Thank you very much for the support you all extended to me by liking & sharing the article with your network. We have already shared the Basics of Friction, Wear & Lubricants. Also, if you are following our articles, you may read our article on Tribology, Tribosystem & Lubrication. In both articles, we have shared What friction & benefits is & disbenefits of friction & also we have shared how you can reduce the bad effects of friction by using lubrication.
Nowadays, science has developed many new lubrication technologies that have outperformed conventional technology in a full-scale industrial application. So, today we will share about the Lubricants. But, before discussing the advanced version of lubrication technology, we need to know the basic method of lubrication & the basics of lubricants.
What is Lubricants?
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If you have gone through the Tribology, Tribosystem & Lubrication article, you may know what lubricants are. By the way, in the very simple word, “A lubricant is a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. The property of reducing friction is known as lubricity.”
Typically, lubricants contain 90% base oil (most often petroleum fractions, called mineral oils) and less than 10% additives & some solid lubricants (as per requirement 5 to 10%). In addition, vegetable oils or synthetic liquids such as hydrogenated polyolefin, esters, silicones, fluorocarbons, and many others are sometimes used as base oils.
Mineral Oil: –
Mineral oils are produced from refined hydrocarbons obtained from crude oil by distillation.
Synthetic oils are manufactured polyalphaolefins, which are hydrocarbon-based polyglycols or ester oils.
Although there are many types of lube oils to choose from, mineral oils are the most commonly used because the supply of crude oil has rendered them inexpensive. Another advantage of mineral-based lube oils is that they can be produced in a wide range of viscosities. Now, if we discuss lubricating oil, we need to know about Viscosity & Viscosity Index.
What is Viscosity:
In normal words, Viscosity is the resistance of any fluid to flow. When any fluid is flowing, then the internal molecules experienced friction due to internal molecular interaction. This means different viscosity fluids flow at different speeds when an external force is applied to them. More viscosity = Less Speed & Less Viscosity = More Speed.
As an example, you can take Water & Honey. Water viscosity is less than honey. So, with the same amount of external force applied, the water flow speed will be much higher than honey.
Types of Viscosity:
As we know, viscosity is the measure of the friction of fluids. There are two ways to measure a fluid’s viscosity as follows:
- Dynamic Viscosity (Absolute Viscosity)
- Kinematic Viscosity
Don’t be confused between the two viscosity measures and consider them to be the same. In reality, they have significant differences between them. For a few applications, kinematic viscosity is more useful than absolute or dynamic viscosity. We will discuss them at a later stage.
The unit of kinematic viscosity is Stokes, named after the British physicist, Sir George Gabriel Stokes. A stoke is defined as one centimeter squared per second.
The viscosity index (VI) is an arbitrary, unitless measure of the viscosity change with temperature, mostly used to characterize the viscosity-temperature behavior of lubricating oils. The lower the VI, the more the viscosity is affected by changes in temperature.
Lubricating grease is a mixture of three main components: lubricating fluid (Base Oil), performance-enhancing additives, and thickener. The lubricating fluid can be petroleum-derived lubricating oil, various synthetic lubricating fluids, or vegetable-based oil. The lubricating fluid is usually the majority component in the grease formulation. The additives are typically present in relatively low concentrations and are added to the grease to enhance multiple performance areas. The thickener is what sets grease apart from liquid lubricants or lubricating oils. This component gives the grease the property of consistency, making the product semi-solid rather than liquid. Many different chemical compounds can be used to thicken grease.
Tasks of a Thickener
- Thickens the oil
- Controls the release.
- Seals the friction point.
- Protects against moisture & dust.
What is NLGI Consistency Number
NLGI is a not-for-profit organization that serves the lubricating grease industry. The organization offers one of the most extensive and unique grease education programs in the industry. The NLGI consistency number expresses the relative hardness of grease used for lubrication, as specified by the standard lubricating grease established by the National Lubricating Grease Institute (NLGI).
A numerical scale for classifying the consistency of lubricating greases, based on the ASTM D217 worked penetration at 25°C
NLGI Consistency Number Worked Penetration Range, 25°C
Some grease suppliers use descriptions such as NLGI Number 1.5, which indicates that the grease is between NLGI Numbers 1 and 2.
I tried to cover some basics information about Lubricating Oils & Lubricating greases. If you have a question in your mind feel free to give us a shout via comment.