MolaKule
Staff member
The advantages to synthetics (PAO's in this case) is that the PAO molecules have a narrow distribution of different molecules of nearly the same size for a particular viscosity, whereas the mineral oils have a wide distribution of many different types of molecules of different sizes (differing molecular weights).
In general, the molecular weight of lubricants will increse with viscosity.
If I mix for example 24% PAO of 8 cSt viscosity and 52% PAO of 40 cSt viscosity I will obtain a fluid of about 16 cSt viscosity@100 C with a minimum VI of 145. This is in essence a 10W40 without any VII's.
Mixing 23% PAO of 8 cSt viscosity with 51% PAO of 100 cSt viscosity gives me a viscosity of 27 cSt@ 100 C with a minumum VI of 150. This is in essence a 20W50 without any VII's.
Mixing 23% PAO of 4 cSt viscosity and 51% PAO of 100 cSt viscosity would give me approximately a 5W50, albeit the CCV might not be what I want.
Mixing different percentages of those same viscosities as the examples above would yield different viscosities as well. The percentages are affected by the application, such as, is the lubricant for engine oils or for gear lubes.
Of course, all of the above are simply virgin base oils. For a fully formulated oil, the consideration of additive package viscosity would have to be included.
Now with mineral oils, I usually have to have three or more oils of differing viscosities to obtain an equivalent viscosity because of each weights narrow viscosity range.
To further complicate things, most of the mineral oils I would use would have to be paraffininc types (for thermal stability) and I would have to add a certain percentage of naphthenic oil of specified viscosity to make the oil more soluble for the additive package, since straight paraffininc oils aren't very miscible with additives.
For synthetic oils using primarily PAO base oils, I have to add an ester (of a specified viscosity) to increase additive solubility and to increase seal swell slighly. However, this last issue has become less of a problem since many additives are now in ester bases or are "esterified" already, such as the dispersants, which are succinimide esters, and for secondary AW additives such as the new boron esters. As you will see in the QOTD section, many EP additives, such as tricresyl phosphate and triphenyl phosphate, have been in ester format for many years.
For a majority polyolester base (such as jet engine lubricant), I would simply select the ester for the target viscosity and then include a small amount of additives, since most additives are miscible in esters.
[ September 05, 2004, 12:39 PM: Message edited by: Patman ]
In general, the molecular weight of lubricants will increse with viscosity.
If I mix for example 24% PAO of 8 cSt viscosity and 52% PAO of 40 cSt viscosity I will obtain a fluid of about 16 cSt viscosity@100 C with a minimum VI of 145. This is in essence a 10W40 without any VII's.
Mixing 23% PAO of 8 cSt viscosity with 51% PAO of 100 cSt viscosity gives me a viscosity of 27 cSt@ 100 C with a minumum VI of 150. This is in essence a 20W50 without any VII's.
Mixing 23% PAO of 4 cSt viscosity and 51% PAO of 100 cSt viscosity would give me approximately a 5W50, albeit the CCV might not be what I want.
Mixing different percentages of those same viscosities as the examples above would yield different viscosities as well. The percentages are affected by the application, such as, is the lubricant for engine oils or for gear lubes.
Of course, all of the above are simply virgin base oils. For a fully formulated oil, the consideration of additive package viscosity would have to be included.
Now with mineral oils, I usually have to have three or more oils of differing viscosities to obtain an equivalent viscosity because of each weights narrow viscosity range.
To further complicate things, most of the mineral oils I would use would have to be paraffininc types (for thermal stability) and I would have to add a certain percentage of naphthenic oil of specified viscosity to make the oil more soluble for the additive package, since straight paraffininc oils aren't very miscible with additives.
For synthetic oils using primarily PAO base oils, I have to add an ester (of a specified viscosity) to increase additive solubility and to increase seal swell slighly. However, this last issue has become less of a problem since many additives are now in ester bases or are "esterified" already, such as the dispersants, which are succinimide esters, and for secondary AW additives such as the new boron esters. As you will see in the QOTD section, many EP additives, such as tricresyl phosphate and triphenyl phosphate, have been in ester format for many years.
For a majority polyolester base (such as jet engine lubricant), I would simply select the ester for the target viscosity and then include a small amount of additives, since most additives are miscible in esters.
[ September 05, 2004, 12:39 PM: Message edited by: Patman ]
