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Lifting chains for hot dip galvanizing plants have to withstand extremely arduous working conditions and as a result require a very special type of product to cope with the rigours of such an environment.
On one side there are the high working temperatures which can reach up to 475°C. Then there is the operation within the zinc bath which constantly removes material from the chain. On top of this there is an acidic bath which is used to clean the goods prior to plating, and it is this process that produces hydrogen which is dangerous to high strength alloy material and can result in hydrogen embrittlement.
Standard chain slings in grade 8, 10 or 12 cannot be used in these galvanizing processes due to the high temperatures involved, which permanently reduces the working load limit of the product (the maximum working temperature being approx. 380°C for pewag Winner 400 G10 chains). As mentioned above, the acidic bath also produces hydrogen that can result in hydrogen induced stress crack corrosion in these grades of chain, hence the need for a special product to overcome these deficiencies.
Looking for a solution to overcome the above mentioned issues, pewag developed a heat treatment process for alloy material which would help avoid these problems. They manufactured chains (slings) that had a working load limit higher than was normally available at the time, and which were not effected by hydrogen damage. These chains had working loads equivalent to grade 3 (roughly mild steel) at 475°C and it was for these chain assemblies that pewag received the approval from the German testing and approval body. When the European standard EN 818-3 was released in 2000 the DGB withdrew that approval and gave a new approval for chains according to EN 818 part 3 and part 5, and it is this standard that now covers chains for hot galvanizing plants. Following this standard the new chains now have a working load limit at 475°C, basically loaded as grade 4. But as required in part 6 of EN818 (details of safe use and maintenance) the WLL must be reduced by 50% when working at 475°C, and the chains are tagged accordingly with a WLL based at this temperature.
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For more information on Pewag Winner Fire Chains for Hot Galvanizing Plants talk to Brindley Chains