spline slippage calculation 2

[goodvibes]

here's a challenging problem.


How would one calculated the min axial force required to cause an involute spline to slip under a continuous torque. This is for a long drive shaft with male spline on one end mating with a female spline (with roon for axial movement). The design requires that the drive shaft be allowed to move axially while turning to accomodate intermittant thrust loads. The only givens are the spline design dimensions and the Torque and RPM for the drive.

Egads! I'm having college flashbacks!!

Thanks in advance for any help.

 

[GregLocock]

Well, I'd start by assuming that the friction was 0.2 and see if it came out as a sensible number.





Cheers

Greg Locock

 

[goodvibes]

Thanks Greg,

But I still need to calculate the spline tooth load under the given torque and speed. What formula would you recommend to derive the tranmitted load? I know that the lewid formula is used for spur gears. Would this apply to splines which have a much higher contact area??

Keith

 

[israelkk]

The calculated load is the transmitted torque divided by the pitch radius of the spline. The friction force is the multiplication of the calculated load by the friction coefficient.

 

[goodvibes]

thanks,

so it is the same formula as for a spur gear.

Take care

 

[sreid]

This may be a dumb quesion from, pimarilly, an electrical guy but wouldn't axial movement of a spline under a torsional load tend to result in rapid wear of the splines?

 

[GregLocock]

It would. But it doesn't, because the splines lock up under any significant torque. If you actually need the joint to plunge under torque then you have to use a plunge joint, of which there are many types.





Cheers

Greg Locock

 

[goodvibes]

In my case the spline needs to accomodate transient axial motion and thermal growth. I needed to calculate the force required to move the spline axially through the female spline. Wow! I just noticed that my spelling is terrible. sorry about that.

Thanks to all

 

[GregLocock]

Is your torque intermittent? If so then the spline will take a new axial position when the torque drops off.

If not then your spline will tend to lock up as described. Then a couple of things can happen: (a) something breaks or (b) other compliances in the system accomodate the axial motion or thermal growth, until the axial force exceeds the breakaway force. You can deliberately engineer the latter by making sure there is a flexible mounting for one machine or the other, or by putting a compliant joint into the driveshaft.




Cheers

Greg Locock

 

[goodvibes]

Greg,

The shaft in question has flexible diaphragms on both the driven and driving ends. These diaphragms are very stiff torsionally but can accomodate axial deflections. the torque load is steady (from an turbofan engine). Axial deflections will be intermittant due to accelerations during certain manuevers. My job (should I choose to accept it) is to calculate the axial force required to compress or extend the diaphragms. I think i have a good idea now.

thanks,

keith