Viscosity and Hardness Comparison
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Technical Tip Viscosity and Hardness Viscosity Viscosity is a measure of the internal resistance or friction when a fluid moves against itself. Viscosity can be effected by the chemical structure of the resin, the molecular weight or Epoxy Equivalent Weight (EEW) of the resin or the type and amount of filler added. The lowest viscosity materials are unfilled, short chained and have low EEW. The internal resistance or viscosity is typically measured using a rotating spindle instrument, such as the Brookfield viscometer. The amount of force needed to turn the spindle (torque) is recorded in Poise or centipoise. There are different surface area spindles which are used to measure different ranges of viscosities. The higher the measured torque value, the higher the viscosity. Poise is a measurement of force, 1.0 Poise (P) equals 0.10 Newton-seconds/meter 2 . Low viscosity materials are commonly expressed in centipoise (cP). The temperature that a viscosity measurement is taken at is very important, especially for epoxies. Silicone materials are not generally effected by temperature. Epoxies, on the other hand, can be effected tremendously by temperature. For some epoxy systems, the change can be a 10% change in viscosity per °C. As temperature rises , the viscosity drops and as temperature drops, the viscosity rises. Measuring viscosity does not always fully describe flow properties. Some resin systems have an apparent shear rate dependence. Materials can be Newtonian (the apparent viscosity remains constant as the shear rate increases), thixotropic (the apparent viscosity decreases as shear rate increases) or dilatant (the apparent viscosity increases as the shear rate increases). Epoxies are usually non-newtonian and are thixotropic in nature at least to some degree. Very few epoxies are dilatant. Thixotropy may be demonstrated by reporting a viscosity at two or more different shear rates (such as 1 and 10 RPM). This chart gives the viscosities of well known, common liquid materials so that you will have a better idea of what viscosity values look like. They are approximate and given in centipoise. Viscosity Comparisons Water 1 cP Kerosene 10 cP SAE #10 Motor Oil 500 cP Castor Oil 1,000 cP Corn Syrup 5,000 cP Honey 10,000 cP Hot Fudge Syrup 25,000 cP Molasses 50, 000 cP Heavy Molasses 100,000 cP (See other side for hardness discussion) Internet Address: www.emersoncuming.com Technical Data Sheet “Our service engineers are available to help purchasers obtain best results from our products, and recommendations are based on tests and information believed to be reliable. However, we have no control over the conditions under which our products are transported to, stored, handled, or used by purchasers and, in any event, all recommendations and sales are made on condition that we will not be held liable for any damages resulting from their use. No representative of ours has any authority to waive or change this provision. We also expect purchasers to use our products in accordance with the guiding principles of the Chemical Manufacturers Association’s Responsible Care® program.”
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Reference Sheet for Viscosity and Hardness
Transcript of Viscosity and Hardness Comparison
Technical Tip
Viscosity and Hardness
ViscosityViscosity is a measure of the internal resistance orfriction when a fluid moves against itself. Viscositycan be effected by the chemical structure of theresin, the molecular weight or Epoxy EquivalentWeight (EEW) of the resin or the type and amountof filler added. The lowest viscosity materials areunfilled, short chained and have low EEW.
The internal resistance or viscosity is typicallymeasured using a rotating spindle instrument, suchas the Brookfield viscometer. The amount of forceneeded to turn the spindle (torque) is recorded inPoise or centipoise. There are different surfacearea spindles which are used to measure differentranges of viscosities. The higher the measuredtorque value, the higher the viscosity. Poise is ameasurement of force, 1.0 Poise (P) equals 0.10Newton-seconds/meter2. Low viscosity materialsare commonly expressed in centipoise (cP).The temperature that a viscosity measurement istaken at is very important, especially for epoxies.
Silicone materials are not generally effected bytemperature. Epoxies, on the other hand, can beeffected tremendously by temperature. For someepoxy systems, the change can be a 10% changein viscosity per °C. As temperature rises , theviscosity drops and as temperature drops, theviscosity rises.
Measuring viscosity does not always fully describeflow properties. Some resin systems have anapparent shear rate dependence. Materials can beNewtonian (the apparent viscosity remains constantas the shear rate increases), thixotropic (theapparent viscosity decreases as shear rateincreases) or dilatant (the apparent viscosityincreases as the shear rate increases). Epoxies areusually non-newtonian and are thixotropic in natureat least to some degree. Very few epoxies aredilatant. Thixotropy may be demonstrated byreporting a viscosity at two or more different shearrates (such as 1 and 10 RPM).
This chart gives the viscosities of well known, common liquid materials so that you will have a better idea ofwhat viscosity values look like. They are approximate and given in centipoise.
Viscosity Comparisons
Water 1 cPKerosene 10 cPSAE #10 Motor Oil 500 cPCastor Oil 1,000 cPCorn Syrup 5,000 cPHoney 10,000 cPHot Fudge Syrup 25,000 cPMolasses 50, 000 cPHeavy Molasses 100,000 cP
(See other side for hardness discussion)
Internet Address:www.emersoncuming.com
Technical Data Sheet
“Our service engineers are available to help purchasers obtain best results from our products, and recommendations are based on tests and information believed to be reliable.However, we have no control over the conditions under which our products are transported to, stored, handled, or used by purchasers and, in any event, all recommendationsand sales are made on condition that we will not be held liable for any damages resulting from their use. No representative of ours has any authority to waive or change thisprovision. We also expect purchasers to use our products in accordance with the guiding principles of the Chemical Manufacturers Association’s Responsible Care® program.”
Donald E Whitehouse
Viscosity and Hardness Technical Tip
© 1999 Emerson & Cuming1755-VAH/12-99
HardnessHardness is a measure of the resistance of a curedmaterial to withstand indention. When speciallyshaped points are applied to a surface with acontrolled, measured force, the penetration depth ismeasured. The hardness can be expressed in anumber of scales. The Shore 00 scale is for verysoft gel materials, the Shore A scale is for softmaterials, the Shore D scale for harder materialsand Rockwell M for even harder materials, usuallymetals.
Typically the hardness testers are the mostaccurate in the middle of their range. For example,if the scale was 0-100, the hardness numberswould be most accurate in the 20-80 range. OtherShore and Rockwell scales exist but are generallynot used for epoxies and silicones.
The following chart compares the Shore A, D andRockwell M scales and compares the conversionamong these methods of measuring hardness.
Hardness Conversion TableShore Rockwell
A D M50 1070 1590 32100 45
74 078 3282 6386 9590 125
Some other methods for measuring hardness are;Barcol which is another penetration test used forharder material, pencil hardness which is normallyused for coatings/inks, Sward hardness which isalso used for coatings, Moh which is used forminerals, and Taber which measures abrasionresistance.
This chart gives the hardnesses of well known, common objects so you will have a better idea of what thehardness values look and feel like.
Hardness ComparisonsShore A Shore D is Equivalent to:
25-30 Eraser35-45 Pink Pearl®* eraser45-55 Rubber stamp55-65 Pencil eraser65-75 Rubber heel75-85 25-30 Rubber sole85-95 30-40 Typewriter roller
95-100 40-50 Pipe stem50-60 Textbook cover60-65 Office desktop65-70 Telephone70-75 Wooden ruler75-80 Fountain pen
* Pink Pearl is the registered trademark of Faber Castell.
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