Re: Flat Conveyor Runs Backwards
Hi Ajacks..
Looks like you might be talking underground, if you are using a fabric belt over such a long length of conveyor.
Otherwise, normally you would use steelcord belt which has about 10 times less stretch, and so you problem would be vastly improved.
Also, if you have a winch take-up, lock it during stopping to maintain the strain until you start it again.
If you have a gravity take-up, then fit a capstan brake on the take-up rope.
Lastly though,.. why on earth are you jamming the tail pulley? I never do that!
Cheers
Taggart LSL Tekpro ■
Re: Flat Conveyor Runs Backwards
Install a V return plough, maintain it and problem goes away. ■
Gary Blenkhorn
President - Bulk Handlng Technology Inc.
Email: garyblenkhorn@gmail.com
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Offering Conveyor Design Services, Conveyor Transfer Design Services and SolidWorks Design Services for equipment layouts.
Same Old Story.
There was an incident where a tail pulley jammed; the motor ran up to stall; along came a guy with a shovel who cleared the obstruction but didn't let go of the shovel fast enough. First the shovel and then himself were dragged through the tail section as the locked in tension broke free.
There used to be a Bibby Gradual Release ARU which was mandatory throughout UK coalfields. I don't know what happened to it: if it is still on the market.
V-ploughs are effective obstruction for smaller lumps. I saw a constant stream of 250mm lumps just rolling over the plough on a steep ore conveyor in Kitwe, Zambia. By some miracle most of them got flipped out the other side by belt flutter(ish). But that was a steep incline and your belt is pretty flat. Are lumps escaping at loading and entering behind the plough? Sounds far fetched doesn't it? ■
Control
Jamming when starting? Was there no chute clogging from upstream conveyor? --> Chute clogging switch, or have someone have a look in person when situation might be not as per spec.
Jamming of tail pulley should be a rare RRR incident and be treated as a "no repetition issue", the dangers have been described by collegues as above, to be taken seriously. And some remedy action as well.
Then there's the VFD, perhaps motor current limiters, PTC thermistors. All of those, but especially VFD, should be checked for a safe technical control procedure to be implemented.
Together with a belt speed / rot. speed sensor at that tail pulley & a specifically attuned ramp-up time at the drive + drive current control & limiter -->t.b. checked with your E-department.
A question to the designer of the belt conveyor, perhaps to the knowledgable community: Why did the drive pulley not slip?
BTW:
At other installations with fluid couplings re failing backstops, that's one of the the scenarios when one could witness the "exploding coupling" issue.
And what concerns the poor "shovel poker", there was an incident when someone got dragged in by his shovel even at relative slow operative belt speed. It was still too fast for him so he could not release the handle. With average human reaction time, the shovel handle was too short to give a chance to let go.
Please give some feedback as to some detail and how you remedied that issue in the end.
Regards
R. ■
Re: Flat Conveyor Runs Backwards
The only way to stop the tail station from running in reverse from a stalled belt is to either place a holdback mechanism or properly designed brake.
The brake has problems with capturing the stored strain energy on the carry strand stretch, but, can be done and it can be designed to gradual release the stored strain in a safe manner.
There are two general types of holdbacks - low speed and high speed. The high speed is mounter to the gear reducer high or intermmediate speed shaft. This holdback can be fitted with a clutch that can be gradually disengage the captured carry side strain. The low speed holdback can also do the same with knowledge of the ocassion such that the captured strain can be gradually released with a hydraulic jack under the torque arm. This might be a little disarming for some (pun intended). ■
Flat Conveyor Runs Backwards
Flat Conveyor Runs Backwards During Aborted Start
I'm looking for advice on how to handle the case of a conveyor running in reverse after an aborted start. The conveyor is approximately 10,000ft long, fairly flat profile, with 1,200HP attached, VFD controlled, and fabric belt. We've had a situation where the tail pulley was jammed, and when the belt was started it began to ramp up until the motor stalled & shut down. At this point the conveyor ran in reverse momentarily due to the high amount of tension in the belt.
So what is the common practice to prevent this? I know many backstop manufacturers recommend installing a backstop. And obviously that would prevent the conveyor from running in reverse. But in the case above (jammed tail pulley) what do you do after the backstop is set? In my opinion, if seems like you now have a "loaded gun" with the carry side of the belt tensioned. If you remove the obstruction at the tail pulley, would it not cause the belt to move forward?
Just looking for advice if any of you have handled similar situations. Thanks - ajacks. ■