Gearbox Lubrication 2

[rlh42]

How do I decide how much oil each gear and bearing needs in a gearbox?

 

[Javier72]

Ask to your oil supplier. Is the best person to answer you. Anyway, it is not needed to have very much oil or grease. Only the needed to guarrantie to have the correct film on the contact surfaces.

 

[rlh42]

Javier,
Many thanks for your response, however the initail contact with the Technical Department of the oil supplier resulted in the following reply :
'Oil specifications and quantities are usually defined by gearbox manufacturers themselves. We then offer our lubricants that meet these specifications and requirements'

I am chasing up via another Oil Supplier (Kluber) who seem a bit more switched on and have asked for details so I will see how that goes. I used to use general rules for quantities (for heat transfer) many years ago but these were based on old fashioned mineral oils whereas modern PAO's have better characterstics. If anyone knows how much oil per kW or HP of transmitted load per gear mesh and for each bearing please let me know.

Many thansk to all.

Ray

 

[Javier72]

No, it is not HP or KW the units that you need to have to select the grease. You must know what is the pressure between the teeth (N/mm2). The other data you need is the tangential speed, to know the adherence needed. With this data, the Kluber technicians gave me the grease that we are using now in some of our gearboxes and the quantity we need to use in each of them (we are gearboxes manufacturers). We did the same with other grease suppliers (Condat, Mobil) and all of them with these data gave us different solutions to prove.

 

[rlh42]

Hi Javier,

Sorry but we may be at cross purposes, I am aware of the low requirement for the EHD lubrication, however I have to shift a total of nearly 100kW of generated heat from the box, and it is this that concerns me most. I used to use 0.4 litres/minutes per 10kW of transmitted power but these are out of date figures based on mineral oils.

Anyone have any more up to date figures for heat transfer from gears and bearing please, preferably utilising a fully sythetic PAO or similar?

Many thanks

Ray

 

[romke]

i am not aware of figures that offer a starting point of an answer to your question. however, since you are on the lookout to carry away heat developed from one place to another, i might offer some guidance. in standard industrial gears bulk oil temperature should not exceed say 80 deg C, and when using PAO based gear oils that figure might be somewhat higher, say 95 deg C. when the bulk oil temperature gets higher the oil used will oxidize faster and will need to be changed more often. you then either have to employ some form of oil cooling or have to change the amount of oil available, effectively creating a larger "heatsink". bear in mind though that too high an oil level (when splash lubrication occurs) may well lead to a higher oil temperature.

the specific heat of paobased gear oils is not much different from mineral oil based gear oils, so, when operating temperatures and viscosities are the same about the same oil temperature would be the result in a given application. that also means that the original figures you quoted may still be appropriate.

often it is said that gears run cooler when using PAO based lubricants. that usually is the result of the more temperature stable viscosity of pao-based lubricants which means that you might be able to go from an ISO VG220 oil to a ISO VG 100 or 150 - and thus generate less heat due to less churning power needed for the lubricant, not because they have better coolant characteristics.

 

[rlh42]

We are planning to use VG320 Grade PAO or similar