In theory, grey iron castings can be manufactured by almost any common casting process. But although grey cast iron is an ancient material and has been used in engineering construction for centuries, it was only recently that mankind started to understand the metallurgy of grey iron. The mechanical properties of grey iron depend not only on the composition but also on the casting practice, especially the cooling rate of the casting. Except for combining with iron to form pearlite in the matrix, all the carbon in grey iron exists in the form of graphite, which varies in size and shape. The presence of these flakes formed during solidification is characteristic of grey iron. The presence of these flakes also gives grey cast iron most of the desired properties.
Grey iron castings are used in many market sectors, including automotive, agriculture, machinery manufacturing, electronics, irrigation, ventilation, construction, construction, and transportation industries.
Iron castings are usually manufactured using multiple melting methods and produce different types of grey cast iron with different properties. Some common types of cast iron manufactured are grey cast iron, ductile iron, and malleable iron. The most commonly used castings are grey cast iron castings because of their inherent advantages. Grey iron castings are usually made by smelting pig iron, which is an alloy of iron and carbon. Grey cast iron also contains traces of phosphorus, sulfur, silicon, and manganese. The main reasons why grey iron castings have become popular choices are their cost efficiency and ability to be made into complex frames. Let's take a look at some of their basic characteristics, functions, and applications.
● High-pressure resistance:
grey iron casting has high compressive strength, about three times its tensile strength. This makes it ideal for large columns and pillars in large buildings.
● High damping capability and machinability:
Grey cast iron is suitable for all types of machine bases, cylinder blocks, and brake parts. Very good at reducing vibration, imprecision, and excessive wear on machinery and bearings.
● High oxidation resistance: grey iron castings are the ideal solution to overcome corrosion problems as the oxidation resistance prevents rust.
● Flexible grey iron casting applications:
300-grade grey iron is mainly used in the production of beds, gears, cylinder blocks, heavy machine tools, high-pressure hydraulic components, cylinder heads, bushings, piston rings, etc. Class 200 and Class 250 are most suitable for manufacturing cylinder bases and bushes, brake wheels, gearboxes, connecting plates, flywheels, and pressure valves. Classes 100 and 150 are commonly used to manufacture hammers, pipes, pulleys, protective covers, handwheels, bearings, and pumps.
Due to the microstructure of graphite, the solidification shrinkage of grey iron casting is also lower than other cast irons. During casting, silicon elements can promote good corrosion resistance and increase fluidity. Grey cast iron is also easy to weld grey iron and it has lower resistance and ductility compared to other cast iron. That is why this material has little resistance to impact and resistance to impact. Sand casting is the most common process on the market for grey iron castings. The sand as mold media processes affects the solidity rate for casting at a slightly similar rate, while the permanent molding process affects the structure and properties very significantly.
Grey iron castings with a certain hardness level are the easiest to machine among the widely used ferrous materials for construction applications. Grey cast iron is free to cut because the chips are small and can be easily removed. Moreover, chips can scratch the finished surface virtually without difficulty. The free cuts result from irregularly distributed graphite flakes, which break the matrix' continuity. While grey iron is processed without a coolant very successfully, it may be necessary to process it at higher processing speeds and with tight tolerance. The cooling fluid not only helps to remove chips but also controls the temperature of the casting, which is necessary for small tolerance work.
Although grey cast iron can be processed easily, it still encounters various machining problems, such as hard edges, shortened tool life, failure to obtain a satisfactory smooth surface, and difficulty maintaining the required dimensional tolerances. Some of these issues are caused by selecting the wrong grade of iron, casting defects, or wrong workflows.
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