1. Under-casting (under-filling, unclear outline, corner defects)

Reason for formation:

(1) The fluidity of the aluminum liquid is not strong, the gas content in the liquid is high, and the scale is large.

(2) The cause of the casting system is bad. The inner gate section is too small.

(3) Reasons for poor exhaust conditions. The exhaust gas is not smooth, the coating is too much, and the mold temperature is too high, so that the gas pressure in the cavity is high, so that the gas is not easily discharged.

Prevention method:

(1) Improve the fluidity of aluminum liquid, especially refining and slag. Appropriately increase the temperature and mold temperature. Increase the casting speed. Improve the structure of the casting, adjust the thickness allowance, and set the auxiliary rib channel.

(2) Increase the cross-sectional area of the ingate.

(3) Improve the exhaust condition, add a liquid flow tank and an exhaust line, and open a vent plug at the deep concave cavity. Make the coating thin and uniform, and then mold it after drying.

2.Crack

The blank is broken or broken, forming elongated cracks, which are irregularly lined, with two kinds of penetration and non-penetration, which develop under the action of external force. The difference between cold and hot crack: the metal in the cold crack is not oxidized, and the hot crack is oxidized.

Reason for formation:

(1) The casting structure is unreasonable, and the shrinkage resistance is too small.

(2) The ejector device is deflected and the force is uneven.

(3) The mold temperature is too low or too high, and it is severely strained and cracked.

(4) The harmful elements in the alloy exceed the standard and the elongation decreases.

Prevention method:

(1) Improve the structure of the casting, reduce the difference in wall thickness, increase the roundness and the arc R, and set the process ribs to make the section change smoothly.

(2) Correct the mold.

(3) Adjust the mold temperature to the working temperature to remove the slope and unevenness and avoid cracking.

(4) Control the composition of the aluminum coating to make it a harmful element.

3.Cold partition

There are traces at the docking or lap joint of the liquid flow, and the intersection edge is smooth, and the development trend continues under the action of external force.

Reason for formation:

(1) The flowability of the liquid flow is poor.

(2) The liquid flow splitting is poorly integrated or the process is too long.

(3) The filling temperature is too low or the exhaust is poor.

(4) Insufficient filling pressure.

Prevention method:

(1) Appropriately increase the temperature of the aluminum liquid and the temperature of the mold, and check and adjust the alloy composition.

(2) Make the filling filling points and arrange the overflow tank reasonably.

(3) Improve the casting speed and improve the exhaust.

(4) Increase the filling pressure.

4. Sag

A concave portion that appears on a smooth surface.

Reason for formation:

(1) The structure of the casting is unreasonable, and a hot section is generated in the local thick portion.

(2) The alloy has a large shrinkage rate.

(3) The gate cross-sectional area is too small.

(4) The mold temperature is too high.

Prevention method:

(1) Improve the structure of the casting, the wall thickness should be as uniform as possible, and the transitional connection should be used. The thick part can be used to eliminate the heat knot.

(2) Reduce the alloy shrinkage.

(3) Appropriately increase the cross-sectional area of the ingate.

(4) Reduce the temperature of the aluminum liquid and the temperature of the mold, use a temperature control and cooling device to improve the heat balance condition of the mold, improve the exhaust condition of the mold, and use a paint with a small amount of gas.

5. Bubbles

Under the skin of the casting, the bubbles formed by the accumulation of gas bulge.

Reason for formation:

(1) The mold temperature is too high.

(2) The filling speed is too fast, and the metal liquid is drawn into the gas.

(3) The paint has a large amount of gas and a large amount of water. It is not volatilized before casting, and the gas is wrapped on the surface of the casting.

(4) The exhaust is not smooth.

(5) It is too early to open the mold.

(6) The temperature of the aluminum liquid is high.

Prevention method:

(1) Cool the mold to the working temperature.

(2) Reduce the filling speed and avoid eddy entrainment.

(3) Select a paint with a small amount of gas, the amount is thin and uniform, and the mold is completely volatilized.

(4) Clean and add exhaust slots.

(5) Correct the mold opening time.

(6) Correct the smelting process.