#Viscosity definition engineering how to#
#Viscosity definition engineering verification#

The problem turned out to be a matter of understanding “shear rate” and how it can affect the viscosity of the ink. But the cup method could not always discriminate successfully between inks that proved acceptable and those that were marginal or outright poor performers. This became one of the earliest quality control (QC) tests that checked systematically for viscosity in a quantifiable way.

#Viscosity definition engineering how to#

The cups were relatively inexpensive and anyone working the press could easily learn how to make the measurement. Printers developed a more scientific approach to viscosity measurement by using cups with holes in the bottom to measure how much time it would take to drain the ink (Figure 1). This rubbing action was, in essence, a viscosity test, the objective being to tell how much resistance was felt between thumb and forefinger. There was a time when pressmen could tell by rubbing an ink between their fingers as to how well it would perform “on press”. When the ink is too thick, smearing may result during printing too thin and there can be serious fading of the printed image. The printing ink industry is one of the best examples to illustrate the need for viscosity measurement. The only alternative in these situations is to find the proper authority at the manufacturer and obtain the relevant test details.

#Viscosity definition engineering verification#

To perform a valid verification check and confirm that the material is within specification requires a duplication of the test method used by the manufacturer. Data sheets for some polymer solutions, for example, may include a discrete number like 4,500 centipoise (cP), but no further information about how the measurement was made, not even the test temperature at which the polymer was measured. Raw materials in the chemical process industries (CPI) usually have a reported viscosity value on the data sheet that accompanies the product. Experiments have shown that the viscosity values obtained at 0.1 or 0.01 rpm can be several orders of magnitude higher than the one recorded at 20 rpm. When pumping asphalt, the startup torque required to get the pump going initially suggests that a second viscosity test at a much lower rotational speed makes sense.

However, this straightforward single-point test does not provide the complete picture for asphalt flow behavior. Record the viscosity value, make sure that it falls within prescribed maximum and minimum limits, and then report whether the number passes or fails. The standard test method for pumpability, according to ASTM D4402, is to use a regular viscosity (RV) torque rotational viscometer at 20 rpm or a low viscosity (LV) instrument at 12 rpm. An important concept, sometimes forgotten, is that a material’s viscosity is not a single-point measurement, but often depends on a number of factors. This article reacquaints the reader with the basic concepts and terminology for viscosity and addresses techniques to quantify it.

The bottom line is to come up with ways to measure viscosity so that you can quantify whether a material will flow the way it needs to. For handlers of all materials that flow, either while being processed or in an end-use, it is important to think about the materials’ flow characteristics. To be brief, viscosity is resistance to flow. Most engineers know what viscosity is, but may have trouble explaining it.