Metal casting process

Solidification mode of castings: layer-by-layer solidification, intermediate solidification and paste solidification

Shrinkage of castings: liquid shrinkage, solidification shrinkage, solid shrinkage

(The actual shrinkage of the casting is related to its chemical composition, casting temperature and casting mold conditions of the casting structure)

Shrinkage cavity and porosity in casting:

① Shrinkage cavity: (eutectic is easy to occur) solidification layer by layer
Concentrated on the upper part of the casting, the holes with small volume in the solidified part after scattering are inverted cone-shaped, that is, the surface is rough

(2) Loose (solid-liquid coexistence: macro shrinkage cavity, micro shrinkage cavity)

③ Prevention and treatment of shrinkage cavity and porosity
Directional solidification (sequential solidification can prevent shrinkage cavity and macro porosity can also be eliminated by this method)

Internal Stress and Crack in Casting

One. Internal stress: thermal stress and mechanical resistance
Thermal stress: Different thicknesses of the four cooling walls of materials and different cooling rates produce different forces (tensile force and pressure, and thermal stress does not disappear)

Prevention of internal stress (internal stress will deform parts)

Methods: A simultaneous solidification B for long and high parts can adopt reverse deformation process C the thick wall of the casting is uniform and the shape is as symmetrical as possible

D Aging treatment shall be adopted for parts with high precision requirements (natural: natural release force. Manual: annealing back to furnace, stress relief annealing)