CASE STUDIES: IN-SITU REBUILDING OF DAMAGED ROPE DRUM SHAFTS OF SSG CRANE AND THE REPAIR OF CIRCUMFERENTIAL CRACK OF CEMENT KILN BY WELDING.

Abstract

Material failures in engineering are characterized by unwanted downtime of equipment and require theapplication of sound engineering principles to rectify the problem so that it does not reoccur. The most widelymethod for repairing damaged steel structures such as rope drum shaft or cracked cement kiln is by Manualmetal arc welding. The equipment mentioned have their main importance that, when they are broken down,they cost a lot of money in lost revenue and affects a lot of people in terms of business and livelihood. Thenominal diameter (DN) 240 rope drum shaft was damaged when the roller bearing failed and abraded the shaftbearing journal in such a way that the diameter decreased. The solution was either to order the new shaft, orrepair the existing shaft in workshops with lathe machines capable of accommodating it. Ordering the new onewill have taken a long time to deliver. Installation process would have been costly taking into consideration theposition of the hoist drum being at a height of over 40 meters above the ground, and no crane was availablein the country with required capacity. The remaining and immediate solution was to repair the damagedbearing journal in-situ. The paper describes how the repair was carried out successfully, and has been inoperation since 1995. Recently, another failure of the same nature occurred on another equipment in whichthe same assistance were sought. In 1994, the cement kiln was found to have a 270 mm length circumferentialcrack on a 65 mm thick plate which needed urgent repair so that the production of cement can proceed whilewaiting for replacement. The immediate repair was necessary to avoid the bending of the kiln which wouldhave caused uneven rotation and poor sealing of refractory bricks. The crack was on the cantilever section ofthe kiln which, if the crack was allowed to grow, would have caused the section with cooler tubes to snap off.The paper explains how the repair was carried out allowing the plant to operate for two years before segmentreplacement.