Mechanical Properties of Gray Iron

The relative ability of a material to absorb vibration is evaluated as its damping capacity. The quelling of vibration by converting the mechanical energy into heat can be very important in structures and in devices with moving parts. Components made of materials with a high damping capacity can reduce noise such as chatter, ringing and squealing, and also minimize the level of applied stresses. Vibration can be critical in machinery and can cause unsatisfactory operation or even failure.

An accumulation of vibrational energy without adequate dissipation can result in an increasing amplitude of vibration. Excessive vibration can result in inaccuracy in precision machinery and in excessive wear on gear teeth and bearings. Mating surfaces normally considered in steady contact can be caused to fret by vibration.

The exceptionally high damping capacity of gray cast iron is one of the most valuable qualities of this material. For this reason it is ideally suited for machine bases and supports, engine cylinder blocks and brake components. The damping capacity of gray iron is considerably greater than that of steel or other kinds of iron. This behavior is attributed to the flake graphite structure of the gray iron, along with its unique stress-strain characteristics. The relative damping capacity of several different metals is illustrated in Table 4.

Damping capacity decreases with increasing strength since the larger amount of graphite present in the lower strength irons increases the energy absorbed. Larger cast section thicknesses increase damping capacity and inoculation usually decreases it. Heat treating can also have an appreciable effect on damping capacity.

Table 4. Relative Damping Capacity
Material	x 10⁴
White Iron	2-4
Malleable Iron	8-15
Ductile Iron	5-20
Gray Iron, Fine Flake	20-100
Gray Iron, Course Flake	100-500
Eutectoid Steel	4
Armco Iron	5
Aluminum	0.4
Natural Log Ratio of Successive Amplitude

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Atlas Foundry Company, Inc.
601 N. Henderson Avenue
Marion, IN 46952-3348
Telephone: (765) 662-2525 • Fax: (765) 662-2902
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Mechanical Properties of Gray Iron - Damping Capacity

Mechanical Properties of Gray Iron