#80-6 roller chain, drive sprocket running max. speed

[JJAV1983]

Hello,

We just received a gearbox with a chain drive ratio of 4.73:1. On top of this GEARBOX, there is a 4-speed transmission and a hydraulic motor to drive it.

One of the most common combinations RPM/torque in this GEARBOX is 781 RPM / 681 FT-LB TORQUE (gearbox output)

The question is the following: when the driven sprocket is running at 781 RPM, the drive sprocket runs at 3694 RPM which seems a bit excessive considering the size of the chain and the power: torque X Speed/5252 equal to 100 HP.

This GB is mounted on a drilling truck and does not operate at this setting 100% of the time, however, there are entire days where the customer will run it at this exact settings.

The customer has not had any issues with the chain or sprockets EVER, HOW DO YOU THINK THEY GET AWAY RUNNING THE DRIVE SPROCKET AT SUCH HIGH SPEED AND RELATIVELY HIGH POWER WITHOUT BREAKING ANYTHING?

you can see a similar arrangement of the gearbox here: (notice that this runs only with 80-3 roller chain but the idea is the same)
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1534371725/tips/GEARBOX_hlsfmm.bmp[/url]

Thanks,

JJAV1983

 

[BrianPetersen]

Motorcycles use what amounts to a #50 chain, and the countershaft sprocket is capable of spinning faster than that (obviously dependent on road speed, but ~ 3500 rpm countershaft sprocket speed corresponds with normal highway speed in a typical case). Granted, they're not operating at 100% output power all the time, either - but I've gotten well over 40,000 km out of a chain.

The ratings on normal #80 chain go out past that RPM but only at a very low power rating.

The ratings on normal #50 chain with a 15 tooth small sprocket (typical motorcycle situation) only go up to about 15 horsepower at ANY rpm (about 1200). At 3000 rpm (highway speed for the countershaft sprocket) it's only rated at 4 horsepower.

I don't own a motorcycle that has that little power. (One of them has north of 200 ... although I will grant that driver's license preservation means that it's not operating at that power level much of the time!)

Translation: Either those ratings tables are extremely conservative, or they are assuming use of chains of absolute garbage quality. (I know that substituting industrial chain for motorcycle chain is a big no-no ... they won't last.)

 

[MikeHalloran]

If the roller chain and sprockets are enclosed, and provided with continuous lubrication, they can survive well beyond the industrial power chain ratings, which so far as I can tell are for near-infinite life with occasional lubrication and no other maintenance.

I suspect that each motorcycle manufacturer has internal tables for chain selection, which they might be hesitant to release for competitive reasons.




Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

The load torque at that speed may be way less than the gearbox capacity. Therefore, the actual hp will be less than your calculated 100hp.

Ted

 

[MintJulep]

I think the simple answer is that 80-6 chain is pretty strong stuff and it is operating within it's capabilities.

What are the sprocket diameters?

 

[Pete_K]

Go to Tsubaki's website and download their ANSI chain catalog...they provide a straight-forward guide to sizing chain.

In your description, you say,

"We just received a gearbox with a chain drive ratio of 4.73:1. On top of this GEARBOX, there is a 4-speed transmission and a hydraulic motor to drive it. One of the most common combinations RPM/torque in this GEARBOX is 781 RPM / 681 FT-LB TORQUE (gearbox output). The question is the following: when the driven sprocket is running at 781 RPM, the drive sprocket runs at 3694 RPM..."

If the hydraulic motor/gearbox is the driver, then the 781 rpm sprocket is the "DriveR" sprocket, not the driven. Are you sure that the chain drive is a speed INCREASING arrangement?

 

[SwinnyGG]

Sounds like a chain running under it's maximum load limit... which isn't confusing at all.

For reference, the rated tension load limit of Tsubaki #80-6 is 105,000 lb. This is a very strong piece of chain.