While manufacturing of good quality gray cast iron is relatively easy as compared to other alloys, it requires skill and experience to produce quality components that are accepted internationally. India has the inherent advantage of low labour cost. Coupled with the fact that Indian foundries are progressive, the grey cast iron from India is at par with the best in the world. It is therefore outsourced by companies in U.S. and European countries that want good quality.
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Casting is a procedure to manufacture finished steel and iron products and components in a foundry. It uses moulds to shape the molten metal in the desired shape. Casting offers exceptional capability for design details and customization. What makes casting popular is that it can eliminate the requirement for added assembly and fabrication. Apart from cast iron of all types (ductile, gray, white, white, S.G., etc.), the casting process can also work on aluminium, ceramics and even synthetic material. However, steel and iron offer excellent mechanical properties for a wide range of applications.(&#;grey&#; cast iron in the British Englsih) is also known as flake graphite cast iron is an iron-carbon casting material in which the carbon in the form of graphite is predominantly present as flakes. In this article, we will use both &#;gray&#; and &#;grey&#; interchangeably.Gray cast iron is suitable for lightweight castings (usually up to 200 kg), medium weight castings (usually from above 200 up to kg) and heavy castings (usually over kg). It is characterized by a random flake graphite pattern in the metal. And what makes grey iron 'grey' is the crystalline carbon found as flakes when the molten metal is cooled. With a strong enough microscope, it is possible to visually see the graphite microstructure that is present as flakes. While the flakes cause fracture in the melt, it also imparts other properties to the gray iron. In other words, the properties of the grey iron will depend upon how the melt is prepared as well as how it is cooled. While gray cast iron is not as strong as ductile cast iron or steel, it has reasonable amount of tensile strength, hardness, and other properties that make gray cast iron ideal for most cast iron components that come out of the foundry. The low degree of shrinkage in gray cast iron makes it favourable for industrial engineering applications since it has a varied tensile strength range from less than 20,000 psi to over 60,000 psi, and hardness from 100 to 300 BHN (Brinell hardness number).The typical gray iron contains around 2.5% - 4.2% carbon, 1.0% - 3.0% silicon, 0.15% - 1.0% manganese, 0.02% - 0.25% sulphur, and 0.02% - 1.0% phosphorus. It has high thermal conductivity, superior vibration damping capability, and acceptable tensile strength. Additionally, this type of cast iron is cost-efficient and has an excellent ability to withstand thermal cycling.The process of manufacturing gray cast iron in a foundry starts with the pig iron being melted, purified to remove contaminants and then poured into a mould to solidify. Often times, scrap iron and even steel is used in the manufacturing of gray iron. Once it is molten and the impurities removed, a small amount of silicon is added to convert the carbon into graphite. It is this graphite that is the characteristic of gray iron as it gives it a &#;flaky&#; appearance. Gray cast iron components are cast by pouring the molten iron in to the mould, which gives it the desired shape. The pouring can happen via gravity, low-pressure or vacuum. The moulds can be expendable moulds (sand) or non-expendable molds (metal). The quality of cast iron is dependent on the care taken while pouring the molten material, coupled with how complicated the mould is. It is equally important to cool the molten metal properly; inefficient cooling results in poor component quality. Quick cooling produces fine grain construction and slow cooling produces coarse grain construction. Other problems faced during the cast iron process include contamination of the iron, gas porosity (the forming of bubbles in the iron), and problems with the fluidity of the metal. This is why it is important to choose a foundry correctly if you want to outsource grey cast iron components.Grey cast is extensively used in piping since a long time now. Apart from that, it is used in the making of automotive parts, pumps, housings, etc.Cast iron has been used extensively throughout the history of mankind. As an industry, it is one of the oldest one. As science progressed, so did the casting industry. While there are many casting processes and material available today, there are many unique benefits of using gray cast iron. The first and foremost is the cost &#; it is one of the most cost effective casting process. Another notable benefit is gray iron&#;s enhanced lubrication. The graphite flakes in gray iron allow for better lubrication creating less wear on the cast iron. This makes gray cast iron a great choice for parts like brake rotors. Gray cast iron also has the ability to dampen vibrations making it an excellent choice for housing applications or industrial applications such as machinery bases. Additionally, gray iron has high thermal conductivity allowing it to move heat more easily through the metal.Gray cast iron can withstand thermal cycling, meaning the iron can go through high and low temperature changes without strain. Thermal cycling can create stress and premature failure in other forms of metal casting, however gray cast iron has continuously proved its ability to withstand thermal cycling. Grey iron is very resistant when it comes to oxidation. It develops a protective film or scale on the surface, making it more resistant to corrosion than wrought iron or mild steel.While it is one of the most popular casting processes, gray cast iron is not without its disadvantages. One of the main disadvantages is that it has a low tensile strength, making it a poor shock resistor due to residual stress. Another disadvantage is that it is very dense, and therefore not suitable for certain applications that are dependent on weight to be cost effective.
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Gray Cast iron VS Ductile iron
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MVPs
(Mechanical)
(OP)
If you are looking for more details, kindly visit Grey Iron casting vendor.
19 Jan 02 09:32For diaphragm valve lined with PTFE, I understand that the fluid will not contact body material. I would like to use gray cast iron instead of ductile iron. Are there any disadvantages for this applicatoin.
Replies continue below
(Mechanical)
21 Jan 02 19:42It depends on your application. Grey cast iron is more brittle than ductile iron so piping should impose minimal forces on the valves. If the fluid contained is flammable you should not used cast iron.
(Mechanical)
24 Jan 02 15:19PAM,
The only set of rules that should concern you is the design code that governs your installation.
Both ASME B31.1 and B31.3 put limitations on use of cast iron in toxic, flammable and steam service. Limitations imposed typically are in the form of pressure/temperature maxima or inclusion only in non-shock service.
If a material is deemed suitable for service (by the piping code) and the component is design rated for that combination of temperature and pressure, then you should be able to use it. Valve manufacturers have excellent experience with succesful and non-successful installations and are usually happy to share it with a customer..
MJC
(Mechanical)
24 Jan 02 16:32Gray cast iron, regard;ess of what you coat your wetted surfaces with, won't meet NACE MR if that is a consideration.
dik
(visitor)
2 Apr 02 17:40The Iron body is not wetted as it is fully insulated by the teflon lining. So there is no discussion on the chemical properties.
Why should you consider cast iron. It will not save you money. The standard for any valve manufacturer is ductile.
My advise, stick to the standard material configuration.
ood luck !
Ed
(Mechanical)
4 Apr 02 17:11A thing you like to consider is if the lining is glass reinforced there may be a danger of cracking the flange in tighteneing the bolts. The teflon will form its own gasket and as such will be raised above the face of the flange. When the bolts are tightened tha CI is subject to a bending moment and shear at the "gasket". CI is weak in tension and examples exist of CI flanges cracking when in a raised face scenario.
For critical service I would always use DI over CI. I beleive that Saunders diaphragm valves are only available in CI but other manufacturers such as Kim or Gemu could well have DI. Of course you would expect to pay more for a DI bodied valve. But this will be a lot less than the repair of a cracked flange.
(Mechanical)
(OP)
5 Apr 02 21:44Thanks for all comments. In our plant's specification, there are both ductile iron and gray cast iron body. I will study more to update the specification.
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