Shelling and surface cleaning of castings
Casting group shell cleaning
Cooling of castings
After the shell is poured, the cooling time of the casting in the mold is related to the material, shape, size and production conditions of the casting. Generally, for alloy castings or materials that are prone to deformation and cracks and castings with complex shapes, the cooling time should be longer; for thin-walled small parts, the cooling time can be shorter.
When single-shell casting, when the shell temperature drops below 450 ℃, the shell can be cleaned.
For castings filled with sand for molding and pouring, the cooling time in the mold is as follows:
Alloy Casting Type | Natural Cooling Time of Mold / h |
Copper alloy castings | ≥0.5 |
Aluminum alloy castings | 1-2 |
Carbon steel castings | ≥2 |
Alloy steel castings | 2-3 |
Heat-resistant steel and heat-resistant alloy steel castings |
4-8 |
Shelling methods and characteristics of castings
Mechanical shelling
Working principle: The mechanical vibration method is used to make the casting mold group reach the purpose of clearing the shell under high-speed vibration impact. The power used for vibration is air pressure and electricity.
Features: The production efficiency is high, but the working conditions are poor, the noise and dust are large, and dust removal equipment and silencers are required. Castings with small holes, deep holes, deep grooves and complex inner cavities cannot be cleaned up.
Electrohydraulic sand cleaning
Working principle: The shock wave and impact pressure generated by the high-voltage discharge between the electrode and the casting (or between the electrode) in the water are repeatedly applied to the shell and core to clean the shell and core.
Features: low power consumption, high efficiency, low cost, no dust, and good working conditions. However, harmful CO, electromagnetic radiation, etc. will be generated during the cleaning process, and safety protection measures must be taken. It is mainly used for cleaning ordinary sand mold castings, and is not used much for investment castings.
High-pressure hydraulic sand cleaning
Working principle: Using a high-power hydraulic system, ordinary water is transformed into a high-speed jet with a pressure of up to 70 MPa or more through a nozzle, and sprayed onto the shell and core, causing the shell (core) to break into pieces or fall off.
Features: safe operation, no dust, high production rate, and can also polish the surface of castings.
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Surface cleaning of castings
After shelling, there are always mold shells and iron oxide scales on the surface of castings, especially castings with complex inner cavities, deep grooves, and blind holes, which must be cleaned on the surface to be cleaned. Cleaning methods include shot blasting, sand blasting, chemical and electrochemical sand cleaning, etc. (Our company mainly uses shot blasting and sand blasting methods)
Shot blasting cleaning
It can clean castings of different sizes and shapes, but it will reduce the accuracy and surface roughness of the castings. It is only used for investment castings with low requirements.
Sand blasting or shot blasting cleaning
Sand blasting (shot) cleaning is to spray iron shots (sand) with air (water) flow at high speed onto the surface of the casting under the action of compressed air or hydraulic power to remove residual sand, sticky sand or iron oxide scale. There are three types of sand blasting devices: suction type, pressure type and gravity type. This method can clean castings of different sizes and shapes, and generally does not reduce the accuracy and surface roughness of the castings. But a dust removal device is required.
Post time: Jan-10-2025