Rinsing Manual

Three Fundamentals of Good Rinsing

• Reduce dragout
• Increase rinsing efficiency
• Control water use

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  Reduce dragout

  Dragout refers to the chemicals that remain on parts after they have been removed from a solution. It includes gross amounts of plating solution held by cup-shaped parts and recesses, but it also includes an unavoidable thin liquid film covering even well-drained surfaces. The job of rinsing is to dilute the remaining dragout as much as possible, so that the parts are as clean as possible as they move on to the next process step.

  The first and most important step toward achieving better rinsing is dragout reduction. The less the dragout volume, the less rinse water will be consumed, and the less sludge will be generated during treatment. There are numerous proven methods, techniques and procedures for reducing dragout. In most cases, several options can be combined to optimize a plating line. Examples include:

  • installing dragout tanks
  • developing improved barrel/rack designs
  • installing spray rinsing systems over process tanks
  • increasing drain times
  • installing drip boards

  Appendix A of this manual describes these options and other common methods of reducing dragout.

  Tip: Whenever you start a rinse improvement project, measure the volume of dragout before you make any changes. This will give you a baseline against which you can compare results after improvements have been made. A simple method of dragout measurement is provided in this manual.

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  Increase rinsing efficiency Rinsing efficiently means using less water and generating less wastewater while still doing the job of getting the parts clean. The most common and effective way of increasing rinse efficiency is to install multiple rinse tanks, and to use the water from a cleaner tank to flow into the tank before it. In the case where there are two rinse tanks, this configuration would be called a two stage counter flow rinse system.

  Time, floor space and money are limited at every metal finishing facility and these three factors will impact decisions on how to increase rinse efficiency. It would be easy to design a rinse system that used only a trickle of water a day -- simply increase the number of rinse tanks in each rinse system. But each additional rinse tank costs money, increases the time needed to process the parts, and takes up valuable floor space that could otherwise be used for production. The best solution for your shop might involve a combination of potential improvements. In addition to multiple rinse tanks, there are many techniques and devices that you should evaluate, including improving tank design, and adding auxiliary devices such as air agitation, and supplementary spray rinses, to mention just a few.

  Appendix B of this manual describes these options and other common methods of increasing rinsing efficiency.

  Tip: In addition to establishing a baseline for dragout volume, you should also measure the rinse efficiency of your existing systems before making changes. This will give you a baseline against which you can compare results after improvements have been made. A simple method of measuring rinsing efficiency is provided in this manual.

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  Control water use The third leg of good rinsing practice is controlling the flow of water so that it is used in proportion to need. Many years ago, it was common to see rinse tanks that flowed steadily 24 hours/day, 7 days/week, regardless of how many parts were being processed and, in the worst cases, whether or not the plating line was even in use.

  Controlling water use means coordinating water needs and water use, which translates to using more or less water as production increases and decreases. There are a wide range of techniques and equipment used for this purpose. What usually works best are approaches that do not rely on operator control, which may or may not be reliable.

  Common water use controls include flow restrictors, conductivity controllers, and timer controllers. The best approach for a facility will depend on a number of factors, including how much production volumes tend to fluctuate, and how much of the production line is automated vs. manually controlled.

  Appendix C of this manual describes these options and other common methods of controlling water use.

  Tip: Water meters that measure and track water use can be a useful adjunct to water control. Every shop has at least one water meter -- the one used by the local water authority for billing purposes. More and more shops are installing additional water meters to find out exactly where and how much water is being used. Supplementary meters can be added to each plating line, or even to individual rinse systems. The more specific the location of the meter, the more useful the data.