Expansion rings dimensioning

Posted in: , on 11. Apr. 2007 - 13:43

Hi everyone,

some specifications recomend to apply a factor of 1.6 to the installed torque for the dimensioning of EACH ringfeder type expansion ring of a drive pulley.

Isn´t it too much??


Alexandre Calijorne


Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097

Re: Expansion Rings Dimensioning

Posted on 12. Apr. 2007 - 11:10

What do Ringfeder say?

John Gateley johngateley@hotmail.com www.the-credible-bulk.com

Lyle Brown
(not verified)

Re: Expansion Rings Dimensioning

Posted on 12. Apr. 2007 - 11:35

Is this not just a "starting" torque factor?


160 % of FLT?

Or maybe something a bit more detailed such as load sharing between the two (assumed) end discs due to flexure of the shaft / shell?

Re: Expansion Rings Dimensioning

Posted on 14. Apr. 2007 - 01:07

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.


Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097

Re: Expansion Rings Dimensioning

Posted on 15. Apr. 2007 - 12:47

I would add to John Gateley's reply " What do Ringfeder say?"

adding what does the shaft say. Crushing the pulley shaft is more common than most people think. The only outward signs are are a slightly offset pulley but the damage results in shaft weakness and loss of grip of the device. The shaft and locking device/torque must be designed/selected together.

Engicon specialises in correcting non-performing plants and low cost de-bottlenecking of systems.

Re: Expansion Rings Dimensioning

Posted on 18. Apr. 2007 - 02:14

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.


Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097
Axel Witt
(not verified)

Locking Devices For Pulleys

Posted on 18. Apr. 2007 - 02:18

Dear Sir,

locking devices are manufactured, amoung others, by Ringfeder, Bikon and TAS. If you select self centering locking devices, you get the following advantages: pulley shaft is smaller (which increases the space between shaft and shell, in order to have enough elasticity), because the "notch factor" of a hub to shaft conncection with locking devices is less than the notch factor of keyways. Pulley shaft is much easier to dismount; besides the production of new pulleys, we carry out the repair and overhauling of pulleys for belt conveyors in the coal and steel plant industry (so we know what we are talking about). In addition to the reduced "notch factor" the transmissible torque and bending moment of locking devices is much higher (esp. wide lockinh devices), than the capacity of keyway connections of the same diameter. Finally the fabrication costs of pulley shafts and pulley discs for locking devices are lower.

To answer your question at the beginning:

I would recommend a factor of min. 1.5 in relation to installed power (torque) and a factor of min. 2 in relation to the power (torque), which is required for steady operation and belt fully loaded, for EACH locking device!

In case of any further questions do not hesitate to contact me.

Best regards from Germany,

Re: Expansion Rings Dimensioning

Posted on 24. Apr. 2007 - 03:11

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.

Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097

Re: Expansion Rings Dimensioning

Posted on 26. Apr. 2007 - 01:15

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.


Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097