In an apparatus for depositing paint on metal articles by an autodeposition process, positively charged metal ions gradually migrate from articles into the dispersion of negatively charged latex resin and pigment particles so as to eventually render the dispersion ineffective for paint deposition. Instead of discarding this contaminated dispersion, it is reconditioned by passing it through a column of ion exchange resin beads in an ion exchange process that removes the metallic ions from the dispersion. After reconditioning, the paint dispersion can be reused. The ion exchange column is provided with screens that allow the paint dispersion to pass while preventing release of ion exchange resin beads into the autodeposition coating working bath. Unfortunately, however, conventionally used screens soon become clogged by a compacted aggregation of ion exchange resin beads, dispersed latex particles, and dispersed pigment particles.
The screening apparatus is constructed so that the paint dispersion passes via a first screen into a bed of ion exchange resin beads and then via a second screen to a riser pipe from which the reconditioned painting dispersion flows. The aggregated beads-latex-pigment are primarily deposited on the input side of the second screen. During backflushing, conducted to remove the latex and pigment dispersion from the bed of ion exchange beads, aggregated beads-latex-pigment are primarily deposited on the input side (input for backflush flow) of the first screen.
A significant disadvantage of the screening system just described is that, even with reversing flow direction across the screens, within a short time it becomes necessary to disassemble the ion exchange column and thoroughly clean the compacted aggregate from the screens. This requires a great deal of time during which the ion exchange column is out of service.