What is Microdieseling?

Microdieseling is also called Compressive Heating and is a form of pressure induced thermal degradation.

The oil goes through 4 stages in this degradation process:

1. There is a transition of entrained air from a low pressure to a high pressure zone

2. This produces localized temperatures in excess of 1000°C

3. The Bubble interface becomes carbonized

4. The oil darkens rapidly and produces carbon deposits due to oxidation

The conditions required for microdieseling can be either:

Low flashpoint with LOW implosion pressure
Low flashpoint with HIGH implosion pressure

For a low flashpoint with a HIGH implosion pressure, this constitutes to ignition products of incomplete combustion such as soots, tars and sludge

However, for a low flashpoint with a LOW implosion pressure, adiabatic compressive thermal heating degradation occurs to produce varnish from carbon insolubles such as coke, tars and resin.

Lubricant Degradation

What is Electrostatic Spark Discharge?

Electrostatic Spark Discharge is real and extremely common for turbine users!

Static electricity at a molecular level is generated when dry oil passes through tight clearances.

It is believed that the static electricity can build up to a point whereby it produces a spark.

There are three stages of ESD.

1. Static Electricity builds up to produce a spark – Temperatures exceed 10,000°C and the lubricant begins to degrade significantly.

2. Free radicals form – These contribute to the polymerisation of the lubricant

3. Uncontrolled polymerisation – Varnish and sludge produced (some may remain in solution or deposit on surfaces) which can also result in elevated fluid degradation and the presence of insoluble materials.

Grease

Grease compatibility

Are all greases compatible?

We recently touched on greases being available in a wide variety based on application but the real question is, “Are all greases compatible?”

The short answer is, “No”.

All greases contain a thickener (which helps with its physical state). Thickeners vary depending on application (such as temperature, water resistance etc). As such, to verify whether two greases are compatible or not, Machinery Lubrication developed a Compatibility Chart based on thickener type.

You can determine the thickener type by looking at your Data Sheet or talking to your OEM.

Not all greases are compatible, so be careful when mixing greases!

Grease

Grease Thickener Types

Grease Thickener Properties

We keep speaking about each grease being different based on their thickener type. However, what are the properties that these thickeners give to the grease?

For instance, if I wanted to use a grease for a roller bearing in a very high temperature environment which should I choose?

Can a multipurpose grease work for that application?

Each area of application may be different and while multipurpose greases are widely used there are some areas where it doesn’t add much value. For example, if a heavy equipment operator uses a backhoe to dig into a river, the multipurpose grease can be easily washed off.

When the grease washes off quickly, the pins holding the bucket can become damaged. (The costs to repair or replace one of these pins are ridiculously high!) However, if he used a Calcium based grease, then there wouldn’t be an issue of water washout and the pins could have a longer life.

Above is a table indicating the various uses of greases based on the thickener types. Know your applications and their environments when choosing the right grease!

Grease

Base oil viscosity of greases

Importance of Base oil Viscosity in Greases

While we’ve focused on the variances in greases due to thickener types, we haven’t touched much on the differences in base oil viscosity.

With gear oils, we need the correct viscosity to allow the gears to turn at the required rate while still being lubricated. If the oil is too thick and the gears are high speed, then the gears will not be lubricated quickly enough and they can become damaged. Similarly, greases are made up of base oil with different viscosities.

Most greases use a viscosity of 220cSt (these are the multipurpose greases). However, greases for electric motors use a base oil viscosity of 100cSt. What’s the difference?

Well, if a multipurpose grease was used for an electric motor the energy used for that motor can be 100W however, if a grease with a base oil viscosity of 100cSt was used, the energy used could be reduced to 70W. Is this significant? Definitely YES!!!

On any manufacturing plant, there are at least 5 – 10 electric motors, in some cases there are 70 or more! If at least 25W were saved per motor per month then the company can a significantly reduced power bill at the end of the year!

Understand your applications before applying “any” grease!

Grease

Grease Thickener Temperatures

Understanding Grease Thickener Temperatures

The grease thickener has a crucial role in deciding the environment in which a grease should be applied.

One of the major environmental conditions revolves around the operating temperatures that greases have to endure.

If the grease goes past its dropping point then it can turn into a liquid, leak out of its designated area and cause the element to be starved for lubrication. Not to mention the mess on the outside of the component after it has leaked out.

Each thickener has a range of operating temperatures. However, some consideration should be applied when designating areas for the application of the grease. As indicated above, a good rule of thumb is to ensure that the application range of the grease does not exceed the Dropping point - 50C. For example, a good operating range for a simple Lithium grease can be 175-50C = 125C. This still falls within the maximum service temperature for a grease with this thickener.

Pay careful attention to your operating temperatures when selecting your grease!

Grease

Understanding NLGI

Does the NLGI grade matter?

Of course it does! That’s why it was invented and classed into different categories for various applications! NLGI stands for National Lubricating Grease Institute, they are composed of companies that manufacture and market all types of lubricating grease.

An NLGI grade can start at 000 (very fluid) to 6 (block like). However, there are different grades for different applications.

For instance, most trucks have a centralized lubrication system. As such, the grease needs to be almost fluid like to get to all the areas. In these cases, a “00” or even “000” grease may be used. However, the most common grade is a “2” grade which is seen frequently in cartridges, pails etc. Some electric motors require a “3” grade grease instead of a “2”.

Here is a table that describes each of the grades, their applications and consistency.

Always check with your OEM to ensure that the correct NLGI grade is being used! Here is another graphic that likens these grades to more easily identifiable consistencies.

Storage & Handling of Lubricants

Colour Coding

What is the importance of Colour Coding?

Quite often when we are correcting or helping companies set up their lubrication storage areas, we get asked a lot of questions regarding colour coding.

Ideally, the concept of colour coding is to allow field personnel to easily identify and associate particular lubricants with their applications.

However, like most things in reliability, this can be customized to suit your organization. There are no hard and fast rules of using only yellow to represent hydraulic oils.

What if we had someone that was colour blind?

Usually, when we start colour coding lubricant storage containers, we include symbols and actual names of the lubricant. This helps to assist personnel in having a 3 point verification system.

First they can verify the colour, then the symbol and of course the name of the lubricant.

Names are crucial! Especially for varying viscosities (such as gear or hydraulic oils). For instance all gear oil would have the same colour and symbol but you wouldn’t want to put an ISO 100 gear oil in a gearbox suited for ISO 680.

Storage & Handling of Lubricants

Lubrication Audit?

Audits usually get people nervous! They are worried about what the auditor may or may not find. When we perform lubrication audits, we’re trying to ensure that your equipment is using exactly what it should to perform efficiently.

Why is that necessary? We’ve found that in most organizations, there may have been a time when the OEM recommended lubricant was not readily available and a substitute was used instead. Once the substitute has been used, it magically becomes the recommended lubricant for the rest of the life of the component.

However, if proper checks were not done initially, then the component could be using the wrong lubricant for most of its life. This can contribute to downtime and replacement of parts before their actual useful life has been reached.

Once, we found a gearbox using an ISO 680 gear oil when it should have used an ISO 320 oil. This gearbox used the wrong oil for 30 years! It greatly impacted the efficiency of the gearbox and they experienced numerous breakdowns throughout its life but they never understood or dared to look at the lubricant.

Always ensure that you have the OEM recommended lubricants for your components!

Used Oil Analysis

ISO 4406

A lot of people get confused when reading the ISO 4406 rating. The rating specifies a range of the number of particles of certain sizes that can pass through 3 particular sized filters namely; 4micron, 6 micron and 14 micron filters respectively.

For instance; a rating of 13/11/8 indicates:

13 represents 4000-6000 particles over the size of 4um
11 represents a range of 1000-2000 particles over the size of 6um and
8 represents a range of 130-250 particles over the size of 14um.

These values are actually the number of particles per milliliter. It does not mean that you have 13, 11 or 18 particles only in your oil, it's much more than that!

There are different ratings for different levels of cleanliness.

If your numbers are really high (25/22/19) then there’s definitely a high level of contamination!

Different components have different ISO cleanliness ratings. For instance, a roller bearing has a higher cleanliness target than a Variable Vane pump.

Understanding the ISO 4406 codes are crucial for determining the steps needed in “cleaning up” your system lubricants.

However, when we test for the cleanliness of an oil, there are a couple things that we need to consider:

When testing, we have exposed the oil to the elements (highly dependent on the method of sampling)
Results are not instantaneous (even with an onsite lab, there will be a timeframe between collecting the sample and processing it)

Since there are lag times involved, the value that is reported for the ISO4406 rating is never really truly representative of the oil. As such, when analysing the results of this test, it is important to consider that the actual value may potentially be higher than reported.

Matt Spurlock CLS, CMRP, MLE explains further about redefining the ISO code in his article entitled; "A Twist on Particle Evaluation: Redefining the ISO Cleanliness Code".

Tagged: lubricants

What is Microdieseling?

What is Electrostatic Spark Discharge?

Are all greases compatible?

Grease Thickener Properties

Importance of Base oil Viscosity in Greases

Understanding Grease Thickener Temperatures

Does the NLGI grade matter?

What is the importance of Colour Coding?