Precautionary Techniques for Common Casting Defects in Cast Iron Processing

Prevention methods for common forging defects in cast iron parts during casting production and processing

Casting production and processing of cast iron often cause many different forging defects, and how to prevent such defects has always been a concern of casting manufacturers.

Pore characteristics: Porosity in castings refers to the existence of bright and clean holes of varying sizes inside, on, or near the surface of the casting. "The air oxidation color is present in the flow around the pores. Due to the differences in the source and cause of the vapor, the modes of expression of the pores are also different, including invasive pores, precipitating pores, and subcutaneous tissue pores.".

1.1 Invasive air holes: These air holes have a small number and large specifications, resulting in pear-shaped or spherical shapes at some positions on the surface of the casting. The key is that the vapor intrusion caused by the mold or sand core cannot escape from the metal material liquid.

Prevention of Misses:

(1) Reduce the amount of gas generated: Grasp the composition of gas generating chemicals in the molding sand or core sand. The moisture content of the wet molding sand should not be too high. The amount of release agent and water used during molding design and repair should not be excessive. The sand core shall be dried through the access hole. The dried sand core is not suitable for storage for too long. The sand core for use the next day shall be refinished and dried before use to prevent moisture from affecting the sand core. Damping and rusty cold iron and core bracing shall not be used.

(2) Improve the breathability of the version sand, select the appropriate molding compactness, effectively place the exhaust eye position to facilitate the exhaust pipe, and ensure the smooth passage of the sand core ventilation hole.

(3) Properly develop the pouring temperature, open vent holes and vent pipe risers, etc., to facilitate the upward discharge of vapor invading the metal material liquid.

1.2 Conduct fire evacuation due to the large number of air holes such as precipitation air holes, which are generally located on the surface of the casting. Generally, large areas of castings poured in the same batch are found to have surface defects. The key to this type of porosity is that during the entire smelting process, the vapor digested and absorbed by the metal material liquid cannot precipitate completely before condensation, resulting in many small fire evacuation pores in the casting.

Prevention of Misses:

(1) Accept clean and dry recycled waste, and limit the use of recycled waste with a high content.

(2) Ensure "three dryness": that is, drying treatment shall be conducted for the tap hole, tap hole, and crossing the river.

(3) The ladle needs drying treatment, and before use, it has powerful functions to straighten the molten iron. If there is molten iron in the warehouse, it is necessary to place a capping agent on the surface of the molten iron.

(4) Many promoters (spheroidizing agents, inoculants, and capping agents) may or may not be maintained dry for a certain period of time. When the ambient humidity is high, they must be dried before use.

1.3 Subcutaneous tissue porosity: This type of porosity mainly occurs at 2-3 mm of the subcutaneous tissue on the surface of the casting, with a diameter of 1 to 3 mm. In addition, there are a large number of castings that will clearly appear after heat treatment or initial processing to remove the skin.

Be prepared for missing;

(1) Properly develop the pouring temperature, strictly control the addition amount of many lifting agents, and minimize the pouring time.

(2) The addition amount of inoculant should be controlled between 0.4% and 0.6% (mass concentration). At the same time, the mass concentration of A1 in the inoculant should be strictly controlled. The high content of w (Al) and the water content on the surface of the mold cause feedback: 2Al+3H2O=Al2O3+3H2 ↑. In general, the amount of Al in the inoculant should not exceed 1.5% in natural environments.

(3) Prevent air oxidation of molten iron, properly supplement the relay running coke, and strictly control the intake and exhaust air volume.