Vacuum suction casting is a casting method in which the casting gate (or riser) is inserted into the metal liquid, and then the casting is vacuumed, so that there is negative pressure in the casting cavity. Under the action of negative pressure, the metal liquid rises along the gate (or riser) and fills the mold, solidifies and forms, so as to obtain the casting.
The process principle of vacuum suction casting is shown in Figure 1. The investment shell is placed in the sealed chamber, the sealed chamber is lowered, the straight runner is immersed in the liquid metal, and then the vacuum pump is started to pump the sealed chamber into a vacuum, and the liquid is simultaneously sucked and cast. After the casting in the mold shell solidifies, the vacuum state is lifted, the residual metal liquid in the runner returns to the furnace, and the vacuum suction casting is obtained by sand cleaning.
Process classification
According to the different pressure difference established by vacuum suction casting process, vacuum suction casting can be divided into direct suction casting method and special vacuum suction casting method.
(1) Direct suction casting method
Taking CLA method as an example, the shell made by ordinary investment process is first placed in the sealed chamber, the sealed chamber is lowered, and the straight runner is inserted into the liquid metal. Start the vacuum pump to vacuum the sealing chamber and fill the liquid metal at the same time. After the liquid metal in the shell is solidified, the sealed chamber is connected to the atmosphere, the vacuum is eliminated, and the liquid metal that has not yet solidified in the runner flows back to the crucible. Finally, the mold shell is removed to clean the casting. In addition to CLA method, there is also tilting and inverted vacuum suction casting, that is, after the vacuum suction casting filling is completed, the cast is inverted, and the remaining metal liquid in the straight runner provides supplementary shrinkage for the casting solidification. This method is easy to realize continuous production and has high production efficiency.
(2) Special vacuum casting method
This kind of vacuum suction casting method mainly adds some special operations to the process of vacuum suction casting according to the process requirements of the cast or the type of alloy. For example, to enhance the filling capacity of vacuum suction casting. Vacuum the sealing chamber on the finish (see Figure 2a); After the liquid metal is filled with the cavity, the lower sealing chamber is then filled with compressed gas to improve the pressure difference between the upper and lower sealing chambers (see Figure 2b), thus enhancing the liquid metal feeding capacity during the crystallization and solidification of the casting. The process diagram is shown in Figure 2. There is also vacuum casting with inert gas protection, the method is mainly used for the production of superalloy and easily oxidized alloy vacuum melting and casting suction casting method (also known as CLV method), the method is to melt the metal under vacuum, to the vacuum melting chamber and suction casting chamber at the same time into the inert gas, and make them maintain the same air pressure. Insert the mold runner or riser into the metal liquid, and then reduce the pressure of the suction casting chamber to perform suction casting. After holding for a certain time, the metal liquid in the straight runner flows back to the crucible after pressure relief.
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