Dear Andrew,

The inclusion of additional drive at tail end will need redesigning the conveyor i.e. new tensions at various points and consequent changes in forces acting at head end structure, tail end structure, take-up, pulleys, belt etc. Then one has to see existing which items will remain unchanged and which items will change. This analysis can be done by conveyor designer for arriving at reliable solution. The quantum of changes will depend upon magnitude of power at tail end in comparison to existing power at head end. If the additional drive is very small compared to existing drive, it will need changes in very few items.

The new tensions will also need checking of concave convex radius at various points and if these need revisions, then it will demand reconstruction of the structures.

There is no quick-fix solution.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

In addition to the above:

You will also need to check for belt sag near the tail ( assuming a horizontal profile) or along its profile, if you have a low point away from the tail.

Drive slip (head and tail) and related takeup tension, to control both drive slip and belt sag, needs to be evaluated.

You will need to check for the alteration of starting and stopping dynamics. Depending on the conveyor's length, the starting timing may need to be phase corrected due to the time delay of the elastic wave response, between head and tail, during its stretching cycle. This may alter the velocity or torque starting curve relationship between head and tail.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Dear Andrew..

Can you give us an indication of the configuration of the conveyor in question?

For example, if it is an incline conveyor, the tension at the tail will be at its lowest, and there would more than likely be no point in putting in a tail drive at all.

If it is an overland conveyor, the rule of thumb is that the power of the tail drive should be sufficient to overcome the return friction and any return belt lift. This means that the conveyor would normally have to be quite long to justify a tail drive and be able to benefit from it. (unless of course it is a dual carry conveyor)

You mention that it is a large capacity conveyor, and therefore probably has large head drives. This implies that the power to drive the return belt could be relatively insignificant, and a tail drive would probably not be worth the effort.

You must remember that a tail drive requires additional electrics, as well as co-ordination and control of the drives a long distance apart, and requires the control of potential transients as Larry Nordell mentioned above.

In other words we have to establish the magnitude of any benefits by analising the configuration and duty before potentially complicating your conveyor with a tail drive.

Regards

Graham Spriggs

LSL Consulting / Tekpro Projects

Johannesburg ■

Dear Mr. Andrew,

You have mentioned that there is a slippage between belt and pulley at tail end. This is a serious matter and it signifies inadequate tension in the belt. Kindly examine this point when incorporating any proposition.

As mentioned earlier, it is advisable that the competent designer should check the design in totality, so that you do not have any problem after rectification instead of changes based on possibilities.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Andrew,

Conveyor Dynamics, Inc. (CDI) has done what you seek to do. We have applied load sharing to inverters, wound rotor motors, and fluid couplings located at head and tail drive arrangements for long single flight overlands up to 16 km.

I am sure the problems are solvable.

We have worked in Ft. McMurray. I do not think the next step should be generalized in this forum. There are too many issues that need discussion and analysis as Mr. Mulani suggests.

If you wish to discuss such in detail please call or email me. We are about 1 hour by air, from Edmonton or Calgary. I can fly out of Vancouver on the day of your choice. Catch the local flight to Ft. McMurray and see you the same day.

Lawrence Nordell

Conveyor Dynamics, Inc.

1111 West Holly St.

Bellingham, WA 98225

ph: 360-671-2200

fx: 360-671-8450

email: nordell@conveyor-dynamics.com

website: www.conveyor-dynamics.com ■

Good morning Andrew..

Could you please confirm your conveyor duty/arrangement.

You seem to have enough power there to move 30 000t/h !!

2400m is not very long, and as you indicate there is no lift, but you have 6250 HP on board. Seems too much. Also, what and where is your take up system?

To answer your other question, any additional power should be applied to the primary head drive pulley. This is the one closest to the material discharging from the belt. (Why you want more than 6250 HP... I have no idea.)

Anyway for interest, if we do our maths, we find that on a dual drive system with two adjacent drive pulleys of equal wrap, the primary drive pulley can transmit 3 x that of the secondary, at a normal value of the coefficient of friction. Additional power on the tail drive would therefore not be correct at all.

Regards

Graham Spriggs

LSL Consulting / Tekpro Projects

Johannesburg

gspriggs@global.co.za ■