Main Causes of Porosity in Stainless Steel Castings

For box-type and trolley-type resistance furnace plates, high temperature tempering should be performed before use, and the temperature should be controlled above 950 degrees as far as possible. The purpose of this is to eliminate internal stress during casting. In addition, during the use of the furnace plate, it is necessary to ensure that the workpiece is placed uniformly, and the work cannot be stacked in a certain local position, otherwise the furnace plate will be uneven during the heat dissipation process during the heating process, which will easily cause the furnace plate to deform and crack. , Reduce the life of the furnace floor.

In the stainless steel casting process, pores often appear, which brings many troubles to the casting processing. Porosity is a bubble defect formed by the metal liquid during the cooling and solidification process, and the gas precipitated in the ingot. The following forestry machinery parts manufacturers analyze the main causes of pores:

01: Poor air permeability of the coating or insufficient negative pressure, poor air permeability of the sand filling, the gas and residue in the cavity cannot be exhausted in time, and pores are formed under the filling pressure.

02: The pouring speed is too slow to fill the spout cup, expose the sprue, get in the air, suck in the slag, and form the entrapment pores and slag holes.

03: Foam model gasification and decomposition generates a large amount of gas and residues that cannot be discharged in time. The foam and coating layer are not dry enough to fill the dry sand. Under the high temperature of the liquid alloy, a large amount of hydrogen and oxygen are cracked to invade the OEM stainless steel casting. The main cause of stomata.

04: Due to the irrational design of the gating system, the filling speed of the metal liquid is faster than the foaming gasification concession and gas discharge speed, which causes the filling front to trap the gasification residue in the metal liquid and gasify again to form the black fumes on the inner wall.

05: The connection 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 well sealed. It is easy to form sand inclusions and pores under the action of negative pressure. This phenomenon can be calculated and explained using Bernoulli's equation.

High Pressure Valve Body

06: The particle size of the molding sand is too fine, the dust content is high, and the air permeability is poor. The negative pressure distortion caused by the internal blockage of the negative pressure pipeline makes the negative pressure around the cavity much lower than the indicated negative pressure. Formation of stomata or wrinkles.

07: The pouring temperature is low, the filling front metal liquid cannot fully vaporize the foam, and the undecomposed residual material has no time to float to the riser and solidify to form pores in the steel casting.

08: Poor deoxidation of molten steel, slag removal in the hearth, the furnace, and the package is not clean, the sedation time is too short, the slag blocking during the pouring process is not good, and the slag hole is caused by the unreasonable pouring process.

09: The opening position of the runner is unreasonable. A dead zone is formed during filling. Due to the gas pressure in the cavity, gasification residues accumulate at the dead corner to form pores. The cross-sectional area of the runner is too large, which makes the filling speed faster Foam gasification yields speed, swallows foam, decomposes and gasifies inside the alloy, and gas cannot be discharged to form pores.

10: The capacity of the gate cup is too small, the metal liquid forms a vortex, and invades the air to generate pores.