Damping teeth chatter:

Dynamo Joe,

First things first, PLEASE send me the web address for the vibration analysis forum as I would like to join in. sminnaar@mhs4.tns.co.za

On your question;
Changing the lubrication will not necessarily alleviate the problem as the elasto hydrodynamic lubrication regime will be affected by the increased viscosity but it is merely a symptomatic approach.
Please supply some more information e. g.;

Is this a new gearbox;

What is the application, a straight forward one stage spur gear set or multiple stage;

Is the current lubrication in accordance with OEM specification or has it been changed to adapt to the environmental conditions;

Did Arne check the FFT spectra for hunting tooth frequency, this will indicate a gear related issue e. g. a fault on the mating gears due to manufacturing, assembly (if the problem was there from the start), orientation (if it was repaired) or in the field.

Check your gear mesh frequency for sideband activity which might point you in the correct direction.

Have the pump efficiency been checked to establish if the gears are in actual fact adequately lubed.

Have a good one.

Wonderful; an answer.
I thought that I might have to be accepted first at this forum by asking questions here and there until someone feels sorry for me and eventually responds. HAHA.

Your questions are making this more interesting. THANKS!

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Warm regards
Joey

Hello Dynamo Joe...

Interesting thread....
As all of you vibe techies know if you change the stiffening in anything exhibiting a natural frequence then you will modify or eliminate that particular frequence (assuming you are not at the node point) So by changing the viscosity you are indeed changing the stifness of the mechanical transfer or power and therby the dampening charestics of the assembly - enough? don't know not enough info.
The nature of spur gears is that they are significently louder in operation than the helical - hyphoid etc. This is the inherent design and has to do with the involute inching or ratcheting mechanical transfer of power between the mating teeth (well documented). Also the AGMA quality level of the gears has an effect on the overall noise level of an operating gear set. ie an AGMA class 8 gear set will operate louder than an AGMA quality 10 gear set in the exact same gear box. These quality ratings have to do with things like total tooth composite error and things like tooth spacing errors etc. But nothing to do with surface finish. So mabey it's just cheep gears causing the noise.
Joey I'm trying to figger out what kind of vehicle, that carries passengers and uses some kind of a manual transmission with a built in spray lubrication it is you (Arne) are talking about. An ISO 340 (360) is normally around the top end for summer applications in Canada with a SAE 80W-140 being a common oil for heavily loaded or trailor towing passenger vehicles. There are some lubrication solutions avaliable to assist in minimising questionable design choices. However they can only go so far. Can they reduce the noise generated by lower AGMA quality gear sets - definately yes.
So back to Arnies question re: try a synthetic/reduce the temp. If the synthetic has a higher viscosity at the operating temperature than the current product a couple of things could happen. Temperature decreasses having a 2 fold positive effect on the noise reduction. Or the temperature increasses because of additional internal fluid friction causing the drive system to run hotter and possibly ending up with the same origional overall viscosity or lower.

and the thread just keeps on going......

regards.....

quote:

---

*...So by changing the viscosity you are indeed changing the stiffness of the mechanical transfer or power and thereby the dampening characteristics of the assembly - enough?
*...Maybe it's just cheap gears causing the noise.
*...Can they reduce the noise generated by lower AGMA quality gear sets - definitely yes.
*...If the synthetic has a higher viscosity at the operating temperature than the current product a couple of things could happen. Temperature decreases having a 2 fold positive effect on the noise reduction.
Or
...the temperature increases because of additional internal fluid friction causing the drive system to run hotter and possibly ending up with the same original overall viscosity or lower.

---

It looks like the questions should be asked, "What viscosity is allowable at the minimum operating temperature and allowable at maximum operating temperature? What would optimize to reduce the sound? Could a tackifier be added? What viscosity would generate heat from friction to lead to deterioration? If the gears are cheap cut, do they make noise because of a type of shock load from being too coarse a cut? Would oil be required here that withstands shock loads?

Hello,
You have asked a bunch of questions that are difficult to answer definitivly in this type of a forum. However I need to point out that us lube guys are really only trying to accomplish 1 thing and that is to derive a reasonable life out of the equipment by using the right amount of the right lube at the right time. What you are questiioning is trying to get the lube to fix the design errors and what we are trying to do is to get 1 lube to satisfy the significently different needs of the gears and bearings, etc that are tyical in a gearbox. So when you drive the viscosity up you sacrafice the bearings and conversly when you drive the viscosity down you sacrifice the gears. Throwing in a tackifier is about the same as increasing the viscosity. Assuming this is a fully flooded application.
It is fairly easy to determine a calculated viscosity for a given gear set in a given set of circumstances and likewise for a set of bearings. This is what us lube guys (and girls) do but normally the concept of trying to reduce noise is kept at a secondary (and consequential) level. It is better to remove the condition through modeling at the design stage than to try to remove the condition after the fact.

It is not so much that he gears are "course" cut it is more that the gear teeth do not have the accuracy required to operate quitely. There are a bunch of QA parameters involved here.
PS. All EP fortified gear oils are designed to accept some level of shock loading.

You have opened up a different scope of questioning here with your thread. Keep up the good efforts, eventually someone will match your questions with answers that wil satisfy you interests.

regards......