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Castings vs Foundry: What’s the Difference?

June 2, 2017

One particular technique that has been used from ancient to modern times is metal casting. Skilled metalworkers pour molten metal into a mold. The inside of this mold or “cavity”, contains the metal which will solidify upon cooling. To obtain the desired shape of the casting, the inside of the mold contains a “pattern”. As the metal cools, it solidifies into the shape of the pattern. The casting is then ejected or broken from the mold.

Over time, various combinations of metals were used to meet a castings desired metallurgical characteristics. Alloys were created by mixing various metal and non-metal content to enhance strength, toughness, durability, and surface hardness. Today’s industrial castings are typically iron castings or steel castings with varying ratios of additional elements.

In parallel to alloy discoveries, new processes emerged in castings. Two classes of casting methods came to be: expendable mold casting (non-reusable molds) and non-expendable mold casting (reusable molds). Expendable mold casting includes sand casting, plaster mold casting, shell molding, investment casting, waste plaster casting, and evaporative-pattern casting. Non-expendable mold casting employs methods such as permanent mold casting, die casting, centrifugal casting, and continuous casting. There are various advantages to each casting process depending on the object’s dimensional requirements, production repeatability, and physical properties.

What can be found in today’s foundry that creates castings?

workers tilting a foundry furnace during the casting process
First, foundries melt metal to extremely hot temperatures. This requires heating raw metal and/or alloying elements into molten form so it can be poured into molds.
Some metals discharge quantities of hydrogen during cooling. Hydrogen bubbles escape to the top of the surface at the moment of cooling and solidification. This will create porosity on the object’s surface and lead to mechanical and chemical deterioration of the object over time. To combat this, a foundry will employ various types of “degassing” equipment to measure and regulate the amount of hydrogen present in the object.
In order to create a casting from an original design, foundries require mold and pattern making equipment. Depending on the casting process involved, a foundry may offer several types of mold making systems. For example, sand casting requires specialized resin bonded sand molds. Investment casting requires the creation of wax patterns and ceramic molds. Die casting involves machining metals into molds using various alloys containing zinc, copper, lead, pewter, and more.
In foundry operations molten metal is transported, contained, or poured. Crucibles, robotic arms, and gravity induced pouring machines are used to move molten metal from one location to another. Metal workers will also pour molten metal by hand using ladles.
Once a mold solidifies, equipment is used to eject the final object from the mold. This requires the use of specialized cutting torches, saw blades, sledge hammers, or even knockout machinery to eject the casting from the mold.
Foundries also employ equipment used to heat treat metals in order to alter their physical properties. Using specific techniques in heating and cooling, a metal’s properties are manipulated through annealing, case hardening, tempering, and quenching.
Once the casting is ready, its surface properties still require treatment. Excess mold media such as sand or metal particulate need to be removed. In this case, various surface treatments are used. This can include high powered compressed air or surface blasting with beads, metals, or other media.
Now that the casting is clean, final finishing takes place. The finishing process involves equipment for grinding, sanding, machining, painting, and welding to achieve whatever is requested by the customer.
Foundries are simply factories that provide steel casting services.Castings are the end product created by foundries. The tools, techniques, and processes used to make castings were berthed under the roof of the foundry.

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