- Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon. It is made by re-melting pig iron, often along with substantial quantities of scrap iron and scrap steel, and taking various steps to remove undesirable contaminants, which weaken the material.
- Carbon and silicon content are reduced to the desired levels, which may be anywhere from 2% to 3.5% for carbon and 1% to 3% for silicon depending on the application. Other elements are then added to the melt before the final form is produced.
- Cast irons melt more easily than similar alloys. The iron-carbon eutectic point lies at 1403 kelvins and 4.3 mass % carbon. Since cast iron has nearly this composition, its melting temperature of 1420 to 1470 K is about 300 K lower than the melting point of pure iron.
- Cast iron tends to be brittle, unless the name of the particular alloy suggests otherwise. The color of a fracture surface can be used to identify an alloy: carbide impurities allow cracks to pass straight through, resulting in a smooth, "white" surface, while graphite flakes deflect a passing crack and initiate countless new cracks as the material breaks, resulting in a rough surface that appears grey.
- Cast iron is a heavy and durable material and is very well suited to furniture which is intended to remain in one position. Since Cast Iron tends to strong in compressive strength, many manufacturers used cast iron for supports, timber, slats and marble for table tops. Cast iron is used to manufacture chairs, benches, tables, urns and planters and other outdoor furniture.
- Cast iron is Heavy and ornate. Weighing three times more than an identical piece in cast aluminum, cast iron is popular for public areas because it weighs too much to be easily pilfered.
- Although all iron furniture requires occasional touch-up, if furniture has a quality coating, it requires less maintenance even use for decades.
Iron is most commonly melted in a small blast furnace known as a cupola. After melting is complete, the molten iron is removed in ladled from the cupola furnace.
This process is thought to have been devised by the late 18th century iron master John Wilkinson, whose innovative ideas revolutionized the field of metallurgy.
Previously, iron was melted in an air furnace, which is a type of reverberatory furnace. Cast iron products are manufactured by melting pig iron and pouring the molten metal into a mould, allowed to cool in the shape of the form, and then ejected to make a fabricated part, always formed by pressing a patterned shape into sand. It is a classic manufacturing procedure, dating from the industrial revolution.
Casting is a process by which a fluid metal is poured into mold, allowed to cool in the shape of the cavity of mold, and then ejected to get the casting of desired shape. Four main elements are required in the process of casting: pattern, mold, cores, and the part.
To create a cast iron product, several precise steps are involved as under:
The Pattern:
The pattern, the original template from which the mold is prepared, creates a corresponding cavity in the casting material. It is necessary to prepare artistic, sharp design prototype of the product. This is called a "pattern". The pattern creates, in every detail, the piece to be cast in iron. It is made slightly larger than the desired size of the finished piece, to allow for the shrinkage of iron as it cools.
Mold:
The prototype or pattern is pressed in the molding box filled with sand. A pattern is than withdrawal carefully to create the cavity exactly as the shape of pattern. The sand surface is than coated with various materials like graphite powder etc to get desired finished surface of cast iron.
The molds are made in two halves. A gate is provided in the mold for pouring liquid metal into the chemical. Two halves now join together and the mold is ready for pour. Sufficient care is taken to make sure that impressions on both halves of mold are matched when joined. Then match the sand impression of the front of casting with the impression of the back making the finished mold.
Molten Iron:
Pig iron can be melted in cupola furnace either gas, electric or cupola furnace. Liquid metal is than removed from the furnace into ladle and poured quickly into the molds.
Casting:
Sufficient time is required to liquid metal get solidify. Solidify metal is than eject from the mold and clean. The excess metal is cut or ground to get the desired shape of casting. This casting is now ready to use for further process can be a part of furniture.
Though it is difficult to weld cast iron at normal temperature it can be weld after overheated to a temperature of about 450°C followed by slow cooling after welding. Gas welding with cast iron rod is ideal to repair minor detects.
New welding technology now allowed welding cast iron at normal temperature with the aid of low heat electros in care of cast iron decorative products. New technology of welding is used to weld different piece together to produce different designs.
Historically Cast Iron earliest uses included cannon and shot. In England, the ironmasters of the Weald continued producing these until the 1760s, and this was the main function of the iron industry there after the Restoration, though probably only a minor part of the industry there earlier.
Cast iron pots were made at many English blast furnaces at that period. In 1707, Abraham Darby patented a method of making pots thinner and hence cheaper than his rivals could.
 In 1770s the use of cast iron began for structural purpose when Abraham Darby III built the Iron Bridge. This was followed by others, but not initially in great numbers.
Another important use of cast iron was in textile mills. The air in these contained flammable fibers from the cotton, hemp, or wool being spun. As a result, textile mills had an alarming propensity to burn down.
The solution was to build them completely of non-combustible materials, and it was found convenient to provide the building with an iron frame, largely of cast iron.
During the Industrial Revolution, cast iron was also widely used for the frame and other fixed parts of machinery, including spinning and later weaving machinery in the textile mills. Cast iron became a widespread material, and many towns had foundries producing machinery, not only for industry but also agriculture.
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