Right Angle Gear Drive unit ran without cooling flow

[fire911]

Hi all;
We have a standby diesel driven fire pump that goes through a right angle gear drive to a vertical shaft turbine type pump. (6 cyl, 325 HP)
The angle gear head is a 6 to 5 ratio with input 2100rpm and output 1760rpm.
The oil is about 11 galons of Mobil DTE BB (VG 220).
The pump is in an enclosed room with temps maintained about ambient, 30-100F

We found the gearbox cooling drain valve closed and it looks like it was shut since Oct 08.
The unit was only run about 5 hours since Oct and not more then an hour at a time.

My question is how long would the gearbox last with the pump running continuously and the cooling drain line closed.
How could I determine the temperatures that it would reach.

Thank you for your time and assistance.
Paul

 

[L17Aurora]

Check the oil, is it burnt? Any paint blisters?
Open the inspection covers, do the gears look nice and shiny or blue?
If the gears run in a sump then it's possible you got away with it, depending on the power they were operating at.
Under no load gears will run for quite a while on marginal lube but as you increase the power the lube acts to remove the heat.

 

[fire911]

This is more of a "what if" question. We did oil analysis and everything was fine for the current condition. The problem is I have to deal with what could have happened if the fire pump automatically started for an emergency. How long could I expect it to run without eating itself? How would I determine the temperature it would have reached without physically testing it? Thanks for the response.

Stay Safe;
Paul

 

[ExRanger]

If you had a good estimate of the coefficient of friction between the gear teeth in the unlubricated condition, you could make an efficiency calculation and thus determine how much power was being lost to heat at the gear mesh. Then you could use that with some kind of thermal model to determine the temperatures that result over time. You could then compare that with say the tempering temperature of the gears to determine when you could have problems.

However, I don't know if there is any good data concerning the coefficient of friction for unlubricated steel gears since that is not really a recommended condition to run the gears in.

 

[mfgenggear]

#1 is there an oil sump in the gearbox?
#2 is there any extream noise difference?

If the yes to #1 then it's OK
If no to #1 & yes to # 2 then inspection & maintenance is required.

It seems to me physically inspecting the gears and bearings for wear &/or damage is the best method.

 

[tbuelna]

As long as there was sufficient oil so that the gears were receiving splash lubrication, and since you ran the gearbox for several hours, I'd say that unless there is ferrous debris in the lube system then it's probably OK.

Most types of 90deg gear sets (spiral bevel, hypoid, etc) are usually scoring limited. And a gear mesh operating with scoring will fail very rapidly, usually within minutes. The scoring failure results in metal transfer between gear teeth and this creates lots of ferrous debris in the lube oil.

Check your oil for debris. If you're still not satisfied, send an oil sample out for analysis.

Good luck.
Terry

 

[unclesyd]

Why not just go ahead change out the lubricant and take the valve out of the drain to prevent further incidents. While the gear case is empty use either a short flexible scope or just a visual while rotating the gears.
As stated above if there aren't any signs of excessive heat externally or internally you are in good shape as gear oils are normally quite forgiving.
On a lot of our gear boxes we have local temperature indication or Tempil dots for registering high temperature.
In most of our boxes we us proprietary gear lubes that give a clear indication if they are going out from overheating. These oils also contain a dry film lubricant to extend protection if the carrier oil fails.

 

[geesamand]

I'm not sure the reason why you need to predict the outcome of what sounds to already be in motion. An infrared thermal gun will tell you all you need. You'll want to ensure your oil temps are not in excess of the Mobil DTE and oil seals.

On the prediction side, it is reasonable to assume a frictional loss in percent of total HP (depends what kind of gearing is at work here) and a heat transfer calculation for the case to ambient. This is a decent rough number for design, but since you have a "prototype" I see no need for it.