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Viscosity help
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TOPIC: Viscosity help

Viscosity help 1 year, 3 months ago #2205

A potential user of my dies has asked for die that would be good for an enamel viscosity of 470 to 570 mpa.s. (27C)

I assume this means at 27 centigrade temp.

Would anyone know how this translates to solids content?

Re: Viscosity help 1 year, 3 months ago #2206


There are a couple of very qualified magnet wire engineers that regularly review messages here and I hope one of them will be able to answer your question.


Yes 27C is Celsius or Centigrade and this equals 80.6 Fahrenheit.


In the meantime, are you familiar with this ASTM specification?

ASTM D3288 / D3288M - 08 Standard Test Methods for Magnet-Wire Enamels


Please note the following copied from from the Physics Hypertextbook

The SI unit of viscosity is the pascal second [Pa·s], which has no special name. Despite its self-proclaimed title as an international system, the International System of Units has had very little international impact on viscosity. The pascal second is rarely used in scientific and technical publications today. The most common unit of viscosity is the dyne second per square centimeter [dyne·s/cm2], which is given the name poise [P] after the French physiologist Jean Louis Poiseuille (1799-1869). Ten poise equal one pascal second [Pa·s] making the centipoise [cP] and millipascal second [mPa·s] identical.

1 pascal second = 10 poise = 1,000 millipascal second (mPa.s)
1 centipoise = 1 millipascal second (mPa.s)

There are actually two quantities that are called viscosity. The quantity defined above is sometimes called dynamic viscosity, absolute viscosity, or simple viscosity to distinguish it from the other quantity, but is usually just called viscosity. The other quantity called kinematic viscosity.


Kinematic viscosity is represented by the symbol ν "nu" and is the ratio of the viscosity of a fluid to its density.

The SI unit of kinematic viscosity is the square meter per second [m2/s], which has no special name. This unit is so large that it is rarely used. A more common unit of kinematic viscosity is the square centimeter per second [cm2/s], which is given the name stokes [St]. Even this unit is also a bit too large and so the most common unit is probably the square millimeter per second [mm2/s] or centistokes [cSt].

1 m2/s = 10,000 cm2/s [stokes] = 1,000,000 mm2/s [centistokes]
1 cm2/s = 1 stokes
1 mm2/s = 1 centistokes


Finally, there is a dynamic viscosity converter here but this is as far as I can go because I am unaware how to relate the solids content to the dynamic viscosity. I suspect it is by direct measurement as per the ASTM specification above. Possibly you should be asking your potential customer for the solids content information.

Peter J. Stewart-Hay P. Eng.
Stewart-Hay Associates

Re: Viscosity help 1 year, 3 months ago #2207

The question was:

“A potential user of my dies has asked for die that would be good for an enamel viscosity of 470 to 570 mpa.s. (27C) I assume this means at 27 centigrade temp. Would anyone know how this translates to solids content?”

Some thoughts; While temperature does have an effect on viscosity, you want temperature to be stabilized and not vary during the process. Some people have effected this by having a heated storage tank. Refilling the tank has to be done on an ongoing basis or you have to normalize the enamel temperature before you put it in the tank. Some enamel applicators have the heat source closer to the dies (and felt applicators) so that the temperature at the die is controlled.

One of the easiest ways to measure viscosity was with a Zahn cup. A #2 works good for solvent based enamels. They come with a chart that should allow you to understand how the Zahn numbers compare to mPa.s

Solids and viscosity are often mutually exclusive characteristics. Nylon and Formvar for example are high viscosity materials but have very low % solids (10-20%). Think molasses syrup. Some urethane enamels have much lower viscosity but at the same time have much higher % solids. Urethanes evolved from about 20% solids to 45% solids with little change in viscosity.

For dies the viscosity is less critical than for felt applicators. Biggest problems with dies is when wire speed increases and the material is high viscosity, it will cause a split die to weep and even open some. Solid dies or clamped dies compensates for this.

Increasing enamel temperate only 5 degrees F can significantly decrease viscosity. Again if the temperature is not stabilized changing temperatures can affect wire quality, especially with roller dies and felts.

I think the die user should tell you the enamel he is using. With the info provided; viscosity and test temperature, there is no way to translate that to % solids.


Below are a couple of links that might help.


Cup Range Seconds Range Centistoke Sensitivity Midrange Oil Number¹ Calibration Number²

1 40 to 60 10 to 36 1.3 G-10/19
2 20 to 60 19 to 156 3.3 G-60/117

3 12 to 60 64 to 596 10.5 G-200/458
4 10 to 60 79 to 784 13.9 G-200/458

5 10 to 60 161 to 1401 24.2 G-350/878

¹ Stated as centistokes per second of efflux time.
² Centistoke values are nominal - actual values printed on labels

Re: Viscosity help 1 year, 3 months ago #2208

Thanks guys ! The fact that viscosity isn't directly related to solids content is very helpful.
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