Aluminum Grease Best?
- Thread starter willbur
- Start date
I dont believe so. it could be more common for it to be like that itd be best to dive into product sheets.
Valvoline is probably a good place to start. they make a ton of greases it wouldn't surprise me if they have a dozen different ones or more and they always give lots of data sheets.
Valvoline is probably a good place to start. they make a ton of greases it wouldn't surprise me if they have a dozen different ones or more and they always give lots of data sheets.
In research I did LONG ago, I chose to use aluminum based grease in the wheel bearings of my boat trailer. Keep in mind I did not pull that trailer very far, or very fast, which may have influenced my decision.
My choice was based on having read that aluminum based grease is the most water repellent grease in fresh water (saltwater may change that, I don't know)
I do know that after replacing those bearings and the grease with that blue aluminum stuff, I never had an issue.
I thought of it this way, Lithium and Moly based greases are "sort of" a soap based grease. Whereas Aluminum based is not, and less prone to water dilution.
My choice was based on having read that aluminum based grease is the most water repellent grease in fresh water (saltwater may change that, I don't know)
I do know that after replacing those bearings and the grease with that blue aluminum stuff, I never had an issue.
I thought of it this way, Lithium and Moly based greases are "sort of" a soap based grease. Whereas Aluminum based is not, and less prone to water dilution.
Aluminum thickeners are also a soap.
https://www.nyelubricants.com/choosing-the-right-grease-thickening-system
https://www.nyelubricants.com/choosing-the-right-grease-thickening-system
Thanks.
Aluminum and lithium thickeners, both simple and complex are soaps. It is true that their fiber structure will vary. Moly is not a thickener. As MoS2 it is a lubricating solid.
Thanks, all-helpful and informative but my original Q was does aluminum grease contain more lubricating oil than the others? Ideas?
The level of thickener in lithium complex and aluminum complex are probably comparable with a slightly higher soap content in the LiX. It really depends on a lot of factors and in a manufacturing environment oil or soap content will vary based on oils used, additive effects and process method.
I think when you are referring to the “oil mesh” theory of grease lubrication in which the soap forms a mesh. Oil and additives are held in the free spaces and squeezed into the contact area under pressure where they lubricate. I think this theory is from the early 1950s. The first I saw it was in a book called Manufacture and Application of Lubricating Grease (1954) by Charles Boner.
If the theory was completely true you would expect the lubricating film in the contact area to be oil and additives. However, in 1999-2000 a PhD. candidate at the Imperial College of London Tribology Research Center named Susan Hurley studied the composition of the grease film in the contact area using an interferometer to form a loaded film and reflective infrared spectroscopy to identify the composition of the film. She found the typical film composition to be oil, additive and thickener. The conclusion was that the thickener actively participated in lubricating the contact and not just the oil and additives.
Today, most people still refer to the oil mesh theory as the primary grease method of lubrication despite evidence suggesting something else.
Thanks- has Ms. Hurley's research/theory been accepted in the lubricant's community?
As with anything new or different, it's a matter of time and additional work in that area before an idea is accepted as fact. The work has been recognized amongst grease researchers...it's hard to completely refute an idea if the research appears to be solid and performed at one of the leading tribology centers in the world. I read the thesis as my boss at the time was president of the organization that funded to research. It was long, very informative and, I thought, reasonable. It was the most reasonable concept of the mechanism of a grease in contact that I've seen to replace the old mesh theory.
I may be wrong but one reason I suspect that the old mesh theory of the oil and additives being forced from the interstices by pressure to lubricate the loaded surfaces may not be true is Darcy's Law. One of the points of this law is that fluid flows through a bed of sand, in the case of grease it is oil through a tangled mass of soap fibers, is from high pressure to low pressure. In the case of a loaded region of a bearing the pressures I suspect that forces are equal of nearly equal through the contact and the lubricant in the spaces. In other words, there is no high pressure region or low pressure region. Pressures are likely equal so flow should be none to minimal. I expect this to be true but I'm not certain and I'm no longer in a position to test it or have it tested.
I only put it out there as an alternate to the earlier theory.
Thank you-
Darcy Q=KiA. The K (hydraulic conductivity) of the "mesh" walls (A) remains constant and "i" the gradient also must remain constant(zero) if no flow across the mesh boundary despite the loads being imposed on the mesh. So, the researcher is saying the applied load is the same on the mesh and oil trapped within. But the loaded mesh (and trapped oil within) has a higher pressure than the adjacent non loaded mesh, releasing oil, unless the mesh walls can resist this induced pressure. Interesting but seems counterintuitive
All I really wanted to know was does AL grease contain more lubricating oil than others and not venture into hydrodynamics LOL
As my original e-mail stated "The level of thickener in lithium complex and aluminum complex are probably comparable with a slightly higher soap content in the LiX. It really depends on a lot of factors and in a manufacturing environment oil or soap content will vary based on oils used, additive effects and process method."
The researcher did not address the pressure gradient. she only looked at film thickness and film composition. I made the assumption that the pressure in her model was in one direction, perpendicular to the surface and essentially constant through to contact and film. In the oil bleed model Darcy's Law is accepted model to account for oil flow. The alternate model saw soap (thickener) as a primary component in the film when they anticipated little or none. One way to account for this is that the oil that may have flowed from the high pressure contact to the adjacent low pressure areas. It did not flow into the contact and did not displace the soap-containing film already there. They also found other compounds including esters which they attributed to decomposition of the soap.
Although this is an interesting alternative to the mesh theory, the mesh theory remains the primary model and little significant work has be done on the alternate model.
RDMgr makes some great points. I think it is true that more oil can be saturated in an aluminum complex soap than other types of thickeners. However just because it can does not mean that is what the manufacturer did. Of course the other things to consider is what the water wash out properties are and ultimately the base oil and additives in the oil doing the work for you are important. Tackifiers are also a good additive to allow the grease to stick in a wet environment. Using a properly formulated a aluminum complex grease can be an excellent choice for your application.
Thank you for the insights. Interesting stuff...
One problem with aluminum complex grease is bleed. Lithium greases have large twisted and tangled fibers, maybe 25 microns by 3 or 4 microns which hold base oil. Aluminum complex fibers are much smaller and are often spheroidal rather than true fibers where length is much greater than width. As a result aluminum complexes can have trouble holding oil. Another problem that results in oil separation is syneresis. This occurs during long term storage when the soap shrinks. This creates an internal pressure that squeezes oil out of the mass. These can be greatly improved by formula and processing.
And more interesting stuff... LOL