In our latest article and on the web site we discuss methods of discovering whether sub-surface oxides are present and in some methods the degree to which they are present. Taking the time to make sure assessments can save significant costs for three reasons: It is very important to know whether a high surface oxide test result is due to high USOs or the presence of high SSOs.
Increasing the IPA content (or other additives) in the pickling solution (or rod cleaning) increases both material and environmental costs. However, increasing these additives will only reduce high uniform surface oxides, but if the results are high due to the significant presence of sub-surface oxides, increasing these additives will not reduce test readings significantly. Actually this is another method to determine if sub-surface oxides are present, namely, if the alcohol content in the mill emulsion is at a high level and effectively applied to the rod surface, but the Surface Oxide readings are still high, the sub-surface are probably high. In such a case, reducing Surface Oxide readings must be reduced by different methods (as described in the next point). Additionally, when the influence of sub-surface oxides is clear, the alcohol additives to the mill emulsion should immediately be reduced to a point that money is not being wasted.
Knowing as as soon as possible when sub-surface oxides begin to appear in rod can alert plant managers sooner, yielding faster remedies to production problems and therefore, less downgraded coils. Also remember that along with increasing the Surface Oxide test readings, but sub-surface oxides also have negative consequences in regard to drawability and the quality of the final wire product. Thus reversing the causes of sub-surfaces as soon as possible decreases manufacturing and scrap costs and increases customer satisfaction. Our latest article, lists some causes of sub-surfaces, namely,
hot cracking in the bar
fold-overs of bar corners
extrusion of material into roll gaps
rod protrusions due to pitting on the rolls
Thus, these are issues to look for when sub-surface oxides are detected.
In some cases a plant may wish to downgrade rod coils for uniform surface oxide thickness over a critical grading limit, but it may not be necessary to downgrade those coils if the Surface Oxide values have been pushed over that limit by the presence of sub-surface oxides. (Of course, this is even more the case if Surface Oxide readings are pushed over the limit due to improper electrolyte maintenance.)