Process Inustry - Elementis Chromium 6.5m dia girth ring repair
Problems with a series of cracks emanating from oval windows between the spokes of a giant 6.5metre diametercast steel main girth drive gear on one of Elementis Chromium’s kilns have been overcome by Metalock Engi-neering using its metal stitching process to secure infill plates into the windows.
The 5 metre diameter 90 metre long kiln is used for chromium calcining and when cracks were first noticed infour of the windows a specialist welding team was used to weld steel plates into the ovals. Two of the windowswere filled in and the cracks welded but unfortunately, they cracked again. Rather than fix plates into the remain-ing two windows, Elementis consulted with Metalock to see if they could suggest a solution. An alternative wasto replace the gear but as well as the high cost, delivery would not be for 9 months. Add to this the downtime tofit a new gear and the cost was estimated to be about £¼ million.
After examining the gear, Metalock engineers decided that a possible solution would be to remove the weldedinserts and fit new ones with tails top, bottom, left and right and secure them with metal stitching.
The Metalock process is the accepted repair technique for all cracked, broken and damaged castings in castiron, aluminium and steel for a wide range of industries in a multitude of applications. The repair consists ofpeening layers of Metalock special nickel alloy multi-dumbbell shaped keys into prepared apertures. These keysare highly ductile and can be peened into a metal-to-metal condition to become almost integral with the compo-nent’s parent metal. Metalock keys are manufactured in a variety of sizes to suit each individual job. Their highstrength ensures the return of a high percentage of the original strength. The essential advantages of theMetalock repair are that no heat stresses are introduced, no distortion occurs and, in many instances, machiningis unnecessary. The process is invaluable in emergency situations and in many cases where the component isaccessible, it can be done in-situ to avoid costly dismantling and re-assembly.
To repair all four windows in one session would have taken 20 days and as Elementis could not allow the kiln tobe out of operation for that length of time, it was agreed that the operation be staggered with one window beingrepaired a month. In the event it took four men on 12-hour shifts 4 days to effect a repair.
As well as the window stitching operation Metalock devised a system to stitch a tie plate located in cut-outs in theribs either side of the repaired window to provide some additional strength. A tie plate was also applied acrossthe remaining welded insert to provide support while Metalock were off site between stitching repairs. Over 12months has passed since the last repair and the gear has shown no further signs of cracking which is evidencethat the Metalock process is suitable for repairing cast steel as well as cast iron components.
The 6.5 metre diameter cast steel gear developedcracks emanating from four of the oval windowsbetween spokes. As well as metal stitching platesinto the windows, Metalock stitched tie platesacross the ovals to provide extra strength