Investigation of Stresses on Tie Band Used to Wrap and Fasten Rolled Coils

The research was motivated to establish a scientific basis for the required number of steel tie bands used in wrapping and fastening hot rolled coils produced in steel manufacture lines for safe delivery and storage. Strain gages were installed on the tie bands and stress was recorded during the banding and delivery procedure of rolls in the field. The stress developing in the bands due to fastening of the roll and that due to springback of the coil were clearly distinguishable from the strain gage signals. Twelve hot rolled coils having different yield strength, thickness, width, and weight were tested in the recoiling field. The results showed the average tensile stress developing in the bands due to the fastening of the roll to be 151.7 ± 53.8MPa, which corresponded to one fourth of the failure strength of the steel band in the buckle region. In addition to the stress caused by fastening, average tensile stress caused by springback of the rolled coils was estimated to be 33 MPa. It increased to 79 MPa when one of the tie bands was removed from the roll. Comparing the measured stress due to springback with the theoretical stress formula yielded a proportional constant value of 0.219, and a correlation coefficient of 0.914, which demonstrate the formula to be useful in predicting springback stress. The average safety factor of the tie band was found to be 3.26 and it decreased to 2.60 when one of the bands was removed from the roll. The safety factor of the band was found to decrease with increased coil thickness because the current factory standard on the number of bands does not significantly take into account of increase in the springback force with increased coil thickness.