Failure analysis of rollers of bloom withdrawal stand in continuous casting machines at visakhapatnam steel plant

In Visakhapatnam Steel Plant, 6 Nos. continuous casting machines (CCM) are installed in Continuous Casting Complex. Each CCM is 12m radius and mould size is 320mmx250mm cross-section. Bloom withdrawal stands are used in continuous casting machines to withdraw and to support the bloom, as the bloom gets solidified from liquid state. Each stand consists of one bottom and one top roller. These bloom withdrawal stands work in a very high temperature zone and corrosion environment. The major problem in these stands is cracks formation on the surface of rollers and subsequent worn-out. Ever year about 70 to 80 rollers needs replacement or reclamation. This premature replacement/reclamation of casting rollers causes machine stoppages and reduces machine availability and incurs production loss and high maintenance cost. Therefore the failure analysis of these rollers carried out in this project, so that by controlling existing parameters to further increase of roller life.Based on the study it is found that roller surface temperature should be maintained below 350°c so that low thermal stresses are induced which leads to better life of casting roller. To reduce the scales formation inside the rollers, the water hardness has to be controlled by adding softeners Na₂ Co₃, and poly electrolytes solutions. At the time of reclamation of rollers, all rollers inside should be cleaned with acid solutions.