Lubricants as a design element

The development of a complex gearbox had already progressed far beyond the basic development stage when Rhenus Lub was asked about a suitable lubricating grease. We were given all of the necessary data so that we could make a basic assessment. This data included drawings, parts lists and the materials used.

The gearbox was to be installed in a sealed housing along with the drive unit and used inside an oil bath. With an application temperature range of -30°C to +130°C and given that the gears were constantly surrounded by oil, comprehensive sealing was essential. Due to the installation location, the customer wanted to ensure lifetime lubrication.

Following detailed analysis of all construction elements and environmental conditions, we identified the following conflicts:

• The material chosen for the outer seal was not compatible with the chemical properties of the surrounding oil.
• Sealing rings of different materials (EPDM and NBR) were used inside the gearbox.

In practice, the component would be destroyed by the ingress of the surrounding oil long before it reached its planned service life. Moreover, a randomly chosen lubricant would have dissolved the EPDM or NBR sealing rings, leading to a malfunction.

When it comes to combinations of materials – such as sealing rings and lubricants – one important factor is polarity. This is a basic property of every material, including every elastomer and every lubricant, and provides information about their solubility. To put it simply, like dissolves in like. This is particularly important in the case of lubricating greases, as the lubricant’s behaviour is either polar (e.g. polyalkylene glycol) or non-polar (e.g. synthetic polyalphaolefins), depending on the base oil. A lubricant with similar polarity causes sealing materials to swell and destroys them over time.

This and other information was relayed to the responsible design engineer, along with clear recommendations for sealing materials and a compatible lubricant. The resulting adjustments while still at the pre-series stage meant it was possible to avoid costly corrections or even damage during series production.

Complex products, a multitude of components and short development periods present challenges for every developer. With Rhenus Lub, you have the right partner at your side.

• Thanks to our internal testing programme, we have an extensive database containing information about media compatibility – not only for base oils but also for all the additives used.
• A compatibility comparison is always carried out in two directions.
• Compatibility with materials and lubricants.
• Resistance of lubricant to ambient media (fuel or exhaust vapour, non-ferrous metals, solvents, etc.).

Incidentally, we also offer chemically neutral special greases for special operating environments. The higher costs are compensated by other benefits in the individual case (e.g. no need for changes to components during series production).