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What causes the phenomenon of porosity in stainless steel castings?

Release time:2020-05-26 16:14:05 

Many people have recently asked why stainless steel castings produce pores. Why is this? The following editor talks about why stainless steel castings produce pores.
Main reasons for porosity of stainless steel castings
The box-type and trolley-type resistance furnace plates are tempered before use and the temperature is controlled to 950 ° C or higher as much as possible to eliminate internal stress during casting. Also, while using the furnace board, it is necessary to evenly arrange the work pieces, and it is not possible to stack the work pieces in a local position. Otherwise, the furnace board will be uneven during the heat dissipation process during the heating process, and the furnace board will easily be deformed or cracked. , Shorten the service life of the hearth.
In the casting process of stainless steel, there are many problems in the porosity, which is a bubble defect caused by the accumulation of gas accumulated in the ingot during cooling and solidification of the metal liquid, which greatly hinders the casting process. Let's analyze the main causes of pores:
01: Poor air permeability of the paint, or lack of negative pressure, poor sand filling, gas and residue in the cavity are not in time, and pores are created by the filling pressure.
02: The injection speed is too slow to fill the gate cup, the sprue is exposed, air is drawn in, slag is sucked in, trapped air holes and slag holes are formed.
03: Large amount of gas and residue generated by gasification and decomposition of foam model cannot be discharged from the mold in time. The foam and paint layers are filled with dry sand. Inadequate drying. Surrounded by the high temperatures of liquid alloys, large amounts of hydrogen and oxygen decompose into castings. The main reason for pores.
04: Due to the irrational design of the injection system, the filling rate of the metal liquid is faster than the foam gasification concession and the gas discharge rate, which allows the filling front to trap the gasification residue in the metal liquid and Evaporates to form black smoke decomposition pores on the inner wall. ..
05: The connection between the sprue cup and the sprue and pouring system is not well sealed. In particular, the connection between the sprue cup and the sprue cup is not well sealed. Also, sand and air holes are easily formed under the action of negative pressure. This phenomenon can be calculated and explained using the Bernoulli equation.
06: Since the particle size of the foundry sand is too small, the dust content is large, the permeability is poor, and the negative pressure is distorted due to the internal blockage of the negative pressure pipeline, the negative pressure value around the cavity is less than the displayed negative pressure. The formation of pores or wrinkled skin where the gasification is not expelled from the film.
07: The pouring temperature is low, the molten metal at the front of the filling cannot completely evaporate the bubbles, and the undecomposed residue floats on the riser and solidifies, making it impossible to form pores in the casting. ..
08: Insufficient deoxidation of molten steel, inadequate removal of slag in furnace table, furnace and bag, sedation time too short, slag weak during injection process, slag hole irrational injection process Is caused by
09: The opening position of the inner runner is impossible and a dead zone is formed during filling. The pressure of the gas in the cavity causes the gasification residue to accumulate in the dead corners and form pores. The cross-sectional area of the inner runner is too large, the filling rate collapses the gasification of the bubbles, swallows the bubbles, decomposes and gasifies inside the alloy and cannot release the gas to form pores.
10: The capacity of the gate cup is too small, the metal liquid forms a vortex, and penetrates into the air to generate pores.

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