A reasanable factor could be

1.6, considering starting conditions, but

also considering the number of installed expansion rings.

This criteria of 1,6 x total torque installed applied to EACH ring is relatively new, because before the citted specifications, everyone used the first criteria without any troubles.

So, someone wrote something for an important consulting company, and then this recomendation is turned to be a taboo.

Regards ■

Yes, and is easy to find this problem at small pulleys, which frequently presents high pressure at the contact region between rings and shaft.

A small pulley shell has small inertia, and the group (shell-lateral discs) can present more deformation than the shaft itself, if the shaft is too rigid.

It can cause these high pressures at the contact region wich can damage the shatf or even the hubs.

So, shell, lateral discs, hubs, expansion rings and shaft should work together as an unique system.

A very rigid shaft , very rigid lateral discs, thicky shells and oversyzed expansion rings can be dangerous for the entire group.

So, I would prefer keyways for small pulleys.

I some cases it is necessary to increase the pulley diameter in order to achieve bearable contact pressures.

Another very frequent problem by the pulleys with Ringfeder connections is when one uses a hub with not enough external diameter...when one applies the necessary torque to compress the rings against the shaft and hub, the hub can not bear the forces and be deformed in its diameter, manytimes forcing the rings to outside the hubs.

I already faced this problem, and solved it changing the hubs.

If a lower torque is applied, the transmitted torque can be not guaranteeded for the drive pulleys.

At the begin (70´s) , it was told that the pulleys with expansion rings were lighter and its shafts easy to dismantle.

Honestly saying, I am in doubt about such advantages, comparing with the old pulleys connected through keyways...

They were not that bad....at least I can not remember reports about problems with them, and this is not the same by the expansion rings pulleys.

Regards ■

Dear Mr. Witt,

Thank you for your reply.

My purpose with the question about the expansion rings is exactly to open the discussion about this theme.

Yes, the notch effect will allow us to use smaller diameters because the notch factor (2 for keyways) will decrease the allowed tensions for the shafts at these points.

By other hand, the allowed deformation (durchhang) for the shafts with rings is supposed to be 1/2000 and for the shafts with keyways the deformation can be bigger, lets say, 1/1500, because one do not have to be worried about the contact surface between rings and shafts.

Naturally, depending on the circunstances, the shaft could be even smaller by keyways, but, as a general rule, it can be understood that expansion rings will allow smaller shafts.

I believe that the great factor wich make the keyway construction more expensive is the cost of the hubs, because, normally we will use much more heavier hubs, normally screwed to the side walls of the pulleys.

But I am not really sure if this will be significant by the small pulleys.

See, I think that this invention (expansion rings) is a great idea, but actually I have indications that at least for the so called "small" pulleys (lets say - under 400 mm) the keyway construction would be better recomended.

The problem by the expansion rings is the pressure between rings and shafts, this pressure, as also the flexibility of the side walls should be well known, if not, one probably will face problems.

About the factor: excuse me, but this factor you indicated is remaining to me not very clear.

If one ring breaks should the other support the transmitted torque??? But in this case, the pulley would be anyway damaged, and this additional safety brings nothing.

I would agree with the same factors refering to the installed torque divided by the number of rings, without any further question.

with friendly Regards from Brazil. ■

Hi everyone,

Another question about the expansion rings is the necessary caution with the torque to be given to the screws in order to guarantee its transmission capability.

If one gives more torque than recomended or if the hubs do not have enough outside diameter a deformation of them will appear.

Be carefull about that.

I know cases where people faced such problems, and they´ve changed their hubs.

I have the impression that this cases are relatively easy to find.

Rgds ■