Treatment method for shrinkage and shrinkage of ductile iron parts

- Aug 05, 2019-

Influencing factors:


1. Carbon equivalent: increase the amount of carbon, increase the expansion of graphitization, and reduce shrinkage and shrinkage. In addition, increasing the carbon equivalent can also increase the fluidity of the ductile iron and facilitate the feeding. The empirical formula for producing high quality castings is C%+1/7Si%>3 9%. However, when the carbon equivalent is increased, the casting should not cause other defects such as graphite floating.


2. Phosphorus: The phosphorus content in the molten iron is high, which makes the solidification range expand. At the same time, the low-melting-point phosphorus eutectic can not be replenished during the final solidification, and the casting shell is weakened, so the shrinkage and shrinkage are increased. Propensity. The general plant control phosphorus content is less than 0 08%.


3. Rare Earth and Magnesium: If the residual amount of rare earth is too high, the graphite shape will be deteriorated and the spheroidization rate will be lowered. Therefore, the rare earth content should not be too high. Magnesium, on the other hand, is a strongly stable carbide element that hinders graphitization. It can be seen that the amount of residual magnesium and the amount of residual rare earth increase the tendency of the white iron of the ductile iron to decrease the expansion of the graphite, so when their content is high, the tendency of shrinkage and shrinkage is also increased.


4. Wall thickness: When the surface of the casting forms a hard shell, the higher the temperature of the internal molten metal, the larger the liquid shrinkage, and the volume of shrinkage and shrinkage not only increases the absolute value, but also increases the relative value. In addition, if the wall thickness changes too suddenly, the isolated thick section cannot be replenished, and the tendency to cause shrinkage shrinkage increases.


5, temperature: high pouring temperature, is conducive to feeding, but too high will increase the amount of liquid shrinkage, is not good for eliminating shrinkage, shrinkage, so the casting temperature should be reasonably selected according to the specific circumstances, generally 1300 ~ 1350 °C is appropriate.


6. The compactness of the sand type: If the compactness of the sand type is too low or uneven, the phenomenon of cavity expansion will occur under the action of metal static pressure or expansion force after casting, resulting in insufficient shrinkage of the original metal. The casting produces shrinkage and shrinkage.


7. Casting riser and cold iron: If the pouring system, riser and cold iron are improperly set, the molten metal cannot be solidified in sequence; in addition, the number and size of the riser and the connection with the casting will not affect the feeding of the riser. effect.