MetalTek offers more metal casting process diversity. Your ability to source centrifugal, sand, investment, HPLT, or continuous cast products from a single company is not available anywhere else in the world. Not sure which precision casting process is right for your components or application? Read the below article on the basics of casting and feel free to contact us if you have questions. We would love to become your metals partner Because You Demand More Than Metal.
Today, metal casting is a complex and intricate process which requires exact chemistry and flawless execution. While current methods may be relatively new when compared to the history of human civilization, the first casting of metals can actually be traced all the way back to around 4000 BC. In those times, gold was the first metal to be cast because of its malleability, and back then, metal from tools and decoration was reused because of the complications of obtaining pure ore. However, a copper frog is the oldest existing casting currently known; it is estimated that it was made in 3200 BC in Mesopotamia (present-day Iraq). Bronze then became the metal of choice to cast with because its rigidity compared to gold, and it was melted and cast into various tools and weapons by way of permanent stone molds. The process of casting made its way to Egypt by 2800 BC, and effectively performing this process was tremendously influential on their gain of power during the Bronze Age. Around 1300 BC, the Shang Dynasty in China were the first to utilize sand casting when melting metals. Then around 500 BC, the Zhou Dynasty introduced cast iron to the world, but it was used mostly for farmers. Cast iron did not become a military tool or decoration until the Qin Dynasty almost 300 years later.
Fast forward almost 1000 years, religion played a major role in advancing and innovating foundry technology during that time. Extraordinary evolution came from the construction of cathedrals and churches, melting and mold-making processes advanced rapidly to keep up with the demand of the dominant Catholic church. This also marked the boundary of the period between casting for the purpose of art and viewing casting as a technology with unknown potential. It was not too long after the advancements of bell casting that, ironically, a monk in Ghent (present-day Belgium) was the first to cast a cannon in 1313 with the same technology. Over 150 years after the first cast cannon, Vannoccio Biringuccio, also known as the father of the foundry industry, recorded the first written account of casting and foundry practices. His work, De Le Pirotechnia, was separated into 10 sections that covered many subjects including minerals, assaying, smelting, alloys, casting, as well as alchemy; it is one of the oldest technical documents still around from the Renaissance era.
If you Google “Casting Terminology”, you get over 7.6 million results. Some of the results will show you a never-ending list of terms so here is a reduced list of select terms that you should be familiar with as a current or potential user of metal castings. To see a complete list of terms on our website, visit us here.
Glossary terms and definitions provided courtesy of the Steel Founders' Society of America.
Aging: A change in properties of metals and alloys which occurs slowly at room temperature and will proceed rapidly at higher temperatures. The change in properties is often, but not always, due to a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy.
Annealing: Heating to and holding at a suitable temperature, followed by cooling at a suitable rate to lower the hardness or alter other mechanical or physical properties.
Argon Oxygen Decarburization (AOD): A secondary refining process in which argon, oxygen and nitrogen are injected into a molten bath of steel. The AOD process improves metal cleanliness and thus gives superior mechanical properties.
Centrifugal Casting Eliminates Mid-wall Defects
- The centrifugal process does not rely on discrete risers or feed points to ensure the absence of trapped porosity. Rather, the inner diameter remains fully liquid during the solidification process, resulting in a continuous supply of metal to feed areas of contraction.
- Unlike conventional gravity or static castings that chill from both the inside and outside surfaces and risk trapping mid-wall shrinkage, centrifugal castings solidify from the outside surface inward. The result is a part consistently free of shrinkage cavities, gas pockets, and blowholes.
Centrifugal Casting Controls Impurities
- Unique to the centrifugal process is the high force that effectively isolates less dense substances in the casting’s bore area. These impurities are later machined away, leaving a defect free part. Molten metal is fed into a rotating mold where a centrifugal force of up to 100Gs is applied to the metal. Centrifugal force is critical for this process. The Gs produced are dependent on the RPM and diameter of the die.
- The centrifugal force pushes high density metal against the mold sidewall while lower density components migrate or "float" toward the I.D. These lower density items include metal oxides, sulfides, gas, and other impurities that would otherwise have been inclusions in the casting. This phenomenon is termed “secondary refining”.
Centrifugal casting is a process that delivers components of high material soundness. As a result, it is the technology of choice for applications like jet engine compressor cases, hydro wear rings, many military products, and other high-reliability applications. It has also proven to be a cost-effective means of providing complex shapes with reduced machining requirements and lower manufacturing costs as compared to forgings and fabrications.
In the centrifugal casting process, molten metal is poured into a preheated, spinning die. The die may be oriented either on a vertical or horizontal axis depending on the configuration of the desired part.
By spinning a mold while molten metal is poured into it, centrifugal force acts to distribute the molten metal in the mold at pressures approaching 100 times the force of gravity. The combination of this applied pressure and the engineering mechanics of controlled solidification and secondary refining produces components of superior quality.