Solid contaminants in lubricating greases

With almost 10,000 tests of used lubricating grease specimens this year, OELCHECK is the world-leading service laboratory for waste grease analyses. Affordable analysis sets are available for the routine inspection of lubricating greases. Almost all everyday problems can be covered off with the testing methods included in the kit.

 

In addition, further special tests are available, for example for experimental observations or questions in connection with stock disturbances. One of these is the determination of the amount and type of particles and solid impurities which are found in the lubricating greases used. Mostly, such particles which originate from slowly running rolling bearings or swing bearings are visible in the grease specimens to the naked eye (>70 µm). Alongside soft particles from the grease ageing and solid impurities (dust) from the surroundings, such greases often contain metallic wear debris from the components of the bearing such as bearing cages, tracks or rolling elements. The shape, hardness, amount and size of the solid impurities influence the service life of the rolling bearings. Therefore, increasingly higher demands for improved cleanliness are placed not only on the oils but also the lubricating greases.

 

Year of publication: 2013

 

For the determination of stubborn component parts there is a method defined in DIN 51813 – however only for fresh greases – of how solid materials of over 25 µm in piece size can be quantitatively detected through high pressure filtration using a filter with a 0.025 mm pore size from a large fresh grease amount of 0.5 kg. This method is not suitable for used grease analyses. Only the sample preparation in accordance with this standard is used in the OELCHECK laboratory for the relatively complex analysis.

For the used grease analysis, the identification of wear or impurity elements and additives belongs to the standard of an analysis set. For this 27 elements such as iron, chromium, silicon, sodium, zinc and phosphorus are identified in accordance with the Rotrode method. The element contents are given in mg/kg. Unfortunately, very large particles can only be viewed with the atom emission spectroscopy up to a size of approximately 5 µm through the LDE arc, with which the individual component parts are stimulated.

If there are visible particles (>70 µm) in a waste grease specimen, the identification of the elements is not always precise. Here, conclusions can be drawn on the wear condition of the lubricated elements with the "Identification of the content of stubborn materials". However, this method only functions for soap thickened lubricating greases without solid lubricants. 20 grams of lubricating grease are required.