More information is required to give a reasonable recommendation. TU travel is made up of:

1. tension variation for all operating conditions

2. thermal stretch variations.

3. permanent stretch of tensile member

4. added splice allowance for maintenance

The conveyor can be designed to have the permanent stretch and splice allowances with belt repair placed in a manually changable tail pulley. This will reduce the belt dynamic travel by about 50%.

THe remaining belt takeup requirement is reduced to about 6-7m assuming the belt is a fabric construction.

Yes, you can design for a fixed TU. You will give up some benefits.

If GTU vertical travel is not available, the fixed TU may be a good option. IF this is considered, and having no data to go by, I would recommend the best place is a tail fixed TU.

These are casual suggestions in the absence of proper engineering information. ■

Why not a horizontal trolley just after the head/drive pulley with a gravity TU tower and weight.

Or do the same but at the tail end ie tail/TU pulley.

Stick to gravity if U can.

Also, a 150m curve looks too small, U will get belt lift off on start up for sure.

Cheers

James ■

Dear Shri S K Bose,

You have to make a choice whether you wish to provide gravity take-up or fixed belt length winch take-up.

If your choice is for gravity type take-up then, you can provide horizontally moving take-up trolley attached to vertical tower with counter weight.

You have mentioned 15 m lift, which is more than adequate for horizontal loop gravity take-up. For the storage yard horizontal conveyor, with stacker cum reclaimer machine, horizontal gravity take-up are accommodated just within 2.5 to 3 m height, when necessary.

Regards,

Ishwar G Mulani.

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

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dear Mr. Bose,

Your travel will be about 17 to 18m. Horizontal gravity type take-up(HGTU) will not work as the distance is more than 600m. I suggest that you must provide HGTU with motorised winch. But winch must have load cell to compensate tension automatically.

Regards.

A.Banerjee ■

Dear Mr. Bose,

Looking at your data, I doubt the elongations during running are anywhere near the figures you have quoted. A distinction should be made between the elongation caused by the static weight of the take-up, which is normally eliminated by keeping the belt in tension during the final splice, and the elongations that occur during running. Then, there is another, which Mr. Nordell has pointed out, the permanent elongation of the belt over time. I not quite sure which of these the 2%+600mm figure you mentioned actually refers to.

To answer your question, if headroom for the GTU is indeed a limitation, a neat and elegant solution would be to use multiple vertical GTUs. Simply adding a second TU will halve the travel. The horizontal trolley method will also work fine if you have a suitable location for it near the lower end of the conveyor. Installing pre-tensioned belts may also be an answer.

Hope this has helped.

Barry Chung ■

As Mr. Nordell suggests you have not given enough information for a substantial response. We need to know the conveyed material specs as well as the belting being used, etc, etc.

The type (fabric or steel cord) and strength of the belting being used will determine the amount of take-up travel req'd. The true travel can only be determined by a formal calculation.

17M to 18M of travel as suggested is not able to be determined from the given information.

Permanent stretch can be removed from a system after a period of time. Leaving you with only elastic stretch requirements for your travel.

If you are only moving 200t at 1.5 m/sec your system is well overdesigned with a loading capacity of only approximately 25% on a 1000mm belt.

If this problem is of a major concern, I would suggest that you have your design analysed by a consultant to determine the correct belt required and the method of take-up.

I have belts running 3000 TPH with only 7M of take-up on a horizontal track operated by a cable double reeved to a 50mm hydraulic cylinder with a 3.5M stroke. The hydraulic circuit has 2 pressure switches. If pressure gets to the low set point the hydraulic pump comes on and raises the pressure to the high set point, then the pump shuts off. This maintains a constaint pressure on the system within the two set points. In other words it simulates gravity.

Hope this helps.

Gary Blenkhorn ■

Dear Mr.Gary,

Normally, the total elongation of NN belt is 2.5%.700 x .025=17.5m. so I have mentioned 17-18m.In all steel plant in yard conveyors more than 600m it would be prudent to provide motorised winch take-up which is really works.

Regards.

A.Banerjee ■

Dear Mr. Bose,

Glad to be of help.

Again, I still have some reservations regarding the 2% figure. If this is something that came out of the design calculations using a particular belt you have selected, then I guess you will have to accomodate for it. In which case, and without further data from you, I still think the multiple GTUs provide the most feasible workaround. However, the question is, if you can make do with a single GTU, why provide more?

As Mr. Blenkhorn has mentioned, the take-up travel is not simply a fixed percentage figure of your conveyor length. It is obtained by applying the modulus of elasticity of the selected belt. Generally, a higher strength belt will have a higher modulus and will therefore stretch less on the same tension. Or, the belt strengths being equal, a polyester warped belt (eg EP) will stretch less than one of nylon (NN).

The selected take-up weight also has an impact but the differences caused by this is mostly removed by prestretching the belt before the final splice. But do bear in mind that a heavier take-up also has greater inertia when in motion and will therefore stretch the belt more on the downstroke and rise slightly higher on the upstroke thus increasing the travel. The point here is not to udersize or oversize but to correctly size.

The hydraulic take-ups should also work fine. It all boils down to relative costs. Nevertheless, I would still give an edge to the multiple GTUs because there is less equipment to contend with and is virtually maintenance free.

All said, I would strongly encourage you to review your belt specifications and see whether you can make do with just a single GTU.

Best regards.

Barry Chung ■

Mr. Bose

As Mr Chung has suggested the N/N construction will stretch much more than a P/N construction.

Nylon is great for puncture and tear resistance but not stretch.

I quickly run the numbers on Belt Analyst II based on the information you have given.

It came up with the following based on using 3 ply/330 PIW P/N (please note this is an North American imperial spec.)

Your system will be 100% loaded at 460 mtph of coal.

Approx carriage travel due to acceleration tension = 1.3M

Approx carriage travel due to permanent stretch = 7.5M

Therefore total travel required is 8.8M

Hope this helps.

Gary Blenkhorn ■

Multiple GTU's.

This conveyor problem is something that I occasionally come across. Please can someone advise on design of multiple gtu. Are all floating vertical pulleys live or are some locked off until belt stretch requires them to be live? ■

Dear Mr. Jones,

We have designed many dual takeups to restrict the peak tension and enhance drive aT1/T2 ratios. One takeup will apply the necessary slack side force for driving whether the load be uphill or downhill. The higher belt tension will eliminate the takup travel in the higher tension region, defering to the lower tension known gravity mass.

The configurations can be seprate and independent assy at great distances from one another or can usse the same counterweight with two trolleys.

Care must be taken with the TUP rate of travel to minimize shock on impact of the takup trolley and gravity mass.

You must design for each state of operation and know when each will be engaged. A proper design will include and moving mass analysis and moving takeup that simulates the transition. Often it is advisable to design a shock absorber into the upward or fore-shortening end of travel. ■

Fixed winch type takeups(TUP) are generally not well understood. There are many pitfalls:

1. Shock wave force amplification during shutdown can be multiples of the steady-state force setpoint due to the quick reoreintation of the strain field within the belt Tail pulleys, return side bend pulleys and vertical or horizontal curves can have belt tensions rise to many times their steady-state tensions. In some cases, up to 10 times.

2. Thermal change over the course of a 24 hour cycle - shut down with load, when temp is high, and startup when temp is low ( temp deff > 30 C) can have a near doubling effect of belt line tension.

3. Thermal swings, loading swings, and range of deadband can have a profound and damaging effect by belt flap on idlers and vibratory coupling of structure to idler spin frequency and belt natural modal frequency. I am witness to such an event today, where over the coarse of one year many hundreds of idlers, idler frames, roll ends, et al have failed, the idler supports have broken welds, the ISO end supports have fractured, structures have been put into oscillation, coupled with the idler spacing and caused lumping of the material in tranport. The lumped or concentrated material causes added stress and fatigue of the idlers and structures.

4. Designers and operators believe that the winch takup is superior in minimizing peak tensions. FOr the many installation we have designed and evaluated, I have found very few cases where this is true. It is true that the winch can be cheaper on initial costs. It is also more portable and is the reason the Germans use it in the shiftable conveyors of the Brown Coal fields.

5. If the diodes, operational amplifiers, or transitors fail, in the strain gauge amplifier ( needed for every load cell system) their state of failure (on or off) can not be predicted. THus, the failure can demand more force or less force with equally bad results. Many operators have change their systems from load cell control to gravity TUP to gain the reliablility and repeatablility of belt tensions. This usually occurs after a major failure.

I discourage their use and can point to many clients with horror stories. I know some will tout their success. THese individuals usually are salesmen for a product or designers defending their choice. I have no such product, only the need to succeed and have testimonial to a propoerly functioning system. ■

DEAR Mr. BOSE

you have given following data

Conveyor c/c distance= 700m

Ht. of lift=12m

Belt Width=1000mm

Belt speed=1.5m/s

Cap=200t

Radius of curvature of 150m.

For this application you can go for any of the following options

1.0 you should procure pre stressed belting in that case

elongation will be less and you can manage vgt in 12 m

length

2.0 If space is available you can go for Horrizontal gravity takeup

by mounting tail pulley n movable trolley wire rope and take

up tower

3.0 you can provide loop take up near tail end by providing

pulley on moving trolley wire rope and take up tower

in my openion you should go for option 1

1000 mm belt width for 200 tph seems to be much higher you may be transporting very light material.

please check up 150 m concave radious which also seems to be inadiquate for this length

With regards

A R SINGH ■

Dear Shri S K Bose,

Looking at the responses by various people on the take-up stroke, I would like to add the following:

The take-up stroke is composed of:

1) Elastic elongation

2) Permanent elongation.

3) Additional time margin for shortening the belt and revulcanising.

The elastic elongation will be reflected in actual movement of the take-up pulley during conveyor operation i.e. standstill to starting to normal running to standstill. This value is quite less compared to 2% or 3% considered for take-up.

The permanent elongation will occur during coarse of time. This value is also less compared to the total provision of the stroke.

The sum of elastic elongation and permanent elongation, forms the basis of take-up stroke. The take-up stroke could be less if margin for permanent elongation is less. Such conveyor will be workable but it will demand shortening and revulcanising of belt more frequently.

Then there is also margin in the take-up to account for temperature variation. The properly designed belt conveyor and the take-up will not require frequent adjustment in the belt length.

Regards,

Ishwar G Mulani.

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

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dear Shri S K Bose,

In addition to points indicated by shri Ishwar G Mulani. provision for one splice joint should always be available in take up travel.

choice should be given for vertical gravity takeup in case same is feasible

Regards,

A R SINGH ■