TPT September 2018

T E CHNOLOG Y

Flux regeneration unit and filtration system FLUXING is the last chemical treatment of the steel surface before the hot galvanising process. 1. Collection of fluxing continuously coming from the fluxing tank into the reaction tank where H 2 O 2 and NH 4 OH are added by metering stations.

The function of fluxing components is to prevent iron re-oxidation from the pickling bath to the plunging of parts in melt zinc, as well as to prepare the steel surface to the iron-metallic coat reaction. This fluxing solution is polluted by iron and acid coming from the material treated in the pickling. Iron deposits have a negative influence on the galvanising, and therefore iron must be periodically removed from the fluxing solution so that its level is maintained within acceptable limits. The pH of the fluxing solution coming from the production tank is normally approximately 3 to 4, and does not allow the precipitation of iron hydrate. For this reason it is necessary to add an alkali to bring the pH to 4 to 4.5, so that formation of Fe(OH) 3 is favoured. As fluxing is basically composed by a double zinc-ammonium salt, it is

2. The reaction is automatically controlled by a pH meter and an RH meter. Transfer to the filter press by means of the feeding pump of the filter press itself. 3. The fluid passes through the filter press, leaving on it ferric hydrate crystals, and comes back to the tank neutralised and filtered. There are standard units that can be incorporated into existing galvanising plants for tubes or can be supplied with new galvanising plants. Precimax, India, offers units that can comfortably handle production of galvanising pipes of up to ten tonnes per hour. Precimax Engineers Ltd – India Fax: +91 22 27544917 Email: marketing@precimaxonline.com Website: www.precimaxonline.com

necessary to use ammonium hydrate as alkali, so that the solution is not polluted with ions other than the ones used in the basic composition. To oxidise the iron II to iron III form in which it can be precipitated, it is necessary to add H 2 O 2 . The fluxing treatment is performed as follows:

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SEPTEMBER 2018