Is Silicone Grease Bad for Automotive Components?
In the early 2000s, original equipment manufacturers (OEM) experienced cratering and fisheyes appearing on painted surfaces. The culprit? Light molecular weight silicone sprays used in automotive assembly plants. When light molecular weight silicone becomes airborne, it can land on unintended areas and ultimately lead to sheet metal contamination. Silicone sprays are typically transparent, making them hard to detect in the painting process, creating many headaches when trying to optimize the perfectly painted metal surface.
Silicones are polymers that can take many forms including oils, rubbers, and resins. They are used in many everyday items, from cooking utensils to cosmetics. In lubricants, a silicone base oil is commonly used in greases for plastic gears, control cables, and seals because they are inert, compatible with most plastics and elastomers, and remain stable over a wide temperature range.
Some automotive OEMs have limited silicone use to specific facilities, and now many people are asking—is silicone really that bad? Silicone greases are like any other lubricant, suitable for some applications, but not all. There are many factors to consider when deciding whether to use a silicone lubricant.
One of the deciding properties of silicone is its tendency to migrate, based on its low surface energy. The ability to migrate can be an advantage or a disadvantage depending on the application. In cables, for example, a lubricant with low surface energy is ideal. Lubricating cables housed in a sheath is challenging. On the other hand, low surface energy lubricants can migrate down and coat the cable’s entire length effortlessly. However, if the application relies on the grease staying in place like in a headrest, a hydrocarbon grease with higher surface energy is ideal. It is important to note that a silicone base-oil that is properly formulated into a grease is less likely to migrate as a silicone oil alone will, if at all.
Like Nye’s Fluorocarbon Gel 880, most silicone lubricants perform exceptionally well at temperature ranges from around -40 to 200 °C. Lubricants with a wide temperature range are beneficial for exterior applications because they can withstand extreme environmental conditions. Additionally, because silicone lubricants are thermally stable, they provide lifetime lubrication in ball joints, struts, shocks, and other enclosed applications without grease fittings. Their surface energy also helps to rewet surfaces if the lubricant were to expel from high load areas.
Silicone is an inert lubricant and does not react with most non-silicone elastomeric seals, or plastics used in automotive interior components. They are also widely used with o-rings because they will not swell or soften the ring. Silicone greases can be used as an assembly aid, as well as providing additional sealing capabilities.
Because of their high viscosity index and low surface energy, silicone greases do not create a robust hydrodynamic film to separate components and prevent wear. As a result, Nye does not recommend silicone greases for most high load applications, like metal-on-metal gearing.
As vehicles shift toward fully electric designs, an electrical failure could affect anything from brake lights to the steering system. At Nye, we do not recommend silicone greases for electrical automotive applications. It has been found that lower quality, light base oil viscosity silicone lubricants present the possibility of outgassing, potentially contaminating nearby switch contacts leading eventually to switch failure and continuity problems. If a silicone is to be used, we recommend higher viscosity base oil options that also bring the benefits of motion control and improved tactile feel.
Additionally, silicone lubricants are also a challenge where arcing conditions are present. Arcing occurs when a substantial current leaps across the gap between contacts. The arc produces a small burst of localized heat (up to 1000 °C), causing the silicone to degrade. When silicone oxidizes, it turns into a hard, insulative, sand-like material that prevents contacts from coming together. Any lubricant that is not clean burning will experience some oxidation, but this can be considered in grease formulations and the expected life cycle of the switch in question. Silicone greases do find some use in low voltage potentiometers, where the potential for arcing is low.
Silicone greases are more expensive than hydrocarbon greases but less expensive than fluorinated greases. If a cost-effective lubricant that operates at high temperatures is required and the impact of possible silicone contamination is low, consider a silicone lubricant.
Our Verdict?
Silicone lubricants have excellent material compatibility, operate within a wide temperature range, and are cost-effective, making them appealing for many automotive applications.
Silicone-Free Grease for Advanced Motion Control
Nye chemists have been hard at work formulating a new silicone-free, hydrocarbon grease for advanced motion control applications. This product is now available for sampling. If you are interested in requesting a sample, Contact Us.
