CTG Technical Blog

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.

Ultrasonics – Cleaning Orifices with Ultrasonics

January 24th, 2013

A few days ago, one of our customers asked one of our sales people what would seem like a very simple question. The question, in paraphrase, was – - ”Do you know the relationship between ultrasonic frequency and the ability of ultrasonics to clean within a certain sized orifice.” Being a bit rushed when I received the email with the question from the sales person and not having a ready reference at hand, I quickly sent a simple answer, “NO,” but promised a more complete answer to follow. The next morning I took another of my strolls to the Blackstone-NEY Ultrasonics R&D Lab (which is about 20 steps from my office) and started to pick the brains of the REAL gurus. We quickly arrived at the conclusion that we don’t have a “graph” that relates ultrasonic frequency to its ability to clean within a certain sized orifice. However, we do have a lot of experience and were able to agree that there are several factors that will have a bearing on how effective ultrasonics will be. Frequency, we further agreed, was only one of them.

First, let’s make the assumption that an “orifice” is a passageway through a solid material and that the passageway is open with access at both ends. (A passageway with access from only one end would be classified as a ”blind hole” and is a completely different situation.) For purposes of our discussion here, we will define the dimensions of our orifices as shown below.

Illustration showing the definition of Orifice Width and Length

As shown above, W is the width of an orifice while L is the length or an orifice. An orifice need not be round but, for simplicity here, we will assume that it is round and that it is a passageway through a solid material such as a metal.

In order to clean the orifice we must first be able to wet the surfaces of the orifice and the contaminant within the orifice. In short, if liquid can’t get into the orifice due to high surface tension or some other condition, the mechanism of ultrasonic cleaning, which relies on a liquid to transmit the sound waves, simply can’t take place. In the case of an orifice that is completely blocked by a contaminant, liquid must, at least, be able to reach far enough into the orifice to “wet” the contaminant from one end or the other. The ability for liquid to penetrate the orifice depends, first of all, on the ratio of its Width (W) to its length (L).

Illustration showing the effect of orifice witdth and length on penetration using the same liquid

Orifices 1, 2, and 3 are all immersed in the same liquid. Although Orifices 1 and 2 are the same length, Orifice 1 which has a smaller width is not penetrated due to the surface tension of the liquid. Orifices 1 and 3 are both the same width but the reduced length of Orifice 3 allows the liquid to fully penetrate the orifice.

Other factors that have an effect on the ability of a liquid to penetrate an orifice are the physical properties of the liquid including its surface tension and viscosity.

Illustration showing the effect of surface tension on orifice penetration

Three different sized orifices submerged in liquids of varying surface tension. The liquid with the lowest surface tension shows best penetration of orifices.

A liquid with lower surface tension will penetrate an orifice that a liquid with a higher surface tension will not penetrate. Higher viscosity or “thickness” of a liquid may hinder or slow the penetration of an orifice but the surface tension is the property that determines if the penetration will ultimately occur or not.

This is just the start of our discussion on the ability of ultrasonics to clean orifices. The next blog will include more detail on the mechanism of ultrasonic cleaning as related to orifices.

- FJF -

Posted in Chemistry, Cleaning, Definitions, Ultrasonics, Uncategorized, Useful Information Miscellaneous, Washing | No Comments »

Ultrasonics – Ultrasonic Power Density vs. Tank Size

January 22nd, 2013

As a leading ultrasonic manufacturer, we are often asked to manufacture large, industrial ultrasonic cleaning systems producing a particular ultrasonic power density based on laboratory trials. In fact, it may not be appropriate to base the watts per gallon requirement for a large industrial application on those found effective on a laboratory scale. A paper at the following link explains, generally, why this is so. The continuing blog below the link provides a little more depth.

Considerations for Ultrasonic Power Density vs. Tank Volume

The effectiveness of an ultrasonic cleaning system really doesn’t depend totally on how many watts of power are delivered per unit of liquid volume. The key to cleaning success is how those watts are utilized. The real goal to assure effective ultrasonic cleaning is to make sure that there are a sufficient number of cavitation events occurring in the tank and that those cavitation events result in energetic implosions. To repeat what I’ve said in previous blogs, cavitation without implosion does very little to enhance the cleaning process.

Let’s analyze, briefly, the life of a sound wave. Once ultrasonic sound waves are introduced into a liquid, all of the energy in the sound waves has to go someplace or we are breaking one of the laws of physics – “conservation of energy.” In an ultrasonic cleaning tank, the ultrasonic energy ends up as either heat or sound radiated into the air. In fact, nearly ALL of the energy goes into heat as very little energy is consumed in sound radiated into air. The following link provides an interesting (and somewhat humorous) demonstration of how little energy is actually contained in sound radiated into air.

http://www.physicscentral.com/explore/poster-coffee.cfm

Although the transformation of sound energy into heat energy is a result of cavitation and implosion, a lot of other heat-producing mechanisms also take place due to the vibrations of the sound waves. Among these are heat losses in the ultrasonic transducers, heat losses due to internal friction of the liquid and heat losses caused by vibrations of the tank (and all of the things connected to it). These vibrations all result in heating due to internal friction. In fact, the ONLY vibration to heat transformation that benefits cleaning is that accounted for by cavitation and implosion. So, the key to effective use of ultrasonic energy is to maximize that portion of the ultimate conversion of sound energy into heat that is provided by the production and implosion of cavitation bubbles.

How does this relate to the reduction in the watts per gallon requirement for effective ultrasonic cleaning? As the tank size is increased, proportionately more sound energy results in the production and collapse of cavitation bubbles. Since cavitation and implosion are somewhat self-limiting (once the liquid is saturated with cavitation bubbles the existing bubbles prevent the growth of further bubbles by becoming absorbers of sound themselves), the addition of more sound energy will not result in additional cavitation but, rather, will be converted to heat by other means. The energy has to go somewhere, but it does not necessarily result in added cavitation and implosion. The key measure is not watts per gallon but, rather, how those watts are utilized that makes the difference.

Unfortunately, many potentially good applications for ultrasonic energy have been passed by for economic reasons because of the assumption that a particular watts per gallon density was required. In fact, they may have been practical had there been a better understanding of the concepts discussed above.

- FJF -

Posted in Definitions, Laboratory Testing, Sound, Ultrasonics, Useful Information Miscellaneous | No Comments »

Chemistry – Solvent Characteristics

January 18th, 2013

Solvents are a bit difficult to understand for a number of reasons. Even for someone who has worked with solvents as much as I have, the permutations of solvents, their combinations and their capabilities are bewildering. But, let’s start with the simple stuff.

A solvent dissolves what is called a solute. In what is probably the most used simple example, salt (solute) is dissolved in water (solvent). Although we usually think of solvents as being liquids, there are cases of both gasses and solids which act as solvents. Likewise, solutes although we commonly think of them as solids or liquids can also be gasses. The salt dissolving in water example makes it all sound very simple, doesn’t it? Well, hang on for a wild ride because that is only the beginning!

When a solvent dissolves a solute, something called a “mixture” is formed. But this particular mixture consisting of a solute dissolved by a solvent is a special type of mixture called a solution. A solution has certain characteristics which distinguish it from a mixture. Mixtures that are not solutions are much different. For now, we will only concern ourselves with mixtures that are solutions and leave mixtures for later.

In a solution, the two components exist in a homogenious state. In somewhat simpler terms again using water and salt as examples, the ratio of salt and water in the solution is the same no matter where you look. Solutions also can not be separated by filtration although, in some cases, some gravity separation may occur over long periods of time. Another characteristic of a solution is that clear liquid solutions will not diffuse a beam of light passing through them. One can not see that water has salt dissolved in it. Although all of the above has been based on liquids, the same or similar rules apply for cases involving gasses and solids.

Terms – Solubility Limit

In most cases there is a limit to how much of something can be dissolved in a liquid. In our salt and water example, if you keep adding salt, you will finally reach a point where the added salt remains as granuals and does not dissolve. At that point, the “solubility limit” has been reached. The solution is “saturated.” Once the solvent has dissolved all of a material that it can, it is no longer a solvent for that material. The solubility limit, though, typically increases as temperature increases. Increasing the temperature of a salt/water solution will allow more salt to be dissolved by raising the sautration limit. However, even a saturated solution may still be a solvent for another material. A saturated salt solution may still dissolve a quantity of alcohol (liquid) for example.

Terms – Miscible

Solvents and solutes that mix in any ratio (and therefore have no solubility limit) are said to be ”miscible.” Any amount of Vodka, for example can be mixed with any amount of water to form a mixture that is a solution. Technically, once you pass the 50% point the solvent and solute change positions as the solvent is usually the material that there is more of.

Terms – Non-Polar and Polar

The final thought for this blog will be that solvents and solutes can be Non-Polar, Polar Protic or Polar Aprotic. The following scale with solvents listed by polarity can be used to determine which solvents and solutes will form a solution. The closer together two materials are, the more soluble they will be in one another.

Solvents of like polarity form solutions more readily with each other.

We will move away from Chemistry for the next couple of blogs but will get back to it in the near future.

FJF

Posted in Chemistry, Definitions, Useful Information Miscellaneous | No Comments »

Cleaning Chemistry – Introduction – Solvents

January 14th, 2013

It doesn’t matter if you call it soap, solvent, surface preparation, or whatever, chemistry is an important part of nearly every cleaning process. The first purpose of the chemistry in a cleaning application is to either dissolve the contaminant or, using some other mechanism, to break the attachment that the contaminant has to the substrate. The second purpose of chemistry in cleaning is to keep whatever has been removed from becoming re-attached to the surface it was removed from. Granted, chemistry doesn’t always do all of this by itself. Mechanical energy supplied by spraying, brushing, agitation, ultrasonics and nearly any other imaginable means plays a large role as well in the overall cleaning process.

Solvents -

Historically a variety of naturally occurring and easily formulated solvents were used to truly dissolve contaminants. Kerosene, various forms of alcohol, naptha, stoddard solvent, mineral spirits were probably among the earliest solvents used in cleaning applications. These were well known mainly because they were studied and used in the formulation of paints used by artists. They were both relatively inexpensive and readily available. In time, advances in chemistry brought us more sophisticated hydrocarbon solvents including things like trichloroethane, perchloroethylene, acetone, MEK, etc. It was also discovered that solvents could be mixed using using defined rules to customize their effects. Solvents could easily be formulated that would dissolve an unwanted contaminants while leaving another desirable component untouched. This notion of selective solubility is used extensively in applications ranging from the cleaning and restoration of masterpiece paintings to the de-caffeinization of coffee beans. More recently developed solvents include the fluorinated hydrocarbon solvents which, today, have been largely banned because of their deleterious effects on the environment.

Along the way, we have learned a lot about solvents. For example, certain solvents when mixed in specific ratios form azeotropic mixtures. An azeotropic mixture of solvents when distilled produces a condensate with the same chemical mixture as the starting mix. In simple terms, the mixture can not be separated by distillation. This property of a solvent can be useful especially when it comes to reclaiming solvent for re-use.

In simple terms, a solvent dilutes whatever it dissolves. The dissolved component does not go away but remains mixed with the solvent. The more material is dissolved, the more concentrated the solution becomes until the solvent finally becomes saturated and can no longer dissolve any more. This concept is important in cleaning because once a solvent has anything dissolved in it, it will re-deposit what it has already dissolved back on the surface of the item being cleaned. This is like the quandary of how many babies can you get clean in the bath – - the second and successive babies pick up the dirt from those who preceded them. The risk with solvent, then, is that it has a limited useful life and, theoretically can thoroughly remove contaminants only if it is used only once!

The answer to the single time use in the cleaning industry was the vapor degreaser. In a vapor degreaser, parts are first immersed in the cleaning solvent. This immersion starts the process of dissolving the contaminant at least to the point allowed by the pre-existing contaminant level of the liquid solvent. After immersion in the solvent, the part being is suspended in vapors of the boiling solvent. As the vapor distillate collects on the surface of the part being cleaned the freshly distilled solvent (less any contaminants left behind by distillation) serve to provide the supposed ultimate in cleaning – the single use solvent. This process, of course, only works with pure solvents or azeotropic blends as described above.

FJF

Posted in Chemistry, Cleaning, Definitions, Uncategorized, Useful Information Miscellaneous, Washing | No Comments »

Washing Clothes With Ultrasonics

November 20th, 2012

Blackstone Ultrasonics was founded in the mid 1950′s in the hope that the addition of ultrasonic agitation to a conventional clothes washer would revolutionize laundering of fabrics. It didn’t take long before it was recognized that ultrasonic techniques weren’t going to be effective – at least not by simply adding ultrasonic transducers to a conventional washing machine. Let’s take a couple of minutes to understand the reason for the initial failures and what promising strides have been made in specialized areas since the 1950′s trials.

The problems with ultrasonic clothes washing are two-fold. First of all, fabrics are very good absorbers of ultrasonic energy. The use of draperies, carpets and upholstered furniture to prevent echos in homes and theatres attest to this fact. Because fabrics are so absorptive of sound, introducing enough ultrasonic energy to overcome the absorption would be a huge and expensive task. This fact alone makes the idea of ultrasonic laundering quite impractical.

The second problem is that most fabrics are, themselves, flexible. In earlier blogs we discussed the fact that resilient materials like rubber and some plastics are difficult to clean ultrasonically for the same reason. Ultrasonics works best when it has a hard surface to work against. Thus the “double-whammy” against laundering with ultrasonics.

Inevitably, the idea of an ultrasonic clothes washing machine has re-surfaced repeatedly over the years. In one exemplification, it was proposed that fabrics be presented to an ultrasonic cleaning device in a single layer to overcome the problem of ultrasonic absorption. Further, it was suggested that the fabrics be stretched (in some cases over a hard surface) to increase their ability to attract cavitation bubble implosions. In the case of stretching the fabric over a hard surface, the surface would actually act as the “receiver” of ultrasonic cavitation bubble implosions. The fabric would just be in the intense cavitation zone adjacent to the hard surface.

After years of exploration, ultrasonic laundering is still not a practical application. There are very few garments (or other items made of fabrics) that can be presented in a single flat layer. A few exceptions, of course, are bed sheets, towels and other large, flat items which, unfortunately, represent a very small percentage of overall laundering requirements.

The final nail in the coffin of the ultrasonic washing machine is, as is often the case, economics. At least at this point in time, even if there were an application that could be accomplished successfully and reasonably using an ultrasonic approach, the cost of the machine would likely be prohibitive.

At least for the time being, it seems that sloshing or agitating clothes in a vat of soapy water has the market pretty much cornered.

And finally, for those of you who have been wondering — NO, I don’t advocate hand washing clothes garment by garment with a washboard or rock. Dishes are one thing, clothes are another. For me, a clothes washing machine does a good job and makes sense as long as it is not over-challenged. But for that, there is stain stick!

FJF

Posted in Cleaning, Economic Issues, Ultrasonics, Washing | No Comments »

Dishwashers and Ultrasonics

November 15th, 2012

Gee Whiz! I was sure somebody would challenge me on the last blog about washing dishes at home. But, since there are no comments (or fire bombs) in my inbox, I guess everybody agrees that the most efficient way to wash dishes at home is the “old fashioned” way with a dish rag and dish drainer. I’m shocked! Dishwashers, then, must be just an easy way to fill that vacant under-cabinet space or purely decoration. Maybe I should go into the business of selling an insert that looks like a dishwasher but at a reasonable price. I think I could make a pretty convincing one for about $10. They should sell like hotcakes!

Despite the fact that nobody took me to task, I know there will always be dishwashers and people who use them. Actually, I think we would all agree that where larger volumes of dishes are involved as in a restaurant, a good, efficient dishwasher probably makes sense just as does an automated industrial parts washer in a high volume production situation.

While we’re on the subject of dishwashers, I have been approached 10′s if not 100′s of times over the past 40 years about the possibility of using ultrasonics to wash dishes. The most notable request was an embarrassing number of years ago from a consultant who had been hired by a major airline to devise a way to wash and re-use dishes in flight on long distance hauls. This was just as the “Jumbo” jets (at that time the 747) were starting to be built and configured. In those days they actually used china dishes on most flights that served meals and not just in first class! This guy was determined that ultrasonics was the answer and approached it as if his job depended on it – - maybe it did. Anyway, I was in sales at the time and of course was seeing $$$’s as the airlines had lots of money and all wanted to be on top of technology. Certainly they would buy lots of machines if we could come up with one that worked and was practical. In the back of my mind, of course, I was thinking that if they will pay $1,000 for a toilet seat they should be equally willing to pay a good price for an in-flight dishwasher.

As it turned out, ultrasonics had lots of problems when it came to washing dishes in flight. The biggest was that ultrasonic cleaning was (and still is) an immersion process. In short, this meant that washing dishes would require a “vat” of sufficient size to accommodate a sizable number of dishes. Well, OK, the 747 is pretty big and surely would have room for such a machine – or did it? We soon learned that the space allocated to the “in-flight dishwasher” in the blue prints was about the same size as a good-sized microwave oven. Surely more space could be made available for the latest technology.

Undaunted, the consultant and I continued the project on the assumption that space could be made available for the right machine. From there, however, we met obstacle after obstacle. One tough one was the amount of water that a large enough machine would use. The only thing that seemed to make sense was to store and re-use the washing solution repeatedly (much like the in-flight sanitary system) and follow ultrasonic cleaning with a spray rinse using a smaller amount of “fresh” water. Frankly, that seemed like a feasible solution to us but not to the airline! All the water had to come from the ground and was carried at a premium. They actually told us how much each gallon of water would cost in terms of added fuel consumption and loss of passenger revenue (I’ve forgotten the number). Another “toughie” was the amount of handling needed to separate the china dishes from the food waste, stack them in the machine and then, after washing, remove them from the machine and prepare them for the next meal.

In the end, it was determined that storing complete sets of dishes with pre-plated food for each meal required less space, weight and labor than any ultrasonic dish washing system that we could come up with would save. A second group working on the more conventional concept of a spray-type dishwasher did no better than we did with the ultrasonic concept so in the end I didn’t feel too defeated. I don’t know if the consultant kept his job or not – I suspect he did – and so did I.

FJF

Posted in Cleaning, Ultrasonics, Useful Information Miscellaneous, Washing, Waste Disposal, Water | No Comments »

Cleaning at Home – Dishwashing

November 8th, 2012

Water, the “universal” solvent is the center of most cleaning applications in the home. Water, at least in my location in the US, is readily available, plentiful and relatively inexpensive. Water plus a small amount of overly expensive and competitively merchandised chemicals does an admirable job of cleaning dishes and clothes which constitute about 50% of cleaning in the home.

Let’s start with dish washing. I prefer the old-fashioned method of filling a dishpan or one side of the kitchen sink with water, letting the dirty dishes soak for a few minutes in soapy water and then finishing the job with a sponge or dish cloth. Once the dishes are washed, they can be rinsed with running water or in a second dish pan or sink filled with clean water. Drying is accomplished by wiping the dishes with a dish towel or putting them in a drying rack (dish drainer) and letting gravity and evaporation do their job overnight. There’s no need to rush this process unless you are of the mind that the first step in preparing a meal is to wash the dishes from the previous meal . . .

My wife, on the other hand, insists that a dishwasher (No, not the kids – - the one under the kitchen counter) provides better cleaning using less effort and energy. A dishwasher is no more than a simpler and less expensive version of a spray washer similar in nearly all regards to an industrial spray washer. The parts (dishes) to be washed are usually “rinsed” to remove uneaten bones, peels and shells are placed in a rack with meticulous care to assure that all surfaces are accessible to the rotating spray bar or bars located at the bottom, middle and/or top of the unit. Of course, there are those special dishes which can’t go in the dishwasher at all and must be washed the old-fashioned way anyway. Once the dishes are placed in the dishwasher’s chamber, a packet or two of chemicals are placed in a little dispenser on the inside of the unit’s door in faith that it will be magically released at the proper time in the washing cycle. In order to be effective, that chemical is really some pretty nasty stuff in an attractive package but we’ll talk about that in a later blog. OH, and don’t forget the “blue stuff” that makes the dishes “shine.” Next you set some dials and push a bunch of buttons. Pots and Pans cycle? Normal Cycle? Glassware Cycle? Sanitizing Wash? Sanitizing Rinse? Air Dry (“Energy Saver)? Heated Air Dry? “Power” Dry? The more expensive the dishwasher, the more buttons it has. Frankly, I’m pretty convinced that it does the same thing no matter what buttons you push – but that’s my opinion.

Finally, about time and energy efficiency – - It seems to me that, since you have to handle the dishes individually to load them into the dishwasher, you might as well finish the washing and rinsing process while you have them in hand. Using the dishwasher, you still have to handle them again to return them to the cupboard so what’s the big deal? It is true that the dishwasher probably does use less water than hand washing dishes. This is especially true if you are one of those who keeps the water running while you wash and rinse by hand. HOWEVER, the savings in water use is likely eclipsed by the increased energy used by the dishwasher. After all, the dishwasher has a respectably-sized pump to spray all that water and a heater to heat the wash and rinse water as well as the air for drying. There are also a bunch of automated valves to control the flow of water in and out of the machine and a fan to circulate air (hot or cold) for drying. In short, a dishwasher uses less water but certainly more energy than hand washing and I’m not convinced that it saves time.

The analogy between industrial parts cleaning and a similar cleaning process at home is interesting. The industrial requirement is quite different and, usually, can easily justify a sophisticated cleaning machine. However, just as at home, bigger and better is not always the best overall solution. The next blog will address the issue of doing laundry at home. Do you think I’ll be in favor of doing laundry by hand?

FJF

Posted in Cleaning, Drying, Useful Information Miscellaneous, Washing | No Comments »

What Makes A Cleaning Requirement Challenging?

November 6th, 2012

The preceeding blog discussed what is probably the “granddaddy” of all cleaning challenges – burned-on carbon. But, as those of us who have been in the cleaning business since Noah launched the ark know, there are a bunch of other cleaning challenges that defy modern technology. In general, these challenges fall into a small group of categories.

The first category is insoluble contaminants bonded to a part surface. These are materials that don’t qualify as “particles” because they are bonded to the part surface by adhesive forces. This category of contaminants includes paints, rubber, plastic, epoxy and silicone compounds like RTV as well as many others. In most cases, these materials are purposely formulated to have excellent adhesion properties and be resistant to chemical and/or mechanical attack. In short, they were never meant to be removed. In addition, many of these materials have resilient physical properties which prevents fracturing them as a viable means of removal. Again, as in removing burned on carbon, these contaminants are often adhered to substrates that are, themselves, susceptible to chemical attack by most of the likely candidate cleaning chemistries.

The second category is removing a “contaminant” that is of the same composition as the substrate it is being removed from. Here, the culprit is usually the cohesive forces that bond the contaminant to the substrate. Good examples of this are removing glass particles from ground glass surfaces and removing carbon particles from machined or polished carbon substrates. Mechanical intervention in the form of brushing, high pressure sprays and ultrasonics are beneficial in most of these applications. A word of caution though – - Any cleaning technology that is able to break the cohesive bond between the contaminant and the substrate is probably just short of being able to break down the substrate itself so control is a major issue. “Overkill” is not an option in these applications.

Magnetism, although not the same as cohesion presents nearly the same problem. Magnetic particles, even if initially removed, tend to re-attach as quickly as they are removed. The problem of magnetized parts or particles was discussed in a previous blog.

Exceptional Particles – Magnetism

The third category of challenging parts cleaning applications involves parts that have a geometry that limits or excludes access to the surface to be cleaned. One typical example of this is tube and plate heat exchangers and reactors with internal contaminants that can not be removed chemically. Their physical properties preclude access for introducing mechanical means to assist in cleaning. Long tubes, parts with deep blind holes or internal passageways and parts with “hems” also fit into this category. A further challenge in cleaning parts in this category is that inspection to assure cleanliness is usually just as difficult as the cleaning itself. In the worst case, cleaning parts in this category may require costly and time consuming dis-assembly which often tilts the scale toward replacement.

As if the above components of challenge aren’t enough, most challenging cleaning applications exhibit more than one component of challenge. Those heat exchangers mentioned above – - Not only is there a lack of access, but the contaminant, usually a buildup of calcium or other material which has been baked on, is only minimally soluble making chemical cleaning alone a non-viable option.

The above list comprises a “red flag” guide to those with cleaning requirements and those attempting to solve them. It, of course, is not all inclusive but applies in a high percentage of cleaning requirements still in search of a solution.

FJF

Posted in Cleaning, Lab Tales, Useful Information Miscellaneous | 3 Comments »

Challenging Cleaning Applications

November 1st, 2012

The technology of parts cleaning is a very sophisticated science today. Most cleaning challenges can be met with the proper combination of equipment, chemistry and technique. In my 45 year involvement with parts cleaning, I have seen many twists and turns along the way. Applications that were considered “impossible” 10 or 20 years ago are now routinely successful. In spite of all the advances, however, there are a few cleaning challenges that still haven’t been conquered. For the applications engineer, it is a very difficult thing to say, “I’m sorry, but I don’t have a solution.” It’s a bit like a Doctor telling a patient that he/she has a disease or condition that can not be cured. It’s something you never like to do. However, like the Doctors, those in the parts cleaning “practice” still keep trying!

Because it’s sometimes more valuable to know what you can’t do than what you can, I would like to spend a little blog time on cleaning applications that are still without a practical or universal solution. The upcoming comments can be taken in two ways – - For some, they may be seen as an aid in preventing promises that can’t be kept. For others, they will provide a list of challenges which, if they can be solved, promise significant noteriety and potential monetary reward since most are associated with real and identified needs with ready customers awaiting solutions.

I would like to start off our discussion of cleaning challenges with one that is very specific and has been bugging me, personally, for a long time – - Removing varnish and carbon deposits from pistons in engine remanufacturing operations. Carbon, in itself, is not really a cleaning challenge. In its pure form as a powder or a compressed solid it’s pretty much just another particle removal requirement that can easily be solved using a mild alkaline chemistry containing wetting agents and with a little mechanical assist. However, when the same carbon has been deposited along with “varnish” products of combustion in the cylinder of an internal combustion engine the story changes drastically. That stuff is on there to stay! Although there are chemistries that may attack and dissolve the varnish holding the carbon in place, most of them are very strong caustics like sodium hydroxide. Unfortunately, many pistons with carbon and varnish buildup are made of Aluminum or one of its alloys. Caustic chemistries attack aluminum and, therefore, can not be used! A caustic chemistry with sufficient strength to remove carbon and varnish deposits will also dissolve an aluminum piston. In a limited number of cases, the challenge has been nearly met using a mild caustic in combination with ultrasonics with extended exposure times (hours to days). In most instances, this is not a practical solution because of the old “time is money” addage. Replacing the piston or the entire engine is a more cost effective solution.

Of course, there are also pistons made of alloys that are not attacked by caustics. These are usually found in larger engines where the potential payback for cleaning may be substantially greater than it is for an automobile engine, for example. So, under the right conditions removing varnish and carbon deposits from pistons may be practical but in the vast majority of cases it remains unsolved with today’s cleaning technologies.

Upcoming blogs will discuss more cleaning applications that are more dream than reality.

FJF

Posted in Chemistry, Cleaning, Lab Tales | 4 Comments »

Ultrasonics and Turbulation Don’t Mix!

October 29th, 2012

Previous blogs have explained the benefits of relative motion between the part being cleaned or rinsed and the liquid in contact with the part. Relative motion can be accomplished by moving either the part or the liquid relative to the other. Ultrasonic agitation has also been identified as beneficial to cleaning and rinsing for somewhat the same reason but on a “micro” scale. Not surprisingly, combining ultrasonic agitation and the larger effect provided by part agitation or liquid turbulation may provide results superior to either those seen when either is used independently.

Now things get interesting! Both turbulation (under water spray) and agitation of the part in the liquid provide relative motion between the part and the liquid. One might assume that, since both provide the same effect, they could be used interchangeably. The fact, however, is that turbulation is detrimental to the ultrasonic effect. Let me explain.

Efficient transmission of sound at any frequency is, at least, somewhat dependant on the continuity of the sound conducting media be it gas, liquid or solid. A good example of the effect of dis-continuity on the transmission of sound waves is two people talking over some distance on a calm vs. on a windy day.

Illustration showing the effect of wind on sound transmission

In the top illustration, the sound waves are not distorted by wind with the result that the listener can easily hear the speaker. In the lower illustration, distortion of the sound waves by wind make it difficult or impossible for the listener to hear the speaker.

On a calm day, sound waves travel effectively between the speaker and the listener. On a windy day, however, the sound waves become distorted by the external effects of the wind with the result that it is difficult or impossible for the listener to hear the speaker. In a more personal example, on a calm day I can easily hear church bells located about a mile from where I live. On a windy day, I hear nothing. I’m sure we can all think of examples of this effect.

Turbulation of liquid produces much the same effect on ultrasonic transmission as wind does on the transmission of audible sounds through air. The effectiveness of ultrasonic waves is significantly reduced once they are distorted by turbulation of the liquid. For this reason, part agitation is often superior to liquid turbulation when it comes to maximizing a cleaning or rinsing effect. The part moving through the liquid at reasonable speed, although it creates essentially the same relative motion between the part and the surrounding liquid, does not cause the liquid distortion seen in turbulated systems using turbulation to create the same relative part to liquid motion. Although it is often a better choice, part agitation may be more difficult or costly than liquid turbulation using eductor nozzles or other devices providing a similar effect.

As an alternative to part agitation, turbulation and ultrasonics can be used sequentially to provide excellent results. There is no real downside to providing ultrasonic agitation continuously in a system with both turbulation and ultrasonics, but the turbulation should be discontinued periodically for sufficient time to allow the ultrasonic waves to become established in the liquid and then resumed to complete the cleaning or rinsing cycle.

FJF

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