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VISCOSITY FORUM: Ask the experts

How do you test construction materials for

Measuring Viscosity? Kinematic or Dynamic Method. How to Choose?

11/21/13 at 11am EST

An Interview With Pat Maggi

Capillary and rotational viscometers are used around the world to measure viscosity. Why are there two different methods? Does each have certain advantages that recommend its use for certain categories of materials? This interview will review various test methods that encompass one or the other technique and provide guidance on how best to proceed when in doubt on the choice. read more

How do you test construction materials for

How do you test construction materials for "flowability"?

11/6/13 at 11am EST

Dr. Guy Rosenthal Interview

How do you test construction materials for "flowability"? For example, when you open a tub of joint compound, does it have the right consistency? Do you know right away when you stick your trowel in? Or is the proof of the pudding in how it spreads? read more

Life Below the Yield

Viscometer vs. Texture Analyzer

10/23/12

An Interview with Ross Clark

When does a viscometer make sense and when does a texture analyzer make sense? read more

 

BROOKFIELD RESPONDS: Q+A

07/2015

CUSTOMER CHALLENGE: Please, can you direct me to an equation to convert % torque (also known as Brookfield Units or BkU to my colleagues) to cP. For example, when measuring a 5000 cp viscosity oil (25.0°C), at 5 rpm with an RV # 4 spindle, using 1/2RV analog viscometer, how does one verify the total allowable error for this oil? This same oil analyzed on a DV2TRH viscometer gives an allowable error of 5000 cP +/- 250 cP. For the analog viscometer, should we think of allowable error in terms of +/- % Torque?

BROOKFIELD ANSWERS:

Yes, you have the right idea. Allowable error or accuracy for a standard Brookfield Viscometer is always +/- 1%, no matter where you are on the torque scale. If you know the maximum viscosity in cP that you can measure at 100% torque (also called Full Scale Range viscosity), then the allowable error or accuracy for any measurement with that specific spindle/speed combination is always 1% of that number.

The formula is FSR Viscosity = TK * SMC * 10,000/RPM

TK is the torque constant. See Operator Manual Appendix: Spindle and Model Codes

SMC is the Spindle Multiplier Constant. See Operator Manual Appendix: Spindle and Model Codes

RPM is the rotational speed.

An easier approach is to push the “Autorange” button on the face of the instrument and that automatically displays the FSR Viscosity value for the spindle and speed that you have entered.

05/2015

Customer Challenge: My new instrument came with several spindles. Most of them have discs on the bottom of the shaft. What is the difference between using a standard disc spindle to measure viscosity and a different type of spindle? Did I make the right choice?

BROOKFIELD ANSWERS:

The so-called disc-type spindles have become known around the world as Brookfield spindles. These were the initial spindles invented at the same time as the Brookfield Viscometer in the 1930s. When you buy a standard rotational viscometer, it will come with a set of spindles, some of which have discs at the bottom.

There are several spindles so that you can measure different viscosity ranges. The larger the disc, the lower the viscosity value it can measure. The smaller the disc, the higher the viscosity value it can measure.

There may be other spindles that look like cylinders. The same principle applies. The larger cylindrical spindle is used to measure low viscosity liquids. The smaller one is used to measure high viscosity liquids.

Look at the Brookfield publication called More Solutions To Sticky Problems for more complete information on the different types of spindles that you can use to measure viscosity.

03/2015

Customer Challenge: My Company just discovered that our viscometer with RV torque is out of calibration. We checked it with a 5000 CPS viscosity standard (rated 4750 cP @ 25°C) using the 27 spindle in Small Sample Adapter at 20 rpm. Our measured viscosity reading is 5475 cP. We are out of calibration by 450 cP. Can we correct our QC viscosity data since the last time we performed a cal check? Do we lower the measured values by 450 cP? Do we need to have our viscometer serviced?

BROOKFIELD ANSWERS:

No, you should not adjust your QC viscosity data. You don’t know exactly when the viscometer went out of calibration. You may want to consider running a cal check more frequently. If you notice that the QC tests on your material are trending higher, you should run a cal check on the viscometer to find out whether your product is changing or the instrument is reading incorrectly.

Return your viscometer to the nearest authorizedBrookfieldServiceCenter. You can usually get a loan instrument if needed while your viscometer is being serviced. The turnaround time is only a few days and the cost is small compared to the problems that might be caused by shipping product that is out of specification. You will also receive a new Certificate of Calibration for your viscometer.

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VISCOSITY OF WATER TABLE

View the viscosity of water at temperatures between 0 - 100° C.

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VISCOSITY OF MATERIALS TABLE

Instant view of some dynamic viscosities of Newtonian fluids.

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VISCOSITY CALCULATOR

The cup to viscosity conversion engine assumes fluid is Newtonian.

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YIELD STRESS VALUES

Examples of values for typical food and personal care products

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