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Viscosity: The measurement of a fluid’s internal resistance to flow. Centipoise (cps) and Poise are the common units of measurement, but viscosity can also be expressed as follows:
MPa s (Millipascal Second) (= 1 centipoise)
Pa s (Pascal Second) (= 1 poise)
Centistoke (centistoke x density = centipoise)
Take a look at the column below. It offers a great understanding of what Viscosity is by comparing common pasts & liquids in terms of viscosity. Simple; The higher number; the thicker the stuff is.
Thixotropic. The tendency for the viscosity of a liquid to decrease when subjected to shear. Mayonnaise is a good example of a thixotropic fluid. At rest, it will not pour, but will flow readily when submitted to shear.
Thixotropic Index (aka TI). The ratio of two viscometer readings. The higher the difference in the two readings, the more thixotropic the material is, and easier to move.
Typically, one may be taken at 10 rpm, the second at 1rpm. Example:
Brookfield Model RVT, Spindle #5, @77º F.
1 RPM 25 X 4000 = 100,000 CPS
10 RPM 62.5 X 400 = 25,000 CPS
Thixotropic Index = 100,000 / 25,000 = 4.0
Newtonian Fluid. Newtonian fluids exhibit neither thixotropy or dilatancy and are referred to as true liquids. Their viscosity remains the same whether at rest or in motion. Typical examples are water and oils.
Dilatant Fluid. The opposite of thixotropic, namely, the tendency of a fluid to increase in viscosity when subjected to shear, the resistance to flow increasing with the amount of force applied. These types of fluids are not generally well suited to use with meter/mix systems.
Paste. This is a term loosely applied to a wide range of materials and can include those that will self-level as well as those which do not. If the specification for the material includes a thixotropic index, one can tell how easily or how hard it will be to move. Low TI materials generally require the use of pressure supplied by ram pumps to move them into a metering system.
Rheology. Loosely defined as “flow properties”.
As you begin to consider choosing specific materials molds, and lures can be made of, from hundreds of available products listed in the LMDFG> FACTORY> MATERIALS Section; having an understanding of this information will be very helpful when reading the Material Product Descriptions.
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