![]() The readings obtained do not directly correspond with any other viscosity scale. The instrument used throughout the industry since 1934 is called a Viscosity Cup or Stein-Hall Cup. Record the time and temperature of adhesive.The time in seconds is the Stein-Hall viscosity.Fill the viscosity cup with strained adhesive and with a stopwatch measure the time it takes for the level in the cup to drop from the upper pin to the lower pin.Continue until the time is 15 seconds (+/- 1 second). If it is shorter than that, bend the pins apart and check the calibration again. If it is longer than that, bend the pins together and check the calibration again. The time should be 15 seconds (+/- 1 second).Remove your finger and, with a stopwatch, measure the time it takes for the level in the cup to drop from the upper pin to the lower pin.Place finger over the orifice of the viscosity cup.Check the orifice to make sure it is not plugged, corroded or worn. Although it applies to general flows, it is easy to visualize and define in a simple shearing flow, such as a planar Couette flow.The Stein hall cup must be calibrated before performing the test. Viscosity is the material property which relates the viscous stresses in a material to the rate of change of a deformation (the strain rate). For instance, in a fluid such as water the stresses which arise from shearing the fluid do not depend on the distance the fluid has been sheared rather, they depend on how quickly the shearing occurs. In other materials, stresses are present which can be attributed to the deformation rate over time. Stresses which can be attributed to the deformation of a material from some rest state are called elastic stresses. For instance, if the material were a simple spring, the answer would be given by Hooke's law, which says that the force experienced by a spring is proportional to the distance displaced from equilibrium. In materials science and engineering, one is often interested in understanding the forces or stresses involved in the deformation of a material. In a general parallel flow, the shear stress is proportional to the gradient of the velocity. ![]() The relative strength of this force is a measure of the fluid's viscosity. Since the shearing flow is opposed by friction between adjacent layers of fluid (which are in relative motion), a force is required to sustain the motion of the upper plate. Definitions Dynamic viscosity Illustration of a planar Couette flow. Viscum also referred to a viscous glue derived from mistletoe berries. The word "viscosity" is derived from the Latin viscum (" mistletoe"). A fluid that has zero viscosity (non-viscous) is called ideal or inviscid. Zero viscosity (no resistance to shear stress) is observed only at very low temperatures in superfluids otherwise, the second law of thermodynamics requires all fluids to have positive viscosity. For example, the viscosity of a Newtonian fluid does not vary significantly with the rate of deformation. However, the dependence on some of these properties is negligible in certain cases. In general, viscosity depends on a fluid's state, such as its temperature, pressure, and rate of deformation. For a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. Experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. Viscosity is expressed in Zahn seconds which are correlated to viscosity in centistokes. Five cups are available differing only in the size of the orifice. Viscosity quantifies the internal frictional force between adjacent layers of fluid that are in relative motion. Inexpensive Boekel cup type viscometers measure viscosity in the 18 to 1725 centistokes range in 90 seconds or less. Thus its SI units are newton-seconds per square metre, or pascal-seconds. Viscosity is defined scientifically as a force multiplied by a time divided by an area. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. The viscosity of a fluid is a measure of its resistance to deformation at a given rate.
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