The main application principle of graphite cold iron block is that graphite cold iron has the advantages of low density, high fire resistance, and high thermal conductivity. Therefore, using graphite cold iron as a refrigerant instead of metal cold iron can effectively address casting defects like porosity and shrinkage in cast steel, cast copper, and cast aluminum. It can also effectively resolve issues such as white spots and porosity caused by using metal cold irons in castings.
In casting production, cold iron plays a crucial role in promoting riser efficiency and preventing shrinkage and porosity in castings, which are vital for ensuring casting quality. Cold irons can be applied in lost foam casting similarly to general casting methods: external cold irons are added during sand molding, while internal cold irons are embedded or bonded inside the model during molding, or extended and fixed in the sand mold. The principles for placing internal and external cold irons, including their types and standards, are similar to those in general casting.
1. Prevent shrinkage in areas difficult for risers to feed.
2. Prevent cracks in areas where wall thicknesses intersect or change abruptly.
3. Cooperating with risers, cold irons can enhance sequential solidification of castings, expand the range of riser shrinkage, and reduce the number or volume of risers.
4. Using cold iron to accelerate cooling of a single hot spot can make the entire casting approach simultaneous solidification, preventing or reducing casting deformation and improving process yield.
5. Improve the local metallographic structure and mechanical properties of castings: refining the matrix, enhancing surface hardness and wear resistance.
6. Reduce and prevent segregation in thick-walled castings. The function of cold iron is to accelerate the cooling rate of specific parts of the casting during pouring. Due to structural requirements, castings often have uneven wall thicknesses: some parts are thick and cool slowly, while thin parts cool rapidly, leading to uneven cooling rates. This can cause shrinkage in thick areas or tearing in thin walls. To prevent this, cold irons are placed on thick-walled areas after molding to absorb heat from the molten iron, accelerate cooling, and reduce the cooling time difference between thick and thin sections.