Sponging is caused by small bubbles of carbon monoxide that emerged as a result of carbon corrosion and remains in slag because the ascending force is not enough to resist of slag alloy. Definite, not excessive sponging in oxygen transducer of top feeding blow influences positively, namely there is an increase and stabilization of oxygen recovery, barriers to metal drops output from converter and absorption of nitrogen from oxygen, drawn in through neck are created.
Excessive sponging causes enormous scopes of slag emission that is for sure inadmissible. In some cases even medium sponging causing spittings is inadmissible as being low-conducted foamed slag reduces heat loss from the flame to metal. It causes the duration of melt and boosts the lining wear, especially furnace arch, because the essential part of heat indigested by metal is taken by lining that provokes its overheat.
One of the reasons of excessive sponging can be the raised content of SiO2 and P2O5 that create surface active anions SiO44- and PO43-, boosting the foam resistance.
Extra fine solid particles have the same effect if presented in slag as they boost mechanical density of cinder (serve as supporting structure).
To reduce the slag liability to excessive sponging caused by increased content of SiO2 and P2O5 the basicity of slag should be made by addition of lime, or, even better, CaF2 (fluorspar) and oxides of alkali metals.
If the excessive sponging is due to the presence of extra fine solid particles, to dissolve these particles the raised temperature is needed.