Knowledge

I. Raw Material Control

1. Select high-quality raw materials: Ensure the quality of raw materials is up to standard, free from gas and impurity contamination. Use high-quality pig iron, scrap steel, etc. as smelting raw materials.

2. Strict laboratory testing and sampling: Conduct thorough laboratory testing and sampling of raw materials to ensure that the gas and impurity content is within a reasonable range.

 

II. Optimization of the Smelting Process

1. Strict control of furnace temperature and holding time: Ensure the furnace temperature is appropriate and stable to avoid excessive or insufficient temperatures that could lead to gas formation and oxidation of alloy elements. A reasonable holding time helps with the dissolution and uniform distribution of alloy elements.

2. Reasonable addition of furnace materials: By adding an appropriate amount, the fluidity and anti-gassing ability of molten iron can be improved, reducing the formation of pores.

3. Enhanced deoxidation and desulfurization treatment: During the smelting process, deoxidation and desulfurization treatments are carried out to reduce the oxygen and sulfur content in the molten iron, thereby minimizing gas formation due to oxidation and sulfidation reactions.

4. Precise control of the addition of inoculants and modifiers: Generally, low-magnesium, low-rare earth inoculants and silicon-barium modifiers are used. The addition of inoculants is controlled at around 12kg, and that of modifiers at around 8kg. This ensures good spheroidization effect and casting performance without excessive addition causing pores.

5. Control of smelting temperature and time: Avoid the dissolution and precipitation of hydrogen and nitrogen in the molten iron to prevent the formation of pores and bubbles.

 

III. Improvement of Pouring Process

1. Optimization of pouring temperature and speed: Select an appropriate pouring temperature and speed to avoid significant temperature gradients and rapid temperature changes in the molten iron during pouring, thereby reducing the formation of pores.

2. Improvement of pouring system and gate design: Design a reasonable pouring system and gate to ensure that the molten iron flows smoothly and evenly into the mold cavity, avoiding the impact of the molten iron on the mold wall and the formation of pores.

 

IV. Control of the Cooling Process

Control the cooling rate of the castings: By strengthening the management of cooling equipment, control the cooling rate of the castings to avoid the formation of pores due to either too fast or too slow cooling.

Adequate cold working treatment: After cooling, subject the castings to adequate cold working treatment to repair and reduce the number of pores.

 

V. Other Measures

Control the humidity of the mold and additives: Maintain the mold humidity at an appropriate level to prevent excessive moisture from causing pores.

Strengthen process monitoring and inspection: Conduct strict process monitoring and inspection of all stages including melting, pouring, and cooling to promptly identify and solve problems, ensuring the quality of ductile iron castings.

 

 

Determining an appropriate cooling rate is crucial to reducing porosity in the production of ductile iron. The cooling rate not only affects the microstructure and mechanical properties of the casting but also directly relates to the formation of defects such as porosity. The following are some methods for determining an appropriate cooling rate to reduce porosity:

 

I. Understanding the Impact of Cooling Rate on Porosity Formation

Gas Evolution: A too rapid cooling rate can cause gases in the molten metal to solidify without being expelled, resulting in the formation of pores and the occurrence of porosity.

Microstructure Transformation: The cooling rate also affects the transformation of the internal microstructure of the casting. An inappropriate cooling rate may lead to an uneven microstructure, thereby increasing the risk of defects such as porosity.

 

II. Determine the Appropriate Cooling Rate

Experimental Verification: Conduct experiments to verify the porosity of castings under different cooling rates. Multiple samples can be made and cooled at different rates, then the number and size of pores in each sample can be observed and compared.

Theoretical Calculation: Utilize thermodynamic and kinetic principles, combined with factors such as the material composition, shape and size of the casting, and pouring conditions, to perform theoretical calculations to predict the appropriate range of cooling rates.

Experience Reference: Refer to the production experience of the same industry or similar products to understand the cooling rates they use in actual production and their effects, thereby providing a reference for one's own production.

 

III. Precautions

Avoid overly rapid cooling rates: Excessively fast cooling rates not only increase the risk of porosity but may also cause cracks, deformations, and other defects in the casting.

Consider the overall cooling of the casting: When controlling the cooling rate, the overall cooling situation of the casting should be comprehensively considered to prevent local overcooling or overheating.

 

Vigor has more than 18 years experience on castings, we know how to avoid defects when production. If you have any question and demand of products development or improve your supply chain, please feel free to contact us at info@castings-forging.com