Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
Choosing the right base stock technology is the starting point for any lubricant formulator as it is the base fluid that primarily determines the final properties of the lubricant itself. Whilst additives are a fundamental part of a well-designed lubricant even the best additives cannot turn a bad base fluid into a good base fluid, so choosing base fluids wisely is absolutely critical.
When deciding which base fluid or combination of base fluids to use the formulator will take into consideration many of the following factors and more:
• Application • Viscosity at 40°C • Viscosity at 100°C • Viscosity at low temperature • Viscosity at high temperature • Viscosity index • Oxidation / thermal stability • Volatility • Pour point • Flash point • Hydrolytic stability • Compatibility with metals • Compatibility with elastomer seals • Friction / Traction properties • Solvency • Gas compatibility (e.g. R134a, hydrocarbon gases, ammonia etc) • SAP value • Biodegradability • Renewability • Aquatic toxicity • Water solubility • Oil / water solubility • Incidental food contact applications • Clean burn properties • Price sensitivities • Etc etc
The more properties that are identified as being essential to the final product will limit the range of base fluids which are suitable for a given application.
32 LUBE MAGAZINE NO.129 OCTOBER 2015
No.100 page 1
Esters The Most Versatile of Base Stock Technologies
The API categorised crude oil derived base stocks based on sulphur content, saturates content and Viscosity Index in order to distinguish between different types of mineral base oils (Group I, Group II and Group III) and added two further categories; one for polyalphaolefins (Group IV) and one for everything else that didn’t fall within the first four categories (Group V).
Table 1. API classification of base stocks
Esters fall into the Group V category along with other notable synthetic base fluids such as polyalkylene glycols, polyisobutylenes, silicone oils, phosphates esters, alkyl naphthalenes and others.
Esters as Group V Synthetic Base Fluids There are essentially three types of esters available to the lubricant formulator: 1. natural esters 2. synthetic oleochemical esters 3. petrochemical esters
Natural esters were the source of the first lubricants ever used and they continue to be highly valued in applications such as metalworking fluids, metal rolling fluids, hydraulic fluids, greases and chain saw lubricants. Natural esters include vegetable crops such as rapeseed, canola oil, olive oil, coconut oil and palm oil and animal fats such as tallow and lard.
Of all the different types of mineral oil and synthetic fluids available to the formulator synthetic oleochemical esters and petrochemical ester are by far the most diverse and versatile, a
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