The principle of low-pressure casting alloy wheels: low-pressure casting alloy wheels are a casting method between pressure casting and gravity casting. In a sealed crucible containing molten metal, pressurize the surface of the molten metal in the crucible with compressed air, so that the molten metal is squeezed from the bottom up along the riser tube into the cavity, and the molten metal is filled with the mold. After the cavity (metal mold casting), increase the air pressure and keep the liquid surface pressure until the casting is completely solidified, then release the pressure in the crucible (exhaust), so that the unsolidified molten metal in the riser pipe and the runner will fall back into the crucible, that is Completed a process of low-pressure casting alloy wheels.
The process of low-pressure casting alloy wheels: it includes liquid lifting, filling, encrustation (sand casting), pressurization, pressure holding (crystallization and solidification), and exhaust (pressure relief).
Boosting—pass compressed air at a certain pressure into the sealed crucible, so that the molten metal rises steadily along the riser pipe to the runner of the mold;
Filling-the molten metal enters the cavity from the runner until it fills the mold. The filling speed can be adjusted and controlled to make the molten metal fill smoothly, which not only ensures the discharge of gas in the cavity, but also avoids the occurrence of defects such as cold barrier and oxidation slag inclusion;
Encrustation-After filling the mold, stop pressurizing and keep the original pressure unchanged for several seconds, so that the surface temperature of the casting will be low and hard (to prevent the sand casting from running out of fire during pressurization, and the casting sticks to the sand. For the low pressure of the metal mold Cast alloy wheels can be directly pressurized without encrusting);
Pressurization—After the molten metal fills the cavity, it can be pressurized through the crust, that is, increase the pressure by a certain value under the original filling pressure;
Pressure keeping—maintain the pressure immediately after boosting, so that the casting will crystallize and solidify under a stable pressure.
Exhaust (pressure relief)-After the casting is solidified, release the pressure in the crucible (ie, exhaust), so that the unsolidified molten metal in the riser pipe and runner will fall back into the crucible. After the casting is cooled, the casting can be opened and taken out.
Process characteristics of low-pressure casting alloy wheels:
Liquid metal fills the cavity smoothly from bottom to top, and the direction of liquid flow in the cavity is the same as the direction of gas discharge, so it can avoid the erosion of the cavity and core by the molten metal, and at the same time, it can also reduce the flow of molten metal into the gas. Possibility of secondary oxidation with molten metal to prevent defects such as porosity and non-metallic slag inclusions in castings, and improve the quality of castings;
The mold is filled under pressure, and the fluidity is increased, which facilitates the pouring of more complex thin-walled parts and makes the contour of the casting clear;
The solidification feeding process of the casting is carried out under external pressure, so the feeding effect is good, the casting is dense and the mechanical properties are good. Generally, the tensile strength and hardness of low-pressure casting alloy wheels can be increased by about 10% compared with gravity casting. This casting method is suitable for producing pressure-resistant and anti-leakage castings;
The pouring system of the low-pressure casting alloy wheel hub is simple, and the riser can be reduced or omitted, and the unsolidified molten metal can flow back into the crucible, reducing metal loss, so the process yield rate is high;
Compared with die casting, the process is simple, the manufacturing is convenient, and the investment is small;
It is easy to realize mechanization and automation, which reduces the labor intensity of workers;
There are also many problems with castings with many hot junctions and poor sequential solidification conditions, and necessary measures should be taken. Such as using cold iron, riser, etc. to solve.
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