What is casting? Isn’t that the process of assigning roles for a play or a movie?
When used in the context of the manufacturing industry, the word refers to a process wherein liquid (molten) metal is poured into a mold containing a cavity in the shape of the desired finished product. After the material cools, the solidified part, known as a casting, is broken out of or ejected from the mold.
So what is sand casting, then? Sand casting is both the most widely used and oldest known casting process. It dates back to earlier than 1000 B.C., and although the technology has, of course, changed and improved, the basics remain the same as they were when ancient casters employed the process.
Note: sand is not the material being cast into a shape. That’s usually metal, but in sand casting, the molds are made from compressed or compacted sand. Sand is less expensive and more expendable than many other materials, and since the mold has to be destroyed in order to remove the casting, sand makes an economical choice for mold material. If you’re wondering what type of sand is used for casting, it’s usually silica sand mixed with a binder that helps the mold maintain its shape and hold up during the pouring process.
The Process of Sand Casting
What is the process of sand casting? There actually are several steps to the process:
- Making the mold– Creating a new mold for each casting is necessary since the molds are expendable and will be destroyed at the end. The caster pours sand into each half of the mold, and then sand is packed around what is called the pattern, which is a replica of the casting’s external shape. Removing the pattern creates the cavity into which the molten metal is poured.
- Clamping– Here, the mold is prepared for the pouring of the molten metal. Lubrication of the cavity facilitates removal of the casting. Cores made from sand prior to making the mold are positioned, and the mold halves are closed and clamped together.
- Pouring– Using a ladle, the caster pours molten metal that has been kept at a set temperature into the mold. An automated machine can also perform the pouring.
- Cooling– Once the molten metal enters the cavity, it will begin to cool and solidify. Until the cooling time elapses, the mold cannot be opened. It’s also important to keep parts of the casting from cooling too quickly because that can cause cracks, shrinkage, and incomplete sections.
- Removal– Also called shakeout, this step involves removing the casting by breaking the mold. Typically, a vibrating machine shakes the sand and casting out, hence the alternative term.
- Trimming– The final stages require trimming excess material via cutting, sawing, or a trimming press.
Applications: What Sand Casting Is Used To Make
Now that you have a basic understanding of what sand casting is, you might be asking “What is sand casting used to make?”
Sand casting is good for making use of many different types of alloys. The most common materials used are aluminum alloys, brass alloys, and cast iron and steel. This process also is good for casting with metals such as nickel, steel, and titanium that have high melting temperatures.
As to the actual types of products sand casting can produce, here are several:
- Connecting rods
- Cylinder heads
- Engine blocks and manifolds
- Heavy machine bases
- Housings for large equipment
- Transmission cases
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