Re: Elastic Stretch For Olc Take-Ups
Hello Jara..
In addition to the normal dynamic stretching of the belt, you will have to include travel to first remove the belt sag (heavy belt you know) as well as some additional so as to be able to make a few repair splices.
What I recommend to do on these long jobs is put in two take-ups if the arrangement easily allows this to be done. The one is a rigid type belt storage, and the other moves to accommodate the varying strain in the belt.
(I am busy right now designing a dual take-up system for an 8km overland with a gravity take-up with capstan brake at one end, and a motorised winch take-up at the other.)
Please don't skimp on the take-up travel..its really not worth it. Put in a good 30m+.
Regards
LSL Tekpro ■
Re: Elastic Stretch For Olc Take-Ups
Thanks for your comments Graham. I have not investigated a dual take-up system before - I will have a look around at some designs and see if this might work for this project.
The reason I asked about elastic stretch alone is that this is the biggest component of the take-up travel allowances. With sag, permanent stretch, thermal allowances (it gets hot in WA), splice, and dynamic travel allowances, plus buffers and trolley - the take up track length could be as long as 104 m, using the most conservative approach. I dont think 104 m of take-up track would look sensible, however I completely agree with you that the track length should not be skimpped on...hence my dilema.
I anticipate that belt manufacturers incorporate some contingency in their recommendations, but in my experience suppliers are reluctant to give information outside of those recommendations, else, they would not have these 'recommended' values in the first place. I wondered if perhaps some of the experiences of the people within this bulletin board might allow me to reduce the elastic stretch to a more resonable figure (than 23 m), either by using a less conservative, more accurate formula, or by describing a method of installation that gave control over the elastic stretch - as can be done to control sag, somewhat.
Thanks again Graham. I will have a look at dual take-up systems. ■
Re: Elastic Stretch For Olc Take-Ups
Your numbers seem unbelievable at 104 m travel. No self respecting conveyor engineer would design a take-up system with 104 m of travel for an 18 km long belt.
Nor would they design to a 30 m travel. I know Graham would not do it if he made the calculation and costs his recommendations.
There are many avenues to a prudent design recommendation.
Take care about the conveyors geometry which may suck a lot of belt into the idler gaps with a downhill-uphill arrangement. ■
Re: Elastic Stretch For Olc Take-Ups
Yes thank you Nordell, I appreciate that 104 metres is a somewhat long take-up track length - this is why i am trying to reduce it, and why I am seeking advice from more experienced industry experts or site operators. Please appreciate that I do have some experience with take-up systems - just not one that standard industry calculations for short conveyors suggest should be 104 m.
The belt length is 36 km - conveyor centres are at 18 km.
104 m is a 'total track length' based on the most conservative approach using methods suggested by Golka et al. This can be reduced by about 30 m using the least conservative approach from industry references such as CEMA, Dunlop & Beckley, however all standard industry references suggest a minimum travel length of 65m, which equates to a track length of around 75m. Dunlop and Helix further suggest an absolute minimum of 43 m of take-up travel, but I am not comfortable with this figure as it arbitrarily calculates allowances based on standard factors of 0.05 to 0.15% of conveyor centres, and does not adequately incorporate actual conditions.
The conveyor geometry has been monitored closely already, and other travel allowances have been reduced as much as I am comfortable.
I am seeking either, more accurate formulae for elastic stretch, comments on people's experiences when comparing calculated travel lengths versus observed (constructed) travel lengths, or alternatively, innovative solutions - such as the dual take up system - that lie outside my experience.
Thanks for your comments though Nordell. ■
Re: Elastic Stretch For Olc Take-Ups
Morning Jara et al..
Just checked the measurements I took of the horizontal take up movements on one of my 6.3km conveyors.
It actually moves 7.3m at the moment, and the rail marks indicate this value increases when the belt has been basking in the good old South African sunshine.
This implies a total working movement of about 1.25% but this value excludes the movement required to get to T2 in the first place and to remove the bit of sag etc.
For information, the take-up tracks on this 6.3km conveyor are 22m long and the carriage is 3.4m long which gives a maximum potential travel of 18.6m.
In practice, this is only just sufficient for all things considered.
Assuming the belt storage for splices is say 3.5m and the clearances are 1m at each end, then your tracks should be:
Tracks for 18km = (18.6-3.5-1-1) x 18/6.3 +3.5+1+1= 43m minimum
This also implies that if dual t-u, you need +23m at one end for dynamic movement and +20m at the other for everything else. (To this you must then add more track length to compensate for the additional dead length you get from having two tracks instead of one)
You also need to do the calcs for your St 5600 belt.... I did not use a percentage basis for getting my t-u length, I did it from scratch based on all predicted tensions and the modulus of the cords, and this fortunately gave me the accuracy that I ended up with.
Final comment ... again don't skip on the travel.
For such a huge capital investment why try and save a few Zimbabwian Dollars worth of moola on the take-up?
('Morning Larry)
Cheers
LSL Tekpro ■
Re: Elastic Stretch For Olc Take-Ups
Thanks for your example Graham. Your figures and methods match my own (pretty much) - Your 43 m minimum, though scaled off your 6.3km conveyor, is identical to the 'recommended minimum' from my texts - which suggests the numbers arent going to come down any futher, unless we change the conveyor profile - which is not really possiblle.
Dynamic travel is around 21 m, which agrees with your suggested value of 23m, also.
I calculated elastic stretch (23 m) by breaking up the belt into sections, assessing the average tension, and then factoring in the belt modulus - as you have done. I have tried to use formulae where possible for all components of TU travel as, like yourself, I dont like the concept of using percentage factors alone on a long take-up like this one.
I dont wish to build too short a track, however I dont really want to build a 104 m track either - it just looks too long, however a 75 m track for 60 m of travel should suffice, else we will assess the extra costs of including a winch take up to remove elastic, sag and permanent stretch.
Thanks for your input Graham - it was both useful and informative....
Regards,
J ■
20 Km Overland Take=Up Travel Allowance
Curragh North is a working 20 km, horizontally curved, overland which has a ST-1500 N/mm belt (more stretch than ST-5600 N/mm), driven by 4250 kW, that we operate with a 50 m tower travel and 60 m horizontal trolley track travel.
This travel allowance includes:
1. Ridge-body tension variation .................... 7 m (min. to max)
2. Thermal allowance .................................... <3 m
3. Permanent stretch .................................... 15 m
4. Splice allowance ....................................... 4 m
5. Clearances ................................................ 2 m
...................................................... subtotal =31 m
6. Elastic Dynamic allowance due to terrain ~15 m
(Good morning Graham) ■
Re: Elastic Stretch For Olc Take-Ups
Sorry,
Wrong File.
Thermal travel for the temperature extremes is > 10 m.
The point is the elementary tension range is not the governing travel. ■
Re: Elastic Stretch For Olc Take-Ups
Respected experts,
I will be glad to receive the answers for the following queries:
1) Such long conveyors! How are they maintained? Absolutely all the safety devices need to be in line. All the mechanicals, Belt and safety devices need constant inspection. What type of automation exist to ensure the above?
2 ) In fabric belts, stretch increases when the rating increases.
Is it different in steel cord conveyors?
3) Have you ever faced snapping of the belt? What method you adopted to put back the conveyor in shortest possible time? You may have the record and experience of the longest belt snapped and the time duration for putting back into operation.
Sharing your knowledge will help us a lot.
Thanks & regards,
S.Ganesh ■
Re: Elastic Stretch For Olc Take-Ups
Respected Enquirer,
We do not design snappy or snapping belts. We have not had/done a snappy belt in all our design days. We do fix snappy or snapped belts from erstwhile designs.
Matter of fact, we are fixing a snapped belt at the moment. Poor client inherited a super stopper that snapped when the stopper over stopped. However, the belt is not an overland, just an aggressive downhill threaded through a tunnel. Designer did not plan for the snapper. Snappers often snap when there is excessive tension, followed by a long downhill ride.
Client grabbed one piece and slowly pulled uphill, back downhill and reconnected the snap. It took three days to pull 5.2 km uphill and downhill and unsnap. It took another week to repair the many lost high-speed brake parts, motor shaft and twisted reducer high-speed shaft. It took time to do the cleanup and correct bent frames and many misplaced idlers. It was a lesson that thou should not use band-brakes on high-speed shafts. ■
Re: Elastic Stretch For Olc Take-Ups
Actually Lawrence, Curragh North was a conveyor I have been using as a measure, but i appreciate the take-up details. I knew that the track was 60 m, but I didnt know the break up.
Some of my colleagues worked on the CN conveyor. Indeed, I believe you know at least one of them quite well...
In conjunction with the overly large, conservative, track length, the NC track length was what sparked my attention....stretchier belt, faster belt speeds (max 7.5 m/s from memory)...however this (18km) conveyor has higher power demands (more than twice NC) and peak capacities (>5000 TPH) on a wider and much stiffer belt.
Elastic stetch is the largest single component of the take-up break-up, according to my calculations, however this is not to imply that it is the most important....merely the component I was hoping to reduce somewhat, as I have already refined the other values as much as I am comfortable to do so.
Thermal travel for this conveyor is about 9 m.
Thanks for your input Lawrence.
Regards
J
sganesh....outta time today..maybe tomorrow. ■
Elastic Stretch for OLC Take-Ups
I am designing the horizontal take-up system for a long overland conveyor carrying iron ore through the Pilbara region of Western Australia and am interested in people's experience and comments on the accuracy of the various methods and formulae used to determine elastic stretch for general (short) conveyors.
Using an ST5600 belt, with a take-up mass of 107 tonnes, and an 18 km conveyor centre distance, standard formulae suggest an elastic stretch allowance of around 23 meters (give or take a few meters depending on the exact method followed).
In general I accept the values calculated via standard formula for short conveyors, as adding in an extra, say, 500 mm to a take-up track is rarely an issue, and better for conservatism - however - at 23 meters for elastic stretch alone, this is leading to a somewhat excessive total track length.
Over 18 km, this figure is not necessarily surprising, however I was intersted in peoples' comments on how realistic this figure might be, or whether there might be a less conservative method to follow which still allows some level of confidence in the take-up design.
Dunlop suggest a standard figure '= 0.15% of Conveyor Centre Distance; = 26 m
Calculating stretch as a function of take-up mass/belt modulus gives 23 m.
Has anyone witnessed the accuracy of take-up travels on longer conveyors calculated according to the above, or other, methods?
...finding justification to half this length to around 12 m would be very beneficial - however I am not sure if this is in any way possible without losing confidence in the final allocation of track length.
Comments and experiences would be very much appreciated.
J ■