ANALYSISofSurfaceRoughnessofColdRolledAluminium.docVIP

PAGE  PAGE 8 ANALYSIS of Surface Roughness of Cold Rolled Aluminium Foil HR Le and MPF Sutcliffe Cambridge University Engineering Department, Trumpington Street, Cambridge, CB2 1PZ, U.K. ABSTRACT This paper describes a detailed analysis of the surface finish of aluminium thin strip and foil which have been cold-rolled under industrial conditions in the mixed lubrication regime. Initial strip was rolled with freshly ground rolls at constant speed for the first pass and at a wide range of speed for the second pass. Strip samples were collected after the second pass. For comparison, samples were also collected after rolling with worn rolls. Surface replicas of the rolls were taken with surface replicating tape. The surface roughness of the strip samples and roll surface replicas was measured with a three-dimensional non-contact interferometric profilometer. The spectrum of the surface roughness was analysed by the Fast Fourier Transform method to identify the way in which different wavelengths of roughness behave. Theory suggests that longer wavelengths of roughness should be crushed more easily. This was confirmed by results. A new image analysis technique has been developed to identify and quantify the area of the micro-pits. To differentiate between these pits and grind marks transferred from the rolls, the height information was first filtered in the rolling direction using a digital filter. The low frequency component of the surface roughness, which represents the contribution from the roll marks, was subtracted off to leave the pits. Results showed a significant decrease in deep pits during the pass schedule. There was a significant increase in hydrodynamic pitting on the surface with increasing rolling speed during a pass. Key words: roughness, surface finish, surface spectrum, hydrodynamic pitting, mixed regime, lubrication and metal rolling Submitted to Wear, Nov 1999. Nomenclature f sampling frequency of surface measurement, hi (i=1~n) data arra