In the iron and steel rolling industry, the proportion of plate and strip production has exceeded 50%, and the demand for alloy thin strips is also increasing. In various rolling equipment, due to the elastic deformation of the rolls and the large rolling force during the rolling process, the four-high rolling mill is not suitable for rolling cold-rolled sheets and strips of high-strength steel and precision alloys. In terms of technical feasibility and economy, the use of multi-roll mills for cold-rolled sheets and strips has unparalleled advantages. The accuracy and life of the support roller bearings of a multi-roll mill have a very important impact on the production and quality of rolled thin strips. Multi-roll mill structure and characteristics Compared with other types of cold rolling mills, multi-roll mills have the following features: (1) In order to reduce the elastic flattening value of the rolls, small diameter work rolls are used to ensure the size of the rolled sheet . (2) The multi-roll roll system is adopted, and the component of the rolling force is transmitted to the stand by the supporting rolls of multiple fulcrums, which greatly improves the rigidity. (3) The manufacturing precision of the parts and rolls of the working stand is high, and the precision of the entire rolling mill is also quite high. Because the multi-roll mill places special emphasis on rigidity and precision, it can roll extremely thin steel plates and ensure that the steel plates have extremely high precision and surface quality, such as stainless steel plates; the thickness is 0.1 D:'ln3. Even 0.002 mill high-precision electrical silicon steel plate Harbin HRB bearings and so on. Since the first multi-roll mill appeared in 1932, the multi-roll mill has developed rapidly, with different structural shapes and geometric dimensions. The models are Sendzimir and Sandvik models. According to the roll system, they can be divided into six rolls and ten rolls. Two-high and twenty-high rolling mills, etc., but the most are 20-high rolling mills, of which Sendzimir type is the dominant one. For ease of introduction, the multi-roll mills mentioned below all refer to Sendzimir mills. The stand housing of the Sendzimir mill is an integral structure with a complete set of rolls inside, which has extremely high rigidity, which can fully ensure the stability of the work roll in the rolling direction and compensate for the deflection of the small diameter work roll. The working machine base is a complex block. The working machine base includes the arch, the supporting roller system, the pressing device, the wear compensation mechanism, the roller shape control and balance mechanism, the transmission device, the guide guard, the lubrication and cooling parameter control system, etc. [. It can be seen from Table 1 that the network carbide grade in the annealed state of the same sample is 0.5-1 grade higher than that in the quenched and tempered state, which is consistent with the theoretically explained results. From the daily metallographic inspection, the network carbide level under normal conditions is generally around 13 and the annealing picric acid etching method can be used. As for the samples with the network carbide grade equal to or higher than 2.5 in the annealed state, quenching inspection can be carried out to ensure the rationality and accuracy of the inspection. Concluding remarks: (1) The reticulated carbide in the annealed state and the reticulated carbide in the quenched and tempered state have a certain corresponding relationship. The network carbide in the general annealed state is 0.5-1 level higher than the network carbide in the quenched and tempered state. (2) Picric acid is used to corrode the network carbide in the annealed state, which is clear and easy to see. If the network carbide grade is below 2.5, the network carbide is qualified and no longer used for quenching inspection; when it is greater than 2.5, the quenching method is used to evaluate the grade to save inspection time. JNS Nose Seiko.