The influence of emulsion usage performance on the surface cleanliness of rolled steel strips is mainly reflected in the following aspects:

Lubrication performance

Saponification value: The saponification value is a key indicator for measuring the content of active oil in emulsions. A high saponification value indicates a high content of rolling oil and low impurity oil in the emulsion, with strong lubricating performance. It can effectively reduce the friction between the steel strip and the rolls, lower the generation of iron powder, and thereby enhance the surface cleanliness of the steel strip. Conversely, a low saponification value will lead to insufficient lubrication, an increase in iron powder, an increase in residual iron and residual oil, and a decrease in surface cleanliness.

Free fatty acid content: An appropriate amount of free fatty acids helps enhance the lubricating effect of emulsions. When the content is moderate, it can improve the lubrication effect, reduce friction and the formation of iron powder. Both excessive and insufficient content will affect the lubrication performance and lead to a decrease in the cleanliness of the steel strip surface.

Cleaning performance

Iron content: If the iron content in the emulsion is too high, it indicates insufficient lubrication or severe equipment wear. Iron powder will adhere to the surface of the steel strip and combine with the rolling oil to form iron soap, which not only increases the residual iron content but also adsorbs more oil stains, deteriorating the surface cleanliness. Controlling the iron content within a reasonable range (generally ≤300mg/L) helps keep the surface of the steel strip clean.

Ash content: Ash mainly comes from inorganic salts, impurities, etc. Excessive ash content will make the emulsion dirty, affecting the cleaning effect, causing spots and stains on the surface of the steel strip, and reducing the cleanliness. The ash content is usually required to be ≤500mg/L.

The content of mixed oil: The intrusion of mixed oil (such as hydraulic oil, mechanical oil, etc.) into the emulsion will disrupt stability, increase ash and carbon residue, and affect the lubrication and cleaning performance. Excessive mixed oil content will lead to an increase in residual oil and a decrease in surface cleanliness.

Stability

pH value: The pH value is a key indicator reflecting the stability of emulsions. The pH value is within the range of 5 to 7. The particle size of the emulsion is moderate, with good stability and normal lubrication and cleaning performance. A pH value that is too low (<5) or too high (>8) can cause abnormal particle size in the emulsion, deteriorate its stability, and affect the lubrication and cleaning effects.

Conductivity: Conductivity reflects the content of inorganic salt components in the emulsion. Excessively high electrical conductivity may indicate that the emulsion is contaminated (such as pickling residues, water quality issues, etc.), which can affect cleanliness and may also lead to corrosion of the steel strip.

Temperature

When the temperature is too low (<40℃), it is not conducive to the function of extreme pressure additives in the rolling oil, the lubricating performance will decline, and it is easy to produce iron powder and oil stains. Excessively high temperatures (above 60℃) will cause the particle size of emulsions to increase, reduce stability, accelerate aging, and affect cleanliness.

Generally, the injection temperature of the emulsion should be between 40 and 50℃, and the temperature of the circulation box should be between 50 and 60℃.

In conclusion, the lubricating performance, cleaning performance, stability and temperature and other performance indicators of emulsions are interrelated and jointly affect the surface cleanliness of the rolled steel strip. Reasonable control of various physical and chemical indicators of the emulsion, selection of appropriate rolling oil, and strengthening of the maintenance and management of the emulsion system are the keys to improving the surface cleanliness of the steel strip.