Cold rolling process knowledge Q&A –part II

1. Process lubrication and cooling

Answer: Process lubrication plays an important role in cold rolling strip production. Good process lubrication can reduce the friction between the strip steel and the roll, thereby reducing the rolling pressure and tension, increasing the reduction to reduce energy consumption, making it possible to roll thinner products. In addition, good cooling and lubrication can improve the thickness accuracy and surface quality of strip steel, and improve the service life of rolls.

2. What are the rolling process parameters? What's the use?

Answer: Contents: ① Temperature parameters, such as heating temperature, rolling temperature and end of cooling temperature; ② Speed parameters, such as deformation speed and cooling speed; ③ Deformation program parameters, such as pass deformation program and total deformation program; ④ Time parameters, such as the interval time between passes, the time from the end of deformation to the start of quenching, etc.

Functions: ① Deformation temperature is an important technological condition to determine the good strength and toughness of steel. Heating before rolling is the first step to achieve controlled rolling. It also plays an important role in the final properties of steel and obtaining the most suitable structure.

② In the controlled rolling process, the grains are generally finer with the increase of deformation degree. Therefore, the strength of the wind material increases and the brittle transition temperature decreases.

③ The cooling rate after rolling has a significant impact on the strength and toughness of steel. At different finishing rolling temperatures, the cooling rate has an impact on the mechanical properties and grain size. When the cooling rate is low, the ferrite grains are coarse.

3. Reasons for roll meat loss

Answer: On the basis of roll cracks, if the roll is not replaced in time, continue to roll at high speed

Rolling under the braking force will cause the roll to lose flesh, so that the strip steel can be rolled through; In addition, because the emulsion is not clean and contains hard impurities or the broken strip steel is pressed into the roll gap, pits are generated on the roll surface, which will also cause similar defects in the strip steel.

4. How does the edge or middle wave shape come into being? What is the impact on cold rolling plant production?

Answer: The wave shape at the edge or middle is often caused by uneven reduction of both sides or middle and both sides during hot rolling, and uneven longitudinal extension of rolled pieces due to uneven heating. When running on a continuous unit, new scratches often appear at the lower part of the wave shape; If the wave shape is serious, there will be many defects such as flesh after trimming and different end tightness after coiling, and there will be deviation, wrinkling and rolling instability in the cold rolling process.

5. What are sickle bends and S-bends? What impact do they have on cold rolling mill production?

Answer: Sickle bend and S-bend refer to the change of sickle shape and S-shape along the strip steel length along the strip steel centerline. It will inevitably lead to strip steel deviation, and in serious cases, it will cause belt breakage. At the same time, when cutting on the disc shear, it is often impossible to ensure that the strip edge is uniform and straight, so that the strip steel will have a tower shape when coiling, and the upper and lower ends of the steel coil are uneven.

6. Why should the strip be cooled during cold rolling plant?

Answer: The experiment shows that about 84% - 88% of the deformation work of cold rolled strip steel is converted into heat energy, which increases the temperature of strip steel and roll. Therefore, cooling measures must be taken. The high temperature of the roll surface will cause the hardness of the quenching layer of the work roll to decrease, which will affect the surface quality of the strip steel and the service life of the roll. The rise of roll temperature and uneven distribution of roll temperature will destroy the normal roll shape and directly affect the strip shape and dimensional accuracy. Effective cooling and roll temperature adjustment measures shall be taken for rolls and strip steels.

7. Effect of tension in still cold rolling mill

Answer: Prevent strip steel from deviation during rolling (i.e. ensure correct centering rolling); Keep the rolled strip straight (including keeping the flatness straight during rolling and good flatness after rolling); Reducing the deformation resistance of metal is conducive to rolling thinner products and plays a role in properly adjusting the load of the main motor of the cold rolling mill. As the change of tension will cause the change of forward slip and roll speed, it has a certain automatic adjustment effect on the cold rolling process.

8. How to inspect the installation of rolls and components?

Answer: In order to ensure the normal rolling, the roll position, main and auxiliary parts of the rolling mill and relevant equipment must be checked before rolling.

① Roll position: whether the roll is horizontal, the roll gap size, whether the pass is aligned, and whether the axial position of the roll is biased to one side.

② Check whether the main and auxiliary parts of the rolling mill are installed correctly, whether the screws of each part are fastened, whether the length of the connecting rod wooden rod is appropriate, and whether the binding is firm; Whether the installation of guide device and cooling water pipe is reasonable and reliable.

③ Check the operation of auxiliary equipment; Whether there are foreign matters in the conveying roller table and enclosure, and whether the safety protection facilities are complete and reliable.

9. How to control the hydraulic roll bending of the cold rolling mill?

Answer: The control of hydraulic bending roll can be divided into two categories: manual regulation system and automatic regulation system.

When the manual adjustment system is adopted, the size of the bending roll force is given by the operator according to the observation, calculation (including computer calculation) or operating experience of the shape, but there is no feedback adjustment of the shape. The requirement of manual adjustment system is that the given bending roll force shall remain unchanged.

10. Effect of rolling speed change on cold rolling plant

Answer: The change of rolling speed changes the metal deformation resistance, or the change of speed affects the change of oil film thickness of oil film bearing, thus changing the rolling pressure and actual roll gap. The increase of speed makes the oil film thicker and the reduction larger, thus making the strip thinner. The friction coefficient decreases with the increase of speed, even if the rolling pressure decreases.

11. In cold rolling strip production, what is the purpose of strip flatness?

Answer: ① Eliminate the yield platform of strip steel and improve the mechanical properties of steel;

② Improve the flatness of the strip steel to obtain a good shape;

③ The surface of the strip steel can reach a certain roughness, thus obtaining different surface structures of the steel plate.