Rangaire LP, Cleburne, Texas, has been increasing in productivity and capacity for the last 20 years, and every time a bottleneck is found, it is quickly removed, replaced or repaired. Such was the case when the reverse osmosis (RO) water system proved too small to allow a second shift in the finishing department without compromising product quality.

Rangaire produces range hoods with a class A finish at a rate of about 6,500 or more per shift. The cosmetic requirement of this product is high; excellent gloss and zero defects on appearance surfaces are mandatory. Pure water for rinsing is one of the keys to good gloss and adhesion, as well as final removal of particulate contamination after phosphating.

The parts first go through a five-stage washer process with an RO halo. Alkaline cleaner, rinse, iron phosphate, rinse and RO rinse all work together to produce cosmetically uniform parts ready for powder coating. The iron phosphate product used in the process is formulated to produce a perfectly uniform surface to prevent any "photographing" of surface inconsistency through the paint. Pure water for rinsing reduces water spotting on reworks and first run parts. The final RO halo is provided with virgin pure water from a holding tank, which is made up by an RO water purification system.

The problem was that the RO system was undersized by design when it was purchased almost 12 years earlier, the idea being that the holding tank would provide enough capacity so that the system could keep up during the day and catch up at night. When Rangaire added a second production shift, the RO immediately was a problem.

Another problem came up one day when suddenly the phosphate stage became impossible to control, cleaning began to suffer and the final rinse TDS (total dissolved solids) went to more than 1,000 parts per million (ppm). After several hours of head scratching and other troubleshooting techniques, it was discovered that the city had activated an old well to keep up with capacity. During the next several weeks, every time the city activated that specific well, the plant manager got complaints from the paint department and immediately called the city to request they turn it off. The RO system was removing some of the solids coming from that source, but the loading was so high (more than 3,800 ppm solids) that the system just could not handle it; water production would fall, and the product water quality became unacceptable.

Rinse water in all washers hits an equilibrium at which there is as much contamination coming into the tank as there is going out via overflow and dragout. The washer system also was modified to counterflow cleaner water upstream to earlier stages, thus saving the pure makeup water for the later stages where it is most important. It turns out that filling your washer with pure water only changes the starting point - the equilibrium is the same no matter where it starts.

Over the years since the system had been installed, the membranes had been well cared for by a service company, and replaced at reasonable intervals, so system productivity was pretty much at the level the system had been designed for, but it wasn't high enough. Rangaire contracted with R₃ Technologies to rebuild the system and upgrade it to 10 gal/min from the original 5 gal/min.

R₃ Technologies started by testing the entire system to be sure all the components were capable of running at the higher level, then built a strategy to upgrade the system by adding capacity where needed. A larger high-pressure pump, more membranes, new plumbing and changes to the pretreatment were necessary to accomplish the upgrade. The control system, one of the most expensive parts of the system, was sufficient without changes. A 480 V motor starter was added to run the larger pump motor instead of the relay that had been used to run the smaller motor before.

With the increased capacity and water quality, the problems with water spotting and drips have been almost completely eliminated. It is a fact that RO water (or any form of purified water) is corrosive to steel. The washer at Rangaire is stainless steel, but even if it was not, a single halo at the end of the washer, which then falls to a rinse tank and is counterflowed to the rest of the washer, is very unlikely to cause corrosion problems anywhere other than in the immediate area of the halo. Those problems are overcome with injected chemistries or non-corroding shroud materials.

The work took place over a weekend and on Monday morning the rebuilt system was producing more than 12 gal/min of fresh RO water to replenish the halo and overflows. After a little adjustment, the system settled in to a 10 gal/min production, keeping up with the needs of the halo and overflows. This upgrade project cost less than a new system and made a smaller disturbance in the plant than installing a whole new system may have. The lead time was short, and because the controls were not changed there was very little learning curve or re-training after the rebuild was complete. Rangaire was able to upgrade its RO system at less than half the cost of installing a new system - a winning proposition in these days of doing more with fewer resources.

R₃ Technologies can be reached at 817-313-6439, or visit www.R3Web.com.