What’s Cooking with Grey Iron Castings

The origins of grey iron casting

Cast iron, the base metal of grey iron, has a long history that touches every part of the world. The earliest versions of it were created for use as a farm and household implements. Though steel had been invented, it was too expensive for simple farmers. Cast iron, though not as durable, was the affordable choice.  In the 5th Century B C, the Chinese used it to make plows and pots. The Europeans discovered its use in the middle of the Renaissance and forged it into cannonballs.
The Chinese used cast iron as cookware in place of clay pots and hand-carved wood.
It was popular because of its durability and strength as well as its resistance to wear. During cooking, the heat from the fire spread evenly and equally over the surface, which enhanced meals and made food preparation more efficient and easier.
The initial use of cast iron cookware in Europe was as large pots or cauldrons that hung in the fireplace to make broths or stew. This method of cooking continued when Europeans migrated to North America and still existed in the early west. Like the Chinese, Europeans enjoyed the even distribution of heat that spread over a cast iron pot to completely cooking the food. When wood and coal stoves were invented, the huge pots from the fireplace were replaced with flat cookware.
The modern version of cast iron began to appear at the end of the 19th Century as flat-bottomed pans were a better fit for stoves. Every kitchen in America had an iron skillet, which was considered to be a standard for any chef. A hundred years later, original cast iron skillets are still in use.
With the advent of aluminum and stainless steel, after World War II, cast iron was replaced with lighter cookware that was designed for modern electric and gas stoves. The two major producers, Griswold and Wagner, were bought out by a larger company and disappeared off the industrial map.

Grey iron casting

Grey cast iron begins like all cast iron products with pig iron. What makes it different, and gives it its grey color, is the creation of graphite from the manufacturing process. Iron is produced by a mixture of carbon, silicon, and manganese with portions of sulfur and phosphorus. The process of making cast iron begins with iron ore being melted and formed into ingots or pigs. Since pigs or ingots still have impurities, they are reheated in a blast furnace and poured into molds. During this process, the iron sediments to the bottom of the mold leaving the impurities on the top in the form of slag. The slag is scrapped off leaving just the molten iron.
A critical part of cast iron production is the solidification of the metal during the cooling process. Rapid cooling produces a very fine grade while slow cooling forms a coarser type. When the molten iron is in the mold, it needs to cool evenly and achieve the same temperature in all sections. Unevenly cooled iron is very poor quality and unusable. The speed of the cooling process can be increased by the insertion of metal plates.
The grey quality of grey iron is created during the cooling process. The graphite flakes are created from carbon that develops from the mixture of raw materials combined to make iron and appear during cooling. The combination of iron ore and the other materials, as well as the casting process, resulting in grey iron.

Molding and forming grey iron casting

Grey iron is cast using two methods – mold or sand. Though these are the two primary types, there are different varieties within each type. How the iron is cast has an effect on its solidification as well as its structure and malleability.
Sand casting – To produce a mold using sand, a bonding material is added to the sand to make it firm and solid. In most cases, clay is mixed in before it is moistened with water. The resulting mixture is encased in a frame or mold box, also known as a flask. Patterns made of wood, metal, or plastic are pressed into the clay sand compound with the sand being compounded around it.  The patterns are made by specialists to exact specifications dictated by an engineer and have a set of rules regarding the type of mold for certain types of metal. Sizing is used to stabilize the sand so that it maintains its pattern once it has been packed down. As with other metal molding processes, there are two parts to the mold assembly that are closed over each other before molten metal is inserted. Any gas or steam in the mold either leaves through the sand or a riser, which is built into the pattern.
The completed mold is set aside to cool and solidify, which can be sped up by metal plates being placed in the mold. The original casting is purposely larger to allow for shrinkage of the part during cooling. When the mold has cooled enough, the sand is removed revealing a completed part. With iron, the part may still be hot and need to have heat treatments to relieve any stress from the cooling process and increase hardness.
Mold casting – Iron casting uses a metal mold, which can be expendable or not depending on the process used. The metal mold has a cavity that is in the shape and design of the part. Normally, gravity is used to put the molten metal in the mold. The process begins by heating the mold to avoid cracking it when the molten metal is poured as well as make for an easy flow. To keep the metal from sticking to the mold, it is coated with a wash. The pouring temperature varies depending on the metal to be molded. Grey iron is poured at 2500o F.
The key to metal casting is the pattern or mold. Permanent, reusable molds are made of a metal that has a higher melting point than the metal it will form. Since molten metal shrinks as it cools, molds are designed to account for this factor so that the final part is at the exact standards required.  Semi-permanent molds have similar use as sand castings and can be recycled at the end of the casting process.
Various metals can be added to the iron mixture to increase its strength since cast iron has tiny fractures that decrease its tensile strength and shock resistance. Controlling the size and shape of the graphite flakes helps in addressing these factors.

Uses of grey cast iron

Though steel and stainless steel have replaced many of the uses of cast iron, it is still used today but not in such great quantities as years ago. Corrosion and magnetic resistance are two reasons that cast iron is still used today as well as its long life. Cast iron skillets and pipes from hundreds of years ago are still being used.
The original use of cast iron as cookware continues to be popular today. As with the original, cooks like the even and equal distribution of heat. Once a cast iron skillet is seasoned, it has as much non-stick capabilities as pans coated with Teflon.  When a recipe calls for ingredients to be mixed on the stove and then placed in the oven, cast iron easily makes the transition without any extra steps. Skillets sold at the beginning of the 20th Century are still in use.
Cast piping has been a favorite of the construction industry for many years. Pipes made from cast iron have a very long usage life and dampen noise. As a safety feature, cast iron is non-combustible making excellent for fire suppression. There are places in the world where cast iron piping has been in place for over 300 years.
The first automobile engines were made from cast iron. Over the years, as it became necessary for cars to be lighter to increase mileage, manufacturers transitioned to aluminum. Recently, the auto industry is re-examining iron as a possible engine block because of its excellent strength.