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Suction casting is a vacuum casting method that insert a mold nozzle (or a riser pipe) into a molten metal, and then vacuum the mold to make a negative pressure in the mold cavity, make the molten metal rise along the nozzle under the action of negative pressure (or the riser tube) and fill the mold, solidify and get the casting.
The process principle of vacuum suction casting is that place the injection mold shell is in the sealed chamber, the sealed chamber is lowered, the sprue is immersed in the liquid metal, then the vacuum pump is started to vacuum the sealed chamber, and the liquid is simultaneously sucked and cast. After the casting in the shell is solidified, the vacuum state is released, and the residual metal liquid in the spruce is returned to the furnace, finally the vacuum suction casting is obtained by cleaning sand.
According to the suction casting process to establish the difference in pressure difference, suction casting can be divided into direct suction casting and special suction casting.
1) Direct Suction Casting
Taking the CLA method as an example, first, place the shell made by the ordinary investment molding process in a sealed chamber, the sealed chamber is lowered, and the sprue is inserted into the liquid metal. The vacuum pump is started to vacuum the sealed chamber, and the liquid metal is simultaneously filled and shaped. After the molten metal in the shell is solidified, the sealed chamber is connected to the atmosphere to eliminate the vacuum, and the liquid metal that has not solidified in the runner flows back into the crucible. Finally, take out the cleaning sand and get the casting. In addition to the CLA method, there is also a tilting inversion vacuum casting process, that is, after the vacuum suction molding is completed, the mold is inverted, and the remaining molten metal in the sprue is used to provide solidification for the solidification of the casting. This method is easy to achieve continuous production and has high production efficiency.
2) Special Suction Casting
This type of vacuum suction casting method is mainly based on the casting process requirements of the cast or the type of alloy adding some special operation for the process of suction casting. For example, to enhance the ability of vacuum suction molding, after the molten metal fills the cavity, the lower sealing chamber inserts the compressed gas to increase the pressure difference between the upper and lower sealed chambers, which can enhance the metal liquid feeding ability during the solidification of the casting. There is also vacuum suction casting using inert gas protection. This method is mainly used for vacuum melting and casting of high temperature alloys and easily oxidized alloys (also known as CLV method). After the metal is melted under vacuum, the inert gas is introduced into both the vacuum melting chamber and the suction casting chamber, and they are maintained at the same gas pressure. Insert the shell runner or riser into the molten metal, then lower the pressure in the suction chamber and start suction casting. After a certain time, the molten metal in the runner flows back after the pressure is released.
1) High yield, good casting quality, stable metal liquid filling, less slag inclusion and spatter, all these characteristics of suction casting reduce defects such as pores and slag inclusions of castings, and improve the yield. In addition, casting can be carried out at a lower pouring temperature to refine the grain of the casting and improve the mechanical properties.
2) Good shape filling performance. When casting, the back pressure in the mold cavity is small and the filling speed is adjustable, so that the filling ability is strong, and the thinnest part of the casting can reach 0.3 mm.
3) The utilization rate of the molten metal and the process yield are greatly improved.
4) Simplify the process and reduce costs.
5) It is easy to mechanize and has high labor productivity. Compared with the common molten molding casting process, each module of suction casting can be assembled with more wax patterns, which generally increases the yield by 85% to 135%.
Suction casting is suitable for molten molding casting, ceramic casting, shell casting, gypsum casting, graphite casting and sand casting. It can be used to produce complete thin-wall castings(such as aluminum alloy, magnesium alloy, titanium alloy, stainless steel and high temperature heat resistant alloy) that its average wall thickness is less than 5 mm and single-piece castings with a weight of less than 100 kg.
