3 questions to ask yourself when choosing the right fat
By Bardahl • The 6/10/2021 • 5 min reading
Greases and pastes are made up of a base oil (mineral or synthetic), a thickener (also called 'soap') and additives. Grease works like a sponge: as soon as the 'soap' is put under pressure by the mechanics, it releases the oil (made up of additives) in order to lubricate. Although each type of soap (calcium, lithium, PTFE, polyurea, etc.) has its own particular properties, oil remains the most important component.
You now understand how grease works. But how do you choose it? Simply by asking yourself the questions below.
What environment?
You need a grease and you know what environment you're going to use it in: is it dry, damp or dusty? Can the grease stick together or not? Should it be water-resistant? These questions form the basis of your purchasing decision.
At what temperature?
Some greases can't stand extreme cold (-30°C) and others will lose all their properties once they've got too hot. That's why it's always useful to know at what point the grease will heat up or cool down in the mechanism. The breaking point is called the "dropping point". Once this temperature is reached, the grease will no longer have any lubricating properties. The label will usually give you a minimum and maximum operating temperature.
You should also pay attention to the storage temperature, especially when cold, as the grease may harden.
What resistance (weight and speed)?
When it comes to strength, the needs of the DIY world and the world of industry can be radically different. Under 280 kg in the 4-ball test (welding), we're not talking about extreme pressure. In the industrial world, certain greases are capable of withstanding well over 500 kg.
The 4 ball test
In industry, the 4-ball test is used to determine the anti-wear and extreme pressure properties of a grease. In this test, 3 steel balls are held in a bowl containing the grease. A 4th ball is rotated on top of the other 3. The load, maintained at 40 kg for one hour for the wear test, is gradually increased to determine the load that welds the 4 balls together.
Another decisive factor in choosing the right grease for the job is whether the movement it is going to lubricate encounters low or high rotational speeds. Low rotation speeds are below 100,000 n.dm and very high rotation speeds above 500,000 n.dm (n = number of rotations; dm = average bearing diameter).
A few more tips
The above technical questions are essential if we are to maintain the mechanics correctly and make them last. To these we can add 3 further thoughts:
- How will I apply the grease: tube, jar, cartridge, etc.? Different formats are often available. Think practical!
- Not all greases are miscible with each other. This means they can't be mixed. Keep this in mind. When you change grease, a thorough cleaning is a good idea.
- Finally, as with motor oil, the quantity of grease is crucial: not too much, not too little! In fact, too little grease prevents proper lubrication and too much grease can hinder the mechanisms, requiring them to expend more energy and leading to abnormal wear or, worse still, breakage.