Calc of Worm Gear Efficiency

[ChrisDuncan]

Worm Lead angle 14.7deg
Worm Wheel Lead angle 11.5deg

0.075 friction coefficient

How do you read this chart to calculate efficiency?

http://farm8.staticflickr.com/7018/6597844643_211237d1dc_z.jpg

the chart is also on this page 1/2 way down.

http://www.roymech.co.uk/Useful_Tables/Drive/Worm_Gears.html

also just to confirm my limited knowledge of efficiency

For a system with 20% efficiency to have an output of 40 watts, does this mean an input of 200 watts?

 

[ChrisDuncan]

Also, trying to confirm what I'm thinking with the friction coefficient chart on the roymech page.

If the output speed of the mechanism is .015m/s then the 10:1 worm sliding speed would be .15m/s?

as the sliding speed increases the friction coefficient goes down?

As the friction coefficient goes down the efficiency goes up?

 

[tbuelna]

ChrisDuncan,

That 0.075 friction coefficient is probably only valid for sliding frictions. The initial breakaway friction value may be higher. And yes, as the mesh contact sliding velocity increases the friction losses can decrease, up to a point. The reduction in friction is due to the contact transitioning from boundary to hydrodynamic conditions.

If you're calculating the total friction losses in a worm gear drive, you'll also need to include the bearing losses. These bearing losses can be quite significant.

With low efficiency gear meshes, you also need to pay close attention to possible scoring failures.

Good luck.
Terry

 

[ChrisDuncan]

Good info.

This is a manually driven mechanism. A 19mm hand-crank shaft drives the worm. The worm wheel drives a 32mm shaft that goes to sprockets/chains which lift a varying load of 100kg to 500kg.

""bearing losses can be quite significant""

So guessing the choice is between ball/roller bearings and bronze bushings? Bearings may be out of budget. What would be a ballpark number for bushing losses in the worm drive?

""low efficiency gear meshes....possible scoring failures.""

Case hardened steel worm, phosphor/bronze worm wheel. Cylinder worm, enveloping worm wheel. Enclosed drive, indoor use. Moly EP grease?

Guessing bushing play could contribute to scoring?

 

[drawoh]

ChrisDuncan,

How can the worm lead angle and the worm wheel lead angle be different?

My machine design textbook has quite a good description of worm gearing. Your's should too.

JHG