Safe opening of bolts in spite of zinc melt
Galvex, part of ArcelorMittal, operates Europe’s largest hot-dip galvanising plant near Tallinn/Estonia. In the plant, which was built in 1997, Galvex processes roughly 500,000 tons of sheet steel every year. The sheet steel passes through a production line with a bath of molten zinc which has a temperature of +542 °C. By the help of a bottom roll the sheets are pressed into the hot zinc bath and fixed there. The bottom roll itself is fastened on plates with bolts and nuts of stainless steel which have to be replaced every five days. Their disassembly caused considerable difficulties again and again as the zinc melt also flows between the bolt-plate-connections causing strong seizure. This made a disassembly by the help of an angle grinder necessary and the bolts could not be used again. Furthermore, the opening of the connecting plates required an extreme amount of force and special tools. Usually, the opening of the plates took four hours.
ADDINOL recommended the application of ADDINOL Anti-Seize Paste GAL. The special paste of silver-grey colour is based on selected synthetic oils, a special thickener, finely dispersed solid lubricants and nonferrous metals. Its application range lies between -40 and +1.200 °C. At Galvex ADDINOL Anti-Seize Paste GAL was applied between all connections fixing the bottom roll. When the bottom roll is heated to up to +530 °C the paste penetrates into the smallest gaps of the connections and builds an efficient protective film. Tarmo Pertlas, Mechanical Supervisor at Galvex Estonia, after the disassembly at the end of five days with ADDINOL Anti-Seize Paste GAL: "During the disassembly of the bottom roll after five days in the zinc bath the bolt connections could be opened without any difficulties for the first time and also the plates could be loosened without any problems. The bolts and nuts cannot only be used once but three times now!"
German article published in Metall 12/2008 (view German article here)