It happens in a split second: at first, static electricity is built up without being noticed, then the metal surfaces of the rolling element and the raceway come into contact - the beginning of the end! Sudden discharge resulting from this contact may entail severe damage. This problem mainly affects machines and installations conveying materials such as plastic foils or paper, applications which encourage static electricity no less than the operation of electric motors.

But this is now a thing of the past. The Munich-based special lubricants manufacturer Klüber Lubrication has developed a new rolling bearing grease, Klüberlectric B 42-72, which is electroconductive and helps preventing local voltage discharge. Heiko Stache, member of the Business Unit Bearing Technology at Klüber München KG reports: "There have already been various attempts in the past at solving this problem by insulation of the external bearing shell or the use of ceramic rolling elements".


Continuous electrical transfer through bearings

However, these efforts have not always proven successful; furthermore, they tend to make substantial design modifications and expenses necessary. As H. Stache says: " the idea of formulating a lubricant which is able to continuously conduct electricity through the bearing seemed to suggest itself - in such a way that damage due to sudden voltage discharge is prevented right from the beginning". This is how Klüberlectric B 42-72 was brought into being.

The electroconductive rolling bearing grease prevents typical damage arising from discharge such as the formation of craters and grooves on rolling bearings which used to cause the bearing to run out of true. In the past, bearings frequently had to be completely replaced, which caused both loss in time and significant expense.


The new grease's electric resistance is comparable to that in semiconductors

In order to show clearly the difference to conventional lubricating greases, Klüber has determined the electric resistance of grease in accordance with DIN 53482. This standard describes how to measure the electric resistance of non-metal materials. In this test, the resistance of two plates with the grease (packed in an isolated hollow cylinder) in between is measured. Electrode gaps of 1 millimeter to several centimeters are possible.

Klüberlectric B 42-72 actually surprised Klüber's R&D team: whilst the specific resistance of "normal" lubricating greases is 108 to 1014 Ohm x cm, the new rolling bearing grease shows a specific resistance of only approx. 105 Ohm x cm. It therefore lies within the range typical of semiconductors. (1). Compared to a grease whose resistance is 108 Ohm x cm, Klüberlectric B 42-72 is able to conduct a current intensity which is 1000 times higher with the same voltage applied! And with a grease having a resistance of 1011 Ohm x cm, which is not unusual for standard greases, the possible current intensity increases by the factor 106. Of course, for all applications of Klüberlectric B 42-72 one has to take into account the current intensities that may flow.


Klüberlectric B 42-72 - tried and tested

Klüber Lubrication is proud of the newly developed product, which has proven successful both in tests and in practice. The grease stands out for its long running times and high reliability. The grease can also be used in a wide service temperature range from -40 to +140°C. Tests performed on rolling bearing test rigs yielded excellent service life and speed factor results. In the FAG-FE9 test according to DIN 51 821, part 2, Fa 1,500 N, n= 6,000 rpm, at 140 °C, Klüberlectric B 42-72 achieved a L50 running time of > 200 hours. The new grease also stands out for its excellent corrosion protection. In the Emcor test (DIN 51 802, 1 week, distilled water), it obtained a corrosion degree of < 1. Furthermore, Klüberlectric B 42-72 easily covers speed ranges up to 350,000 mm x min^-1, which is important for numerous applications. All these advantages and outstanding characteristics are due to the selection of special synthetic base oils, soap types as well as solid lubricants.


Further product data of Klüberlectric B 42-72:

Base oil / thickener	ester oil, synthetic hydrocarbon oil, special lithium soap, solid lubricant
Color, aspect	black, homogeneous
Worked penetration, DIN ISO 2137, at 25 °C, 0.1 mm	265 - 295
Water resistance acc. to DIN 51 807, pt. 1, 3 h / 90 °C, rating	1 - 90
Copper corrosion acc. to DIN 51 811, 24 h / 140 °C, corrosion degree	1 - 140
Base oil viscosity, DIN 51 561, at 40 °C, mm²/s at 100 °C, mm²/s	approx. 70 approx. 25
Speed factor for deep groove ball bearings** (n x dm) mm x min-1	approx. 350.000

*Service temperatures are guide values which depend on the lubricant's composition, the intended use and the application method. Lubricants change their consistency, apparent dynamic viscosity or viscosity depending on the mechano-dynamical loads, time, pressure and temperature. These changes in product characteristics may affect the function of a component.


*** Speed factors are guide values which depend on the type and size of the rolling bearing type and the local operating conditions, which is why they have to be confirmed in tests carried out by the user in each individual case.


References:

(1)	Vgl. Holleman-Wiberg: "Lehrbuch der Anorganischen Chemie", S. 153 (Verlag Walter de Gruyter, Berlin-New York, 101. Aufl., 1995)

For more information on Klüberlectric B 42-72 please contact:
Klüber Lubrication München KG
Geisenhausenerstr. 7, 81379 München
Tel. 089/78 76-0, Fax 089/78 76-333
e-mail: marketing.service@klueber.com