Six Sigma – Monitoring Variables in Cleaning – Part 1

As discussed earlier, monitoring variables in a process is a critical part of Six Sigma.  The following are some examples of parameters that can be monitored in a cleaning process and some suggestions regarding how the monitoring can be done.

Chemical Concentration –

Chemistry (detergent, acid, rinse aid, etc.) is one of the most important components of the cleaning system.  Its condition and concentration changes constantly as work is processed through the system.  Too little chemistry (or too much in some cases) will result in rejected parts. One way that chemical concentration can be measured automatically is through the use of a conductivity meter.  In some cases, a conductivity meter used in conjunction with a pump can be used to maintain the chemistry level by reading its concentration and pumping in the exact amount needed to stay within the process bounds.   The best conductivity meter for most applications is a toroidal probe. This type of device uses an insulated coil that makes a magnetic field and thereby reads the conductivity of the fluid as it changes due to changes in chemical concentration. These devices are quite stable because they are not easily fouled.

Another method for adding chemistry automatically is a proportional metering pump. It works by adding a measured amount of chemistry for each gallon of make up water added.  It works fine when a machine is in stable production but can add too much or too little when production changes or during idle times so some other means of measuring chemical concentration should also be utilized.

One other method is simply daily or each shift titrations.  The up side, it is cheap and accurate.  The down side, you are relying on people to perform this task daily for years which does not fit the Six Sigma methodology.

Ultrasonics –

Although today’s ultrasonic equipment is very reliable, but it can fail.  Look for a system to monitor the power of the ultrasonics and alarm when they get out of range.  This can, in some cases, be accomplished with an ammeter but often requires more sophisticated means based on the recommendations of the supplier.  Some units have built in monitoring that can initiate a local or remote alarm if parameters are not within the normal operating range. The blog Ultrasonics – Monitoring Ultrasonic Performance provides further insight into monitoring ultrasonic performance.


Good filtration is essential in producing particulate free parts especially in the rinse.  Depending on the final cleaning requirements there are several filtering options to consider.  The first is a standard bag filter which is well suited for cleaning requirements above 250 micron.  Bags are available from 5 to 500 micron so choose one that is about 50% of the cleaning specification but remember that the smaller the micron size the more often you will be changing it.  Bag filtering sizes less than 25 micron might not even last an entire shift.  Below 250 microns, a cartridge type filter may be a better choice.  Again, a means to measure filter performance is helpful in determining when filter media should be changed.  There are several options to consider some of which are discussed in the blog Sorting Out Filters – Monitoring Filter Health.

Since six sigma is best achieved by eliminating human intervention another consideration might be to install an automatic backwashing filter.  There are several brands on the market that monitor the pressure of the filter and automatically backwash to keep it at its peak performance.

The next blog will further explore even more cleaning process variables that can be monitored to help achieve Six Sigma performance.

–  FJF  –

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