Six Sigma – Monitoring Variables in Cleaning – Part 3 (final)

A few more things to monitor –

Dirty rinse

An effective rinse is critical to most cleaning processes.  Only in very limited cases can residues from the cleaning step be left on parts after they are cleaned.  It does not, of course, do any good to clean the parts if they become re-contaminated by a dirty rinse.  Carry-over from the cleaning stage is nearly impossible to prevent.  It can be slowed by using good practices such as allowing drain time and perhaps using a pre-rinse that goes to drain but, ultimately, an immersion rinse does become contaminated.  Contaminants include not only residues of the cleaning detergent but, in many cases, also some of the original contaminants removed from the parts by cleaning.  Therefore, contaminants in the rinse can include detergent, oil, particles or whatever.

A good rinse is essential.  The rinse must be cleaned of detergent, oil and particulate to be effective.  In some cases, something as simple as a standard bag filter may be sufficient in removing particles but it does nothing to remove the carryover of detergent or oils. To control the detergent level a conductivity meter can be used to monitor the detergent level and purge (or add fresh water at a faster rate) to the tank when the detergent carryover gets too high.

Detecting and removing oil from a rinse provides a somewhat greater challenge especially if the detergent being used does not emulsify it.  Overflow weirs, oil coalescers, ultrafiltration and oil “scavengers” are possible solutions to the problem of oil in a rinse.  This is one case, however, where prevention is a better solution if oil is potentially present.

For higher standards additional rinsing options might be needed such as a line-rinse or an ultra-filtered rinse.  A line rinse (usually a spray sourced directly from the water line) can be effective for batch systems because the rinse does not need to spray for very long.  However, it is usually not the most environmentally friendly method because of the amount of water that goes to waste.  Also it can cool down the part making drying more difficult.

Clogged nozzles

In processes using a spray it is important that all nozzles be functioning and properly aimed.  Nozzles should be inspected daily for optimal performance.  Therefore, the machine should have a good system for inspection.  Although back-pressure on the supply to the spray nozzles is often considered as a way of determining the health of spray system, sole reliance on this means does not necessarily assure the proper flow.  Such sensors are not often effective in systems with many nozzles because critical nozzles could be clogged before the flow is affected enough to trigger an alarm.  Back-pressure also does not detect a nozzle that has been knocked out of position.  Daily inspection is the best method for determining nozzle health.

Dirty dryer

The effectiveness of any washer can be compromised by a dirty dryer or conveyor.  Build up in the dryer section can re-contaminate the parts.  Proper maintenance and frequent cleaning are the best protection against buildup in a dryer.  In some cases, one might consider automatic dryer rinse system to prevent buildup.  These work by having a spinning nozzle that sprays down the dryer after each shift thereby preventing buildup.

Employee Training

Employee turnover in the washer department is common. Employees must be trained in operation, detergent control, and maintenance of the washer.  Untrained employees my not operate the washer correctly or do the proper maintenance which will effect the      operation of the washer.

The list of cleaning system variables that can be monitored as given in the past several blogs is, I realize, not all-inclusive.  Those that are important are dependent on each application.  Hopefully, however, the above will give the reader some ideas for putting a system in place that will produce Six Sigma performance resulting in no more than 3.4 defective parts due to cleaning for every million parts cleaned.  It’s a good goal to shoot for and worth the effort!

–  FJF  –


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