Afrim:

Its is a subject that needs more dialog. However, some critical points are not referenced in your list such as:

1. Lump Size

2. Lump Shape( sharpness; abrasive index, or similar measure)

3. Lump distribution by size

4. Ore density

5. Ore velocity at impact on belt

6. Ore direction at impact on belt

7. Chute geometry and ore flow direction at impact (5 & 6)

8. Cohesive and adhesive rheology ( Wet, sticky; dry...)

9. Feed speed of ore into chute and its fall distance

10. Change in direction of ore flow or asymmetric behavior

11. Characterization of skirt zone on ore turbulence

12. Belt cover thickness

13. Belt resilience ........ Steel cord, nylon, polysester weave

Can you expand upon your study for us to see the sensitivities?

All these points can be used to quanitified belt life using Discrete Element Method (DEM) technology. See our website for some illustrated examples of chute flow and analysis:

www.conveyor-dynamics.com More to come soon.

DEM was used to extend the life of the Palabora belt from 3 years (standard rockbox) to estimated 30 years (curved chute spoon) by small change to chute design. Crusher liners, drill bits, shovel teeth,etc. no longer puncture the belt. It has now been in operation for almost 9 years with little sign of wear. Palabora conveyor specifications are:

1. Belt width ................ 1800 mm

2. Speed ...................... 4.1 m/s

3. Capacity .................. 6000 t/h nominal

4. Belt length ............... 1130 m

5. Lumps size .............. 300 mm max and moderately sharp

6. Product .................... Primary crushed copper ore (carbonotite)

7. Ore Density .............. 1600 kq/cm (bulk) ; dry

8. Conveyor slope ........ 15.5 degrees

9. Drop distance ........... 3 m discharge belt feeder to belt

10. Belt steel cord ........ ST-6600 N/mm; 18x9 mm covers

11. Belt abrasive index <100 (DIN) covers

12 Items you mentioned that we can quantify

PLease tell us your expected life estimation with the formula. It will be helpful to see all input parameters.

Progress in Sharing,

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Dear Mr. Afrim,

Does your study cover belts carrying hot material as well or is it limited only to study of wear characteristics ?

If heat resistant belts have not been covered, are you working on establishing a similar empirical formula for such applications ? ■

Dear Afrim Dushi

In general, belt life can be calculated on 2 aspects:

1. Belt covers wear life.

2. Belt fabric fatigue life / time (aging) life.

The belt life will be minimum of above two ( issues such as edge wear due to misaligning running, abnormal deterioration due to unfavourable environment etc. are additional issues).

The belt cover wear life can be calculated as per formulae / method given in Contitech Germany publication (there may be formulae by other manufacturers also). The leading belt manufacturers will certainly be calculating fatigue life / aging life of fabric. Only they will be in a position to say on this aspect. In general, this information is not available from belt manufacturers published literature.

Broadly saying fatigue life should include belt bending, lump impact etc.

Regards

Ishwar G Mulani - Author, Book - Engineering Science and Application Designs on Belt Conveyors

EmailID: parimul@pn2.vsnl.net.in ■

While we are talking about belt wear, I would like to pose a question about the wear profile on belts. I know for example that this is very pronounced in the downstream end of iron ore operations that I am familiar with. Surprisingly, when I was discussing this with a leading expert in the field of conveyor belts, he was not aware of the phenomenon. So it seems that is not ubiqitous.

The wear profile reflects the idler configuration. For example, in a 4 idler configuration there is a high spot in the middle. In a three idler configuration, there is a low spot in the middle.

I would be interested to hear views on this phenomenon. Do people in any other industies see this phenomenon? Has anyone got a belt with different idler configurations along its length?

The wear profile in the belts I referred to above does not mirror the transfer chute geometry. If it did, one would expect to see a distinct band that is of the same width as the chute discharge. This is not the case.

In a correlation of years of data on about 70 of these belts, my conclusion was that the main indicator of wear was the elevation from the loading point to the discharge, when other factors such as tonnage and belt length were normalised. The energy involved in this elevation is considerably greater than that involved in the acceleration at the transfer chutes.

I do not think it is feasible to correlate all belt wear into a single formula. I think the wear mechanisms are diverse and to a large extent indeterminate. These are complex phenomena.

Even with a single ore type and a barrage of laboratory tests it is a very difficult task to correlate any measure of wear with any laboratory measurement of belt parameters, which incidentally change over time according to the environment.

I remain a heretic in the matter of deterministic prediction of belt wear in all but the narrowest of applications. ■

Dear sirs,

I should be interesting to hear what is the true life time of differents typical applications in working hours.

My experience is that the manufacturer of rubber belts tell that the life time is very long (i.e about 50,000 hours for belts with steel cord in open cast lignite mines). On the other side the users need mainly a big maintenance team which indicates that they have to repair the belts all the time. As example, the maintenance managers of crushers or surface miners tell that the average life time of these very short belts is less than 1,000 working hours. Sometime they have to repair it after only 50 hours.

Apparently it is very difficult to know what is the real life time of the belts. A mathematic approch is interesting in order to determinate the right belt but don't provide a real prediction of the belt life time. If you want to help the users give them an overview of the reality with examples. ■

Dear Peter,

I give a plausible explanation to your 3 and 4 roll idler configuration wear behaviors.

On a 3 roll set, the flow impact hard spots are at the mid roll center where the high flow force impacts the belt and where elastic custioning is minimum. Also, on the lower third of the wing roll length, there is a hard spotthat will regisiter high relative wear.

One a 4 roll set the vee center, between wing roll sets, is more flexible providing cushioning and therefore less wear with respect to the 3 roll set. The hard zones are on the two lower wing idlers.

Always willing to learn,

Lawrence Nordell

www.conveyor-dynamics.com ■

IMr Jakob,

I do not understand the relavance of hours in operation as opposed to cycle of loading. A long belt (10000m) the cycles of loading may be less than one per hour. A short belt (100m) may have 100 times that many per hour. There is a 100 times difference in the expected load station cycle repairs. At 50 hours between repairs (every two days) of the shorter belt is about one repair per year on the longer belts.

This is not rocket science. However, as I have commented many times, the chute design is the major key to longer life and minimal repairs. Get it right and a new standard of wear and puncture life becomes the norm.

I

Lawrence Nordell

www.conveyor-dynamics.com ■

Dear Colleagues,

It is finally great to see that we have a discussion going on as related to belt wear and the factors which will give you the wear and what causes the wear. As few of you point out the top cover most of the time is the limiting factor in belt life, also it relates to the cost of the belt. As you all point out in order to predict the belt life we must decide what causes that maximum wear and how can we minimize it. In most belt conveyor system application the poor design of the transfer point is the primary cause of belt wear, I would think that most of you would agree with that.

In my opinion in order to minimize wear you have to minimize what causes it and than you can predict it. In this case Discrete Element Methods/Modeling (DEM) are a good approach to seeing what the shear work on the belt top cover is based on the material flow and chute geometry. Overland Conveyor Company, Inc. does a great job at that and has extensive experience in chute design, analysis/simulation and optimization. Chute Analyst is their software for analyzing chutes based on DEM technology.

Just to give you one example we have done a retrofit of an existing chute for one of our clients mining hard rock and the original belt had a life of 3-4 months. After the retro fit a new belt was placed and the new chute and it has been in operation for over 3years and the estimated life based on the top cover measurements is over 100 years but lets not kid ourselves the belt will fail way before than. This is just an example of what a good chute design will do for you but now you have to decide what the belt life limiting factor will be after you have an optimized Transfer Station.

In any cases, upfront engineering does pay in a long run. This is where most of the companies should invest since it will save them a lot more money in a long run and make the operations more efficient.

In any case, numerical modelling and mathematical approaches are the way to start it should not be a guess.

If you would like to know more and find out about DEM please visit our webpage at www.overlandconveyor.com and/or www.applieddem.com .

Best regards,

Grzegorz ■