Basics of lubricating oils

In the first part of our training Basics of lubrication technology, we wrote about friction and wear as well as the various types of lubricants. In this part, we want to provide information on the basics of lubricating oils. It is to give you an overview of what lubricating oils are, what their structure and composition is, what types of oils there are and what benefits and drawbacks each one of them have.

What is a lubricating oil?

Lubricating oils are fluid media which act as intermediate substances depending on the frictional condition of the friction point, and normally assume the function of a design element. They are one of the most important types of lubricants and are also vital components when making lubricating greases.

"Oils" are fluid organic compounds, which have to meet various quality requirements depending on their intended use. Which requirements a lubricant must meet depends on the specific application.

1. Reduction of friction
2. Reduction of wear
3. Reduction of energy losses
4. Increase of service life using synthetic oils
5. In line with food law
6. Readily biodegradable
7. Corrosion protection
8. Heat transfer medium
9. Coolant of heat dissipation medium
10. Reduction of maintenance costs

What is the composition of a lubricating oil?

Depending on the intended use and field of application, the formulation of a lubricating oil comprises the following ingredients:

What is viscosity?

The viscosity is a measure for the thickness of a fluid. Viscosity is also referred to as the internal friction of a fluid. The higher the viscosity, the less capable of flowing is the fluid (e.g. honey). The lower the viscosity, the thinner is the fluid, i.e. capable of flowing quicker under the same conditions (e.g. water). The viscosity of an oil changes as a function of temperature. At low temperatures, oils become more viscous, at elevated temperatures they become thinner. Engine and vehicle gear oils are classified acc. to SAE classes, industrial oils acc. to ISO viscosity grades (ISO VG).

Which ISO viscosity grades (ISO VG) are there?

According to DIN 51519 there are 18 different viscosity grades. Every viscosity grade is determined for a temperature of 40°C (V40).

Viscosities and their uses in practice

1. Low viscosity oils (ISO VG 2 - 100):

These are used as penetration oils, rust dissolvers, hydraulic oils, compressor and vacuum pump oils or low-temperature oils for components like chains, bearings and gears.

1. Medium-viscosity oils (ISO VG 150 - 460):

These are used as gear and chain oils in industry.

1. High-viscosity oils (ISO VG 680 - 1500):

These are used as adhesive oils for low-speed open drives and gears or for chain lubrication.

What are the most common industrial base oil types?

1. Mineral oil (paraffinic, naphtenic and aromatic) (MIN)
2. Polyalphaolefins (PAOs)
3. Ester oils (E)
4. Polyalkylene glycols (PAG)
5. Silicone oils
6. Perfluoropolyether oils (PFPE)

What is a mineral oil?

Mineral oil is made from crude oil by means of distillation and refining. It consists of hydrocarbon compounds. Depending on the molecular composition, we classify them into paraffinic, naphtenic and aromatic mineral oils.

There are applications where an inexpensive mineral oil can be a wise choice. It should generally be noted, though, that a high-performance synthetic oils is often economically more viable in the long term.

Price ranges of mineral vs. synthetic oils

What is a polyalphaolefin oil?

Polyalphaolefins are synthetic hydrocarbons (SHC) made from ethylen as the starting material. For this reason they are often referred to as "synthetic mineral oils". Polyalphaolefins consist of iso-paraffins with varying numbers of hydrocarbon side chains of the same length.

What is an ester oil?

Ester oils are synthetic lubricants. Esters are chemical compounds originating primarily from the reaction of acids (mostly organic/fatty acids) and ethanol, going along with the removal of water.

What is a polyalkylen glycol oil?

Polyalkylen glycols, also known as polyglycols, are polymerised ethylen oxide or propylen oxide entities or combinations thereof started by addition to an ethanol. For their solubility in water, the ethylen oxide content is what matters most.

What is a silicone oil?

Silicone oils are polymerised siloxanes with organic side chains. They are made by means of chemical synthesis, with silicon being their main component. Due to their excellent penetration and spreading behaviour, they are used as sliding agents, defoaming agents, sealing and hydraulic fluids, or as high-end lubricants. Silicone oils are clear, colourless, neutral in odour and taste and non-toxic.

What is a perfluorinated polyether oil?

Perfluorinated polyether oils are synthetic oils made up of carbon, fluorine and oxygen. They are used where stresses are extreme (e.g. at very high temperatures and pressure) and are resistant to most aggressive media.

Which base oils are intermiscible?

The following table serves for rough guidance. For a reliable determination of oil miscibility, we would in any case recommend to have corresponding tests conducted at the lubricant manufacturer.

What are additives?

Additives are soluble substances added to an oil to enhance its chemical and physical characteristics.

What additives might be added to industrial oils?

What are solid lubricants?

Solid lubricants are minute particles and flakes that are added to lubricating oils, greases and pastes. They smoothly slide against one another, thereby reducing friction. The most common solid lubricants are graphite, MoS2, ceramics and PTFE.

What are the characteristics of additives and solid lubricants?

Do you wish to acquire more in-depth knowledge of the subjects tribology, lubrication technology and lubricants?

Then the trainings offered by Klüber Lubrication might be an option for you. Twice to three times per year, we offer two-day trainings in Munich. Alternatively, you can order individual trainings tailored to your needs on the subject of "lubrication and lubricants" to be held on your premises.

Do you have any questions or need consulting?

Klüber Lubrication can look back on more than 90 years of experience in the fields of friction optimisation and specialty lubricants. We will be pleased to provide personal advice for your specific requirements regarding refrigeration compressor oils.

This is how you can reach us:
Stefan Zuber
Global Business Team Compressors
Phone: +49-89-78 76 502
Email: Stefan.Zuber@klueber.com

Website: www.klueber.de

Editor and copyright: Klüber Lubrication München SE & Co. KG
Reprints, total or inpart, are permitted only prior consultation with Klüber Lubrication München SE & Co. KG and if source is indicated and voucher copy is forwarded. The data in this document is based on our general experience and knowledge at the time of publication and is intended to give information of possible applications to a reader with technical experience. It constitutes neither an assurance of product properties nor does it release the user from the obligation of performing preliminary tests with the selected product. It constitutes neither an assurance of product properties nor a guarantee of the suitability of the product for a specific application. They do not release the user from from the obligation of performing preliminary field tests with the product selected for a specific application. All data are guide values which depend on the lubricant's composition, the intended use and the application method. The technical values of lubricants change depending on the mechanical, dynamical, chemical and thermal loads, time and pressure. These changes may affect the function of a component. We recommend contacting us to discuss your specific application. Products from Klüber Lubrication are continually improved. Therefore, Klüber Lubrication reserves the right to change all the technical data in this document at any time without notice.

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Munich District Court, HRA 46624