Molykote® G-9000 Series:
New Siloxane Fluids with Enhanced Lubrication Properties
Article based on presentation given by Dr. Manfred Jungk, Industry Scientist, Automotive Europe, Dow Corning at LUBMAT Conference. Abstract
Silicone lubricants are known in the industry for having high viscosity indexes as well as being able to perform well across high temperatures, which is why they are usually used in high temperature applications and when lubricant longevity is required. Despite these benefits silicone lubricants have generally had a poor reputation when it comes to metal-to- metal applications and are more generally sought after for plastic applications. This perception has mostly been due to the characteristics of polydimethyl siloxane lubricants (PDMS), where lubricity limitations do exist. However, Dow Corning has recently developed a new phenyl/fluoro siloxane copolymer which exhibits good lubrication properties. This paper will demonstrate that this new family of silicone lubricants showcase high viscosity indexes, perform well in high temperatures, but also demonstrate strong wear resistance. They are also compatible with additives, allowing for customized performance. And very importantly, their lower density offers potential for significant cost-in-use savings over traditional PFPE lubricants.
Introduction
Silicone lubricants have been on the market for decades. They display high viscosity indexes and perform stably under high temperatures where lubricant longevity is required. Unlike hydrocarbons, the chemical backbone of silicone lubricants allows for a range of chain lengths which determine the different viscosity levels of a lubricant- this is not possible to the same extent with hydrocarbons. This backbone also makes them stronger and more flexible than hydrocarbons. Silicone lubricants impart unique properties, such as low melting temperature, fluidity, low glass transition temperature and increased compactness, rendering them useful for a diverse number of applications across different industries. This is what sets silicones apart from other synthetic lubricant based fluids.
Despite these strong properties, silicone-based lubricants are seen to be poor lubricants, especially in metal-to-metal applications. Advances in the 1950s introduced variations into the mix of silicone lubricants to strengthen the performance properties, which brought about the phenylmethyl siloxanes (PMS). These display higher temperature resistance and carry load better than traditional silicone lubricants, but have lower viscosity indexes. In the 1970s, fluoro-based silicones were introduced displaying strong load carrying capacity and wear resistance. However, in achieving higher load carrying capacity, the fluoro-based silicones underperformed in temperature performance and viscosity indexes. The thermal and oxidative properties of silicone lubricants are still among the highest
20
available, but load carrying capacity has remained an area for improvement – until now. With this in mind, Dow Corning has developed a new silicone-based lubricant, which combines the properties of both phenyl and fluoro-based silicone lubricants to further improve load carrying capacity, and therefore, lubrication.
Molykote® G-9000 Series
Dow Corning developed a totally new patented technology that could very well change the way we think about specialty lubricants. The new lubricant, Molykote®
G-9000 Series,
combines the thermal and oxidative resistance properties of phenyl-silicone lubricants with the strong wear protection and load carrying capacity of fluoro silicones into one chain. This innovative phenyl/fluoro copolymer thus displays excellent temperature stability and enhanced wear resistance properties. The formulation flexibility of the neat copolymer can be achieved through the tailoring of the ratio between the phenyl and fluoro groups. Furthermore, it is worth noting that this new copolymer allows commercially available additives to be easily added to the copolymer to fine tune the characteristics of the grease. This family of lubricants could also develop into a lower-cost alternative to PFPE (perfluoropolyether) in applications that do not require the ultimate high-temperature performance and where ester-based lubricants will be limited in temperature.
Benefits & Properties In order to demonstrate the performance of the phenyl/fluoro copolymer, Dow Corning has tested the new lubricant under various conditions. This article will demonstrate a range of properties and benefits the new Molykote®
offer the industry. Thermal Stability
The oxidative and thermal stability of three different fluoro- to-phenyl ratios was determined by thermally treating them with both open and closed cup at 250°C and then measuring the viscosity weekly. Figure 1 demonstrates that the viscosity of phenyl/fluoro lubricants are stable over a period of more than 20 days when stored in open cups. As seen in the graphs, lubricants with a higher phenyl content (75:25) demonstrate a better thermal stability than those with a higher fluoro content (25:75). Figure 2 shows that in closed cups, where limited oxidation occurs, the viscosity is stable over a period of more than 100 days. It should also be noted that Molykote®
G-9000
Series lubricants not only deliver on performance lubricity at high temperatures, but they also do not sacrifice performance at low temperatures either – with stable performance at -35° C.
G-9000 Series can
LUBE MAGAZINE NO.137 FEBRUARY 2017
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