EOW May 2007

english

Rinsing methods in the wire and tube industry By K D Nittel, Member of Chemetall GmbH, Frankfurt/M, Germany

1. Technical terms In the following description of rinsing methods certain terms are used which are briefly explained here. Together with the wire coils or tube bundles a certain amount of treatment solution – carry- over – is transferred from one bath to the next. Depending on the viewpoint, this may also be termed the drag-out or the drag-in. The amount of the carry-over varies considerably; it is dependent on the geometry of the work pieces and the drain-off times. A guideline figure for a wire dip line based on a wire diameter of 5.5mm is 150ml/m 2 . For tubes, based on an outer diameter of 30mm, with 100ml/m 2 . The ‘ rinsing factor ’, also known as the ‘ rinsing criterion’, is the ratio between the concentration in the rinsing bath and that in the previous process bath; it is often given as a ratio, eg 1:100. In addition to the carry-over, when considering rinsing methods allowance should be made for a possible overflow – into the waste water or effluent pre- treatment system or into another treatment tank – and a possible influx – of fresh water or overflow from another treatment tank. The stationary concentration would occur in a rinsing bath if all processes – treatment, influx, and overflows – were to operate continuously. The following balance would then apply:

Rinsing operations form an essential part of a treatment line in the wire and tube industries, and water rinse processes have a strong effect in the following areas: Poor rinsing methods may not only result in unnecessary carry-over of chemicals into the subsequent process baths, associated with sludge formation, higher consumption and lower bath life, but they may also jeopardise the quality of the conversion coat formation; High water consumption is a major cost factor, in addition to the related treatment costs; In many areas water is becoming short in supply. Tap water is needed for human consumption and not for industrial rinsing processes; It is believed that just one rinse tank may help to save water. Two rinse tanks connected in the right way are not only much more efficient, but also save a lot of water. Chemetall is the leading chemical supplier in Europe as far as the wire and tube industries are concerned. • • • •

The company not only sells cleaners, activators and phosphating products, but also all related lubricants, and believes in working in partnership to increase quality and productivity. This article describes the typical rinsing methods. It gives a clear guideline as to which technology and treatment line layout may minimise water consumption to the lowest possible levels or provide a higher quality level as far as surface treatment is concerned. The mathematic formulas allow each technician to adapt the figures to his needs. The target is to provide help and ideas for new lines as well as for the optimisation of lines already in use. The author and the company feel the responsibility to be a true partner for these industries under both technical and economical aspects. This summary does not refer to administrative regulations or any other legal aspect.

Figure 1 : Drag out rinse

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drag–in + influx = drag-out + overflow,

both to the volume and also to the substances dissolved in it, if the evaporation losses and consumption due to chemical reactions are disregarded.

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EuroWire – May 2007