Split Helical Gear 6

[kilnguy2]

Can anyone help me? I'm drawing a Split helical gear, and my question is - How exactly is the gear split? Is it split perp. to the side of the gear face through the teeth?Or does it split throught the center of the root of the tooth along the Helix angle? And if this is the case would the bolting pattern follow that angle as-well?

Any help I could get would be greatly appreciated.

Thanks, Kiln.

 

[unclesyd]

I assume you are asking about a double helical.
Check this site out and and go to "Gear Collection".

http://www.gearlab.org/

 

[MikeHalloran]

A double helical gear comprises two gears of opposite hand, fixed relative to each other, and sometimes generated from the same blank, as in the referenced photograph. Torque transmitted by the paired gears produces thrust loads that try to drive the gears axially, i.e. together or apart, but the forces are in opposing directions and the gears are fastened together or integral, so there is theoretically no net thrust load generated external to the gear itself, so the gearsets need relatively small thrust bearings. Double gears are commonly found in very high power drives where the added cost of the second gear pair is less than the cost of thrust bearings and housings strong enough to deal with the reaction forces from a single helical gear pass.

A split gear comprises two adjacent coaxial gears, both meshing with the same single (wider) mating gear. One of the split gears is free to rotate relative to the other over a limited range. Relative rotation between the gears is resisted by springs nested circumferentially within the gear pair, rather like the damping springs within a disc clutch hub. At assembly time, the gears are rotated relative to each other, compressing the springs, so that the restoring torque provided by the springs causes adjacent teeth of the split gear to close, scissor- like, on the teeth of the mating gear. Thus, imperfect gears on imperfect bearings can run at zero lash. They are typically found in mechanical computers, i.e., in instrument sizes, and with straight spur teeth, not helical. There's no reason why you couldn't make split helical gears (two of the same hand), or in really large sizes, but I've never seen a big one.

I.e., the gear is split in a plane perpendicular to the axis of rotation.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[kilnguy2]

No, I am speaking of a single Righthand helical. The customer calls for the gear to be in two pieces, as the equipment it drives cannot be dissassembled. Therefore the gear needs to be in 2 pieces and bolted together around the kiln.

 

[Carburize]

I think I would split it along the root.

 

[ruble3]

Was trying to find a good picture for you but it was harder than I thought- we have 4 large split helical gear sets,(284 teeth, 28 tooth pinions)the split is through the root & they are bolted on the 'spokes' - best picture I found was at

http://www.kyungingear.co.kr

( its a Korean site , ignore the language , but look at the girth gears- they show a split gear for a cement kiln and how its bolted together( I have no idea who they are- just found the pictures!

 

[GregLocock]

It must be split along the root, otherwise the gear will wear preferentially along the join.

Cheers

Greg Locock

 

[gearguru]

If you have odd number of teeth it can be difficult...
You have to cut the gear in the root. If you cut through the tooth, you'll make that tooth weak, it can easily break / wear (as GregLocock already mentioned)

 

[MikeHalloran]

Ah; solved the wrong problem. Again.

Yes, split it in the root. The split could be a diagonal slice, or multiple steps inside the dedendum, or if you want to get fancy, multiple steps with reverse taper or secondary steps forming hooks, so the joint can carry tension in something other than the fasteners.

I wouldn't split the gear in just two pieces, because half- rings like that are not very rigid, and waste a lot space in a shipping container.

Make it in three, four, five, six or more pieces. Or just use a big roller chain.

These days, if it _had_ to be a gear and not a chain, I'd try making it in enough pieces so that a blank for each segment wasn't too deep relative to its other dimensions. Then, instead of assembling segments and generating teeth in the assembled gear and then disassembling it, I'd cut each segment from the solid to its finished shape, including teeth, in a CNC milling machine, and assemble the segments to each other once, on-site.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[unclesyd]

Splitting gears is a very common procedure used in the repair of kilns and dryers. In fact all our equipment had split bull or girth gears. Even three that were chain driven had a split sprocket (bull) by design. We change from gear drives to chain drives.
The gear on the rotary kiln type dryer we cast steel and were spliced and axially bolted to a flange on the dryer so the splice really wasn’t in play.


Here is another picture of a split girth gear that used splice plates instead of flanges. Our were similar but had a locating pin on the mating faces and bolt holes on the hub part of the gear.

http://www.rotaryservicecompany.com/girthgear.htm

 

[kilnguy2]

Thanks for the help Guys.

Happy Holidays to All.

Best Regards,
Kiln.