Low-pressure casting

Low-pressure casting refers to the method that which liquid metal fills the mold under the action of low pressure (0.02 ~ 0.06mpa) and crystallizes under pressure to form castings. Pour the molten metal into the heat preservation crucible, install the sealing cover, connect the molten metal with the mold through the liquid riser, lock the mold, and slowly inject dry compressed air into the crucible furnace. The molten metal is under the action of gas pressure, fills the mold cavity along the liquid riser and pouring system from bottom to top, and crystallizes under pressure. After the casting is formed, remove the pressure in the crucible, and the molten metal in the liquid riser drops back to the metal level in the crucible.

Advantage

During pouring, the rising speed of molten metal and crystallization pressure can be adjusted, so it can be applied to various casting molds (such as metal mold, sand mold, etc.), casting various alloys and castings of various sizes; The bottom injection mold filling is adopted, and the liquid metal mold filling is stable without splashing, which can avoid the involvement of gas and the scouring of the mold wall and core, and the casting has fewer defects such as pores and slag inclusions, which improves the qualification rate of the casting; The casting crystallizes under pressure, with compact structure, clear outline, smooth surface, and high mechanical properties, which is particularly beneficial to the casting of large and thin-walled parts; The feeding riser is omitted, and the metal utilization rate is increased to 90% - 98%; Low labor intensity, good working conditions, simple equipment, easy to realize mechanization and automation.

Disadvantages and limitations

The service life of the liquid riser is short, and the liquid metal is easy to oxidize and produce slag inclusion during the heat preservation process. It is mainly used to cast aluminum and magnesium alloy castings with high-quality requirements, such as thin-walled parts such as cylinder block, cylinder head, crankcase, and aluminum pistons of a high-speed internal combustion engine.

Centrifugal casting

Centrifugal casting is a casting method in which molten metal is poured into a rotating mold, filled into the mold, and solidified under the action of centrifugal force. According to the position of the mold rotation axis in space, common centrifugal casting can be divided into two types: horizontal centrifugal casting: centrifugal casting when the mold rotation axis is horizontal or the included angle with the horizontal line is very small (<4 °). Vertical centrifugal casting: centrifugal casting when the rotation axis 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 shaft centrifugal casting, but it is rarely used.

Advantage

When centrifugal casting is used to produce hollow rotary castings, the core, gating system, and riser can be omitted; Due to the centrifugal force generated by the liquid metal during rotation, the metal with high density is pushed to the outer wall, while the gas and slag with low density move to the free surface to form directional solidification from the outside to the inside. Therefore, the feeding conditions are good, the casting structure is dense, and the mechanical properties are good; It is convenient to cast a "bimetallic" bearing sleeve and bearing bush. If a thin layer of the copper bushing is embedded in the steel sleeve, the more expensive copper material can be saved; Good filling ability; Eliminate and reduce the consumption of the gating system and riser.

Disadvantages and limitations

The free surface inside the casting is rough, with large dimensional error and poor quality; It is not suitable for alloys with high-density segregation (such as lead bronze) and aluminum, magnesium, and other alloys.

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