If static discharge poses is an issue or poses a hazard to your device, consider using a conductive grease. For example, any rotating component supported by ball bearings is essentially isolated from the rest of the device by the lubricant in the bearing raceway. There might be other contacts such as slip rings or commutator brushes; however if such a component is building up some type of electrical potential or static charge, there could be troublesome implications as it may prove difficult to bleed or dissipate this charge.
A non-conductive lubricant allows static charges or arcs to pit the rolling elements which accelerates wear. With a conductive grease the charge passes through the bearing with minimal electrical damage and often motor life is also extended.
An example is a treadmill manufacturer that found a solution with a conductive grease. The treadmill’s rubber belt was generating static electricity which made it’s way to the bearing, arced and fluted the raceway. A conductive grease helped to maintain the ground and extend the bearing life. In a similar but more common application, conductive greases bleed statice electricity away from the toner cartridge towards the shell in laser printers and copiers.
There are many more application examples where using a conductive grease to provide a current path between two moving parts proves to be a cost effective approach rather than comparatively expensive hardware solutions.
Designing a conductive grease is a challenge. The best base oil and thickener for an application depends on a number of factors and there are a few options to consider. Of course in a bearing application for example, it cannot be forgotten that the grease has to perform as a bearing lubricant in addition to being a conductive lubricant. The conductivity of any grease will fall short of that provided by metals, the grease having a definite level of electrical resistance, but a sufficient degree of electrical conductivity is achieved such that static charges are successfully dissipated through the ball bearing lubricant film. Sticking with the bearing example; certain adjustments may need to be accommodated, a higher percentage grease fill may be necessary and possibly a higher degree of pre-loading may also be required.
Conductive Grease Formulations
Generally the conductive feature of a grease is provided by the thickener or additives within the formula, not the base oil; modern conductive grease formulations do not use metal particles. If considering the use of a conductive grease for the first time, you will experience the frustration of the typical ‘trade offs’ when choosing a formulation. A common example is that an Ester is generally the best base oil for metal on metal wear prevention but Ester cannot cope with exposure to moderate to high levels of moisture. A PAO based conductive grease is a great cost effective option and PAO base oils make great all rounder greases.
Going back to the conductive ball bearing lubricant example, the use of special dispersants in existing ball bearing greases has permitted our design department to add highly conductive carbon (that has oil absorption capabilities) to the formula. We find that conductive carbon is generally the best way to give a grease electrically conductive characteristics.
We have an excellent pedigree in conductive grease, especially in ATEX (explosive) environment applications (specifically a product called Tribosyn 610), with a great number of customers relying on our conductive lubricants to discharge static safely.
Note: Although much of this introduction article has a mechanical bias, we also know that a conductive grease does have electrical applications. There are some electrical applications that are not suitable for a conductive grease; we never recommend using conductive grease on sliding switches, which could malfunction if a conductive grease is mis-applied to the contacts. Another example is multi-pin electrical connectors; a conductive grease is not recommended. Instead, please consider a dielectric connector grease.
Now take a look at our overview or our conductive grease range?
R&D project or prototyping stage and interested in this product? Small amounts of our synthetic conductive grease range can be purchased at our online shop (opens in new tab).