The first problem you are going to have is that a convwyor belt take up unit is not fixed as it has to move back and forth to absorb shock loading from the load in question and maintain tension on the conveyor to allow proper traction for the conveyor to move.

The second problem is the belt is gong to stretch during its life and your take up will take up the slack until it cannot retract anymore and then you will have to cut out a section to allow it to maintain traction around the drive pullies and head pulley which also allows the conveyor belt to maintain its track across the pulleys and maintain its training profile.

My question is are you referring to a weighted tensioning box that moves in a verticle travel distance maintaining tension on the take up pulley? if so they are the simplest type of take up to use and maintain. ■

Dear Mr. John Coupe,

You have got a 300 m long conveyor, you need to have take-up stroke of at least 2% + 0.6 m. Preferably it should be about 2.25 % of centre length + 0.6 m. Such take-up stroke will avoid frequent revulcanising of the belt as it stretches during course of the operation. You have following three options to provide the take-up arrangement :

1) Vertical gravity take-up : This will need head room around 8.5 m or so. If you do not have this space then opt for take-up as per serial no. 2 and 3.

2) Horizontal gravity take-up either at tail end or by forming the belt loop at intermediate point : Possibly you may not have space at tail end but you can create this at intermediate point. Take-up tower can be some distance away where there is space. Ropes can be suitably and safely routed to the take-up tower.

3) Most compact arrangement would be the winch take-up unit with load cells etc. for tension monitoring and warning etc. This is a very compact arrangement and it can be accommodated just underneath the conveyor in say about 1.2 m height. Such take-up gets accommodated even in shiftable conveyor without any problem. The take-up arrangement has a belt loop at intermediate point.

Please do not compromise on take-up. Though it looks simple but it is a critical item in conveyor influencing the performance of conveyor.

As a last resort if you still want to have the minimum take-up stroke then use steel cord belt which will need take-up stroke of only say about 1.5 m but it cannot be simple screw take-up. If it is simple screw take-up, it needs hydraulic tensioner tools while setting the tension.

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 ■

Conveyor Dynamics, Inc. (CDI) has designed and installed or rectified more than 100 such systems. The belt lengths range from short <10m to > 5000 km. There is no limit on conveyor length. There are conditions which would favor gravity (GTU) over winch (WTU) with load cell control or visa versa.

1. thermal range - take care especially with steel cord belts -- steel cord thermal expansion for ranges of day to night time temperatures can cause operating problems.

2. strain and shock wave propogation w/ WTU requires low tension pulleys and structures to be designed for at least 50% more force.

3. Load cell amplifiers boosting microvolt measurements can failure as a short circuit or open circuit. This means the control logic does not know whether to pull to the limit of the TU force or to relax the force causing drive pulley slip and TUP instability.

4. WTU is a constant strain system with a dead-band +/- +10% about a setpoint -- this means when the strain stays constant, the net growth in belt stretch between empty and full loading must equalize the low tension zone to high tension when the material loading drops off. This causes belt splice fatigue and low tension pulleys as well as their supports to be significantly overdesigned.

5. Building structures can be at risk due to drive slip from the WTU not being able to apply the necessary tension response to a quick acceleration start. ■

Well, 5000 km is a litle exaggeration. No excuse. Just not thinking.. ■

Dear John

We actually covered this very interesting topic at great length in a previous thread.

We showed that you cannot just "go by the book" with fixed take-ups.

For example, I have seen successful conveyors over a kilometre long using a fixed take-up, but I had no end of problems with a 30m long one with fixed take-up purely because it had a vertical concave profile.

Therefore see previous thread for all you need to know.

Regards

LSL Tekpro ■

Others have made some good suggestions

With fixed TU types, U will need hydraulic tensioning and also need to take care about design forces for the mechanical and structural parts.

U did not say at which section of the conveyor was the issue wrt locating a GTU system - head ends, tail end or intermediate.

I am sure that if really pushed, one could come up with an idea of how to get around not having a fixed TU system.

Cheers

James ■

As James has said, a number of good suggestions.

One issue not covered is how to minimise the amount of work a fixed take up will need to do on such a long conveyor. If you start the belt very slowly then the dynamics between start and operating will be a lot less hence less belt stretch. If the belt is inclined and there is a reasonable amount of tension then you may need to consider using steel cord belt rather than fabric to minimise belt stretch.

Colin Benjamin ■