progressive HP rating in multi reduction gearbox
progressive HP rating in multi reduction gearbox
(OP)
100 HP motor driving a mixer through a dual reduction gearbox. First reduction via helical gears. Second reduction is via spiral bevels. The gearbox supplier designed the spiral bevels using 85 input HP, claiming that is what gets passed on thru the helicals.
Is this commonly done?
thanks
Dan T
Is this commonly done?
thanks
Dan T





RE: progressive HP rating in multi reduction gearbox
Does the end product have to fly, or is there some other reason to design on the razor's edge?
How long has the supplier been in business? Maybe they know something I don't know, but I didn't think helicals were that lossy.
Mike Halloran
Pembroke Pines, FL, USA
RE: progressive HP rating in multi reduction gearbox
A normal helical gear mesh should not lose more than about 2%, even with poor lubrication. To be honest, a typical single helical gear mesh with 15% losses would likely fail very rapidly in scoring. So I can't believe that number is correct.
It may be possible that you misunderstood what the supplier meant, or that the supplier spoke incorrectly. Gear teeth are commonly designed for fatigue loads that are less than 100% of the input power, since the gearbox does not tend to operate at 100% power for 100% of life. Your supplier may have meant that the spiral bevel gearset was designed for a max continuous input power of 85HP, which would seem quite reasonable.
Good luck.
Terry
RE: progressive HP rating in multi reduction gearbox
If they are; I can see an interesting scenario beginning to develop here.
What is the required duty cycle?
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: progressive HP rating in multi reduction gearbox
the scenario is on chapter 16.
Duty cycle = REAL close to 100% load, all day, every day, except for an outage for plant maintenance every now and then.
Dan T
RE: progressive HP rating in multi reduction gearbox
85HP seems too low to me, considering the 100% duty cycle.
Electric motors can develop significantly higher power values than the name plate value.
Without knowing the full details of your set; I would have started at 100HP and gone up from there after applying application/service and safety factors.
The damage suggests that the gears are not fit for purpose and perhaps what you have discovered is why.
Seems like now might be a good time to get an independent party to validate the design.
IMO this should always be the first step before ordering a gearbox.
My experience has been to never ultimately trust what a gearbox supplier is telling you will do the job.
Most of the failure analysis I do is on gearboxes which are relatively new and have been found to be not fit for the application.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: progressive HP rating in multi reduction gearbox
Unless the shaft speeds are low, it's quite normal for those spiral bevel gears to be power limited.
Terry
RE: progressive HP rating in multi reduction gearbox
I agree with you comments about power vs torque.
This set of spiral bevels is also the set mentioned in a previous post where Timoose mentions the details. Speed is low suggesting high torque.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: progressive HP rating in multi reduction gearbox
I would also ask, is this an Amarillo gearbox?
RE: progressive HP rating in multi reduction gearbox
We've had a few break ring gear teeth. One ran less than two weeks after having a brand new Ring and pinion installed during a factory rebuild. Some others showed levels of localized spalling when disassembled for other reasons. Mobilgear 600 XP 220 should be up to the task.
So I'd say we've repeatedly exceeded the gears limits for bending strength and contact stress. Unfortunately it looks like the relative influences of manufacturing vs design (with subset of manufacturer's predicted operating loads, plus wildcards) won't be answered any time soon.
RE: progressive HP rating in multi reduction gearbox
Was something in the mixer changed after the gearbox was selected?
Mike Halloran
Pembroke Pines, FL, USA
RE: progressive HP rating in multi reduction gearbox
Yes, the LS gear ratio was changed on the twelve units at this first installation when the motors were drawing excessive amps. The installations that followed got smaller impellers in place of a ratio change. Reports are They have not suffered gear breakage, spalling, etc, so I'm personally keeping "bad bucket o'gears" on the list of suspects. This installation's (reportedly unique) Visible low frequency vibration and fairly strong blade pass have captured most folks attention. I'd like to measure instantaneous power to see if the 100 HP is ~steady, or has a big 3X component. I hesitate to say or think this level of vibration is "causing" a problem for the gearbox.