Exponential Rinsing

Originally Published June 2017

Question: Why should you consider using multiple rinse tanks? Wouldn’t it be cheaper to build one big rinse tank? Won’t automation and parts handling be easier with one tank? Wouldn’t the cleaning process run faster?

Before we answer this… Let’s review product cleaning during manufacturing. Soil is matter out of place; cleaning is removing matter out of place. Most cleaning processes – industrial cleaning, precision cleaning, and critical cleaning – include wash, rinse, and dry steps. The wash step effectively removes soil from surfaces of the part and to keeps that soil away from the vicinity of the part. The rinse step removes residual soil and cleaning agent; typically you don’t want that cleaning agent any more – so we consider it to be a soil. The dry step removes residual water and/or adsorbed solvent.

And the answer is… Multiple, smaller rinses are better than a single large rinse.

To understand why, let’s look at two scenarios:

1: A single 300 gallon rinse tank is used. Let’s assume that it is 99.67% effective in removing cleaning agent containing residual soil. After rinsing, 0.33% or 3300 parts per million( ppm) of the soil will remain.

2: Three 100 gallon tanks are used sequentially. The same total amount of water is used, but each tank is 1/3 as big as in Scenario 1. Assuming that the rinse efficiency is proportional to the volume of water, three times as much residue will remain after the first rinse. That’s 1% or 10000 ppm of the soil. However, after the second rinse, only 1% of the 10000 ppm soil residue, or 100 ppm remains. The third rinse reduces the residue another factor of 100 to 1 ppm!

Multiple small rinses are more effective than fewer big rinses. Rinsing efficiency increases by the power of the number of rinses. We usually recommend at least two rinses. Frequently three rinses or occasionally even four may be needed depending on cleanliness requirements.

There’s a lot more to rinsing
Without effective rinsing, you more than likely won’t get clean surfaces; designing a great rinsing system takes “cleaning street smarts. The examples above do not include all the variables. In addition to multiple rinse tanks, you need to consider factors like cleaning action, soil loading, bath monitoring, corrosion prevention, and water quality. Stay tuned for more rinsing ideas to improve productivity and product quality. If you’d like to talk about rinsing right away, just contact us.

This article originally appeared in the May/June 2017 issue of Clean Source

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