8 replies to this topic

[Emax]

This ia a duplicate post from the "industry-only" section. I post it here in hope of prompting some insight from engineering types that do not access that forum. All thoughts are welcome.



There are several braking systems in every lift and each of them is required to be capable of bringing the lift to a complete, controlled stop under the worst possible condition. This is usually assumed to be the failure of all other brakes, roll-backs or regerative drive systems - with a fully loaded line. There remains (at least) one possible common point of failure that would negate the best efforts of all these stopping devices: a loss of traction between the haul rope and the drive sheave liner. Lacking adequate traction (for whatever reason), all systems designed to control the rope via the drive sheave are rendered useless.

I have been in a machine room during a load test when rope traction was lost for a moment. It's exciting. When it happened, a design engineer in the room turned white as a sheet. He later described what could have happened, mentioning that given enough slippage the liner would begin to act as a lubricant. It occurs to me that this is one worst possible condition that has not yet been addressed. If it has, I'd be interested to know how.

One possible back-up for such a scenario might be a main sheave brake - similar to the drive sheave brake - that acts on the return terminal bullwheel. The liner on this sheave is not subjected to the same day-to-day rigors as the one on the drive sheave and in any case would not lose tractionl at the same moment. In fact, the only scenario it would not protect against would be the loss of rope tension - in which case, the only thing that works is a traction rope brake (ala Riblett). Are traction rope brakes ever used on high-load lifts? With clamp-style grips? I don't know.

[ccslider]

I recall an incident when a top drive lift lost traction under full uphill load. The cause was the untimely scheduling of a rope lubing procedure just days before opening for the season. The solution was the rather frantic application of kitty litter between the rope and drive sheave liner.

[Emax]

ccslider, on Nov 15 2005, 07:53 AM, said:

I recall an incident when a top drive lift lost traction under full uphill load. The cause was the untimely scheduling of a rope lubing procedure just days before opening for the season. The solution was the rather frantic application of kitty litter between the rope and drive sheave liner.

Well, so it's not unheard of. Perhaps an automatic kitty litter injector would do the trick!

My only point was that slippage IS a possible scenario for which there seems to be no plan. Very un-Swiss.

[arialropewaymillwright]

This event can be alot more common than you like to think.
The first and most likely candidates are bottom drive lifts. The amount of tension required is incredible and as you mentioned under the correct circumstances like full capacity it becomes a reality.
This can be a nightmare to diagnos as its the last thing any one wants to imagine happening. 9 times out of ten it gets mis diagnosed as a bullwheel bearing failure.
Kitty litter... Hadn't heard of that one ---

[Emax]

arialropewaymillwright, on Nov 19 2005, 01:12 AM, said:

This event can be alot more common than you like to think.
The first and most likely candidates are bottom drive lifts. The amount of tension required is incredible and as you mentioned under the correct circumstances like full capacity it becomes a reality.
This can be a nightmare to diagnos as its the last thing any one wants to imagine happening. 9 times out of ten it gets mis diagnosed as a bullwheel bearing failure.
Kitty litter... Hadn't heard of that one ---

While the "kitty litter contingency" (KLC) is both imaginative and apparently effective, it seems to lack elegance. Not only does it rely on the ready availability of the stuff but also the presence of mind to use it. I also have to wonder about the proximity of KLC personnel to very hazardous areas of the lift machinery. Since you seem to have some experience with this ropeway phenomenon, what remedy would you suggest? I think we should exclude prevention since that really isn't possible under all imaginable circumstances.

[arialropewaymillwright]

Hello Emax, I agree with you 100% on not wanting to be the designated "KLC" person. There was a horible fatality just last year out east involving a scenario just like that on a smaller lift....
So you want answers??
Well if you have experienced this problem it would be imparative to hear the circumstances. The last example I heard was full uphill capacity on a Garaventa stealth bottom drive detach in very very specific weather conditions. (and it was very very difficult to diagnos)
The example posted by ccslider stated the issue arrising from an "untimely haul rope lubing". That basically says it all. I don't work for Fatzer or Trefel europe but I can tell you now that haul rope lubing is a very very grey area. When,How,Where and with what equipment and lubrication and at what rate is very lift specific. Its a giant pain in the ass is what it is.
Please feel free to disagree or add anything I might have waffled off on.
A.R.M out

[Emax]

arialropewaymillwright, on Nov 19 2005, 12:00 PM, said:

Hello Emax, I agree with you 100% on not wanting to be the designated "KLC" person. There was a horible fatality just last year out east involving a scenario just like that on a smaller lift....
So you want answers??
Well if you have experienced this problem it would be imparative to hear the circumstances. The last example I heard was full uphill capacity on a Garaventa stealth bottom drive detach in very very specific weather conditions. (and it was very very difficult to diagnos)
The example posted by ccslider stated the issue arrising from an "untimely haul rope lubing". That basically says it all. I don't work for Fatzer or Trefel europe but I can tell you now that haul rope lubing is a very very grey area. When,How,Where and with what equipment and lubrication and at what rate is very lift specific. Its a giant pain in the ass is what it is.
Please feel free to disagree or add anything I might have waffled off on.
A.R.M out

Nope - I have no disagreement with you. My point of embarkation on this subject was that IT DOES OCCUR and that there are no designed-in remedies at this time. Probably, the most likely cause would be improper rope lubrication - but we must admit that other factors might come into play - just what they might be is for the designers of safety systems to consider.

Allow me to pay you the compliment of being blunt: I know of no incident where the lift just "got away... for keeps" due to loss of traction - but we must admit that it is a conceivable event. That said, there really ought to be some plan in place to deal with it. This is not a matter rightly to be resolved by industry personnel that care for the equipment. Rather, I challenge the manufacturers to address this issue, since preventative measures can only offer limited protection against a possible disaster.

[arialropewaymillwright]

Wow I have never come across anyone as pationate about this as you.
Thank you for being blunt,it helps in my case.
Yes it would be a case for the manufacturers. That being said knowing how North America engineers follow European suit its obvious nothing will change unless there was a disaster.
There are several other more plausible safety concerns to be addressed and I know other industry personel that agree....JMHO!
A.R.M.
Ps If it does ever happen I will be sure to say "You told them so!!" :)
Pss They should have tried it at the Eskimo lift destruction tests on the cinderblock rollback simulation!

[Emax]

arialropewaymillwright, on Nov 19 2005, 12:59 PM, said:

Wow I have never come across anyone as pationate about this as you.
Thank you for being blunt,it helps in my case.
Yes it would be a case for the manufacturers. That being said knowing how North America engineers follow European suit its obvious nothing will change unless there was a disaster.
There are several other more plausible safety concerns to be addressed and I know other industry personel that agree....JMHO!
A.R.M.
Ps If it does ever happen I will be sure to say "You told them so!!" :)
Pss They should have tried it at the Eskimo lift destruction tests on the cinderblock rollback simulation!

Your HO is duely noted. I also agree that ther are far more pressing safety issues for manufacturers to consider. Disaster breeds rules - it's an unfortunate fact. No harm, no foul.