Definition
AFNOR viscosity cup is an outflow viscosity measurement device designed according to the standards of the French Institute for Standardization, mainly used for the rapid determination of the kinematic viscosity of Newtonian or near-Newtonian fluids in the laboratory or production site. It is designed to meet specific standard specifications and evaluates the flow characteristics of a fluid by measuring the time it takes for a volume of fluid to flow out of a standard orifice under gravity.
Principle
The measurement of AFNOR viscosity cups is based on the simplified application of Poissou's law. When the fluid flows out through the standard pore size of the cup bottom driven by gravity, the outflow time is positively correlated with the kinematic viscosity of the fluid within a certain range. Its basic relationship can be expressed as:
η = k × (t - c)
Among them η represents the kinematic viscosity, t is the outflow time, and K and C are instrumental constants, which are related to the geometric structure of the cup and the surface tension of the fluid, respectively. This formula is suitable for fluids under laminar flow conditions where inertia effects are negligible.
Measurement method
Ensure that the viscosity cup and the fluid to be measured are at a standard test temperature before measurement. Position the viscosity cup vertically, plug the bottom orifice with your fingers, and inject fluid to the edge of the overflow. Remove the finger to start the timer at the same time, stop the timer when the continuous flow of the fluid is interrupted for the first time, and record the outflow time. After each measurement, the cup body should be thoroughly cleaned to avoid residual effects. It is usually recommended to average three repeated measurements to ensure consistency of results.
Influencing factors
Temperature is a key factor in measurement accuracy, and fluid viscosity often varies significantly with temperature, so it needs to be operated under constant temperature conditions. The cleanliness of the cup body and the state of the pore have a direct impact on the flow rate, and any wear or contamination may alter the instrument constants. The non-Newtonian properties of fluids can deviate from the linear region of the outflow time and viscosity relationship. The verticality of the cup body, the consistency of liquid level control and timing judgment during operation will also introduce human error.
Application:
AFNOR viscosity cups are widely used in the quality control process of coatings, inks, adhesives and other chemical products. In the food industry, it can be used to determine the consistency of liquids such as syrups and vegetable oils. In addition, it is often used as an aid in rapid screening in the production of petroleum derivatives, resins and some daily chemicals. The measurement results can be used as a reference for production process adjustments or product batch consistency assessments.
Selection
The expected viscosity range of the fluid to be measured should be considered when selecting, and different pore size models correspond to different measurement intervals. Attention should be paid to the standard version that the instrument meets to ensure consistency with industry testing requirements. In terms of material, stainless steel cups have good corrosion resistance and wear resistance. For conventional quality control, the single-hole model has been able to meet the demand; If the measurement range is wide, consider equipping multiple viscosity cup sets with different pore sizes. Confirm that the instrument constant is validly calibrated before use.