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| Q1. How is gray iron graded? |
Gray Iron is classified into different grades, depending upon the desired tensile strength. The IS standards for gray iron are tabulated below:
IS : 210 – 1970
(CGS UNIT) |
IS : 210 – 1978
(SI UNIT) |
| Grade |
Tensile Strength
Kgf/mm²(min.) |
Grade |
Tensile Strength
N/mm²(min.) |
B H N |
| 15 |
15 |
FG 150 |
150 |
130 – 180 |
| 20 |
20 |
FG 200 |
200 |
160 – 220 |
| 25 |
25 |
FG 220 |
220 |
180 – 220 |
| 30 |
30 |
FG 260 |
260 |
180 – 230 |
| 35 |
35 |
FG 300 |
300 |
180 – 230 |
| 40 |
40 |
FG 350 |
350 |
207 – 241 |
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FG 400 |
400 |
207 – 270 |
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| Q2. How do I select the moulding process for my foundry? |
Various factors such as castings quality, complexity of the shape, tooling costs, quantity required and capital costs need to be considered during selection of moulding process. A comparative chart of various molding processes is given in the following table. | | Green Sand | Precision Molding | Chemically Bond Mold | | Sand Casting | Perm Mold | Die casting | Ceramic & Invest. | Shell, CO2 Nobake | | Typ. dimen. tol. | ±.010" ±.030" | ±.010" ±.050" | ±.001" ±.015" | ±.010" ±.020" | ±.005" ±.015" | | Rel. cost in qty. | Low | Low | Lowest | Highest | Med. High | | Rel. cost for small qty. | Lowest | High | Highest | Medium | Med. High | | Permiss. cast wt. | Unlimit. | 100 lb | 75 lb | oz-100 lb | Shell (oz.-250 lb.)CO2 & Nobake(.5 lb-tons) | | Thinnest cast sect. | 1/10" | 1/8" | 1/32" | 1/16" | 1/10" | | Rel. surface fin. | Fair-Good | Good | Best | V-good | Shell-goodCO2-fair | | Ease of casting complex design | Fair-good | Fair | Good | Best | Good | | Ease of designchange in production | Best | Poor | Poorest | Fair | Fair | | Range of alloys thatcan be cast | Unlimit. | Al-base & Cu-base preferr. | Al-base preferr. | Unlimit. | Unlimit. | | (Characteristics are approximate and depend upon the metal.) | | *This article has been excerpted from the publication, "Casting Buyers' Guide," American Foundrymen's Society, Des Plaines, Illinois. |
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| Q3. Which type of nobake moulding system is preferable – furan based or phenol based? |
Phenol based nobake moulding system is commonly used in Indian foundries. However moulds made using phenolic binders tend to crack easily. Furan resins are easier to use especially for preparing larger moulds. Due to its advantages, furan based nobake moulding system is preferred internationally by foundry units over phenol system. |
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