What is lost foam casting? Lost foam casting problems a […]
What is lost foam casting? Lost foam casting problems and solutions
Lost foam casting (also known as full mold casting) is to combine paraffin wax or foam models similar in size and shape to the castings into model clusters. After brushing and drying refractory coatings, they are buried in dry quartz sand for vibration modeling. It is a new type of casting method that makes the mold gasify, liquid metal occupies the position of the mold, and solidifies and cools to form a casting.
The advantages of this method are good casting precision and low pollution. However, due to process operations and other reasons during the casting process, the casting is prone to porosity or sand inclusions. The technicians of Liu's Mould will analyze the main causes of pores and sand inclusion in lost foam casting.
1. Due to the unreasonable design of the gating system, the filling speed of the molten metal is greater than the foam vaporization and gas discharge speed, causing the filling front to entrap the gasification residue in the metal liquid and vaporize again to form a black decomposition body on the inner wall.
2. The location of the inner runner is unreasonable, and a dead corner area is formed during filling. Due to the gas pressure in the cavity, the gasification residue accumulates in the dead corner to form pores, and the cross-sectional area of the inner runner is too large.
3. The pouring speed is too slow to fill the sprue cup, exposing the sprue, entraining air, sucking in the slag, and forming enveloping air holes and slag holes.
4. The gasification and decomposition of the foam model generates a large amount of gas and residues that cannot be discharged in time, and the foam, coating layer and dry sand filling are poorly dried. Surrounded by the high temperature of liquid metal, a large amount of hydrogen and oxygen are cracked into the casting. It is the main reason for the formation of pores.
5. The connection between the sprue cup and the sprue and the pouring system is not well sealed, especially the connection between the sprue and the sprue cup is not well sealed, and it is easy to form sand and pores under the action of negative pressure.
6. The particle size of the molding sand is too fine, the dust content is high, the air permeability is poor, and the negative pressure is distorted due to the blockage of the negative pressure pipe. The negative pressure value of the sand box is much lower than the negative pressure value of the indicator, and the vapors cannot be discharged from the coating in time And the formation of pores or wrinkled skin.