REMCO RINSING

Counterflow or cascade rinsing, (CFR), is generally accepted as a preferred method of removing chemical residues from process solutions. A single step rinse is only as clean as the solution after a rinsed rack or basket is removed. The usual means of of keeping the tank as clean as possible is to run a lot of water through the tank before the next rack enters so that the inevitable buildup of dragout ions is minimized. By going to a counterflow rinse process, the amount of water needed to cleanse the tank is minimized because as the second rinse tank is only about one-tenth as dirty as the initial rinse. To maintain the same ion level in a single rinse as a CFR rinse requires ten times the flow. (See appnote #2)

Several other factors affect the rinsing and cleanliness of the processed parts. The initial dilution factor when entering a tank is important. Here is an experiment you can perform to satisfy yourself that what I am about to suggest is valid. (see timers and flow controls here)

First select a process tank with a colored solution that can be seen mixing with the rinse water. Second, run enough water through the following rinse tank to make it appear colorless. Third, most rinse tanks are air agitated so turn off the air. Also turn up the water flow so that the surface seems to be flowing to the drain. Fourth, select a process rack or basket of work and run it as a normal work load. When entering the selected rinse, allow the work to slowly enter the water and watch the flow of the color.

If the above experiment is run, you should see that 75-95% of the color is removed in the top inch or two as the work enters the rinse. The rapid flow of the rinse water should carry most of the color to the drain before it can be mixed and diluted in the bath. The results indicate that you can maintain a much cleaner bath and therefore reduce part contamination and drag through using a few simple modifications to your present operation. To take advantage of this phenomena requires two different strategies depending on the type for rinsing you do. If you have a single flow rinse tank following you process tanks, you should turn off your air agitation and turn on your water flow when starting to rinse a part. Most of the contamination will be rinsed off the part as to interfere the bath. After the part is in the tank, the air can be turned on again. When the proper amount of water has flushed out the tank, it can be turned off. Your overall water consumption should not decrease and you will have a much cleaner part and a lower concentration level in the rinse upon exiting the bath.

If you are using a counterflow (cascade) rinse tank, the process is easier. Turn off the air entirely in the first rinse. When the work enters the tank, turn the flow up to maximum. You should have the total flow needed to maintain a clean rinse calculated (See appnote #2), use it all over the shortest period possible but not less than the total rinsing time. For example, if 15 gallons per basket is the required water usage to maintain a 30 ppm contamination level and two minutes are required in each side of a dual counterflow rinse, then, 1.5 gpm should be run for 1.5 minutes, then the rinse should be turned off.

The advantages of the above process change are many, but the major ones are a reduction in panel contamination, a reduction in process solution drag through, and if you don't already control rinse water, the installation of (rinse water control procedures) with the resulting savings of thousands of dollars in sewer fees, water cost, and waste treatment costs.