Blog Purpose

The CTG Technical Blog is intended as a source of information on subjects related to industrial and precision cleaning technology. The writer of the blog, John Fuchs, has 40+ years of experience covering the entire gamut of cleaning. Mr. Fuchs has extensive knowledge of ultrasonic cleaning technology having been employed by Blackstone-Ney ultrasonics and its predecessors since 1968. The blog is also intended to serve as a forum for discussion of subjects related to cleaning technology. Questions directed to the blog will be responded to either in the blog (if the topic has general interest) or directly by email. Emails with questions about the current blog should be entered in the comments section below. Off-topic questions related to cleaning may be sent to jfuchs@ctgclean.com.

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

January 27th, 2014

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  -

 

Six Sigma – Monitoring Variables in Cleaning – Part 2

January 22nd, 2014

Here are a few more variables that can be monitored in cleaning systems in pursuit of a Six Sigma process -

Oil laden detergent -

A good oil removal system is paramount in controlling the quality of the detergent in a cleaning system.  An oily bath can quickly become ineffective in removing additional oil and even particulate from the parts.  Several options are available for continuous removal of oil from a cleaning system.  A simple oil coalescer may be sufficient in maintaining the bath of some machines but a more sophisticated ultra-filtration system may be required to maintain the effectiveness of the detergent by controlling the oil level in other,  usually more critical, applications.

Note – Realizing that I haven’t yet talked about oil removal in the blog, I will address both oil coalescers and ultrafiltration in soon to be published blogs.  Check back if you are looking for more information on either of these oil removal methods. – FJF

When selecting an oil removal system test the oil to see how it reacts in the oil removal system.  For a coalescer to function effectively the oil must float to the surface of the cleaning solution so that it can be easily skimmed off.   For an ultra-filtration system the membrane must be able to discriminate between detergent and oil and oil and/or detergent must not clog the pores of the membrane.

An ultra-filtration would be beneficial to achieving six sigma cleaning because it will remove the oil and particulate down to .5 micron. Thus keeping the wash or rinse in like-new conditions for months.  By eliminating the variances of the detergent cleanness the probability of meeting the cleaning specification is greatly increased. Ultra-filtration can also pay for itself by eliminating machine downtime due to frequent dumping of detergent.

Temperature -

The system should have a digital temperature control system to maintain the temperature.  The control should have the ability to both control the source of heat and report its readings to a remote device to produce an alarm in the event a significant deviation from the desired temperature is detected.  Redundant temperature sensors help to insure proper temperature control and should be considered.  In most cases, electric heat is easier to control and maintain and is recommended.  Steam heat is more difficult to control and is especially prone to being out of range and should be avoided.

Dirty Filters -

Filters are a critical factor in most cleaning systems.  As filters blind off due to the collection of particles from the cleaning solution, the flow slows to the detriment of the cleaning process.  Means to monitor and indicate that filters are operating effectively or are approaching the end of their life are an important part of process monitoring.  Notification of the need for filter replacement or maintenance should come with enough advance notice to allow the required action to be initiated while the machine is still meeting specifications.

One obstacle to changing the bag filters when needed is that the machine must be taken out of service to change the filter.  This can cause the operator to choose between production and part quality — production wins every time.  A dual filter option could be added so the filter canisters can be switched from one to another while the machine is running.

Further information on monitoring filters is available at Sorting Out Filters – Plumbing Options and Tips and Sorting out Filters – Monitoring Filter Health.

In the next blog we will explore even more process variables that can be monitored to help achieve Six Sigma performance.

-  FJF -

Six Sigma – Monitoring Variables in Cleaning – Part 1

January 20th, 2014

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.

Filtration -

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  -

Six Sigma – Importance of “Head Room”

January 14th, 2014

When in the quest for six sigma performance it never hurts to have a little “head room” in the process. In simple terms, this means that the equipment used should not be “maxed out” to achieve the desired result. I’m sure that none of us would be comfortable if we had to keep the accelerator pedal on our car “floored” to keep up with traffic flow or had to turn our radio to full volume to be able to hear the music at all. Similarly, in a cleaning system, operating in a “maxed out” condition is seldom a sustainable operating mode and opens the door for failure. The occasional need for getting a little “extra” from the system should be anticipated and accommodated.

An example – - I have always been an advocate of the use of laboratory testing to verify process prior to equipment specification. However, laboratory testing is usually conducted under ideal conditions and, in effect, gives results indicating what will happen if everything is exactly right. It seldom anticipates a clogged filter, a missing or mis-directed spray nozzle, a part that is more contaminated than normal, a dirty rinse and a host of other real-life variables. In anticipation of these aberrations, the process engineer should always be confident that the system will perform even under extreme circumstances.

Insurance -

There are many ways to assure that six sigma results will be achieved in a given cleaning system. Some may be as simple as adding slightly more heat or pump capacity. Maybe a spray bar in the rinse of an immersion system or an “extra” spray bar in a spray system. Duplicate sensors where appropriate are another way to increase confidence. Realizing that extra features such as these will increase system cost, the benefits and cost of these added features must be weighed against the cost of producing bad product.

Although I don’t advocate hunting mice with an elephant gun, there are times when the addition of some relatively major system features may make sense. One such example is the addition of a pre-clean or an additional cleaning step. The price of such additions is relatively low in the initial build of a system as compared to that of retrofitting the same feature once the system has been placed in operation. Adding ultrasonics to an immersion cleaning system or as an added step in a spray system, although relatively expensive in some systems can make the difference between a system that has to run “balls out” to achieve six sigma results and one that easily achieves the required goal with a little “extra” in reserve.

Anticipating the requirements for a system capable of six sigma performance is important but the real goal is to monitor and analyze real-time data to determine and maintain the “health” of the process. In the next blog, I’ll explore some of the variables that can be measured which, in conjunction with a thorough Process Failure Mode Effects Analysis can provide six sigma results.

- FJF -

Electropolishing

January 10th, 2014

“Electropolishing,” (often shortened to E-P) is a term frequently heard in cleaning circles. Electropolishing of surfaces of cleaning equipment is employed to provide enhanced cosmetic appearance and, more importantly, to enhance their functionality.

What is Electropolishing?  -

Electropolishing is a lot like electroplating except in reverse. In electropolishing, metal is removed rather than added as it is in a plating process. The equipment is very similar. Parts to be electropolished are immersed in a liquid media called an “electrolyte” while a source of electric current is applied. The part to be electropolished is one electrode called the “anode” and is positively charged. The negatively charged electrode or “cathode” completes the conductive path. The cathode does not enter into the process chemically but its construction can be critical to the success of the process. Other features often include a means to heat the electrolyte and a means of ventilation since gasses evolved during the electropolishing process can be explosive.

Illustration of electropolishing setup

Electropolishing uses the same basic setup as plating except in reverse. Electropolishing is a metal removal process unlike plating where metal is deposited.

The formulation of the electrolyte is varied depending on the substrate being electropolished and the surface finish desired. Ions removed from the substrate are absorbed into solution in the electrolyte or end up as sludge on the bottom of the processing tank.  The electrolyte must be carefully monitored and has a limited useful life.

Prior to electropolishing, surfaces to be electropolished have features undesirable in their intended application. These features may include burrs, slivers or irregularities due to the use of welding, machining or abrasives in the manufacturing process. During electropolishing, features that protrude from the surface act to concentrate current flow (much like a lightning rod attracts lightning) so that they are preferentially attacked by the combination of the electrolyte and the electrical current. The result is that the surface becomes smoother as protrusions are removed.

Illustration showing a surface before and after electropolishing

Concentrated high current density along with the electrolyte remove projections from the surface being electropolished. The result is a smoother surface which benefits the appearance and/or functionality of the part.

Note – In some cases, the electrolyte used in electropolishing process will dissolve the substrate without the benefit of electric current being applied. However, without electric current, the rate of removal would be more uniform rather than concentrated on the protrusions requiring removal. Adding current helps concentrate the effect to produce the desired result of a smooth surface.

As mentioned above, the cathode, although it doesn’t enter into the process directly can, by its placement and geometry, have a significant effect on the success of the process. Parts with complex geometry may require use of a specially shaped cathode to provide uniform current density as current density may vary depending on the proximity of the cathode and the part being electropolished (anode).

A partial list of things that can affect the electropolishing process are temperature, formulation and freshness of the electrolyte, proximity of the cathode and part (in irregularly shaped parts) and the cleanliness of the part prior to electropolishing. Since, in order to be effective, the electrolyte must uniformly contact the surface being electropolished, any barrier, especially scale, oil, grease and other hydrophobic films must be completely removed prior to electropolishing to prevent a non-uniform result.

Benefits of Electropolishing -

Electropolishing produces a shiny surface nearly mirror-like in appearance. The smooth surface is also easy to clean and prevents the surface from collecting contaminants, especially fine particles and biological contaminants. Another benefit that is somewhat less known is that when stainless steel surfaces are electropolished, nickel and other components of the alloy are preferentially removed leaving a chromium-rich surface with benefits similar to those of passivation and chrome plating.

-  FJF  -

Ultrasonic Cleaning – Benefits of Agitation

January 7th, 2014

I have written before that there are four major variables we consider in cleaning – - Time, Temperature, Chemistry and Agitation. Based on some recent feedback from the field, however, I guess I need to provide a little more emphasis on the benefits and definition of agitation as it relates specifically to ultrasonic cleaning processes.

“Agitation” is a pretty loose definition that can be applied to a wide variety of mechanical processes. For example, ultrasonic cavitation and implosion provide agitation on a micro-scale. Turbulation, part rotation, physical part displacement and even spraying a part with liquid are forms of agitation on a larger scale. It is difficult to think of a cleaning situation where agitation of one form or another is not beneficial. Selection of the agitation alternative and how it is applied is a critical part of the process development process. In some cases two (or more) forms of agitation applied in a specific way may maximize process results.

Enough for generalities – - let’s look at an example or two that illustrate the benefits of agitation in cleaning. Two earlier blogs explain the benefits of ultrasonic cavitation and implosion in removing soluble contaminants and particles.

Ultrasonic Cleaning – Soluble Contaminants

Ultrasonic Cleaning – Removing Particles

In both cases there are two possible scenarios to consider that may limit the effectiveness of ultrasonic agitation (cavitation and implosion) alone. The first is an excess amount of contamination. Ultrasonics, as we know, is great for removing thin layers of contamination but falls short when it comes to removing a thick buildup of contamination. The application of more aggressive agitation (spraying, for example) may remove a significant portion of the contamination allowing ultrasonics to be effective in removing the final layers of contaminant. In this case, agitation acts as a “pre-clean.” In another case, ultrasonic cavitation and implosion might be effective in removing a contaminant but, once removed, the released contaminant may not disburse and, as a result, limit the effectiveness of ultrasonic cleaning as the solution surrounding the cleaning site becomes saturated with contaminant. Note – This can occur with either soluble or insoluble contaminants. In this case, larger scale agitation may be used to disburse the released contaminants to allow continued efficiency of the ultrasonic cleaning process. In both cases, larger scale agitation benefits the effectiveness of ultrasonic cleaning.

Although beneficial to the overall process, agitation can, when improperly applied, be detrimental to ultrasonic cleaning. One notable example is that of turbulation as discussed in the blog Ultrasonics and Turbulation Don’t Mix! Although turbulation (high velocity jets of liquid provided by submerged nozzles, pump returns etc.) can be beneficial in some cleaning processes, any significant turbulation in an ultrasonic cleaning tank has been demonstrated to severely diminish the effectiveness of ultrasonic cleaning.

Probably the most effective means of adding agitation to an ultrasonic cleaning tank is to physically move the parts relative to the cleaning liquid. Although this is commonly done using an “agitation platform,” similar benefits can be derived by rotation or any other means that moves the parts being cleaned relative to the liquid cleaning media. One common mistake in the design of agitation systems is that agitation is too slow to provide a beneficial effect. Vertical displacement of a part 2 or 3 inches at a rate of 5 or 6 oscillations per minute seldom provides a significant cleaning benefit. Twenty to 30 oscillations per minute (less, of course as the displacement magnitude is increased) provides much better results.

Over the years, I have seen such substantial benefits using agitation in the form of part displacement through a liquid during ultrasonic cleaning that I would recommend its use whenever possible within budgetary and physical constraints. It is a tool that is, in my opinion, underutilized.

 

Ultrasonic Cleaning Time – Enough is Enough

December 11th, 2013

In The BIG Four, I talked about the four important variables in cleaning. These are time, temperature, chemistry and agitation. In that blog, I mentioned that a shortcoming in one variable can, to a point, be overcome by changing another of the variables. For example, increasing temperature or changing chemistry may reduce the time required for ultrasonic cleaning. It is important, however, to understand that the interactions of these four variables are not absolute and, in many cases, non-predictable. Also, most processes have constraints on one or more variable. In one case, for example, cleaning may need to be accomplished with a chemical that has a pH of 7 ± 1. In another, the total cleaning time might need to be under 2 minutes to meet the required production. In still another, the temperature might need to be under 100°F to prevent damage to the part. Finding the right combination of variables to produce the desired result while not violating the constraints put on the process often requires some degree of testing and ingenuity.

In ultrasonic cleaning involving soluble contaminants, one must think of ultrasonics as a means of agitation which enhances the cleaning process. Ultrasonics, by itself, is seldom the only mechanism required to produce a desired cleaning result any more than is temperature. Simply applying ultrasonic energy to or heating a part to a given temperature alone is not likely to make it clean (although there are exceptions). In ultrasonic cleaning as practiced in removing soluble contaminants (as opposed to particles), the primary mechanism is usually the interaction of the cleaning chemistry with the contaminant. The blog Ultrasonic Cleaning – Soluble Contaminants provides more detail on this.

Typical Ultrasonic Cleaning Times -

In my experience, typical, appropriate ultrasonic cleaning times range from a few seconds to several minutes. Times above several minutes may be simple “overkill.” Although less time may still produce the desired result, the relationship between cleanliness and ultrasonic time has not been adequately investigated to show this. Somewhere along the way it was determined that 20 minutes, for example, was “enough,” and shorter times were never investigated.

When times as determined by applications testing exceed a few minutes it usually indicates one of two things – -

  • There is a shortcoming in one or more of the other of the “big four” process variables. A change in chemistry or temperature may reduce the required ultrasonic time significantly.
  • Ultrasonic cleaning alone is not the appropriate process for this particular cleaning application. In some cases, the addition of a pre-cleaning step prior to ultrasonics may be the answer. In others, other cleaning options such as spray washing may be more effective and appropriate.

Why Does Ultrasonic Time Matter? -

First and foremost, if cleaning can be accomplished in a shorter time, higher production rates can be achieved. This is important especially in cases where cleaning is a process bottleneck. If production rate is not an issue, the same work can be done using a smaller, less expensive ultrasonic cleaning system which uses less resources (water, electricity, manpower, etc.).

The life of an ultrasonic cleaning system is directly related to its use. Operating an ultrasonic system longer than necessary during each cleaning cycle may shorten its life.

Excessive exposure to ultrasonic cavitation and implosion may cause part damage. Limiting ultrasonic cleaning times on materials including aluminum, brass and many other soft metals which are subject to cavitation damage is imperative.

Summary -

Ultrasonic cleaning times in excess of several minutes should trigger an investigation into the rational or background that lead to using an ultrasonic time that may be inappropriate.  Simple applications testing may justify reducing the time or indicate process changes which will shorten and/or enhance cleaning.

-  FJF  -

Six Sigma – Process Selection and Monitoring

December 9th, 2013

In order to achieve six sigma results, one must evaluate, measure and statistically control ALL phases of the cleaning process.  A typical cleaning process is comprised of three main stages – - washing, rinsing and drying.  Each of these must be addressed and controlled separately as any one of the three being out of control will jeopardize the overall process.

Process Selection –

Not all cleaning methods lend themselves to six sigma process control.  Let’s look at a couple that do.  Spray washing is by far the most common method of washing parts and can in some cases meet six sigma capabilities depending on the part and the cleaning specification. Parts are typically conveyed through a washer with a halo of spray covering them. Spray is a directional process and is best suited for cleaning external surfaces but, with properly directed sprays, internal passages may be cleaned as well. Spray is quite versatile in its application because many features can be varied such as pressure, direction, nozzles and flow to meet the cleaning needs. Pressures can vary from 30psi for general cleaning to more than 3,000psi for de-chipping and deburring applications. Performing trial testing can determine the optimum spray pattern to meet a specific need. In addition to spray, immersion cleaning with ultrasonics is particularly well-suited to meeting six sigma quality levels as well as meeting even more stringent cleaning requirements. The cavitation intensity achieved in the cleaning tank scrubs the surface of parts and allows the cleaning solution to be more effective than it would be using only immersion, spray, agitation or brush methods. The cleaning action of almost any detergent, soap or solvent improves through the application of ultrasonics making it a natural choice for meeting six sigma quality standards. Ultrasonics can reach into the smallest cavity or blind hole, cleaning a part inside and out. For proper cavitation to occur the fluid must not have much movement. Select a system with slow part movement through the bath. The ultrasonic solution should be filtered when there are not parts in the bath. An important attribute of ultrasonics based cleaning that makes it so well suited for six sigma cleaning is that it produces consistent results over an extended period of time.

Selection of a cleaning method alone, however, does not by itself assure six sigma results.  Assuring proper performance requires monitoring and control of a number of variables within each process.  This can be achieved by analyzing the process upfront using Process Failure Mode Effects Analysis (PFMEA) on the parts washer, which helps to identify the variables that need to be eliminated or reduced to maintain a consistent cleanliness level.

Monitoring Variables –

As we have stated before, the “big four” of cleaning are time, temperature, chemistry and agitation.  A thorough PFMEA will identify means to monitor and control ALL of these variables.  In many cases, there may be several factors that contribute to proper monitoring and control of each of these “big four.” To achieve six sigma, feedback on “health” of the cleaning system must be acquired regularly to assure that any deviation is corrected BEFORE it reaches a point that jeopardizes the overall process.  For example, let’s say that we have a process that we have determined through testing requires a temperature of between 120 and 140°F to be effective.  A higher or lower temperature will produce unacceptable results.  A start, of course, is to provide sensor-controlled heaters set to maintain a temperature of 130°F.  To achieve six sigma, however, a secondary sensor is required that will indicate any deviation from the ideal 130°F temperature before it reaches the process limits to allow for corrective action.  Such a device, for example, might indicate that the temperature is 5 degrees over or 5 degrees below the target of 130°F thereby sounding an alarm before further deviation results in ineffective cleaning.

to be continued

Six Sigma – - The Role of Cleaning

December 3rd, 2013

Achieving Six Sigma Capability Parts Washing

“Six Sigma” methodology is one of many tools that can be used to improve process efficiency.  The following several blogs are excerpted from an article written by Dale Bowden of the Cleaning Technologies Group and was published in Process Cleaning Magazine.  Mr. Bowden specifically explores the role of cleaning in meeting six sigma standards.  – FJF -

Many companies are moving towards work that requires higher cleaning standards in order to compete in today’s marketplace. The six sigma quality system is one such approach to meeting higher standards. For those that are not familiar with the six sigma methodology, it is a system that combines statistics and system analysis to reduce variables in the system.  As a result, the probability of meeting the specification is increased. Statistically speaking, six sigma is the probability that the next part produced will be within the specification. A six sigma process produces less than 3.4 defective parts per million parts produced.

Until recently, parts washers were considered a necessary evil. They contributed no perceived value to the end product and were seen as adding cost to the process. This is changing! Parts cleaning is becoming a more important and is now frequently seen as a valuable step in the manufacturing process. With many production parts, the onset of the six sigma quality system reveals that the quality and reliability of the final product is directly related to the cleanliness of the parts. For example, the particulate size and the number of particles left on transmission parts have been shown to be directly related to the number of transmission failures in automobiles. Residual oil on torque converters interferes with the laser welding, which in turn results in both diminished weld strength and increased smut and weld splatter. For a company to produce a six sigma product, each step – including cleaning – must also meet a six sigma level of quality.

Where to Start?

The first and most important step in achieving six sigma capabilities in parts cleaning is to define a quantifiable cleanliness specification. Without a measureable specification, a parts washer can not be considered six sigma. To develop the cleaning specification, it is necessary to perform a downstream Process FMEA (Failure Mode Effects analysis) to determine the effects of residual contamination. The analysis should determine what effect residual contaminants such as particles, oils or lubricants, moisture, detergent or corrosion preventatives will have on the product and process. In addition, particle size and exit temperature can be critically important. Typical cleaning specifications include: less than 1,000 micron particles for valve spools, less than 1.0 mg total organics for brake parts going to laser weld, and an exit temperature ± 15°F for gauging. It is important not to create a specification that is too tight because it will significantly increase the cost of both the capital equipment and operation costs with little return on value. By applying a six sigma statistical analysis to the cleaning results, one can determine the probability of a process to consistently fall below the upper specification limit. The next step is to begin to select parts washing equipment and do verification testing to assure that the desired cleanliness level is met.

- to be continued -

Ultrasonic Dishwasher? – Probably Not

November 21st, 2013

A reader has asked about the possibility of using ultrasonics to wash dishes.

He writes – - – “Ultrasonic cleaning in a dishwashing application is something that I am currently interested in. Having read some of your other blog posts which mention sequential use of turbulation in the liquid to supplement the ultrasonics, I was wondering whether this is an application where you found or think that this would be necessary? Having experimented on a small scale on this topic, I certainly found that trying to remove a thick layer of contaminant with ultrasonics alone was very difficult or impossible.”

In an earlier blog I expounded on why I feel dishwashers are a bit of a waste compared to hand washing. I also revealed in another blog the fact that using ultrasonics to wash dishes is probably not feasible but neglected to provide details other than the water consumption required to provide a device that would be able to immerse the dishes as required for ultrasonic cleaning.

The reader has hit the nail on the head when he mentions the issue of removing thick buildups of food using ultrasonic cleaning alone. I addressed this issue in a preceding blog as well but it is worth going into a little further. First, let’s look at the kinds of things that one might find on dirty dishes. One classification, liquids, don’t often leave a very thick buildup once drained. Also, most liquids (water-based liquids) are, of course, water soluble. Residues of fruit juice, wine, soda, beer, milk (?), and other beverages are well within the realm of ultrasonic cleaning because they are very thin films. However, food residue left on dirty dishes after a meal is not what I would call a “thin” buildup of contaminant. Usually there are scraps of meat, gravy, vegetable residue, sticky gooey stuff that just can’t be removed using ultrasonics alone. And the longer these residues are left on the plate, the more they dry out making removal even more difficult.

Not being able to remove thick buildups of food residue, therefore, is a major stumbling block in the way of using ultrasonics to clean the typical overall range of dishes although it might be suitable for glassware and other lightly soiled pieces. It is true that using turbulation, agitation or some other means of providing additional mechanical scrubbing would probably render most residues otherwise resistant to ultrasonic cleaning removable . . . . . but then we would be right back to the standard dishwasher which, primarily, uses spray technology along with chemistry to clean the entire range of dishes effectively.

In summary, there are several reasons why ultrasonic dishwashers are probably not in our future -

  • The need to immerse items to be cleaned in a liquid uses much more water than spray technology. A typical home dishwasher fills and drains 3 times using only a few gallons of water per fill. Filling and draining the entire cavity of a dishwasher would require more on the order of 150 gallons.
  • The inability of ultrasonics to remove dried-on residues of food like gravy, spaghetti sauce and mashed potatoes.
  • Cost – Ultrasonic technology has not yet advanced to the point that it can compete on a price basis with a typical home dishwasher which sells for from $300 to $1,200. An ultrasonic cleaner with the same volume as a dishwasher (approx. 50 gallons) would be priced at several thousand dollars or more even before customization for dishwashing.

In summary, having traveled this road several times before in my 45 year career in ultrasonic cleaning, my guess is that we will be washing dishes the same way we do today at least for the rest of my lifetime. Despite the big “carrot” out there, I don’t think the challenge can be met, at least with ultrasonic cleaning technology as we know it today.

- FJF -