After rolling and annealing, there are many residues on the surface of the strip. Is it because the quality of the rolling oil is not good?

In industrial application sites, the factors affecting the surface cleanliness of strip steel are in addition to the performance of the rolling oil, the on-site operating technology, rolls, hot-rolled raw materials, the surface quality of the strip after pickling, and the flow rate of the emulsion. Use and maintenance are the most critical factors.

◆The state and position of the magnetic filter and oil skimming system in the box.

In the field, the emulsion concentration is the most important factor to ensure lubrication. Increasing the system concentration within a certain range and strengthening lubrication can improve the cleanliness of the strip surface. For the dual-system emulsion circulation system, if the B system has low requirements for lubrication, the emulsion concentration should be much lower than that of the A system to reduce the residual oil on the board.

The saponification value is an indicator reflecting the content of active oil in the emulsion. A high saponification value means that the content of rolling oil in the emulsion is high and the miscellaneous oil is less. The cleanliness is also significantly higher than the latter.

The hydraulic lubrication on the rolling mill, the thin oil lubrication of the gear bearing and the oil film bearing lubrication system all have different degrees of leakage. These oils are mostly anti-emulsification oils, containing demulsifiers or surfactants that affect the HLB (water-oil amphiphilic balance). If they enter the emulsion, they will destroy the stability of the emulsion. The content of ash and residual carbon are much higher than those of rolling. Oil making. The intrusion of a large amount of miscellaneous oil will inevitably cause the increase of ash and residual carbon in the emulsion, which will affect the cleanliness. The intrusion of miscellaneous oil will also cause poor lubrication, produce a larger amount of iron powder, make the emulsion look gray, and have poor stability, which is the main factor affecting the cleanliness of the strip surface.

The oil film bearing oil has high viscosity and demulsification characteristics. Its invasion increases the particle size of the emulsion. At the same time, due to the high viscosity, it is easy to adhere to the plate surface. The hydraulic oil does not contain surfactants. Its components are mainly mineral oils with a viscosity close to that of rolling oil, and contain less ash. Therefore, it is generally believed that the emulsion can contain about 15% of the hydraulic oil without causing too much Big impact. The intrusion amount of miscellaneous oil can be judged by the saponification value. When the saponification value drops quickly, it should be suspected that miscellaneous oil leaks. At this time, it is necessary to strengthen the skimming of floating oil, and open the magnetic filter to remove the iron powder and the absorbed oil. If the leakage is large, the emulsion should be partially discharged or even completely discharged and then re-constituted.

Temperature plays a pivotal role in process lubrication. The emulsion temperature must be strictly controlled within the process requirements. Too high or too low temperature is not conducive to the maintenance of lubrication and cleanliness. Too low temperature is good for bacteria to multiply and cause emulsion corruption, but lower temperature is also not good for extreme pressure additives and other components in rolling oil to play a role, thereby affecting lubrication; too high temperature will intensify molecular thermal movement and emulsion particles The temperature will gradually increase, the stability will decrease, and the aging process will speed up. Roll surface temperature also plays an important role. It was found on the site that the rolled strip steel just after the roll change was generally darker, but after 300-400 tons of rolling, the temperature and condition of the roll surface were relatively ideal, and the surface of the strip steel was also bright. The relevant theories of lubricating oil generally believe that the five best ranges of temperature in the deformation zone are conducive to the development of the lubrication performance of the rolling oil. The temperature of the cold roll is too low when it is just running on the machine, which affects the lubrication, so the cleanliness is low.

Pickling incoming materials, plant environment, and water sources may all cause the contamination of the emulsion, of which chloride ions brought in by pickling incoming materials and water have the greatest impact. If the content of chloride ions in the emulsion is high, it will affect the particle size of the emulsion and cause corrosion of the plate surface. If the situation is serious, it will also cause the emulsion to demulsify. Therefore, the surface condition and water quality of the pickling material should be strictly controlled.

If the PH value of the emulsion is too high, the particle size of the emulsion will decrease, and the emulsion will be too stable, resulting in poor lubrication, thereby affecting the cleanliness of the strip surface. Generally speaking, the PH value of the system is more appropriate in the range of 5-7.

In general, if the iron powder content in the emulsion is high, the amount of iron soap will inevitably increase. If the amount of iron powder and iron soap in the emulsion cannot be lowered, they will re-enter the oil supply area along with the emulsion. When sprayed into the frame again, they will easily adhere to the surface of the strip, reducing the cleanliness of the surface of the strip. 

◆The aging loss of lubricating components in the roll gap can be supplemented for a relatively long time, and the average diameter of the emulsion particles that have become smaller after strong shearing can be restored;

◆ Foreign substances such as miscellaneous oil can float for a relatively long time;

◆Iron powder, ash, mechanical impurities, etc. have time to settle to keep the emulsion clean.

In actual production, it is generally required that the residence time of the emulsion in the tank is 20-25 minutes.

The good particle size distribution of the emulsion is the basis for achieving good lubrication. If the particles are too large, the emulsion is unstable and the oil is easy to precipitate; if the particles are too small, the emulsion is too stable and the oil film is not easy to form, resulting in insufficient lubrication. Factors such as PH value, miscellaneous oil, shearing effect, iron powder content in the emulsion can affect the particle size distribution, and then affect the lubrication and cleanliness.

The newly-prepared emulsions tend to have a relatively large particle size, and it takes more than one shift to achieve the ideal particle size distribution. The cleanliness of the strip rolled before this is generally unsatisfactory. After a large amount of oil is added, the particle size of the emulsion will also increase, and the surface of the rolled strip steel will have a large amount of residual oil and the surface of the plate will be darker. The use of a small-flow refueling method in front of the pump can reduce the impact of a large amount of refueling on the particle size of the emulsion.