Efficiency of gears?
Efficiency of gears?
(OP)
Hi all,
I will be measuring power consumed by rotary kiln drives the following days. The drives are in the 300 - 500 kW range and there are gears taking down motor speed from around 1500 RPM to something like 10 or 20 RPM. The gears are plain "cog-wheel" gears. I am sure there is a correct name for that type of gear, but it slipped my mind - if it ever was there...
Anyhow. What would the efficiency of such a gear be? How does it change with load and how does it change with speed?
I am guessing losses around 3 - 5 percent at rated speed and load. But would like to have a sanity check on that. Or, even better, a table or curve showing efficiency over the operating envelope.
I will be measuring power consumed by rotary kiln drives the following days. The drives are in the 300 - 500 kW range and there are gears taking down motor speed from around 1500 RPM to something like 10 or 20 RPM. The gears are plain "cog-wheel" gears. I am sure there is a correct name for that type of gear, but it slipped my mind - if it ever was there...
Anyhow. What would the efficiency of such a gear be? How does it change with load and how does it change with speed?
I am guessing losses around 3 - 5 percent at rated speed and load. But would like to have a sanity check on that. Or, even better, a table or curve showing efficiency over the operating envelope.
Gunnar Englund
www.gke.org





RE: Efficiency of gears?
Its a spur-gear that you describe but thats as far as I can go, this link might help you but my guess is the guys in the Gear and Pulley Engineering forum will answer the question.
http://
RE: Efficiency of gears?
RE: Efficiency of gears?
A quick search of "girth gear" and "efficiency" turned up something that indicates that such a gear set can be more than 99% efficient.
RE: Efficiency of gears?
There are many types of gears, the straight cut spur gears are the most efficient, but helical gears with sliding tooth action run more silently.
There will be losses from oil shear between the teeth, and losses from windage and oil pumping between the gears, and both will change with speed and load, and type of lubricant. It all ends up as heat if that is any help.
The only way I have ever seen this done is to run the thing for many hours to thermal equilibrium and measure the oil temperature rise in the sump above ambient. Then you switch on the electrical resistance heater you cunningly inserted into the oil drain plug, and run it for many more hours. The total oil temperature rise will be proportional to the power being dissipated into the oil, so it is then a fairly simple matter to work out your gearbox losses if you know the wattage of your heater. Simple in theory, anyhow.
This sort of thing can be almost as much fun as electronics.
Good luck Gunnar...
RE: Efficiency of gears?
While spur and helical gearing often worked out to be slightly more efficient, these "rules of thumb" always worked out quite well, especially for thermal estimates.
RE: Efficiency of gears?
RE: Efficiency of gears?
There are four typical characteristic gear types:
Helical Gear Units
Bevel-helical Gear Units
Planetary Gear Units
Worm Gear Units
It depends on the ratio but I guess if you are looking at a 100:1 and possibly Helical Gear unit then the efficiency will be 95-92%. It is typical to work out the losses as the figure quoted by the gearbox manufacturer given for rated output torque. The rated output torque will include for efficiency losses so it is a case of subtracting this from the theoretical calculation of output torque to derive the efficiency. Speed control will not have too much effect on losses as long as it is not oversped.
Looking at the power in your particular application, I would possibly expect a helical bevel. These are slightly lower efficiency, but not much (90-95%)
A few useful sites to check on the gearbox losses using this method would be:
http://
http://www.sew-eurodrive.co.uk/products/index.html
http://www.bonfiglioli.com/riduttori_uk.html
RE: Efficiency of gears?
RE: Efficiency of gears?
(if your're going to give an example, get it right....)