Vacuum pumps are a small but extremely critical part in a much larger vacuum coating process. Oils meant for these vacuum pumps need to be very reliable since one doesn’t want unnecessary stops in the vacuum cycle. Apart from giving us the desired vacuum level, these oils should protect and preserve the pump interiors and not form oil sludge. Just a couple of decades ago, finding these qualities in vacuum pump oils would have been impossible by users. Back then, options to using mineral oils were nearly zero. These mineral oils could never deliver consistent vacuum; uniform viscosity levels were missing; oil changes had to be frequent as the oil oxidized pretty frequently; and formation of sludge in the pump was a constant headache for engineers. That was before the advent of synthetic vacuum pump oil. What are synthetic oils? Unlike mineral oils that are derived directly from crude oil, synthetic oils are lubricants with synthetic base stock plus other performance enhancing chemical compounds. Because of being artificially made, in synthetic oils it becomes possible to tweak certain parameters to better suit the application for which they are manufactured. Advantages of Synthetic oils: Just like advent of Silicone Diffusion Pump oils revolutionised the way Diffusion pumps worked (Hard to believe but it is true that about 15 years back all Diffusion Pumps worked
on mineral diffusion pump oils). Same way Synthetic Rotary vacuum pump oils are enhancing efficiency of Rotary vacuum pumps to unbelievable levels. Synthetic oils make it possible for Rotary Pump to reach higher vacuum and faster! These oils make sure that there is hardly any pump maintenance requirements, they last longer and work out more economical and so on. You can easily infer this from table below which compares major properties and characteristics of these oils.
Synthetic Rotary Pump Oil
Mineral Rotary Pump Oil
1
Synthetic base stock
Petroleum base stock
2
Has a high viscosity index because of Has a low viscosity index because of which which it can withstand extreme working chances of it evaporating or turning to temperatures thick tar are high
3
Better chemical stability
Not very chemically stable
4
High resistance to oxidation
Low resistance to oxidation
5
High resistance to process gases
Degrades faster when exposed to certain process gases
6
No oil sludge formation
Oil sludge problem
7
Longer life means less frequent oil Shorter life means more frequent oil changes changes
8
Molecules are uniform in shape and size, High intra molecular friction caused by so minimum intra molecular friction. jumbled up molecules. This gives mineral This imparts better film strength. oils lesser film strength.
9
No sulphur and carbon impurities
Sulphur and carbon impurities cause faster break down of the oil. Also sludge forms due to these impurities
10
Higher flashpoint
Lower flashpoint
11
Lower vapour pressure
Higher vapour pressure
12
Better lubricity at both high and low Reduced lubricity at extreme temperatures temperatures causing no friction causing friction between the moving parts between the moving parts
13
Initial cost of Synthetic oils is about 50% Initial cost is low but comes out costlier on more but since the life of oil is more by account of less working life. about 150%, so it works out to be cheaper.
Conclusion: Having compared the two types of oils, one can safely conclude in the end that for rotary vacuum pumps, the properties of synthetic oil are unbeatable. Using mineral vacuum pump oil can serve our purpose too but that is akin to driving an Ambassador car on a race track.