The main reason is that the gas generated

In the production process of cast iron parts, various casting defects often occur in cast iron parts. How to prevent these defects has always been a concern of casting manufacturers. This article introduces the author's knowledge and practical experience in this regard. 1 Pore characteristics: Pore holes in castings refer to lubricating holes of different sizes existing in or near the surface of the casting. The pore walls are often oxidized, because the origin and composition of the gas are different, and the manifestation of the pores is also different. There are invasive pores, separate pores, and subcutaneous pores. 1.1 Separating blowholes. Such blowholes are numerous and scattered. Generally, most of the castings that are cast in the same batch are found on the surface of the casting.
The main reason for this type of pores is that during the melting process, the gas absorbed by the molten metal cannot be completely separated out before condensation, and many loose pores are formed in the casting. [Precautions] (1) Choose clean and dry furnace materials and restrict the use of furnace materials with more gas content. (2) Ensure the "three dry": the iron trough, the iron outlet, and the bridge should be completely dried. (3) The ladle should be dried. It is best to use iron liquid to iron it before use. If there is iron liquid in the ladle, be sure to put a masking agent on the surface of the molten iron. (4) Various additives (spheroidizing agent, inoculant, masking agent) should be kept dry and high humidity, and it can be used after drying. 1.2 Invasive stomata The number of such stomata is small, the scale is large, and it occurs in some parts of the outer surface of the casting, which is pear-shaped or spherical.
The main reason is that the gas generated by the mold or the sand core penetrates into the metal liquid and fails to escape. [Precautions] (1) Reduce the amount of gas generated: control the content of gas-generating substances in the molding sand or core sand. The moisture content of the wet molding sand should not be too high. The sand core should be ensured to be dry. The sand core after drying should not be stored for too long. The sand core used the next day should be returned to the furnace for drying before use to prevent the sand core from absorbing moisture. No damp, rusty cold iron and core are used. Hold on. (2) Improve the permeability of the molding sand, select the appropriate air tightness, reasonably arrange the position of the air outlet to facilitate the exhaust, and ensure that the sand core ventilation holes are cleared. (3) Properly increase the pouring temperature, open the vent hole and the exhaust riser, etc., so that the gas intruding into the molten metal can float up and be discharged. 1.3 Subcutaneous porosity This type of porosity mainly appears in the surface of the casting 2 ~ 3mm, with a diameter of about 1 ~ 3mm. And there are many in number. After the heat treatment or rough machining removes the outer skin, the casting will be clearly revealed.
[Precautions] (1) Properly increase the pouring temperature, strictly control the amount of various additives, and shorten the pouring time as much as possible. (2) The participation amount of inoculant bronze cast Suppliers should be controlled within (mass fraction) 0.4% ～ 0.6%, and the mass fraction of A1 in inoculant should be strictly controlled. W (Al) is too high and simple, and the water on the surface of the cavity will react: 2Al + 3H2O = Al2O3 + 3H2 ↑, in general, the Al content of the inoculant should not exceed 1.5%. (3) Avoid the oxidation of molten iron, add relay coke properly, and strictly control the air intake.