Measures to avoid porosity in casting include:

1. Control the gas content of the metal liquid, and minimize the dissolution of gas elements into the metal liquid when smelting metal. This mainly depends on the raw materials used, reasonable smelting operations, and appropriate smelting equipment.

2. Reduce the gas generation of sand molds (cores) during pouring.

3. Take certain measures to ensure that the gas generated during pouring is easily discharged from the sand mold. To ensure the necessary breathability of the sand mold, multiple air vents should be tied, thin walled or hollow sand cores filled with coke in the middle should be used, avoiding large flat surfaces in horizontal pouring positions, setting air vents, appropriately increasing pouring temperature, and paying attention to air entrainment.

4. Increase the resistance of gas entering the liquid metal. For example, ensuring the required height of the sprue and the rising speed of the metal liquid inside the mold, applying coatings on the surface of the sand core to reduce surface pores, etc.

5. Ensure uniform heating during pouring. For example, furan resin binder casting is very sensitive to the pouring temperature, and there will be no hot subcutaneous pores below 1350 degrees Celsius. Different parts of the mold cavity will also generate hot subcutaneous pores in the hot zone due to different degrees of heating. Therefore, the pouring system should disperse the metal liquid into the mold cavity to ensure a uniform thermal field, shorten the flow distance of the filled metal liquid, and prevent local heating of the mold cavity from causing the decomposition of furan resin.

Extended Information

1、 Invasive pores are relatively small in number and larger in size, often occurring on certain parts of the outer surface of the casting, in the shape of pears or balls. Mainly due to the gas generated by the mold or sand core invading the molten metal and failing to escape.

Preventive measures:

(1) Reduce gas generation: Control the content of gas generating substances in the molding sand or core sand, and ensure that the moisture content of wet molding sand is not too high. The amount of release agent and water used during molding and repair should not be too high. The sand core should be ensured to be dried, and the dried sand core 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 moisture absorption of the sand core, and damp or rusty cold iron and core support should not be used.

(2) Improve the air permeability of molding sand, select appropriate mold space compactness, and reasonably arrange the position of air outlet to facilitate air exhaust, so as to ensure that the air vent of sand core is unblocked.

(3) Properly increase the pouring temperature, open exhaust holes and exhaust risers, etc., to facilitate the upward floating and discharge of gas invading the metal liquid.

2、 Precipitation porosity is a type of porosity that is numerous and dispersed, usually located on the surface of castings. It is often found in most castings cast in the same batch. This type of porosity is mainly due to the fact that during the melting process, the gas absorbed by the molten metal does not completely precipitate before solidification, resulting in the formation of many dispersed small pores in the casting.

Preventive measures:

(1) Use clean and dry furnace materials to limit the use of furnace materials with high gas content.

(2) Ensure the "three dryness": that is, the iron trough, iron outlet, and bridge must be thoroughly dried.

(3) The ladle should be dried and scalded with molten iron before use. If there is molten iron in the ladle, it is necessary to put a covering agent on the surface of the molten iron.

(4) Various additives (spheroidizing agents, inoculants, covering agents) should be kept dry periodically. When the humidity is high, they should be dried before use.