The test results are shown in the table.
|Sprue height (mm)||Total mold filling time (s)||Average filling speed (cm/s)|
In dry sand, the coating has air permeability. From this boundary condition, it can be seen that only when the pressure of liquid metal flow is higher than the gas pressure Pa at the boundary, it flows in a full state. At this time, the coating has a restraining effect on the metal flow. In addition to the pressure of the coating on the metal, the capillary pressure formed by the pores between the coatings and the gas pressure in the pores jointly prevent the liquid metal from penetrating into the pores. When the liquid metal flow pressure P drops to the gas pressure PA equal to the boundary, the liquid metal begins to leave the boundary and appears in a non full state.
The gating system is regarded as a pipe full of flowing metal. According to Bernoulli equation in hydraulics, the filling speed V of liquid metal in lost foam casting can be expressed by the following formula:
According to the above formula, in the air gap layer δ When the internal gas pressure, vacuum negative pressure, liquid metal density and liquid metal flow resistance coefficient are certain, the filling speed of liquid metal in lost foam casting is only related to the static head of liquid metal.
The figure shows the relationship between the average mold filling speed of liquid metal and the static head of liquid metal in lost foam casting under the same other conditions. When the static head is 100mm, the filling speed is 12.60cm/s; The hydrostatic head of molten metal is increased to 150mm, and the filling speed is increased to 13.48cm/s; When the static head is 200mm, the filling speed reaches 22.99cm/s. The liquid metal hydrostatic head is doubled, and the liquid metal filling speed is almost doubled. The liquid metal hydrostatic head has a great impact on the filling speed. With the increase of the liquid metal hydrostatic head, the liquid metal filling speed of lost foam casting increases significantly.