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PRINCIPLE NO. 8-

TRUST THE FOUNDRY

Foundrymen producing Ductile Iron are well aware of choices in manufacturing processes, effects of chemical composition, the effects of heat treatment, and the in-plant controls necessary, to produce a serviceable casting.

If the designer prescribes how the castings should be manufactured he obviously trespasses the foundryman's domain. The designer representing the buyer will probably succeed in this interference, but gains nothing by it and often ends up paying more for the castings than he would have, had he left the choice of manufacturing process to the foundryman.

The most common unnecessary instructions are those on chemical composition, heat treatment, and quality control.

For instance, it is well known that increasing silicon content increases impact transition temperature. If the designer decides that a certain minimum impact test value is desired at a given temperature, he should specify that, rather than the silicon content. Most properties can be obtained via heat treatment but, provided proper production

controls are exercised, they can be obtained as-cast as well. It should remain the foundryman's choice to deliver castings as-cast or heat treated as long as the casting properties meet specifications.

Tight quality control needs to be exercised throughout the entire casting process, particularly when producing a high performance material like Ductile Iron.

Whether or not the specified properties have been met should not be a matter of trust. It is not only the right but also the duty of the designer to either request or to perform tests as extensive as (safety) considerations require, in order to be satisfied that the casting indeed exhibits the properties expected.

COURTESY: PARTEN MACHINERY CO., MINNEAPOLIS, MN

This one-piece ductile carriage wheel replaces four former parts. In the redesign to ductile, total cost dropped from $251 per unit to $75. Machining was cut from $189 to $38, and the number of production operations dropped from 7 to 3. The 100-70-03 Ductile Iron was specified because of its good response to Tufftride treatment.

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