The article briefly explains about traditional casting, which is one of the popular casting methods.
Nowadays, foundries adopt various metal casting technologies such as sand casting, traditional casting, furan casting etc. Each of these methods maintains its own distinctive characteristics and is suitable for casting. ... several types of products.
What is traditional casting process?
In this method, the molded sample is made from foam, wood or CNC aluminum.
How is traditional casting process?
Making core: core mold, core bone, air outlet, core forming mix are required
Core forming mixture includes: sand + glass water + CO2 gas (hard, hard to remove core), sand + water + clay powder + sawdust (moderate hardness, easy to remove from casting) ⇒ After making core is put into the drying oven.
The casting mold will be equipped with a wide sand base, the casting sand is mixed with clay powder, coal powder, additives and water in suitable proportions.
When the sand base has met the standards for casting, the mold will be placed in the foundation half below the ground surface, half will be placed in the casting box.
When workers put the sand into the compaction, create a pouring system, close the hole, and apply a heat-resistant chalk layer to help the casting sand reduce sticking to the casting when cast iron. Then take the sample out of the mold, put the core into the mold (if necessary) and finally cover the upper mold to match the sand bottom mold.
Each finished casting mold, when created, will be pressed with 1 or more objects with a total weight equal to or greater than the casting to avoid deformation as well as weight errors during casting.
Cooking: the furnace and the electric furnace are the two most commonly types used when cooking cast iron.
The electric furnace can apply the analyzer and add the chemical composition of cast iron according to the proportion of each cast iron, as well as perform the process of transforming cast iron from gray cast iron to spherical cast iron. But there are investment costs – high operating costs, once cooking should not be less than 10 tons, information about the types of electric furnaces you are interested in.
Low cost, easy to invest, usually to cook gray cast iron a batch can cook from 1.5 tons to more than 10 tons, but the quality of cast iron water depends a lot on the ratio and quality of coal, the quality of the cast iron, as well as the experience of the cook.
To cook a batch of gray cast iron from the oven you need to prepare:
- Oven (made from iron shells with heat-resistant bricks)
- Ice bar 20÷25%.
- CaCO3 limestone to dilute the slag floating on the surface of the cast iron water flowing out of the furnace by the furnace's slag discharge pipe.
- Pig iron, machined iron, Raw materials (waste products + filling system, steam beans, hot beans).
Casting iron into the mold: with traditional casting technology and cast iron casting, the machine mainly uses 3 types of pouring buckets depending on the weight of the casting.
Ladle: Use a solid iron Ø 18-25 to attach a cup used to store molten cast iron that has been covered with clay. The amount of cast iron contained in the ladle has a weight of about 15kg, 1 user.
Tilt bucket: Consists of 2 iron bars with Ø 25 attached to a cylindrical container with a diameter of 400 and a depth of 300, the inside is covered with clay. The amount of cast iron contained in the dipper weighs about 50kg, 2 people carry.
Tilted bucket with small roaster: It is a round cylindrical iron barrel lined with heat-resistant brick and lime mortar. There is gear attachment and tilt movement by turning the handlebars. Carry out transporting this bucket by lifting crane. The amount of cast iron contained in the bucket weighs about 100-200 kg, 1 operator.
Casting iron into the mold is an extremely important stage of all casting technology, to ensure a gentle and quick pouring process. The bucket must be completely dried to avoid the wet bucket phenomenon, which reduces the temperature of the liquid metal, causing oxidation and pitting.
Moreover, the water in the bucket will evaporate causing the liquid metal to bubble vigorously and shoot out.
Cool, unload the casting from the mold, clean and inspect the casting
Cooling time for castings depends on the average product size from 12h - 48h, small products cool down quickly in just a few hours. With cast iron furniture, thin details such as the table top, if removed from the sand early to cool, may be bent.
When water is poured into the hot casting to cool, it will cause gray cast iron to turn white.
When the product is cooled down, it will go to the sand cleaning stage with a ball gun, steel balls with a size of Ø2 will shoot into the product, causing the sand to be removed from the casting.
Inspection of castings (molded products)
Appearance Check: Appearance, Defects (Visual), Cast Surface Gloss
Dimension check: Casting wall Warping, deformation
Check the fracture surface: there is whiteness (with gray cast iron when cast, the fracture surface is gray, with white cast iron, it will be white).
The product after inspection will be grinded to clean the excess cast iron and mechanically processed on the lathe.
After completing the process on the product, it is painted with anti-rust paint or finished by electrostatic painting technology.
With traditional gray cast iron casting technology: it is possible to cast a variety of products from 1 ton or less with not too strict requirements on surface as well as weight tolerance.
This method has a lower investment cost than the other methods and is often used to cast products for daily life, traffic, and machine parts such as: installing gas pits, cast iron chairs. pellets, decorative light poles, cast iron tables and chairs, loads, cast iron weights, gas stoves, pulleys, ...
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