Investigations on Ways to Improve the Scuffing and Wear Behavior of Oil-Free Water-Based Lubricants for Gear Applications

Today, mineral or synthetic oils that are made out of fossil raw materials are the most common lubricants in gear drive applications. Most of them are nonbiodegradable and may pose a risk to the environment. An important step to minimize the risk and the ecological footprint is the use of biodegradable and eco-friendly lubricants. Former research shows the potential of water-based lubricants in gear applications. Therefore, an oil-free, water-based lubricant was developed for this study. The base lubricant contains plant-based thickeners to generate an appropriate viscosity for a sufficient lubricant film thickness in the tooth contact. In experimental investigations, the sliding wear and scuffing performance has been examined under variation of the added polymers and additives. The scuffing tests A/8.3/RT are performed according to DIN ISO 14635-1. The wear test procedure is based on DGMK 377-01. In both scuffing tests with the sample, the failure load stage = 8 was achieved. For case-carburized gears, a "medium" to "high" amount of wear can be detected. Additional tests with nitrided gears show a "low" amount of wear. This article aims to show the great potential of water-based oils for gear lubrication and suggests operating conditions for maximum wear and scuffing carrying capacity.