Start Torque and Time

Posted in: , on 2. Sep. 2012 - 15:22

Currently doing some study work for conveyors with big drives up to about 3000 kW. Conveyor lengths are up to 2.5 km long. Capacities are up to 9000 tph. Steel chord belts are to be used. What start factors (starting torque : 100 % motor FLT) and start up times are typical for such installations. We're pretty well boxed in with some of the conveyors so minimizing concave radii is critical. I'm looking for some numbers to put us in the ball park of what we can expect when we get to detail design.At present we've assumed a start factor of 150 % but I suspect that is conservative. If I use say a 25 second start time the start factor drops back to 80 to 90 %. What do you think about factors this low and the startup times mentioned? Haven't yet decided on the startup method but it will be either VVVF, liquid resistance or resistor banks.

Kind Regards Derek Bishop
(not verified)

Concave Radii Problems? Here's A Solution From The Dark Side....

Posted on 7. Sep. 2012 - 11:11

G'day Derek, I am not going to try to answer your quantitative q's but what I have found works reliably before when "boxed in" is there is a radius for empty start and another one for laden. If you can "get away" with the laden radius as far as the site is concerned then I have found putting a flat roller over the apex point to protect the structure against the unladen radius is a neat solution. Believe me it is a beautiful thing to behold the belt starting up pressing firmly on the hold down roller, then just slowly dropping away as the product approaches and the clearance just nicely increasing at a rate to mean the burden just misses the hold down roller all the way, maybe with a couple of taps when lumps protruding get a nudge, until the belt is finally fully laden and sitting in its proper place.

The only real risk of any kind is for a failed start where the re-start tensions will pull a partially laden belt back into the hold down roller. However by then you also have some shape to the belt so there is a partial edge sealing effect to counter the plough effect and not much spillage actually occurs in this rare event. In my opinion this may be a solution that offends the purists, but it is an elegant "hack" of the underlying engineering principles and worth considering. Good luck......

Re: Start Torque And Time

Posted on 24. Sep. 2012 - 05:32

Hello Derek..

For conveyors which have a concave radius, and such a high power for only 2.5km long, I would assume the lift to be of some significance.

Generally, the greater the lift, the less the inertia involved. Compare this to a long overland, where the kW per km would be less, but the inertia becomes very large. This would indicate a long start time

Conversely an inclined belt would indicate a short start-up time.

Be that as it may, I would look at a start factor of no more than 1.35 (or 135%) and make sure the extra start torque tails off nicely as you reach full speed.

Good luck

Taggart LSL Tekpro

Graham Spriggs