Hello Gary,

although my only experience has been with the Hewitt Robins cable supported and CCC steel stand belts with hydraulic take ups, I would be more worried about the no load conditions you would have and possibly overstretching the belt and damaging the splice or splices as the gravity take up will give and take with the load encountered at all times which leads me to wonder if the

belt snubber takes up quickly you may end up cutting out and splicing belt from stretching of the belt.

Leon Z

Gary, I think I emptied my mailbox properly this time :^) ■

Mr. Blenkhorn,

1.) The 30" screw take-up (stroke) is marginal at 1.56% os the conveyor's length.

2.) A screw type take-up is not automatic. The tensioning imparts a constant strain energy that, (if done properly) when the conveyor operates at design load, the tension distribution is the same as with the automatic take-up. At less than design load the low tensions are higher than with the automatic take-up. Worse case, with regard to uplift, will be when the conveyor is loaded up to and possibly into the curve but not beyond. This must be checked in detail.

Joseph A. Dos Santos ■

Hi Gary..

I inherited a shorter conveyor than that, but it had a concave radius and a tail screw take-up.

I could not train the blasted thing as I could not control the tension in the curve sufficiently to get a decent trough when empty to lightly loaded.

So... don't do it Gary.

Cheers

LSL Tekpro ■

Dear Mr. Gary,

If you are opting for screw take-up then possibly you may need somewhat longer screw take-up, say about 1 m (36 / 40”). This depends upon percentage of tension rating in the belt. This is not known whether it is less than 60% or more than 60% etc.

The correct approach would be to redesign this conveyor in context of screw take-up instead of gravity take-up. I do not mean to say change of items. It is only redesigning for the tensions in the existing conveyor equipped with screw take-up. Then one has to see the occurring belt tensions at concave curvature, during steady running and starting. This will enable to check the belt stability in concave zone.

I suggest you to design as above or you may take assistance from some designer in your country. This is the rational approach. The other approach would be guess work / judgement and consequent risk (in context of suitability / workability).

If you are using screw take-up then it is recommended that the tension setting should be by hydraulic tensioner or load cell tensioner (maintenance tool). The manual setting by judgement is not advisable.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

My pleasure Gary..

Pleased to be of help.

Incidentally I totally disagree with the theoretically based reply with bells, whistles, longer screw, jacks, load-cells....

Just stick to good old gravity, as invented by Issac Newton, and it will work.

Cheers

LSL Tekpro ■

Screw take up is normally considered for conveyors less than 50m long and having space constraint to put gravity take up. Gravity take up is the best solution for belt conveyor to adjust tensions in starting, braking and running situation. I don't find any reason to change the gravity take up (already existing) to screw take up, unless there is any other issues to do that change. If at all needs to change to screw take up, it is important to analyse the tensions in concave curve for light loading or halfway loading on the curve to check that the existing radii is workable without lift off. ■

Mr. Blenkhorn,

I certainly agree that leaving the conveyor as it is (with gravity take-up) will not create any new problems and is the safest thing to do. So, if you already reached that conclusion, it seems that your post is to find someone who will tell you what you want to hear.

In the various posts (for this thread) no one has said that the screw take-up replacement will work. Indeed all responses express concerns with the available take-up travel and the new tension distribution. The point is that the analysis tools and methods exist to find out and it appears that this will end in hand waving rather than analysis followed by a rational conclusion.

I am equally concerned about some sweeping statements. For instance:

"Just stick to good old gravity, as invented by Issac Newton, and it will work"

"Screw take up is normally considered for conveyors less than 50m long and having space constraint to put gravity take up"

I must remind the readers that Sir Issac Newton did not invent gravity he discovered it.

Gravity take-ups, or automatic-constant tension take-ups for that matter, are not the only soluions for long overland conveyors. Fixed discplacement, winch type take-ups are used very successfully throughout the German lignite fields on very long, very high capacity and hig powered conveyors.

You just have to do the analysis and then you will know. And likely this analysis indeed will tell you what you want to hear.

Joseph A. Dos Santos ■

Gravity take up is not suitable rather practicable for long overland conveyor, mainly because long take up travel distance, needs huge take up tower. Modulating winch take up is the ideal solution for such long conveyors. This take up acts very much similar to gravity take up while in running condition. During starting (i.e acceleration case) and braking (deceleration case), it acts as fixed winch keeping the same extension as per the running load cases. Thus, maximum required belt tensions will be minimum with modulating winch take up.

However, fixed winch take up will increase the maximum belt tension requirement, because, take up movement need to be fixed considering the worst situation to allow for maximum take up travel distance. Fixed winch take up is never a good solution as the belt looses the flexibility to adjust tensions at different load case situation. Rather, modulating winch is the best solution to use for take up, as it is very effective to control belt tensions at different load cases and reduces the addtional cost of take up tower and saves extra space to put up tower.

It is important to have a reliable auotomatic control system for modulating winch take up to function without any trouble. ■

Mr. Kundu,

I am unclear what you mean by modulating. Indeed there are constant tension winches that are automatc by hydraulic drives or by vector control tied to load cell readings and even others. The winch take-up systems to which I refer are not automatic and hold a fixed position during steady state operation. They do have load cell feedback and the readings are used to manually set the initial tension that sets the basis for the dispalcement loacation, basically taking up the permanent stretch. These systems lock in higher initial tension settings during starting and stopping but these are locked displacements and these behave like fixed take-ups during operation incurring the extreme low and high tensions associated with any fixed take-up. The optional initial settings availadble for starting, stopping and steading-state running are to mitigate the duty not the magnitude of the tensions on the equipment.

Joseph A. Dos Santos ■

Mr Kundu..

So you can't use a gravity take-up (as invented of course by Sir Issac Newton) on long overland conveyors!!!.

This is nonsense..

My dual carry conveyor is nearly 7km long now with a conveying distance of 13km, and has a single gravity take-up

The Twistdraai 11km overland at Sasol has a gravity take-up

The 17km one in Zimbabwe has a gravity tail take-up

The 12.8km Syverfontein overland ran for 20 years with a winch take-up and has now been converted to gravity type

The MAN Takraf 8km curved downhill conveyor has a gravity take-up at the bottom.

Please do not mislead our readers

I rest my case

LSL Tekpro ■

Mr. Spriggs,

I am not misleading any readers in this forum. Only expressing my views and experience. Further, I have never said gravity take up couldn't be used. Rather, gravity take up is the best solution for any conveyor. However, depending upon the take up travel length for long conveyor, the take up tower may become very large. Modulating winch take up can be used in such condition. If you don't have any knowledge about modulating winch take up, I am sorry for that.

Please don't use your technical word like "NONSENSE" in this forum. If you have any concern about someone's view try to explain that in cool manner. ■

Dear Mr. Kundu,

You quote: "Gravity take up is not suitable rather practicable for long overland conveyor, mainly because long take up travel distance, needs huge take up tower. Modulating winch take up is the ideal solution for such long conveyors"

I believe you are/were preaching, with your above statement-of-fact. It needs to be corrected. Some of us do not enjoy having twisted logic passed off as the gospel. Gravity is infinitely superior to any winch in its: predictability, repeatability, response-ability, maintainability, and workability technical-ability, et al. There are occasions when a power winch has benefit. It is an infrequent case. It certainly can be made to work in a satisfactory manner.

There have been many prior postings on the subject. Joe says go powered with manual settings – experience from Rhinebraun and runaway automated electronic control. From the Alcoa Pilbara overlands, US Borax in the Death Valley areas, et al, having automated runaway powered winches replaced with gravity do to failed electronics.

First, you fail to understand that the take-up travel distance will not vary between a gravity system and powered system or fixed system. Try one criterion: drive slip – it is satisfied by appropriate belt slack side tension. Try other criteria: belt sag – simply controlled by tension. Their values can be controlled by a number of TUP options. Limiting TUP travel is not one of them. Thus, we fail to see why you ponder this thought.

Maybe, your point is the TUP tower size and cost? What about the multiple sheaves and rope of the winch system with its larger hysteresis that jacks up the needed tension level and resulting belt rating? What about failed electronic components in the strain-gauge amplifier circuit?

TUP towers can be multiple reeved to bring down the height. There are other methods to bring down the tower height. By example, I am working on a 17km overland that requires about 24 m of TUP travel. The arrangement has no TUP tower and has a gravity TUP trolley motion of 6 m. ■

Thank you Larry for correcting Mr Kundu's subjective comments.

I hope there won't be a hail storm... we actually agree on something!

LSL Tekpro ■

Larry,

We don't disagree on the merits of the gravity take-up systems. I disagree that it is the only way to go. I know how knowledgeable you are in this field so I can only guess that your interpretation of what I described is intentional.

You are familiar with the systems of the German lignite fields dating back 20 years or more. These are entirely manual winch systems with their operating positions locked by a winch brake. They have load cell feed-back but nothing electronic is done with this. Based on instructions (pursuant to calculations) the tension is manually increased for starting and then manually relaxed for steady state running. There is no running response to any electronics. These are fixed displacement during the entire run.

The development of these systems was undoubtedy for compactness as many of these are shiftable conveyors whose tension has to be relaxed quickly then retensioned quickly (for the shifting operation). The results are undoubtedly good because these systems are used in many fixed conveyors as well.

Joe Dos Santos ■

Gentlemen...

The issue is that the following statement was made:

"Gravity take up is not suitable rather practicable for long overland conveyor, mainly because long take up travel distance, needs huge take up tower......."

It is this statement that is incorrect

We are not saying you can't use winch take-ups, of course you can, but with the advent of the capstan counterweight brake, I will not normally use a winch again unless for some other valid reason.

Cheers

LSL Tekpro ■

Graham,

I agree that the gravity take-up is suitable, indeed preferred for a long overland conveyor.

Joe Dos Santos ■

Thanks Joe..

We got there in the end..

Cheers

LSL Tekpro ■

It seems the original question which is of simple nature has got somewhat sidetracked, but at the same time it has created interesting debate on the subject, with valuable information from different respondents. I would like to state as below to take a rational approach and proper analysis.

There are basically two types of take-up device (1) Fixed belt length during operation (w.r.t particular setting for a specific period). (2) Varying belt length take-up, during operation.

The serial no.1 can have screw take-up or winch take-up. The serial no.2 can have commonly used gravity take-up or it can have a winch take-up responding to the feedback from drive or other sensors. Such system is used for important conveyors where proper maintenance etc. is also under priority.

Each of the above take-up device has specific functional / technical and price characteristics. One uses the take-up device which is the most suitable on consideration of application, functional / technical characteristics and price.

Therefore, the designer analyses each application on case to case basis and chooses the take-up which is the most suitable in context of the application (the designer analysis does not mean lengthy exercise all the time. For regular cases, designer just takes the decisions because he has already done the analysis of such cases many times). Therefore, one has to use the take-up which is befitting to the case rather than prejudicial approach for a particular type.

Most of the shitable conveyors are equipped with winch take-up, fixed belt length take-up device. Such conveyors are extensively used in India at lignite mines, primarily designed from Germany. But once I also came across shitable conveyor equipped with steel cord belt and horizontal gravity take-up (but may not be of huge conveying capacity. Also, the frequency of shifting may not be frequent. The device was mounted on shiftable pontoon).

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Mr. I. G. Mulani,

You have summarized it well, though I would add to class 2 (automatic) hydraulic take-ups using constant pressure (operating in vary narrow pressure range) hydraulic tensioning cylinders.

Joseph A. Dos Santos ■