1. Low pressure casting
Low-pressure casting refers to a method in which liquid metal is filled into a mold under a relatively low pressure (0.02 to 0.06 MPa) and crystallized under pressure to form a casting. Pour the smelted metal liquid into the heat-preserving crucible, install the sealing cap, and the liquid-lifting duct connects the metal liquid to the mold, lock the mold, and slowly pass dry compressed air into the crucible furnace. The metal liquid is under gas pressure. The role is to fill the cavity along the riser tube and the pouring system from bottom to top, and crystallize under pressure. After the casting is formed, the pressure in the crucible is removed, and the metal liquid in the riser tube is returned to the metal liquid level in the crucible. Open the mold and remove the casting.
The rising speed and crystallization pressure of the molten metal can be adjusted during pouring, so it can be applied to various casting molds (such as metal molds and sand molds), casting various alloys and castings of various sizes; using bottom-injection filling, metal Liquid filling is smooth and no splash phenomenon, which can avoid the involvement of gas and the erosion of the mold wall and core. The casting has less defects such as pores and slag inclusions, which improves the qualification rate of the casting. The casting crystallizes under pressure and the casting structure is dense. , Clear outline, smooth surface, high mechanical properties, especially for the casting of large and thin-walled parts; eliminating the need to fill the riser, the metal utilization rate increased to 90% to 98%; low labor intensity, good labor conditions, simple equipment , Easy to achieve mechanization and automation.
Disadvantages and limitations:
The riser has a short life, and the metal liquid is susceptible to oxidation and slag inclusion during the heat preservation process. It is mainly used to cast some high-quality aluminum and magnesium alloy castings, such as thin-walled parts such as cylinder blocks, cylinder heads, crankcases, and aluminum pistons for high-speed internal combustion engines.
2. Centrifugal casting
Centrifugal casting is a casting method in which a metal liquid is poured into a rotating mold, and the mold is filled and solidified under the action of centrifugal force. According to the position of the axis of rotation of the mold in space, common centrifugal casting can be divided into two types: horizontal centrifugal casting: centrifugal casting when the axis of rotation of the mold is horizontal or the angle with the horizontal line is small (<4 °). Vertical centrifugal casting: Centrifugal casting when the axis of rotation of the mold is vertical is called vertical centrifugal casting. Centrifugal casting with a large angle between the rotating axis of the mold and the horizontal and vertical lines is called inclined axis centrifugal casting, but it is rarely used.
When producing hollow rotating body castings by centrifugal casting, the core, gating system and riser can be omitted; due to the centrifugal force generated by the liquid metal during rotation, the denser metal is pushed to the outer wall, and the denser gas, The slag moves to the free surface to form a directional solidification from the outside to the inside, so the filling conditions are good, the casting structure is dense, and the mechanical properties are good; it is easy to cast "bimetal" bushings and bushes, such as casting a thin layer in a steel sleeve Copper bushing can save expensive copper material; good filling capacity; eliminate and reduce the consumption of pouring system and feeder.
Disadvantages and limitations:
The free surface inside the casting is rough, with large dimensional errors and poor quality; it is not suitable for alloys with high density segregation (such as lead bronze) and alloys such as aluminum and magnesium.
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