Gray Iron Castings for Any Industry

Gray Iron Castings

Gray Iron (or grey iron) is the most common type of ferrous cast material in the world. It is named after the gray color of the fracture surfaces created by it, which is caused by the presence of graphite. Gray iron is commonly used in static castings where the rigidity or stiffness of the part is more important than the tensile strength or elongation, such as engine blocks, various housings, valve bodies, mold castings, and so on.

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Applications of Gray Iron Castings

Gray iron is extensively used across various industries due to its excellent properties and cost-effectiveness.

• Engine Blocks: Providing the necessary stiffness and durability.
• Housings: Ideal for various mechanical housings and casings.
• Valve Bodies: Common in industrial applications requiring rigidity.
• Mold Castings: Used in foundry molds and other applications.

Common grades of gray iron include Class 30, Class 40, and Class 50.

Gray Iron Chemical Composition

A normal chemical composition for a graphitic gray iron microstructure for grey iron castings is 2.5 to 4.0% carbon and 1 to 3% silicon by weight. Graphite may occupy 6 to 10% of the volume for the material. Silicon is important as opposed to white cast iron, because silicon is a graphite stabilizing element in cast iron, which means it allows the alloy to produce graphite instead of iron carbides; at 3% silicon almost no carbon is held in chemical combination with the iron. Another factor affecting graphitization is the solidification rate; the slower the rate, the greater the time for the carbon to diffuse and accumulate into graphite. A moderate cooling rate forms a more pearlitic matrix, while a fast cooling rate forms a more ferritic matrix. To achieve a fully ferritic matrix the alloy must be annealed. Rapid cooling partly or completely suppresses graphitization and leads to the formation of cementite, which is called white iron.

Benefits of Gray Iron Castings

The unique composition and properties of gray iron make it highly beneficial for various applications.

1. Machinability: Easily machinable due to the presence of graphite flakes.
2. Damping Capacity: Excellent vibration damping properties.
3. Cost-Effective: Economical for producing large and complex parts.
4. Thermal Conductivity: Good heat dissipation characteristics.

The graphite takes on the shape of a three-dimensional flake. In two dimensions, as a polished surface will appear under a microscope, the graphite flakes appear as fine lines. The graphite has no appreciable strength, so they can be treated as voids. The tips of the flakes act as preexisting notches; therefore, it is brittle. The presence of graphite flakes makes the grey iron easily machinable as they tend to crack easily across the graphite flakes. This material also has very good damping capacity and hence it is mostly used as the base for machine tool mountings.

Uses of Gray Iron Castings

The versatility of gray iron allows it to be used in a wide range of applications, balancing strength and cost.

• Cylinder Heads and Casings: Providing strength and stability in engines.
• Engine Blocks: Commonly used in automotive and industrial engines.
• Pressure Containing Applications: Suitable for parts that need to withstand pressure.

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What is Cast Iron?

Cast iron is an iron-carbon alloy with a carbon content greater than 2.11% (generally 2.5-4%). It is composed primarily of iron, carbon and silicon as the core elements and may including manganese, sulfur and phosphorus as impurities. Sometimes alloying elements may be added in order to enhance mechanical or chemical properties of cast iron parts.

History of Cast Iron

Cast iron has its roots in China in the 4th century BC and is defined as an iron alloy with an extremely high carbon content – typically 2-4%. To produce cast iron, melting iron ore into liquid iron and then adding carbon at appropriate times is involved. Due to its good fluidity, casting performance, and economic advantages, cast iron can then be used in manufacturing mechanical components and daily necessities.

Cast iron was first utilized in China during the Zhou Dynasty during the Spring and Autumn and Warring States periods, during which its technology flourished rapidly. People then started mass producing cast iron tools and weapons, such as iron plows and swords from this material. By the Han Dynasty, cast iron technology had reached its full potential, being employed not only for producing daily necessities like pots and ironware but also artworks such as potters’ wheels.

Cast iron technology first appeared in Europe during the Middle Ages. However, production only truly began in earnest during the 15th and 16th centuries—especially during Britain’s Industrial Revolution, when cast iron became widely utilized for the construction of bridges, railways, machinery, etc.

At the close of the 18th century, Henry Scott made significant advancements to improve both the quality and production efficiency of cast iron production. The ironmaking furnace he invented can continue producing high-grade iron which played an instrumental role in industrial revolution applications of cast iron. Over time, with the advancement of technology and continued application, cast iron has since found application across industries like construction, industry, and transportation – as evidenced by continued global applications today.

Cast iron has long been recognized for its distinctive properties and economic advantages. Even nowadays, it is still one of the main metal casting material used in China foundries like CFS Foundry.

How Is Cast Iron Made?

Cast iron is manufactured through a casting process that involves several critical steps. The final cast iron parts should meet the desired dimensional accuracy and properties from each drawing. At CFS Foundry, we start the manufacturing process with the selection of raw materials. The materials are selected following the type of cast iron being produced, and the composition must be carefully inspected by spectrometer. This step is very critical, which can effectively avoid the error of material compositions.

Then, the liquid iron metal is then melted in a furnace at a high temperature, typically ranging from 1,150℃ to 1,200℃, to achieve a liquid status for further pouring job. After reaching the desired temperature, the moten iron is treated to remove impurities. This purification step can help to achieve the required quality and properties of the cast iron parts. For ductile cast iron, magnesium is added to transform the carbon into spherical graphite nodules, which can help to improve the material’s ductility.

Finally, the molten cast iron is poured into mold, which is designed to match the exact shape of the final product. Once cooling and solidification, the castings are removed from the molds. After casting, cast iron pieces may still require some post-processing operation, such as heat treatment to improve mechanical properties, machining to achieve precise dimensions and higher surface finish. Through this intricate steps, CFS Foundry ensures the production of high-quality cast iron products to meet the specific specifications.

Types of Cast Iron

Cast iron is an iron-carbon alloy with carbon content exceeding 2%, available in various types with different compositions and properties. Here are the common 4 types of cast iron:

Gray Cast Iron

Gray cast iron is the most frequently type of cast iron. Due to the presense of graphite flakes in its composition, gray cast iron is named for the gray color of the fracture. This cast iron type offers excellent compressive strength with limited brittleness and excellent machinability. Therefore, it finds widespread application in engine blocks, pipes, and cookware production.

Ductile Cast Iron

Ductile cast iron (nodular cast iron), also referred to as nodular iron, features nodules of graphite nodules that provide flexibility and toughness compared to gray cast iron, making the material less brittle overall. Due to this feature, it offers superior tensile strength and impact resistance, making ductile cast ideal for applications requiring high strength or toughness such as automotive components, gears, crankshafts etc.

White Cast Iron

White cast iron features high levels of carbon content and has an eye-catching white, shiny appearance due to this. However, unlike gray cast iron, which contains graphite for carbon absorption purposes; instead, it utilizes cementite (iron carbide). White cast iron’s hard and wear-resistant surface makes it suitable for many wear-intensive applications, including manufacturing mill liners and grinding balls.

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Malleable Cast Iron

Malleable cast iron is created through heat treating white cast iron to alter its carbon molecules into irregular nodules instead of flake shapes, increasing ductility, toughness, and malleability by changing how carbon bonds to form irregular nodules instead. This process increases malleability while lessening brittleness to produce malleable material that is easily machined, welded, or formed into various shapes, making this material suitable for applications requiring strength with flexibility, including pipe fittings, automotive parts, or agricultural equipment manufacturing.

Advantages of Cast Iron

• Good Castability: Cast iron has excellent fluidity after melting, enabling it to be cast into complex shapes with intricate details, which is suitable for casting intricate designs or components.
• High Wear Resistance: Cast iron, especially white cast iron, can provide excellent wear resistance for the hard carbides in the structure .
  Excellent Machinability: The graphite in cast iron, like a natural lubricant, can reduce wear when working and enable easier machining. Gray cast iron, with its graphite flakes, offers superior machinability compared with other cast iron types.
• Compression Strength: Like cast steel, cast iron also has good strength, which is ideal for buildings and structures, in which compressive loads are required.
• Low Cost: It is generally less expensive than cast steel or cast aluminum, making it a cost-effective option for many applications.

Disadvantages of Cast Iron

• Brittleness: Although cast iron has good strength, it is relatively brittle and may fracture under shock or pressure, so it is not suitable for applications where toughness is critical.
• Prone to Rusting: Cast iron is very easy to get rusted due to the high Fe content, so it is usually surface painted or plated to protect from rusting.
• Weight: Cast iron is relatively heavy, when weight is a concern, cast aluminum can be an alternative choice.

Surface Finishing Options of Cast Iron Parts

Like other cast metal parts, cast iron parts also require surface treatment to improve surface quality or corrosion resistance. There are various surface finishing methods available, such as shot blasting, painting, powder coating, electroplating and so on. CFS Foundry understands process and advantages of each surface finish way, and can recommend a suitable suitable method following the specific application of cast iron parts. Below are the most common surface finishing methods for reference:

Shot Blasting

Shot blasting is the basic surface finishing process for cast iron parts. If there is no special surface treatment requirement, casting manufacturers usually perform shot blasting process to remove the impurities, rust, scale, and other contaminants. It is operated by propelling a stream of abrasive material against the surface of a cast iron part under high pressure. The main advantages of shot blasting is its low cost and can creat a ratively smooth surface. After shot blasting, the residual compressive stress will be generated on the surface of the parts, and the fatigue strength of the cast iron parts will be significantly improved, so as to enhance the durability and crack propagation resistance of the parts.

Painting

Painting is also a common finishing process to form a protective layer available in different colors, such as black, red, green, blue, grey, etc. It is formed by applying a liquid or powdered paint on the surface of cast iron parts. This surface finishing type can not only improve the appearance, but also improve the corrosion resistance of iron castings. So, painting is a cost effective choice for applications in harsh conditions. CFS Foundry has in house painting workshop to coat cast iron parts with several colors.

Powder Coating

Similar to painting, powder coating is also a color coating process available in multi-colors. It is a process by spraying powder material onto the surface of cast iron parts, then achieving a uniform, durable and attractive finish. Powder coating offers more advantages than painting. For example, it can provide a thicker and more uniform surface quality. Besides, it is more environmentally friendly due to less volatile organic compounds (VOCs). Moreover, powder coated finish is more durable and resistant to corrosion, making it ideal for cast iron parts that require a high level surface finish than painting. Of course, the cost is also slightly higher than painting, but is affordable.

Electroplating

Electroplating is a surface finishing process in which a thin layer of metal atoms is deposited to the surface of cast iron parts through electrolysis. The most common electroplating for cast iron is zinc plating. By adding a layer of zinc, the surface of cast iron parts can achieve a shiny and refletive finish. Futhermore, after electroplating, both the surface hardness and corrosion resistance is improved. Besides, it can also help to improve the electrical conductivity of cast iorn parts. However, its cost os higher than other finishing ways, so electroplating is suitable for parts used in high corrosive environments.

How Cast Iron Compares with Other Materials

Common Cast Iron Applications

For excellent durability, wear resistance, and great machinability, cast iron is a versatile material for casting production, making it suitable for a wide range of applications. Here, we would like to summarize the most common application of cast iron parts.

Automotive Industry

Cast iron has widely used in automotive industry, as it can withstand high temperatures and pressures while remaining cost-effective for manufacturing automotive components. Typical cast iron automotive parts are: engine blocks, cylinder heads, brake rotors, gears and other key components.

Construction Industry

Cast iron is also a popular material in the construction of buildings, bridges and pipes for its good strength and deformation resistance. So, cast iron is a ideal to cast architectural components as well as pipe fittings.
CFS Foundry can also produce cast iron anti-parking bollards at a competitive price.

Cookware

One of the most common uses of cast iron is in the kitchen. It’s better to cook with cast iron because it won’t leach any toxic chemicals and heavy metals into your food. In addition, compared to aluminum and stainless steel, cast iron has a non-stick surface and can use more radiant heat for thorough cooking. You can also use cast iron cookware on an outdoor grill or campfire.

Pump & Valves

Cast iron is a preferred material for manufacturing pumps and valves. This is mainly due to its comprehensive advantages of cast iron, including: excellent mechanical properties, durability, cost-effectiveness, and versatility. CFS Foundry can not only produce valve and pump parts by iron casting, but also offering some hydraulic components in cast iron.

Heating and Cooling Systems

Radiators and heat exchangers made from cast iron have been used for decades, thanks to their durability and excellent heat diffusion properties. Cast iron stove and fireplace inserts are also popular for their ability to provide sustained heat over long periods.

Outdoor Furniture and Decorative Application

Cast iron’s ability to be cast into intricate designs makes it a favorite for outdoor furniture and decorative items, such as benches, lamp posts, and garden statues. Its resistance to weathering allows these items to endure harsh outdoor conditions.

Conclusion

Cast iron is a metal material types allowing for creating complex shapes of products, which are widely used in various industries. Compared to other cast metals, this type of material is the cheapest and cost effective for some projects. CFS Foundry are able to customize cast iron components by sand casting or lost foam casting process. If you have any inquiry on iron casting, pls contact us to request a fast quote!

FAQs

1. Why is Cast Iron Commonly Used?

Cast iron is highly durable, offering excellent wear resistance and heat resistance. It also has superior machinability and the casting process is also relatively simple, making it ideal choice for a wide range of applications.

2. How to Protect Cast Iron from Rusting?

The cheapest way to protect cast iron from rusting is anti-rust oil painted. Besides, other surface finishing options, such as painting, powder coating or zinc plating can also be considered, depending on the usage of the parts. CFS Foundry can deal with several surface finishing options for cast iron parts.

3. How to Order Cast Iron Parts from CFS Foundry?

It usuallly takes several steps before delivering cast iron parts. To start, purchasing companies should first provide the CAD drawings as well as other related information, such as material grade, machining areas if necessary, then we can quote and produce accordingly!

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