railway reducer

[LUKE27]

hello to everyone, since I just entered this forum I introduce myself:
My name is luca and I attend the third year of mechanical engineering at the bari polytechnic.
If I opened this discussion is because I would kindly like some "connect" to clarify my doubts.
This is the project of a reducer (in the photo). What is not clear to me is the mounting of the bearings on the reference shaft (the one with the conical pinion).
do not look at the bearings in the design because you are not obliged to make the choices on the same.
our professor showed us how to proceed, but he made a decision for me questionable: we have a tree leaning in three sections and the radial and axial forces that I have written to you; the prof chose an isostatic assembly (axially) with a left zipper (with 1 ball bearing) and two trolleys (two cylindrical roller bearings). what does not convince me is the fact that the ball bearing should absorb an axial load that exceeds 70% of the radial load (when the norm says that you should not exceed 30%).The same professor said that it is not advisable to make this choice.
Now I ask you: what would be the most correct choice? maybe a x/o hyperstatic mounting? but the fact is that there are three supports.. .
I hope in your disappointment.
Thank you.

 

[meccanicamg]

the isostatic system allows the expansion of the shaft without loading bearings or other dangerously. classic ball bearings are not indicated to bear large axial spins, however it is necessary to make the verification of duration.
definitely an oblique contact bearing or 4 contacts is more suitable for bearing larger axial components.
then it is necessary to understand if the axial force is to the left you can put an oblique contact. the bike should not be reversed.

There is to say that of isostatic has nothing that system of bond in the original design.
The beam is one, there are three vertical reactions of the roller bearing, the ball bearing close to one roller will never allow rotation of a quarter degree to hinge mode.

the best system could be having a two row oscillating roller bearing that hinge face with high radial and axial thrusts, a toroidal bearing at a row of carb type rollers in between which it makes from cart carrying high radial loads and to the right axial free support with a ball bearing so that it holds the bendings.

 

[LUKE27]

Thank you for the very exhaustive answer, however in our design course we treated only rigid radial ball bearings, cylindrical rollers and conical rollers.
therefore with this limited choice, you decided to use the ball bearing as a hinge. of course everything has been verified with the calculation of the equivalent load capacity which is less than that of the chosen bearing.
Therefore in the end it is sufficient that the latter verification is satisfied and all the problem of the axial force beyond 30% of the radial force does not arise, or is it wrong?

 

[tecnico_plast]

about bearings, if you haven't already done, you can ask the skf for the student kit.
You might be useful in the future. This is the link:
http://www.skf.com/it/our-company/skf-italia/progetti-e-sponsorizzazioni/collaborazioni-mondo-istruzione/docenti-e-studenti.html

 

[LUKE27]

Yes thank you, I already sent the email Sunday, but I did not receive any response. Do you know if you have to receive a confirmation e-mail from skf and you would also know how long it takes for shipping?

 

[tecnico_plast]

I don't remember, I don't think you get any confirmation mail.
in 10-15 days they send you the package.

 

[meccanicamg]

That's right. if the duration is verified you may also have 80% axial on a ball bearing.

 

[LUKE27]

Thank you very much.

 

[Luca_mech]

from the highlighted pattern it seems obvious to me that you have 3 radial roller bearings (of which one could also work axially?!) and a 4-point radial (the one on the left), which is an oblique bearing to all effects. two radial places very close to each other can fulfill the function of ink. .