Sand casting is the most traditional casting method
Sand casting process is a casting method in which sand is used as the main molding material to prepare the mold. Sand casting is the most traditional casting method. Sand casting is still the most widely used casting method in casting production, especially for single-piece or small-batch castings, because of its own characteristics (not limited by the shape, size, complexity of parts and alloy types, short production cycle and low cost).
The basic flow of traditional sand casting process includes the following steps:
sand mixing, mold making, core making, molding, pouring, sand falling, grinding and inspection.
1. In the sand mixing stage, molding sand and core sand are prepared for molding. Generally, a sand mixer is used to put the old drawings and a proper amount of clay into the sand to stir.
2. In the mold making stage, molds and core boxes are made according to part drawings. Generally, wooden molds can be used for single pieces, plastic molds or metal molds (commonly known as iron molds or steel molds) can be made by mass production, and mold plates can be made by mass casting. At present, the molds are basically made of engraving machines, so the production cycle is greatly shortened, and it usually takes 2~10 days to make molds.
3. Modeling (core making) stage: including modeling (forming the cavity of the casting with molding sand), core making (forming the inner shape of the casting) and mold matching (putting the core into the cavity and closing the upper and lower sand boxes). Modeling is the key link in casting.
4. Melting stage: distribute the chemical composition according to the required metal composition, and select a suitable melting furnace to melt the alloy material to form qualified liquid metal (including qualified composition and temperature). Generally, cupola or electric furnace is used for smelting (cupola is now basically banned and electric furnace is basically used due to environmental protection requirements).
5. Pouring stage: the molten iron in the electric furnace is injected into the finished mold with a ladle. Pay attention to the pouring speed when pouring molten iron, so that the molten iron can fill the whole cavity. In addition, pouring molten iron is dangerous, so you need to pay attention to safety!
6. Cleaning stage: After pouring, after the molten metal solidifies, take a hammer to remove the gate and shake off the sand of the casting, and then use a sandblasting machine to carry out sandblasting, so that the surface of the casting will look very clean! The casting blanks with less strict requirements can basically leave the factory after inspection.
7. Casting processing. For some castings with special requirements or some castings that cannot meet the requirements, simple processing may be required. Generally, grinding wheels or polishing machines are used for processing and polishing to remove burrs and make the castings smoother.
8. Casting inspection, casting inspection is generally in the process of cleaning or processing stage, and unqualified ones are generally found and picked out. However, some castings have individual requirements and need to be checked again. For example, if some castings need a 5 cm shaft inserted into the central hole, then it is necessary to try the 5 cm shaft.
After the above eight steps, the casting is basically formed.
For the casting with high precision, machining is needed, because it does not belong to the casting scope and will not be described here. With the progress of casting technology, traditional sand casting is either improved or replaced by other casting methods. Continuous innovation is the eternal theme, which is the inherent quality and foundation that a foundry must possess!
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