“The most important aspect in guaranteeing the reliability of a cast component is a casting quality verification process.”
In accordance with the cast industry standards, specific industry regulations, and/or the customer’s specified quality instructions, visual inspection is required to ensure genuine casting quality from start to finish. In terms of casting quality this means that we make sure parts are properly filled with metal (no cracking, tearing, holes or voids, non-fill, etc.). Our casting quality control experts also meticulously inspect each part, making sure there are no distortions or bends before moving forward in the casting quality process. During the final phase of inspection, parts are inspected and compared to the casting quality control plan and written process instructions. Lastly, the casting quality results are documented and stored for future use by production department staff and process engineers.
MOULDING & CLOSING
“Moulding is the process of making pliable raw material using a rigid frame called a mold.”
There are several types of molding methods. These include:
In general, we can distinguish between two methods of sand casting; the first one using green sand and the second being the air set method.
These castings are made using sand molds formed from “wet” sand which contains water and organic bonding compounds, typically referred to as clay. The name “Green Sand” comes from the fact that the sand mold is not “set”, it is still in the “green” or uncured state even when the metal is poured in the mould. Green sand is not green in color, but “green” in the sense that it is used in a wet state (akin to green wood). Contrary to what the name suggests, “green sand” is not a type of sand on its own (that is, not greensand in the geologic sense), but is rather a mixture of:
- silica sand (SiO2), chromite sand (FeCr2O4), or zircon sand (ZrSiO4), 75 to 85%, sometimes with a proportion of olivine, staurolite, or graphite.
- bentonite (clay), 5 to 11%
- water, 2 to 4%
- inert sludge 3 to 5%
- anthracite (0 to 1%)
“The preparation of molten metal for casting is referred to as melting.”
Melting may be done by gas or electricity. Various methods of pouring the molten metal are in use (e.g. gravity pouring, bottom pouring, vacuum or pressure assisted pouring).
The melting process begins with the metal specification for the casting, determining the type of scrap metal to be used to ‘charge’ the furnace. Once charged, the furnace uses electrodes, each supplying roughly 6,500 amps of electricity, to melt the scrap metal. Samples are taken at various points in the melt process, to ascertain the chemical composition of the molten metal. Using a spectrometer as a guide, alloys are added to the furnace to bring the molten metal to the proper specification.
At a temperature of around 3,000° F the metal reaches the desired specification. It is then poured into a preheated ladle for transfer to the pouring lines. At the pouring lines, molten metal is ‘poured’ into the requisite molds. Due to the lifting pressure of molten steel, molds will often be ‘weighted’ or ‘clamped’ to prevent them from separating at the Cope/Drag meeting point. Thereafter, the mold is allowed to cool for approximately 30 minutes before it is taken to the shakeout. Poured molds are then dumped into a vibrating conveyor, wherein they are broken up by the vibration, exposing the casting for removal.
Finally the sand from the mold is separated and processed through a reclamation system for further use.
“Heat Treatment is a method of controlled heating and cooling of metals to alter their mechanical and physical properties without changing the product shape.”
Heat Treatment is a method of controlled heating and cooling of metals to alter their mechanical and physical properties without changing the product shape. The technique involves the use of heating or chilling, usually to extreme temperatures, to attain a desired result, such as – hardening or softening of a metal. Some of the common techniques of heat treatment include annealing, case hardening, precipitation strengthening, tempering and quenching. As a matter of fact, the term heat treatment applies only to processes where the heating and cooling is done for the basic objective of altering the properties intentionally. Heating and cooling, however, sometimes occur as incidental phases of other manufacturing methods such as hot forming or welding.
Primarily associated with increasing the strength of material, heat treatment can also be used to change certain manufacturing objectives such as improved machining, improved formability, and to restore ductility after a cold working operation. Hence it is a very enabling manufacturing process, which can not only help other manufacturing methods, but can also enhance product performance by increasing the strength or other desirable characteristics.
The four basic types of heat treatment processes used today are –
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