CH-18A
ZINC PHOSPHATING
$er-DuctolEJagitation improveszinc phosphate tank sludge removal
Advanced Technical Coatings Ltd. of Haslingdenin Lancashire, England, has been one of the largerand more diverse subcontract trade powder coatersin northwest England for over 25 years. The companycaters to most needs of the polymer finishing indus-try with a wide range of coating materials for dealingwith all kinds of components, large or small. It is theirstrong orientation to quality, a commitment to meet-ing agreed delivery schedules, and an experiencedworkforce, which has madeAdvanced Technical Coat-ings Ltd. a leader in their field. It was this commitmentthat gaveAdvanced Technical Coatings the determi-nation to solve, once-and-for-all, the industry-wideproblem of accumulated sludge in their zinc phosphatetank.
For many types of paint and powder coatings, itis necessary to pretreat with a zinc phosphate coat-ing, either by an immersion or a spray process. Zinc
' phosphate is a heavy sludge generating processwhich, if allowed to accumulate in the spray sump orthe immersion tank, can leave a whitish phosphatesalt deposit on the component product that results inpoor adhesion and poor "wetting out" of the coatingduring melt. In addition, this accumulation of sludgewill produce a hard, baked-on scale on the heatersor burner tubes that results in poor temperature controland failed heaters, not to mention the continual prob-lem of blocked nozzles on spray systems. The usual
method of solving this problem is to let the sludge settleto the bottom until an unacceptable level is reached,and then to decant off the clear liquid and either getin the tank and dig it out or, more commonly, to em-ploy the services of a waste disposal contractor tocome and suck out the liquid sludge.
To maintain their commitment to product quality,and their policy of SPC (statistical process control)on production, Advanced Technical Coatings Ltd.realized that they had to find a better way of keepingthe phosphate tank clean. They installed a SERFILCOAutomatic Fabric Filter with pumped agitation toremove the sludge continuously and automatically.This equipment replaced an existing filter chamberwhich simply could not keep up with the amount ofsludge being produced.
While similar types of filters have been used insuch an application in the past, Advanced TechnicalCoatings Ltd. has achieved success more as a resultof the way the equipment is installed and used. Thekey to the success of a filter system is to keep thesludge in suspension, not to let it settle, and to removeit as quickly as it is produced. This is where pumpedagitation plays an important role. The basic principleis to continuously recirculate the phosphate solutionthrough a manifold arrangement in the bottom ofthe tank using a high flow/high pressure pump.SER-DUCTOR@ nozzles which greatly increase
solution movement are spaced at regularintervals along the manifold as illustratedin the schematic arrangement (on page 2).
. From this recirculation pipework, a bleedis taken to the Automatic Fabric Filter at apredetermined optimum flow rate and fedonto the fabric media on the filter bed. The
phosphate solution drains through the fil-ter media and into the filter sump fromwhich it is piped back to the tank. As thefilter media gradually becomes blocked withsludge, the solution level on the filter bedrises, trips a float switch which indexes the
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bed, and introduces fresh, clean filter media~ ." to the pumped solution.
Meanwhile the sludge layer built up on the filtermedia is discharged off the end of the bed and col-lected in a suitable container. By elevating the filterabove the phosphate tank, a gravity return of solu-tion to the tank is possible, allowing a sludge hopperto be placed below the end of the bed and it also pre-vents accidental syphoning of the tank contents.
All pipework, as well as the SER-DUCTOR@nozzles and recirculation pump, is plastic for totalchemical resistance and, being smooth bore, will mini-mize the "furring" effect so common with zinc phos-phate solution in metal pipework.
For powder coaters who are zinc, iron or manga-nese phosphating, or chromating, the advantages andbenefits of desludging using anAutomatic Fabric Filterin this fashion are considerable. They are:
1. No need for the maintenance staff to climb into the
tank and manually shovel out the sludge; filtrationand sludge removal are continuous.
2. No need to periodically decant off the solution andhave the liquid sludge sucked out by tanker, elimi-nating the associated high cost, volume-relatedcharges so incurred.
3. No downtime is required for cleaning or descalingthe heat exchanger tubes. Production and uniformtank temperature can both be maintained.
4. No more tank sludging; no more blocking of spraynozzles. Once a clean solution is made up, the bathremains clean. Phosphating quality is improvedand the higher quality level is maintained.
5. It is easier to dispose of the sludge. There's lessvolume by consolidating it in a hopper and lesstreatment cost as well.
6. Chemical loss is greatly reduced; the resultantsludge contains far less liquid than can beachieved by simply decanting.
Taking all of this into consideration, paybackoften occurs in less than 12 months.
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CH-18APage 2
Installation schematic ofAutomatic Fabric Filter
desludging the zinc phosphate tank.
AutomaticFabric Filter
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Sludge. 0,
Hopper
Ser-Ducto~AgitationNozzles
Advance Technical Coatings Managing Director,Mr. Gordon Nicholass, says "from the first moment thatwe switched the machine on, there was a significantimprovement in the standard of zinc phosphating onour components. . . we are considering extending thismethod of filtration to our iron phosphating andchromating processes".
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fS=1SYSTEMS ANDl:eJLJTECHNOLOGYCo.61 Iran Street, Dokki, Cairo, EgyptTel: 202-761-4150 335-3664Fax: 202-337-0597Web: www.sat-eng.comem ail [email protected]
~~~110I1rs(!)~(!.U'[D.1777ShermerRoad 847.559-1777Northbrook,IL60062-5360U.S.A. 800.323-5431Email: [email protected] FAX:847-559.1995
Web:http://www.serfilco.com
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