Casting in sand models
This casting method consists of a series of working steps. To understand them, it is first necessary to understand the terminology, without which it is impossible to do without in production.
So, regardless of the casting method chosen in this or that case, in order to obtain castings you need special casting molds, the cavity of which will correspond to the configuration of the required part or, as it is also called – the model.
A model is – a metal or wooden part that has the configuration of the outer surface of the casting. And a casting rod is used to form the inner surface. It is installed inside the mold. It is an integral part of the mold. It is made from a special core mixture, which includes sand, bonding substances.
The space formed between the rod and the cavity of the mold is filled with liquid metal. After the metal hardens, you get a casting with holes, cavities, or other complex contours inside.
Shapes: the technology of manufacturing
A casting mold – is a production tool whose working cavity, when poured into it with liquid metal, forms a casting of a given configuration. Special molding mixtures are used to make such molds. Their components are sand, clay, water and binding materials.
The molds are made in several stages. A flask is placed on the pattern plate, and a filled frame, the height of which is equal to the degree of compaction of the molding sand in the mold. Then the flask and the frame are filled with the molding sand from the hopper. There it is compacted (different methods are used for this: manual, machine: pressing, shaking, sand molding machine) and the model is extracted from it. The result of these manipulations is the casting mold.
Mixtures: molding and core mixes
A molding compound is a multi-component molding material that meets all the conditions and requirements of the non-metal mold making process. This material is poured into so-called casting flasks. They are used as a result of model casts.
The casting flask is also a production tool that helps hold the molding compound in place while the molten metal is being made, transported and poured into the mold.
As mentioned above, molding and core sands consist of a number of components (sand, clay, binders) that have certain properties. Their extraction is carried out in pre-explored quarries. The main requirements to be met by the finished mixtures are good plasticity, flowability, gas permeability, high strength, non-stick coverage.
The last property for the production of steel castings must meet the highest indices. Therefore, to improve non-stick properties, ordinary clay is replaced by refractory clay. In order to obtain large-sized ingots, chromium ironstone is added to the molding mixture.
Rods: application, manufacturing
Casting cores are needed to form the inner surface of the casting. Special mixtures are used to make them. The mixture is compacted in the core box (manually or with special equipment). Volumetric cores with complex configuration are produced in separate parts, which are subsequently glued, assembled into blocks and installed in the mold.
To strengthen the strength and gas permeability indicators, rods are dried in special continuous dryers. At certain temperatures (from 150 to 300 degrees) during the drying process, the binder materials in the mixture are sintered, oxidized or, due to internal chemical reactions, the sand particles are glued together.
Sand casting process
This type of casting is a multi-step process. First the molds and cores are made, then they are assembled and poured with an alloy. In the last step, the castings are knocked out of the molds, cleaned and trimmed.
Splitting is done with pneumatic hammers and chisels, and air-arc cutting is used to remove castings. The purpose of the subsequent cleaning is to remove burrs (consisting of compound residues) from the surface of the casting. This step is performed in a blast chamber.
Burrs can occur on the surface of the ingot due to the penetration of liquid metal into the pores of the mold. To eliminate this defect, the mold cavity is coated with a special non-stick paint. To avoid gas pockets, which are a consequence of intense gas formation, so-called ventilation channels are made on the upper and lower half molds.
After cleaning, ingots go to the workshop for mechanical processing and to the warehouse in a clean condition.