# Friction: aluminium on carbon

nilsvoorkamp1
I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
It's nowhere to be found on the internet.

Homework Helper
Gold Member
Summary:: I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
It's nowhere to be found on the internet.

on carbon.
Graphitic? Amorphous? Diamond?
Summary:: I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
It's nowhere to be found on the internet.

greasy aluminium
Anodized? Hard? Soft?

berkeman
Summary:: I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
It's nowhere to be found on the internet.

I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
It's nowhere to be found on the internet.

You could also try to measure it yourself.

berkeman
Mentor
I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
0.15 +/- 0.03

You're welcome.

anorlunda
nilsvoorkamp1
0.15 +/- 0.03

You're welcome.
Do you have the source of where you find this number?

nilsvoorkamp1
Graphitic? Amorphous? Diamond?

Anodized? Hard? Soft?
hard

Cutter Ketch
Summary:: I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
It's nowhere to be found on the internet.

I need the coefficient of kinetic friction for movement between greasy aluminium on carbon.
It's nowhere to be found on the internet.

Greasy? As in lubrication? Your answer is going to be more about the grease than the aluminum and carbon. Although the texture of the aluminum and carbon will have effects on the grease, the coefficient of friction will depend on the viscosity of the grease which will in turn depend on the temperature and pressure (and of course the make up) of the grease. Heck, it will depend on how old the grease is and how long it has been working. This information will be measured. It can’t reasonably be calculated. The only place you will find published tables for the measured behavior of a lubricating grease will be from the manufacturer of the grease.

As an example, here is a paper turned up in a quick internet search that highlights the complexity of the behavior of the coefficient of friction of lubricating grease.

https://res.mdpi.com/d_attachment/l...-00042/article_deploy/lubricants-05-00042.pdf

anorlunda
0.15 +/- 0.03

You're welcome.
I suspect it's more like 0.15+/- 0.5, depending on the details of the grease and the surfaces. I don't think you can nail it down nearly that precisely without more information.

berkeman
nilsvoorkamp1
I suspect it's more like 0.15+/- 0.5, depending on the details of the grease and the surfaces. I don't think you can nail it down nearly that precisely without more information.
Do you have a source for that?

Mentor
There is no such thing as an exact coefficient of friction between two materials. The friction is a function of the materials, their surface properties, surface roughness, surface topology, speed, load, lubricant properties, amount of lubricant, entrance conditions (is the leading edge sharp or upturned like a ski?), and more. Some search terms are Stribeck curve, tribology, friction, and coefficient of friction.

There is an SAE paper, 950698, titled Variation of Friction in a Strip Test Apparatus with Controllable Drawbead Penetration, that goes into the reasons why the friction coefficient changed (for example) from 0.15 to 0.075 and back to 0.15 during a single test. It was not due to the Stribeck curve. And it was repeatable with different materials, lubricants, and test conditions.

If you need a reasonably accurate friction coefficient, you will need to do your own testing.

berkeman
Do you have a source for that?
No, but I don't think I need a source for saying that the friction coefficient can vary widely depending on the details of the grease, surfaces, etc.

berkeman
nilsvoorkamp1
No, but I don't think I need a source for saying that the friction coefficient can vary widely depending on the details of the grease, surfaces, etc.
I'm talking about the value 0.15. I understand the number is not exact but that's ok. So i just want to put it in my project but I can't do that without showing where I got it form besides an internet forum.