Gears general maintenance information request 1

[vicasazn]

Hello.

Recently I saw in a blog that the output shaft of a gear stands more load than the inpout shaft. This surprised me because I remembered that the load is constant in all the shafts. My questions are:

- Is it this way?
- Which is the gear that failS before input or output? and why?
- Which is the rolling bearing that fails before input or output? and why?
- Somebody has a link or pdf with gears general maintenance information?

Best regards and thank you in advance.

G

 

[gearcutter]

You need to learn the difference between power and torque. Heaps of information available on the internet if you look for it.
There is actually a little less power at the output shaft due to inherent inefficiencies of the gearbox.


Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[vicasazn]

Hello.

Yes. Excuse me. Power is constant but no torque. I didn't remember it well...!!!

Best regards

 

[geesamand]

"Hello.

Recently I saw in a blog that the output shaft of a gear stands more load than the inpout shaft. This surprised me because I remembered that the load is constant in all the shafts. My questions are:

- Is it this way?
- Which is the gear that failS before input or output? and why?
- Which is the rolling bearing that fails before input or output? and why?
- Somebody has a link or pdf with gears general maintenance information?"

In the simplest case, a gearbox absorbs only torque on both ends. In the real world, additional loads come from:
- misalignment of couplings
- bending or axial load caused by overhung masses, belt tensions, imbalances, or other external load sources. A great example is mounting a reducer and letting the weight of the reducer rest on the shaft - the gearbox itself is the overhung weight.
- variances in torque can also contribute, because torque usually creates axial and bending reactions within the gearbox.

These things all directly effect the bearings, particularly the ones holding the shaft with the additional load. However due to the normal flex of the components you'll have misalignment added to the gearing, which can severely reduce the effective life of the gearing. If the load is on the output shaft you'll tend to see the failure on the output gearing. This is why you can buy not just plain gear reducers, but also crusher drives, mixer drives, conveyor drives, etc. Those specialty drives are reinforced to handle the additional external loads in the most cost-effective and reliable way possible (putting bigger generic gear reducers is not usually cost-effective). Improper understanding of external loads is a big reason for persistent drive failures.

Maintenance boils down to this:
- Keep the lubricant clean and free of water. Use the correct lubricant for the application, including site-specific factors such as ambient temperature and duty. Change the lubricant when it's no longer within specifications.
- Monitor temperatures and gear wear. Repair the drive when damage is discovered.
- Monitor bearing temperatures and bearing wear. Repair the drive when damage is discovered.
I don't have a single PDF reference to offer on that but those are the main topics and you can research them independently.

David

 

[mfgenggear]

that was great gees

do not forget, to check the oil for metal chips. and have the oil analyzed.

 

[tbuelna]

What do you mean by "loads" the gearbox input and output shafts are subject to?

Due to mechanical losses (like contact sliding at the gear meshes, viscous losses in the bearings, and windage losses in the rotating components ) produced at every component in the gearbox, there will be less power at the output shaft than at the input shaft. Depending on the gearbox configuration and ratio there might be more or less torque from the input shaft to the output shaft.

Assuming you are using the conventional notion of "loads" in your gearbox, the bearing/shaft/gear loads are mostly a function of the forces applied at each of the individual gear mesh contact points. And these are mainly related to applied torque and gear tooth geometry. So it is quite normal for the output shaft of a gearbox having a high speed reduction ratio and decent efficiency to have significantly greater torsional "loads" than the input shaft, even though there is a loss of power from input to output.

Lastly, consider the extreme example where your gearbox has 50 stages, each stage produces a mechanical loss of around 1%, and the input/output speed ratio is 1:1. There would be a massive drop in power/torque between the input and output, but no change in shaft speed.

 

[vicasazn]

Hello Again.

First thanks everyone!!. I'm not english speaker therefore I translate the best I can.

Geesamand: One question: What is the advantage of installing a hollow shaft gear for istance for a bucket elevator beared in the shaft and in another point. Could it be called "pendular"? I don't know the english word. Could it be to bear better forces due to a bent shaft?. In this case if we bolted the gear to a frame could we have problems?

What are advantages and disadvanags of this assembly that is very common.

What is the best way to measure gear backslash: dial indicators? shims?. An old mechanic told me that if you put a piece of paper between the teeth and when turn the gears they don't break the paper this were good.¿?¿?

Best regards

 

[tbuelna]

vicasazn-

The only advantages to using a hollow shaft gear are reduced mass and reduced polar inertia.

The easiest way to measure single mesh gear backlash is by using a dial indicator. The optimum amount of backlash will depend on the size of the gear teeth, the pitch center distance, the contact ratio, and the CTE mismatch between the gear and housing materials. If there is a large CTE mismatch between the gear and housing materials (ie. an aluminum housing and steel gears) and the PCD between gears is large, you should take this into account when establishing the mesh backlash measurement at RT conditions.

No offense to your old mechanic friend, but a typical sheet of paper is only about .004"-.005" thick. And this amount of backlash is too tight for anything other than small diameter gears having a DP of around 12 or higher.

 

[gearcutter]

Gearboxes with hollow output shafts are generally designed for a specific purpose.
They are known as 'shaft mount' gearboxes. This type of gearbox does not require a fixed mounting base (and all of the alignment and coupling issues that this creates). The whole transmission pad floats on the shaft with a torque reaction arm being the only component that is securely fixed.
The arrangement can save a lot of time and money.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[tbuelna]

gearcutter-

Nice work. After reading your last post I looked at some commercial shaft mounted gearboxes, and it became apparent what vicasazn was asking about- "Could it be called "pendular"? I don't know the english word.". Although "floating" might be a better description than "pendular".

I do some design of aircraft transmission systems, and almost every gearshaft or driveshaft is made hollow to reduce weight. And it is common practice to design structural mounts of engines/gearboxes and shaft connections so that they allow some radial, axial and angular displacement without over-stressing the components. The engines and gearboxes might be attached with flexures and spherical bearings, while the shaft connections might use crowned splines or flex couplings. You can't afford the weight penalty from making the mounting structures super stiff, so you have to design your drivetrain components and structural attachments such that they have enough compliance to accommodate a flexible airframe.

 

[gearcutter]

tbuelna,

These forums are a great place to learn.
I've certainly learned heaps from your posts.
Really appreciate how much you try to help people here.


Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181