in the cavity, the gasification residue accumulates at the dead corner to form a pore, and the cross-sectional area of ​​the inner runner is too large, so that the filling speed is greater than The foam gasifies the rate of retreat, swallows the foam, decomposes and vaporizes inside the alloy, and the gas cannot be discharged to form pores.
10. The capacity of the gate cup is too small, and the molten metal forms a vortex, which invades the air to form pores.

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