Hello,

The bucket elevator is conceptually vertical conveyor. The vertical conveyor will require more powerful (bigger) drive in comparison to horizontal conveying. Accordingly elevator drive unit moment of inertia is relatively large in comparison to moment of inertia of elevator proper. Therefore, even with DOL starting factor 2.5, the starting factor with respect to chain / belt line is often around 1.75 at design capacity. Thus equipment characteristic is such that it is as good as soft start at chain / belt line. One can work out this actual figure by dynamic (motional) analysis, for each elevator, while designing.

If one want to use variable speed drive, it can have following benefit:

A) 1: 10 reduction can be useful for inspection and commissioning (empty run).

B) Elevator operation speed is fixed, such that material discharge trajectory should pass into discharge chute mouth. Therefore, the discharge trajectory at other speed will result into material falling back into boot, and non-workable equipment (failure). This is different from belt conveyor, wherein discharge material will always fall into large chute below, whether conveyor speed is less or more. So variable speed drive’s other use for bucket elevator will be for more moderation in starting factor only, rather than regular operational speed.

C) Variable speed can be useful to fine tune operation speed, for least carry over of material as a remedial measure for design inadequacy. Once such speed setting is done; the elevator regular operation will be at that fixed speed only.

Well one opts for complexity in machine if there are benefits. ‘If’ variable speed drive’s use is quite less for usual elevators, then it implies that engineers / users may not have found it appealing. For special heavy class elevator the situation may be different.

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 ■

How big is your elevator? I am not aware of vfds or a fluid couplings being installed on a bucket elevators.

I am going to side with Mr Mulani on this one. Within reason, you want to run your buckets as empty as possible to avoid spillage so that begs to question as to why you would want to install a VFD. I have heard some electrical engineers (I am not one) talk about being able to run a VFD at 5 to 10 % overspeed. If you needed the additional capacity maybe That would be one of the only reasons I could see for installing a VFD. I guess if you wanted to use the same bucket elevator for two different materials with very different densities. Every bucket I have purchased was with a main drive, an inching drive for bucket maintenance and an external backstop. You should not need a vfd for maintenance. I believe we have always used soft starts, it just seems to be a better use of money ■

Did you mean bucket reclaimer? ■

Mr. Mulani.

According to your comments, it is possible to replace a fluid coupling with a soft-starter, provided that soft-starter starting ramp is similar to fluid coupling starting ramp.

I appreciate your comments.

Regards

Originally Posted by I G Mulani

Hello,

The bucket elevator is conceptually vertical conveyor. The vertical conveyor will require more powerful (bigger) drive in comparison to horizontal conveying. Accordingly elevator drive unit moment of inertia is relatively large in comparison to moment of inertia of elevator proper. Therefore, even with DOL starting factor 2.5, the starting factor with respect to chain / belt line is often around 1.75 at design capacity. Thus equipment characteristic is such that it is as good as soft start at chain / belt line. One can work out this actual figure by dynamic (motional) analysis, for each elevator, while designing.

If one want to use variable speed drive, it can have following benefit:

A) 1: 10 reduction can be useful for inspection and commissioning (empty run).

B) Elevator operation speed is fixed, such that material discharge trajectory should pass into discharge chute mouth. Therefore, the discharge trajectory at other speed will result into material falling back into boot, and non-workable equipment (failure). This is different from belt conveyor, wherein discharge material will always fall into large chute below, whether conveyor speed is less or more. So variable speed drive’s other use for bucket elevator will be for more moderation in starting factor only, rather than regular operational speed.

C) Variable speed can be useful to fine tune operation speed, for least carry over of material as a remedial measure for design inadequacy. Once such speed setting is done; the elevator regular operation will be at that fixed speed only.

Well one opts for complexity in machine if there are benefits. ‘If’ variable speed drive’s use is quite less for usual elevators, then it implies that engineers / users may not have found it appealing. For special heavy class elevator the situation may be different.

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

■

Originally Posted by adesito

Have anyone have experience with frequency inverters with soft starter in bucket elevators?

I dont see much information about it in bucket elevators manufacturers.

It could avoid the hydraulic coupling and also be useful in starting with load and low speed after

an emergency, as well as in inspection and maintenance.

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Good evening adesito,

All the bucket elevators I have ever worked with have an electric motor drive with

three phase power operating a reduction grar box that powers the drive gear at the

top of the bucket elevator on its platform.

With a reduction gearbox there is no need for soft starting as the power transmitted

is reduced in speed and delivered through the gearbox over a very narrow power band with

power spikes at start up.

These elevators have been made the same way for over a hundred years and the single

speed hoist is there to do several things-

1. maintain productivity at a set tonnage per hour

a. add tonnage per hour by adding buckets to the elevator chain links

2. operate the bucket lifting system at a preset speed within its

desired delivery tonnage per hour with X number of buckets or X + X +X

number of buckets at the same hoisting speed with the same numbe of X

buckets using minimum power delivered to a sprocket drive system which is sized to deliver

the material to the end point which is the tipping point at the top of the

elevator where the bucket dumps into a another tube or tubes to be gravity fed to a bin

The standard issue Dodge/Falk rubber coupler or chain coupler from the electric motor shaft

to the reduction gear shaft is all that is needed.

3. there is nothing to be gained by using fluid couplers or soft start systems as the reduction

gearing mechanism is your soft start where the key stock in the drive sprocket is acting as

your circuit breaker.

No point in reinventing the wheel when the wheel has worked well into the 21st century ■

Depending on the length of the bucket elevator there will be tremendous inertia to get everything moving. The elevator motor could draw multiple times the FLA for several seconds.

I recommend a soft-starter unless you really need to adjust the running speed. Either will need to be oversized for the starting amps, and the oversized soft-starter will be much less expensive. ■