PCB007 Magazine

PCB007-Aug2019

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50 PCB007 MAGAZINE I AUGUST 2019 tank. Conventionally, a two-stage rinse which has been properly designed should be suffi- cient to minimize flow. Typically, a two-station counterflow rinse requires 2–3 U. S. gallons per minute (gpm) of rinse water compared to 5–10 gpm for a well-used single-station rinse. A three-station rinse requires only 1–3 gpm. A four-station rinse may be used when a rinse must be collected and batch treated in a small volume. For initial planning purposes, a dilu- tion ratio of 1,000 to 1.0 is used to determine proper rinsing. Every rinse tank water inlet pipeline should contain a flexible orifice-type flow restric- tor limiting the flow rate of water while the rinse tank is in use. For constantly used rins- es, continuous low flow is desirable (for ex- ample, where selective ion exchange systems will be used to remove copper). Under other conditions, water use should be intermittent. For these applications, a solenoid valve, timer, and activation system (a tank- or wall-mount- ed push button or a foot peddle, which is less desirable) should be provided. Turn off the rinse water when the rinse is not required. This can be accomplished on convey- orized equipment by installing photoelectric cells and/or timers on the immersion rinses to activate and deactivate the water inlet lines only when required. Just being able to activate a rinse and deactivate a rinse when the ma- chine is activated is not enough. Alternating Side Spray Rinses Side pulsating spray rinses for the acid cop- per and etch resist plating lines are an alter- native to flood rinsing to conserve water. We recommend evaluating the use of single-stage pulsating spray rinses in place of immersion rinses in acid copper plating lines. The reduc- tion in water consumption using a pulsating spray rinse is about 85–90% of that consumed using an immersion-type rinse. In practice, the fan-type water spray pattern would first be applied to one side of the panel, and then the source of water would alternate to spray the other side of the panel. This will require two (normally closed) solenoid valves for each rinse station where the spray system is used. The system would be activated by a wall- or tank-mounted push button. When the spray rinse is activated, its instantaneous flow rate may be as high as 95 lpm (25 gpm). How- ever, the rinse would only be activated when a panel requires rinsing, and the panel is located within a specific rinse tank. For example, as- suming a one-minute immersion time for each load of (or "work rack" carrying) panels and 30 loads during a 40-hour week, the weekly average rinse flow rate could be as low as 1.1 lpm (0.31 gpm) compared to 18.9 lpm (5 gpm). That is a reduction of 94% for just that flow rate. Another advantage of spray rinsing is that it will eliminate the need to dump the entire contents of an immersion-type rinse tank, for cleaning purposes, on a periodic basis. Flexible Orifice-type Flow Restrictor Fittings (If Available) The use of flexible orifice-type flow restric- tors with timers may be more efficient than conductivity controllers for immersion-type rinse tanks. We recommend the use of a flex- ible orifice-type flow restrictor located on the water inlet to every immersion-type rinse tank. We are not in favor of using conductiv- ity sensors unless they can be calibrated at least once per week. Conductivity controllers are useful when one desires to reduce water consumption. One reason to use a conductivity controller is when one must collect and then batch treat a rinse if that rinse cannot effectively be treat- ed in the continuous wastewater treatment system. The purpose of an efficient conductiv- ity controller is to reduce the volume of waste, the floor space required, and the cost required to treat a specific waste. With conductivity sensors, the rate of rinse water flow into a rinse tank is a function of the water inlet pipe size (diameter) and the water pressure in the pipeline. The larger the pipe and the higher the pressure, the higher the rinse water flow rate. A conductivity control- ler is used to open or close a valve based on measuring the cleanliness of the water in the rinse tank (assuming the conductivity probe is

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