CSC Scientific Blog

Is Sieve Calibration Really the Holy Grail? Part II

Art Gatenby — Tue, 07 Feb 2012 21:44:00 GMT

Is Sieve Calibration Really the Holy Grail? Part II: Inside a Sieve Test

As I start on this second installment of The Adventures of Pequeño: The 150 Micron Particle, I wonder why I get myself into these serial onslaughts. However, a promise is a promise, so I shall press on.

You will recall from Part I: Sieve Certification, our little friend Pequeño, a particle on a determined quest to make it through sieves -- particularly those through which he should be too large to pass. In this scenario, Pequeño along with some of his family and friends -- all small particles about 150 microns in size -- are on their way to a sieve test.

Harry is a Quality Control Manager. He loads a stack of sieves onto a sieve shaker. From the top, the sieves are:

#80 – 177 micron

#100 – 150 micron

#120 – 125 micron

#140 – 105 micron

He dumps Pequeño and large quantities of other .-sized particles into the top sieve. Pequeño’s first impression is that getting through the first #80 sieve is no problem. Then, the Shaker starts (violent motion – up/down and circular).

Almost immediately, Pequeño and his little companions get to the #150 sieve -- his size. If the sieve is perfect, he might not make it to the 125 micron sieveHowever, it is not perfect; just certified to be within standard ASTM tolerances. He quickly finds over-sized holes, which lead the way to the 125 micron sieve, which is supposed to be smaller than Pequeño and most of his family.

As the shaker continues its vigorous movement, he looks for the certified largest allowable opening on the #125 sieve. That is 168 microns, through which he and and some of his colleagues should find easy passage. If they don't shut off that damnable shaker, he’ll find one of these and pass through to the 125 micron sieve along with some of his cadre.

As it turns out, the #140 (105 micron) sieve gives Pequeño trouble; only a few of his ever-shrinking cohort squeeze through the max 141 micron opening.

Harry is depending on Brad’s (the professional Sieve Certifier from Part I) previous work to retain all particles like Pequeño on the #120 to125-micron sieve and would thus never expect to find Pequeño sitting on the 105-micron sieve.

Brad’s job was to make sure that sieves meet the Calibration Sieve Category (the highest standard) and thus apply a sufficiently rigorous standard to his measurements. It still leaves a high probability of 168 Micron holes on the #125 sieve.

Harry’s job is to run the sieve tests to see if his product meets predetermined particle size distributions. This specification did not call for Pequeño to pass beyond #125 (124 micron) sieve.

It turns out that the ASTM standard that Brad certified left a lot of wiggle room for Pequeño’s passage to a sieve specified as smaller than his natural size. This leaves Harry with some tough QC question.

I appreciate your taking this journey with me to follow Pequeño’s (hopefully unsuccessful) quest to get through ever-smaller sieves. In the next installment, we’ll explore what happens to him and his clan of similar sized particles after they transit the sieves.

Until then feel free to contact me with questions, concerns and/or suggestions,

Art

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P.P.S. If you need to see the available sieve types sizes and mesh click on the button.

Which Type of Tensiometer do I Need?

Art Gatenby — Thu, 22 Dec 2011 23:55:00 GMT

As followers of these rants know, Fisher Scientific stopped offering its Tensiomat Tensiometer about a year ago. As a tensiometer manufacturer, we at CSC Scientific were very interestedin this and have tried to let the world know that we might be able to help with things such as replacement rings, trade-ins and the like.

In discussing alternatives with Tensiomat users, we are often asked, “if I am going to replace my tensiometer, which one should I get?”

Let's explore the alternatives and compare their respective capabilities.

The simplest tensiometer has a duNouy Ring hanging by a hook from a level arm. This is a staple for measuring surface tension in simple liquids as well as measuring interfacial tension between oil and water. As the liquid thickens, an option with the ring rigidly fixed to the lever arm is helpful. This version can also measure the interfacial tension between two liquids in a downward direction.

Beyond these classic models, which cost in the $4,000 range, are the starting electronic balance-driven digital versions that can perform the duNouy ring tests as well as the Wilhelmy Plate technique. This level of tensiometer works well for static surface tension analysis. Depending on the test procedure’s degree of automation, these digital tensiometers cost between $6,500 and $10,000

As the testing requirements expand to include as the likes of Lamella length, sedimentation rates and temperature studies, automation and computer analysis; tensiometer capabilities grow as well. Instruments that require such features range from $12,000 to $20,000. The cost levels usually depend on the number of alternative techniques included.

As requirements expand to include determining dynamic surface tension, powder contact angle, powder wettability and dynamic surface tension, the cost level can increase to the $40,000 plus range.

When the requirement is for just surface tension, the basic units can usually meet the needs for periodic testing. However, wth high test volumes and expanded test functions, the higher-cost units become important alternatives.

Our affiliate Scientific Gear constructed a capability comparison table to help determine the type of instrument needed to best support an application. Click on the button for a copy.

We are available to discuss your specific application and help identify the instrument that will most effectively meet your needs. We hope this short review will be helpful in understanding the tensiometer alternatives and their particular capabilities.

I remain a continually astonished,

Art

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Who Beats Up Your Bostwick?

Art Gatenby — Wed, 16 Nov 2011 17:11:00 GMT

Sometimes we encounter a product that is so simple and rugged that it would be tempting to deem it indestructible. Consider a stainless steel trough with a gate and etched numbers on the bottom. Seems simple and the stainless would make it tough, right? That is not the case, but it has survived nearly unchanged for more than 85 years.

Just described the Bostwick Consistometer, which CSC has been making since the beginning.

You may familiar with some of its uses such as checking sauces, toppings, slurries, paints and other types of flowing materials. It is used in many challenging environments such as:

The tropics
Pristine labs
Production lines
Airports in the Winter when de-icing airplane wings and bodies
Anywhere else you want to check a process that makes a flowing product

Ensuring proper measurement requires cleaning after testing. Detergent, high-temperature washers, solvent baths and other cleaning/scouring media are used.

The Bostwick Stands Up

Ingenuity is helpful in finding ways to destroy the bubble level that indicates when the set-up is ready for testing. Using King Kong-like staff members, you can trash the gate mechanism. Further, with King Kong or mechanical vises, the Bostwick can be bent beyond recognition. However, in normal use it is difficult to wreck a Bostwick.

Nonetheless, production operators drop Consistometers on concrete floors, toss them from great distances into cleaning sinks or otherwise lose physical control of their Bostwicks. Like prisoners facing repeated interrogation, Bostwicks eventually succumbs. Typicaly, damage involves a bent support deck for the leveling screws along with destruction of the leveling screw supports – fatal failures, no longer will it measure Consistency.

We at CSC Scientific get many of these sent to us for partial reconstruction.

Recently, a long-time friend and customer gave us a design to highly challenge these King Kong operators. Almost had to throw the modified Bostwick under a bus or forklift to cause fatal failures. We call this design the “Abuse Protection Option.”

Click the button to review the results and how the Abuse Protection Option (APO)may thwart prospective Bostwick destroyers.

I hope this has been at least a little fun. If you have recurring fatal failures, perhaps you should consider an ABO on your next Bostwick.

I am still searching to useful insights on test equipment secrets.

Art

Is Sieve Calibration Really the Holy Grail? -- Part I: Certification

Art Gatenby — Mon, 07 Nov 2011 20:13:00 GMT

Sieve calibrationis the final step in determining whether processes yield suitable end results. In other words:

Is your concrete going to be strong enough?
Will you chocolates taste right?
Will your washing powder flow and dissolve as advertised?
Is there dangerous residue in your pill stock?
Will the “frack sand” keep the fractures open?
Is my salt of the correct grade?

If these are not correct, serious consequences could result (e.g. spoiled product, returned batches, rework or scrap).

These are the particle-size issues for which we test, frequently using woven wire mesh sieving techniques. For a long time, I've made sporadic attempts to understand how to ensure that tests really represent particle distribution. Many phenomena can affect these determinations.

I have decided to undertake clarifying this murky process. There are inherent irregularities in most woven materials. Regarding woven wire mesh used in sieves, standards organizations attempt to determine the acceptable range of these irregularities and then set acceptable variation limits.

Mesh problems also arise from the testing process as well as cleaning and various forms of abuse. How do we determine if these processes affect sieve performance?

By means of illustration, I offer a particle’s perspective, the particle which I've named Pequeño. He encounters a sieve, undergoes a test, is cleaned out of an undersized hole and attacks several calibration operations.

Pequeño is doing this in Four episodes, the first of which we will explore now and the others in later blogs:

Bouncing around in a test
Getting cleaned
Beating the calibration

***

Episode I: Certification

I am Pequeño, a particle with a passion to get through any sieve and not be amongst the particles retained.

My story begins as I observe Brad, a professional sieve certifier, at work squinting through a microscope at a series of nearly square openings bounded by sections of wire that span the entire sieve. In one direction, the wires go straight across the sieve (Weft). In the other direction, the wires alternately go over and under the straight wires (Warp).

I'm from a large family of very small (about 150 micron) siblings. Brad is working on a number 100 8-inch diameter sieve with 150-micron nominal apertures, holes or openings (they can be called any of these). It has about 500,000 of these openings. It should be easy for me to migrate to the next sieve.

Brad is inspecting and measuring 200 of these holes (about 0.04% of the total). He is measuring the wire in each as well as one side along the weft and one side along the warp. When finished, he will apply ASTM-specified formulae and determine if the sieve meets specifications.

Within the acceptable specs for these 200 openings, the average could be as large as 156.6 microns. There should be no problem of my getting through openings that size. However, this average could be as low as 143.4 microns.This could finish me, but the another specified dimension is the 193-micron maximum allowable size of an individual opening.

If I look around enough, I should even be able to get through a sieve that Brad calculates as the minimum. Remember, Brad only measured 1-in-2500 openings.

If his task was to certify that the sieve meet the highest standard -- the Calibration Sieve Category -- he would apply a reasonably tight standard deviation to his measurements. This would reduce my chances of getting through on the small average, which would only make it more of a challenge to find an opening through which I can pass.

In fact, I even have a shot at getting through a sieve with the next smallest designation (number 120 with 125 microns nominally sized holes). The allowable maximum of any individual hole measured can be 168 micron -- an easy transit for me.

I like the theoretical odds of feeding my passion of getting through my size and smaller sieves (hate to be in the retained category). In fact, I might even nvite some of my larger siblings to join me.

In my next visit, I'll take you with me on some real production tests that use the sieve that Brad measured and professionally certified.

Until then,

Pequeño

***

I hope you found this entertaining and somewhat informative.Take a look at some sieve alternatives.

Thanks for your attention, I remain distracted, mystified but still swinging,

Art

P.S. If these musings on lab test equipment are interesting, subscribe above.

Why Do I Get Inconsistent Moisture Test Results?

Art Gatenby — Fri, 14 Oct 2011 18:32:00 GMT

“Why are my Moisture Test results inconsistent?”

That is an issue for many of you who test for moisture. We discussed the complexities and multiplicity of issues involved with moisture content determination in our “Loss-on Drying Moisture Analysis and other Moisture Mysteries” series.

In addition to intrinsic properties of test samples that may adversely affect moisture testing systems, automatic equipment parameter set-up, operator oversights and sample handling contribute to seemingly intractable moisture test result inaccuracies.

Common test sample vagaries include:

Volatiles other than water that are released at close to the same vapor pressure as water evaporation.
Strange conditions of entrapped moisture that release water at capricious times.
Samples not representative of the principal batch

It is important to determine if these test sample quirks are responsible, because test protocols may require changing. Variations can also be minimized by running more tests to statistically reduce variation effects. In some cases, changes in test methods may be needed (i.e. Karl Fischer rather than Loss-on-Drying).

While trouble-shooting such problems, it is important to check automatic setting level and operation, which determine when a test is completed. With the Loss-on Drying method, these settings relate to measuring sample weight changes. If the instrument is set to stop too soon, the weight-loss curve will slope steeply and the moisture result will be subject to irregular variations from test to test. If the end-of-test calculation is based upon too small of a weight change, there is a potential for burning the sample -- another cause of inconsistency.

Similar problems can arise if widely different test-to-test sample weights are used in a timed test environment.

Another source of inconsistent analysis can be that a small amount of moisture requires detection. A small amount of sample and a very sensitive balance are frequently used for this type of test. Operators must carefully follow test procedures or the balance’s high sensitivity will yield wide result variations from test to test ( Often A switch to the Karl Fischer Method will Solve this Problem).

As equipment manufacturers, we will ultimately consider the possibility of instrument malfunctions. Our experience with instrument service leads us to either clear instrument failure or consistent high or low results signaling equipment problems and not just inconsistent results.

Our troubleshooting protocols require duplicating clients’ problems in our lab. When we cannot, experience leads us to consider environmental conditions at our customers' facilities. Frequently, we find electrical power conditions to be responsible. Special power-conditioning equipment will usually solve this problem.

On occasion, we cannot find the sources of variation.

In summary, issues relating to test sample properties and/or or incorrect test parameters normally yield inconsistent results. Occasionally it is operator error. However, on rare occasions, test site environmental conditions are responsible.

Sometimes it requires painstaking investigation to find the cause. When found, we can usually then develop workable solutions.

I hope this sheds some light on the sources of inconsistent test results.

As usual, there is still a bit of witchcraft and folklore needed to solve the more elusive measurement problems.

Still trying to get answers, I remain a puzzled,

Art

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Why Calibrate a CSC DuNouy Tensiometer?

Art Gatenby — Tue, 13 Sep 2011 15:14:00 GMT

Within the catalog of questions we are asked is a category related to Calibrating duNouy Ring Tensiometers. The subject matter ranges from how, why and what is proven?

I guess the immediate and wise-assed answers are:

To see if the Tensiometer is working.

To determine if it is working correctly

Because it gives a reference for ISO traceability

Some of the calibration schemes pertain specifically to the unique design of the CSC Tensiometer and its application of torsion balance concepts.

Our tensiometers determine vertical force by measuring the twist or torsion in a wire. Starting from an equilibrium point where a our scale dial is at zero;

1. We pull a duNouy ring through a liquid surface

2. This twists the wire as it resists the surface tension force and

3. We measure the amount of twist or torsion in the wire needed to pull the ring completely through the surface.

A calibration procedure is needed to produce a measurement in accepted units of surface tension (dynes/cm),as well as obtaining a reading that relates to a traceable measure or value. Thus, the real answer is all three of the above; the Tensiometer is working, working correctly and the results are traceable.

I shall describe the procedure which assures that a test reading is accurate.

The procedure goes as follows:

Set up the Tensiometer so the indicator is on the “0” line in the mirror and the dial reads Zero. Like a Seesaw or Teeter Toder,in balance with equal sized kids ( Ralph and Rachel) on either side. The ring (Ralph) on “teeter” side and the arm (Rachel) on the “totter” side.

Now we add a known weight to the ring which pulls down the indicator. (We handed Ralph some free weights).

We now turn our dial until the indicator goes back to Zero, (We give Rachel some stones until until it balanced again).

At this point we apply a magical formula that lets a wizard tell us what the dial should read if every thing is in correct balance.

We reconcile any difference between that number and the dial reading by adjusting the arm length. Thus, the wizard says Ralph should have more weights or that Rachael should move in or out on her side of the “totter” until the Seesaw balances again.

Now we know that for a given weight, along with Ralph’s and Rachel’s specific position, the seesaw will be in balance. In other words, we know how much force will be needed to move the dial by one dyne. This magical formula makes the translation of the weight added to the number the dial should read.

We have a short video that shows how this calibration process works. You can get to it by clicking on the bubble.

I had fun putting this together and hope it simplified understanding of the tensiometer calibration process (except for the magical formula the basis of which is a designer’s secret).

Let me know what your interests are and we'll try to rail about them. You can do this by commenting below or by emailing me at artgatenby@gmail.com

I thank you for following my rants.

A befuddled as usual,

Art

P.S. Hope you enjoyed meeting Ralph and Rachel. By the way sign up and subscribe to our Test Equipment Rants.

Karl Fischer Moisture – Answers to Questions We Get Asked

Art Gatenby — Fri, 29 Jul 2011 20:08:00 GMT

When People are first introduced to the Karl Fischer Moisture Determination Method, eyes glaze over and we can perceive a mental “Why did I Ask?”

If you have any history with moisture analysis, you will have found, that for some applications, the Karl Fischer Titration Method is the best and sometimes the only way to get an accurate moisture measurement.

Most non-chemists react to the thought of titrations with “Not for me – do I have to do this?” Even the chemical formula for the Karl Fischer reactionis mind blowing.

However, these days most of the pain is removed with automatic Karl Fischer instruments such as our Aquapal III, that make conducting Karl Fischer tests quite simple. There are still times when your not sure if the equipment is reading correctly or when it gives arcane messages like "Over Titration" that you feel panic. A host of other subtle problems bring on the question “What does this Mean?”

Recently Hank Levi, a colleague of ours at Scientific Gear, developed a list of 20 questions that are periodically asked. He also developed concise answers. They are questions like;

Why won't my instrument get to the Ready Mode?
What kind of reagent should I use?
Is my instrument giving me correct results?
How much sample should I use?

We would like to share these with you. If you click on the button you can down-load the full list of Karl Fisher questions and answers.

Hank tells us that some of his customers post this list in the lab where it is available for reference at any time to the staff conducting Karl Fischer moisture determinations.

Maybe this will help reduce trepidation about Karl Fischer and help get good repeatable results.

We hope that you check out this list and that it is useful to you. Again thanks for visiting.

I remain a wary respectful friend of Karl Fischer,

Art

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Sieves – Old and New QC Issues

Art Gatenby — Wed, 06 Jul 2011 19:13:00 GMT

In April, we published an article in "Powder-Bulk Solids" comparing certification process veracity with a sieve calibration process using calibrated glass microspheres (or beads). The certification process merely indicates that a sieve mesh conforms to a standard that has a wide tolerance regarding mesh openings. It is performed on a small number of openings. On the other hand, calibration using the calibrated beads results in a number representing the mean opening -- a result generated by actually performing a test encompassing at least 80% of the mesh openings.

Given that the calibration process highlights the actual performance of a given sieve, we recommended that QC departments switch to a calibration method to determine the suitability of the sieves used in tight-tolerance situations. This requires a different mindset from test sieve manufacturers as well as QC departments responsible for controlling sieve processes.

We recently had a real-life example of the the difference between actual sieve performance and certification statistics. A customer recently acquired four 45 micron (#325) ASTM certified sieves. Given that their manufacturing process was critical, they decided to check the four sieves with calibration beads. The results on each sieve showed a mean aperture of 49 microns. Because the certification spec allowed a variation of up to 3 microns in average opening size (allowing up to 48 microns in average opening) They returned the sieves to the manufacturer for re-certification. All four sieves passed. The customer also had them double-checked by an outside laboratory. Each of the four sieves tested the same; consistent with a real-world sample as well as bead calibration results.

What to do? --- Whom to believe? --- What ARE these sieves?

In light of this, let's consider the most recent ASTM specification (ASTM E 11-09). The customer's sieves were 8 inches in diameter, which represented approximately 15 million openings. The most exact ASTM certification requires examining only 1,000 openings ---- less than .01% of the number in an 8-inch #325 sieve. For these 1,000 measured openings, the maximum allowable average opening size variation is 3 microns with an allowable maximum opening of 67 microns. Given that the bead calibration produced a mean opening of 49 microns, the customer felt that the sieve was out of spec compared to the maximum allowable average of plus three microns (45+3 ) of the observed 1,000 openings. Note that these statistics are all based on measurements and not on actual sieve test performance.

The bead calibration tolerance is about 1 micron in mean opening resulting from a sieve test using a calibrated sphere sample.

This real-life situation makes it clear that certification, while an insurance policy of some value, does not predict a sieve’s actual performance. It does nothing more than sample some openings and determine if the sieve mesh is within prescribed tolerances.

Calibration performs a live sieve test and yields the actual results.This leads us to the conclusion that calibration with glass spheres is the optimal procedure for determining the suitability of a test sieve as well as checking and controlling a process.

We can compare mesh sieve performance to the results on the same sample, but predicting it can only be accomplished by conducting an actual sieve test using a precise sample such as Calibration Beads.

To date, calibrated spheres are the best method for this and for determining the actual calibration of any test sieve.

As with most of the things I rail about here, real world conditions often lead to confusion about theory and when analyzed question established practice.

I hope this has been helpful. Call me at 703-876-4030 if you want to discuss the certification/calibration dichotomy.

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for e-mail notice by jotting your address in the box just to the right of the title.

Loss-on Drying and Other Moisture Mysteries - Part V: Drying

Art Gatenby — Wed, 15 Jun 2011 16:55:00 GMT

Just over six months ago, I began this journey explaining the simplest approach to measuring or determining moisture: Loss-on Drying. Little did I know how involved and esoteric it would become.

This voyage has taken me down mysterious paths through spooky theories, back to age-old chemistry concepts and into the vagaries of thermodynamics related to evaporation, vapor pressure, bound water and water activity. I have come full-circle; back to explaining Loss-on Drying -- a form of drying that I had assumed would be the simplest of all.

I thought the first four topics [evaporation, vapor pressure, bound moisture, water activity] were tough, complex, confounding and less-than-obvious. Drying -- defined as “the mass-transfer process of removing water (or other solute) by evaporation from a solid, semi solid or liquid” -- seemed easy.

As is often the case, reality makes “easy” a non-operative word. Such has turned out to be so with respect to the issue of drying.

To begin, there is the process in which heat is transferred to create a temperature in a solid that evaporates moisture from the surface and causes it to migrate from the inside outward. This internal migration occurs through several mechanisms such as diffusion, capillary action and the internal pressure created by shrinkage. It is not as simple as hanging laundry on a clothes line to dry on a breezy, sunny day.

Firstly, there is the initial and underlying issue of product classification. Here are some examples:

Non-hygroscopic Capillary Porous Solids: These are materials such as sand, crushed minerals, certain crystals, polymer particles and some ceramics. They have recognizable pore space filled with liquid, little bound moisture and do not shrink on drying.
Hygroscopic Porous Solids: Clay, molecular sieves, wood, textiles, silica gels, alumina and zeolites are examples. They are characterized by clearly seen pore space, physically bound moisture and shrinkage in the early stages of drying.
Colloidal (non Porous) Solids: Examples include soap, glue, polymers like nylon and various food products. There is no pore space and all moisture -- except that on the surface -- is physically bound.

There are other less-common classifications and combinations as well.

In the drying process, the rate of moisture removal varies widely between these classifications. In some, the rate is linear throughout. In others, the removal-rate is high at the beginning and diminishes as drying progresses [as illustrated in the dreaded drying-rate curves]. The principles of evaporation, equilibrium pressure, vapor pressure, partial pressure, temperature, relative humidity, dew point, moisture sorption isotherms and ideal gas laws all apply. As you may remember, some of these concepts have effect in other sections of the Moisture Mysteries Series. They all apply to this concluding phenomenon of drying, to which in the beginning I naively referred as just plain drying.

Most products from today's industry undergo drying at some stage. For example, drying is an important element in a wide range of products such a food, pharmaceuticals, lumber, paper, fiberboard and a host of chemical products. In fact, approximately 10% of the energy consumption in the US and Canada is directly related to production drying.

All of the issues that stretched my thought process are present with the development of production systems. Consequently, dryer designs are not universal across product classifications because of the inherent complexities in the drying process. Production drying systems are developed for specific products. These include convection, belt, fluid bed, rotary, spray, flash and drum dryers.

One of the more difficult issues is to get at is the bound water. Among other techniques to deal with this is freeze-drying. Additionally, there are mechanical methods of removing moisture [e.g. centrifuging] that are referred to as dewatering rather than drying.

A compromise is often sought between the cost of transportation (lower moisture) and the cost of drying. Further, the level of drying is often a measure of a product’s suitability for market -- i.e. color, flavor, shrinkage, palatability and cracking. To check the effectiveness of these processes in meeting the diverse objectives, the moisture content after drying needs to be determined. The most frequently used technique of moisture determination is Loss-on Drying. That was the reason for this series of articles that sought to explain the factors of drying.

The Loss-on Drying moisture measurement process involves all issues and considerations concerned with production drying. People regularly ask us, “at what temperature should we run the test and for how long?” This discussion of drying should help them understand why we reply “It depends”.

I hope this “Loss-on Drying and Other Moisture Mysteries” series has been interesting and useful. Also I hope it was fun.

Now that I have finished Part V, the last in the series, I remain more astonished than ever with the mysteries of the test equipment world.

Thanks for visiting.

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for email notice by entering your address into the box just to the right of the title.

Why Not A Bostwick Consistometer Calibration Standard?

Art Gatenby — Wed, 11 May 2011 16:35:00 GMT

Customers want Bostwick Consistometer Calibrations.

When told that CSC Scientific does not calibrate Bostwick Consistometers, people ask . “Then how can I calibrate my consistometer and where can I get a calibration standard?”.

We recommend sampling the selected product to be measured using the Bostwick Consistometer. The sample should represent your product in its ideal state. The temperature should be carefully recorded and a test run. The time it takes to get about half way down the trough should then be recorded.

This process will set a standard or an expected result for a perfect product. From this baseline, acceptable limits should be set by time. For example, a reading of 16 in 85 seconds might be the standard for a perfect product at 30° C. Acceptable variations can range from a reading of 16 in 81 seconds to a reading of 16 in 89 seconds. Again, the product temperature should be 30° C.

A similar procedure should be followed for each of your products tested with the Bostwick Consistometer. The standards thus should be recorded in a QC results chart and stored as reference for ISO or similar quality control inspections.

This table shows typical standards and acceptable limits for three hypothetical products:

	Marbleized A	Syrup C	Mission 5
Product Temperature	30°C	42° C	50°C
Distance Standard	16	17.5	15
Time Standard	85 Seconds	58 Seconds	42 Seconds
Allowable + Time	81 Seconds	62 Seconds	46 Seconds
Allowable - Time	89 Seconds	55 Seconds	40 Seconds

We have had frequent requests to develop a reference standard for ISO and other quality control inspections. In an attempt to meet these requests, CSC Scientific conducted extensive research to find a suitable material - a material with a consistent viscosity that would repeat results from test to test. The problem we had with seemingly promising materials was a high sensitivity to small temperature changes. After exhaustive experimentation, we concluded that the prevalent effect of temperature on Bostwick Consistometer results abrogated the practicality of a universal standard.

The critical issue in consistent and repeatable CSC Bostwick Consistometer operation is in the set-up. Leveling the trough is the principal requirement for getting repeatable results on a sample at a fixed temperature.

Establishing and recording Bostwick results on the perfect or quality control standard product is the only practical way to develop a calibration. This should be done with the user’s product at the testing site.

Sorry to have to carry this message. You have to do your own calibration for each of your products.

I hope this was helpful to you.

As always a perplexed,

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for e-mail notice by jotting your address in the box just to the right of the title.

Surface Tension – Tensiometer Update

Art Gatenby — Fri, 29 Apr 2011 18:11:00 GMT

This ramble is about changes in the Surface Tension Equipment landscape.

For decades it seems -- I guess it has been decades -- CSC Scientific (with the Precision and Interfacial Models) and Fisher Scientific (with the Tensiomat^©) have shared success in supplying the need for liquid surface tension tensiometers throughout the World.

Fisher has periodically evaluated discontinuing Tensiomat© manufacture. This year, the company decided to cease production. The CSC Scientific models are recommended as replacements. Fisher Scientific can provide either of the CSC Scientific Tensiometers.

CSC has two Tensiometer models:

Precision Tensiometer - Readings are obtained from an upward pull through the sample.

Interfacial Tensiometer – Readings can be obtained from an upward pull or a downward push

The CSC Interfacial Tensiometer is needed when interfacial tension is calculated between a less-dense fluid and a heaver one located below the interface. The ring is rigidly attached to the measuring arm to obtain a downward measurement. The Interfacial Tensiometer is also recommended when the tested material is a thick liquid. This more easily facilitates setting up the ring below the liquid surface.

One important consideration in the tensiometer transition is the availability of duNouy Rings to replace damaged ones. Several Tensiomat© customers have successfully used CSC-manufactured rings. We believe that this will be the experience in most instances.

In order to further help with the transition, we will repair Tensiomat© brand Tensiometers and will do so as long as parts are available.

New replacement rings (part number: 70537000) can be ordered directly from our on-line store or by telephone at 800-621-4778. Of course, we can help you with a new unit. Also, we offer background and application information on our Tensiometer Models.

If you are a a user of CSC Tensiometers or are otherwise not affected by this discontinuation but have a colleague with a Tensiomat^©, perhaps you can forward this article, thus providing them with a source for answers to questions about repairs and replacements.

We hope this has been helpful to you or to one of your colleagues.

A still somewhat dazed,

Art

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries Part IV: Water Activity [del.icio.us]

artgatenby — Thu, 07 Apr 2011 10:59:46 PDT

Answer to the Question. Who Cares About Water Activity?

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries Part IV: Water Activity

Art Gatenby — Thu, 31 Mar 2011 19:39:00 GMT

Loss-On-Drying moisture analysis seemed like a simple process until, in a state of naïve bliss, I promised to look at evaporation, vapor pressure and bound water. While I was otherwise occupied with these realities, I offered to enter the world of witchcraft and folklore; water activity.

I offer what will hopefully be an uncomplicated definition:

The energy or escaping tendency of water.

I would be happy if I could leave it at that, but I am compelled to relate water activity to good old Loss-On-Drying. Unfortunately, the concept begins in the complex world of Boyle, Charles and Dalton and their gas laws. These populate the Ideal Gas Law with considerations of pressure, partial pressure, temperature (at Kelvin no less) volume, molecules and moles.

Herein is my attempt to integrate these physics/chemistry phenomena to formulate a comprehensible description of water activity.

Let us first reflect upon a question I recently asked:

“Should we care about the presence and amount of bound water?”

The answer is very often yes and the reason frequently involves water activity.

There are many reasons water activity (a_w) is important. If it is too high, it can cause spoilage, browning, mold growth, clumping and a host of other unpleasant effects. In fact, excessive a_w can screw up a perfect blend of fruit and breakfast cereal (dried up fruit and soggy corn flakes).

It seems that water has an energy quotient that can lead it to enhance chemical reactions, cause bad things like bacteria growth or mix with other materials to mess up a good combination of components. Moisture content alone is not a predictor of this energy, however.

Each material has a natural relationship between moisture content and water activity, called its Moisture Sorption Isotherm (MSI) defined as:

“The relationship at equilibrium between water content and the equilibrium humidity of a material.”

This is effectively a moisture fingerprint. These isotherms change with temperature so it is not a static attribute.

The implications of water activity in the food industry are related to shelf-life, contamination, health, texture and taste issues. Thus, the a_wmeasurement is becoming an ever-increasing factor in food product design and food process quality control.

Also, water activity is becoming a serious consideration in the development and production of pharmaceutical products. It is water activity and its relationship to moisture content [not moisture content alone] that determines whether microorganisms can access water in a system, adding an important dimension to production process control.

The relationship of a_w to moisture content is likewise of growing importance in other products where water action affects either the production process or a product’s physical characteristics.

Water activity measurement is a relative humidity technique; a comparison of a sample’s vapor pressure at equilibrium to that of pure water. The measurement consists of placing a sample in a closed space, waiting for equilibrium to be reached and then measuring the resulting relative humidity in the air space. This is done using a calibrated capacitance cell or a chilled mirror (a technique that gets a dew point and converts that to relative humidity). The a_w number is the percentage of relative humidity divided by 100.

Knowing the MSI of a product, you can convert moisture content measurements to water activity. Loss-On-Drying results can be converted to water activity for many products. When the Loss-On-Drying process removes only -- and all -- of the water, a conversion of the moisture percentage to a_wcan be made with the MSI for the product.

In my musings and reflections on the science of the gas laws and mystical scientific witchcraft of water activity, I decided that to get you past a superficial understanding of water activity, you need a more expert source.

To get in-depth understanding about the action of water activity and how the measurements are used, I recommend Dr. Ted P. Labuza (tplabuza@umn.edu) at the University of Minnesota. He is an internationally recognized expert on water activity. You can find a bio of Dr Labuza and a link to his publications at this site.

I hope this helped in some way to cultivate an appreciation of the implications of water activity and the relationship of a_w measurement to loss-on drying.

As usual I remain a confounded,

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for e-mail notice by jotting your address in the box just to the right of the title.

Who's Concerned About Sieve Shakers? [del.icio.us]

artgatenby — Fri, 11 Mar 2011 10:28:52 PST

Good summary of sieve shakers issues

Who's Concerned About Sieve Shakers?

Art Gatenby — Fri, 11 Mar 2011 17:33:00 GMT

The primary purpose of a sieve shaker is to provide motion to a sample in a test sieve.

An effective sieve shaker creates a motion that presents all the particles to all of the sieve openings and assists particles in passing through. This requires both rotary and vertical motion.

This process seems simple enough, but let's not be taken in.

Historically, sieve shakers have been very, very loud. Even with ear protection, workers do not want to be in the same room while one of these shakers is performing a sieve test.

How Did This Happen?

Prior to standardization, each lab did sieve tests their own way. Angry disputes erupted between suppliers and their customers about whose method of particle size determination was most accurate. In 1935, a group of engineers and laboratory researchers collaborated on how to standardize a sieve test.

The result was ASTM E-11, which standardized how sieves were manufactured and tested. Here is a summary of the test procedure stated in ASTM E-11.

Hold a test sieve in one hand.
Place a pre-weighed sample in the sieve.
Rotate the sieve with one hand.
Tap the sieve with the other hand.
Weigh the sample that remains.

In other words, rotate the sieve while tapping it. The process requires a certain level of coordination and patience. This is especially true when one considers performing the process for four or five sieve sizes stacked together.

The First Sieve Shaker Solution

This method was an improvement over the various processes used before ASTM E-11. Due to the patience and dexterity needed to perform the procedure, there were still wide variations from test to test.

About that time, W.S. Tyler Industries developed a mechanical device called the RoTap® Sieve Shaker, which reproduced the ASTM-11 Rotational motion while Tapping the sieves with a hammer-like device.

This innovation ushered in many standards related to the oscillation rate and the number of taps per minute. Thus, RoTap® rotation and taps became a de facto standard in many industries. Test procedures and results were compared to this official and/or acknowledged standard.

In meeting ASTM requirements, however, the sieve shaker was like a whirling dervish that made ear-splitting bangs and crashes every second or two. It consequently became necessary to leave the lab or build a large sound-proof enclosure. If you have ever used one of these historic machines, you will recall how it would creep around the room if not bolted down.

Overcoming Sieve Shaker Noise

Over the years, several sieve shaker designs were offered that reduced the mechanical stresses and significantly dropped the noise level. These designs have had to meet the test of producing equivalent results to the RoTap® based standards.

The new designs included advanced mechanical systems that provided up-and-down motion amplitude control and adjustment. Several techniques of varying the rotational aspect of the sieve shaking process have been employed in these designs.

New Sieve Shaker Challenges

As material research progressed, new low-density material developed -- the particles of which tended to swirl above the sieve mesh, rather than becoming exposed to the holes. Some solutions to this problem included periodically letting the particles land on the mesh by interrupting the sieve shaker's vertical motion.

Other products had agglomeration issues, which had to be solved by more violent break-down measures or utilizing wet sieving and shaking techniques. Other new materials require separating smaller and smaller particles, which in turn led to developing equipment that uses ultrasonic sound or vacuum approaches to get the product exposed-to-and-through these smaller sieve openings, at times smaller than 25 microns.

A further and recent complication is the emergence of world-wide quality standards. If a sieving process is used in a system of multi-locations, sieve shakers must be able to duplicate results throughout the system. Similar to matching the results of the oscillating bang-bang machines, these new system sieve shakers must operate quietly and identically regarding how they present the sample to the sieves. This is an additional complication added to on going sieve calibration issues.

It seems like every time I start out to present a simple explanation of something we do, I end up weaving a fabric of complications.

Until the next time I remain as puzzled as always.

Art

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries Part III: Free and Bound Water

Art Gatenby — Tue, 25 Jan 2011 21:18:00 GMT

In my previous missive about Loss-On drying, we discussed Vapor Pressure -- because logically it was next. As we continue to explore moisture, we learn how vital vapor pressure is when regarding the quirky issues of free and bound water.

The easy part of the loss-on drying concept is free [or unbound] water. This is water in or on the surface that will evaporate with a moisture balance.

Things get tricky when we consider bound water, which may be caught in capillaries, fibers or held onto via chemical reactions.

You may recall that when water vapor pressure is at equilibrium, nothing evaporates. When the sample is heated, the vapor pressure rises and the water will begin to evaporate -- which does a neat job of reducing the sample’s weight. This weight stops changing when all of the water is gone, allowing us to determine the amount of water via the attendant weight change.

But wait! All of the water may NOT be gone. Bound moisture -- which, it turns out, has a lower Vapor Pressure than the pure water we just removed -- did not evaporate. A paradox perhaps; we seemingly got rid of all the water but maybe did not because the bound water still remained.

How do we know if there is any of this bound water left? The answer depends upon the test material’s hydro-characteristics. Hygroscopic materials attract water and find ways to bind the moisture while non-hygroscopic [or hydrophobic] materials keep water out of the capillaries, the fibers and the chemical reactions.

Some examples of hygroscopic are biological materials, sugar, and some engineered polymers. Hydrophobic examples are hydrocarbons, fats and lipids.

There are exotic ways to determine if and how much bound water remains. There also are intricate techniques to remove most of this residual.

Before attacking these, a question should be asked: should we care about the presence and amount of bound water?

I need a rest before dealing with these complexities, so I'm deferring further ‘enlightenment’ until another time.

Now we know that my original assumption that Loss-On drying was an easy means toward moisture testing is wrong. It is further complicated by abstruse manifestations such as vapor pressure as well as moisture binding to material via chemical reactions, capillaries and fiber.

Again we find that certain things are not as simple as they might seem.

Until next time I am a bewildered,

Art

P. S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for e-mail notice by jotting your address in the box just to the right of the title.

How Does Surface Tension Relate to Viscosity?

Art Gatenby — Tue, 18 Jan 2011 02:58:00 GMT

You may recall that I promised to offer my interpretation as to how Surface Tension is related to Viscosity.

To begin with, liquid surface tension and viscosity share a common trait: they both involve properties of fluids. After that, things start to get murky.

Let us start with surface tension. This relates to the property of a liquid’s surface that resists force; it serves as a barrier to foreign materials as well as keeping the liquid together. This ever-present property is caused by unbalanced forces on surface molecules that pull toward the main part of the liquid.

Viscosity, on the other hand, is related to a liquid’s resistance to being deformed or moved. This is caused by the friction between molecules.

Compared to viscosity, surface tension is a simpler phenomenon. It is basically stable, changed mostly by temperature and chemicals that modify the bonding characteristics of the molecules. As temperature decreases, surface tension increases. The effects of adding an unrelated substance is illustrated by the example of putting soap (a surfactant) in water to reduce the surface tension, which allows the dirt on your hands to more easily mix with the water.

Regarding viscosity, knowing the type of liquid is essential. For example, there are Newtonian fluids that react to forces (sometimes called shear rate) that move the liquid (sometimes called shear stress) in a straight-forward, linear manner.

However, non-Newtonian fluids follow different sets of rules. Shear-thinning fluids decrease in viscosity as the pressure or force increases. Thixotropic fluids change viscosity over time -- Example gels and colloids, and yes ketchup are stable at rest, but become fluid when agitated.

Thus we see that finding the true value of viscosity [which some of us may think of as simply thickness] is a complex process. Viscosity, unlike surface tension [which tends to be a static phenomenon], is all about movement. All that should concern us in regard to measuring surface tension is whether to use a Wilhelmy Plate or a duNouy Ring. (That is enough to keep me entertained.)

The last question, which perhaps should have been the first, is about the correlation between surface tension and viscosity. You would think that thick fluids would translate to a high surface tension and that thin fluids would produce lower surface tension. Not true. In fact, my research has shown that there is no conclusive correlation.

This got into a lot more theoretical entanglement than I expected when I first considered taking on what seemed like a simple comparison. The answer, however, is clear: no correlation. The reasons are not so simple. I guess a good summary would be that surface tension is about steady state and viscosity is about movement.

Until next time, I remain as confused as ever.

Art

Over-Stocked Sieves: Complexity or Incompetence? - Mixx : science [del.icio.us]

artgatenby — Mon, 13 Dec 2010 09:58:26 PST

Over-Stocked Sieves: Complexity or Incompetence?

Art Gatenby — Mon, 13 Dec 2010 17:13:00 GMT

As CSC approaches another year-end inventory review, our Accountants ready their annual question: “How long has this item been on the shelf?” If the answer is more than few days, they then scream “ANOTHER OVER-STOCK?” in a tone that would intimidate Attila the Hun and which carries a strong implication of our incompetence.

As most of you know, we provide test sieves to organizations that do particle size analysis. We work hard to provide good turnaround for our sieve customers. That means maintaining substantial inventory.

When challenged with the “Another Over-Stock” protestation, I usually have a creative or point-the-finger explanation: marketing screwed up, needed large quantities for lower prices, got a bunch so we could hedge foreign currency, the customer’s new product was a dud, our email broke and the like.

However, when it comes to sieves, I always have a scientific answer --- the phenomenal number of discrete items needed to meet our service objectives is massive. Here are the facts:

There are seven frame diameters, two material types, two standards and three quality levels. That leads to a minimum of 168 variations for each mesh size -- of which there are 43 listed by ASTM. That is a minimum of 7,224 combinations. I say a minimum, because between ISO and DIN there are an additional 24 mesh sizes. Furthermore, some customers use wet-wash frames, electroformed mesh and perforated plate.

With all of that, we are still not off the hook. After querulously listening to my story, the accountants' typical response is “GET THEM OUT OF HERE.”

Guess what -- just like your favorite department store -- we are having our first Sieve Over-Stock Sale.

If you use sieves, you might find a budget helper at our sale. If you are not a sieve user, I hope this provided a little amusement and an interesting insight into the business of supplying test sieves.

Thanks for visiting.

Art

P.S. Help me get the Accountants out of my life. Buy a sieve or two. Thanks !!!

Loss On Drying Moisture Analysis and Other Moisture Mysteries - II [del.icio.us]

artgatenby — Wed, 24 Nov 2010 14:02:02 PST

Sequel to Moisture Mystery Evaporation

Loss On Drying Moisture Analysis and Other Moisture Mysteries II Vapor Pressure

Art Gatenby — Mon, 22 Nov 2010 22:55:00 GMT

A while ago on these pages I agonized about loss-on-drying moisture analysis . As you may recall, my explorations of the drying process overwhelmed me with evaporation concepts , vapor pressure notions, water content complexities and water activity witchcraft, all just to dry something.

I started by weighing-in with a shot at interpreting evaporation, while hinting that I'd take on the other principles that effect loss-on-drying moisture tests at some point in the future.

I've decided to have a go at vapor pressure. Why vapor pressure now --- because it's next on the list.

I guess as good a place to start as any, is with a definition:

Vapor Pressure is the Equilibrium Pressure of a vapor above its liquid or the pressure of the vapor resulting from evaporation of a liquid above the sample.

To refresh the image , from the past musing on Moisture Mysteries, of evaporation, molecules bounce out of a liquid into a gas. When the evaporation settles down rather than flying off into the vapor, the molecules above the liquid in the vapor or gas ,continuously exchange places with the molecules at the surface of the liquid, the liquid and vapor are in equilibrium. That is when you have Equilibrium – Vapor Pressure.

This vapor pressure is a unique characteristic of a pure liquid. The molecular bonding of the pure liquid defines its unique vapor pressure.

Weak bonding high vapor pressure
Strong bonding low vapor pressure

To see how it works you have to look at the dynamics. Dynamics have always complicated my life.

For any pure liquid, dynamics fortunately are only related to temperature. We stated that each pure liquid has a unique vapor pressure, but that value changes with temperature. Unique but changing – can that be? Yes because a unique vapor pressure is defined at a each temperature. It goes up as the temperature rises and goes down as the temperature declines.

Fortunately for our understanding, the surface area of a liquid has zero effect on Vapor Pressure. I'm not 100% sure why I even mention this except that if this was not a constant, it would confuse the energy issues related to getting evaporation, which is why we started this whole rant.

Because we are rambling about moisture, the liquid we refer to will be water.

To generate evaporation and get the water out , which we need to do when we conduct Loss On Drying Tests, energy needs to be added to the test sample. The energy is some form of heat which increases the Vapor Pressure, the molecules start bouncing around and move from the liquid state to gas. With loss-on-drying moisture test equipment, the gas or water vapor is moved away from the sample so that the water vapor has no chance to get back to the water surface and start an equilibrium exchange with the water.

That's how Vapor Pressure relates to a loss-on-drying moisture test.

I'm not sure but, in future ramblings, I might take on water content complexities, water activity witchcraft and just plain drying. Should I?

I hope this expose/rant was somewhat interesting and useful. I welcome your comments. Thanks for reading it.

As usual a perplexed,

Art

P.S. Did you know that you can subscribe to these exposes, rants, raves and ramblings. All you have to do is click on the RSS Feed symbol at the upper left and you'll get a notice when a new one is published. Or if you prefer, you can also subscribe for Email notice by jotting your address in the box just to the right of the title.

Surface Tension Testing of high viscosity samples [del.icio.us]

artgatenby — Mon, 15 Nov 2010 13:20:58 PST

Article on Surface Tension Testing

Having Trouble Performing a duNouy Ring Test in Thick Samples?

Art Gatenby — Mon, 15 Nov 2010 20:29:00 GMT

My musings were interrupted this week with a pressing challenge. It was stated like this:

“My duNouy ring kept falling off the arm hook when attempting to immerse it into a high-viscosity sample.”

This is the first time any of us at CSC Scientific recall being presented with such a dilemma. This client was using a single arm tensiometer to do surface tension measurements

The ring, on a single-arm tensiometer is attached by putting the top through a hook as shown in the photo. It is clear that when dealing with a high-viscosity sample, you would have to push the ring through it with your finger -- a somewhat cumbersome process.

This problem is solved with our interfacial tensiometer, in which the ring is affixed to the stationary vertical arm by way of a rigid joint. Thus, when the ring is inserted into the sample, the vertical arm pushes it down, breaking the surface.

Given this, from now on we will recommend only the interfacial model for high-viscosity samples.

In the course of developing a solution to this problem, I delved into the relationships of surface tension and viscosity. My next discourse on surface tension will attempt to interpret these relationships.

Let us know of your experiences with duNouy ring tests on high viscosity samples.

As always a totally perplexed,

Art

Is Particle-Size Analysis Boring? Trivial? Amazing? Exciting? Vital?

Art Gatenby — Tue, 02 Nov 2010 19:57:00 GMT

When I tell people at cocktail parties that we specialize in Particle-Size Analysis. I usually get a polite response of ------ “OH !!,” which translates to “So who cares?”

I have finally decided to answer that question.

Well, it seems that most companies that perform milling or grinding have a vital interest in the size and distribution of the resulting particles. These include companies in the fields of Pharmaceuticals, Chemicals, Mining, Building Materials, Food Processing to name a few.

Soooo.... there really is a significant need for particle-size analysis.

How is this accomplished? The most economical and easiest method is to utilize a series of sieves, with each one having different sized holes from the others. The product is sifted through these sieves and the amount that passed through each size hole is then measured. Such methods have been used since ancient Egyptian farmers sorted their grain this way. Today however, there is a growing number of materials; many with unique characteristics -- that inhibit particle separation. Furthermore, there is an accelerating trend toward smaller and even nano particles.

Standard test sieves, which are made of woven wire mesh, can work to sizes down to the 25 micron range -- smaller than a human hair. As wire mesh sieves reach their limits, sieve mesh made with the Electroforming Process may be needed. (Electroforming is a process for fabricating high-precision mesh by electro-deposition in a plating bath.

Some powder materials and small particles are difficult to separate. In these cases, particle-size distribution analysis calls for sophisticated shaking or separation methods such as ultrasonic vibrating or vacuum sieving.

After the capabilities of mechanical sieving have been exhausted, one of the new measuring methods available is Particle Sizing by Laser Diffraction. In a recent article, Bryn McDonagh of ATA Scientific did a magnificent job of describing this highly complex technique.

“Laser diffraction has become one of the most commonly used particle sizing methods, especially for particles in the range of 0.5 to 1000 microns. It works on the principle that when a beam of light (a laser) is scattered by a group of particles, the angle of light scattering is inversely proportional to particle size (i.e. the smaller the particle size, the larger the angle of light scattering). Laser diffraction has become very popular because it can be applied to many different sample types, including dry powders, suspensions, emulsions and even aerosols. It is also a very fast, reliable and reproducible technique and can measure over a very wide size range.”

Laser diffraction is often the method-of-choice when particles are very small or hard to separate mechanically.

If the test material can be separated mechanically and the particles are within the size ranges of wire or electroformed mesh, sieving provides the most economical approach by a wide margin. Sieve testing is easy to administer and requires little training.

Bottom line: If sieving will work, use it. Otherwise, you need to consider more elaborate processes such as Laser Diffraction.

Now that I have prepared this discourse, perhaps I can get more people at cocktail parties excited about Particle Size Analysis.

Thanks for listening,

Art

P.S. How do you do your particle size analysis?

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries I

Art Gatenby — Mon, 25 Oct 2010 19:52:00 GMT

One quiet night, I was musing over moisture analysis and how easy it is to do using loss-on drying. Little did I know what was in store.

Of course, everybody knows that all you do is 1. weigh a sample, 2. dry it out and then 3. weigh it again. However, I decided that a modicum of research about drying would be prudent before I started. As I got into it, this small inquiry into moisture testing expanded into a lot more about evaporation, vapor pressure, water content complexities -- and the spookiest of the bunch, water activity -- all just to determine the effects of drying something.

Do I talk about it all at once or break it into individual mysteries? I found the former approach overwhelming, but with respect to the latter --- Where to start?

After brooding for a while, I concluded that evaporation was important to the loss-on drying process; simple in concept and easy to understand. Consequently, I start with evaporation because it is elementary -- if you don't consider the influence of vapor pressure, atmospheric pressure, temperate and humidity.

It seems that evaporation is all about water molecules bumping into each other. If they are highly agitated by an energy source, they fly away from their neighbors and transform a closely packed liquid into a loosely packed gas or vapor. At various times, the flow balances; some switch to vapor, some switch back to liquid (or as we know it, water). Changing the ambient pressure, temperature or humidity changes this balance, requiring more or less energy to affect the evaporation volume.

When things settle into equilibrium, the gas molecules sit at the liquid surface and exchange positions with the liquid molecules. At this gas-liquid boundary, vapor pressure increases with heat and decreases if cooled. The more the vapor pressure, the more flying gas molecules are generated, thus resulting in more evaporation.

The energy, usually heat, gets the highly agitated molecules to fly out of the liquid. These hot ones leave behind the cooler ones, cooling the liquid. This is how perspiration evaporating from your brow cools you on a hot, dry summer day.

All of these influence loss-on drying tests. I thought it was “just turn on the heat and wait;” -- No considerations of bouncing molecules, summer or winter, clear or stormy weather to confuse and change evaporation.

Now we know some of the reasons that loss-on drying tests sometimes take longer or shorter than normal periods.

Maybe, someday I'll get the courage to take on vapor pressure, water content, drying and even water activity. Look for it.

Thanks for reading this rant, hope it was amusing and maybe helpful.

As always, a mystified,

Art

P.S. I'd very much like to hear your comments. Is this fun, interesting or informative?

CSC Scientific Introduces Automatic Tensiometers -- Now Computer Controlled Surface Tension Measurements For Liquids and Powders [del.icio.us]

artgatenby — Fri, 24 Sep 2010 09:32:37 PDT

CSC Scientific Company, a manufacturer and distributor of surface tension measurement products, introduces a new product line of fully Automatic Tensiometers that greatly expand the scope of its surface energy analysis domain. These tensiometers are computer controlled. This makes complex testing simple. This product line expands the Company's testing capability to include analysis of dynamic surface tension and contact angle, liquid density and lamella length. It's capabilities also include the measurement of powder wettability, powder contact angle and true powder density.

Surface Tension by duNouy Rings or Wilhelmy Plates – Which to Choose? [del.icio.us]

artgatenby — Fri, 20 Aug 2010 12:51:04 PDT

A discussion of the pros and cons of the duNouy Ring and the Wilhelmy Plate methods of surface tension measurement..

Surface Tension by duNouy Rings or Wilhelmy Plates – Which to Choose?

Art Gatenby — Thu, 19 Aug 2010 21:16:00 GMT

When tempted to think I know all there is about surface tension measurement, further information brings me back to earth. I’m conversant with the principal applications: surfactant analysis, plating, detecting contaminants, development of ink and the like. I have assisted customers to set up and calibrate duNouy Ring tensiometers for most applications -- all the while taking for granted that the Ring technique was the method of choice -- with only infrequent questions arising about Wilhelmy Plate tensiometers.

My lack of concern had a least some justification. The duNouy method has been around for more than 50 years -- twice as long as the Wilhelmy -- and is the most widely used technique. Several ASTM standards call for it.

There are more Ring-style instruments used worldwide than any other type.

CSC Scientific is readying plans to introduce an automatic tensiometer, the manufacturer of which is a strong proponent of the Wilhelmy Plate method. Prudence therefore dictates gaining an education on this technique -- which I'm sharing with you here.

The two tensiometer methods differ in that the duNouy Ring is pulled though the surface to make the measurement, while the Wilhelmy Plate is stationary.

Using the Ring technique, causes a non-equilibrium state in the liquid as the ring is pulled through the surface.

The Wilhelmy Plate, by contrast, is placed at the liquid’s surface and a meniscus is formed on its perimeter, causing a downward pull. The Plate is not in motion thus the entire surface is in equilibrium. The force is constant or varies only with a change in surface tension.

There are other noteworthy differences regarding applicability of these tensiometer methods.

Measuring surface tension variations over time, (such as measuring time and end-point surface tension for formation of Critical Micelle Concentration of a surfactant) can be made with the Wilhelmy Plate, but not the duNouy Ring. Because high-viscosity liquids cause larger stress on the somewhat fragile ring, the Wilhelmy technique is preferred for these applications.

The Ring method is easier to use on a manual instrument. Although it tends to yield higher surface tension readings, there is a significant body of historical data for the duNouy technique.

Automatic tensiometer evolution has made Wilhelmy Plate use easy. These instruments also adapt to the duNouy technique. The automated techniques permit the easy evaluation of the two methods on the same sample, facilitating comparisons of test resuls.

Watch for the announcement of the New Automatic Tensiometer.

Hopefully this short story about duNouy Rings and Wilhelmy Plates has been somewhat informative and helpful.

Until the next time.

Warmest regards,

Art

P.S. If you'd like to discuss your application, call me at 703-876-4030.

Certify Sieves or Calibrate Sieves --- Should You Do It?

Art Gatenby — Wed, 30 Jun 2010 20:57:00 GMT

The relative value of a sieve certification process vs a sieve calibration has perplexed me for a long time.

Eventually it dawned on me that the entire certification process is an insurance policy of sorts. Firstly, it confirms that the mesh is within the ASTM or ISO spec -- even though the spec allows for significant variation. Secondly, it meets the traceability demands of ISO mandates.

However, the inspection reports only minimally predict a sieve's performance. I recall a situation in which a customer with a high-powered QC program had trouble matching the performance of a new shipment of mid-point sieves. [Mid-point sieves must conform to a much tighter tolerance than the standard spec.] After an exhaustive investigation, the old batch of sieves was determined to be at the low end of the spec while the new ones were at the high end. The mid-point certification reports did not indicate this discrepancy.

The customer then used a procedure that compared the performance between the two batches. That process finally pinpointed the problem. This is what I think calibration is all about -- ensuring predictable performance in an operating environment.

Calibration techniques vary from comparing a sieve result with a master set of sieves (Master Stack) to comparing result with a known sample (Master Sample). Both of these techniques are application-specific.

Another approach to calibration involves utilizing calibration spheres or beads, which compares a specific sieve's performance to a traceable high-precision standard. It provides a result as a single specific quantitative measure of the expected sieve performance. The result is a mean sieve opening size.

Given that the high-precision beads are traceable to an ISO-recognized standard, this calibration method serves the insurance purpose of meeting ISO or internal company QC audit demands. Unlike the certification report, a calibration using this technique also yields a single performance indicator. In most circumstances, using the calibration bead method eliminates the need to use Master Stacks or Master Samples.

Whitehouse Scientific has a process that provides a sieve calibration that results in a mean sieve size to approximately +/- one micron. It took them approximately three years to develop their traceable calibration process. For more on this see Sieve Calibration

I hope this rant stimulates some questions and discussion.

Thanks for reading this.

A still perplexed,

art

View from Inside a Karl Fischer Titration Cell. [del.icio.us]

artgatenby — Tue, 18 May 2010 15:26:57 PDT

How a moisture test look from inside a titration cell

View from Inside a Karl Fischer Titration Cell.

Art Gatenby — Mon, 17 May 2010 20:26:00 GMT

When people are looking for a way to measure small amounts of moisture, we often recommend the Karl Fischer method.

The first question many ask is

"What is Karl Fischer?"

The second question usually is

"How does it work?"

I thought it might be interesting to answer the second question from the perspective of actually being inside the Karl Fischer Titration Cell.

First, I climbed into a jar that has four openings at the top.

Through one of the openings, an operator pushed a glass tube with a funny kind of mesh at the bottom. They call this the Generator.

Next, through another opening, they push a second glass tube that has wires sticking out of the bottom. They call this the Detector.

Sitting at the bottom of this jar is a little rod, which they call the Stirrer.

Comfortably sitting on the stirrer rod at the bottom of the jar, I observe an operator pouring a liquid into the top of the generator above the funny mesh.

Then, they tell me to be ready to swim as they fill the main part of the jar about halfway with another liquid they refer to as the Reagent. As I'm treading water in this reagent, they seal off all the openings so they are air-tight.

They yell down that they are going to start clearing out all of the moisture from inside the jar. The stirrer bar starts spinning, causing chaos in the reagent. I feel like I am in a Waring Blender.

As I'm bouncing around the jar -- or as the operators call it the Titration Cell -- they tell me to be ready for a little shock. They turn on the machine and the detector says, "Hey! There is water in here. Push some electric current into the cell." Zap Zap Zap.......

The maelstrom starts to turn yellow. What is this? It is a whole bunch of Iodine; the very same substance you used to put on a cut finger.

They tell me that the shock I felt caused the Reagent to produce the Iodine. Apparently, the Iodine reacts with the water and gets rid of it.

By that time, the detector says, "Water's All Gone" and they turn off the stirrer. I'm almost drowned.

An operator yells down, "Here comes a real test!" The dammed stirrer starts and I'm in the blender again.

Now I see the business end of a syringe - the needle. The syringe pushes the sample to be tested into this chaotic whirlpool in the cell and the shocks start again. Zap Zap Zap... The detector found water.

I'm racked with shocks for a minute or two and the yellow returns. The Iodine does its job and the detector says, "No More Water."

The shocks stop. The test is over. The operators shut down the stirrer and pull me out --- totally waterlogged. Or should I say reagent-logged?

The machine measured the amount of shock it took to generate enough Iodine to get rid of the water. All of this was done just to measure a few micrograms of water.

I hope you found this amusing and maybe a little informative.

By the way, I am never going inside a Karl Fischer Titration Cell again.

A very soggy Art

CSC Scientific Blog [del.icio.us]

artgatenby — Wed, 21 Apr 2010 11:57:39 PDT

Problem, issues and maybe some fun about test equipment

Solving Static Problems in Sieve testing [del.icio.us]

artgatenby — Wed, 21 Apr 2010 11:52:52 PDT

Static Electricity and Sieves: No Problem -- Maybe

Art Gatenby — Wed, 21 Apr 2010 18:02:00 GMT

I'll bet that most of you have experienced the shock of walking on a thick wool rug on a dry winter's day and getting zapped out of your reverie when reaching for the metal door knob.

The same process of static electricity generation can play havoc with your sieving process.

"Static electricity" (also called charge separation) occurs whenever four conditions exist:

1. Humidity is fairly low
2. Two surfaces are touched together, then separated
3. The surfaces are made of two different materials
4. Both surfaces are electrically insulating

For many products -- particularly hydrocarbon-based materials, plastics, reactive metals, paint pigments and powders with a large fraction of fines -- the sieve action provides a fertile environment for charges to build up on the particles and sieve components. This causes clinging, agglomeration and blinding. In other words, as material bumps and bounces around in the sieve stack, they generate that same type of electrical charge that zapped you last winter.

So what to do?

There is a sure, but messy (and a pain-in-the-butt) solution.

Wet Sieving

In wet-sieving, the separation of fines from the coarse portion of a sample is done while it is suspended in an aqueous solution introduced to each test sieve.

The liquid is used to negate static charges, break down agglomerates and lubricate near-size particles.

After the fines have been washed through the sieve, the residue is oven-dried and re-weighed.

---- Difficult, but effective.

Anything Easier?

A material that makes the particles slippery can be added to the sample, such as silica, activated charcoal, talc, magnesium carbonate, tricalcium phosphate or silicon dioxide.

If you make the optimal selection, the sample stops being an electrical generating plant as well as an agglomerator. It goes through the sieves and gets the desired result.

The problem is, you have to know the additive's size and adjust your results by the amount of this material that is retained.

----- This is another fix but it is still a pain.

A simple approach that might work.

Perhaps strips of anti-static sheeting , such as those used in your clothes dryer will work. This is as easy as putting a few strips in at least the small mesh sieves.

If this is effective, it is the simplest solution we know.

Static Electricity and Sieves

Yet again -- one of Nature's ways to make a simple process difficult.

Please let me know if you've found any other effective solutions to a static problem in your sieve testing.

Thanks,

Art

Is My Test Equipment Lying?

Art Gatenby — Tue, 09 Mar 2010 21:45:00 GMT

I keep running into this kind of thing.

There is a recurring question we are asked as instrument manufacturers:

"Is my equipment working OK?"

This is of particular concern when a production process seems to be off standard.

QC says: "Clearly Process Problems"

Production says: "Bad Test Results"

These challenges arise often.

What to do?

Must we call in our outside certifier, send it to the manufacturer for calibration and/or run it on a known standard? What else can resolve this issue? Most of the solutions can take hours if not days to obtain. With a measure of analysis, equipment know-how -- and a bit of diplomacy -- the dilemma can be resolved on-the-spot.

The first option is a quick test to determine if the equipment is working properly, which answers the questions:

Is the Instrument Lying ?
Is QC right or is Production right?

Another major annoyance is when results don't seem to match between instruments of the same type. The initial conclusion is that all but one is lying, but which one?

Run the quick test to determine if each instrument is working properly. If a problem is found in one or more, the answer is fairly clear.

If all instruments pass the quick test, we are then confronted with a mystery that impels further investigation:

Are the testing environments different?
Are the product samples identical?
Are the test parameters the same?
Can the differences be duplicated with different operators?

If answering these questions do not resolve the mystery, it is clear that we are being lied to by one or more of the instruments. However, we must keep looking for some outside influence. ---- Need we find someone who can perform magic?

Yet another challenge arises when multiple labs are convinced that a test instrument is lying about given results. This can happen when the Corporate R&D people, a new outside lab or new QC staff determine that an industry standard test will be needed for samples. Frequently, this test will be off-site or the results will take hours if not days to obtain.

This is a major quandary.

We are faced with issues that require careful analysis of testing method differences, product sample reaction to these different methods, environmental differences between test locations and strongly biased opinions. Finding rational answers to the "Is my instrument lying?" question is tough. A bit of luck is always welcome.

I would like to hear of your experiences with Lying Test Equipment and how you solved these problems. Comment about that here or email me at artgatenby@cscscientific.com.

I will share these experiences in future rants.

Art

P.S. These kinds of things happen for Moisture, Particle Size and Surface Tension instruments. No area of measurement escapes the question: Is My Instrument Lying to Me?

CSC Scientific Blog

Is Sieve Calibration Really the Holy Grail? Part II

Is Sieve Calibration Really the Holy Grail? Part II: Inside a Sieve Test

Which Type of Tensiometer do I Need?

Who Beats Up Your Bostwick?

Is Sieve Calibration Really the Holy Grail? -- Part I: Certification

Why Do I Get Inconsistent Moisture Test Results?

Why Calibrate a CSC DuNouy Tensiometer?

Karl Fischer Moisture – Answers to Questions We Get Asked

Sieves – Old and New QC Issues

Loss-on Drying and Other Moisture Mysteries - Part V: Drying

Just over six months ago, I began this journey explaining the simplest approach to measuring or determining moisture: Loss-on Drying. Little did I know how involved and esoteric it would become.

As is often the case, reality makes “easy” a non-operative word. Such has turned out to be so with respect to the issue of drying.

Firstly, there is the initial and underlying issue of product classification. Here are some examples:

Non-hygroscopic Capillary Porous Solids: These are materials such as sand, crushed minerals, certain crystals, polymer particles and some ceramics. They have recognizable pore space filled with liquid, little bound moisture and do not shrink on drying.

Hygroscopic Porous Solids: Clay, molecular sieves, wood, textiles, silica gels, alumina and zeolites are examples. They are characterized by clearly seen pore space, physically bound moisture and shrinkage in the early stages of drying.

Colloidal (non Porous) Solids: Examples include soap, glue, polymers like nylon and various food products. There is no pore space and all moisture -- except that on the surface -- is physically bound.

There are other less-common classifications and combinations as well.

One of the more difficult issues is to get at is the bound water. Among other techniques to deal with this is freeze-drying. Additionally, there are mechanical methods of removing moisture [e.g. centrifuging] that are referred to as dewatering rather than drying.

The Loss-on Drying moisture measurement process involves all issues and considerations concerned with production drying. People regularly ask us, “at what temperature should we run the test and for how long?” This discussion of drying should help them understand why we reply “It depends”.

I hope this “Loss-on Drying and Other Moisture Mysteries” series has been interesting and useful. Also I hope it was fun.

Now that I have finished Part V, the last in the series, I remain more astonished than ever with the mysteries of the test equipment world.

Thanks for visiting.

Art

Why Not A Bostwick Consistometer Calibration Standard?

Customers want Bostwick Consistometer Calibrations.

When told that CSC Scientific does not calibrate Bostwick Consistometers, people ask . “Then how can I calibrate my consistometer and where can I get a calibration standard?”.

We recommend sampling the selected product to be measured using the Bostwick Consistometer. The sample should represent your product in its ideal state. The temperature should be carefully recorded and a test run. The time it takes to get about half way down the trough should then be recorded.

A similar procedure should be followed for each of your products tested with the Bostwick Consistometer. The standards thus should be recorded in a QC results chart and stored as reference for ISO or similar quality control inspections.

This table shows typical standards and acceptable limits for three hypothetical products:

Marbleized A

Syrup C

Mission 5

Product Temperature

30°C

42° C

50°C

Distance Standard

16

17.5

15

Time Standard

85 Seconds

58 Seconds

42 Seconds

Allowable + Time

81 Seconds

62 Seconds

46 Seconds

Allowable - Time

89 Seconds

55 Seconds

40 Seconds

The critical issue in consistent and repeatable CSC Bostwick Consistometer operation is in the set-up. Leveling the trough is the principal requirement for getting repeatable results on a sample at a fixed temperature.

Establishing and recording Bostwick results on the perfect or quality control standard product is the only practical way to develop a calibration. This should be done with the user’s product at the testing site.

Sorry to have to carry this message. You have to do your own calibration for each of your products.

I hope this was helpful to you.

As always a perplexed,

Art

Surface Tension – Tensiometer Update

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries Part IV: Water Activity [del.icio.us]

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries Part IV: Water Activity

Who's Concerned About Sieve Shakers? [del.icio.us]

Who's Concerned About Sieve Shakers?

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries Part III: Free and Bound Water

How Does Surface Tension Relate to Viscosity?

Over-Stocked Sieves: Complexity or Incompetence? - Mixx : science [del.icio.us]

Over-Stocked Sieves: Complexity or Incompetence?

Loss On Drying Moisture Analysis and Other Moisture Mysteries - II [del.icio.us]

Loss On Drying Moisture Analysis and Other Moisture Mysteries II Vapor Pressure

Surface Tension Testing of high viscosity samples [del.icio.us]

Having Trouble Performing a duNouy Ring Test in Thick Samples?

Is Particle-Size Analysis Boring? Trivial? Amazing? Exciting? Vital?

Loss-On-Drying Moisture Analysis and Other Moisture Mysteries I

CSC Scientific Introduces Automatic Tensiometers -- Now Computer Controlled Surface Tension Measurements For Liquids and Powders [del.icio.us]

Surface Tension by duNouy Rings or Wilhelmy Plates – Which to Choose? [del.icio.us]

Surface Tension by duNouy Rings or Wilhelmy Plates – Which to Choose?

Certify Sieves or Calibrate Sieves --- Should You Do It?

View from Inside a Karl Fischer Titration Cell. [del.icio.us]

View from Inside a Karl Fischer Titration Cell.