System for determining rheological properties of grease and associated method

A method for determining rheological properties of grease, comprising:

• (a) moving a piston in a first direction inside a cylinder containing the grease to push the grease through holes of the piston, a seal being provided between the piston and the cylinder,
• (b) measuring the force required to push the grease through the holes of the piston,
• (c) moving the piston in a second direction opposite to the first direction inside the cylinder,
• (d) measuring the temperature of the cylinder,
• (e) maintaining the temperature of the cylinder at a predetermined temperature,
• (f) repeating steps (a), (b) and (c) during a predetermined number to obtain a set of measured forces, and
• (g) determining at least one rheological property and the total energy density transferred to the grease, the at least one rheological property being determined from the measured forces and from the seal friction, the total energy density being determined by the following steps:
• filtering the set of measured forces,
• modelling the piston velocity according to the filtered set of measured forces,
• determining the seal friction according to predetermined fitting parameters and to the piston velocity,
• determining a second set of forces from the filtered set of measured forces and the seal friction,
• calculating the instantaneous power density transferred to the grease according to the second set of forces, the velocity model of the piston and the volume of grease inside the cylinder,
• calculating the average power density transferred to the grease for each piston stroke between the first and second directions of the cylinder from the instantaneous power density, and
• calculating the total energy density by summing the instantaneous power density or by integrating the instantaneous power density.