Gear lube nozzle placement

[EnglishMuffin]

I was once told by Ken Gitchel of UTS that the correct way to position gear lube nozzles is to direct them at the out-running side of the mesh, because there is actually a negative air pressure there. Does anyone else concur with this ? (In this case I am using oil-air lubrication).

 

[Carburize]

If we are talking high speed gears then this is correct - there is a partial vacuum produced at the out-mesh side which draws in the lubricant towrds the teeth. Spraying into the in-mesh of high speed gears can cause significant power losses.

 

[EnglishMuffin]

Well, I would think the power losses created by oil-air lubrication would be fairly small, regardless of nozzle placement. I also recall Ray Drago (another well known gear expert) telling me that there were counter arguments to the out-running mesh theory, but I can't remember what they were. There is also the "axial placement" possibility, especially in the case of helicals, which have an axial pumping action. Any more comments ?

 

[Carburize]

The losses are a big deal particularly in high speed power generation gear sets. These units are designed for continuous operation producing electrical power and fractions of a percent of ineffeciency add up to big numbers finacially over the life of an installation. Feeding into the in-mesh on these types of gears causes significant churning of the oil, the pumping action you describe on an apex-leading gear set can also lead to more losses and also high temperature rises towards the center of the gear.
Slow speed gears are a different situation and indeed may benefit from in-mesh oil feeding. I know Ray does a lot of work on slower speed steel mill and similar gearing and he may have been refering to this type of application in his comment.

 

[EnglishMuffin]

But the churning effect here would be miniscule - we are talking about an oil supply rate of less than a cc/hour. The question I have is whether it is really true that oil will not find it's way into the mesh as readily with oil/air lube positioned on the in-running side as it would on the out-running side. Is it not possible that the high pressure air jet would overcome any positive pressure developed on the in - running side ? I have had apparently successful results with oil-air on the in-running side in the past, but I was wondering about changing it around on a new design.

 

[Carburize]

What speed is your unit?

 

[EnglishMuffin]

Variable speed - anywhere between 10 and 8350 fpm - helical gears. Can occasionally run in reverse.

 

[Carburize]

I would put all of the oil to what is the normal out-mesh side at these speeds.