Changing center distance in spur gears 1

[dmason83]

Hi, i'm currently looking at a problematic gear train on a machine my company made. It's being used in a roll-forming application and the gear teeth are snapping clean off at the root of the tooth due to the fact it is under-designed (i did not design this).

Currently: 14.5 degree pressure angle and center distance between 2 gears changes a total of .133"

Some specs are being changed so that the center distance change is only .075".

I'm wanting to make the gears 20 degree pressure angle. I am also enlarging the face width as much as possible (dimensional limitations). Does anyone know how this will affect the backlash on the gears and any other important aspects of the operation?? the gears are operating at approximately 10 rpm.

Material change should not be a factor. Astralloy-v is being used and is doing better than 4340HTSR performed.

 

[Compositepro]

Are you lubricating the strip that you are roll forming? There is a lot of slip that must occur between the the strip and the forming rolls because the rolls have many diameters and therefore many surface speeds. If there is too much friction which could be caused by the strip being pinched between the rollers so hard that there is no slip, then the gears would get overloaded. Grit on the strip could contribute to this, also.

 

[dimjim]

Increasing the pressure angles do make the
gears stronger by a magnitude of 11 percent.
Increasing the fillet radius may give you
another 5 percent. By spreading the center
distances, you decrease the contact ratio
and exert the same contact load at a higher
point on the gear. You are actually changing
the operating pressure angles when you spread
the center distances. I think your greatest
gain will come from dropping the one tooth
on the pinion and cutting it on the same gear
blank using the 14.5 degree pressure angle
tooling. It should also run smoother.
Seems like an easy change.

 

[MikeHalloran]

Doubling the face width of the gears would probably do more to help than screwing around with the geometry. Can you make room for that in the gearbox?

Could you run the gearbox at the correct gear center distance, and squeeze a sliding block coupling between the gearbox output and the rolls?



Mike Halloran
Pembroke Pines, FL, USA

 

[dmason83]

Everyone, It turns out in the end that 14.5 degree spur gears with the larger face width and dropping a tooth on either gear is the best i'm going to be able to do. This is also the simplest and best solution to this problem since there is such little room in the gearbox to add anything such as double moving idlers and/or sliding block couplings.

I'd like to thank everyone for their helpful opinions on the subject. They have helped me confirm the solution to the problem.

DM