Читать книгу The Rheology Handbook - Thomas Mezger - Страница 144

Recommendations: measuring temperature of T = +25 °C, use of a CP 25-1 measuring geometry (cone-and-plate, diameter of 25 mm, and cone angle of 1°)

Test program consisting of five intervals

 1 st interval: rest phase (for t = 1 min): at γ ̇ = 0

 2 nd interval: pre-shear phase (for t = 1 min): at γ ̇ = 100 s-1 = const

 3 rd interval: rest phase (for t = 2 min): at γ ̇ = 0

 4 th interval: shear rate ramp upwards (in t = 1 min): with γ ̇ = 0 to γ ̇ max

 with γ ̇ max = 1000 s-1 for greases exhibiting soft consistency (showing NLGI classes 000 to 1; NLGI is the National Lubrication Grease Institute in the USA),

 and with γ ̇ max = 500 s-1 for greases exhibiting rigid consistency (i. e., NLGI class 2),

 5 th interval: high-shear phase (for t = 5min): at γ ̇ = γ ̇ max = const

Analysis: With the viscosity values η1 at the beginning and η2 at the end of the fifth interval, the “relative viscosity change” is calculated as follows:

ηrel = (η1 - η2) ⋅ 100/η1 (specification of ηrel in [%])