[China Aluminum Industry Network] aluminum hot-rolled emulsion with liquid water and influencing factors
The aluminum strip rolling includes hot rolling of aluminum strips, which mainly produce plate and coil, and cold rolling, which mainly produces aluminum strips and foils. The aluminum rolling process lubricants used include hot-rolled aluminum plate emulsions, cold-rolled aluminum plate rolling oils, aluminum foil rolling oils, and cold-rolled aluminum plate oil-water-spraying techniques. Aluminum hot-rolled emulsions are prepared from hot-rolled oil and water. The concentration of the emulsion is usually in the range of 2 to 10%, and the aqueous phase accounts for approximately 90 to 98% of the emulsion. Therefore, aluminum hot-rolling emulsification is used. The water in the liquid plays a very important role in the production of aluminum hot rolling and the quality of the strip. This article will briefly discuss the use of hot water for aluminum hot-rolling emulsions and related influencing factors.
I. Classification of water and related water
Water (H2O) is an inorganic substance composed of two elements, hydrogen and oxygen. It is a transparent liquid that is colorless and odorless under normal temperature and pressure. Water can be divided into: hard water (natural water), soft water, and deionized water. Hard water is water containing calcium ions (Ca2+) and magnesium ions (Mg2+) and other water-soluble ions. Soft water is water that removes only calcium and magnesium ions in hard water. Deionized water refers to water that removes all negative and positive ions in water by an ion exchange device.
Water can be classified according to its hardness as:
Hardness/(mmol·dm-3)
>4.5
3.0~4.5
1.5~3.0
0.5~1.5
<0.5
name
Extremely hard water
hard water
Medium hard water
soft water
Very soft water
Generally, hardness and conductivity can be used to measure the purity of water. The hardness of water is the total concentration of calcium and magnesium ions in water, and the conductivity is the size of the ion conductivity in water.
Natural water: In addition to containing Ca2+ and Mg2+ ions, it also contains other ions that have different effects on water quality.
Soft water (sodium ion exchange water): The water is softened by sodium ions to remove Ca2+ and Mg2+ from the water. The characteristics of the water: the hardness of the obtained water is reduced, but the pH is constant; the total amount of cations and cations in the water is basically unchanged, the content of Na+ is obviously increased, the conductivity is basically unchanged, and the sodium ion is softened because the regenerant is NaCl. In water, the chlorine ion (Cl-) content is higher than the chloride ion content in raw water.
Deionized water: Since all ions dissolved in water are removed, the hardness and conductivity of water are greatly reduced, which is beneficial to production use.
Conductivity reflects the amount of cations and anions in the water. The higher the ion content, the greater the conductivity of the water and the lower the purity of the water. For example, if the hardness and conductivity of a certain natural water are certain, then the hardness of the softened water produced will be greatly reduced, and the electrical conductivity will be basically unchanged. The hardness and the conductivity of the deionized water produced will be greatly reduced. Under normal circumstances, The hardness of deionized water is almost 0, and the conductivity is below 3uS/cm.
Second, aluminum hot rolling emulsion liquid selection and influencing factors
1, using natural water solution
Calcium and magnesium ions in natural water are harmful to the emulsion. Calcium and magnesium ions can form insolubles with the emulsifier and some active ingredients in the emulsion, thus exerting great influence on the stability of the emulsion and the efficacy of the active ingredients. They not only affect the stable use of the emulsion, but also It may affect the normal progress of rolling production.
In addition to calcium and magnesium ions, other ions in the water will also have adverse effects on the emulsion, such as high Na+ content will increase the tendency of water corrosion, reduce the chemical adsorption of the active ingredients in the emulsion. Emulsions formulated with high hardness water, where sulfates or oxides are present, also reduce the stability of the emulsion. The following are the possible effects of several major ions.
The main effect of ions in water on water quality:
1. Ca2+, Mg2+ (calcium, magnesium ions): reacts with alkaline substances to form insolubles, such as fouling in the exchanger; reacts with relevant active ingredients in the emulsion.
2. Cl- (chlorine ion): Corrosive ions that cause pitting corrosion on metals; increase salt content in water.
3, SO42-: (sulfate ion): increase the salt content of water; combined with Ca2 + calcium sulfate scale.
4, HCO3-: (bicarbonate ion): decomposition will produce alkaline corrosion; CO2 corrosion generated in steam.
5, Na + (sodium ion): increase the salt content of water; increase the corrosion tendency of water.
2, using soft water with liquid,
Because of the greater hazards of calcium and magnesium ions, people use sodium ion exchange resin to replace monovalent sodium with divalent calcium and magnesium. This reduces the damage caused by calcium and magnesium ions to some extent. . With sodium instead of calcium and magnesium, the hardness of the water is reduced a lot, but the content of metal ions in the emulsion is not reduced, so the conductivity does not change significantly.
If the natural water used has a higher hardness, then in the preparation of sodium ion exchange water, a large amount of Na+ ions and a certain amount of Cl- ions will enter the emulsion and become the main ions in the emulsion. When the content of Na+ ions and Cl- ions in the emulsion is low, their influence on the use of the emulsion and the production is often small. However, as the rolling progresses, the water in the emulsion continuously evaporates, ions in the emulsion do not evaporate, and these ions continue to accumulate, and their hazards continue to increase. As the sodium ion content in the water increases, the electrical conductivity increases and the corrosion rate increases, because at this time, the resistance of the water decreases, and the corrosion current easily passes through, so that the electrochemical action is accelerated. In addition, the sodium ion has a small ionic radius, strong penetrating ability, and strong polarity. As its content continuously accumulates, a large amount of sodium ions will destroy the chemical adsorption of the active ingredient molecules on the roll to a certain extent, thereby affecting the emulsion. The lubricating effect is affected, and the sodium soap formed by a large amount of sodium ions will deteriorate the emulsion separation and affect the lubricity. At the same time, the presence of bubbles will further deteriorate the lubricity. Therefore, when the Na+ ion content is too high, surface stickiness, etc. may occur. Defects, in addition, excessive sodium content may also increase the amount of emulsion used.
In this case, it occurred at a customer, because the conductivity of the demineralized water (sodium ion-exchanged water) used was too high and a large amount of sodium ions accumulated rapidly. When the conductivity of the emulsion reached 1500 uS/cm, the surface quality was rolled. Began to have problems. After the user changed the deionized water, their production and use of the emulsion were significantly improved.
As mentioned above, the presence of chloride ions tends to cause pitting corrosion to the metal and also accelerates the progress of the corrosion reaction;
3, using deionized water with liquid
Deionized water is a good choice as aluminum hot-rolled emulsion liquid water. The use of deionized water for the dosing of water can fundamentally eliminate the effects that the water quality may have on the emulsion, and the hazards that the ions in the water may bring will no longer exist. The direct hazards of Ca2+, Mg2+, and the accumulation of Na+, Cl-plasma will reduce the hazard to a lower level. Then, in the use of daily emulsions, the metal ions that the plate rolls into the emulsion can be eliminated or reduced through routine maintenance, so that the emulsion can be better and long-term stable for rolling and Get good surface quality and service.
Three, aluminum hot rolling emulsion with water indicators and related liquid requirements
1. General testing items and indicators requirements for liquid water
project
Test results
Hardness (ppm)
0
Conductivity (uS/cm)
<10~20
pH
6-7
Chloride ion content (ppm)
0
In addition to the requirements for the indicators for liquid water use, aluminum hot-rolled emulsions are also required to have certain requirements for the temperature and dosing method of the liquid water.
2, the liquid temperature
The temperature of the dosing water is preferably greater than 40 degrees, the surface tension of the water is large (73), and the interface does not wet the oil, and it is difficult to emulsify the oil into the water, and the surface tension of the hot water is relatively small. The viscosity of the oil becomes smaller, and the thermal motion facilitates the movement and dispersion of molecules. In addition, the rational use of the emulsifier and the necessary mechanical shearing force of the circulation make it possible to disperse the oil droplets into the aqueous phase and form a relatively good one. A good oil-in-water emulsion and used well in aluminum hot rolling.
3, dispensing method
As far as aluminum hot rolling is concerned, the emulsions used are mostly metastable and have strict requirements on the particle size distribution or the stability of the emulsion. Therefore, there are also certain demands on the method of refueling and system circulation during the liquid dosing.
To prepare aluminum hot-rolled emulsions, the rolling oil must be added to the water. If the emulsifying properties of the rolling oil are good, the emulsion can be directly added to the water, stirred, and the emulsified emulsion can be quickly formed. However, most of the rolling oil preparation requires the addition of liquid in front of the circulation pump. With the mechanical shear force of the circulation pump, an oil-in-water emulsion suitable for hot rolling production can be formed with reasonable oil distribution.
Fourth, the conclusion
The aqueous phase in the aluminum hot rolling emulsion occupies a large proportion, and the selected liquid water plays a crucial role in the stability of the emulsion and the production and quality of the strip. Deionized water is the preferred choice for aluminum hot-rolled emulsions. The selection of liquid water indicators for detection and control, as well as the temperature of the dosing liquid and the dosing method are also very beneficial for obtaining good production and aluminum sheet quality.
(The author is a good futon (Shanghai) Advanced Industrial Media Co., Ltd. Wang Jianing)
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