Porosity problems occur during the production of stainless steel castings

In the process of stainless steel castings, pore problems often occur, which brings a lot of trouble to the processing of stainless steel castings. Porosity is a bubble defect formed by the residual precipitated gas in the steel ingot during the cooling and solidification process of the metal liquid. Let us analyze it The main causes of porosity in stainless steel castings:

1. The coating has poor permeability or lacks negative pressure. The filling sand has poor air permeability, and the gas and residue in the cavity cannot be discharged in time, forming pores under the filling pressure.

2. The pouring speed is too slow and the pouring cup cannot be filled. The pouring opening is exposed, trapped in the air, and sucks in slag, forming load-bearing holes and slag holes.

3. The gasification and decomposition of the foam model produces a large amount of gas and residue that cannot be discharged in time. The main reason for the formation of pores is that the foam paint layer is filled with dry sand and dried, surrounded by high-temperature liquid alloy, and a large amount of hydrogen and oxygen enter the casting.

4. Due to the unreasonable design of the gating system, the filling speed of molten metal is greater than the bubble vaporization and gas discharge speed, causing the gasification residue to be sealed in the metal liquid and then evaporated to form the inner wall of the black hole.

5. The connection between the pouring cups and the sealing of the pouring system are not good, especially the connection between the pouring cups is not good, and sand and pores are easily formed under the action of negative pressure. This phenomenon can be solved by Bernu Use equations to calculate and explain.

6. The molding sand particle size is too fine, the dust content is high, the air permeability is poor, and the internal pressure of the negative pressure tube causes negative pressure deformation. Therefore, the negative pressure value around the mold cavity is much lower than the indicated negative pressure, and the steam cannot be discharged from the coating in time. Pores or pores are formed. wrinkle.

7. The pouring temperature is low, the molten metal before filling cannot completely evaporate the foam, and the undecomposed residue cannot float on the riser, forming pores in the casting.

8. The molten steel is poorly deoxidized, the slag is not cleaned, the furnace and packaging are short, the slag time is short, the slag blockage is not firm, and the pouring process is unreasonable, resulting in slag holes.

9. The position of the internal flow is unreasonable. When the filling is completed, a dead zone is formed. Due to the gas pressure in the cavity, the gasification residue accumulates in the dead zone, forming pores, and the cross-sectional area of ​​the pouring opening is too large, so The filling rate is greater than the foam gasification rate. When the foam is reduced and swallowed, the gas decomposes and evaporates in 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 eddy currents and intrudes into air to create pores.