Answer :
To ensure that a certain part supplied by a foundry always meets or exceeds ASTM No. 20 specifications for cast iron, the hardness should be specified at 220 Brinell.
ASTM No. 20 specifications for cast iron require a minimum Brinell hardness of 220. This means that the part must be at least this hard in order to meet the standard. If the part is not hard enough, it may not be strong enough to withstand the forces that it will be subjected to in use.
The hardness of a material is a measure of its resistance to indentation. It is measured using a Brinell hardness tester, which applies a force to a small ball indenter until it makes a permanent impression in the material. The size of the impression is then used to calculate the hardness.
In this case, the part must be at least 220 Brinell hard in order to meet the ASTM No. 20 specifications for cast iron. This can be achieved by specifying the correct heat treatment process for the part.
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