Dear Mr. D Martinez,

Your query relates to constructional and design feature of fluid coupling, so fluid coupling designer and manufacturer are the right people to comment about this.

However, engineering general perception implies that the efficiency of the fluid coupling would be the indicator of the energy lost in fluid coupling, which would be converted into heat. Suppose, fluid coupling efficiency is 98.5% then 1.5% is the loss of energy related to fluid coupling. This energy loss is occurring due to external windage and mainly due to oil churning. So, convert this energy into the temperature rise of the fluid coupling assembly i.e. fluid coupling mechanical parts plus oil within the fluid coupling. There is a energy loss at the fluid coupling surface due to heat loss to the air and radiation. The energy expended in fluid coupling will tend to increase the temperature, which would also increase the heat losses to the surrounding. At a particular situation both will get balanced and that situation will result in to specific temperature of the fluid and fluid coupling.

If you are the user of fluid coupling, then best option is to refer to your supplier / manufacturer of the fluid coupling and they will have a ready data to inform you the temperature when fluid coupling of particular model is operated under specific kW load and rpm.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dear all,

Rarely I come across situations, where the fusible plugs are found blown off. Though I could not find any reason at the site. After refilling the oil, again the conveyor is running for months together.

Could there be any problems from electrical side contribute to this? Say, motor RPM becoming less etc., ?

Thanks a lot & regards,

S.Ganesh ■

When considering the characteristics of, or problems with, proprietary equipment or components, I usually find the equipment/component manufacturer is the best source of information, although persistence may be required to get to the right person in an organisation. ■

Dear Mr.Designer,

If the problem is occurring constantly in only one manufacturer I would have called the manufacturer. But it happened almost all the manufacturer.

If there is any mechanical problems it would be visible for the over loading of fluid couplings.

But the site condition is very clear. After filling the oil, it runs perfectly for months together.

I feel other members also faced this problem.

Regards, ■

Originally Posted by sganesh

But it happened almost all the manufacturer.

Then it is clear that the couplings are being wrongly selected or applied, or maybe they are from a poor manufacturer. It's easy to copy a design, harder to understand it's characteristics. In all the 30 + years I have used fluid couplings they have operated with minimal problem (but they were all from an established UK manufacturer).

The most useful site I have found for information is the Voith site. http://www.voithturbo.com/

But don't expect to be able to look up the minute detail of such components, a manufacturer needs to keep some of his knowledge to himself, not give it away to the copy manufacturers of this world, or he'll go out of business ■

Hi,

One of the reasons that the manufacturers don't publish curves, or estimation of the time a coupling takes to reach a critical temperature, is because there are just to many variables to take into consideration. Things like the ambient temperature, number of previous starts, load of the machine, to name but a few, all have significant influence on the coupling temperature rise.

Most manufacturers will have theoretical data on heating, which will be reasonable accurate for design conditions, but to publish it in a meaningful manner, for every possible condition the coupling is likely to endure, is more or less impossible.

As a general rule of thumb, only traction type couplings have fusible plugs fitted, and they are fitted as 'last resort' protection for the system in case of overload or stall conditions. The first line of defense, in an overload or stall situation, should always be to trip the motor electrical overload protection. These should be easier to reset than the coupling, and a lot cleaner too!!!

Most manufacturers should be able to advice what the maximum coupling full load torque capabilities are, therefore giving you an idea where to set the motor electrical trips. Typically for a straight forward, non delayed fill traction coupling the full load torque capabilities will be approximately 200%.

All this of course assumes that the coupling has been correctly selected for the application.

If you use 'clutch' type couplings, something like a Fluidrive SCR coupling, then the conditions are slightly different. Again the motor electrical trips are a good starting point for overload/stall protection, but it is possible to monitor these coupling types for temperature, and where required fit additional external cooling. The internal working circuit oil temperature is always significantly higher than the oil temperature in the couplings external galleries and pipes, but if you limit the external temperature of the oil to no more than 90 degree C, the coupling will normally be fine.

If the couplings are overheating, and the system is not operating in an overload or stall condition, then there would appear to be an issue with the coupling sizing. If you have any further details, I would be happy to try and help.

David

Fluid Coupling Engineering

Cell +44 (0) 791 202 3945

www.fluidcouplings.co.uk ■