Cast Iron

Any time is good to review your vendors, their offerings, and their ability to produce as you expect. With the global economy in a state of flux, now may be the best time to review your suppliers. To better understand Kirsh Foundry offerings, let’s review the cast irons category and suitable uses for those castings.

Cast irons include gray, ductile and malleable iron. Kirsh Foundry uses gray iron and ductile iron.

Cast Iron Basics

All cast irons are alloys of the same basic ingredients: iron, carbon and silicon with small amounts of other elements. By varying the amounts of elements, the different properties of each cast iron are produced. Testing is by a spectrograph to determine chemical analysis. Strength is determined by pouring test bars.

Cast irons are melted primarily in a batch or using a continuous method. The major melt material is steel scrap. The final properties are created by adding various alloying elements.

Gray Iron

The most common cast iron by tonnage, gray iron is produced “as cast”, meaning no additional alloying elements will be added and it has its final properties. This also means that gray iron is rather brittle and cannot be used where it will receive an impact load. The defining feature of gray iron is that it has no ductility. It is brittle and will break under any significant impact load.

Gray iron is defined by tensile strength. For example, Class 25, or G2500, gray iron has a minimum tensile strength of 25,000 psi. Class 30, or G3000, has tensile strength of 30,000 psi, and so forth.

Gray iron has two advantages. The first is cost. Gray iron is the least expensive cast iron and is ideal for items such as table bases, counterweights, covers and other applications where durability are not a concern. Secondly, gray iron has good vibration damping ability. This makes gray iron excellent for gear, transmission or bearing housings, and applications where the casting holds moving parts.

Ductile Iron

Ductile iron starts in the furnace with the same basic chemistry as gray iron but it is inoculated with magnesium to produce its ductility. Unlike gray iron, Ductile iron can take an impact without changing its form. In other words, it will bend but not break.

That ductility is its advantage. Ductile iron castings can flex instead of breaking when used in impact situations. This is why gears are a common application for ductile iron. The hardness of ductile iron allows gear teeth to stand up to the repetitive impact of starting and stopping.

The magnesium added in the manufacturing process increases the price of ductile iron over gray iron.

Ductile iron is defined by three numbers: tensile strength, yield strength, and elongation percentage. Yield strength is the point at which the iron will no longer return to its original shape when bent. Elongation percentage measures the amount of ductility. Grade 60-40-18 ductile iron has a 60,000 psi tensile, 40,000 psi yield and 18% elongation. Other common grades are 65-45-12, 80-55-06, and 100-70-03.

 

Everything Custom

To learn more about how Kirsh can help you consolidate your castings, give Jim Kirsh a call (920) 887-0395. We’ll listen to your needs and talk about how we can customize a program for you based on your needs.