Originally Posted by sganesh

Dear experts,

For motors below 30 KW, would it be necessary to use fluid coupling ?

Regards,

No there are alternatives, take a look at www.magnadrive.com We are MagnaDrive suppliers in the UK, most of our retrofits have been to replace fluid drives, all of which are running well, in some cases for 10 years or more with zero maintenance. ■

New thread started as the post were not related the original post in the thread these were moved from. ■

Hello,

Referring to your query about need for fluid coupling, some information is as below:

1) During steady speed, the induced stress is as per load / resistance.

2) During starting, the induced stresses are total of stress due to resistance (load) plus inertial stress.

3) As is the common experience, smoother the start up lesser is the inertial stress (like sudden release of clutch versus gradual release of clutch).

4) So if designer wants to have lesser stress during start up (i.e. less belt tension, belt of lower rating, pulley economisation, etc.), he can opt for fluid coupling. For small conveyor there is no economisation in belt which is often on the basis of minimum ply to support load, so people do not opt for fluid coupling. Not because of lesser kW.

5) Less tension in belt implies smaller concave radius. If there is space limitation then one can opt for fluid coupling irrespective of kW.

6) Conveyor equipped with traveling tripper can function much better by having fluid coupling because it reduces the concave radius magnitude and thereby minimises the belt lift up, spillage, take up misbehavior, etc.

7) If the load has large moment of inertia compared to motor power, load will take long time to reach the full speed. Directly coupled motor will be also forced to rotate accordingly and will draw very large current for long time beyond the permissible limit of motor / electricals. Fluid coupling allows motor to reach full speed in few seconds and load can take its own time to reach full speed, without straining electricals and motor.

8) Etc. (this is too big a topic to continue).

9) One can use alternative options to fluid coupling, if same satisfies the functional requirement.

Regards,

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Great Explanation Mulani Sir. Recently I came across a slimier problem in one of our coal mine infrastructure project in Indonesia. Hope this platform is the right place to share this.

There were some problem in RC (underground conveyor under neath of a dump hopper) starting. The motor is 190kw which equipped with VSD is only 160kw so the motor cannot get the starting current required instead.

The question came up about why only now after 3 years of running with the same coal flow on the reclaims.

It is all to do how the system is now being operated, there was substantial time (2-3hours) between the starting of the RC and also only ran for short periods when loading the barge and because of this the core temperature (rotor) did not raise high had cooled down to ambient temperature allowing the motor to have starting torque with less power. This is due to internal rotor resistance, when hot requires more starting power to break away and the motor stalls due to the VSD limiting the current.

Power is the combination of current and voltage. When hot the rotor voltage increases due to rise of internal resistance and current falls due to this voltage increase then the rotor has less magnetic force and greater frequency slip and due to the current limiting of the VSD the power in the rotor effectively reduces)

The same conveyor/reclaim with the same load and settings on the VSD with the first start of the day can pull away the load whereas the day before when hot it could not.

As the day went on and the internal temperature rises the torque output is less for the same power input, where finally it will stall due to the VSD current threshold.

So the VSD selection must be one step higher than the motor Size (Ex: for 160Km motor need 200Kw VSD)

Also motor design plays an important role in the VSD size selection. Standard motors have different starting characteristics to special design. (VSD, high efficiency, etc.)

Thanks & Regards

Karthik

conveyorkarthik@gmail.com ■