Formation of residual stresses owing to tension levelling of cold rolled strip

Abstract

that some form of shape correction will be necessary within the process route. Shape defects introduced at the cold Unacceptable shape defects in light gauge strip mill can be classified into two main types, the first being a products may be introduced as a result of differential surface area differential defect such as coilset or crossbow. reduction being applied across the width of the Second, edge to edge (crosswidth) length differentials are material at rolling mills. Consumer specifications generally associated with edge wave, centre buckle, camber, and quality procedures demand that the resulting and twist. defects are removed by subsequent processingThe means by which these defects are removed are operations. Such an operation is tension levelling, predominantly pure stretch levellers, stretch-bend levellers which attempts to remove the resulting defects (i.e. tension levellers), and multiroll levellers (roller levellers). such as edge waves by ensuring that all Pure stretch levelling processes require considerably high longitudinal material 'fibres' possess the same bridle drum tensions to flatten the incoming material. In length. Shape removal is achieved by subjecting this case, the tensions employed induce stresses in the material the material to a series of alternate bends under higher than the yield stress. Tension levellers demand somesuperimposed tension. Consequently, imbalanced what smaller line tensions of ~10-40% of the initial yield residual stress fields may be present in the as stress. Multiroll levellers need use only enough applied levelled strip, resulting in bowed material in a tension to pull the strip through the machine. In all cases, further downstream slitting operation. Much work selective elongation of the shortest material fibres ensures has been published on the mechanics of the that strain equalisation of all fibres takes place across the process, and many advances have been made, width, thus removing the initial shape defects. The magniespecially in the design of levelling systems to tude of tension required in each of these processes, to improve shape removal and reduce internal stress remove the incoming defect, is dependent upon the number levels. However, residual stresses and specifically and diameter of bending rolls (workstations) employed. In the imbalance of these stresses post-levelling is an pure stretch levelling no specific bending rolls are used. issue that has failed to be addressed in its entirety.High tensions, therefore, must be generated as a result of To investigate the generation and effects of residual considerable velocity differentials at large diameter bridle stresses owing to tension levelling, a finite element drums. Consequently, this can lead to plastic instabilities (FE) model has been developed with validation in the process and prevalent 'Lu ¨dering', or differential yielding, carried out on an experimental laboratory leveller.in the case of annealed strip. At progressively higher strain The analysis is performed in real time using the levels (1...

Eliminación De Irregularidades Dimensionales De Láminas Trabajadas En Frío Mediante Tensionivelado

“…El proceso de tensionivelado ha sido estudiado por diversos autores [4]; [5]; [6]; [7], con el fin de desarrollar modelos numéricos que permitan simular y predecir el comportamiento de la lámina bajo ciertas condiciones o modelos analíticos que permiten calcula por ejemplo el radio mínimo de curvatura para evitar la fractura del material de cierto espesor y a una determinada tensión [8].…”

Görüntü İşleme Teknikleri İle Rulo Sac Hassas Doğrultmada Silindir Konumlarının Belirlenmesi

“…Hassas doğrultma, sac ruloların açılması ve açıldıktan sonra bir dizi çalışma silindiri arasından geçirilerek düzleştirilmesi işlemidir. Morris ve arkadaşları (2001) yapmış oldukları çalışmada yarı mamul halindeki sac malzemede bulunan kusurların ve eğriliklerin malzemenin mekanik özelliklerini etkilediklerini göstermiştir [8]. Bu nedenle hassas doğrultmada hem kusurların giderilmesi hem de artık gerilme dağılımının dengelenmesi istenir.…”

Prediction of mechanical stress in roller leveler based on vibration measurements and steel strip properties

“…A vast number of these models are concerned with process simulation and parameter analysis. On the other hand, several studies focus on the analysis and control of material behavior in the leveling process (Dratz et al 2009;Madej et al 2011;Morris et al 2001;Park and Hwang 2002). These approaches have a major significance for the design and the improvement of the leveling process.…”