Midwest producer of water based latex paints and stains recently added a line of interior one-step polyurethane stain and finish products to its manufacturing and filling operations. The production of these new products presented little challenge to plant formulator’s and chemists, however; when it came to getting the product into its quart containers, plant management, engineering, and the filling supervisor all required a lesson in finish filtration.
Being an environmentally friendly producer of paints and coatings previous production techniques incorporate the latest in mechanical clean-in-place filtration technology in an effort to close the process loop, reduce waste at the source, and address local, state and federal environmental issues. While this filtration technology, provided by Ronningen-Petter Engineered Filter Systems, Portage MI USA, performs flawlessly meeting and exceeding plant quality standards while addressing corporate environmental objectives, the DCF Series clean-in-place filter systems which employ slotted wedge wire media regenerated by a cleaning disc device were unable to meet the quality at retention required when filtering the polyurethane stain and finish.
Filter Media Challenges:
While a welcome contribution when removing unwanted paint "skins" and undisperssed pigments from latex paint it seemed slotted wedge wire was not suitable for the removal of the extremely small debris distributed sporadically throughout the polyurethane stain and finish products.
Slotted wedge wire elements use nominal ratings. This simply means that a very small number of screen openings may be larger than the specified retention rating. Further, no surface media such as the screens can be rated "absolute" for irregular-shaped solids. Surface media rated absolute would be only for spherically-shaped solids since elongated solids could pass an opening lengthwise because its girth can be smaller than the absolute retention rating of the media.
When testing the self-cleaning filter technology with wedge wire elements at retention’s well below that required it was apparent that the alignment of the debris would still present passage of unwanted debris jeopardizing product integrity and quality. Corporate engineering suggested filtering the polyurethane products with Cuno cartridge filters. To simply "Cuno It.." was the statement which represented the tested, proven method for filtration of the polyurethane products for many years, possibly to many years in plant opinion.
While plant management and engineering respected the "Cuno It…" mentality, and with appreciation it would work, it seemed to these individuals to be a step backwards in terms of their environmental and plant mission statement. It was decided at this time to investigate alternative polishing filtration technologies.
Bag & Cartridge Filters:
When comparing filtration methods plant engineering and maintenance thoroughly investigated the difference between surface and depth filtration, and cartridge and bag filters. Already familiar with cartridge filtration and its negative issues it was decided to pursue the possibility of incorporating a R-P Products bag filter as the final filter.
Unlike the Cuno filter which would require the disposal of four fluid laden cartridges when differential pressures approached 12psid, a set of four cartridges designated for each polyurethane product, and the maintenance required to change cartridges between dissimilar products, the R-P Products SE Series filter proved to be much simpler by design, and provided the media flexibility to accomplish the task at hand while minimizing the waste.
Having little experience with polyurethane stains plant engineering elected to install the R-P Products SE Series bag filter and perform tests prior to its permanent employment.
Filtration goals were in order:
The Process:Once prepared, the high gloss polyurethane product was sent to the filling line in 500 gallon totes where it would be agitated continuously during the filling process. A flexible hose located coupled at the bottom of the tote is coupled to a 2" air-operated double diaphragm pump inlet. The diaphragm pump pushes the polyurethane finish through a Ronningen-Petter DCF-800 (less element) and into the top inlet of a R-P products SE-224 2" single filter vessel.
The filter vessel incorporated a 510"2 polypropylene filter bag at a retention below that requested by the chemists and formulator. As the filtrate exited the R-P Products bag filter it entered the rotary drum of the quart filling machine. The flow to the rotary filler is controlled by using an electronic level sensor within the drum which automatically opens and closes the rotary supply valve and starts/stops the diaphragm pump just prior to the valve operation. Controlling the rotary valve in this manner avoids hydraulic pressure surges and relatively high process pressures when the diaphragm pump would stall as the supply valve to the rotary would close.
When the filling process was started (with no element in the DCF-800) the clean pressure drop across the bag filter was approximately 8psid and quality tests were acceptable. Another successful quality test was conducted at 100 gallons with a filter differential of 10psid which illustrated an equivalent solids loading of 2psi. At the end of the 500 gallon batch solids loading contributed to a 3psi increase in filter differential and all subsequent quality tests were acceptable.
The original R-P Products filter bag had been proven successful for four 500 gallon batches at which time, for security reasons, a new bag was installed and the original cleaned and air dried. There was no need to "scalp" the polyurethane finish with the Ronningen-Petter DCF-800, or implement the High Efficiency R-P Products filter bag to meet quality concerns.
This Midwest manufacturer of one step high gloss polyurethane stain and finishes has no need to "Cuno It…" which would have resulted in higher capitol expense, residual cartridge purchases and the affiliated cost of waste cartridge disposal.
By implementing the R-P Products bag filtration technology waste is kept to a minimum by incorporating reusable polypropylene media, high product yield is maintained, and operator costs are reduced significantly as no bag changes or cleanings are required throughout the entire batch.
With R-P Products bag filter performance proven the corporate "Cuno It…" mentality may soon become the "R-P Polish It…" philosophy.
