Ash

I have installed two gravity take-up pulleys in the same take-up system with 5 pulleys in the system. This will reduce the travel distance by 50% but it requires the counterweight to be doubled.

The belt travels into the system over a bend pulley, turns down 90 degrees then around the first take-up pulley turns 180 degrees and back up around a center bend, then turns 180 degrees and back down around the second take-up pulley, turns 180 degrees and back up to the last bend and then turns 90 degrees towards the tail end.

This system was installed because we changed from a steel cord belt to a fabric belt and did not have the take-up room to allow for the difference in the stretch. The project was very successful and has been operating for 7 years with no problems.

Gary Blenkhorn ■

Dear Mr. A K Bhatnagar,

I agree with the view of Mr. Gary Blenkhorn. He has given a very good description of the system. I have seen such arrangement working in a power station in Malaysia.

Just for everyone’s additional clarity, both the take-up pulleys are on single sliding frame acted by one counterweight.

It would be better to be a bit liberal in pulleys diameter as belt is subjected to reversal of bending in quick succession.

Regarding disadvantage aspects, one is the point just referred above, but it is very minor in nature. Such take-ups are quite voluminous and relatively expensive, as everything is double for take-up.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Adding to the above and assuming we are talking about gravity counterweight (CWT):

1. The take-up describe is a double reeved arrangement where four belt strands are resisted by the counterweight mass. There is more than one type of double reeved take-up. Many underground fabric conveyors use multiple reeving to achieve short throw vs high force to save space by nesting pulleys.

2. There are other more complex double takeups. Geometric undulating conveyors may have both positive and negative power of sufficient magnitude to warrant takeups to be placed on either side of the drives. This happens when partial loading ocurrs. For example: Belt is inclined and then decline, like going over a mountain or large hill, when the incline is loaded the power is positive and pulls up the takeup, ahead of the drives, as the belt tension exceeds the CWT tension, and visa versa for the decline where the same take-up is active and take-up following the drives is under high tension. We have installed such take-up. They can use a single take-up mass. Care must be taken on the slewing rate and shock omabsorb the upper travel.

3. Some have tried individual takeups at conveyor ends (head /tail). These can be a disaster if proper dynamic analysis is not performed. The same is true for item two above.

4. There are semi-fixed and gravity, and gravity and semi-fixed similar to item two but controlled by other means to achieve special tension controls.

CDI has published and/or has been intrumental in the design on these special conditions such as:

a) Exampe of multi reeved TUP: "Zisco Installs World's Longest Trough Belt 15.6 km....." Presented at Beltcon is South Africa around 1997,



b) Example of dual take-ups: La Ciopa downhill/overland in Chile published by Derek Cieplinski of Fluor many years ago. The paper is archived in our office but I believe it was published in SME around 1992 after successful commisioning.



Regards,

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Further comment:

After rereading your query, it is unclear where you are asking the question of double reeving or dual separate CWT placement. Consider this:

a) with one location ie. one takeup mass and dual takeup pulleys the belt tension is constant, excluding hysteresis, this is true for nested on separate bends but one counterweight. Dont' do two separate counterweights. There is enough difference between them that one will have a small but significant bias to a larger force which will take all travel. The second counterweight will stay parked in the up position. You can get into oscillations due to the hysteresis.

b) with two locations and two separate counterweights can be very difficult to implement -- you do not know the true belt tension at each location in the design stage -- such that the true forces are not in balance and one take-up will do all the travelling -- big problem. Temperature can also bias performance.

How do you get them to properly respond according to your design numbers? It is almost impossible. Don't do it. We have witnessed those that have. B



By your query, I would guess you are about to try it. You seem to be uninformed. There is much you need to know. Be wise and have an experience designer give you proper guidance.

Take Care,

Lawrence Nordell

Conveyor Dyanmics, Inc. ■

In my opinion we need to know what conveyor type and configuration we are talking about.

How fast does the belt travel?

What are the load patterns?

I also believe that the distance between take-up assemblies is important.

I'm saying this because multiple configurations in the form of accumulators are generally used on web machines running at speeds over 1000 fpm and perform well. In view that the tension control in these manufacturing processes are several orders of magnitude superior to that of a conveyor, I believe that such multiple systems can work provided one is willing to use today's tension control technologies.

On the other hand, from a cost point of view, there is little incentive to create two take-up assemblies.

Antonio Reis

Vitrom Mfg Consultants

www.vitrom.com ■

Dear Ash,

It is feasible, as the other respondants have indicated, to use more than one gravity take-up for a single conveyor. The most that I have seen is three for a long fold belt installation near Las Vegas, Nevada in the US. This has performed well for over 15 years.

The caution given by Mr. Nordell is extremely important as uncontrolled multiple take-ups can be extremely frustrating for the operator.

If the desire is to have additional belt available for system expansion or belt repair/removal purposes, a more common practice is to use a belt bank with fixed pulleys and only one "take-up" pulley. This is a practice used in tunneling operations, where it is too expensive to shut down the large boring machine on a frequent basis.

As far as advantages / disadvantages of multiple take-ups are concerned. The advantage include additional belt storage; additional take-up capacity (as with the example given by Gary Blenkhorn), and vertical space savings. Disadvantages include added cost for both the belt and pulleys; increased chance of belt damage and mistracking; and extra maintenance costs.

Hope this helps in your evaluation. ■