Castings: production features
Foundries are engaged in the production of castings or cast parts. These products are in great demand in modern society, and in absolutely different spheres of human activity. Casting is the cheapest and easiest way to produce billets or finished parts with complex geometric shapes. It is used to produce castings weighing from a few grams to 300 tons and measuring from a few centimeters to two dozen meters.
The technological process itself takes place in stages:
- First, a mold is made for casting according to the model;
- Then cores are made (round clay cores to form inner holes in the casting);
- Metal is melted and poured into the mold cavity;After crystalliza
- ion, the ingot is knocked out of the mold;
- Cleaning of risers and gating system;
- At the end of the process, if necessary, the part is transferred for processing (mechanical, laser, thermal, etc.).
The main task of any foundry is to obtain castings that are as close in shape and size as possible to the parameters of the required product or part. At the same time, the last technological stage (machining) should not go beyond cleaning and grinding processes.
The majority of all castings for mechanical engineering and large-scale equipment are made of steel. The challenge for the molder is to choose an alloy based on its properties and cost.
Steel (which is an iron-carbon alloy) is ideal for making complex-shaped parts that are subsequently subject to stringent performance requirements – strength, impact toughness, and so on. Three types of foundry steel can be used here:
-with special properties.
The first type goes to the production of parts designed for mechanical loads (static, dynamic or vibration). These steels are classified according to their composition (carbon steel class and alloy steel class) and structural features (ferritic-pearlitic steel class and pearlitic steel class).
The second type is ideal for casting various cutting, stamping and measuring tools. Metals are classified according to their chemical composition. There are three classes: medium-carbon, high-carbon and alloy steels of the pearlitic, martensitic and carbide types.
Steels of the third type, having increased properties of resistance to corrosion, heat resistance, acid resistance, wear resistance, are used for products used in conditions of exposure to various environments, loads, temperature regimes. These steels are divided into two classes – ferritic and austenitic.
Processes and equipment
Steel is melted in special melting furnaces. From there it is liquid and transferred to the so-called pouring ladle, from which the metal is poured into molds or crystallizers in the plant. There the metal solidifies and takes the desired shape of the part, which is then sent for machining.
The pouring ladle has a refractory body lined with refractory bricks and a ceramic bowl-shaped bottom with a hole for pouring metal through it. The opening is closed and opened manually or with a remote-controlled hydraulic actuator.
The ladle is chosen according to its capacity (from 5 to 260 tons), taking into account the volume of the furnace and the slag layer, which usually reaches 100-200 mm. Large units assume the use of large-capacity buckets – from 350-480 tons.
Ladle molds are cast iron molds for casting. Their configuration depends directly on the type of steel used for casting, and their size depends on the weight of the ingot. Boiling steel is poured into molds with an enlarged bottom, and low-carbon steel with an enlarged top.
It is economically advantageous for production to get solid castings, as it significantly reduces labor costs, metal losses, casting time and the cost of refractory materials.