Chemical Concentration – Economic and Process Considerations (cont.)

My previous blog addressed the chemical cost of using too much (or perhaps too little) “soap” in a cleaning process based on chemical cost.  Today we look at process issues.

You might be saying, “What the heck?  So I use too much chemical.  Soap is cheap and I look at it as “insurance”.”  Well, that “insurance” might not be as insuring as you think!  Excess chemistry can lead to a number of related issues including but not limited to the following – –

Physical Effects –

Most cleaning chemistries are soluble (or miscible) in water only up to a given concentration.  This is true of both liquids and powders.  Excessive chemical concentration may result in the separation or stratification of liquids or, in the case of powders, failure of the chemical to completely dissolve thereby leaving sludge in the cleaning tank or reservoir which may interfere with the proper operation of pumps, nozzles and filters as described in more detail below.  Excessive concentration of liquid chemistries may result in a “slick” of surfactant on the liquid surface which may add to part contamination.

Equipment –

Most cleaning equipment is designed for use with a particular level of chemistry concentration.  Things like pumps, valves, pressure and level sensors and filters, are selected with the assumption that they will operate in a “friendly” environment (unless it is known in advance that other conditions can be expected).  Pumps, as one example, require different materials of construction and seals for use with a 50% solution of sodium hydroxide than they do for use with a 5% solution of the same chemistry.  Improperly specified optical, capacitive or conductivity-based level sensors may be “blinded” by excess chemical buildup.  I the case of the more conventional mechanical type level sensor, the mechanism may get “gummed up” with residue from excess chemicals over time.

Spraying systems and  overflow weirs are, likewise, designed for a particular concentration of chemistry.  Excessive use of chemistry and the resulting physical changes in the cleaning solution may cause plugging of spray nozzles or excessive foaming in pumping systems as well as overflow weir reservoirs.  Yes, these problems are typically a result of radical chemical overuse but there are others that can result from relatively minor changes in chemical concentration.

Rinsing –

The more soap used in cleaning, the more difficult it is to rinse cleaned parts to remove the soap residue remaining from the cleaning process.  A relatively small change in chemical concentration can have a significant impact on the effectiveness of a rinsing process.  And even if the rinsing is adequate from a equipment standpoint, one must consider the increased cost of makeup water to maintain rinsing effectiveness and, finally, the cost of waste disposal (since all of that soap has to go someplace).

The proper use of cleaning chemicals is an important part of a successful cleaning process.  The best “early warning” of excess chemical concentration is usually found in the rinse.  If parts are not rinsing properly (streaks, haze, fogging) there is a good chance it is due to an excess of cleaning chemistry.  You could, of course, “fix” the rinse by increasing the makeup flow, time, or any one of several other parameters but, as I have stated frequently, the root cause of the problem may be found upstream from the point of its manifestation.  Don’t overlook the possibility of excess chemical concentration in the cleaning stage.

–  FJF  –

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