a) Nodules on the surface of the rolls must first have nodular substances, that is, various small particles, which are relative to strip steel in this regard. The greater the surface roughness of the coating, the greater the friction with the strip, and the easier it is to cause the oxides and iron filings attached to the surface of the strip to wear and fall off.
b) Nodules on the surface of the rollers must have sliding friction between the strip and the rollers, so that the small particles falling off the surface of the strip can be aggregated and squeezed into large particles. In this regard, the greater the surface roughness of the coating, the greater the coefficient of friction with the strip, and the less likely it is to cause sliding friction.
However, exit in the fast cooling section. The relationship between the strip and the tension roll is more complicated, where the temperature of the furnace gas is very low, and the temperature base of the end of the roll is similar to the temperature of the furnace gas, which causes the temperature of the strip to be higher than that of the roll. In addition, the temperature in the middle of the strip is higher than the temperature at the edge, and the pressure between the edge of the strip and the furnace rolls is higher than the pressure between the middle of the strip and the furnace rolls, which often results in tiny sliding friction between the strip edge and the furnace rolls. This sliding friction caused by temperature difference and internal stress cannot be hindered by roughness.
c) The nodules on the surface of the rolls must also adhere to the surface of the rolls after sliding friction occurs between the strip and the rolls, causing the small particles that fall off the strip surface to become large particles. In this regard, of course, the rougher the surface of the furnace roll, the easier it is to stick.
Within a certain range, the greater the surface roughness of the roller, the easier it is to produce nodule defects. The nodules of the tension roll at the outlet of the fast cooling section often occur in the position near the two ends of the roll where the edge of the strip is in contact with the furnace roll, and the corresponding embossing on the surface of the strip is also more at the edge than in the middle.
