With energy costs soaring and getting ready to blast off - should we be looking at synthetics from an energy savings or energy efficiency standpoint?

Are the energy gains significant?

Terry O

My gut feel is there is a lot more potential energy savings in the area of lubrication improvement than there is through machinery balancing (which was a recent topic on the vib board)

If we can make a bearing run cooler by changing the oil type, then we are saving energy.

I have heard a few anecdotal stories where changing to synth can decrease temperatures by 10C. I don't have many details.

Below is a thread where we talked through a lot of these issues, but there were more questions than answers:

http://maintenanceforums.com/eve/forums/a/tpc/f/3191034...241060221#9241060221

One question that remains somewhat unresolved for me is the role of viscosity index. If in the process of switching from standard to synthetic oil we increase viscosity index but keep the viscosity grade constant, that would suggest to me that the viscosity would likely be higher at operating temperature.... which works against you (generates more het). I guess I can overlook this aspect for rolling bearings and gearboxes where viscosity may not be the most important parameter in determining friction (lubricity and pressure-viscosity coefficient are more important). But in sliding bearings, it seems to me that the heat generation is directly related to viscosity-dependent shear, so I have a hard time understanding how the savings could occur for sleeve bearings unless we decrease the viscosity grade.

I'll be interested to hear others comments on improvements in temperature or efficiency when switching lubrication (other than viscosity grade changes)

Very interesting discussion electripete - I must have missed it as it was going on.

I think we will be hearing much more from the marketers on the energy savings from Synthetics so I wanted to get ahead of the curve.

Anyone else have information.

Terry O

An interesting article here:
http://www.machinerylubrication.com/article_detail.asp?...ookgroup=Lubrication

The beginning of Case 1 mentions a gearbox experienced ~ 1% gain in efficiency when converting to synthetic (PAO) oil of the same viscosity grade and ~3% when converting to synthetic oil of a lower viscosity grade. This addresses my question above somewhat... when switching to synth oils on equipment that operates well above 40C, we need to take advantage of the higher viscosity index by lowering the viscosity grade if possible (if we don't, then the high viscosity index becomes a disadvantage because it tends to create higher operating viscosity at high temperatures). Later in case 1 they mention 8 - 10% improvements in efficiency (one wonders what efficiency was before the change). Case 2 mentions 10C improvement on some gearboxes.

Is it increasing the designed efficiency of the machines or getting the operating efficiency of the machines back to their designed efficency?

ElectricPete: Is it the metal-on-metal friction of the gears that is at issue with these gearboxes? When you first mentioned a few messages ago that the viscosity difference would be seen primarily by sliding contact situations, rather than roller bearings, etc., my first thought was that there were relatively rather few non-rolling bearings left in the average plant. However, the sliding of gears is pretty much universal, and if switching from 220 to 150 cSt oil, for instance, in the large gear reducers (100 - 500HP input) could make a significant difference in efficiency then it's very much worth looking at for me in my plant.

When I was talking about rolling vs sliding, I was referring to the difference between elastohydrodynamic (rolling) and hydrodynamic (sliding) lubricaiton. Hydrodynamic lubrication seems to me simpler and more predictable and more directly predictable with changes in viscosity. Elastohydrodynamic lubrication also improves, but the mechanisms are more complex and involve not just change in viscosity but also lubricity and p/v coefficient. In that respect, I put gears in the same category as rolling bearings (elasohydrodynamic).

In searching on machinerylubrication and looking through my own references, it seems like there are a lot of articles addressing energy saving lubrication improvements on gears than on bearings. I think the reason is that gears (at least certain types such as worm gears anyway) are much less efficient to begin with (numbers mentioned around 70% which if I'm understanding right means that 30% of the energy transmitted through the gears are lost as heat! Not all gears are this low I'm sure. Rolling bearings aren't directly rated in efficiency since they don't directly transmit power, but I think the losses in a rolling bearing might typically be 1% or less of machine output.

Here are two more article excerpts:


HANDBOOK of LUBRICATION and TRIBOLOGY - Application and Maintenance
Vol 1, 2nd Ed
ISBN 0-8493-2095-X


Improved energy efficiency may also be realized through the use of synthetic lubricants, especially in wormdrive applications (Table 23.7). Relative to mineral-derived lubricants, synthetics have a greater film thickness at high temperatures due to their higher viscosity index [33]. In rolling element bearings this can result in afourfold increase in bearing life [34].
TABLE 23.7 Comparison of Efficiency of Lubricants in Worm
Gear Applications
Lubricant Viscosity index Percent efficiency (%)
ISO460 Mineral oil 95 60
ISO460 Polyalphaolefin >150 68
ISO460 Polyalkylene glycol >220 78
Source: Lauer, D.A., Gear Solutions, August 2004, pp. 21–30.



Practical Lubrication for Industrial Facilities by Bloch ISBN ISBN 0-8247-0407-X

Properly formulated special synthetic gear lubricants will not only improve gear
efficiency; their anti-wear additives can optimize the gear's wear behavior. Figures 14-6
and 14-7 show the efficiency and wear curves of synthetic Klüber lubricants and mineral
hydrocarbon oil. The pertinent worm gear had a center distance of 63 mm, a worm speed
of 350 rpm and a drive torque of 300 Nm.

[Figure 14-6 shows Klubersynth GH 6-460~75%; Kluberoil 4 US-1460~70%, Klubersynth GEM 4-460 ~ 65% and Mineral oil ~ 60%.]

quote:

Originally posted by electricpete:
ISO460 Mineral oil 95 60
ISO460 Polyalphaolefin >150 68
ISO460 Polyalkylene glycol >220 78
Source: Lauer, D.A., Gear Solutions, August 2004, pp. 21–30.

Maybe I'm reading this wrong, but doesn't this except show a higher efficiency for thicker oil? I'm assuming that the 150 and 220 are the viscosity in centistokes. Granted the two oils have a different base...

Sorry, this is a table that was a lot easier to read before I cut/paste it as text format.

All three oils are ISO VG 460. The viscosity indexes are 95, 150, 220. The efficiencies are 60, 68, 78.

I have read a few studies on mechanical efficiency when switching to synthetics.

Our company advertises 3-5% on fuel economy, and if you read anything about the MEHF for mobile hydraulic equipment it's about 6 to 15% in efficiency.

http://www.mehf.com/

Michael - is the main feature of that product that improves hydraulic system efficiency the high viscosity index (low change of viscosity with temperature)? Anything else about the product that improves efficiency?