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The Development of Casting, Manufacturing Process in Current Foundry

 

Mankind’s industrial rise would not have been possible without the evolution of metal working. The earliest evidence of copper working indicated our ability to manipulate metals into desired shapes. As civilization grew in trade and expansion, tools and techniques were required to form metal objects. Metalworkers grew in skill and technique; mastering the production in adornments, weaponry, artifacts, ships, and machinery. As centuries passed, various techniques in metal working were created to meet the demands of the industrial age. These processes eventually came together under one roof.

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 casting’s 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. With the advent of carbon steel castings, alloys containing different ratios of carbon are used to achieve specific properties. One example of carbon steel universally used in casting is ASTM A27 Cast Steel.

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.

A foundry is a factory that will house any combination of the casting processes mentioned above. Since ancient history, groups of metalworkers, metallurgists, engineers, artisans, and laborers worked together in a location that could accommodate their services. In 3000 BC the Mesopotamians discovered bronze by adding a small amount of tin with copper during smelting. The Egyptians of 1500 BC depicted tomb paintings with pictures of smelting operations, blast air, and crucibles filled with molten metal. In Ancient Greek artwork, craftsmen are seen working with hot furnaces and casting pits. For the modern day foundry, the same fundamental casting processes exist - but with advances in technology and production.

What can be found in today’s foundry that creates castings? Similar to a factory’s production line, the manufacturing chain is composed of nine primary sections:

1. 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. In order to achieve these temperatures, specialized furnaces are used. Foundries may house different furnaces based on the type of material or casting process involved.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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. To this day, the pillars of our industry depend on foundries to create castings of all sizes and for every sector of our society.

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