Worn Involute Spline? 3

[mojo41]

Hi. I am trying to understand the mechanism that is causing the teeth of this involute spline to fail within a moderate number of operating hours.

This is an image of a worn involute spline. This spline is from an electric motor with a moderate amount of hours. The female coupling spline is also failing in a similar pattern.

1. Is this failure indicative of wear? Both male and female splines are HRC 50.

2. Lubrication? There is an O-ring that keeps grease on the spline.

3. Is this failure a classic example of misalignment?

There have been a number of manufacturers of the coupling, and they all wear. It is difficult to quantify the tightness of the couplings, but some are loose and some are tight. The couplings provided by the manufacturer of the electric motor also fail, but they are a pretty good fit.

Is there a source available that discusses failure of involute splines? It seems that Machinery's Handbook, and some old SAE documents are all that is available on this topic. Thanks.

 

[mojo41]

Here is an image of the coupling. I don't know if I can upload more than one picture per post.

Thanks.

 

[btrueblood]

Presumably the male side was made with a cylindrical section, then the dishing of the teeth seen in the first photo strongly suggests misalignment to me. Parts also look pretty dirty, how often is the grease replenished?

 

[mojo41]

btrueblood.

Here is an image of another failure. It looks like it has been cleaned.

The grease is never replenished. Once assembled, this spline is inaccessible.

As for the cylindrical section question, I'm not sure, but I would assume it is.

Thx.

 

[mojo41]

Hi,

Here is the external spline data.

The max torque for the electric motor is 340N-m. From a design perspective the spline seems adequate for the load applied.

It seems a little short and stubby, but adequate.

Thx.

 

[Strong]

What is the motor driving? Are the shafts in a vertical or horizontal orientation? What is coupling surface temperature? Has any vibrations, sound or torsional vibrations been measured?

The spline damage and poor lubricant condition indicate possible causes:
1) Shaft misalignment (as mentioned)
2) Grease deterioration from incorrect grease, overheating, contamination, dynamic overloading (torsional vibrations)
3) High torsional vibraitons from operating at resonance and/or high dynamic forces

We need more information than a picture of a beatup spline shaft!

Walt

 

[mojo41]

Hi Strong,

There is another thread on the same issue presented by a fellow engineer. We inadvertently both posted the same issue. His description has more information.

http://www.eng-tips.com/viewthread.cfm?qid=438357

Thx.

 

[Strong]

I just read the other Thread. Grease squirting out suggests considerable pumping action, possibly caused by misalignment, sloppy spline fit, or high torsional vibrations. If the motor is or acts like a stepper motor, then electrically-induced torque pulsations can be produced. Make some vibration measurements and possibly alter the motor control characteristics to see if the drive chatter can be minimized.

Walt

 

[CouplingGuru]

Splines are not meant to take up misalignment. This is an improper application of a spline. If this is a floating connection between 2 shafts, then you really need a coupling designed to take up misalignment. Once this spline starts to wear, little particles that get ground off will actually accelerate the wear.

You need a coupling to take up misalignment. You can focus on reducing misalignment but most often that is more difficult to solve especially when comparing the static to dynamic alignment conditions of operation. Keep in mind any misalignment will make this spline fail (hence why they shouldn't be used to take up misalignment) you would almost need perfect alignment to make this somewhat viable, which is impossible.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM