influence of the convective activity of the mold in the forging of the
precision forging is mainly manifested in the resistance and the thermal
conductivity of the mold. In the mold, all factors that increase the
flow resistance of gold and increase the cooling rate all reduce the
fluidity. For example, the small cross section of the runner, the rough
surface and the poor permeability will increase the flow resistance of
the molten metal and reduce the flow rate, thereby reducing the fluidity
of the molten metal. The quicker the heat of the liquid will be, the
worse the fluidity will be.
the process of solidification and cooling, the reduction in volume and
size is called shrinkage. After pouring the rhyme molten gold to room
temperature, three interrelated contracting stages are required by
liquid shrinkage, solidification shrinkage and solid contraction.
shrinkage refers to the volume shrinkage of metal when forging liquid
at precise temperature due to the decrease of temperature. The reduction
of volume shift to temperature is proportional to the difference of
starting solidification temperature, which is one of the main reasons
for shrinkage cavity and porosity.
solidification contraction refers to the volume contraction of the
metal liquid in the solidification stage, the pure metal and the
isothermal crystallization of the alloy, whose solidification is caused
by a solid phase transformation. The alloy with a certain crystal
temperature range is contracted in addition to a solid phase transition,
and the shrinkage of the temperature decrease during the solidification
stage. Generally, the decrease of the liquid level in the cavity is the
main cause of the shrinkage of the castings.