Chemical detection and evaluation of rolling emulsion
April 27, 2023
1. Concentration:
Control range (thin plate: 2.5% -3.5%)
(Thick plate: 1.5% -2.5%)
An appropriate emulsion concentration is the foundation for ensuring process lubrication and plate surface cleaning.
Excessive concentration: may cause excessive lubrication during rolling, causing slipping, increasing the residual oil on the rolled plate surface, and reducing the cleanliness of the plate surface;
Low concentration: may lead to insufficient lubrication during rolling, causing thermal scratches, and increasing the wear of iron powder.
Concentration control method: Supplement simultaneously according to the ratio of oil and water.
2. pH value
The pH value of the general emulsion is between 5.0-8.0, with a fluctuation range of 0.2-0.5. When the pH value is below 4.5 or above 9.0, abnormal situations occur.
Function of measuring pH value:
1) The Degree distribution of emulsion particles is closely related to the pH value of emulsion. Usually, the particle size of the emulsion remains constant within the pH range of 5-8.
2) When the pH value is below 4.5, the particle size tends to increase, leading to instability of the emulsion. When the pH value is between 8-9, the particle size of the emulsion tends to decrease, leading to a lack of lubricity during the cold rolling process.
3) When the pH value is above 9.5, there may be related phenomena where the particle size of lipids/esters in the emulsion tends to decrease, while the particle size of alkaline substances in the emulsion tends to increase.
When the pH value of the rolling emulsion suddenly changes, accompanied by changes in conductivity, it may be contaminated by acids, salts, or alkaline substances.
Acid pollution is usually caused by pickling lines.
Possible sources of salt pollution: pickling line, water quality of the solution.
Alkali pollution is generally caused by the use of cleaning agents.
Bacteria can cause a decrease in pH value without changing electrical conductivity. Especially when shutting down without using emulsion, it often occurs. Emulsions that are invaded by bacteria will emit an unpleasant odor.
3. Conductivity
The conductivity distribution of rolling emulsion is directly related to iron. High iron content is prone to binding with H+, OH -, Cl -, SO42-, while less binding with Ca2+, Mg2+, and organic acids.
Under normal conditions, the conductivity of the emulsion can increase by up to 20 us/day per day, and a daily increase above this value is considered abnormal.
Control range ＜ 300us/cm
Reasons for changes in conductivity:
1) The conductivity slowly increases while the pH value remains unchanged.
Reason: High salt content in the mixing solution.
2) The conductivity increases and the pH value suddenly drops
Reason: The pickling and rinsing water is contaminated.
3) Sudden increase in conductivity and pH value
Reason: The emulsion is contaminated with cleaning agents.
4) The conductivity slightly increases or remains basically unchanged, while the pH value slowly decreases
Reason: The emulsion has been invaded by bacteria.
5) The conductivity rapidly increases while the pH value remains unchanged
Reason: The emulsion is affected by neutral salts, please check the acid washing and rinsing water.
4. Saponification value
By measuring the total oil concentration and the saponification value of the oil in the emulsion, the current percentage of active rolling oil and impurities can be obtained.
Active oil content=(measured saponification value/fresh saponification value) * measured total oil concentration
Percentage content of miscellaneous oil=measured total oil concentration - active oil content
Saponification value control range 50-160mgKOH/g
1) Excessive saponification value: An increase in acid value leads to false saponification value and deterioration of the emulsion;
2) Low saponification value: Mixing of dissimilar oils can affect the lubrication effect.
Saponification value control method: skimmer, manual skimming after stopping stirring, partial discharge and replacement with new oil.
Usually, if the content of impurities in the emulsion exceeds 20%, it will reduce the lubricity.
5. Iron powder content
Control range<300ppm
An appropriate iron powder content helps with lubrication.
1) Excessive iron powder: The emulsion is dirty and affects the cleanliness of the board surface; Too high oil-water separation, poor stability
2) Low iron powder: Increase rolling oil consumption.
Iron powder control method: Check the operation status of magnetic filtration and control the operation time of magnetic filtration.
6. Ash content
Control range ＜ 500ppm
Excessive ash content: The emulsion is dirty and affects the cleanliness of the board surface;
Ash control method: Check the paper feeding status of the vacuum filter and increase the paper feeding frequency.
7. Chloride ion content
Control range<30ppm
Excessive chloride ion: can cause fluctuations in the pH value of the emulsion, increase conductivity, and affect rust prevention performance. If it is too high, the oil and water will separate.
Chlorine ion control method: Check the water quality of pickling and rinsing water, and partially discharge.
8. Acid value
Control range ≤ 20mgKOH/g
High acid value: mixed with heterogeneous oil or emulsion spoilage, deterioration.
The control method for acid value: skimming oil, partially discharging and supplementing with new oil replacement, and briefly heating and sterilization.
9. ESI (Stability Factor)
Control range 70-90%
Excessive ESI: Refined oil droplet size, affecting lubrication;
Low ESI: Oil droplet size increases, uneven distribution, and affects concentration response.
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