Rheology, Tribology and Direct Performance Measurement of Rolling Element Bearings Using the Physica MCR Rheometer by Anton Paar

Topics Covered

Background
Introduction
Rheology
Tribology
Rolling Element Bearing

Background

Anton Paar GmbH produces high-end measuring and laboratory instruments for industry and research. It is the world leader in the measurement of density, concentration and CO2 and in the field of rheometry. Anton Paar GmbH is owned by the charitable Santner Foundation.

Over 1180 employees at the headquarters in Graz and the thirteen sales subsidiaries worldwide ensure that Anton Paar products live up to their excellent reputation. The core competence of Anton Paar – high -precision production – and close contact to the scientific community form the basis for the quality of Anton Paar's instruments.

Introduction

The flow and friction behavior of lubricants strongly influence the lubrication performance. Rheology and tribology are established techniques for the characterization of lubricants in their early state of development. Both techniques give insights into the lubricant’s behavior during the application.

The Physica MCR rheometer, equipped with suitable accessories, enables rheology and tribology with one single instrument and allows direct performance measurement of rolling element bearings.

Rheology

Mineral oils are newtonian liquids which means that the viscosity is constant independent of the applied shear rate. Greases exhibit viscoelastic flow behavior, the apparent viscosity is therefore dependent on the applied shear. A Physica MCR rheometer measures the viscosity and determines the viscoelastic properties allowing you to design oils and greases which have the desired consistency, viscosity and flow behavior at given temperatures.

Diagram: Amplitude sweep on greases of NLGI classes 0 (blue), 1 (red), 2 (black). NLGI class 2 has the highest structural strength, and NLGI class 0 the lowest.

Tribology

The Physica MCR rheometer can be equipped with a tribological accessory which turns the instrument into a high-performance tribometer. The system is based on the ball-on-three-plates principle in which a ball is pressed on self-centering plates with a given normal load up to 70 N. The instrument can be run in speed-controlled and torque controlled mode, allowing the determination of Stribeck curves and static friction in the temperature range from -40 to 200 °C. Further test types can be designed, programmed and displayed in the flexible software.

Diagram: Stribeck curve measured with a steel ball on dry (blue) and lubricated (red) Polyoxymethylene (POM). Stribeck curve measured with a steel ball on lubricated (green) steel plates.

Rolling Element Bearing

The best way to check the performance of a lubricant is during the application because it is almost impossible to simulate all influencing environmental factors within a model system. The reliability of the result increases the closer a model system represents the application.

Greases are used in various types of rolling element bearings under different conditions. A ball bearing holder for the tribology device was therefore designed so that lubricated bearings are directly measurable. It allows direct performance measurements of the lubricant in the bearing within the temperature range from -40 up to 200°C.

Diagram: Speed ramp of a grease (NLGI 0) lubricated bearing at –40 °C (red), 25 °C (blue) and 60°C (black).

Source: Anton Paar GmbH.

For more information on this source please visit Anton Paar GmbH.

Date Added: Oct 26, 2010 | Updated: Dec 2, 2014
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