Q & A
for low rolling resistance and long life
because of the high costs of maintenance, repair, and associated downtime of the gearbox assemblies once
they have been erected. We have
to carefully document and control
every step in the manufacturing of
these gears to achieve the high accuracy and reliability needed for operation
in extremely high-wind environments.
Modify Tooling
Minimize Distortion,
Cracking
We machine the gears
out of carburized steel.
The heat treatments and
stress-relief operations
associated with that material must be exacting to minimize part
distortion and expansion, as well as to
achieve the required metallurgical properties. Often we have to preheat the
forging or barstock.
To minimize gear distortion, we insert the gear vertically into a quench
tank during the hardening phase. The
dwell time in the quench tank is critical
to performance and material stability.
Even the slightest variations in the cooling rates can cause distortion that might
be undetected in normal inspection.
Heat treatment itself can cause mi-crocracking that must be ground out,
so we have to allow enough stock to
achieve final case depth. When you
heat it up at 1,600, 1,700 degrees F
and drop it into the quench tank, it goes
from 1,600 degrees to 300 degrees
just like that. If you don’t do everything
right during that transformation, it’ll
distort. So after, we grind all the faces,
and then gear-grind.
Some of these very fussy components that have to be just right, we
don’t compromise. We use magnetic
particle inspection and grinding burns
using nital etching to detect cracks.To
properly distribute the load on the gear
teeth, we sometimes off-center crown-grind the tooth geometry.
Rigid, heavy-duty hobbing machines using
roughing hobs or gear
milling (gashing) cutters are required for
the coarse-pitch gears.
We use coarse-pitch diamond dressing
rolls and special grinding wheel abrasives to machine the large, high-accu-racy gear grinders to produce efficient,
accurate results and to prevent grinding
burns and cracks.
The cutting fluids must have the
proper viscosity, the right amount of
extreme-pressure additives, and must
be directed to the exact location of the
workpiece and cutting tool interface to
optimize results. We routinely sample
and adjust the fluids.
Build for
Durability
Using the correct bearing
clearances and preloads
is critical to long life and
proper gearbox operating
temperature.
Gearboxes must last a long time.
They are 200 feet up in the air, and they
are very, very heavy. If you have to take
the gearbox out, it’ll cost quarter of a
million, half a million dollars.
We are not a typical gear manu-
facturer. All of them can make gears.
Some of them can assemble gear-
boxes. But they do not design them.
If they do not design them, they miss
finer points, like a bearing preload, a
very critical application. And when you
do a bearing in a gearbox assembly,
you set the looseness of the bearing. If
you set the preload properly, there has
to be a little bit of leeway in the align-
ment. And also when the gears have
a longer shaft, they deflect differently
than a shorter shaft. So the gear is not
in the middle. You have to make an ad-
justment for those things.
N.K. Chinnusamy is president of Excel Gear
Inc., 11865 Main St. Roscoe, IL 61073,
815-623-3414, sales@excelgear.com, www.
excelgear.com. Chinnusamy is a member of
the Great Lakes Wind Network.
