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Calculating liquid metal temperature loss due to bath additions.

Molten metal baths react to alloying additions by some temperature loss. It is often advantageous to the melter to be able to calculate that loss to allow for any necessary corrective action.

A frequent question on the foundry floor (and often in the foundry office)is: "How much heat is lost by adding a specific alloy to a metal bath?" Many times it is also desirable to know how many pounds of an alloy or other addition can be made without lowering the temperature of a melt below a certain limit. The answer to either of these questions can be estimated quite readily using the temperature loss formula:

This formula states that the temperature loss can be computed by multiplying the ratio of addition weight to liquid metal weight by 3500. Both the addition weight and the liquid metal weight are expressed in pounds. The temperature loss is expressed in degrees Fahrenheit.

This formula was originally developed for stainless steel production in steel refining furnaces, but has also proven reliable in ladles. Reliability is maintained whether the metal is steel, gray iron, ductile iron or brass. Tests have shown that the formula is quite dependable in larger ladles and furnaces greater than two tons in capacity.

The formula does not take into consideration radiant heat losses from the surface of the melt nor heat losses through the sides of the ladle or furnace. This cooling rate, which must be determined for each application, becomes increasingly important with small ladles. The accuracy of the formula decreases as ladle size becomes smaller.

The addition may be either metallic or non-metallic, and the formula is equally reliable for such material melt additions as graphite, lime and calcium carbide. The use of an exothermic alloy such as 75% ferrosilicon will influence the accuracy of the formula. Again, we are only concerned with the weight of the addition and of the metal bath.

The formula was derived from experimental data because theoretical calculations do not agree with the experimental results. The 3500 factor in the formula obtained experimentally became 2600 when theoretical calculations were used. This suggests that the circumstances associated with additions made to a given ladle or furnace of liquid metal must be considered. However, in actual foundry floor practice the formula has proven to be a reliable method to estimate the temperature loss associated with making relatively small quantity solid additions to a liquid metal bath.

Examples are offered in the attached table to illustrate the use of this formula.

it is the intention here to provide temperature loss guidelines due to the effect of material mass (weight) only. The actual total temperature loss will vary from one ladle or furnace to the other as well as from one foundry to another. The formula does provide, however, a method to quickly estimate the temperature loss to a quantity of liquid metal due to the addition of a quantity of material to it.
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Title Annotation:molten metal baths in foundry furnaces
Author:Kern, Ronald
Publication:Modern Casting
Date:Oct 1, 1990
Previous Article:AFS Art Casting IV highlights improving operations, service.
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