A Simple Measurement System for Optimization of Auto Aluminum Body Sheet Coil Cleaning Lines

摘要

The cleaning of rolled aluminum surfaces is the most important process step before the application of pretreatment on a coil finishing line. Once residual lubricants have been removed by a degreasing treatment before the continuous solution heat treatment furnace, then the critical next step is the removal of the near surface deformed layer. This layer is formed, mainly in the early stages of hot rolling, in the breakdown mill due to the high shear deformation between the strip and the surface of the steel rolls. It is now well understood that sheet surface cleanliness is mainly determined by the residual amount of the near-surface deformed layer on the alloy surface. This layer has nano-sized grains with their grain boundaries decorated and pinned by oxide particles and lubricant residues that reduce the reflectivity of visible light, particularly in the short wavelength range, resulting in a brownish appearance. Innoval has examined the optical characteristics of the deformed layer in detail using a combination of optical metallography, spectrophotometry, and colorimetry to provide a quantitative measurement of the level of cleanliness. We have then used this knowledge and the developed measurement technique to help aluminum ABS producers qualify their products with major automotive OEM's. Our longer-term goal is to develop a simple technique to measure sheet cleanliness that could be developed to provide an online measurement capability. We think that a near to line device could be as simple as using a mobile phone converted to a digital microscope and a colorimeter.