Hi there Willem..

I think you might well be barking up the wrong tree here.

You see there are numerous far more important things to consider in addition to the idler configuration. To get excellent belt life you must have an excellent overall conveyor design. Give us a bell Willem, and I will gladly fill you in on the finer points.

Cheers

LSL Tekpro ■

Dear Willem, I have put the information you gave "roughly" into a conveyor belt calculation programme we use. I say roughly, as I didn't really have that much info, but I feel it should give a good idea of what should happen.

As I increased the diameter of the roller/idler, I found that the pretension and the actual tension was increased. The power to actually pull the belt around increased too, though not significantly (244.91 KW for 200mm diameter to 250.74 for 218mm). This was by making the theoretical conveyor length 1000m. I also made this conveyor system flat and level.

This may seem odd, but you must understand the extra weight that the belt must pull at start (I estimated the weight of the rollers to be 32.26kg and 35.161kg respectively) and the power to keep this momentum. I think this may probably be exagerated too on an inclined system.

Conveyor belts are designed to have a maximum sag allowed and so I think the roller size (so long as the tensile strength and load support are correct) should not make a drastic difference. I can see the issues here but even if the calculations were worked out to be positive for you, then the extra cost would(should) make it not efficient to do so.

If you should like me to make any further calculations concerning this, then please do not hesitate to contact me. And if I can be of assistance in selling you a belt for this installation, then please let me know!! ;-)

Kindest regards,

stan Holcroft,

Dunlop Conveyor Belting,

Netherlands.

stan.holcroft@dunlopcb.com ■

Dear Willem,

There are many factors that make up the deformation between idler rollers and belt bottom cover. We have not spoken of the finer points that can reduce power further than has been published. Some of these are now in the patent process.

The comments of roll mass influencing power is not relevant. You only need to turn the acceleration time dial to eliminate the roll mass addition. However, increasing the roll diameter can have a profound affect . There are reasons published and not published. I wrote an articles showing the relevance and suggest you view our website: www.conveyor-dynamics.com

1. The Channar 20 km Overland - BSH Vol. 11, No. 4, Nov 1991

2. The Power of Rubber - Part I - BSH Vol. 16, No. 3, July 1996

3. Improving Belt Conveyor Efficiencies: Power, Strength & Life - IIR Conference in Australia, April 1998

Rubber Indent Power Reduction = 1- (d1/d2)^.667, where

d1: smaller roll diameter (mm)

d2: larger roll diameter (mm)

In addition, the larger roll has a lower belt line bearing drag for two reasons: 1) better torque arm advantage, and 2) lower bearing viscous lubricant drag with lower RPM.

In February, 2007, we successfully commissioned the Curragh 20 km overland. Curragh has 193mm center roll and 178 wing roll diameters. The belt is 1200mm wide and has a 5 meter carry side spacing. The belt transports 2500 t/h at a belt speed = 7.5 m/s.

There are nuances to the design. First, you must do testing on roll drag vs RPM, bearing type, and lubricants. Second, you must understand the viscoelastic losses due to rubber compound, temperature, belt speed, idler trough configuration (Curragh has shorten and offset center rolls), belt cover thickness, belt steel cord diameter and construction, ..........

People will tell you it does not matter .... rubbish. We stopped trying to convince them. Time and competition will show them what they do not know.

Take care with the idler junction stress, strain and fatigue.

Take care of coupled vibration of belt, rollers, and idler supports.

We win most of the overlands we bid on. Comming soon will be a new generation of belt conveyors far more competitive than the present lot. ■

Hello Willem,

I believe there is a paper out there on the Henderson Project where a combination of 'large' (220mm) and small (152mm) rollers were used on the centre and wing roll respectively.

Alternatively, on the basis of the last papers presented at Beltcon you may try Craig Wheeler of TUNRA.

I belive that these discuss the aspects of reduced indentation effects encountered with the use of large roll diameters.

Regards,

Adi Frittella ■

Why the hyperbole? Why not make the arguments with facts.

The idler mass difference has a trivial affect on power. Look at the bearing drag (not seal) u=.0007 x roll mass difference x no. of rolls x convert to Newtons x belt speed = kW difference.

KW= (35.16kg-32.26kg) x (9.806 N/kg) x (6000/4.5 +6000/9.0) x (.0007) x 6m/s(est.) = 0.24 kW.....

Assuming the est. of roll mass difference is correct. Why is this even being discussed for a 1/4 kW?

Beware of the high belt speed. The drag values will exceed published numbers. Beware of temperature, lubricant, vulcanizing press releasing compound altering rubber indention behavior, type of bearing, et al.

The thread starter is talking about design. So, things are designed to work properly.

I referenced things that make a difference, not hyperbole. ■

As somebody said: the best practice is good theory. It is somehow sad that there is still and argument going on if factors mentioned by Mr. Nordell are to be researched, known and applied in practice. For some in the industry research done over the years seems to be of no practical consequence - a sort of academic frivolity .

There is discussion going on about power demand of pipe conveyor which well illustrates the state of affairs as well.

Regards,

Marian Otrebski ■

Thanks to Stephen & Tecmate:

Stephen:

Can you provide some details on the new scanner and belt cover gauge measurement equipment? Please correspond through my email below.

There is a large pent-up need. I hope you are able to allow clients to do their own scanning. Do you post accuracies, and examples of resulting reports?

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Dawson:

I hear Dawson is producing something, but, not to specification, its very, very late, and they seem to have many operating difficulties – cables dislodging, adding many sheaves to control cables and spillage, unusual vibrations, belt cleaning(?), and other critical issues. It’s a work in progress(?).

This leads to the question about the Cable Belt viability. Will Anglo indorse it to other clients? How long will it take before Metso is successful in meeting the intended scope?

Metso and Anglo had a profit sharing deal. Wonder what profits they are going to share?

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Tecmate:

Will Anglo reissue Lake Lindsey for bid with a conventional trough conveyor or, will they put themselves in double jeopardy? Maybe this is the replacement?

Maybe we can make a trip to Curragh with Stephen?

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Marian:

Yes, the adage is still true - you can take the horse to water, but you can't make him drink.

There are good theories and bad theories. Practice makes the good theory a fact and bad theory a metaphor for illiteracy.

The sad token to our industry is that the "blue-suede shoe salesman" mentality still works. If you say it long enough, loud enough, repeat ad nausium(sic), many will take it as gospel. ■