Patent ID: 7070655

Claim:
A pre-treatment tunnel for preparing metal workpieces for a coating process, comprising: a pre-treatment path for workpieces located ahead of a coating apparatus; a overhead conveyor extending along said pre-treatment path and for conveying top-suspended workpieces in sequence in a vertical orientation of the workpieces; a liquid supply at the tops of the said workpieces, facing opposing surfaces of each workpiece at a level below said overhead conveyor and configured for continuously and repeatedly pouring onto said opposing surfaces a free-falling pre-treatment corrosive liquid that extends liquid-flow along a front directed parallel to a development direction of the said pre-treatment path, that covers entirely said surfaces in an almost uniform manner and percolates from tops of said surfaces to bottoms of said surfaces; at least one collection tank for pretreatment liquid discharged from each workpiece; and a recycling system designed to re-circulate liquid collected in said collection tank.