Sand casting

Most of the sand molds are still handmade.

Sand casting is mainly used for the production of cast iron, cast steel, cast copper, cast aluminum and other materials. When designing the casting structure, it is necessary to consider the requirements of the casting process and the performance of the metal to prevent defects such as shrinkage cavities, shrinkage porosity, insufficient pouring, cold isolation, deformation and cracks. The following issues should be paid attention to:

①The casting should have a reasonable wall thickness and structural slope, and the wall thickness of the casting should be as uniform as possible.

②Connection of casting wall: There should be structural rounded corners at the connection of casting wall. Avoid crossing and acute angle connections, and the connection between thick and thin walls should be gradually transitioned.

③ Castings should avoid excessively large horizontal planes.

④In order to prevent warping and deformation of castings, for larger flat castings and elongated boxes with uneven wall thickness, they should be designed into symmetrical shapes or rib plates should be added to improve their rigidity.

⑤ Avoid blocking the casting shrinkage

Such as common wheel-shaped castings, the spokes are even and straight. However, for alloys with a large shrinkage rate, cracks may occur due to excessive stress. In order to prevent cracks, curved spokes can be made to reduce internal stress by slight deformation of the spokes or rims.

⑥ Design the casting structure according to the principle of sequential solidification

The cast steel shell shown in the figure is changed to the one on the right, with a uniform wall thickness of 76mm at the bottom of the shell, and the wall thickness is gradually increased upward until it is connected to the flange, which ensures that the shell solidifies in sequence, and no longer Shrinkage defects are produced.

2. Special casting

① Investment casting, which uses wax as a material to make molds, also known as "lost wax manufacturing", can cast various non-ferrous and ferrous metal castings.

② Metal mold casting, the model can be used repeatedly 40,000 times, the casting has good accuracy (reaching IT12~IT14), the surface is smooth, and it can be used with little or no processing, and can be mechanized production.

③ Die casting: liquid or semi-liquid metal is poured in the pressure chamber of the die-casting machine, filling the mold, and forming and crystallizing under high pressure. Commonly used die casting specific pressure is 5~150MPa, and the metal flow rate is 5~100m/s. High efficiency and easy automation, good product quality, less chip and chip-free machining, and low cost.

④ Low pressure casting.

⑤ Centrifugal casting: The molten metal is added to the rotating mold.